DISPLAY DEVICE AND ELECTRONIC DEVICE

A novel display device that is highly convenient, useful, or reliable is provided. The display device includes a first light-emitting device, a second light-emitting device, an insulating film, a conductive film, a first reflective film, and a second reflective film; the first light-emitting device includes a first electrode, a second electrode, and a first unit; and the first electrode is interposed between the first unit and the insulating film. The second light-emitting device includes a third electrode, a fourth electrode, and a second unit; the third electrode is interposed between the second unit and the insulating film; and a first gap is provided between the third electrode and the first electrode. The conductive film electrically connects the second electrode and the fourth electrode to each other, and the first gap is interposed between the conductive film and the insulating film. The first reflective film is interposed between the first electrode and the insulating film, and there is a first distance DR between the first reflective film and the second electrode. The second reflective film is interposed between the third electrode and the insulating film, and there is a second distance DG between the second reflective film and the fourth electrode. The second distance DG is longer than the first distance DR and the difference is larger than 20 nm and smaller than 85 nm.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device, an electronic device, or a semiconductor device.

BACKGROUND ART

Light-emitting devices (organic EL devices) including organic compounds and utilizing electroluminescence (EL) have been put to more practical use. In the basic structure of such light-emitting devices, an organic compound layer containing a light-emitting material (an EL layer) is interposed between a pair of electrodes. Carriers (holes and electrons) are injected by application of a voltage to the element, and light emission can be obtained from the light-emitting material by using the recombination energy of the carriers.

Such light-emitting devices are of self-light-emitting type and thus have advantages over liquid crystal, such as high visibility and no need for backlight when used in pixels of a display, and are suitable as flat panel display elements. Displays including such light-emitting devices are also highly advantageous in that they can be thin and lightweight. Another feature is an extremely fast response speed.

Since light-emitting layers of such light-emitting devices can be successively formed two-dimensionally, planar light emission can be obtained. This feature is difficult to realize with point light sources typified by incandescent lamps and LEDs or linear light sources typified by fluorescent lamps; thus, the light-emitting devices also have great potential as planar light sources, which can be applied to lighting and the like.

Displays or lighting devices including light-emitting devices are suitable for a variety of electronic devices as described above, and research and development of light-emitting devices has progressed for more favorable characteristics.

Known is a structure of a light-emitting apparatus that emits light of a plurality of colors in which the light-emitting apparatus includes a first light-emitting element and a second light-emitting element; the first light-emitting element includes a first lower electrode, a first light-emitting layer over the first lower electrode, a second light-emitting layer over the first light-emitting layer, and an upper electrode over the second light-emitting layer; the second light-emitting element includes a second lower electrode, the first light-emitting layer over the second lower electrode, the second light-emitting layer over the first light-emitting layer, and the upper electrode over the second light-emitting layer; an emission spectrum peak of the first light-emitting layer is positioned on a longer wavelength side than that of the second light-emitting layer; and a distance between the first lower electrode and the first light-emitting layer is shorter than a distance between the second lower electrode and the first light-emitting layer (Patent Document 1).

Organic EL devices are sometimes used in display portions of display devices and HMDs for AR or VR. Non-Patent Document 1 discloses a method employing standard UV photolithography for manufacturing an organic optoelectronic device, which is one of organic EL devices.

REFERENCES

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

An object of one embodiment of the present invention is to provide a novel display device that is highly convenient, useful, or reliable. Another object is to provide a novel electronic device that is highly convenient, useful, or reliable. Another object is to provide a novel display device, a novel electronic device, or a novel semiconductor device.

Note that the description of these objects does not preclude the existence of other objects. Note that one embodiment of the present invention does not have to achieve all the objects. Other objects will be apparent from the description of the specification, the drawings, the claims, and the like, and other objects can be derived from the description of the specification, the drawings, the claims, and the like.

Means for Solving the Problems

(1) One embodiment of the present invention is a display device including a first light-emitting device, a second light-emitting device, an insulating film, a conductive film, a first reflective film, and a second reflective film.

The first light-emitting device includes a first electrode, a second electrode, and a first unit. The first unit is interposed between the first electrode and the second electrode, and the first electrode is interposed between the first unit and the insulating film.

The second light-emitting device includes a third electrode, a fourth electrode, and a second unit. The second unit is interposed between the third electrode and the fourth electrode, and the third electrode is interposed between the second unit and the insulating film. A first gap is provided between the third electrode and the first electrode.

The conductive film electrically connects the second electrode and the fourth electrode to each other, and the first gap is interposed between the conductive film and the insulating film.

The first reflective film is interposed between the first electrode and the insulating film, and there is a first distance DR between the first reflective film and the second electrode.

The second reflective film is interposed between the third electrode and the insulating film, and there is a second distance DG between the second reflective film and the fourth electrode.

The second distance DG has a relation with the first distance DR satisfying Formula (1) to Formula (3) below.

(2) One embodiment of the present invention is the display device in which the above second unit has a function of emitting first light and an emission spectrum of the first light has a maximum peak in a range greater than or equal to 480 nm and less than or equal to 600 nm.

Thus, a step generated between the first light-emitting device and the second light-emitting device can be reduced. A step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. Green light can be used for display. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

(3) One embodiment of the present invention is the above display device including a filler.

The filler is interposed between the first electrode and the third electrode, and the filler is interposed between the insulating film and the conductive film. Furthermore, the filler is interposed between the first unit and the second unit.

Thus, the second light-emitting device can be separated from the first light-emitting device. A gap formed between the first light-emitting device and the second light-emitting device can be filled using the filler. A step due to the gap formed between the first light-emitting device and the second light-emitting device can be reduced. The step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

(4) One embodiment of the present invention is the above display device including a third light-emitting device and a third reflective film.

The third light-emitting device includes a fifth electrode, a sixth electrode, and a third unit. The third unit is interposed between the fifth electrode and the sixth electrode, and the fifth electrode is interposed between the third unit and the insulating film. A second gap is provided between the fifth electrode and the third electrode.

The conductive film electrically connects the fourth electrode and the sixth electrode to each other, and the second gap is interposed between the conductive film and the insulating film.

The third reflective film is interposed between the fifth electrode and the insulating film, and there is a third distance DB between the third reflective film and the sixth electrode.

The third distance DB has a relation with the first distance DR and the second distance DG satisfying Formula (1) to Formula (3) below.

(5) One embodiment of the present invention is the above display device in which the third distance DB is shorter than or equal to 200 nm.

Thus, the step generated between the first light-emitting device and the second light-emitting device can be reduced. A step generated between the second light-emitting device and the third light-emitting device can be reduced. A step generated between the first light-emitting device and the third light-emitting device can be reduced. The step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. As a result, a novel optical functional device that is highly convenient, useful, or reliable can be provided.

(6) One embodiment of the present invention is the above display device including a third light-emitting device and a third reflective film.

The third light-emitting device includes a fifth electrode, a sixth electrode, and a third unit. The third unit is interposed between the fifth electrode and the sixth electrode, and the fifth electrode is interposed between the third unit and the insulating film. A second gap is provided between the fifth electrode and the third electrode.

The conductive film electrically connects the fourth electrode and the sixth electrode to each other, and the second gap is interposed between the conductive film and the insulating film.

The third reflective film is interposed between the fifth electrode and the insulating film, and there is a third distance DB between the third reflective film and the sixth electrode.

The third distance DB has a relation with the first distance DR and the second distance DG satisfying Formula (1) to Formula (3) below.

(7) One embodiment of the present invention is the above display device in which the first distance DR is shorter than or equal to 150 nm.

Thus, the step generated between the first light-emitting device and the second light-emitting device can be reduced. The step generated between the second light-emitting device and the third light-emitting device can be reduced. The step generated between the first light-emitting device and the third light-emitting device can be reduced. The step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. As a result, a novel optical functional device that is highly convenient, useful, or reliable can be provided.

(8) One embodiment of the present invention is the above display device in which the first unit has a function of emitting second light; the second light has a wavelength greater than or equal to 600 nm and less than or equal to 740 nm; the third unit has a function of emitting third light; and the third light has a wavelength greater than or equal to 400 nm and less than or equal to 480 nm.

Thus, the step generated between the first light-emitting device and the third light-emitting device can be reduced. The step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. Red light can be used for display. Blue light can be used for display. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

(9) One embodiment of the present invention is the above display device in which the first light-emitting device includes a first layer and the second light-emitting device includes a second layer.

The first layer is interposed between the first unit and the first electrode, and the first layer contains a substance having an electron-accepting property and a material having a hole-transport property. Furthermore, the first layer has an electrical resistivity higher than or equal to 1×102[Ω·cm] and lower than or equal to 1×108[Ω·cm].

The second layer is interposed between the second unit and the third electrode, and a third gap is provided between the second layer and the first layer. Furthermore, the second layer contains the substance having an electron-accepting property and the material having a hole-transport property.

Accordingly, current flowing between the first layer and the second layer can be reduced. Furthermore, a crosstalk phenomenon between the first light-emitting device and the second light-emitting device can be inhibited. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

(10) One embodiment of the present invention is the above display device including a display region, a first functional layer, and a second functional layer.

The display region includes a pixel set, and the pixel set includes a first pixel and a second pixel.

The first pixel includes the first light-emitting device and a first pixel circuit, and the first light-emitting device is electrically connected to the first pixel circuit. Furthermore, the first pixel circuit is supplied with a first image signal.

The second pixel includes the second light-emitting device and a second pixel circuit, and the second light-emitting device is electrically connected to the second pixel circuit. Furthermore, the second pixel circuit is supplied with a second image signal.

The first functional layer includes the first pixel circuit and the second pixel circuit. The first functional layer is interposed between the first light-emitting device and the second functional layer, and the first functional layer is interposed between the second light-emitting device and the second functional layer.

The second functional layer includes a driver circuit, and the driver circuit generates the first image signal and the second image signal.

Thus, the driver circuit can be positioned so as to overlap with the first pixel circuit and the second pixel circuit. An outer area can be smaller than a region displaying image information. Furthermore, a distance between the first pixel circuit and the driver circuit can be shortened. In addition, an image signal can be transmitted without delay. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

(11) One embodiment of the present invention is an electronic device including an arithmetic portion and the above display device. The arithmetic portion generates image information, and the display device displays the image information.

(12) One embodiment of the present invention is an electronic device including an arithmetic portion and the above display device. The second functional layer includes the arithmetic portion, the arithmetic portion generates image information, and the display device displays the image information.

Effect of the Invention

According to one embodiment of the present invention, a novel display device that is highly convenient, useful, or reliable can be provided. Alternatively, a novel electronic device that is highly convenient, useful, or reliable can be provided. Alternatively, a novel display device, a novel electronic device, or a novel semiconductor device can be provided.

Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not need to have all of these effects. Other effects will be apparent from the description of the specification, the drawings, the claims, and the like, and other effects can be derived from the description of the specification, the drawings, the claims, and the like.

MODE FOR CARRYING OUT THE INVENTION

A display device of one embodiment of the present invention includes a first light-emitting device, a second light-emitting device, an insulating film, a conductive film, a first reflective film, and a second reflective film. The first light-emitting device includes a first electrode, a second electrode, and a first unit; the first unit is interposed between the second electrode and the first electrode; and the first electrode is interposed between the first unit and the insulating film. The second light-emitting device includes a third electrode, a fourth electrode, and a second unit; the second unit is interposed between the fourth electrode and the third electrode; the third electrode is interposed between the second unit and the insulating film; and a first gap is provided between the third electrode and the first electrode. The conductive film electrically connects the second electrode and the fourth electrode to each other, and the first gap is interposed between the conductive film and the insulating film. The first reflective film is interposed between the first electrode and the insulating film, and there is a first distance DR between the first reflective film and the second electrode. The second reflective film is interposed between the third electrode and the insulating film, and there is a second distance DG between the second reflective film and the fourth electrode. The second distance DG is longer than the first distance DR and the difference is larger than 20 nm and smaller than 85 nm.

Thus, a step generated between the first light-emitting device and the second light-emitting device can be reduced. A step generated in the conductive film can be reduced. A step generated in the conductive film can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film can be inhibited. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

In this embodiment, a structure of a display device700of one embodiment of the present invention will be described with reference toFIG.1toFIG.3.

FIG.1is a cross-sectional view illustrating the structure of the display device of one embodiment of the present invention.

FIG.2is a cross-sectional view illustrating the structure of the display device of one embodiment of the present invention.

FIG.3is a cross-sectional view illustrating the structure of the display device of one embodiment of the present invention.

Structure Example 1 of Display Device

The display device700described in this embodiment includes a light-emitting device550R(i,j), a light-emitting device550G(i,j), an insulating film521, a conductive film552, a reflective film REFR(i,j), and a reflective film REFG(i,j) (seeFIG.1).

The light-emitting device550R(i,j) includes an electrode551R(i,j), an electrode552R(i,j), and a unit103R(i,j).

The unit103R(i,j) is interposed between the electrode552R(i,j) and the electrode551R(i,j), and the electrode551R(i,j) is interposed between the unit103R(i,j) and the insulating film521.

The light-emitting device550G(i,j) includes an electrode551G(i,j), an electrode552G(i,j), and a unit103G(i,j).

The unit103G(i,j) is interposed between the electrode552G(i,j) and the electrode551G(i,j), and the electrode551G(i,j) is interposed between the unit103G(i,j) and the insulating film521.

<<Structure Example of Electrode551G(i,j)>>

A gap551RG(i,j) is provided between the electrode551G(i,j) and the electrode551R(i,j).

Structure Example 1 of Conductive Film552

The conductive film552electrically connects the electrode552R(i,j) and the electrode552G(i,j) to each other. Note that one conductive film can be used for the conductive film552, the electrode552R(i,j), and the electrode552G(i,j). In that case, a region of the one conductive film that overlaps with the electrode551R(i,j) can be used for the electrode552R(i,j), a region of the one conductive film that overlaps with the electrode551G(i,j) can be used for the electrode552G(i,j), and a gap between the electrode552R(i,j) and the electrode552G(i,j) of the one conductive film can be used for the conductive film552.

The gap551RG(i,j) is interposed between the conductive film552and the insulating film521.

<Structure Example of Reflective Film REFR(i,j)>

The reflective film REFR(i,j) is interposed between the electrode551R(i,j) and the insulating film521. There is a distance DR between the reflective film REFR(i,j) and the electrode552R(i,j).

<Structure Example of Reflective Film REFG(i,j)>

The reflective film REFG(i,j) is interposed between the electrode551G(i,j) and the insulating film521. There is a distance DG between the reflective film REFG(i,j) and the electrode552G(i,j).

The distance DG has a relation with the distance DR satisfying all of Formula (1) to Formula (3) below. In other words, the distance DR is longer than the distance DG and the difference is larger than 20 nm and smaller than 85 nm. Further preferably, the distance DR is longer than the distance DG and the difference is larger than 20 nm and smaller than 40 nm.

<<Structure Example of Unit103G(i,j)>>

The unit103G(i,j) has a function of emitting light ELG. The emission spectrum of the light ELG has a maximum peak in a range of 480 nm to 600 nm inclusive.

Thus, a step generated between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be reduced. A step generated in the conductive film552can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film552can be inhibited. Green light can be used for display. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

Structure Example 2 of Display Device

The display device700described in this embodiment includes a filler529RG(i,j) (seeFIG.1).

Structure Example 1 of Filler529RG(i,j)

The filler529RG(i,j) is interposed between the electrode551R(i,j) and the electrode551G(i,j). In other words, the filler529RG is located in the gap551RG, for example, filling the gap551RG.

The filler529RG(i,j) is interposed between the insulating film521and the conductive film552. For example, the filler529RG fills a gap between the insulating film521and the conductive film552.

The filler529RG(i,j) is interposed between the unit103R(i,j) and the unit103G(i,j). For example, the filler529RG fills a gap between the unit103R and the unit103G.

Thus, the light-emitting device550G(i,j) can be separated from the light-emitting device550R(i,j). A gap formed between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be filled using the filler529RG(i,j). A step due to the gap formed between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be reduced. The step generated in the conductive film552can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film552can be inhibited. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

Structure Example 2 of Filler529RG(i,j)

For example, an insulating inorganic material, an insulating organic material, or an insulating composite material containing an inorganic material and an organic material can be used for the filler529RG(i,j).

Specifically, an inorganic oxide film, an inorganic nitride film, an inorganic oxynitride film, or the like, or a stacked-layer material in which a plurality of films selected from these films are stacked can be used for the filler529RG(i,j).

For example, a film including a silicon oxide film, a silicon nitride film, a silicon oxynitride film, an aluminum oxide film, or the like, or a film including a stacked-layer material in which a plurality of films selected from these films are stacked can be used for the filler529RG(i,j). Note that the silicon nitride film is a dense film and has an excellent function of inhibiting diffusion of impurities.

For example, the filler529RG(i,j), polyester, polyolefin, polyamide, polyimide, polycarbonate, polysiloxane, an acrylic resin, or the like, or a stacked-layer material, a composite material, or the like of a plurality of resins selected from these resins can be used.

Structure Example 3 of Filler529RG(i,j)

The filler529RG(i,j), for example, includes a filler529(1) and a filler529(2).

For example, an insulating inorganic material can be used for the filler529(1). Specifically, aluminum oxide or the like can be used for the filler529(1). For example, a dense film that is formed by a chemical vapor deposition method, an atomic layer deposition (ALD) method, or the like can be used for the filler529(1).

For example, an insulating organic material can be used for the filler529(2). Specifically, polyimide or an acrylic resin can be used for the filler529(2). For example, the filler529(2) can be formed using a photosensitive material.

Structure Example 3 of Display Device

The display device700described in this embodiment includes a light-emitting device550B(i,j) and a reflective film REFB(i,j) (seeFIG.2). The display device700includes a filler529GB(i,j) and a filler529BR(i,j). Note that the light-emitting device550B(i,j) is adjacent to a light-emitting device550R(i,j+1).

The light-emitting device550B(i,j) includes an electrode551B(i,j), an electrode552B(i,j), and a unit103B(i,j).

The unit103B(i,j) is interposed between the electrode552B(i,j) and the electrode551B(i,j), and the electrode551B(i,j) is interposed between the unit103B(i,j) and the insulating film521.

<<Structure Example of Electrode551B(i,j)>>

A gap551GB(i,j) is provided between the electrode551B(i,j) and the electrode551G(i,j).

Structure Example 2 of Conductive Film552

The conductive film552electrically connects the electrode552G(i,j) and the electrode552B(i,j) to each other.

The gap551GB(i,j) is interposed between the conductive film552and the insulating film521.

Structure Example 1 of Reflective Film REFB(i,j)

The reflective film REFB(i,j) is interposed between the electrode551B(i,j) and the insulating film521. There is a distance DB between the reflective film REFB(i,j) and the electrode552B(i,j).

The distance DB has a relation with the distance DR and the distance DG satisfying all of Formula (1) to Formula (3) below. In other words, the distance DB is longer than the distance DR, the distance DR is longer than the distance DG, a difference between the distance DB and the distance DR is smaller than 60 nm, and a difference between the distance DR and the distance DG is smaller than 35 nm.

Structure Example 2 of Reflective Film REFB(i,j)

The distance DB is shorter than or equal to 200 nm.

Thus, the step generated between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be reduced. A step generated between the light-emitting device550G(i,j) and the light-emitting device550B(i,j) can be reduced. A step generated between the light-emitting device550R(i,j) and the light-emitting device550B(i,j) can be reduced. In addition, the step generated in the conductive film552can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film552can be inhibited. As a result, a novel optical functional device that is highly convenient, useful, or reliable can be provided.

Structure Example 4 of Display Device

The display device700described in this embodiment includes the light-emitting device550B(i,j) and the reflective film REFB(i,j) (seeFIG.3).

Structure Example 3 of Reflective Film REFB(i,j)

The reflective film REFB(i,j) is interposed between the electrode551B(i,j) and the insulating film521. There is the distance DB between the reflective film REFB(i,j) and the electrode552B(i,j).

The distance DB has a relation with the distance DR and the distance DG satisfying all of Formula (1) to Formula (3) below. In other words, the distance DR is longer than the distance DG, the distance DG is longer than the distance DB, a difference between the distance DR and the distance DG is smaller than 35 nm, and a difference between the distance DG and the distance DB is smaller than 35 nm.

Structure Example 4 of Reflective Film REFR(i,j)

The distance DR is shorter than or equal to 150 nm.

Thus, the step generated between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be reduced. The step generated between the light-emitting device550G(i,j) and the light-emitting device550B(i,j) can be reduced. The step generated between the light-emitting device550R(i,j) and the light-emitting device550B(i,j) can be reduced. In addition, the step generated in the conductive film552can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film552can be inhibited. As a result, a novel optical functional device that is highly convenient, useful, or reliable can be provided.

<<Structure Example of Unit103R(i,j)>>

The unit103R(i,j) has a function of emitting light ELR and the light ELR has a wavelength greater than or equal to 600 nm and less than or equal to 740 nm (seeFIG.3).

For example, the structure described in Embodiment 2 can be used for the unit103R(i,j).

<<Structure Example of Unit103B(i,j)>>

The unit103B(i,j) has a function of emitting light ELB and the light ELB has a wavelength greater than or equal to 400 nm and less than or equal to 480 nm (seeFIG.3).

For example, the structure described in Embodiment 2 can be used for the unit103B(i,j).

Thus, the step generated between the light-emitting device550R(i,j) and the light-emitting device550B(i,j) can be reduced. The step generated in the conductive film552can be reduced. Furthermore, a phenomenon in which a cut or a split is generated along the step in the conductive film552can be inhibited. Red light can be used for display. Blue light can be used for display. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

The light-emitting device550R(i,j) includes a layer104R(i,j), and the layer104R(i,j) is interposed between the unit103R(i,j) and the electrode551R(i,j).

<<Structure Example of Layer104R(i,j)>>

The layer104R(i,j) contains a substance AM having an electron-accepting property and a material HTM having a hole-transport property. The layer104R(i,j) has an electrical resistivity higher than or equal to 1×102[Ω·cm] and lower than or equal to 1×108[Ω·cm].

For example, the structure of a layer104described in Embodiment 3 can be used for the layer104R(i,j).

The light-emitting device550G(i,j) includes a layer104G(i,j), and the layer104G(i,j) is interposed between the unit103G(i,j) and the electrode551G(i,j). A gap104RG(i,j) is provided between the layer104G(i,j) and the layer104R(i,j). Note that the gap104RG(i,j) can be formed by an etching method, for example.

Specifically, in Step 1, a film that is to be the layer104R(i,j) over the electrode551R(i,j), a stacked film that is to be the unit103R(i,j), and a first sacrificial layer protecting the unit103R(i,j) are formed in this order. In Step 2, the first sacrificial layer, the unit103R(i,j), and the layer104R(i,j) are formed into a predetermined shape by a photolithography method and an etching method. Note that in the case where an unnecessary portion of the stacked film that is to be the unit103R(i,j) is removed by an etching method, a smaller thickness of the stacked film is less likely to generate a residue, leading to easy processing.

Next, in Step 3, the first sacrificial layer protecting the unit103R(i,j), a film that is to be the layer104G(i,j) over the electrode551G(i,j), a stacked film that is to be the unit103G(i,j), and a second sacrificial layer protecting the unit103G(i,j) are formed in this order. In the fourth step, the second sacrificial layer, the unit103G(i,j), and the layer104G(i,j) are formed into a predetermined shape by a photolithography method and an etching method. Note that in the case where an unnecessary portion of the stacked film that is to be the unit103G(i,j) is removed by an etching method, a smaller thickness of the stacked film is less likely to generate a residue, leading to easy processing.

In Step 4, the gap104RG(i,j) can be formed.

<<Structure Example of Layer104G(i,j)>>

The layer104G(i,j) contains the substance AM having an electron-accepting property and the material HTM having a hole-transport property.

For example, the structure of the layer104described in Embodiment 3 can be used for the layer104G(i,j).

Thus, current flowing between the layer104R(i,j) and the layer104G(i,j) can be reduced. Furthermore, a crosstalk phenomenon between the light-emitting device550R(i,j) and the light-emitting device550G(i,j) can be inhibited. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

Note that in this specification and the like, a device fabricated using a metal mask or an FMM (fine metal mask) may be referred to as a device having an MM (metal mask) structure. In this specification and the like, a device fabricated without using a metal mask or an FMM may be referred to as a device having an MML (metal maskless) structure. A display device having an MML structure is fabricated without using a metal mask and thus has higher flexibility in designing the pixel arrangement, the pixel shape, and the like than a display device having an FMM structure or an MM structure.

Note that in the method of fabricating a display device having an MML structure, an island-shaped EL layer is formed not by patterning with the use of a metal mask but by processing an EL layer formed over an entire surface. Accordingly, a high-resolution display device or a display device with a high aperture ratio, which has been difficult to be formed so far, can be obtained. Moreover, EL layers of different colors can be formed separately, which enables the display device to perform extremely clear display with high contrast and high display quality. In addition, a sacrificial layer provided over an EL layer can reduce damage to the EL layer in the fabrication process of the display device, increasing the reliability of the light-emitting device.

The display device of one embodiment of the present invention can have a structure not provided with an insulator that covers the end portion of the pixel electrode. In other words, a structure not provided with an insulator between the pixel electrode and the EL layer is employed. With such a structure, light emission can be efficiently extracted from the EL layer, leading to extremely low viewing angle dependence. For example, in the display device of one embodiment of the present invention, the viewing angle (the maximum angle with a certain contrast ratio maintained when a screen is seen from an oblique direction) can be greater than or equal to 1000 and less than 180°, preferably greater than or equal to 1500 and less than or equal to 170°. Note that the viewing angle refers to that in both the vertical direction and the horizontal direction. The display device of one embodiment of the present invention can have improved viewing angle dependence and high image visibility.

In the case where a display device is a device having a fine metal mask (FMM) structure, the pixel arrangement structure or the like is limited in some cases. Here, the FMM structure will be described below.

In order to fabricate the FMM structure, a metal mask provided with an opening portion (also referred to as an FMM) is set to be opposed to a substrate so that an EL material is deposited to a desired region at the time of EL evaporation. Then, the EL material is deposited to the desired region by EL evaporation through the FMM. When the size of the substrate at the time of EL evaporation is larger, the size of the FMM is increased and accordingly the weight thereof is also increased. Heat or the like is applied to the FMM at the time of EL evaporation and may change the shape of the FMM. There is a method in which EL evaporation is performed while a certain level of tension is applied to the FMM, for example; thus, the weight and strength of the FMM are important parameters.

Thus, in the case where the pixel arrangement structure of a device with an FMM structure is designed, the above parameters and the like need to be taken into consideration, which imposes certain restrictions. By contrast, the display device of one embodiment of the present invention is fabricated using an MML structure and thus offers an excellent effect such as higher flexibility in the pixel arrangement structure or the like than the FMM structure. This structure is highly compatible with a flexible device or the like, for example; thus, one or both of a pixel and a driver circuit can have a variety of circuit arrangements.

Note that the display device of one embodiment of the present invention has a structure including the OS transistor and the light-emitting device having an MML (metal maskless) structure. With this structure, leakage current that might flow through the transistor and leakage current that might flow between adjacent light-emitting elements (also referred to as lateral leakage current, side leakage current, or the like) can become extremely low. With this structure, a viewer can notice any one or more of the image crispness, the image sharpness, a high chroma, and a high contrast ratio in an image displayed on the display device. With the structure where the leakage current that might flow through the transistor and the lateral leakage current between light-emitting elements are extremely low, display with little leakage of light at the time of black display (i.e., with few phenomena in which the black image looks whitish) (such display is also referred to as deep black display) can be achieved.

Note that this embodiment can be combined with any of the other embodiments described in this specification as appropriate.

In this embodiment, a structure of a light-emitting device that can be used in a display device of one embodiment of the present invention will be described with reference toFIG.4.

FIG.4Ais a cross-sectional view illustrating a structure of a light-emitting device550of one embodiment of the present invention, andFIG.4Bis a diagram illustrating energy levels of materials used for the light-emitting device550of one embodiment of the present invention.

The structure of the light-emitting device550described in this embodiment can be applied to the light-emitting device550R(i,j), the light-emitting device550G(i,j), or the light-emitting device550B(i,j). Specifically, the reference numeral “550” used in the description of the light-emitting device550can be used for the description of the light-emitting device550R(i,j), the light-emitting device550G(i,j), and the light-emitting device550B(i,j) by replacing “550” with “550R(i,j)”, “550G(i,j)”, and “550B(i,j)”, respectively. Similarly, the reference numerals for components of the light-emitting device550can be replaced as appropriate.

For example, the reference numeral “103” used in the description of the unit103can be used for the description of the unit103R(i,j), the unit103G(i,j), and the unit103B(i,j) by replacing “103” with “103R(i,j)”, “103G(i,j)”, and “103B(i,j)”, respectively.

The light-emitting device550described in this embodiment includes an electrode551, an electrode552X, and the unit103. The electrode552X includes a region overlapping with the electrode551, and the unit103includes a region interposed between the electrode551and the electrode552X.

<Structure Example of Unit103>

The unit103has a single-layer structure or a stacked-layer structure. For example, the unit103includes a layer111, a layer112, and a layer113(seeFIG.4A). The unit103has a function of emitting light EL1.

The layer111includes a region interposed between the layer112and the layer113, the layer112includes a region interposed between the electrode551and the layer111, and the layer113includes a region interposed between the electrode552X and the layer111.

For example, a layer selected from functional layers such as a light-emitting layer, a hole-transport layer, an electron-transport layer, and a carrier-blocking layer can be used in the unit103. Moreover, a layer selected from functional layers such as a hole-injection layer, an electron-injection layer, an exciton-blocking layer, and a charge-generation layer can be used in the unit103.

<<Structure Example of Layer112>>

For example, a material having a hole-transport property can be used for the layer112. The layer112can be referred to as a hole-transport layer. A material having a wider band gap than the light-emitting material contained in the layer111is preferably used for the layer112. In that case, energy transfer from excitons generated in the layer111to the layer112can be inhibited.

A material having a hole mobility higher than or equal to 1×10−6cm2/Vs can be suitably used as the material having a hole-transport property.

As the hole-transport material, an amine compound or an organic compound having a π-electron rich heteroaromatic ring skeleton can be used, for example. Specifically, a compound having an aromatic amine skeleton, a compound having a carbazole skeleton, a compound having a thiophene skeleton, a compound having a furan skeleton, or the like can be used. The compound having an aromatic amine skeleton and the compound having a carbazole skeleton are particularly preferable because these compounds are highly reliable and have high hole-transport properties to contribute to a reduction in driving voltage.

As the compound having a thiophene skeleton, for example, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV), or the like can be used.

As the compound having a furan skeleton, for example, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II), 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II), or the like can be used.

<<Structure Example of Layer113>>

A material having an electron-transport property, a material having an anthracene skeleton, or a mixed material can be used for the layer113, for example. The layer113can be referred to as an electron-transport layer. A material having a wider band gap than the light-emitting material contained in the layer111is preferably used for the layer113. In that case, energy transfer from excitons generated in the layer111to the layer113can be inhibited.

For example, a metal complex or an organic compound having a π-electron deficient heteroaromatic ring skeleton can be used as the material having an electron-transport property.

A material having an electron mobility higher than or equal to 1×10−7cm2/Vs and lower than or equal to 5×10−5cm2/Vs in a condition where the square root of the electric field strength [V/cm] is 600 can be favorably used as the material having an electron-transport property. Thus, the electron-transport property in the electron-transport layer can be inhibited. Alternatively, the amount of electrons injected into the light-emitting layer can be controlled. Alternatively, the light-emitting layer can be prevented from having excess electrons.

As an organic compound having a π-electron deficient heteroaromatic ring skeleton, a heterocyclic compound having a polyazole skeleton, a heterocyclic compound having a diazine skeleton, a heterocyclic compound having a pyridine skeleton, a heterocyclic compound having a triazine skeleton, or the like can be used, for example. In particular, the heterocyclic compound having a diazine skeleton or the heterocyclic compound having a pyridine skeleton has favorable reliability and thus are preferable. In addition, the heterocyclic compound having a diazine (pyrimidine or pyrazine) skeleton has a high electron-transport property to contribute to a reduction in driving voltage.

As a heterocyclic compound having a pyridine skeleton, 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), or the like can be used, for example.

An organic compound having an anthracene skeleton can be used for the layer113. In particular, an organic compound having both an anthracene skeleton and a heterocyclic skeleton can be suitably used.

For example, an organic compound having both an anthracene skeleton and a nitrogen-containing five-membered ring skeleton can be used. Alternatively, an organic compound having both an anthracene skeleton and a nitrogen-containing five-membered ring skeleton where two heteroatoms are included in a ring can be used. Specifically, a pyrazole ring, an imidazole ring, an oxazole ring, a thiazole ring, or the like can be favorably used as the heterocyclic skeleton.

For example, an organic compound having both an anthracene skeleton and a nitrogen-containing six-membered ring skeleton can be used. Alternatively, an organic compound having both an anthracene skeleton and a nitrogen-containing six-membered ring skeleton where two heteroatoms are included in a ring can be used. Specifically, a pyrazine ring, a pyrimidine ring, a pyridazine ring, or the like can be favorably used as the heterocyclic skeleton.

[Structure Example of Mixed Material]

A material in which a plurality of kinds of substances are mixed can be used for the layer113. Specifically, a mixed material that contains a substance having an electron-transport property and any of an alkali metal, an alkali metal compound, and an alkali metal complex can be used for the layer113. Note that it is further preferable that the HOMO level of the material having an electron-transport property be −6.0 eV or higher.

For example, a composite material of a substance having an electron-accepting property and a material having a hole-transport property can be used for the layer104. Specifically, a composite material of a substance having an electron-accepting property and a substance having a relatively deep HOMO level HMT, which is greater than or equal to −5.7 eV and lower than or equal to −5.4 eV, can be used for the layer104(seeFIG.4B). The mixed material can be suitably used for the layer113in combination with a structure using such a composite material for the layer104. As a result, the reliability of the light-emitting device can be increased.

Furthermore, a structure using a material having a hole-transport property for the layer112can be suitably combined with the structure using the mixed material for the layer113and the composite material for the layer104. For example, a substance having a HOMO level HM2, which is within the range of −0.2 eV to 0 eV from the relatively deep HOMO level HM1, can be used for the layer112(seeFIG.4B). As a result, the reliability of the light-emitting device can be increased. Note that in this specification and the like, the structure of the above-described light-emitting device is referred to as a Recombination-Site Tailoring Injection structure (ReSTI structure) in some cases.

The concentration of the alkali metal, the alkali metal compound, or the alkali metal complex preferably differs in the thickness direction of the layer113(including the case where the concentration is 0).

For example, a metal complex having an 8-hydroxyquinolinato structure can be used. A methyl-substituted product of the metal complex having an 8-hydroxyquinolinato structure (e.g., a 2-methyl-substituted product or a 5-methyl-substituted product) or the like can also be used.

As the metal complex having an 8-hydroxyquinolinato structure, 8-hydroxyquinolinato-lithium (abbreviation: Liq), 8-hydroxyquinolinato-sodium (abbreviation: Naq), or the like can be used. In particular, a complex of a monovalent metal ion, especially a complex of lithium is preferable, and Liq is further preferable.

Structure Example 1 of Layer111

A light-emitting material or a light-emitting material and a host material can be used for the layer111, for example. The layer111can be referred to as alight-emitting layer. The layer111is preferably provided in a region where holes and electrons are recombined. In that case, energy generated by recombination of carriers can be efficiently converted into light and emitted.

Furthermore, the layer111is preferably provided apart from a metal used for the electrode or the like. In that case, a quenching phenomenon caused by the metal used for the electrode or the like can be inhibited.

It is preferable that a distance from an electrode or the like having reflectivity to the layer111be adjusted and the layer111be placed in an appropriate position in accordance with an emission wavelength. Thus, the amplitude can be increased by utilizing an interference phenomenon between light reflected by the electrode or the like and light emitted from the layer111. Light of a predetermined wavelength can be intensified and the spectrum of the light can be narrowed. In addition, bright light emission colors with high intensity can be obtained. In other words, the layer111is placed in an appropriate position, for example, between electrodes and the like, and thus a microcavity structure (microcavity) can be formed.

For example, a fluorescent substance, a phosphorescent substance, or a substance exhibiting thermally activated delayed fluorescence (TADF) (also referred to as a TADF material) can be used as the light-emitting material. Thus, energy generated by recombination of carriers can be released as the light EL1from the light-emitting material (seeFIG.4A).

A fluorescent substance can be used for the layer111. For example, any of the following fluorescent substances can be used for the layer111. Note that without being limited to the following ones, any of a variety of known fluorescent substances can be used for the layer111.

Condensed aromatic diamine compounds typified by pyrenediamine compounds such as 1,6FLPAPm, 1,6mMemFLPAPm, and 1,6BnfAPm-03 are particularly preferable because of their high hole-trapping properties, high emission efficiency, or high reliability.

A phosphorescent substance can be used for the layer111. For example, any of the following phosphorescent substances can be used for the layer111. Note that without being limited to the following ones, any of a variety of known phosphorescent substances can be used for the layer111.

For the layer111, it is possible to use, for example, an organometallic iridium complex having a 4H-triazole skeleton, an organometallic iridium complex having a 1H-triazole skeleton, an organometallic iridium complex having an imidazole skeleton, an organometallic iridium complex having a phenylpyridine derivative with an electron-withdrawing group as a ligand, an organometallic iridium complex having a pyrimidine skeleton, an organometallic iridium complex having a pyrazine skeleton, an organometallic iridium complex having a pyridine skeleton, a rare earth metal complex, or a platinum complex.

As an organometallic iridium complex having a 4H-triazole skeleton or the like, tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp)3]), tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Mptz)3]), tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPrptz-3b)3]), or the like can be used.

As an organometallic iridium complex having a 1H-triazole skeleton or the like, tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Mptz1-mp)3]), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Prptz1-Me)3]), or the like can be used.

As an organometallic iridium complex having an imidazole skeleton or the like, fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpmi)3]), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: [Ir(dmpimpt-Me)3]), or the like can be used.

As an organometallic iridium complex having a phenylpyridine derivative with an electron-withdrawing group as a ligand, or the like, bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) picolinate (abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C2′}iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) acetylacetonate (abbreviation: FIracac), or the like can be used.

Note that these are compounds exhibiting blue phosphorescence and are compounds having an emission wavelength peak at 440 nm to 520 nm.

As an organometallic iridium complex having a pyrazine skeleton or the like, (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(acac)]), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-iPr)2(acac)]), or the like can be used.

An example of a rare earth metal complex is tris(acetylacetonato) (monophenanthroline)terbium(III) (abbreviation: [Tb(acac)3(Phen)]).

Note that these are compounds mainly exhibiting green phosphorescence and have an emission wavelength peak at 500 nm to 600 nm. An organometallic iridium complex having a pyrimidine skeleton excels particularly in reliability or emission efficiency.

As an organometallic iridium complex having a pyrimidine skeleton or the like, (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm)2(dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm)2(dpm)]), bis[4,6-di(naphthalen-1-yl)pyrimidinato] (dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm)2(dpm)]), or the like can be used.

As an organometallic iridium complex having a pyrazine skeleton or the like, (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr)2(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: [Ir(Fdpq)2(acac)]), or the like can be used.

As an organometallic iridium complex having a pyridine skeleton or the like, tris(1-phenylisoquinolinato-N,C2′)iridium(III) (abbreviation: [Ir(piq)3]), bis(1-phenylisoquinolinato-N,C2′)iridium(III) acetylacetonate (abbreviation: [Ir(piq)2(acac)]), or the like can be used.

As a rare earth metal complex or the like, tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: [Eu(DBM)3(Phen)]), tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato] (monophenanthroline)europium(III) (abbreviation: [Eu(TTA)3(Phen)]), or the like can be used.

As a platinum complex or the like, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP) or the like can be used.

Note that these are compounds exhibiting red phosphorescence and have an emission peak at 600 nm to 700 nm. Furthermore, from the organometallic iridium complex having a pyrazine skeleton, red light emission with chromaticity favorably used for display devices can be obtained.

A TADF material can be used for the layer111. For example, any of the TADF materials given below can be used as the light-emitting material. Note that without being limited thereto, any of a variety of known TADF materials can be used as the light-emitting material.

In the TADF material, the difference between the S1 level and the T1 level is small, and reverse intersystem crossing (upconversion) from the triplet excited state into the singlet excited state can be achieved by a little thermal energy. Thus, the singlet excited state can be efficiently generated from the triplet excited state. In addition, the triplet excitation energy can be converted into light.

An exciplex whose excited state is formed of two kinds of substances has an extremely small difference between the S1 level and the T1 level and functions as a TADF material capable of converting triplet excitation energy into singlet excitation energy.

A phosphorescence spectrum observed at a low temperature (e.g., 77 K to 10 K) is used for an index of the T1 level. When the level of energy with a wavelength of the line obtained by extrapolating a tangent to the fluorescent spectrum at a tail on the short wavelength side is the S1 level and the level of energy with a wavelength of the line obtained by extrapolating a tangent to the phosphorescent spectrum at a tail on the short wavelength side is the T1 level, the difference between S1 and T1 of the TADF material is preferably smaller than or equal to 0.3 eV, further preferably smaller than or equal to 0.2 eV.

When a TADF material is used as the light-emitting substance, the S1 level of the host material is preferably higher than that of the TADF material. In addition, the T1 level of the host material is preferably higher than that of the TADF material.

Examples of the TADF material include a fullerene, a derivative thereof, an acridine, a derivative thereof, and an eosin derivative. Furthermore, porphyrin containing a metal such as magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd) can be also used for the TADF material.

Specifically, any of the following materials whose structural formulae are shown below can be used: a protoporphyrin-tin fluoride complex (SnF2(Proto IX)), a mesoporphyrin-tin fluoride complex (SnF2(Meso IX)), a hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (SnF2(OEP)), an etioporphyrin-tin fluoride complex (SnF2(Etio I)), an octaethylporphyrin-platinum chloride complex (PtCl2OEP), and the like.

Furthermore, a heterocyclic compound including one or both of a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring can be used, for example, for the TADF material.

Such a heterocyclic compound is preferable because of having excellent electron-transport property and hole-transport property owing to a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring. Among skeletons having the π-electron deficient heteroaromatic ring, in particular, a pyridine skeleton, a diazine skeleton (a pyrimidine skeleton, a pyrazine skeleton, and a pyridazine skeleton), and a triazine skeleton are preferable because of their high stability and reliability. In particular, a benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and a benzothienopyrazine skeleton, which have high electron-withdrawing properties and favorable reliability, are preferable.

Among skeletons having the π-electron rich heteroaromatic ring, an acridine skeleton, a phenoxazine skeleton, a phenothiazine skeleton, a furan skeleton, a thiophene skeleton, and a pyrrole skeleton have high stability and reliability; therefore, at least one of these skeletons is preferably included. A dibenzofuran skeleton is preferable as a furan skeleton, and a dibenzothiophene skeleton is preferable as a thiophene skeleton. As a pyrrole skeleton, an indole skeleton, a carbazole skeleton, an indolocarbazole skeleton, a bicarbazole skeleton, and a 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole skeleton are particularly preferable.

Note that a substance in which the π-electron rich heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring is particularly preferable because the electron-donating property of the π-electron rich heteroaromatic ring and the electron-accepting property of the π-electron deficient heteroaromatic ring are both improved, the energy difference between the S1 level and the T1 level becomes small, and thus thermally activated delayed fluorescence can be obtained with high efficiency. Note that an aromatic ring to which an electron-withdrawing group such as a cyano group is bonded may be used instead of the π-electron deficient heteroaromatic ring. As a π-electron rich skeleton, an aromatic amine skeleton, a phenazine skeleton, or the like can be used.

As a π-electron deficient skeleton, a xanthene skeleton, a thioxanthene dioxide skeleton, an oxadiazole skeleton, a triazole skeleton, an imidazole skeleton, an anthraquinone skeleton, a skeleton containing boron such as phenylborane or boranthrene, an aromatic ring or a heteroaromatic ring having a nitrile group or a cyano group such as benzonitrile or cyanobenzene, a carbonyl skeleton such as benzophenone, a phosphine oxide skeleton, a sulfone skeleton, or the like can be used.

As described above, a π-electron deficient skeleton and a π-electron rich skeleton can be used instead of at least one of the π-electron deficient heteroaromatic ring and the π-electron rich heteroaromatic ring.

Structure Example 2 of Layer111

A material having a carrier-transport property can be used as the host material. For example, a material having a hole-transport property, a material having an electron-transport property, a substance exhibiting thermally activated delayed fluorescence TADF, a material having an anthracene skeleton, or a mixed material can be used as the host material. A material having a wider band gap than the light-emitting material contained in the layer111is preferably used as the host material. In that case, energy transfer from excitons generated in the layer111to the host material can be inhibited.

A material having a hole mobility higher than or equal to 1×10−6cm2/Vs can be suitably used as the material having a hole-transport property.

For example, a material having a hole-transport property that can be used for the layer112can be used for the layer111. Specifically, a material having a hole-transport property that can be used for the hole-transport layer can be used for the layer111.

For example, a material having an electron-transport property that can be used for the layer113can be used for the layer111. Specifically, a material having an electron-transport property that can be used for the electron-transport layer can be used for the layer111.

An organic compound having an anthracene skeleton can be used as the host material. In particular, when a fluorescent substance is used as the light-emitting substance, an organic compound having an anthracene skeleton is preferably used. In that case, alight-emitting device with high emission efficiency and high durability can be obtained.

As the organic compound having an anthracene skeleton, an organic compound having a diphenylanthracene skeleton, in particular, a 9,10-diphenylanthracene skeleton is chemically stable and thus is preferable. The host material preferably has a carbazole skeleton, in which case the hole-injection and hole-transport properties are improved. In particular, the host material preferably has a dibenzocarbazole skeleton, in which case the HOMO level thereof is shallower than that of carbazole by approximately 0.1 eV, so that holes enter the host material easily, the hole-transport property is improved, and the heat resistance is increased. Note that in terms of the hole-injection and hole-transport properties, a benzofluorene skeleton or a dibenzofluorene skeleton may be used instead of a carbazole skeleton.

Thus, a substance having both a 9,10-diphenylanthracene skeleton and a carbazole skeleton, a substance having both a 9,10-diphenylanthracene skeleton and a benzocarbazole skeleton, or a substance having both a 9,10-diphenylanthracene skeleton and a dibenzocarbazole skeleton is preferable as the host material.

A TADF material can be used as the host material. When the TADF material is used as the host material, triplet excitation energy generated in the TADF material can be converted into singlet excitation energy by reverse intersystem crossing. Moreover, excitation energy can be transferred to the light-emitting substance. In other words, the TADF material functions as an energy donor, and the light-emitting substance functions as an energy acceptor. Thus, the emission efficiency of the light-emitting device can be increased.

This is very effective in the case where the light-emitting substance is a fluorescent substance. In that case, the S1 level of the TADF material is preferably higher than that of the fluorescent substance in order that high emission efficiency can be achieved. Furthermore, the T1 level of the TADF material is preferably higher than the S1 level of the fluorescent substance. Therefore, the T1 level of the TADF material is preferably higher than that of the fluorescent substance.

It is also preferable to use a TADF material that emits light whose wavelength overlaps with the wavelength on a lowest-energy-side absorption band of the fluorescent substance. This enables smooth transfer of excitation energy from the TADF material to the fluorescent substance and accordingly enables efficient light emission, which is preferable.

In addition, in order to efficiently generate singlet excitation energy from the triplet excitation energy by reverse intersystem crossing, carrier recombination preferably occurs in the TADF material. It is also preferable that the triplet excitation energy generated in the TADF material not be transferred to the triplet excitation energy of the fluorescent substance. For that reason, the fluorescent substance preferably has a protecting group around a luminophore (a skeleton which causes light emission) of the fluorescent substance. As the protecting group, a substituent having no π bond and a saturated hydrocarbon are preferably used. Specific examples include an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms. It is further preferable that the fluorescent substance have a plurality of protecting groups. The substituents having no π bond are poor in carrier-transport performance, whereby the TADF material and the luminophore of the fluorescent substance can be made away from each other with little influence on carrier transport or carrier recombination.

Here, the luminophore refers to an atomic group (skeleton) that causes light emission in a fluorescent substance. The luminophore is preferably a skeleton having a π bond, further preferably includes an aromatic ring, still further preferably includes a condensed aromatic ring or a condensed heteroaromatic ring.

Examples of the condensed aromatic ring or the condensed heteroaromatic ring include a phenanthrene skeleton, a stilbene skeleton, an acridone skeleton, a phenoxazine skeleton, and a phenothiazine skeleton. Specifically, a fluorescent substance having any of a naphthalene skeleton, an anthracene skeleton, a fluorene skeleton, a chrysene skeleton, a triphenylene skeleton, a tetracene skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, and a naphthobisbenzofuran skeleton is preferable because of its high fluorescence quantum yield.

For example, the TADF material that can be used as the light-emitting material can be used as the host material.

Structure Example 1 of Mixed Material

A material in which a plurality of kinds of substances are mixed can be used as the host material. For example, a material that contains an electron-transport material and a hole-transport material can be used as the mixed material. The weight ratio between the hole-transport material and the electron-transport material contained in the mixed material may be (the hole-transport material/the electron-transport material)=(1/19) or more and (19/1) or less. Accordingly, the carrier-transport property of the layer111can be easily adjusted. In addition, a recombination region can be controlled easily.

Structure Example 2 of Mixed Material

A material mixed with a phosphorescent substance can be used as the host material. When a fluorescent substance is used as the light-emitting substance, a phosphorescent substance can be used as an energy donor for supplying excitation energy to the fluorescent substance.

Structure Example 3 of Mixed Material

A mixed material containing a material to form an exciplex can be used as the host material. For example, a material forming an exciplex whose emission spectrum overlaps with the wavelength of the absorption band on the lowest energy side of the light-emitting substance can be used as the host material. This enables smooth energy transfer and improves emission efficiency. Alternatively, the driving voltage can be reduced. With such a structure, light emission can be efficiently obtained by ExTET (Exciplex-Triplet Energy Transfer), which is energy transfer from the exciplex to the light-emitting substance (phosphorescent material).

A phosphorescent substance can be used as at least one of the materials forming an exciplex. Accordingly, reverse intersystem crossing can be used. Alternatively, triplet excitation energy can be efficiently converted into singlet excitation energy.

A combination of materials forming an exciplex is preferably such that the HOMO level of a material having a hole-transport property is higher than or equal to the HOMO level of a material having an electron-transport property. Alternatively, the LUMO level of the material having a hole-transport property is preferably higher than or equal to the LUMO level of the material having an electron-transport property. In that case, an exciplex can be efficiently formed. Note that the LUMO levels and the HOMO levels of the materials can be derived from the electrochemical characteristics (the reduction potentials and the oxidation potentials). Specifically, the reduction potentials and the oxidation potentials can be measured by cyclic voltammetry (CV).

The formation of an exciplex can be confirmed by a phenomenon in which the emission spectrum of a mixed film in which the material having a hole-transport property and the material having an electron-transport property are mixed is shifted to a longer wavelength than the emission spectrum of each of the materials (or has another peak on the longer wavelength side) observed in comparison of the emission spectrum of the material having a hole-transport property, the emission spectrum of the material having an electron-transport property, and the emission spectrum of the mixed film of these materials, for example. Alternatively, the formation of an exciplex can be confirmed by a difference in transient response, such as Furthermore, a phenomenon in which the transient photoluminescence (PL) lifetime of the mixed film has longer lifetime components or has a larger proportion of delayed components than that of each of the materials, observed in comparison of transient PL of the material having a hole-transport property, the transient PL of the material having an electron-transport property, and the transient PL of the mixed film of these materials. The transient PL can be rephrased as transient electroluminescence (EL). That is, the formation of an exciplex can also be confirmed by a difference in transient response observed in comparison of the transient EL of the material having a hole-transport property, the transient EL of the material having an electron-transport property, and the transient EL of the mixed film of these materials.

Note that this embodiment can be combined with any of the other embodiments described in this specification as appropriate.

In this embodiment, a structure of a light-emitting device that can be used in a display device of one embodiment of the present invention will be described with reference toFIG.4.

The structure of the light-emitting device550described in this embodiment can be applied to the light-emitting device550R(i,j), the light-emitting device550G(i,j), or the light-emitting device550B(i,j). Specifically, the reference numeral “550” used in the description of the light-emitting device550can be used for the description of the light-emitting device550R(i,j), the light-emitting device550G(i,j), and the light-emitting device550B(i,j) by replacing “550” with “550R(i,j)”, “550G(i,j)”, and “550B(i,j)”, respectively. Similarly, the reference numerals for components of the light-emitting device550can be replaced as appropriate.

For example, the reference numeral “551” used in the description of the electrode551can be used for the description of the electrode551R(i,j), the electrode551G(i,j), and the electrode551B(i,j) by replacing “551” with “551R(i,j)”, “551G(i,j)”, and “551B(i,j)”, respectively.

Furthermore, the reference numeral “104” used in the description of the layer104can be used for the description of the layer104R(i,j), the layer104G(i,j), and a layer104B(i,j) by replacing “104” with “104R(i,j)”, “104G(i,j)”, and “104B(i,j)”, respectively.

The light-emitting device550described in this embodiment includes the electrode551, the electrode552X, the unit103, and the layer104. The electrode552X includes a region overlapping with the electrode551, and the unit103includes a region interposed between the electrode551and the electrode552X. The layer104includes a region interposed between the electrode551and the unit103. For example, the structure described in Embodiment 2 can be used for the unit103.

<Structure Example of Electrode551>

For example, a conductive material can be used for the electrode551. Specifically, a single layer or a stacked layer of a metal, an alloy, or a film containing a conductive compound can be used for the electrode551.

For example, a film that efficiently reflects light can be used for the electrode551. Specifically, an alloy containing silver, copper, and the like, an alloy containing silver, palladium, and the like, or a metal film of aluminum or the like can be used for the electrode551.

Alternatively, for example, a metal film that transmits part of light and reflects the other part of the light can be used as the electrode551. Thus, a microcavity structure (microcavity) can be provided in the light-emitting device550. Light of a predetermined wavelength can be extracted more efficiently than other light. Light with a narrow half width of a spectrum can be extracted. Light of a bright color can be extracted.

A film having a property of transmitting visible light can be used for the electrode551, for example. Specifically, a single layer or a stacked layer of a metal film, an alloy film, a conductive oxide film, or the like that is thin enough to transmit light can be used for the electrode551.

In particular, a material having a work function higher than or equal to 4.0 eV can be suitably used for the electrode551.

For example, a conductive oxide containing indium can be used. Specifically, indium oxide, indium oxide-tin oxide (abbreviation: ITO), indium oxide-tin oxide containing silicon or silicon oxide (abbreviation: ITSO), indium oxide-zinc oxide, indium oxide containing tungsten oxide and zinc oxide (abbreviation: IWZO), or the like can be used.

Furthermore, for example, a conductive oxide containing zinc can be used. Specifically, zinc oxide, zinc oxide to which gallium is added, zinc oxide to which aluminum is added, or the like can be used.

Furthermore, for example, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), a nitride of a metal material (e.g., titanium nitride), or the like can be used. Alternatively, graphene can be used.

<<Structure Example of Layer104>>

For example, a material having a hole-injection property can be used for the layer104. The layer104can be referred to as a hole-injection layer.

Specifically, a substance having an electron-accepting property can be used for the layer104. A composite material containing a plurality of kinds of substances can be used for the layer104. This can facilitate injection of holes from the electrode551, for example. Alternatively, the driving voltage of the light-emitting device can be lowered.

An organic compound and an inorganic compound can be used as the substance having an electron-accepting property. The substance having an electron-accepting property can extract electrons from an adjacent hole-transport layer or an adjacent material having a hole-transport property by the application of an electric field.

For example, a compound having an electron-withdrawing group (a halogen group or a cyano group) can be used as the substance having an electron-accepting property. Note that an organic compound having an electron-accepting property is easily deposited by evaporation and its film can be easily formed. As a result, the productivity of the light-emitting device can be increased.

A compound in which electron-withdrawing groups are bonded to a condensed aromatic ring having a plurality of heteroatoms, such as HAT-CN, is particularly preferable because it is thermally stable.

Alternatively, a [3]radialene derivative having an electron-withdrawing group (in particular, a cyano group or a halogen group such as a fluoro group) is preferable because it has a very high electron-accepting property.

Specifically, it is possible to use, for example, α,α′,α″-1,2,3-cyclopropanetriylidenetris[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile], α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile], or α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,3,4,5,6-pentafluorobenzeneacetonitrile].

As the substance having an electron-accepting property, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used.

Alternatively, it is possible to use phthalocyanine (abbreviation: H2Pc), a phthalocyanine-based complex compound such as and copper phthalocyanine (CuPc), and compounds having an aromatic amine skeleton such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) and N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (abbreviation: DNTPD).

Furthermore, it is possible to use, for example, a high molecular compound such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS).

Structure Example 1 of Composite Material

For example, a composite material containing a substance having an electron-accepting property and a material having a hole-transport property can be used for the layer104. Thus, not only a material having a high work function, but also a material having a low work function can be used for the electrode551. Alternatively, a material used for the electrode551can be selected from a wide range of materials regardless of its work function.

As the material having a hole-transport property in the composite material, for example, a compound having an aromatic amine skeleton, a carbazole derivative, an aromatic hydrocarbon, an aromatic hydrocarbon having a vinyl group, a high molecular compound (such as an oligomer, a dendrimer, or a polymer), or the like can be used. A material having a hole mobility of 1×10−6cm2/Vs or higher can be suitably used as the material having a hole-transport property in the composite material.

A substance having a relatively deep HOMO level can be suitably used as the material having a hole-transport property in the composite material. Specifically, the HOMO level is preferably higher than or equal to −5.7 eV and lower than or equal to −5.4 eV, in which case hole injection to the unit103can be facilitated. In that case, hole injection to the unit103can be facilitated. Alternatively, hole injection to the layer112can be facilitated. Alternatively, the reliability of the light-emitting device can be increased.

As the aromatic hydrocarbon having a vinyl group, for example, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), or the like can be used.

As another example, a substance having any of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton can be favorably used as the material having a hole-transport property in the composite material. Moreover, as the material having a hole-transport property in the composite material, it is possible to use a substance including any of an aromatic amine having a substituent that includes a dibenzofuran ring or a dibenzothiophene ring, an aromatic monoamine that includes a naphthalene ring, and an aromatic monoamine in which a 9-fluorenyl group is bonded to nitrogen of amine through an arylene group. With the use of a substance including an N,N-bis(4-biphenyl)amino group, the reliability of the light-emitting device can be increased.

Structure Example 2 of Composite Material

For example, a composite material containing a substance having an electron-accepting property, a material having a hole-transport property, and a fluoride of an alkali metal or a fluoride of an alkaline earth metal can be used as the material having a hole-injection property. In particular, a composite material in which the proportion of fluorine atoms is higher than or equal to 20% can be suitably used. Thus, the refractive index of the layer104can be reduced. Alternatively, a layer with a low refractive index can be formed inside the light-emitting device. Alternatively, the external quantum efficiency of the light-emitting device can be improved.

Note that this embodiment can be combined with any of the other embodiments described in this specification as appropriate.

In this embodiment, a structure of a light-emitting device that can be used in a display device of one embodiment of the present invention will be described with reference toFIG.4.

The structure of the light-emitting device550described in this embodiment can be applied to the light-emitting device550R(i,j), the light-emitting device550G(i,j), or the light-emitting device550B(i,j). Specifically, the reference numeral “550” used in the description of the light-emitting device550can be used for the description of the light-emitting device550R(i,j), the light-emitting device550G(i,j), and the light-emitting device550B(i,j) by replacing “550” with “550R(i,j)”, “550G(i,j)”, and “550B(i,j)”, respectively. Similarly, the reference numerals for components of the light-emitting device550can be replaced as appropriate.

For example, the reference numeral “552X” used in the description of the electrode552X can be used for the description of the electrode552R(i,j), the electrode552G(i,j), and the electrode552B(i,j) by replacing “552X” with “552R(i,j)”, “552G(i,j)”, and “552B(i,j)”, respectively.

The light-emitting device550described in this embodiment includes the electrode551, the electrode552X, the unit103, and a layer105. The electrode552X includes a region overlapping with the electrode551, and the unit103includes a region interposed between the electrode551and the electrode552X. The layer105includes a region interposed between the unit103and the electrode552X. For example, the structure described in Embodiment 2 can be used for the unit103.

<Structure Example of Electrode552X>

A conductive material can be used for the electrode552X, for example. Specifically, a single layer or a stacked layer of a metal, an alloy, or a material containing a conductive compound can be used for the electrode552X.

For example, the material that can be used for the electrode551described in Embodiment 3 can be used for the electrode552X. In particular, a material having a lower work function than the electrode551can be favorably used for the electrode552X. Specifically, a material having a work function lower than or equal to 3.8 eV is preferable.

For example, an element belonging to Group 1 of the periodic table, an element belonging to Group 2 of the periodic table, a rare earth metal, or an alloy containing any of these elements can be used for the electrode552X.

Specifically, lithium (Li), cesium (Cs), or the like; magnesium (Mg), calcium (Ca), strontium (Sr), or the like; europium (Eu), ytterbium (Yb), or the like; or an alloy containing any of these (MgAg or AlLi) can be used for the electrode552X.

<<Structure Example of Layer105>>

A material having an electron-injection property can be used for the layer105, for example. The layer105can be referred to as an electron-injection layer.

Specifically, a substance having a donor property can be used for the layer105. Alternatively, a material in which a substance having a donor property and a material having an electron-transport property are combined can be used for the layer105. Alternatively, electride can be used for the layer105. This can facilitate injection of electrons from the electrode552X, for example. Alternatively, besides a material having a low work function, a material having a high work function can also be used for the electrode552X. Alternatively, a material used for the electrode552X can be selected from a wide range of materials regardless of its work function. Specifically, Al, Ag, ITO, indium oxide-tin oxide containing silicon or silicon oxide, or the like can be used for the electrode552X. Alternatively, the driving voltage of the light-emitting device can be lowered.

For example, an alkali metal, an alkaline earth metal, a rare earth metal, or a compound thereof (an oxide, a halide, a carbonate, or the like) can be used as the substance having a donor property. Alternatively, an organic compound such as tetrathianaphthacene (abbreviation: TTN), nickelocene, or decamethylnickelocene can be used as the substance having a donor property.

As an alkali metal compound (including an oxide, a halide, and a carbonate), lithium oxide, lithium fluoride (LiF), cesium fluoride (CsF), lithium carbonate, cesium carbonate, 8-hydroxyquinolinato-lithium (abbreviation: Liq), or the like can be used.

As an alkaline earth metal compound (including an oxide, a halide, and a carbonate), calcium fluoride (CaF2) or the like can be used.

Structure Example 1 of Composite Material

A material in which a plurality of kinds of substances are combined can be used as the material having an electron-injection property. For example, a substance having a donor property and a material having an electron-transport property can be used for the composite material.

A metal complex or an organic compound having a π-electron deficient heteroaromatic ring skeleton can be used as the material having an electron-transport property. For example, a material having an electron-transport property usable for the unit103can be used for the composite material.

Structure Example 2 of Composite Material

A material including a fluoride of an alkali metal in a microcrystalline state and a material having an electron-transport property can be used for the composite material. Alternatively, a material including a fluoride of an alkaline earth metal in a microcrystalline state and a material having an electron-transport property can be used for the composite material. In particular, a composite material containing a fluoride of an alkali metal or a fluoride of an alkaline earth metal at higher than or equal to 50 wt % can be suitably used. Alternatively, a composite material including an organic compound having a bipyridine skeleton can be suitably used. In that case, the refractive index of the layer105can be reduced. Alternatively, the external quantum efficiency of the light-emitting device can be improved.

Structure Example 3 of Composite Material

For example, a composite material containing a first organic compound having an unshared electron pair and a first metal can be used for the layer105. The sum of the number of electrons of the first organic compound and the number of electrons of the first metal is preferably an odd number. The molar ratio of the first metal to 1 mol of the first organic compound is preferably greater than or equal to 0.1 and less than or equal to 10, further preferably greater than or equal to 0.2 and less than or equal to 2, still further preferably greater than or equal to 0.2 and less than or equal to 0.8.

Accordingly, the first organic compound having an unshared electron pair interacts with the first metal and thus can form a singly occupied molecular orbital (SOMO). Furthermore, in the case where electrons are injected from the electrode552X into the layer105, a barrier therebetween can be lowered. The first metal has a low reactivity with water or oxygen; thus, the moisture resistance of the light-emitting device can be improved.

For the layer105, a composite material that allows the spin density measured by an electron spin resonance method (ESR) to be preferably higher than or equal to 1×1016spins/cm3, further preferably higher than or equal to 5×1016spins/cm3, still further preferably higher than or equal to 1×1017spins/cm3can be used.

For example, a material having an electron-transport property can be used for the organic compound having an unshared electron pair. For example, a compound having an electron deficient heteroaromatic ring can be used. Specifically, a compound having at least one of a pyridine ring, a diazine ring (a pyrimidine ring, a pyrazine ring, and a pyridazine ring), and a triazine ring can be used. Accordingly, the driving voltage of the light-emitting device can be reduced.

Note that the lowest unoccupied molecular orbital (LUMO) level of the organic compound having an unshared electron pair is preferably greater than or equal to −3.6 eV and less than or equal to −2.3 eV. In general, the HOMO level and the LUMO level of an organic compound can be estimated by CV (cyclic voltammetry), photoelectron spectroscopy, optical absorption spectroscopy, inverse photoelectron spectroscopy, or the like.

Alternatively, for example, copper phthalocyanine can be used for the organic compound having an unshared electron pair. The number of electrons of the copper phthalocyanine is an odd number.

For example, when the number of electrons of the first organic compound having an unshared electron pair is an even number, a composite material of a metal that belongs to an odd-numbered group in the periodic table and the first organic compound can be used for the layer105.

For example, manganese (Mn), which is a metal belonging to Group 7, cobalt (Co), which is a metal belonging to Group 9, copper (Cu), silver (Ag), and gold (Au), which are metals belonging to Group 11, aluminum (Al) and indium (In), which are metals belonging to Group 13 are odd-numbered groups in the periodic table. Note that elements belonging to Group 11 have a lower melting point than elements belonging to Group 7 or Group 9 and thus are suitable for vacuum evaporation. In particular, Ag is preferable because of its low melting point.

The use of Ag for the electrode552X and the layer105can increase the adhesion between the layer105and the electrode552X.

When the number of electrons of the first organic compound having an unshared electron pair is an odd number, a composite material of the first metal that belongs to an even-numbered group in the periodic table and the first organic compound can be used for the layer105. For example, iron (Fe), which is a metal belonging to Group 8, is an element belonging to an even-numbered group in the periodic table.

For example, a substance obtained by adding electrons at high concentration to an oxide where calcium and aluminum are mixed, or the like can be used as the material having an electron-injection property.

Note that this embodiment can be combined with any of the other embodiments described in this specification as appropriate.

In this embodiment, a structure of a display device of one embodiment of the present invention will be described with reference toFIG.5.

FIG.5Ais a top view illustrating the structure of the display device of one embodiment of the present invention, andFIG.5Bis a perspective view illustrating part ofFIG.5A.

Structure Example 5 of Display Device

The display device700described in this embodiment includes a region231, a functional layer520, and a functional layer510(seeFIG.5A,FIG.5B, andFIG.6A).

<Structure Example of Region231>

The region231includes a pixel set703(i,j) (seeFIG.5A). The region231has a function of displaying image information.

For example, the region231includes 500 or more pixel sets per inch. Furthermore, the region231includes 1000 or more groups of pixel sets per inch, preferably 5000 or more groups of pixel sets per inch, further preferably 10000 or more groups of pixel sets per inch. Thus, this can reduce a screen-door effect in the case where the display panel is used for a goggle-type display device, for example.

The region231includes a plurality of pixels. For example, the region231includes 7600 or more pixels in the row direction and 4300 or more pixels in the column direction. Specifically, 7680 pixels are provided in the row direction and 4320 pixels are provided in the column direction. Thus, a high-resolution image can be displayed.

<<Structure Example of Pixel Set703(i,j)>>

The pixel set703(i,j) includes a pixel702R(i,j) and a pixel702G(i,j) (seeFIG.5B). Furthermore, the pixel set703(i,j) includes a pixel702B(i,j).

For example, a plurality of pixels capable of displaying colors with different hues can be used. Note that the plurality of pixels can be referred to as subpixels. A set of subpixels can be referred to as a pixel.

This enables additive mixture or subtractive mixture of colors displayed by the plurality of pixels. It is possible to display a color of a hue that an individual pixel cannot display.

Specifically, the pixel702B(i,j) displaying blue, the pixel702G(i,j) displaying green, and the pixel702R(i,j) displaying red can be used in the pixel703(i,j). The pixel702B(i,j), the pixel702G(i,j), and the pixel702R(i,j) can each be referred to as a subpixel.

A pixel displaying white or the like can be used in addition to the above set in the pixel703(i,j), for example. A pixel displaying cyan, a pixel displaying magenta, and a pixel displaying yellow can be used in the pixel703(i,j).

A pixel emitting infrared rays can be used in addition to the above set in the pixel703(i,j), for example. Specifically, a pixel that emits light including light with a wavelength greater than or equal to 650 nm and less than or equal to 1000 nm can be used in the pixel703(i,j).

<<Structure Example of Pixel702R(i,j)>>

The pixel702R(i,j) includes the light-emitting device550R(i,j) and a pixel circuit530R(i,j) (seeFIG.6A). The light-emitting device550R(i,j) is electrically connected to the pixel circuit530R(i,j). For example, the light-emitting device550R(i,j) is electrically connected to the pixel circuit530R(i,j) through an opening portion591R.

Note that the pixel circuit530R(i,j) is supplied with a first image signal.

<<Structure Example of Pixel702G(i,j)>>

The pixel702G(i,j) includes the light-emitting device550G(i,j) and a pixel circuit530G(i,j). The light-emitting device550G(i,j) is electrically connected to the pixel circuit530G(i,j). For example, the light-emitting device550G(i,j) is electrically connected to the pixel circuit530G(i,j) through an opening portion591G.

Furthermore, the pixel circuit530G(i,j) is supplied with a second image signal.

<Structure Example of Functional Layer520>

The functional layer520includes the pixel circuit530G(i,j) and the pixel circuit530R(i,j).

The functional layer520is interposed between the light-emitting device550R(i,j) and the functional layer510. Furthermore, the functional layer520is interposed between the light-emitting device550G(i,j) and the functional layer510.

<Structure Example of Functional Layer510>

The functional layer510includes a driver circuit SD. Furthermore, the functional layer510includes a driver circuit GD. For example, a single crystal silicon substrate can be used for the functional layer510.

<<Structure Example of Driver Circuit SD>>

The driver circuit SD generates the first image signal and the second image signal.

Thus, the driver circuit SD can be positioned so as to overlap with the functional layer520that includes the pixel circuit530R(i,j) and the pixel circuit530G(i,j). An outer area can be smaller than the region231displaying image information. Furthermore, a distance between the pixel circuit530R(i,j) and the driver circuit SD can be shortened. In addition, the first image signal can be transmitted without delay. As a result, a novel display device that is highly convenient, useful, or reliable can be provided.

The driver circuit SD has a function of supplying an image signal and a control signal, and the control signal includes a first level and a second level. For example, the driver circuit SD is electrically connected to a conductive film S1g(j) to supply the image signal, and is electrically connected to a conductive film S2g(j) to supply the control signal (seeFIG.7).

<<Structure Example of Driver Circuit GD>>

The driver circuit GD has a function of supplying a first selection signal and a second selection signal. For example, the driver circuit GD is electrically connected to a conductive film G1(i) to supply the first selection signal, and is electrically connected to a conductive film G2(i) to supply the second selection signal.

Structure Example 1 of Pixel Circuit530G(i,j)

The pixel circuit530G(i,j) is supplied with the first selection signal, and the pixel circuit530G(i,j) obtains an image signal on the basis of the first selection signal. For example, the first selection signal can be supplied using the conductive film G1(i) (seeFIG.7). The image signal can be supplied using the conductive film S1g(j). Note that the operation of supplying the first selection signal and making the pixel circuit530G(i,j) obtain the image signal can be referred to as “writing”.

Structure Example 2 of Pixel Circuit530G(i,j)

The pixel circuit530G(i,j) includes a switch SW21, a switch SW22, a transistor M21, a capacitor C21, and a node N21(seeFIG.7). In addition, the pixel circuit530G(i,j) includes a node N22, a capacitor C22, and a switch SW23.

The transistor M21includes a gate electrode electrically connected to the node N21, a first electrode electrically connected to the light-emitting device550G(i,j), and a second electrode electrically connected to the conductive film ANO.

The switch SW21includes a first terminal electrically connected to the node N21, a second terminal electrically connected to the conductive film S1g(j), and a gate electrode having a function of controlling the conduction state or the non-conduction state on the basis of the potential of the conductive film G1(i).

The switch SW22includes a first terminal electrically connected to the conductive film S2g(j) and a gate electrode having a function of controlling the conduction state or the non-conduction state on the basis of the potential of the conductive film G2(i).

The capacitor C21includes a conductive film electrically connected to the node N21and a conductive film electrically connected to a second electrode of the switch SW22.

Thus, the image signal can be stored in the node N21. The potential of the node N21can be changed using the switch SW22. Alternatively, the intensity of light emitted from the light-emitting device550G(i,j) can be controlled with the potential of the node N21.

<<Structure Example of Transistor M21>>

A bottom-gate transistor, a top-gate transistor, or the like can be used in the functional layer520. Specifically, a transistor can be used as a switch.

The transistor includes a semiconductor film508, a conductive film504, a conductive film507A, and a conductive film507B (seeFIG.6B). The transistor is formed over an insulating film501C, for example.

The semiconductor film508includes a region508A electrically connected to the conductive film507A and a region508B electrically connected to the conductive film507B. The semiconductor film508includes a region508C between the region508A and the region508B.

The conductive film504includes a region overlapping with the region508C, and the conductive film504has a function of a gate electrode.

An insulating film506includes a region interposed between the semiconductor film508and the conductive film504. The insulating film506has a function ofa gate insulating film.

The conductive film507A has one of a function of a source electrode and a function of a drain electrode, and the conductive film507B has the other of the function of the source electrode and the function of the drain electrode. The conductive film507A is electrically connected to a conductive film512A, and the conductive film507B is electrically connected to a conductive film512B.

A conductive film524can be used for the transistor. The conductive film524includes a region where the semiconductor film508is interposed between the conductive film524and the conductive film504. The conductive film524has a function of a second gate electrode. An insulating film501D is interposed between the semiconductor film508and the conductive film524, and has a function of a second gate insulating film. Note that an insulating film518covers the transistor, and the insulating film501C is interposed between an insulating film501B and the insulating film501D. An insulating film516includes an insulating film516A and an insulating film516B.

Note that the semiconductor film used in the transistor of the driver circuit can be formed in the step of forming the semiconductor film used in the transistor of the pixel circuit. A semiconductor film having the same composition as the semiconductor film used in the transistor of the pixel circuit can be used in the driver circuit, for example.

Structure Example 1 of Semiconductor Film508

A semiconductor containing a Group 14 element can be used for the semiconductor film508, for example. Specifically, a semiconductor containing silicon can be used for the semiconductor film508.

For example, hydrogenated amorphous silicon can be used for the semiconductor film508. Alternatively, microcrystalline silicon or the like can be used for the semiconductor film508. Thus, a functional panel having less display unevenness than a functional panel using polysilicon for the semiconductor film508, for example, can be provided. The size of the functional panel can be easily increased.

For example, polysilicon can be used for the semiconductor film508. Specifically, low temperature polysilicon (LTPS) can be used for the semiconductor film508. In this case, the field-effect mobility of the transistor can be higher than that of a transistor using hydrogenated amorphous silicon for the semiconductor film508, for example. The driving capability can be higher than that of a transistor using hydrogenated amorphous silicon for the semiconductor film508, for example. The aperture ratio of the pixel can be higher than that in the case of using a transistor that uses hydrogenated amorphous silicon for the semiconductor film508, for example.

The reliability of the transistor can be higher than that of a transistor using hydrogenated amorphous silicon for the semiconductor film508, for example.

The temperature required for fabrication of the transistor can be lower than that required for a transistor using single crystal silicon, for example.

The semiconductor film used in the transistor of the driver circuit can be formed in the same step as the semiconductor film used in the transistor of the pixel circuit. The driver circuit can be formed over the same substrate where the pixel circuit is formed. The number of components included in an electronic device can be reduced.

For example, single crystal silicon can be used for the semiconductor film508. In this case, a functional panel with higher resolution than a functional panel using hydrogenated amorphous silicon for the semiconductor film508, for example, can be provided. A functional panel having less display unevenness than a functional panel using polysilicon for the semiconductor film508, for example, can be provided. Smart glasses or ahead-mounted display can be provided, for example.

Structure Example 2 of Semiconductor Film508

For example, a metal oxide can be used for the semiconductor film508. In this case, for example, the pixel circuit can hold an image signal for a longer time than a pixel circuit utilizing a transistor using silicon for a semiconductor film. Specifically, a selection signal can be supplied at a frequency lower than 30 Hz, preferably lower than 1 Hz, further preferably less than once per minute with the suppressed occurrence of flickers. Consequently, fatigue accumulation in a user of a data processing device can be reduced. Moreover, power consumption for driving can be reduced.

A transistor using an oxide semiconductor can be used, for example. Specifically, an oxide semiconductor containing indium, an oxide semiconductor containing indium, gallium, and zinc, or an oxide semiconductor containing indium, zinc, and tin can be used for the semiconductor film.

A transistor having a lower leakage current in an off state than a transistor using silicon for a semiconductor film can be used, for example. Specifically, a transistor using an oxide semiconductor for a semiconductor film can be used as a switch or the like. In that case, a potential of a floating node can be held for a longer time than in a circuit in which a transistor using silicon is used as a switch.

A transistor using a metal oxide in a semiconductor film (also referred to as an OS transistor) has much higher field-effect mobility than a transistor using amorphous silicon. In addition, the OS transistor has an extremely low leakage current between a source and a drain in an off state (hereinafter, also referred to as off-state current), and charge accumulated in a capacitor that is connected in series to the transistor can be retained for a long period. Furthermore, power consumption of the display device can be reduced with the use of an OS transistor.

The off-state current value per micrometer of channel width of an OS transistor at room temperature can be lower than or equal to 1 aA (1×10−18A), lower than or equal to 1 zA (1×10−21A), or lower than or equal to 1 yA (1×10−24A). Note that the off-state current value per micrometer of channel width of a Si transistor at room temperature is higher than or equal to 1 fA (1×10−15A) and lower than or equal to 1 pA (1×10−12A). In other words, the off-state current of an OS transistor is lower than the off-state current of a Si transistor by approximately ten orders of magnitude.

To increase the emission luminance of the light-emitting device included in the pixel circuit, the amount of current fed through the light-emitting device needs to be increased. For this, it is necessary to increase the source-drain voltage of a driving transistor included in the pixel circuit. Since an OS transistor has a higher withstand voltage between the source and the drain than a Si transistor, a high voltage can be applied between the source and the drain of the OS transistor. Accordingly, when an OS transistor is used as the driving transistor included in the pixel circuit, the amount of current flowing through the light-emitting device can be increased, so that the emission luminance of the light-emitting device can be increased.

When transistors operate in a saturation region, a change in source-drain current relative to a change in gate-source voltage can be smaller in an OS transistor than in a Si transistor. Accordingly, when an OS transistor is used as the driving transistor included in the pixel circuit, the amount of current flowing between the source and the drain can be set minutely by a change in gate-source voltage; hence, the amount of current flowing through the light-emitting device can be controlled. Accordingly, the number of gray levels in the pixel circuit can be increased.

Regarding saturation characteristics of current flowing when the transistor operates in a saturation region, the OS transistor can make current (saturation current) flow more stably than the Si transistor even in the case where the source-drain voltage gradually increases. Thus, by using an OS transistor as the driving transistor, stable current can be fed through a light-emitting device that contains an EL material even in the case where the current-voltage characteristics of the light-emitting device vary, for example. In other words, when the OS transistor operates in the saturation region, the source-drain current hardly changes with an increase in the source-drain voltage; hence, the emission luminance of the light-emitting device can be stable.

As described above, with use of an OS transistor as a driving transistor included in the pixel circuit, it is possible to achieve “inhibition of black floating”, “increase in emission luminance”, “increase in gray level”, “inhibition of variation in light-emitting devices”, and the like.

Structure Example 3 of Semiconductor Film508

For example, a compound semiconductor can be used for the semiconductor of the transistor. Specifically, a semiconductor containing gallium arsenide can be used.

For example, an organic semiconductor can be used for the semiconductor of the transistor. Specifically, an organic semiconductor containing any of polyacenes or graphene can be used for the semiconductor film.

Structure Example 3 of Pixel Circuit530G(i,j)

For example, when both an LTPS transistor and an OS transistor are used, the display device can have low power consumption and high drive capability. Note that a structure in which the LTPS transistor and the OS transistor are combined is referred to as LTPO in some cases. As a favorable example, it is preferable to use an OS transistor as a transistor or the like functioning as a switch for controlling electrical continuity between wirings and an LTPS transistor as a transistor or the like for controlling current.

For example, one of the transistors included in the pixel circuit functions as a transistor for controlling current flowing through the light-emitting device and can be referred to as a driving transistor. One of a source and a drain of the driving transistor is electrically connected to the pixel electrode of the light-emitting device. The LTPS transistor is preferably used as the driving transistor. Thus, current flowing through the light-emitting device in the pixel circuit can be increased.

Meanwhile, another transistor included in the pixel circuit functions as a switch for controlling selection and non-selection of the pixel and can be referred to as a selection transistor. A gate of the selection transistor is electrically connected to a gate line, and one of a source and a drain thereof is electrically connected to a source line (signal line). The OS transistor is preferably used as the selection transistor. Thus, the gray level of the pixel can be maintained even when the frame frequency is extremely reduced (e.g., 1 fps or lower), whereby power consumption can be reduced by stopping the driver in displaying a still image.

Structure Example 4 of Pixel Circuit530G(i,j)

The structures of the transistors used in the display panel may be selected as appropriate depending on the size of the screen of the display panel. For example, in the case where single crystal Si transistors are used as transistors in the display panel, the single crystal Si transistors can be used for a screen having a diagonal size greater than or equal to 0.1 inches and less than or equal to 3 inches. In addition, in the case where LTPS transistors are used as transistors in the display panel, the LTPS transistors can be used for a screen having a diagonal size greater than or equal to 0.1 inches and less than or equal to 30 inches, preferably greater than or equal to 1 inch and less than or equal to 30 inches. In addition, in the case where LTPO transistors are used as transistors in the display panel, the LTPO transistors can be used for a screen having a diagonal size greater than or equal to 0.1 inches and less than or equal to 50 inches, preferably greater than or equal to 1 inch and less than or equal to 50 inches. In addition, in the case where OS transistors are used as transistors in the display panel, the OS transistors can be used for a screen having a diagonal size greater than or equal to 0.1 inches and less than or equal to 200 inches, preferably greater than or equal to 50 inches and less than or equal to 100 inches.

With single crystal Si transistors, a size increase is extremely difficult because of the size of a single crystal Si substrate. Furthermore, since a laser crystallization apparatus is used in the manufacturing process, LTPS transistors are unlikely to respond to a size increase (typically to a screen diagonal size greater than 30 inches). By contrast, since the manufacturing process does not necessarily require a laser crystallization apparatus or the like or can be performed at a relatively low process temperature (typically, lower than or equal to 450° C.), OS transistors are applicable to a display panel with a relatively large area (typically, a diagonal size greater than or equal to 50 inches and less than or equal to 100 inches). In addition, LTPO is applicable to a display panel with a size midway between the case of using LTPS transistors and the case of using OS transistors (typically, a diagonal size greater than or equal to 1 inch and less than or equal to 50 inches).

The light-emitting device550G(i,j) is electrically connected to the pixel circuit530G(i,j) (seeFIG.7). Note that the light-emitting device550G(i,j) has a function of operating on the basis of the potential of the node N21.

The light-emitting device550G(i,j) includes the electrode551G(i,j) and the electrode552G(i,j). Note that the electrode551G(i,j) is electrically connected to the pixel circuit530G(i,j), and the electrode552G(i,j) is electrically connected to a conductive film VCOM2.

For example, an organic electroluminescence element, an inorganic electroluminescence element, a light-emitting diode, a QDLED (Quantum Dot LED), or the like can be used as the light-emitting device550G(i,j).

Structure Example 6 of Display Device

The display device700includes a terminal519B and the conductive film VCOM2(seeFIG.5A).

The terminal519B is electrically connected to the functional layer510. The display device can receive and transmit a signal with the outside of the display device through the terminal519B.

Furthermore, the display device700includes an insulating film705and a base770(seeFIG.6A).

The insulating film705is interposed between the functional layer520and the base770, and the insulating film705has a function of bonding the functional layer520and the base770together.

Note that the light-emitting device550R(i,j) and the light-emitting device550G(i,j) are interposed between the base770and the functional layer520. The display device displays information through the base770(seeFIG.6A). In other words, the light-emitting device550G(i,j) emits light toward the direction in which the functional layer520is not placed. The light-emitting device550G(i,j) can be referred to as a top-emission light-emitting device.

Note that this embodiment can be combined with any of the other embodiments described in this specification as appropriate.

In this embodiment, a display device and a display system of one embodiment of the present invention will be described with reference toFIG.8toFIG.13.

FIG.8is a block diagram illustrating a structure of a display device of one embodiment of the present invention.

FIG.9is a block diagram illustrating a structure of a display portion illustrated inFIG.8.

FIG.10is a block diagram illustrating a structure of a display device of one embodiment of the present invention.

FIG.11shows circuit diagrams illustrating the structure of a pixel illustrated inFIG.10.

FIG.12is a block diagram illustrating a structure of a display device of one embodiment of the present invention.

FIG.13Ais a flowchart for a correction method, andFIG.13Bis a schematic diagram explaining the correction method.

Structure Example 7 of Display Device

Next,FIG.8is a block diagram illustrating components included in a display device10. The display device includes a driver circuit40, a functional circuit50, and a display portion60.

Structure Example 1 of Driver Circuit40

The driver circuit40includes agate driver41and a source driver42, for example. The gate driver41has a function of driving a plurality of gate lines GL for outputting signals to pixel circuits62R,62G, and62B. The source driver42has a function of driving a plurality of source lines SL for outputting signals to the pixel circuits62R,62G, and62B. The driver circuit40supplies voltage for performing display with the pixel circuits62R,62G, and62B to the pixel circuits62R,62G, and62B through a plurality of wirings.

Structure Example 1 of Functional Circuit50

The functional circuit50includes a CPU51, and the CPU51can be used for arithmetic processing of data. The CPU51includes a CPU core53. The CPU core53includes a flip-flop80for temporarily retaining data used for arithmetic processing. The flip-flop80includes a plurality of scan flip-flops81, and each of the scan flip-flops81is electrically connected to a backup circuit82provided in the display portion60. The flip-flop80inputs and outputs data of the scan flip-flops (backup data) to/from the backup circuit82.

FIG.9andFIG.8illustrate a structure example of the layout of the backup circuit82and the pixel circuits62R,62G, and62B functioning as subpixels in the display portion60.

FIG.9illustrates a structure in which a plurality of pixels61are arranged in a matrix in the display portion60. The pixels61each include the backup circuit82in addition to the pixel circuits62R,62G, and62B. As described above, the backup circuit82and the pixel circuits62R,62G, and62B can be formed using OS transistors and thus can be placed in the same pixel.

The display portion60includes the plurality of pixels61each including the pixel circuits62R,62G, and62B and the backup circuit82. The backup circuit82is not necessarily placed in each of the pixels61that are repeating units, as described with reference toFIG.9. The backup circuit82can be placed freely in accordance with the shape of the display portion60, the shapes of the pixel circuits62R,62G, and62B, and the like.

Structure Example 8 of Display Device

FIG.10is a block diagram schematically illustrating a structure example of the display device10that is a display device of one embodiment of the present invention. The display device10includes a layer20and a layer30, and the layer30can be stacked above the layer20, for example. An interlayer insulator or a conductor for electrical connection between different layers can be provided between the layer20and the layer30.

A transistor provided in the layer20can be a transistor containing silicon in a channel formation region (also referred to as a Si transistor), such as a transistor containing single crystal silicon in a channel formation region, for example. In particular, the use of a transistor containing single crystal silicon in a channel formation region as the transistor provided in the layer20can increase the on-state current of the transistor. This is preferable because circuits included in the layer20can be driven at high speed. The Si transistor can be formed by microfabrication to have a channel length of 3 nm to 10 nm, for example; thus, the display device10can be provided with a CPU, an accelerator such as a GPU, an application processor, or the like.

The driver circuit40and the functional circuit50are provided in the layer20. The Si transistor of the layer20can have a high on-state current. Thus, each circuit can be driven at high speed.

Structure Example 2 of Driver Circuit40

The driver circuit40includes a gate line driver circuit, a source line driver circuit, and the like for driving the pixel circuits62R,62G, and62B. The driver circuit40includes, for example, the gate line driver circuit and the source line driver circuit for driving the pixels61in the display portion60. With a structure in which the driver circuit40is provided not in the layer30where the display is provided but in the layer20, an area occupied by the display portion in the layer30can be large. In addition, the driver circuit40may include an LVDS (Low Voltage Differential Signaling) circuit, a D/A (Digital to Analog) converter circuit, or the like functioning as an interface for receiving data such as image data from the outside of the display device10. The Si transistor of the layer20can have a high on-state current. The channel length, the channel width, or the like of the Si transistor may be varied in accordance with the operation speed of each circuit.

As a transistor provided in the layer30, an OS transistor can be used, for example. In particular, a transistor including an oxide containing at least one of indium, an element M (the element M is aluminum, gallium, yttrium, or tin), and zinc in a channel formation region is preferably used as the OS transistor. Such an OS transistor has a characteristic of an extremely low off-state current. Thus, it is particularly preferable to use the OS transistor as a transistor provided in a pixel circuit included in a display portion, in which case analog data written to the pixel circuit can be retained for a long period.

The display portion60including the plurality of pixels61is provided in the layer30. The pixel circuits62R,62G, and62B that control emission of red light, green light, and blue light are provided in the pixels61. The pixel circuits62R,62G, and62B function as the subpixels of the pixels61. Since the pixel circuits62R,62G, and62B include the OS transistors, analog data written to the pixel circuits can be retained for a long period. The backup circuit82is provided in each of the pixels61included in the layer30. Note that the backup circuit is sometimes referred to as a storage circuit or a memory circuit. The backup circuit inputs and outputs data of the scan flip-flops (backup data BD) to/from the flip-flop80.

Structure Example 1 of Pixel Circuit

FIG.11AandFIG.11Billustrate a structure example of a pixel circuit62that can be used as the pixel circuits62R,62G, and62B and a light-emitting element70connected to the pixel circuit62.FIG.11Ais a diagram illustrating connection between elements, andFIG.11Bis a diagram schematically illustrating the vertical positional relationship of the driver circuit40, the pixel circuit62, and the light-emitting element70.

In this specification and the like, the term “element” can be replaced with the term “device” in some cases. For example, a display element, a light-emitting element, and a liquid crystal element can be replaced with a display device, a light-emitting device, and a liquid crystal device, respectively.

The pixel circuit62, which is illustrated as an example inFIG.11AandFIG.11B, includes the switch SW21, the switch SW22, the transistor M21, and the capacitor C21. The switch SW21, the switch SW22, and the transistor M21can be formed of OS transistors. Each of the OS transistors of the switch SW21, the switch SW22, and the transistor M21preferably includes a back gate electrode, in which case the back gate electrode can be supplied with the same signal as the gate electrode or the back gate electrode can be supplied with signals different from those supplied to the gate electrode can be used.

The transistor M21includes a gate electrode electrically connected to the switch SW21, a first electrode electrically connected to the light-emitting element70, and a second electrode electrically connected to the conductive film ANO. The conductive film ANO is a wiring for supplying a potential for supplying current to the light-emitting element70.

The switch SW21includes a first terminal electrically connected to the gate electrode of the transistor M21, a second terminal electrically connected to a source line SL, and a gate electrode having a function of controlling the on state or the off state on the basis of the potential of a gate line GL1.

The switch SW22includes a first terminal electrically connected to a wiring V0, a second terminal electrically connected to the light-emitting element70, and a gate electrode having a function of controlling the on state or the off state on the basis of the potential of a gate line GL2. The wiring V0is a wiring for supplying a reference potential and outputting current flowing in the pixel circuit62to the driver circuit40or the functional circuit50.

The capacitor C21includes a conductive film electrically connected to the gate electrode of the transistor M21and a conductive film electrically connected to a second electrode of the switch SW22.

The light-emitting element70includes a first electrode electrically connected to the first electrode of the transistor M21and a second electrode electrically connected to a conductive film VCOM. The conductive film VCOM is a wiring for supplying a potential for supplying current to the light-emitting element70.

Accordingly, the intensity of light emitted by the light-emitting element70can be controlled in accordance with an image signal supplied to the gate electrode of the transistor M21. Furthermore, the amount of current flowing to the light-emitting element70can be increased by the reference potential of the wiring V0that is supplied through the switch SW22. Moreover, it is possible to estimate the amount of current flowing to the light-emitting element by monitoring the amount of current flowing through the wiring V0with an external circuit. Thus, a defect of a pixel or the like can be detected.

Structure Example 2 of Pixel Circuit

Note that in the structure illustrated as an example inFIG.11B, the wirings electrically connecting the pixel circuit62and the driver circuit40can be shortened, so that wiring resistance of the wirings can be reduced. Thus, data can be written at high speed, which enables high-speed driving of the display device10. Accordingly, even when the number of pixels61included in the display device10is large, a sufficient frame period can be ensured, thereby increasing the pixel density of the display device10. In addition, the increased pixel density of the display device10can increase the resolution of an image displayed by the display device10. For example, the pixel density of the display device10can be higher than or equal to 1000 ppi, higher than or equal to 5000 ppi, or higher than or equal to 7000 ppi. Thus, the display device10can be, for example, a display device for AR or VR and can be suitably used in an electronic device with a short distance between the display portion and the user, such as an HMD.

Although the gate line GL1, the gate line GL2, the conductive film VCOM, the wiring V0, the conductive film ANO, and the source line SL are supplied with signals and voltage from the driver circuit40below the pixel circuit62through the wirings inFIG.11B, one embodiment of the present invention is not limited thereto. For example, wirings for supplying signals and voltage of the driver circuit40may be led to an outer region of the display portion60and electrically connected to the pixel circuits62arranged in a matrix in the layer30. In this case, a structure in which the gate driver41included in the driver circuit40is provided in the layer30is effective. That is, a structure in which OS transistors are used as transistors of the gate driver41is effective. A structure in which part of the function of the source driver42included in the driver circuit40is provided in the layer30is effective. For example, a structure in which a demultiplexer distributing signals output from the source driver42to source lines is provided in the layer30is effective. A structure in which OS transistors are used as transistors of the demultiplexer is effective.

As the backup circuit82, for example, a memory including OS transistors is suitable. The backup circuit formed using OS transistors has advantages of, for example, inhibiting a decrease in voltage corresponding to data to be backed up and consuming almost no power for data retention, because the OS transistors have an extremely low off-state current. The backup circuit82including the OS transistors can be provided in the display portion60in which the plurality of pixels61are placed.FIG.10illustrates a state in which the backup circuit82is provided in each of the pixels61.

The backup circuit82formed using the OS transistors can be stacked over the layer20including the Si transistor. The backup circuits82may be arranged in a matrix like the subpixels in the pixels61; alternatively, one backup circuit82may be provided for every plurality of pixels. That is, the backup circuits82can be arranged in the layer30without being limited by the arrangement of the pixels61. Therefore, the backup circuits82can be arranged without any increase in the circuit area and the degree of flexibility in the layout of the display portion or the circuits is enhanced, so that memory capacity of the backup circuits82required for arithmetic processing can be increased.

Structure Example 9 of Display Device

FIG.12illustrates a modification example of the components included in the display device10described above.

A block diagram of a display device10A illustrated inFIG.12corresponds to a structure in which an accelerator52is added to the functional circuit50in the display device10inFIG.8.

The accelerator52functions as a dedicated arithmetic circuit to product-sum operation processing of an artificial neural network NN. In the arithmetic operation using the accelerator52, processing for correcting the outline of an image by up-conversion of display data or the like can be performed, for example. During the arithmetic processing with the accelerator52, it is possible to reduce the power consumption by power gating control on the CPU51.

<Structure Example of Display System>

In the display device of one embodiment of the present invention, the pixel circuit and the functional circuit can be stacked; thus, a defective pixel can be detected using the functional circuit provided below the screen circuit. Information on the defective pixel can be used to correct a display defect due to the defective pixel, leading to normal display.

Part of a correction method described below as an example may be performed by a circuit provided outside the display device. Part of the correction method may be performed by the functional circuit50of the display device10.

A more specific example of the correction method will be described below.FIG.13Ais a flowchart for the correction method described below.

First, the correction operation starts in Step S1“Start”.

Next, in Step S2“Read current of pixel”, current of the pixels is read. For example, each of the pixels can be driven to output current to a monitor line electrically connected to the pixel.

Then, in Step S3“Perform conversion into voltage”, the read current is converted into voltage. In the case of using a digital signal in a subsequent process, conversion into digital data can be performed in Step S3. For example, analog data can be converted into digital data using an analog-digital converter circuit (ADC).

Next, in Step S4“Obtain pixel parameter”, pixel parameters of the pixels are obtained on the basis of the acquired data. Examples of the pixel parameters include the threshold voltage and field-effect mobility of a driving transistor, the threshold voltage of a light-emitting element, and a current value at a certain voltage.

Subsequently, in Step S5“Determine abnormality”, each of the pixels is determined to be abnormal or not on the basis of the pixel parameter. For example, a pixel is determined to be abnormal when its pixel parameter has a value exceeding (or lower than) a predetermined threshold value.

An abnormal pixel is recognized as a dark spot defect when luminance is significantly lower than that corresponding to an input data potential, or recognized as a bright spot defect when luminance is significantly higher than that corresponding to an input data potential, for example.

The address of the abnormal pixel and the kind of the defect can be specified and acquired in Step S5.

Then, correction processing is performed in Step S6“Perform correction processing”.

An example of the correction processing is described with reference toFIG.13B.FIG.13Bschematically illustrates 3×3 pixels. Here, a pixel61D at the center is regarded as a dark spot defect.FIG.13Bschematically illustrates a state in which the pixel61D is in a non-lighting state and pixels61N around the pixel61D are in lighting states with predetermined luminance.

A dark spot defect is due to a pixel unlikely to have normal luminance even when correction for increasing a data potential input to the pixel is performed. Hence, correction for increasing luminance is performed on the pixels61N around the pixel61D recognized as a dark spot defect, as illustrated inFIG.13B. As a result, a normal image can be displayed even when a dark spot defect exists.

In the case of a bright spot defect, the luminance of pixels around the defect is decreased, so that the bright spot defect can be less noticeable.

Such a correction method for compensating for an abnormal pixel by pixels around the abnormal pixel is effective particularly in the case of a display device with a higher resolution (e.g., 1000 ppi or higher) because it is difficult to see individual pixels separately from each other.

It is preferable that correction be performed such that a data potential is not input to an abnormal pixel recognized as a dark spot defect, a bright spot defect, or the like.

As described above, a correction parameter can be set for each pixel. When the correction parameter is used for image data to be input, correction image data that enables the display device10to display an optimal image can be generated.

As well as in an abnormal pixel and pixels around the abnormal pixel, pixel parameters vary in pixels not determined to be abnormal; thus, display unevenness due to the variation might be recognized when an image is displayed, in some cases. Hence, correction parameters for the pixels not determined to be abnormal can be set so as to cancel (level off) the variation of the pixel parameters. For example, a reference value based on the mean value, average value, or the like of pixel parameters of some or all of the pixels can be set, and a correction value used for canceling a difference of a pixel parameter of a certain pixel from the reference value can be set as a correction parameter of the pixel.

For each of the pixels around an abnormal pixel, it is preferred to set correction data that takes into consideration both a correction amount for compensating for the abnormal pixel and a correction amount for canceling pixel parameter variation.

Next, the correction operation ends in Step S7.

After that, an image can be displayed on the basis of the correction parameters obtained in the correction operation and image data to be input.

Note that a neural network may be used for the correction operation. In the case where an arithmetic operation based on an artificial neural network is performed in the above-described display correction system, a product-sum operation is repeatedly performed. In the arithmetic operation using the accelerator52, the above-mentioned correction of the display defects can be performed. During the arithmetic processing with the accelerator52, it is possible to reduce the power consumption by power gating control on the CPU51. The neural network can determine correction parameters on the basis of inference results obtained by machine learning, for example. Estimation can be performed by executing an arithmetic operation based on an artificial neural network such as a deep neural network (DNN), a convolutional neural network (CNN), a recurrent neural network (RNN), an autoencoder, a deep Boltzmann machine (DBM), or a deep belief network (DBN), for example. In the case where correction parameters are determined by a neural network, high-accuracy correction can be performed to make an abnormal pixel less noticeable without using a detailed algorithm for correction.

The above is the description of the correction method.

Note that during the arithmetic operation by the display correction system, which is performed for correcting current flowing through a pixel, data in the arithmetic operation can be retained as backup data in the CPU51. Therefore, the display correction system is particularly effective in arithmetic processing performed with an enormous amount of calculation, such as an arithmetic operation based on an artificial neural network. Note that it is also possible to reduce power consumption in addition to a reduction in display defects by making the CPU51function as an application processor, in combination with, for example, driving that makes a frame frequency changeable.

This embodiment can be combined with the description of the other embodiments as appropriate.

In this embodiment, an example of a cross-sectional structure of the display device10one embodiment of the present invention will be described.

Structure Example 10 of Display Device

FIG.14is a cross-sectional view illustrating a structure example of the display device10. The display device10includes an insulator421and the base770, and the insulator421and the base770are bonded to each other with a sealant712. It is preferable to use an OS transistor for the pixel circuit. Furthermore, at least part of the driver circuit may be formed using an OS transistor. In addition, at least part of the functional circuit may be formed using an OS transistor. Moreover, at least part of the driver circuit may be externally provided. At least part of the functional circuit may be externally provided.

Any of a variety of insulator substrates such as a glass substrate and a sapphire substrate can be used for the insulator421. An insulator214is provided over the insulator421, and an insulator216is provided over the insulator214.

An insulator222, an insulator224, an insulator254, an insulator280, an insulator274, and an insulator281are provided over the insulator216.

The insulator421, the insulator214, the insulator280, the insulator274, and the insulator281function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

An insulator361is provided over the insulator281. A conductor317and a conductor337are embedded in the insulator361. Here, the top surface of the conductor337and the top surface of the insulator361can be substantially level with each other.

An insulator363is provided over the conductor337and the insulator361. A conductor347, a conductor353, a conductor355, and a conductor357are embedded in the insulator363. Here, the top surfaces of the conductor353, the conductor355, and the conductor357and the top surface of the insulator363can be substantially level with each other.

A conductor341, a conductor343, and a conductor351are embedded in the insulator363. Here, the top surface of the conductor351and the top surface of the insulator363can be substantially level with each other.

The insulator361and the insulator363function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder. For example, the top surface of the insulator363may be planarized by planarization treatment using a chemical mechanical polishing (CMP) method or the like to have the increased planarity.

A connection electrode760is provided over the conductor353, the conductor355, the conductor357, and the insulator363. An anisotropic conductor780is provided to be electrically connected to the connection electrode760, and an FPC (Flexible Printed Circuit)716is provided to be electrically connected to the anisotropic conductor780. A variety of signals and the like are supplied to the display device10from the outside of the display device10through the FPC716.

AlthoughFIG.14illustrates three conductors of the conductor353, the conductor355, and the conductor357as conductors having a function of electrically connecting the connection electrode760and the conductor347, one embodiment of the present invention is not limited thereto. The number of conductors having a function of electrically connecting the connection electrode760and the conductor347may be one, two, or four or more. Providing a plurality of conductors having a function of electrically connecting the connection electrode760and the conductor347can reduce the contact resistance.

A transistor750is provided over the insulator214. The transistor750can be the transistor provided in the layer30described in Embodiment 6. For example, the transistor provided in the pixel circuit62can be used. An OS transistor can be suitably used as the transistor750. The OS transistor has a feature of an extremely low off-state current. Thus, the retention time for image data or the like can be increased, so that the frequency of the refresh operation can be reduced. Accordingly, the power consumption of the display device10can be reduced.

The transistor750can be the transistor provided in the backup circuit82. The OS transistor can be suitably used as the transistor750. The OS transistor has a feature of an extremely low off-state current. Thus, data in the flip-flop can be retained even in a period during which the sharing of power supply voltage is stopped. Hence, a normally-off operation (the intermittent stop operation of the supply of the power supply voltage) of the CPU can be performed. Accordingly, the power consumption of the display device10can be reduced.

A conductor301aand a conductor301bare embedded in the insulator254, the insulator280, the insulator274, and the insulator281. The conductor301ais electrically connected to one of a source and a drain of the transistor750, and the conductor301bis electrically connected to the other of the source and the drain of the transistor750. Here, the top surfaces of the conductor301aand the conductor301band the top surface of the insulator281can be substantially level with each other.

A conductor311, a conductor313, a conductor331, a capacitor790, a conductor333, and a conductor335are embedded in the insulator361. The conductor311and the conductor313are electrically connected to the transistor750and function as a wiring. The conductor333and the conductor335are electrically connected to the capacitor790. Here, the top surfaces of the conductor331, the conductor333, and the conductor335and the top surface of the insulator361can be substantially level with each other.

As illustrated inFIG.14, the capacitor790includes a lower electrode321and an upper electrode325. An insulator323is provided between the lower electrode321and the upper electrode325. In other words, the capacitor790has a stacked-layer structure in which the insulator323functioning as a dielectric is provided between the pair of electrodes. AlthoughFIG.14illustrates the example in which the capacitor790is provided over the insulator281, the capacitor790may be provided over an insulator different from the insulator281.

In the example illustrated inFIG.14, the conductor301a, the conductor301b, and a conductor305are formed in the same layer. In the illustrated example, the conductor311, the conductor313, the conductor317, and the lower electrode321are formed in the same layer. In the illustrated example, the conductor331, the conductor333, the conductor335, and the conductor337are formed in the same layer. In the illustrated example, the conductor341, the conductor343, and the conductor347are formed in the same layer. In the illustrated example, the conductor351, the conductor353, the conductor355, and the conductor357are formed in the same layer. Forming a plurality of conductors in the same layer simplifies the fabrication process of the display device10and thus the manufacturing cost of the display device10can be reduced. Note that these conductors may be formed in different layers or may contain different types of materials.

The display device10illustrated inFIG.14includes the light-emitting element70. The light-emitting element70includes a conductor772, an EL layer786, and a conductor788. The EL layer786contains an organic compound or an inorganic compound such as quantum dots.

Examples of materials that can be used as the organic compound include a fluorescent material and a phosphorescent material. Examples of materials that can be used as the quantum dots include a colloidal quantum dot material, an alloyed quantum dot material, a core-shell quantum dot material, and a core quantum dot material.

Note that the luminance of the display device10can be, for example, 500 cd/m2or higher, preferably higher than or equal to 1000 cd/m2and lower than or equal to 10000 cd/m2, further preferably higher than or equal to 2000 cd/m2and lower than or equal to 5000 cd/m2.

The conductor772is electrically connected to the other of the source and the drain of the transistor750through the conductor351, the conductor341, the conductor331, the conductor313, and the conductor301b. The conductor772is formed over the insulator363and functions as a pixel electrode.

A material that transmits visible light or a material that reflects visible light can be used for the conductor772. As alight-transmitting material, for example, an oxide material containing indium, zinc, tin, or the like is preferably used. As a reflective material, for example, a material containing aluminum, silver, or the like is preferably used.

The light-emitting element70is a top-emission light-emitting element, which includes the conductor788with alight-transmitting property. Note that the light-emitting element70may have a bottom-emission structure in which light is emitted to the conductor772side or a dual-emission structure in which light is emitted towards both the conductor772and the conductor788.

The light-emitting element70can have a micro optical resonator (microcavity) structure. Accordingly, light of predetermined colors (e.g., RGB) can be extracted, and the display device10can display high-luminance images. In addition, the power consumption of the display device10can be reduced.

On the base770side, a light-blocking layer738and an insulator734that is in contact with the light-blocking layer738are provided. The light-blocking layer738has a function of blocking light emitted from adjacent regions. Alternatively, the light-blocking layer738has a function of preventing external light from reaching the transistor750or the like.

In the display device10illustrated inFIG.14, an insulator730is provided over the insulator363. Here, the insulator730can cover part of the conductor772. Although the structure where the insulator730is provided is described in this embodiment, the present invention is not limited thereto. For example, the insulator730is not necessarily provided. Note that it is preferable that insulator730not be provided because the opening portion of the display device can be increased.

The light-blocking layer738is provided to include a region overlapping with the insulator730. The light-blocking layer738is covered with the insulator734. A gap between the light-emitting element70and the insulator734is filled with a sealing layer732.

A component778is provided between the insulator730and the EL layer786. Moreover, the component778is provided between the insulator730and the insulator734.

Although not illustrated inFIG.14, an optical member (an optical substrate) such as a polarizing member, a retardation member, or an anti-reflection member can be provided in the display device10, for example.

In addition, a coloring layer can be provided. The coloring layer is provided to include a region overlapping with the light-emitting element70. Providing the coloring layer can improve the color purity of light extracted from the light-emitting element70. Thus, the display device10can display high-quality images. Furthermore, all the light-emitting elements70, for example, in the display device10can be light-emitting elements that emit white light; hence, the EL layers786are not necessarily formed separately for each color, leading to higher resolution of the display device10.

Structure Example 11 of Display Device

FIG.15is a cross-sectional view illustrating a structure example of the display device10. The display device10includes a substrate701and the base770, and the substrate701and the base770are bonded to each other with the sealant712. The display device10illustrated inFIG.15is different from the display device10illustrated inFIG.14in including a transistor601.

As the substrate701, a single crystal semiconductor substrate such as a single crystal silicon substrate can be used. Note that a semiconductor substrate other than a single crystal semiconductor substrate may be used as the substrate701.

The transistor441is formed of the conductor443functioning as a gate electrode, the insulator445functioning as a gate insulator, and part of the substrate701and includes the semiconductor region447including a channel formation region, the low-resistance region449afunctioning as one of a source region and a drain region, and the low-resistance region449bfunctioning as the other of the source region and the drain region. The transistor441may be either a p-channel transistor or an n-channel transistor.

The transistor441is electrically isolated from other transistors by an element isolation layer403.FIG.15illustrates the case where the transistor441and the transistor601are electrically isolated from each other by the element isolation layer403. The element isolation layer403can be formed by a LOCOS (LOCal Oxidation of Silicon) method, an STI (Shallow Trench Isolation) method, or the like.

Here, in the transistor441illustrated inFIG.15, the semiconductor region447has a projecting shape. Moreover, the conductor443is provided to cover the side surface and the top surface of the semiconductor region447with the insulator445therebetween. Note thatFIG.15does not illustrate the state where the conductor443covers the side surface of the semiconductor region447. A material adjusting the work function can be used for the conductor443.

A transistor having a projecting semiconductor region, like the transistor441, can be referred to as a fin-type transistor because a projecting portion of a semiconductor substrate is used. An insulator functioning as a mask for forming a projecting portion may be provided in contact with an upper portion of the projecting portion. AlthoughFIG.15illustrates the structure in which the projecting portion is formed by processing part of the substrate701, a semiconductor having a projecting shape may be formed by processing an SOI substrate.

Note that the structure of the transistor441illustrated inFIG.15is an example; the structure is not limited thereto and can be changed as appropriate in accordance with the circuit structure, an operation method for the circuit, or the like. For example, the transistor441may be a planar transistor.

The transistor601can have a structure similar to that of the transistor441.

The insulator405, the insulator407, the insulator409, and the insulator411are provided over the substrate701, in addition to the element isolation layer403, the transistor441, and the transistor601. The conductor451is embedded in the insulator405, the insulator407, the insulator409, and the insulator411. Here, the top surface of the conductor451and the top surface of the insulator411can be substantially level with each other.

The insulator405, the insulator407, the insulator409, and the insulator411function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

The insulator421and the insulator214are provided over the conductor451and the insulator411. The conductor453is embedded in the insulator421and the insulator214. Here, the top surface of the conductor453and the top surface of the insulator214can be substantially level with each other.

The insulator216is provided over the conductor453and the insulator214. The conductor455is embedded in the insulator216. Here, the top surface of the conductor455and the top surface of the insulator216can be substantially level with each other.

The insulator222, the insulator224, the insulator254, the insulator280, the insulator274, and the insulator281are provided over the conductor455and the insulator216.

The conductor305is embedded in the insulator222, the insulator224, the insulator254, the insulator280, the insulator274, and the insulator281. Here, the top surface of the conductor305and the top surface of the insulator281can be substantially level with each other.

The insulator421, the insulator214, the insulator280, the insulator274, and the insulator281function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

The insulator361is provided over the conductor305and the insulator281.

As illustrated inFIG.15, the low-resistance region449bfunctioning as the other of the source region and the drain region of the transistor441is electrically connected to the FPC716through the conductor451, the conductor453, the conductor455, the conductor305, the conductor317, the conductor337, the conductor347, the conductor353, the conductor355, the conductor357, the connection electrode760, and the anisotropic conductor780.

Structure Example 12 of Display Device

FIG.16is a cross-sectional view illustrating a structure example of the display device10. The display device10includes the substrate701and the base770, and the substrate701and the base770are bonded to each other with the sealant712. The display device10inFIG.16is different from the display device10illustrated inFIG.15in that the transistor750has the same structure as the transistor441.

As the substrate701, a single crystal semiconductor substrate such as a single crystal silicon substrate can be used. Note that a semiconductor substrate other than a single crystal semiconductor substrate may be used as the substrate701.

The transistor441is formed of the conductor443functioning as a gate electrode, the insulator445functioning as a gate insulator, and part of the substrate701and includes the semiconductor region447including a channel formation region, the low-resistance region449afunctioning as one of a source region and a drain region, and the low-resistance region449bfunctioning as the other of the source region and the drain region. The transistor441may be either a p-channel transistor or an n-channel transistor.

As illustrated inFIG.16, the low-resistance region449bfunctioning as the other of the source region and the drain region of the transistor441is electrically connected to the FPC716through the conductor451, the conductor453, the conductor455, the bump458, the conductor305, the conductor317, the conductor337, the conductor347, the conductor353, the conductor355, the conductor357, the connection electrode760, and the anisotropic conductor780.

The transistor441is electrically isolated from other transistors by an element isolation layer403.FIG.16illustrates the case where the transistor441and the transistor601are electrically isolated from each other by the element isolation layer403. The element isolation layer403can be formed by a LOCOS (LOCal Oxidation of Silicon) method, an STI (Shallow Trench Isolation) method, or the like.

Here, in the transistor441illustrated inFIG.16, the semiconductor region447has a projecting shape. Moreover, the conductor443is provided to cover the side surface and the top surface of the semiconductor region447with the insulator445therebetween. Note thatFIG.16does not illustrate the state where the conductor443covers the side surface of the semiconductor region447. A material adjusting the work function can be used for the conductor443.

A transistor having a projecting semiconductor region, like the transistor441, can be referred to as a fin-type transistor because a projecting portion of a semiconductor substrate is used. An insulator functioning as a mask for forming a projecting portion may be provided in contact with an upper portion of the projecting portion. AlthoughFIG.16illustrates the structure in which the projecting portion is formed by processing part of the substrate701, a semiconductor having a projecting shape may be formed by processing an SOI substrate.

Note that the structure of the transistor441illustrated inFIG.16is an example; the structure is not limited thereto and can be changed as appropriate in accordance with the circuit structure, an operation method for the circuit, or the like. For example, the transistor441may be a planar transistor.

The transistor601can have a structure similar to that of the transistor441.

The insulator405, the insulator407, the insulator409, and the insulator411are provided over the substrate701, in addition to the element isolation layer403, the transistor441, and the transistor601. The conductor451is embedded in the insulator405, the insulator407, the insulator409, and the insulator411. Here, the top surface of the conductor451and the top surface of the insulator411can be substantially level with each other.

The insulator405, the insulator407, the insulator409, and the insulator411function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

The insulator421and the insulator214are provided over the conductor451and the insulator411. The conductor453is embedded in the insulator421and the insulator214. Here, the top surface of the conductor453and the top surface of the insulator214can be substantially level with each other.

The insulator216is provided over the conductor453and the insulator214. The conductor455is embedded in the insulator216. Here, the top surface of the conductor455and the top surface of the insulator216can be substantially level with each other.

A bonding layer459is provided over the insulator216. A bump458is embedded in the bonding layer459. The bonding layer459bonds the insulator216and a substrate701B. The bottom surface of the bump458is in contact with the conductor455and the top surface of the bump458is in contact with the conductor305so that the conductor455and the conductor305are electrically connected to each other.

As the substrate701B, a single crystal semiconductor substrate such as a single crystal silicon substrate can be used. Note that a semiconductor substrate other than a single crystal semiconductor substrate may be used as the substrate701B.

The transistor750is provided over the substrate701B. The transistor750can be the transistor provided in the layer30described in Embodiment 6. For example, the transistor provided in the pixel circuit62can be used.

The transistor750can have a structure similar to that of the transistor441.

An insulator405B, the insulator280, the insulator274, and the insulator281are provided over the substrate701B, in addition to an element isolation layer403B and the transistor750. The conductor305is embedded in the insulator405B, the insulator280, the insulator274, and the insulator281. Here, the top surface of the conductor305and the top surface of the insulator281can be substantially level with each other.

The insulator405B, the insulator280, the insulator274, and the insulator281function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

The insulator361is provided over the conductor305and the insulator281

Structure Example 13 of Display Device

The display device10illustrated inFIG.17is different from the display device10illustrated inFIG.15mainly in that a transistor602and a transistor603that are OS transistors are provided in place of the transistor441and the transistor601. Moreover, the OS transistor can be used as the transistor750. That is, the display device10illustrated inFIG.17includes a stack of OS transistors. In the example illustrated inFIG.17, the transistor602and the transistor603are provided over the substrate701. As the substrate701, a single crystal semiconductor substrate such as a single crystal silicon substrate, or another semiconductor substrate can be used as described above. In addition, a variety of insulator substrates such as a glass substrate or a sapphire substrate may be used as the substrate701.

An insulator613and an insulator614are provided over the substrate701, and the transistor602and the transistor603are provided over the insulator614. Note that a transistor or the like may be provided between the substrate701and the insulator613. For example, a transistor having a structure similar to those of the transistor441and the transistor601illustrated inFIG.15may be provided between the substrate701and the insulator613.

The transistor602and the transistor603can be the transistors provided in the layer20described in Embodiment 6.

The transistor602and the transistor603can be transistors having a structure similar to that of the transistor750. Note that the transistor602and the transistor603may be OS transistors having a structure different from that of the transistor750.

An insulator616, an insulator622, an insulator624, an insulator654, an insulator680, an insulator674, and an insulator681are provided over the insulator614, in addition to the transistor602and the transistor603. A conductor461is embedded in the insulator654, the insulator680, the insulator674, and the insulator681. Here, the top surface of the conductor461and the top surface of the insulator681can be substantially level with each other.

An insulator501is provided over the conductor461and the insulator681. A conductor463is embedded in the insulator501. Here, the top surface of the conductor463and the top surface of the insulator501can be substantially level with each other.

The insulator421and the insulator214are provided over the conductor463and the insulator501. The conductor453is embedded in the insulator421and the insulator214. Here, the top surface of the conductor453and the top surface of the insulator214can be substantially level with each other.

As illustrated inFIG.17, one of a source and a drain of the transistor602is electrically connected to the FPC716through the conductor461, the conductor463, the conductor453, the conductor455, the conductor305, the conductor317, the conductor337, the conductor347, the conductor353, the conductor355, the conductor357, the connection electrode760, and the anisotropic conductor780.

The conductor305is embedded in the insulator222, the insulator224, the insulator254, the insulator280, the insulator274, and the insulator281. Here, the top surface of the conductor305and the top surface of the insulator281can be substantially level with each other.

The insulator613, the insulator614, the insulator680, the insulator674, the insulator681, and the insulator501function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

When the display device10has the structure illustrated inFIG.17, all the transistors included in the display device10can be OS transistors while the bezel and size of the display device10are reduced. Accordingly, the transistors provided in the layer20and the transistors provided in the layer30described in Embodiment 6 can be fabricated using the same apparatus, for example. Consequently, the fabrication cost of the display device10can be reduced, making the display device10inexpensive.

Structure Example 14 of Display Device

FIG.18is a cross-sectional view illustrating a structure example of the display device10. The display device10inFIG.18is different from the display device10illustrated in FIG.15mainly in that a layer including a transistor800is provided between the layer including the transistor750and the layer including the transistor601and the transistor441.

In the structure ofFIG.18, the layer20described in Embodiment 6 can include the layer including the transistor601and the transistor441and the layer including the transistor800. The transistor750can be the transistor provided in the layer30described in Embodiment 6.

An insulator821and an insulator814are provided over the conductor451and the insulator411. A conductor853is embedded in the insulator821and the insulator814. Here, the top surface of the conductor853and the top surface of the insulator814can be substantially level with each other.

An insulator816is provided over the conductor853and the insulator814. A conductor855is embedded in the insulator816. Here, the top surface of the conductor855and the top surface of the insulator816can be substantially level with each other.

An insulator822, an insulator824, an insulator854, an insulator880, an insulator874, and an insulator881are provided over the conductor855and the insulator816. A conductor805is embedded in the insulator822, the insulator824, the insulator854, the insulator880, the insulator874, and the insulator881. Here, the top surface of the conductor805and the top surface of the insulator881can be substantially level with each other.

The insulator421and the insulator214are provided over a conductor817and the insulator881.

As illustrated inFIG.18, the low-resistance region449bfunctioning as the other of the source region and the drain region of the transistor441is electrically connected to the FPC716through the conductor451, the conductor853, the conductor855, the conductor805, the conductor817, the conductor453, the conductor455, the conductor305, the conductor317, the conductor337, the conductor347, the conductor353, the conductor355, the conductor357, the connection electrode760, and the anisotropic conductor780.

The transistor800is provided over the insulator814. The transistor800can be the transistor provided in the layer20described in Embodiment 6. The transistor800is preferably an OS transistor. For example, the transistor800can be the transistor provided in the backup circuit82.

A conductor801aand a conductor801bare embedded in the insulator854, the insulator880, the insulator874, and the insulator881. The conductor801ais electrically connected to one of a source and a drain of the transistor800, and the conductor801bis electrically connected to the other of the source and the drain of the transistor800. Here, the top surfaces of the conductor801aand the conductor801band the top surface of the insulator881can be substantially level with each other.

The transistor750can be the transistor provided in the layer30described in Embodiment 6. For example, the transistor750can be the transistor provided in the pixel circuit62. The transistor750is preferably an OS transistor.

The insulator405, the insulator407, the insulator409, the insulator411, the insulator821, the insulator814, the insulator880, the insulator874, the insulator881, the insulator421, the insulator214, the insulator280, the insulator274, the insulator281, the insulator361, and the insulator363function as an interlayer film and may function as a planarization film that covers an uneven shape thereunder.

In the example illustrated inFIG.18, the conductor801a, the conductor801b, and the conductor805are formed in the same layer. In the illustrated example, a conductor811, a conductor813, and the conductor817are formed in the same layer.

In this embodiment, a transistor that can be used in the display device of one embodiment of the present invention will be described.

<Structure Example of Transistor>

FIG.19A,FIG.19B, andFIG.19Care a top view and cross-sectional views of a transistor200A that can be used in the display device of one embodiment of the present invention and the periphery of the transistor200A. The transistor200A can be used in the display device of one embodiment of the present invention.

FIG.19Ais the top view of the transistor200A.FIG.19BandFIG.19Care the cross-sectional views of the transistor200A. Here,FIG.19Bis a cross-sectional view of a portion indicated by the dashed-dotted line A1-A2inFIG.19Aand is a cross-sectional view of the transistor200A in the channel length direction.FIG.19Cis a cross-sectional view of a portion indicated by the dashed-dotted line A3-A4inFIG.19Aand is a cross-sectional view of the transistor200A in the channel width direction. Note that some components are omitted in the top view ofFIG.19Afor clarity of the drawing.

As illustrated inFIG.19, the transistor200A includes a metal oxide230aplaced over a substrate (not illustrated); a metal oxide230bplaced over the metal oxide230a; a conductor242aand a conductor242bthat are placed apart from each other over the metal oxide230b; the insulator280that is placed over the conductor242aand the conductor242band has an opening between the conductor242aand the conductor242b; a conductor260placed in the opening; an insulator250placed between the conductor260and each of the metal oxide230b, the conductor242a, the conductor242b, and the insulator280; and a metal oxide230cplaced between the insulator250and each of the metal oxide230b, the conductor242a, the conductor242b, and the insulator280. Here, as illustrated inFIG.19BandFIG.19C, preferably, the top surface of the conductor260is substantially aligned with the top surfaces of the insulator250, the insulator254, the metal oxide230c, and the insulator280. Hereinafter, the metal oxide230a, the metal oxide230b, and the metal oxide230cmay be collectively referred to as a metal oxide230. The conductor242aand the conductor242bmay be collectively referred to as a conductor242.

In the transistor200A illustrated inFIG.19, the side surfaces of the conductor242aand the conductor242bon the conductor260side are substantially perpendicular. Note that the transistor200A illustrated inFIG.19is not limited thereto, and the angle formed between the side surfaces and the bottom surfaces of the conductor242aand the conductor242bmay be greater than or equal to 10° and less than or equal to 80°, preferably greater than or equal to 30° and less than or equal to 60°. The side surfaces of the conductor242aand the conductor242bthat face each other may have a plurality of surfaces.

As illustrated inFIG.19, the insulator254is preferably placed between the insulator280and each of the insulator224, the metal oxide230a, the metal oxide230b, the conductor242a, the conductor242b, and the metal oxide230c. Here, as illustrated inFIG.19BandFIG.19C, the insulator254is preferably in contact with the side surface of the metal oxide230c, the top surface and the side surface of the conductor242a, the top surface and the side surface of the conductor242b, the side surfaces of the metal oxide230aand the metal oxide230b, and the top surface of the insulator224.

In the transistor200A, three layers of the metal oxide230a, the metal oxide230b, and the metal oxide230care stacked in and around a region where a channel is formed (hereinafter, also referred to as a channel formation region); however, the present invention is not limited thereto. For example, a two-layer structure of the metal oxide230band the metal oxide230cor a stacked-layer structure of four or more layers may be employed. Although the conductor260is illustrated to have a stacked-layer structure of two layers in the transistor200A, the present invention is not limited thereto. For example, the conductor260may have a single-layer structure or a stacked-layer structure of three or more layers. Furthermore, each of the metal oxide230a, the metal oxide230b, and the metal oxide230cmay have a stacked-layer structure of two or more layers.

For example, in the case where the metal oxide230chas a stacked-layer structure including a first metal oxide and a second metal oxide over the first metal oxide, the first metal oxide preferably has a composition similar to that of the metal oxide230band the second metal oxide preferably has a composition similar to that of the metal oxide230a.

Here, the conductor260functions as a gate electrode of the transistor, and the conductor242aand the conductor242bfunction as a source electrode and a drain electrode. As described above, the conductor260is formed to be embedded in the opening of the insulator280and the region interposed between the conductor242aand the conductor242b. Here, the positions of the conductor260, the conductor242a, and the conductor242bare selected in a self-aligned manner with respect to the opening of the insulator280. That is, in the transistor200A, the gate electrode can be placed between the source electrode and the drain electrode in a self-aligned manner. Thus, the conductor260can be formed without an alignment margin, resulting in a reduction in the area occupied by the transistor200A. Accordingly, the display device can have higher resolution. In addition, the display device can have a narrow bezel.

As illustrated inFIG.19, the conductor260preferably includes a conductor260aprovided on the inner side of the insulator250and a conductor260bprovided to be embedded on the inner side of the conductor260a.

The transistor200A preferably includes the insulator214placed over the substrate (not illustrated); the insulator216placed over the insulator214; a conductor205placed to be embedded in the insulator216; the insulator222placed over the insulator216and the conductor205; and the insulator224placed over the insulator222. The metal oxide230ais preferably placed over the insulator224.

The insulator274and the insulator281functioning as interlayer films are preferably placed over the transistor200A. Here, the insulator274is preferably placed in contact with the top surfaces of the conductor260, the insulator250, the insulator254, the metal oxide230c, and the insulator280.

The insulator222, the insulator254, and the insulator274preferably have a function of inhibiting diffusion of hydrogen (e.g., at least one of a hydrogen atom and a hydrogen molecule). For example, the insulator222, the insulator254, and the insulator274preferably have a lower hydrogen permeability than the insulator224, the insulator250, and the insulator280. Moreover, the insulator222and the insulator254preferably have a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule). For example, the insulator222and the insulator254preferably have a lower oxygen permeability than the insulator224, the insulator250, and the insulator280.

Here, the insulator224, the metal oxide230, and the insulator250are separated from the insulator280and the insulator281by the insulator254and the insulator274. This can inhibit entry of impurities such as hydrogen contained in the insulator280and the insulator281into the insulator224, the metal oxide230, and the insulator250or excess oxygen into the insulator224, the metal oxide230a, the metal oxide230b, and the insulator250.

A conductor240(a conductor240aand a conductor240b) that is electrically connected to the transistor200A and functions as a plug is preferably provided. Note that an insulator241(an insulator241aand an insulator241b) is provided in contact with the side surface of the conductor240functioning as a plug. That is, the insulator241is provided in contact with the inner wall of an opening in the insulator254, the insulator280, the insulator274, and the insulator281. In addition, a structure may be employed in which a first conductor of the conductor240is provided in contact with the side surface of the insulator241and a second conductor of the conductor240is provided on the inner side of the first conductor. Here, the top surface of the conductor240and the top surface of the insulator281can be substantially level with each other. Although the transistor200A has a structure in which the first conductor of the conductor240and the second conductor of the conductor240are stacked, the present invention is not limited thereto. For example, the conductor240may have a single-layer structure or a stacked-layer structure of three or more layers. In the case where a component has a stacked-layer structure, layers may be distinguished by ordinal numbers corresponding to the formation order.

In the transistor200A, a metal oxide functioning as an oxide semiconductor (hereinafter, also referred to as an oxide semiconductor) is preferably used as the metal oxide230including the channel formation region (the metal oxide230a, the metal oxide230b, and the metal oxide230c). For example, the metal oxide to be the channel formation region of the metal oxide230preferably has a band gap of 2 eV or more, further preferably 2.5 eV or more.

The metal oxide preferably contains at least indium (In) or zinc (Zn). In particular, indium (In) and zinc (Zn) are preferably contained. In addition to them, an element M is preferably contained. As the element M, one or more of aluminum (Al), gallium (Ga), yttrium (Y), tin (Sn), boron (B), titanium (Ti), iron (Fe), nickel (Ni), germanium (Ge), zirconium (Zr), molybdenum (Mo), lanthanum (La), cerium (Ce), neodymium (Nd), hafnium (Hf), tantalum (Ta), tungsten (W), magnesium (Mg), and cobalt (Co) can be used. In particular, the element M is preferably one or more of aluminum (Al), gallium (Ga), yttrium (Y), and tin (Sn). Furthermore, the element M preferably contains one or both of Ga and Sn.

As illustrated inFIG.19B, the metal oxide230bin a region not overlapping with the conductor242sometimes has a smaller thickness than the metal oxide230bin a region overlapping with the conductor242. The thin region is formed when part of the top surface of the metal oxide230bis removed at the time of forming the conductor242aand the conductor242b. When a conductive film to be the conductor242is formed, a low-resistance region is sometimes formed on the top surface of the metal oxide230bin the vicinity of the interface with the conductive film. Removing the low-resistance region positioned between the conductor242aand the conductor242bon the top surface of the metal oxide230bin the above manner can prevent formation of the channel in the region.

According to one embodiment of the present invention, a display device that includes small-size transistors and has high resolution can be provided. A display device that includes a transistor with a high on-state current and has high luminance can be provided. A display device that includes a transistor operating at high speed and thus operates at high speed can be provided. A display device that includes a transistor having stable electrical characteristics and is highly reliable can be provided. A display device that includes a transistor with a low off-state current and has low power consumption can be provided.

The structure of the transistor200A that can be used in the display device of one embodiment of the present invention will be described in detail.

The conductor205is placed to include a region overlapping with the metal oxide230and the conductor260. Furthermore, the conductor205is preferably provided to be embedded in the insulator216.

The conductor205includes a conductor205a, a conductor205b, and a conductor205c. The conductor205ais provided in contact with the bottom surface and the side wall of the opening provided in the insulator216. The conductor205bis provided to be embedded in a recessed portion formed by the conductor205a. Here, the level of the top surface of the conductor205bis lower than the levels of the top surface of the conductor205aand the top surface of the insulator216. The conductor205cis provided in contact with the top surface of the conductor205band the side surface of the conductor205a. Here, the top surface of the conductor205cis substantially level with the top surface of the conductor205aand the top surface of the insulator216. That is, the conductor205bis surrounded by the conductor205aand the conductor205c.

For the conductor205aand the conductor205c, it is preferable to use a conductive material having a function of inhibiting diffusion of impurities such as a hydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, a nitrogen molecule, a nitrogen oxide molecule (N2O, NO, NO2, or the like), and a copper atom. Alternatively, it is preferable to use a conductive material having a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule).

When the conductor205aand the conductor205care formed using a conductive material having a function of inhibiting diffusion of hydrogen, impurities such as hydrogen contained in the conductor205bcan be inhibited from diffusing into the metal oxide230through the insulator224and the like. When the conductor205aand the conductor205care formed using a conductive material having a function of inhibiting diffusion of oxygen, the conductivity of the conductor205bcan be inhibited from being lowered because of oxidation. As the conductive material having a function of inhibiting diffusion of oxygen, for example, titanium, titanium nitride, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used. Thus, the conductor205ais a single layer or stacked layers of the above conductive materials. For example, titanium nitride is used for the conductor205a.

For the conductor205b, a conductive material containing tungsten, copper, or aluminum as its main component is preferably used. For example, tungsten is used for the conductor205b.

The conductor260sometimes functions as a first gate (also referred to as top gate) electrode. The conductor205sometimes functions as a second gate (also referred to as bottom gate) electrode. In that case, by changing a potential applied to the conductor205not in synchronization with but independently of a potential applied to the conductor260, Vth of the transistor200A can be controlled. In particular, by application of a negative potential to the conductor205, Vth of the transistor200A can be higher than 0 V and the off-state current can be made low. Thus, drain current at the time when a potential applied to the conductor260is 0 V can be lower in the case where a negative potential is applied to the conductor205than in the case where the negative potential is not applied to the conductor205.

The conductor205is preferably provided to be larger than the channel formation region in the metal oxide230. In particular, it is preferable that the conductor205extend beyond an end portion of the metal oxide230that intersects with the channel width direction, as illustrated inFIG.19C. In other words, the conductor205and the conductor260preferably overlap with each other with the insulator placed therebetween, in a region outside the side surface of the metal oxide230in the channel width direction.

With the above structure, the channel formation region of the metal oxide230can be electrically surrounded by an electric field of the conductor260functioning as the first gate electrode and an electric field of the conductor205functioning as the second gate electrode.

As illustrated inFIG.19C, the conductor205extends to function as a wiring as well. However, without limitation to this structure, a structure in which a conductor functioning as a wiring is provided below the conductor205may be employed.

The insulator214preferably functions as a barrier insulating film that inhibits entry of an impurity such as water or hydrogen into the transistor200A from the substrate side. Accordingly, it is preferable to use, for the insulator214, an insulating material having a function of inhibiting diffusion of impurities such as a hydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, a nitrogen molecule, a nitrogen oxide molecule (e.g., N2O, NO, and NO2), and a copper atom (an insulating material through which the impurities are less likely to pass). Alternatively, it is preferable to use an insulating material having a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule) (an insulating material through which the oxygen is less likely to pass).

For example, aluminum oxide or silicon nitride is preferably used for the insulator214. Accordingly, it is possible to inhibit diffusion of an impurity such as water or hydrogen to the transistor200A side from the substrate side through the insulator214. Alternatively, it is possible to inhibit diffusion of oxygen contained in the insulator224and the like to the substrate side through the insulator214.

The permittivity of each of the insulator216, the insulator280, and the insulator281functioning as an interlayer film is preferably lower than that of the insulator214. When a material with a low permittivity is used for an interlayer film, the parasitic capacitance generated between wirings can be reduced. For the insulator216, the insulator280, and the insulator281, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, porous silicon oxide, or the like can be used as appropriate.

The insulator222and the insulator224function as a gate insulator.

Here, the insulator224in contact with the metal oxide230preferably releases oxygen by heating. In this specification, oxygen that is released by heating is referred to as excess oxygen in some cases. For example, silicon oxide, silicon oxynitride, or the like can be used as appropriate for the insulator224. When an insulator containing oxygen is provided in contact with the metal oxide230, oxygen vacancies in the metal oxide230can be reduced, leading to improved reliability of the transistor200A.

Specifically, an oxide material that releases part of oxygen by heating is preferably used for the insulator224. An oxide that releases oxygen by heating is an oxide film in which the amount of released oxygen converted into oxygen atoms is greater than or equal to 1.0×1018atoms/cm3, preferably greater than or equal to 1.0×1019atoms/cm3, further preferably greater than or equal to 2.0×1019atoms/cm3or greater than or equal to 3.0×1020atoms/cm3in TDS (Thermal Desorption Spectroscopy) analysis. Note that the temperature of the film surface in the TDS analysis is preferably within the range of 100° C. to 700° C. or 100° C. to 400° C.

As illustrated inFIG.19C, the insulator224in a region overlapping with neither the insulator254nor the metal oxide230bsometimes has a smaller thickness than that in the other regions. In the insulator224, the region overlapping with neither the insulator254nor the metal oxide230bpreferably has a thickness with which the above oxygen can be adequately diffused.

Like the insulator214and the like, the insulator222preferably functions as a barrier insulating film that inhibits entry of an impurity such as water or hydrogen into the transistor200A from the substrate side. For example, the insulator222preferably has a lower hydrogen permeability than the insulator224. When the insulator224, the metal oxide230, the insulator250, and the like are surrounded by the insulator222, the insulator254, and the insulator274, entry of an impurity such as water or hydrogen into the transistor200A from the outside can be inhibited.

Furthermore, it is preferable that the insulator222have a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule) (it is preferable that the oxygen be less likely to pass through the insulator222). For example, the insulator222preferably has a lower oxygen permeability than the insulator224. The insulator222preferably has a function of inhibiting diffusion of oxygen and impurities, in which case oxygen contained in the metal oxide230is less likely to diffuse to the substrate side. Moreover, the conductor205can be inhibited from reacting with oxygen contained in the insulator224or the metal oxide230.

As the insulator222, an insulator containing an oxide of one or both of aluminum and hafnium, which is an insulating material, is preferably used. As the insulator containing an oxide of one or both of aluminum and hafnium, aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like is preferably used. In the case where the insulator222is formed using such a material, the insulator222functions as a layer inhibiting release of oxygen from the metal oxide230and entry of impurities such as hydrogen into the metal oxide230from the periphery of the transistor200A.

The insulator222may be a single layer or a stacked layer using an insulator containing what is called a high-k material, such as aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3(BST). With scaling down and higher integration of transistors, a problem such as leakage current may arise because of a thinned gate insulator. When a high-k material is used for the insulator functioning as a gate insulator, a gate potential at the time of the operation of the transistor can be reduced while the physical thickness is maintained.

Note that the insulator222and the insulator224may each have a stacked-layer structure of two or more layers. In that case, without limitation to a stacked-layer structure formed of the same material, a stacked-layer structure formed of different materials may be employed. For example, an insulator similar to the insulator224may be provided below the insulator222.

The metal oxide230includes the metal oxide230a, the metal oxide230bover the metal oxide230a, and the metal oxide230cover the metal oxide230b. Since the metal oxide230aunder the metal oxide230bis provided, it is possible to inhibit diffusion of impurities into the metal oxide230bfrom the components formed below the metal oxide230a. Moreover, since the metal oxide230cover the metal oxide230bis included, it is possible to inhibit diffusion of impurities into the metal oxide230bfrom the components formed above the metal oxide230c.

Note that the metal oxide230preferably has a stacked-layer structure of a plurality of oxide layers that differ in the atomic ratio of metal atoms. For example, in the case where the metal oxide230contains at least indium (In) and the element M, the proportion of the number of atoms of the element M contained in the metal oxide230ato the number of atoms of all elements that constitute the metal oxide230ais preferably higher than the proportion of the number of atoms of the element M contained in the metal oxide230bto the number of atoms of all elements that constitute the metal oxide230b. In addition, the atomic ratio of the element M to In in the metal oxide230ais preferably greater than the atomic ratio of the element M to In in the metal oxide230b. Here, a metal oxide that can be used as the metal oxide230aor the metal oxide230bcan be used as the metal oxide230c.

The energy of the conduction band minimum of each of the metal oxide230aand the metal oxide230cis preferably higher than the energy of the conduction band minimum of the metal oxide230b. In other words, the electron affinity of each of the metal oxide230aand the metal oxide230cis preferably smaller than the electron affinity of the metal oxide230b. In this case, a metal oxide that can be used as the metal oxide230ais preferably used as the metal oxide230c. Specifically, the proportion of the number of atoms of the element M contained in the metal oxide230cto the number of atoms of all elements that constitute the metal oxide230cis preferably higher than the proportion of the number of atoms of the element M contained in the metal oxide230bto the number of atoms of all elements that constitute the metal oxide230b. In addition, the atomic ratio of the element M to In in the metal oxide230cis preferably greater than the atomic ratio of the element M to In in the metal oxide230b.

Here, the energy level of the conduction band minimum gently changes at junction portions between the metal oxide230a, the metal oxide230b, and the metal oxide230c. In other words, at the junction portions between the metal oxide230a, the metal oxide230b, and the metal oxide230c, the energy level of the conduction band minimum continuously changes or the energy levels are continuously connected. This can be achieved by decreasing the densities of defect states in mixed layers formed at the interface between the metal oxide230aand the metal oxide230band the interface between the metal oxide230band the metal oxide230c.

Specifically, when the metal oxide230aand the metal oxide230bor the metal oxide230band the metal oxide230ccontain the same element (as a main component) in addition to oxygen, a mixed layer with a low density of defect states can be formed. For example, an In—Ga—Zn oxide, a Ga—Zn oxide, gallium oxide, or the like may be used as the metal oxide230aand the metal oxide230c, in the case where the metal oxide230bis an In—Ga—Zn oxide. The metal oxide230cmay have a stacked-layer structure. For example, a stacked-layer structure of an In—Ga—Zn oxide and a Ga—Zn oxide over the In—Ga—Zn oxide or a stacked-layer structure of an In—Ga—Zn oxide and gallium oxide over the In—Ga—Zn oxide can be employed. In other words, the metal oxide230cmay have a stacked-layer structure of an In—Ga—Zn oxide and an oxide that does not contain In.

Specifically, as the metal oxide230a, a metal oxide with In:Ga:Zn=1:3:4 [atomic ratio] or 1:1:0.5 [atomic ratio] can be used. As the metal oxide230b, a metal oxide with In:Ga:Zn=4:2:3 [atomic ratio] or 3:1:2 [atomic ratio] can be used. As the metal oxide230c, a metal oxide with In:Ga:Zn=1:3:4 [atomic ratio], In:Ga:Zn=4:2:3 [atomic ratio], Ga:Zn=2:1 [atomic ratio], or Ga:Zn=2:5 [atomic ratio] can be used. Specific examples of a stacked-layer structure of the metal oxide230cinclude a stacked-layer structure of a layer with In:Ga:Zn=4:2:3 [atomic ratio] and a layer with Ga:Zn=2:1 [atomic ratio], a stacked-layer structure of a layer with In:Ga:Zn=4:2:3 [atomic ratio] and a layer with Ga:Zn=2:5 [atomic ratio], and a stacked-layer structure of a layer with In:Ga:Zn=4:2:3 [atomic ratio] and a layer of gallium oxide.

At this time, the metal oxide230bserves as a main carrier path. When the metal oxide230aand the metal oxide230chave the above structure, the densities of defect states at the interface between the metal oxide230aand the metal oxide230band the interface between the metal oxide230band the metal oxide230ccan be made low. This reduces the influence of interface scattering on carrier conduction, and the transistor200A can have a high on-state current and high frequency characteristics. Note that in the case where the metal oxide230chas a stacked-layer structure, not only the effect of reducing the density of defect states at the interface between the metal oxide230band the metal oxide230c, but also the effect of inhibiting diffusion of the constituent elements contained in the metal oxide230cto the insulator250side can be expected. Specifically, the metal oxide230chas a stacked-layer structure in which an oxide not containing In is positioned in the upper layer of the stacked-layer structure, whereby the diffusion of In to the insulator250side can be inhibited. Since the insulator250functions as a gate insulator, the transistor has defects in characteristics when In diffuses. Thus, the metal oxide230chaving a stacked-layer structure allows a highly reliable display device to be provided.

When the conductor242is provided in contact with the metal oxide230, the oxygen concentration of the metal oxide230in the vicinity of the conductor242sometimes decreases. In addition, a metal compound layer that contains the metal contained in the conductor242and the component of the metal oxide230is sometimes formed in the metal oxide230in the vicinity of the conductor242. In such cases, the carrier density of the region in the metal oxide230in the vicinity of the conductor242increases, and the region becomes a low-resistance region.

Here, the region between the conductor242aand the conductor242bis formed to overlap with the opening of the insulator280. Accordingly, the conductor260can be placed in a self-aligned manner between the conductor242aand the conductor242b.

The insulator250functions as a gate insulator. The insulator250is preferably placed in contact with the top surface of the metal oxide230c. For the insulator250, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, or porous silicon oxide can be used. In particular, silicon oxide and silicon oxynitride, which are thermally stable, are preferable.

As in the insulator224, the concentration of an impurity such as water or hydrogen in the insulator250is preferably reduced. The thickness of the insulator250is preferably greater than or equal to 1 nm and less than or equal to 20 nm.

A metal oxide may be provided between the insulator250and the conductor260. The metal oxide preferably inhibits oxygen diffusion from the insulator250into the conductor260. Accordingly, oxidation of the conductor260due to oxygen in the insulator250can be inhibited.

The metal oxide functions as part of the gate insulator in some cases. Therefore, when silicon oxide, silicon oxynitride, or the like is used for the insulator250, a metal oxide that is a high-k material with a high dielectric constant is preferably used as the metal oxide. When the gate insulator has a stacked-layer structure of the insulator250and the metal oxide, the stacked-layer structure can be thermally stable and have a high dielectric constant. Accordingly, a gate potential applied during the operation of the transistor can be reduced while the physical thickness of the gate insulator is maintained. In addition, the equivalent oxide thickness (EOT) of the insulator functioning as the gate insulator can be reduced.

Specifically, a metal oxide containing one kind or two or more kinds selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like can be used. It is particularly preferable to use an insulator containing an oxide of one or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate).

Although the conductor260is illustrated to have a two-layer structure inFIG.19, the conductor260may have a single-layer structure or a stacked-layer structure of three or more layers.

The conductor260ais preferably formed using the aforementioned conductor having a function of inhibiting diffusion of impurities such as a hydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, a nitrogen molecule, a nitrogen oxide molecule (e.g., N2O, NO, and NO2), and a copper atom. Alternatively, it is preferable to use a conductive material having a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule).

When the conductor260ahas a function of inhibiting diffusion of oxygen, the conductivity of the conductor260bcan be inhibited from being lowered by oxidation due to oxygen contained in the insulator250. As a conductive material having a function of inhibiting oxygen diffusion, for example, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used.

A conductive material containing tungsten, copper, or aluminum as its main component is preferably used for the conductor260b. The conductor260also functions as a wiring and thus is preferably formed using a conductor having high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as its main component can be used. The conductor260bmay have a stacked-layer structure, for example, a stacked-layer structure of titanium or titanium nitride and the above conductive material.

As illustrated inFIG.19AandFIG.19C, the side surface of the metal oxide230is covered with the conductor260in a region where the metal oxide230bdoes not overlap with the conductor242, that is, the channel formation region of the metal oxide230. Accordingly, an electric field of the conductor260functioning as the first gate electrode is likely to act on the side surface of the metal oxide230. Thus, the on-state current of the transistor200A can be increased and the frequency characteristics can be improved.

The insulator254, like the insulator214and the like, preferably functions as a barrier insulating film that inhibits entry of an impurity such as water or hydrogen into the transistor200A from the insulator280side. The insulator254preferably has a lower hydrogen permeability than the insulator224, for example. Furthermore, as illustrated inFIG.19BandFIG.19C, the insulator254is preferably in contact with the side surface of the metal oxide230c, the top and side surfaces of the conductor242a, the top and side surfaces of the conductor242b, the side surfaces of the metal oxide230aand the metal oxide230b, and the top surface of the insulator224. Such a structure can inhibit entry of hydrogen contained in the insulator280into the metal oxide230through the top surfaces or side surfaces of the conductor242a, the conductor242b, the metal oxide230a, the metal oxide230b, and the insulator224.

Furthermore, it is preferable that the insulator254have a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule) (it is preferable that the oxygen be less likely to pass through the insulator254). For example, the insulator254preferably has a lower oxygen permeability than the insulator280or the insulator224.

The insulator254is preferably formed by a sputtering method. When the insulator254is formed by a sputtering method in an oxygen-containing atmosphere, oxygen can be added to the vicinity of a region of the insulator224that is in contact with the insulator254. Thus, oxygen can be supplied from the region to the metal oxide230through the insulator224. Here, with the insulator254having a function of inhibiting upward diffusion of oxygen, oxygen can be prevented from diffusing from the metal oxide230into the insulator280. Moreover, with the insulator222having a function of inhibiting downward diffusion of oxygen, oxygen can be prevented from diffusing from the metal oxide230to the substrate side. In the above manner, oxygen is supplied to the channel formation region of the metal oxide230. Accordingly, oxygen vacancies in the metal oxide230can be reduced, so that the transistor can be inhibited from having normally-on characteristics.

As the insulator254, an insulator containing an oxide of one or both of aluminum and hafnium is preferably formed, for example. Note that as the insulator containing an oxide of one or both of aluminum and hafnium, aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like is preferably used.

The insulator224, the insulator250, and the metal oxide230are covered with the insulator254having a barrier property against hydrogen, whereby the insulator280is isolated from the insulator224, the metal oxide230, and the insulator250by the insulator254. This can inhibit entry of impurities such as hydrogen from the outside of the transistor200A, resulting in excellent electrical characteristics and high reliability of the transistor200A.

The insulator280is provided over the insulator224, the metal oxide230, and the conductor242with the insulator254therebetween. The insulator280preferably includes, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, or porous silicon oxide. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In particular, materials such as silicon oxide, silicon oxynitride, and porous silicon oxide are preferably used, in which case a region containing oxygen to be released by heating can be easily formed.

The concentration of an impurity such as water or hydrogen in the insulator280is preferably reduced. In addition, the top surface of the insulator280may be planarized.

Like the insulator214and the like, the insulator274preferably functions as a barrier insulating film that inhibits entry of an impurity such as water or hydrogen into the insulator280from the above. As the insulator274, for example, the insulator that can be used as the insulator214, the insulator254, and the like can be used.

The insulator281functioning as an interlayer film is preferably provided over the insulator274. As in the insulator224or the like, the concentration of an impurity such as water or hydrogen in the insulator281is preferably reduced.

The conductor240aand the conductor240bare placed in openings formed in the insulator281, the insulator274, the insulator280, and the insulator254. The conductor240aand the conductor240bare provided to face each other with the conductor260therebetween. Note that the top surfaces of the conductor240aand the conductor240bmay be level with the top surface of the insulator281.

The insulator241ais provided in contact with the inner wall of the opening in the insulator281, the insulator274, the insulator280, and the insulator254, and the first conductor of the conductor240ais formed in contact with the side surface of the insulator241a. The conductor242ais positioned on at least part of the bottom portion of the opening, and the conductor240ais in contact with the conductor242a. Similarly, the insulator241bis provided in contact with the inner wall of the opening in the insulator281, the insulator274, the insulator280, and the insulator254, and the first conductor of the conductor240bis formed in contact with the side surface of the insulator241b. The conductor242bis positioned on at least part of the bottom portion of the opening, and the conductor240bis in contact with the conductor242b.

The conductor240aand the conductor240bare preferably formed using a conductive material containing tungsten, copper, or aluminum as its main component. The conductor240aand the conductor240bmay each have a stacked-layer structure.

In the case where the conductor240has a stacked-layer structure, the aforementioned conductor having a function of inhibiting diffusion of an impurity such as water or hydrogen is preferably used as the conductor in contact with the metal oxide230a, the metal oxide230b, the conductor242, the insulator254, the insulator280, the insulator274, and the insulator281. For example, tantalum, tantalum nitride, titanium, titanium nitride, ruthenium, ruthenium oxide, or the like is preferably used. The conductive material having a function of inhibiting diffusion of an impurity such as water or hydrogen can be used as a single layer or stacked layers. The use of the conductive material can inhibit oxygen added to the insulator280from being absorbed by the conductor240aand the conductor240b. Moreover, an impurity such as water or hydrogen can be inhibited from entering the metal oxide230through the conductor240aand the conductor240bfrom a layer above the insulator281.

As the insulator241aand the insulator241b, for example, the insulator that can be used as the insulator254or the like can be used. Since the insulator241aand the insulator241bare provided in contact with the insulator254, an impurity such as water or hydrogen in the insulator280or the like can be inhibited from entering the metal oxide230through the conductor240aand the conductor240b. Furthermore, oxygen contained in the insulator280can be inhibited from being absorbed by the conductor240aand the conductor240b.

Although not illustrated, a conductor functioning as a wiring may be placed in contact with the top surface of the conductor240aand the top surface of the conductor240b. For the conductor functioning as a wiring, a conductive material containing tungsten, copper, or aluminum as its main component is preferably used. Furthermore, the conductor may have a stacked-layer structure and may be a stack of titanium or titanium nitride and the above conductive material, for example. Note that the conductor may be formed to be embedded in an opening provided in an insulator.

Materials that can be used for the transistor are described.

As a substrate where the transistor200A is formed, an insulator substrate, a semiconductor substrate, or a conductor substrate can be used, for example. Examples of the insulator substrate include a glass substrate, a quartz substrate, a sapphire substrate, a stabilized zirconia substrate (e.g., an yttria-stabilized zirconia substrate), and a resin substrate. Examples of the semiconductor substrate include a semiconductor substrate of silicon, germanium, or the like and a compound semiconductor substrate of silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, or gallium oxide. Another example is a semiconductor substrate in which an insulator region is included in the semiconductor substrate, e.g., an SOI (Silicon On Insulator) substrate. Examples of the conductor substrate include a graphite substrate, a metal substrate, an alloy substrate, and a conductive resin substrate. Other examples include a substrate including a metal nitride and a substrate including a metal oxide. Other examples include an insulator substrate provided with a conductor or a semiconductor, a semiconductor substrate provided with a conductor or an insulator, and a conductor substrate provided with a semiconductor or an insulator. Alternatively, these substrates provided with elements may be used. Examples of the elements provided for the substrates include a capacitor, a resistor, a switching element, a light-emitting element, and a memory element.

Examples of an insulator include an oxide, a nitride, an oxynitride, a nitride oxide, a metal oxide, a metal oxynitride, and a metal nitride oxide, each of which has an insulating property.

With scaling down and higher integration of transistors, for example, a problem such as leakage current may arise because of a thinned gate insulator. When a high-k material is used for the insulator functioning as a gate insulator, the voltage at the time of the operation of the transistor can be reduced while the physical thickness is maintained. By contrast, when a material with a low dielectric constant is used for the insulator functioning as an interlayer film, the parasitic capacitance generated between wirings can be reduced. Thus, a material is preferably selected depending on the function of an insulator.

Examples of the insulator having a high dielectric constant include gallium oxide, hafnium oxide, zirconium oxide, an oxide containing aluminum and hafnium, an oxynitride containing aluminum and hafnium, an oxide containing silicon and hafnium, an oxynitride containing silicon and hafnium, and a nitride containing silicon and hafnium.

Examples of the insulator having a low dielectric constant include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, porous silicon oxide, and a resin.

When a transistor using an oxide semiconductor is surrounded by insulators having a function of inhibiting the passage of oxygen and impurities such as hydrogen (e.g., the insulator214, the insulator222, the insulator254, and the insulator274), the electrical characteristics of the transistor can be stable. An insulator having a function of inhibiting the passage of oxygen and impurities such as hydrogen can be formed to have a single layer or a stacked layer including an insulator containing, for example, boron, carbon, nitrogen, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, chlorine, argon, gallium, germanium, yttrium, zirconium, lanthanum, neodymium, hafnium, or tantalum. Specifically, as the insulator having a function of inhibiting the passage of oxygen and impurities such as hydrogen, a metal oxide such as aluminum oxide, magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, or tantalum oxide or a metal nitride such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride oxide, or silicon nitride can be used.

An insulator functioning as a gate insulator is preferably an insulator including a region containing oxygen to be released by heating. For example, when a structure is employed in which silicon oxide or silicon oxynitride that includes a region containing oxygen to be released by heating is provided in contact with the metal oxide230, oxygen vacancies included in the metal oxide230can be filled.

A plurality of conductors formed using any of the above materials may be stacked. For example, a stacked-layer structure combining a material containing the above metal element and a conductive material containing oxygen may be employed. In addition, a stacked-layer structure combining a material containing the above metal element and a conductive material containing nitrogen may be employed. Furthermore, a stacked-layer structure combining a material containing the above metal element, a conductive material containing oxygen, and a conductive material containing nitrogen may be employed.

In the case where a metal oxide is used for the channel formation region of the transistor, the conductor functioning as the gate electrode preferably has a stacked-layer structure combining a material containing the above metal element and a conductive material containing oxygen. In that case, the conductive material containing oxygen is preferably provided on the channel formation region side. When the conductive material containing oxygen is provided on the channel formation region side, oxygen released from the conductive material is easily supplied to the channel formation region.

It is particularly preferable to use, for the conductor functioning as the gate electrode, a conductive material containing oxygen and a metal element contained in the metal oxide where the channel is formed. A conductive material containing the above metal element and nitrogen may be used. For example, a conductive material containing nitrogen, such as titanium nitride or tantalum nitride, may be used. Indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide to which silicon is added may be used. Indium gallium zinc oxide containing nitrogen may be used. With the use of such a material, hydrogen contained in the metal oxide where the channel is formed can be captured in some cases. Alternatively, hydrogen entering from an external insulator or the like can be captured in some cases.

Described in this embodiment is a metal oxide (hereinafter, also referred to as an oxide semiconductor) that can be used in the OS transistor described in the above embodiment.

<Classification of Crystal Structures>

First, the classification of the crystal structures of an oxide semiconductor will be described with reference toFIG.20A.FIG.20Ais a diagram showing the classification of the crystal structures of an oxide semiconductor, typically IGZO (a metal oxide containing In, Ga, and Zn).

As shown inFIG.20A, an oxide semiconductor is roughly classified into “Amorphous”, “Crystalline”, and “Crystal”. The term “Amorphous” includes completely amorphous. The term “Crystalline” includes CAAC (c-axis-aligned crystalline), nc (nanocrystalline), and CAC (cloud-aligned composite) (excluding single crystal and poly crystal). Note that the term “Crystalline” excludes single crystal, poly crystal, and completely amorphous. The term “Crystal” includes single crystal and poly crystal.

Note that the structures in the thick frame shown inFIG.20Aare in an intermediate state between “Amorphous” and “Crystal”, and belong to a new crystalline phase. That is, these structures are completely different from “Amorphous”, which is energetically unstable, and “Crystal”.

A crystal structure of a film or a substrate can be evaluated with an X-ray diffraction (XRD) spectrum.FIG.20Bshows an XRD spectrum, which is obtained by GIXD (Grazing-Incidence XRD) measurement, of a CAAC-IGZO film classified into “Crystalline”. Note that a GIXD method is also referred to as a thin film method or a Seemann-Bohlin method. The XRD spectrum that is shown inFIG.20Band obtained by GIXD measurement is hereinafter simply referred to as an XRD spectrum. The CAAC-IGZO film inFIG.20Bhas a composition in the neighborhood of In:Ga:Zn=4:2:3 [atomic ratio]. The CAAC-IGZO film inFIG.20Bhas a thickness of 500 nm.

As shown inFIG.20B, a clear peak indicating crystallinity is observed in the XRD spectrum of the CAAC-IGZO film. Specifically, a peak indicating c-axis alignment is detected at 2θ of around 31° in the XRD spectrum of the CAAC-IGZO film. As shown inFIG.20B, the peak at 2θ of around 310 is asymmetric with the angle at which the peak intensity is detected as the axis.

A crystal structure of a film or a substrate can also be evaluated with a diffraction pattern obtained by a nanobeam electron diffraction method (NBED) (such a pattern is also referred to as a nanobeam electron diffraction pattern).FIG.20Cshows a diffraction pattern of the CAAC-IGZO film.FIG.20Cshows a diffraction pattern obtained by the NBED method in which an electron beam is incident in the direction parallel to the substrate. The CAAC-IGZO film inFIG.20Chas a composition in the neighborhood of In:Ga:Zn=4:2:3 [atomic ratio]. In the nanobeam electron diffraction method, electron diffraction is performed with a probe diameter of 1 nm.

As shown inFIG.20C, a plurality of spots indicating c-axis alignment are observed in the diffraction pattern of the CAAC-IGZO film.

Here, the above-described CAAC-OS, nc-OS, and a-like OS are described in detail.

Note that each of the plurality of crystal regions is formed of one or more minute crystals (crystals each of which has a maximum diameter less than 10 nm). In the case where the crystal region is formed of one minute crystal, the maximum diameter of the crystal region is less than 10 nm. In the case where the crystal region is formed of a large number of minute crystals, the size of the crystal region may be approximately several tens of nanometers.

In the case of an In-M-Zn oxide (the element M is one or more kinds selected from aluminum, gallium, yttrium, tin, titanium, and the like), the CAAC-OS tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium (In) and oxygen (hereinafter, an In layer) and a layer containing the element M, zinc (Zn), and oxygen (hereinafter, an (M,Zn) layer) are stacked. Indium and the element M can be replaced with each other. Therefore, indium may be contained in the (M,Zn) layer. In addition, the element M may be contained in the In layer. Note that Zn may be contained in the In layer. Such a layered structure is observed as a lattice image in a high-resolution TEM image, for example.

When the CAAC-OS film is subjected to structural analysis by out-of-plane XRD measurement with an XRD apparatus using θ/2θ scanning, for example, a peak indicating c-axis alignment is detected at or around 2θ of 31°. Note that the position of the peak indicating c-axis alignment (the value of 2θ) may change depending on the kind, composition, or the like of the metal elements contained in the CAAC-OS.

The CAAC-OS is an oxide semiconductor with high crystallinity in which no clear grain boundary is observed. Thus, in the CAAC-OS, a reduction in electron mobility due to the grain boundary is less likely to occur. Moreover, since the crystallinity of an oxide semiconductor might be decreased by entry of impurities, formation of defects, or the like, the CAAC-OS can be regarded as an oxide semiconductor that has a small amount of impurities or defects (e.g., oxygen vacancies). Therefore, an oxide semiconductor including the CAAC-OS is physically stable. Accordingly, the oxide semiconductor including the CAAC-OS is resistant to heat and has high reliability. In addition, the CAAC-OS is stable with respect to high temperatures in the manufacturing process (what is called thermal budget). Accordingly, the use of the CAAC-OS for the OS transistor can extend the degree of freedom of the manufacturing process.

Next, the CAC-OS is described in detail. Note that the CAC-OS relates to the material composition.

Note that the atomic ratios of In, Ga, and Zn to the metal elements contained in the CAC-OS in an In—Ga—Zn oxide are denoted by [In], [Ga], and [Zn], respectively. For example, the first region in the CAC-OS in the In—Ga—Zn oxide has [In] higher than [In] in the composition of the CAC-OS film. Moreover, the second region has [Ga] higher than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region has [In] higher than [In] in the second region and [Ga] lower than [Ga] in the second region. Moreover, the second region has [Ga] higher than [Ga] in the first region and [In] lower than [In] in the first region.

Specifically, the first region includes indium oxide, indium zinc oxide, or the like as its main component. The second region includes gallium oxide, gallium zinc oxide, or the like as its main component. That is, the first region can be referred to as a region containing In as its main component. The second region can be referred to as a region containing Ga as its main component.

For example, in EDX mapping obtained by energy dispersive X-ray spectroscopy (EDX), it is confirmed that the CAC-OS in the In—Ga—Zn oxide has a structure in which the region containing In as its main component (the first region) and the region containing Ga as its main component (the second region) are unevenly distributed and mixed.

In the case where the CAC-OS is used for a transistor, a switching function (on/off switching function) can be given to the CAC-OS owing to the complementary action of the conductivity derived from the first region and the insulating property derived from the second region. That is, the CAC-OS has a conducting function in part of the material and has an insulating function in another part of the material; as a whole, the CAC-OS functions as a semiconductor. Separation of the conducting function and the insulating function can maximize each function. Accordingly, when the CAC-OS is used for a transistor, a high on-state current (Ion), high field-effect mobility (μ), and excellent switching operation can be achieved.

An oxide semiconductor can have any of various structures that show different properties. Two or more of the amorphous oxide semiconductor, the polycrystalline oxide semiconductor, the a-like OS, the CAC-OS, the nc-OS, and the CAAC-OS may be included in an oxide semiconductor of one embodiment of the present invention.

Next, a case where the oxide semiconductor is used for a transistor will be described.

When the oxide semiconductor is used for a transistor, the transistor can have high field-effect mobility. In addition, the transistor can have high reliability.

A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states and accordingly has a low density of trap states in some cases.

Charges trapped by the trap states in an oxide semiconductor take a long time to be released and may behave like fixed charges. A transistor whose channel formation region is formed in an oxide semiconductor having a high density of trap states has unstable electrical characteristics in some cases.

Accordingly, in order to obtain stable electrical characteristics of a transistor, reducing the impurity concentration in an oxide semiconductor is effective. In order to reduce the impurity concentration in the oxide semiconductor, the impurity concentration in an adjacent film is also preferably reduced. Examples of impurities include hydrogen, nitrogen, alkali metal, alkaline earth metal, iron, nickel, and silicon.

Here, the influence of impurities in the oxide semiconductor will be described.

When the oxide semiconductor contains alkali metal or alkaline earth metal, defect states are formed and carriers are generated in some cases. Accordingly, a transistor using an oxide semiconductor that contains alkali metal or alkaline earth metal tends to have normally-on characteristics. Thus, the concentration of alkali metal or alkaline earth metal in the oxide semiconductor, which is obtained by SIMS, is lower than or equal to 1×1018atoms/cm3, preferably lower than or equal to 2×1016atoms/cm3.

An oxide semiconductor containing nitrogen easily becomes n-type by generation of electrons serving as carriers and an increase in carrier concentration. As a result, a transistor using, as a semiconductor, an oxide semiconductor containing nitrogen tends to have normally-on characteristics. When nitrogen is contained in the oxide semiconductor, a trap state is sometimes formed. This might make the electrical characteristics of the transistor unstable. Thus, the nitrogen concentration in the oxide semiconductor, which is obtained by SIMS, is lower than 5×1019atoms/cm3, preferably lower than or equal to 5×1018atoms/cm3, further preferably lower than or equal to 1×1018atoms/cm3, still further preferably lower than or equal to 5×1017atoms/cm3.

When an oxide semiconductor with sufficiently reduced impurities is used for a channel formation region in a transistor, stable electrical characteristics can be given.

In this embodiment, electronic devices each including the display device and the display system of one embodiment of the present invention will be described.

FIG.21Ais a diagram illustrating an external view of a head-mounted display8200.

The head-mounted display8200includes a wearing portion8201, a lens8202, a main body8203, a display portion8204, a cable8205, and the like. A battery8206is incorporated in the wearing portion8201.

The cable8205supplies electric power from the battery8206to the main body8203. The main body8203includes a wireless receiver or the like and can display an image corresponding to the received image data or the like on the display portion8204. The movement of the eyeball and the eyelid of the user can be captured by a camera provided in the main body8203and then coordinates of the sight line of the user can be calculated using the information to utilize the sight line of the user as an input means.

A plurality of electrodes may be provided in the wearing portion8201at a position in contact with the user. The main body8203may have a function of sensing current flowing through the electrodes along with the movement of the user's eyeball to recognize the user's sight line. The main body8203may have a function of sensing current flowing through the electrodes to monitor the user's pulse. The wearing portion8201may include various sensors such as a temperature sensor, a pressure sensor, and an acceleration sensor to have a function of displaying the user's biological information on the display portion8204. The main body8203may sense the movement of the user's head or the like to change an image displayed on the display portion8204in synchronization with the movement.

The display device of one embodiment of the present invention can be used in the display portion8204. Thus, the power consumption of the head-mounted display8200can be reduced, so that the head-mounted display8200can be used continuously for a long time. The power consumption of the head-mounted display8200can be reduced, which allows the battery8206to be downsized and lighter and accordingly allows the head-mounted display8200to be downsized and lighter. Thus, a burden of the user of the head-mounted display8200can be reduced, and the user is less likely to feel fatigue.

FIG.21B,FIG.21C, andFIG.21Dare external views of a head-mounted display8300. The head-mounted display8300includes a housing8301, a display portion8302, a fixing band8304, and a pair of lenses8305. A battery8306is incorporated in the housing8301, and electric power can be supplied from the battery8306to the display portion8302and the like.

A user can see display on the display portion8302through the lenses8305. It is suitable that the display portion8302be curved and placed. When the display portion8302is curved and placed, a user can feel a high realistic sensation. Note that although the structure in which one display portion8302is provided is described in this embodiment as an example, the structure is not limited thereto, and a structure in which two display portions8302are provided may also be employed. In that case, one display portion is placed for one eye of the user, so that three-dimensional display using parallax or the like is possible.

The display device of one embodiment of the present invention can be used in the display portion8302. Thus, the power consumption of the head-mounted display8300can be reduced, so that the head-mounted display8300can be used continuously for a long time. The power consumption of the head-mounted display8300can be reduced, which allows the battery8306to be downsized and lighter and accordingly allows the head-mounted display8300to be downsized and lighter. Thus, a burden of the user of the head-mounted display8300can be reduced, and the user is less likely to feel fatigue.

Next,FIG.22AandFIG.22Billustrate examples of electronic devices that are different from the electronic devices illustrated inFIG.21AtoFIG.21D.

The electronic devices illustrated inFIG.22AandFIG.22Bhave a variety of functions. Examples of the functions include a function of displaying a variety of information (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of controlling processing with a variety of software (programs), a wireless communication function, a function of being connected to a variety of computer networks with a wireless communication function, a function of transmitting and receiving a variety of data with a wireless communication function, and a function of reading out a program or data stored in a memory medium and displaying it on the display portion. Note that functions of the electronic devices illustrated inFIG.22AandFIG.22Bare not limited thereto, and the electronic devices can have a variety of functions. Although not illustrated inFIG.22AandFIG.22B, the electronic devices may each include a plurality of display portions. The electronic devices may each include a camera and the like and have a function of taking a still image, a function of taking a moving image, a function of storing the taken image in a memory medium (externally attached or incorporated in the camera), a function of displaying the taken image on the display portion, and the like.

The details of the electronic devices illustrated inFIG.22AandFIG.22Bare described below.

FIG.22Ais a perspective view illustrating a portable information terminal9101. The portable information terminal9101has a function of, for example, one or more selected from a telephone set, a notebook, an information browsing system, and the like. Specifically, the portable information terminal can be used as a smartphone. The portable information terminal9101can display text or an image on its plurality of surfaces. For example, three operation buttons9050(also referred to as operation icons, or simply, icons) can be displayed on one surface of the display portion9001. Information9051indicated by a dashed rectangular can be displayed on another surface of the display portion9001. Examples of the information9051include display indicating reception of an e-mail, an SNS (social networking service), a telephone call, or the like; the title of an e-mail, an SNS, or the like; the sender of an e-mail, an SNS, or the like; the date; the time; remaining battery; and the reception strength of an antenna. Alternatively, the operation buttons9050or the like may be displayed on the position where the information9051is displayed, in place of the information9051.

The display device of one embodiment of the present invention can be used for the portable information terminal9101. Thus, the power consumption of the portable information terminal9101can be reduced, so that the portable information terminal9101can be used continuously for a long time. The power consumption of the portable information terminal9101can be reduced, which allows the battery9009to be downsized and lighter and accordingly allows the portable information terminal9101to be downsized and lighter. Thus, the portability of the portable information terminal9101can be increased.

FIG.22Bis a perspective view of a watch-type portable information terminal9200. The portable information terminal9200can execute a variety of applications such as mobile phone calls, e-mailing, viewing and editing texts, music reproduction, Internet communication, and computer games. The display surface of the display portion9001is curved, and display can be performed on the curved display surface.FIG.22Billustrates an example in which time9251, operation buttons9252(also referred to as operation icons, or simply, icons), and a content9253are displayed on the display portion9001. The content9253can be a moving image, for example.

The portable information terminal9200is capable of executing near field communication conformable to a communication standard. For example, mutual communication with a headset capable of wireless communication enables hands-free calling. The portable information terminal9200includes the connection terminal9006, and data can be directly transmitted to and received from another information terminal via a connector. Power charging through the connection terminal9006is also possible. Note that the charging operation may be performed by wireless power feeding not through the connection terminal9006.

The display device of one embodiment of the present invention can be used for the portable information terminal9200. Thus, the power consumption of the portable information terminal9200can be reduced, so that the portable information terminal9200can be used continuously for a long time. The power consumption of the portable information terminal9200can be reduced, which allows the battery9009to be downsized and lighter and accordingly allows the portable information terminal9200to be downsized and lighter. Thus, the portability of the portable information terminal9200can be increased.

<Supplementary Notes on Description in this Specification and the Like>

The following are notes on the description of the foregoing embodiments and the structures in the embodiments.

One embodiment of the present invention can be constituted by appropriately combining the structure described in an embodiment with any of the structures described in the other embodiments. In addition, in the case where a plurality of structure examples are described in one embodiment, some of the structure examples can be combined as appropriate.

Note that a content (or part thereof) described in one embodiment can be applied to, combined with, or replaced with another content (or part thereof) in the same embodiment and/or a content (or part thereof) described in another embodiment or other embodiments, for example.

Note that in each embodiment, a content described in the embodiment is a content described with reference to a variety of diagrams or a content described with text disclosed in the specification.

Note that by combining a diagram (or part thereof) described in one embodiment with another part of the diagram, a different diagram (or part thereof) described in the embodiment, and/or a diagram (or part thereof) described in another embodiment or other embodiments, much more diagrams can be formed.

In this specification and the like, components are classified on the basis of the functions, and shown as blocks independent of one another in block diagrams. However, in an actual circuit and the like, such components are sometimes hard to classify functionally, and there is a case where one circuit is associated with a plurality of functions and a case where a plurality of circuits are associated with one function. Therefore, the blocks in the block diagrams are not limited by the components described in the specification, and the description can be changed appropriately depending on the situation.

In drawings, the size, the layer thickness, or the region is shown arbitrarily for description convenience. Therefore, the size, the layer thickness, or the region is not limited to the illustrated scale. Note that the drawings are schematically shown for clarity, and embodiments of the present invention are not limited to shapes, values, or the like shown in the drawings. For example, variation in signal, voltage, or current due to noise or variation in signal, voltage, or current due to difference in timing can be included.

In this specification and the like, the terms “one of a source and a drain” (or a first electrode or a first terminal) and “the other of the source and the drain” (or a second electrode or a second terminal) are used to describe the connection relationship of a transistor. This is because a source and a drain of a transistor are interchangeable depending on the structure, operation conditions, or the like of the transistor. Note that the source or the drain of the transistor can also be referred to as a source (or drain) terminal, a source (or drain) electrode, or the like as appropriate depending on the situation.

In addition, in this specification and the like, the terms “electrode” and “wiring” do not functionally limit these components. For example, an “electrode” is used as part of a “wiring” in some cases, and vice versa. Furthermore, the term “electrode” and “wiring” also includes the case where a plurality of “electrodes” or “wirings” are formed in an integrated manner, for example.

In this specification and the like, voltage and potential can be replaced with each other as appropriate. The term voltage refers to a potential difference from a reference potential, and when the reference potential is a ground potential, for example, voltage can be replaced with potential. The ground potential does not necessarily mean 0 V. Potentials are relative values, and a potential supplied to a wiring or the like is sometimes changed depending on the reference potential.

In this specification and the like, a switch is in a conduction state (on state) or in a non-conduction state (off state) to determine whether current flows therethrough or not. Alternatively, a switch has a function of selecting and changing a current path.

In this specification and the like, the channel length refers to, for example, the distance between a source and a drain in a region where a semiconductor (or a portion where current flows in a semiconductor when a transistor is on) and a gate overlap with each other or a region where a channel is formed in a top view of the transistor.

In this specification and the like, the channel width refers to, for example, the length of a portion where a source and a drain face each other in a region where a semiconductor (or a portion where current flows in a semiconductor when a transistor is on) and a gate electrode overlap with each other or a region where a channel is formed.

In this specification and the like, the expression “A and B are connected” means the case where A and B are electrically connected to each other as well as the case where A and B are directly connected to each other. Here, the expression “A and B are electrically connected” means the case where electric signals can be transmitted and received between A and B when an object having any electric action exists between A and B.

EXAMPLE

In this example, a light-emitting device that can be used for the display device of one embodiment of the present invention will be described with reference toFIG.23toFIG.39.

FIG.23AandFIG.23Bare diagrams illustrating the structure of the light-emitting device550.

FIG.24is a graph showing current density-luminance characteristics of a light-emitting device1.

FIG.25is a graph showing luminance-current efficiency characteristics of the light-emitting device1.

FIG.26is a graph showing voltage-luminance characteristics of the light-emitting device1.

FIG.27is a graph showing voltage-current characteristics of the light-emitting device1.

FIG.28is a graph showing an emission spectrum of the light-emitting device1emitting light at a luminance of 1000 cd/m2.

FIG.29is a graph showing current density-luminance characteristics of a light-emitting device2.

FIG.30is a graph showing luminance-current efficiency characteristics of the light-emitting device2.

FIG.31is a graph showing voltage-luminance characteristics of the light-emitting device2.

FIG.32is a graph showing voltage-current characteristics of the light-emitting device2.

FIG.33is a graph showing an emission spectrum of the light-emitting device2emitting light at a luminance of 1000 cd/m2.

FIG.34is a graph showing current density-luminance characteristics of a light-emitting device3and a light-emitting device4.

FIG.35is a graph showing luminance-current efficiency characteristics of the light-emitting device3and the light-emitting device4.

FIG.36is a graph showing voltage-luminance characteristics of the light-emitting device3and the light-emitting device4.

FIG.37is a graph showing voltage-current characteristics of the light-emitting device3and the light-emitting device4.

FIG.38is a graph showing luminance-blue index characteristics of the light-emitting device3and the light-emitting device4.

FIG.39is a graph showing emission spectra of the light-emitting device3and the light-emitting device4emitting light at a luminance of 1000 cd/m2.

FIG.40AtoFIG.40Dare diagrams illustrating the structure of the light-emitting device550.

FIG.41is a graph showing current density-luminance characteristics of a light-emitting device5.

FIG.42is a graph showing luminance-current efficiency characteristics of the light-emitting device5.

FIG.43is a graph showing voltage-luminance characteristics of the light-emitting device5.

FIG.44is a graph showing voltage-current characteristics of the light-emitting device5.

FIG.45is a graph showing an emission spectrum of the light-emitting device5emitting light at a luminance of 1000 cd/m2.

FIG.46is a graph showing a change in normalized luminance over time of the light-emitting device5emitting light at a constant current density (50 mA/cm2).

The fabricated light-emitting device1described in this example can be used for the display device of one embodiment of the present invention. The light-emitting device1has a structure similar to that of the light-emitting device550(seeFIG.23A).

Table 1 shows the structure of the light-emitting device1. Structural formulae of materials used for the light-emitting device described in this example are shown below. Note that in the tables in this example, subscript characters and superscript characters are written in ordinary size for convenience. For example, subscript characters in abbreviations and superscript characters in units are written in ordinary size in the tables. Such notations in the tables can be replaced by referring to the description in the specification. In the light-emitting device1, there is the distance DG of 112 nm between a reflective film REFG(2) and an electrode552G.

The light-emitting device1described in this example was fabricated using a method including the following steps.

In Step 1, a conductive film REFG(1) was formed. Specifically, the conductive film REFG(1) was formed by a sputtering method using titanium (Ti) as a target.

Note that the conductive film REFG(1) contains Ti and has a thickness of 50 nm.

In Step 2, the reflective film REFG(2) was formed over the conductive film REFG(1). Specifically, the reflective film REFG(2) was formed by a sputtering method using aluminum (Al) as a target.

Note that the reflective film REFG(2) contains Al and has a thickness of 70 nm.

In Step 3, a conductive film REFG(3) was formed over the reflective film REFG(2). Specifically, the conductive film REFG(3) was formed by a sputtering method using Ti as a target.

Note that the conductive film REFG(3) contains Ti and has a thickness of 6 nm.

In Step 1, an electrode551G was formed. Specifically, the electrode551G was formed by a sputtering method using indium oxide-tin oxide containing silicon or silicon oxide (abbreviation: ITSO) as a target.

Note that the electrode551G contains ITSO and has a thickness of 10 nm and an area of 4 mm2(2 mm×2 mm).

Next, a base material over which the electrode551G was formed was washed with water, baked at 200° C. for an hour, and then subjected to UV ozone treatment for 370 seconds. After that, a substrate was transferred into a vacuum evaporation apparatus where the inside pressure was reduced to approximately 10−4Pa, and vacuum baking was performed at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus. Then, the substrate was cooled down for approximately 30 minutes.

In Step 5, the layer104was formed over the electrode551G. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer104contains N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) and an electron-accepting material (OCHD-003) at PCBBiF:OCHD-003=1:0.03 (weight ratio) and has a thickness of 10 nm. Note that the electron-accepting material OCHD-003 contains fluorine, and has a molecular weight of 672.

In Step 6, the layer112was formed over the layer104. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112contains PCBBiF and has a thickness of 10 nm.

In Step 7, a layer111G was formed over the layer112. Specifically, materials were co-evaporated by a resistance-heating method.

In Step 8, a layer113(1) was formed over the layer111G. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(1) contains 2-[3-(3′-dibenzothiophen-4-yl)biphenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II) and has a thickness of 15 nm.

In Step 9, a layer113(2) was formed over the layer113(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(2) contains 2,9-di(2-naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) and has a thickness of 15 nm.

In Step 10, the layer105was formed over the layer113(2). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer105contains lithium fluoride (abbreviation: LiF) and has a thickness of 1 nm.

In Step 11, the electrode552G was formed over the layer105. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the electrode552G contains silver (abbreviation: Ag) and magnesium (abbreviation: Mg) at Ag:Mg=1:0.1 (volume ratio) and has a thickness of 25 nm.

In Step 12, the conductive film552was formed over the electrode552G. Specifically, the conductive film552was formed by a sputtering method using indium oxide-tin oxide (abbreviation: ITO) as a target.

Note that the conductive film552contains ITO and has a thickness of 70 nm.

When supplied with electric power, the light-emitting device1emitted the light EL1(seeFIG.23A). The operation characteristics of the light-emitting device1were measured at room temperature (seeFIG.24toFIG.28). The luminance, CIE chromaticity, and emission spectrum were measured using a spectroradiometer (SR-UL1R, manufactured by TOPCON TECHNOHOUSE CORPORATION).

Table 2 shows the results of main initial characteristics of the fabricated light-emitting device emitting light at a luminance of approximately 1000 cd/m2. Note that the distance shown in the table is a distance from the reflective film REFG(2) to the electrode552G, a distance from a reflective film REFR(2) to an electrode552R, or a distance from a reflective film REFB(2) to an electrode552B. Furthermore, the table also shows characteristics of other light-emitting devices and comparative devices described later.

Note that the blue index (BI) is one of the indicators representing characteristics of a blue-light-emitting device, and is a value obtained by dividing current efficiency (cd/A) by chromaticity y. In general, blue light with high color purity is useful in expressing a wide color gamut. In addition, blue light with higher color purity tends to have lower chromaticity y. Thus, the value obtained by dividing current efficiency (cd/A) by chromaticity y is the indicator representing usefulness of a blue-light-emitting device. In other words, a blue-light-emitting device with high BI is suitable for achieving a display device with a wide color gamut and high efficiency.

The light-emitting device1was found to have favorable characteristics. For example, the light-emitting device1can be driven at a lower voltage than a comparative device1. High luminance can be obtained by the light-emitting device1with lower power than the comparative device1. The amount of materials used for the light-emitting device1can be smaller than that of the comparative device1. In addition, the time required for manufacturing the light-emitting device1can be shortened.

Reference Example 1

In the fabricated comparative device1described in this reference example, the layer112has a thickness of 137.5 nm instead of a thickness of 10 nm, the layer111G has a thickness of 50 nm instead of a thickness of 40 nm, and the layer105contains LiF and Yb at LiF:Yb=1:1 (weight ratio) instead of LiF and has a thickness of 1.8 nm. The comparative device1is different from the light-emitting device1in that the electrode552G has a thickness of 15 nm instead of a thickness of 25 nm. Note that in the comparative device1, there is the distance DG of 250.3 nm between the reflective film REFG(2) and the electrode552G.

The fabricated light-emitting device2described in this example can be used for the display device of one embodiment of the present invention.

Table 3 shows the structure of the light-emitting device2. Structural formulae of materials used for the light-emitting device described in this example are shown below. Note that in the light-emitting device2, there is the distance DR of 137 nm between the reflective film REFR(2) and the electrode552R.

The structure of the light-emitting device2is different from that of the light-emitting device1in that the electrode551R is provided instead of the electrode551G, the layer112has a thickness of 30 nm instead of a thickness of 10 nm, a layer111R is provided instead of the layer111G, the layer113(2) has a thickness of 20 nm instead of a thickness of 15 nm, and the electrode552R is provided instead of the electrode552G.

The light-emitting device2described in this example was fabricated using a method including the following steps.

The method for fabricating the light-emitting device2is different from the method for fabricating the light-emitting device1in Step 6 for forming the layer112, Step 7 for forming the layer111R, and Step 9 for forming the layer113(2). Different portions are described in detail here, and the above description is referred to for portions formed by a similar method.

In Step 6, the layer112was formed over the layer104. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112contains PCBBiF and has a thickness of 30 nm.

In Step 7, the layer111R was formed over the layer112. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer111R contains 9-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine (abbreviation: 9mDBtBPNfpr), PCBBiF, and a phosphorescent dopant (abbreviation: OCPG-006) at 9mDBtBPNfpr:PCBBiF:OCPG-006=0.6:0.4:0.1 (weight ratio) and has a thickness of 40 nm.

In Step 9, the layer113(2) was formed over the layer113(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(2) contains NBPhen and has a thickness of 20 nm.

When supplied with electric power, the light-emitting device2emitted the light EL1(seeFIG.23A). The operation characteristics of the light-emitting device2were measured at room temperature (seeFIG.29toFIG.33). The luminance, CIE chromaticity, and emission spectrum were measured using a spectroradiometer (SR-UL1R, manufactured by TOPCON TECHNOHOUSE CORPORATION).

Table 2 shows the results of main initial characteristics of the fabricated light-emitting device emitting light at a luminance of approximately 1000 cd/m2.

The light-emitting device2was found to have favorable characteristics. For example, the light-emitting device2can be driven at a lower voltage than a comparative device2. High luminance can be obtained by the light-emitting device2with lower power than the comparative device2. The amount of materials used for the light-emitting device2can be smaller than that of the comparative device2. In addition, the time required for manufacturing the light-emitting device2can be shortened.

In a display device including the light-emitting device1and the light-emitting device2, the light-emitting device1has the distance DG of 112 nm between the reflective film REFG(2) and the electrode552G. Furthermore, the light-emitting device2has the distance DR of 137 nm between the reflective film REFR(2) and the electrode552R.

The distance DR of 137 nm is 25 nm longer than the distance DG of 112 nm.

The display device including the light-emitting device1and the light-emitting device2has a smaller step than a display device including the comparative device1and the comparative device2.

Reference Example 2

In the fabricated comparative device2described in this reference example, the layer112has a thickness of 192.5 nm instead of a thickness of 30 nm and the layer105contains LiF and Yb at LiF:Yb=1:1 (weight ratio) instead of LiF and has a thickness of 1.8 nm. The comparative device2is different from the light-emitting device2in that the electrode552R has a thickness of 15 nm instead of a thickness of 25 nm. Note that in the comparative device2, there is the distance DR of 300.3 nm between the reflective film REFR(2) and the electrode552R.

In the display device including the comparative device1and the comparative device2, the comparative device1has the distance DG of 250.3 nm between the reflective film REFG(2) and the electrode552G. Furthermore, the comparative device2has the distance DR of 300.3 nm between the reflective film REFR(2) and the electrode552R.

The distance DR of 300.3 nm is 50 nm longer than the distance DG of 250.3 nm.

The fabricated light-emitting device3described in this example can be used for the display device of one embodiment of the present invention. The light-emitting device3has a structure similar to that of the light-emitting device550(seeFIG.23B).

Table 4 shows the structure of the light-emitting device3. Structural formulae of materials used for the light-emitting device described in this example are shown below. Note that in the light-emitting device3, there is the distance DB of 193.8 nm between the reflective film REFB(2) and the electrode552B.

The structure of the light-emitting device3is different from that of the light-emitting device1in that the electrode551B is provided instead of the electrode551G, a layer112(1) and a layer112(2) are provided instead of the layer112, a layer111B is provided instead of the layer111G, the layer105contains LiF and Yb at LiF:Yb=1:1 (weight ratio) instead of LiF and has a thickness of 1.8 nm, and the electrode552B is provided instead of the electrode552G. Note that a conductive film REFB(1) has a structure similar to that of the conductive film REFG(1) and a conductive film REFB(3) has a structure similar to that of the conductive film REFG(3).

The light-emitting device3described in this example was fabricated using a method including the following steps.

The method for fabricating the light-emitting device3is different from the method for fabricating the light-emitting device1in Step 6 for forming the layer112(1) instead of the layer112, Step 6-2 for forming the layer112(2) over the layer112(1), Step 7 for forming the layer111B, and Step 10 for forming the layer105. Different portions are described in detail here, and the above description is referred to for portions formed by a similar method.

In Step 6, the layer112(1) was formed over the layer104. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112(1) contains PCBBiF and has a thickness of 96 nm.

In Step 6-2, the layer112(2) was formed over the layer112(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112(2) contains N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation: DBfBB1TP) and has a thickness of 10 nm.

In Step 7, the layer111B was formed over the layer112(2). Specifically, materials were co-evaporated by a resistance-heating method.

In Step 10, the layer105was formed over the layer113(2). Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer105contains LiF and Yb at LiF:Yb=1:1 (weight ratio) and has a thickness of 1.8 nm.

When supplied with electric power, the light-emitting device3emitted the light EL1(seeFIG.23B). The operation characteristics of the light-emitting device1were measured at room temperature (seeFIG.34toFIG.39). The luminance, CIE chromaticity, and emission spectrum were measured using a spectroradiometer (SR-UL1R, manufactured by TOPCON TECHNOHOUSE CORPORATION).

Table 2 shows the results of main initial characteristics of the fabricated light-emitting device emitting light at a luminance of approximately 1000 cd/m2.

The light-emitting device3was found to have favorable characteristics. For example, the light-emitting device3emitted light having a deep blue chromaticity. Furthermore, since the light-emitting device3exhibits high blue index, it can be said that the light-emitting device3is suitable for the display device.

In a display device including the light-emitting device1, the light-emitting device2, and the light-emitting device3, the light-emitting device1has the distance DG of 112 nm between the reflective film REFG(2) and the electrode552G. Furthermore, the light-emitting device2has the distance DR of 137 nm between the reflective film REFR(2) and the electrode552R, and the light-emitting device3has the distance DB of 193.8 nm between the reflective film REFB(2) and the electrode552B.

The distance DB of 193.8 nm is 81.8 nm longer than the distance DG of 112 nm. The distance DB of 193.8 nm is 56.8 nm longer than the distance DR of 137 nm. The distance DR of 137 nm is 25 nm longer than the distance DG of 112 nm.

The display device including the light-emitting device1, the light-emitting device2, and the light-emitting device3has a smaller step than a display device including the comparative device1, the comparative device2, and the light-emitting device3.

The fabricated light-emitting device3described in this example can be used for the display device of one embodiment of the present invention. The light-emitting device4has a structure similar to that of the light-emitting device550(seeFIG.23B).

Table 5 shows the structure of the light-emitting device4. Note that in the light-emitting device4, there is the distance DB of 82 nm between the reflective film REFB(2) and the electrode552B.

The structure of the light-emitting device4is different from that of the light-emitting device1in that the electrode551B is provided instead of the electrode551G, the layer104has a thickness of 5 nm instead of a thickness of 10 nm, the layer112(1) and the layer112(2) are provided instead of the layer112, the layer111B is provided instead of the layer111G, the layer113(2) has a thickness of 10 nm instead of a thickness of 15 nm, and the electrode552B is provided instead of the electrode552G.

The light-emitting device4described in this example was fabricated using a method including the following steps.

The method for fabricating the light-emitting device4is different from the method for fabricating the light-emitting device1in Step 5 for forming the layer104, Step 6 for forming the layer112(1) instead of the layer112, Step 6-2 for forming the layer112(2) over the layer112(1), Step 7 for forming the layer111B, Step 8 for forming the layer113(1), and Step 9 for forming the layer113(2). Different portions are described in detail here, and the above description is referred to for portions formed by a similar method.

In Step 5, the layer104was formed over the electrode551B. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer104contains PCBBiF and OCHD-003 at PCBBiF:OCHD-003=1:0.03 (weight ratio) and has a thickness of 5 nm.

In Step 6, the layer112(1) was formed over the layer104. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112(1) contains PCBBiF and has a thickness of 5 nm.

In Step 6-2, the layer112(2) was formed over the layer112(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112(2) contains DBfBB1TP and has a thickness of 5 nm.

In Step 7, the layer111B was formed over the layer112(2). Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer111B contains αN-βNPAnth and 3,10PCA2Nbf(IV)-02 at αN-βNPAnth:3,10PCA2Nbf(IV)-02=1:0.015 (weight ratio) and has a thickness of 25 nm.

In Step 8, the layer113(1) was formed over the layer111G. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(1) contains 2mDBTBPDBq-II and has a thickness of 15 nm.

In Step 9, the layer113(2) was formed over the layer113(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(2) contains NBPhen and has a thickness of 10 nm.

When supplied with electric power, the light-emitting device4emitted the light EL1(seeFIG.23B). The operation characteristics of the light-emitting device1were measured at room temperature (seeFIG.34toFIG.39). The luminance, CIE chromaticity, and emission spectrum were measured using a spectroradiometer (SR-UL1R, manufactured by TOPCON TECHNOHOUSE CORPORATION).

Table 2 shows the results of main initial characteristics of the fabricated light-emitting device emitting light at a luminance of approximately 1000 cd/m2.

The light-emitting device4was found to have favorable characteristics. For example, the light-emitting device4can be driven at a low voltage. The light-emitting device4exhibited high current efficiency. High luminance can be obtained by the light-emitting device4with low power. In addition, the amount of materials used for the light-emitting device4can be smaller than that of the light-emitting device3. Furthermore, the time required for manufacturing the light-emitting device4can be shortened.

In a display device including the light-emitting device1, the light-emitting device2, and the light-emitting device4, the light-emitting device1has the distance DG of 112 nm between the reflective film REFG(2) and the electrode552G. Furthermore, the light-emitting device2has the distance DR of 137 nm between the reflective film REFR(2) and the electrode552R, and the light-emitting device4has the distance DB of 82 nm between the reflective film REFB(2) and the electrode552B.

The distance DR of 137 nm is 55 nm longer than the distance DB of 82 nm. The distance DR of 137 nm is 25 nm longer than the distance DG of 112 nm. The distance DG of 112 nm is 30 nm longer than the distance DB of 82 nm.

The display device including the light-emitting device1, the light-emitting device2, and the light-emitting device4has a smaller step than the display device including the comparative device1, the comparative device2, and the light-emitting device3.

The fabricated light-emitting device5described in this example has a structure similar to that of the light-emitting device550(seeFIG.23AandFIG.40AtoFIG.40C).

Table 6 shows the structure of the light-emitting device5. The fabricated light-emitting device5described in this example is different in that the layer111G contains 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm) and 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) instead of 8BP-4mDBtPBfpm and PCCP, and the layer113(1) contains 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) instead of 2mDBTBPDBq-II.

The area of the electrode551G of light-emitting device5is 7.32 μm2(6.42 μm×1.14 μm), which is smaller than the area of the electrode551G of the light-emitting device1. A unit103G of the light-emitting device5is separated from an adjacent light-emitting device (seeFIG.40C). The filler529(1) and the filler529(2) are provided between the light-emitting device5and the adjacent light-emitting device.

The light-emitting device5described in this example was fabricated using a method including the following steps.

In Step 1, a reflective film REFG(1) was formed. Specifically, the reflective film REFG(1) was formed by a sputtering method using titanium (Ti) as a target.

Note that the reflective film REFG(1) contains Ti and has a thickness of 50 nm.

In Step 2, the reflective film REFG(2) was formed over the reflective film REFG(1). Specifically, the reflective film REFG(2) was formed by a sputtering method using aluminum (Al) as a target.

Note that the reflective film REFG(2) contains Al and has a thickness of 70 nm.

In Step 3, a reflective film REFG(3) was formed over the reflective film REFG(2). Specifically, the reflective film REFG(3) was formed by a sputtering method using Ti as a target.

Note that the reflective film REFG(3) contains Ti and has a thickness of 6 nm.

Next, a substrate was heated at 300° C. in the air for an hour to oxidize Ti of the reflective film REFG(3). Accordingly, the light-transmitting property of the reflective film REFG(3) is improved, and light that has passed through the reflective film REFG(3) is reflected by the reflective film REFG(2).

In Step 4, the electrode551G was formed over the reflective film REFG(3). Specifically, the electrode551G was formed by a sputtering method using indium oxide-tin oxide containing silicon or silicon oxide (abbreviation: ITSO) as a target.

The electrode551G contains ITSO, has a thickness of 10 nm, and has an area of 7.32 μm2(6.42 μm×1.14 μm). Note that a plurality of electrodes551G are arranged in a region of 4 mm2(2 mm×2 mm) (seeFIGS.40A and40B) and the center distance (pitch) is 7.92 μm. In other words, pixels703with a pixel density of 3207 ppi are regularly arranged in the region of 4 mm2.

Next, the substrate over which the electrode551G was formed was washed with water, baked at 200° C. for an hour, and then subjected to UV ozone treatment for 370 seconds. After that, the substrate was transferred into a vacuum evaporation apparatus where the inside pressure was reduced to approximately 10−4Pa, and vacuum baking was performed at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus. Then, the substrate was cooled down for approximately 30 minutes.

In Step 5, the layer104was formed over the electrode551G. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer104contains PCBBiF and OCHD-003 at PCBBiF:OCHD-003=1:0.03 (weight ratio) and has a thickness of 10 nm.

In Step 6, the layer112was formed over the layer104. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer112contains PCBBiF and has a thickness of 10 nm.

In Step 7, the layer111G was formed over the layer112. Specifically, materials were co-evaporated by a resistance-heating method.

In Step 8, the layer113(1) was formed over the layer111G. Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(1) contains 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) and has a thickness of 20 nm.

In Step 9, the layer113(2) was formed over the layer113(1). Specifically, a material was evaporated by a resistance-heating method.

Note that the layer113(2) contains NBPhen and has a thickness of 15 nm.

In Step 10, a sacrificial layer(1) was formed over the layer113(2). Specifically, the substrate provided with components up to the layer112(2) was taken out from a vacuum evaporation apparatus and then transferred into an ALD deposition apparatus, and a material was deposited by an ALD method. Note that the sacrificial layer(1) contains aluminum oxide and has a thickness of 30 nm.

In Step 10-2, a sacrificial layer(2) was formed over the sacrificial layer(1). Specifically, the substrate provided with the sacrificial layer(1) was taken out from the ALD deposition apparatus and then transferred into a sputtering apparatus, and a material was deposited by a sputtering method. Note that the sacrificial layer(2) contains tungsten and has a thickness of 50 nm.

In Step 11, the sacrificial layer(1) and the sacrificial layer(2) were processed into a predetermined shape. Specifically, after the substrate provided with the sacrificial layer(2) was taken out from a sputtering apparatus, a resist was formed over the sacrificial layer(2) so as to overlap with the electrode551G and etching treatment was performed by a photolithography method.

In Step 11-2, each of the unit103G and the layer104was processed into a predetermined shape. Specifically, the sacrificial layer(1) and the sacrificial layer(2) were used as resists and an unnecessary portion was etched while a portion overlapping with the electrode551G was left.

In Step 11-2, the sacrificial layer(2) was removed. Specifically, the sacrificial layer(2) was etched by a dry etching method.

In Step 12, an insulating film to be the filler529(1) later was formed. Specifically, the insulating film was formed by an ALD method to cover the top surface of the sacrificial layer(1) and the side surfaces of the unit103G and the layer104. Note that the insulating film contains aluminum oxide and has a thickness of 10 nm.

In Step 13, the filler529(2) was formed into a predetermined shape. Specifically, a photosensitive resin was used. Furthermore, a portion overlapping with the electrode551G was removed while a portion between the electrode551G and another electrode adjacent to the electrode551G was left, whereby an opening portion was formed.

In Step 13-2, the insulating film formed in Step 12 was processed into a predetermined shape, whereby the filler529(1) was formed. Specifically, the filler529(2) was used as a resist and a portion overlapping with the electrode551G was removed while a portion between the electrode551G and another electrode adjacent to the electrode551G was left, whereby an opening portion was formed in the insulating film. Furthermore, the sacrificial layer(1) overlapping with the electrode551G was removed by a wet etching method. Accordingly, the layer113(2) is exposed in the opening portion. After that, the substrate was transferred into a vacuum evaporation apparatus where the inside pressure was reduced to approximately 10−4Pa, and vacuum baking was performed at 70° C. for 90 minutes in a heating chamber of the vacuum evaporation apparatus. Then, the substrate was cooled down for approximately 30 minutes.

In Step 14, the layer105was formed over the layer113(2). Specifically, materials were co-evaporated by a resistance-heating method.

Note that the layer105contains LiF and Yb at LiF:Yb=1:1 (volume ratio) and has a thickness of 2 nm.

In Step 15, the electrode552G was formed over the layer105. Specifically, materials were co-evaporated by a resistance-heating method.

Note that the electrode552G contains Ag and Mg at Ag:Mg=1:0.1 (volume ratio) and has a thickness of 25 nm.

In Step 16, the conductive film552was formed over the electrode552G. Specifically, the conductive film552was formed by a sputtering method using indium oxide-tin oxide (abbreviation: ITO) as a target.

Note that the conductive film552contains ITO and has a thickness of 70 nm.

When supplied with electric power, the light-emitting device5emitted the light EL1(seeFIG.40C). The operation characteristics of the light-emitting device5were measured at room temperature (seeFIG.41toFIG.45). The luminance, CIE chromaticity, and emission spectrum were measured using a spectroradiometer (SR-UL1R, manufactured by TOPCON TECHNOHOUSE CORPORATION).

Table 7 shows main initial characteristics of the fabricated light-emitting device emitting light at a luminance of approximately 1000 cd/m2. Table 8 shows a time LT90 taken for the luminance to drop to 90% of its initial value, which were obtained under the condition where the light-emitting device5emitted light at a constant current density (50 mA/cm2). Table 7 and Table 8 also show the characteristics of a comparative device3having a structure described later.

A light-emitting device with an extremely small area was achieved. Specifically, the area of the light-emitting device5was 7.32 μm2(6.42 μm×1.14 μm). Furthermore, a plurality of light-emitting devices were able to be arranged with a center distance (pitch) of 7.92 μm. In other words, the plurality of light-emitting devices were able to be arranged with a pixel density of 3207 ppi. In addition, the light-emitting device5was found to have favorable characteristics. For example, the light-emitting device5exhibited higher current efficiency than the comparative device3which was fabricated without processing the unit103G or the layer103. The light-emitting device5showed a luminance of approximately 1000 cd/m2at a low voltage. Furthermore, the light-emitting device5showed along LT90 and favorable reliability. The layer104of the device5is separated from an adjacent light-emitting device and a phenomenon in which current flows to the adjacent light-emitting device through the layer104is inhibited. In the light-emitting device5of one embodiment of the present invention, steps can be reduced, so that the unit103G and the layer104can be easily processed. Thus, manufacture of the display device is easy.

Reference Example 3

The fabricated comparative device3described in this reference example has a structure similar to that of the light-emitting device550(seeFIG.40D).

In the comparative device3, components from the layer104to the conductive film552were formed without the substrate being taken out from a vacuum evaporation apparatus. Thus, neither deposition of the sacrificial layer(1) and the sacrificial layer(2) nor processing of the unit103G and the layer104was performed. The comparative device3is different from the light-emitting device5in that a partition528is provided instead of the filler529(1) and the filler529(2) (seeFIG.40D). The other components are the same as those of the light-emitting device5.

<<Fabrication Method of Comparative Device3>>

The method for fabricating the comparative device3is different from the method for fabricating the light-emitting device5in that the partition528is formed in the step for forming the electrode551G and neither the filler529(1) nor the filler529(2) is used. In other words, a method that proceeds to Step 14 after Step 9 without performing Step 10 to Step 13-2 is employed.

REFERENCE NUMERALS