Patent ID: 12225761

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiments can be implemented in many different modes, and it will be readily appreciated by those skilled in the art that modes and details of the embodiments can be changed in various ways without departing from the spirit and scope thereof. Thus, the present invention should not be interpreted as being limited to the following description of the embodiments.

Note that in each drawing described in this specification, the size, the layer thickness, or the region of each component is exaggerated for clarity in some cases. Therefore, they are not limited to the illustrated scale.

Note that in this specification and the like, ordinal numbers such as “first,” “second,” and the like are used in order to avoid confusion among components and do not limit the number.

Note that the expressions indicating directions such as “over” and “under” are basically used to correspond to the directions of drawings. However, in some cases, the direction indicating “over” or “under” in the specification does not correspond to the direction in the drawings for the purpose of description simplicity or the like. For example, when a stacked order (formation order) of a stacked body or the like is described, even in the case where a surface on which the stacked body is provided (e.g., a formation surface, a support surface, an attachment surface, or a planarization surface) is positioned above the stacked body in the drawings, the direction and the opposite direction are referred to as “under” and “over”, respectively, in some cases.

Moreover, in this specification and the like, the term “film” and the term “layer” can be interchanged with each other. For example, in some cases, the term “conductive layer” and the term “insulating layer” can be interchanged with the term “conductive film” and the term “insulating film”, respectively.

Note that in this specification, an EL layer means a layer containing at least a light-emitting substance (also referred to as a light-emitting layer) or a stacked body including the light-emitting layer provided between a pair of electrodes of a light-emitting element.

In this specification and the like, a display panel that is one embodiment of a display device has a function of displaying (outputting) an image or the like on (to) a display surface. Thus, the display panel is one embodiment of an output device.

In this specification and the like, a substrate of a display panel to which a connector such as an FPC (Flexible Printed Circuit) or a TCP (Tape Carrier Package) is attached, or a substrate on which an IC is mounted by a COG (Chip On Glass) method or the like is referred to as a display panel module, a display module, or simply a display panel or the like in some cases.

Note that in this specification and the like, a touch panel that is one embodiment of a display device has a function of displaying an image or the like on a display surface and a function of a touch sensor capable of sensing the contact, press, approach, or the like of a sensing target such as a finger or a stylus with or to the display surface. Thus, the touch panel is one embodiment of an input/output device.

A touch panel can be referred to as, for example, a display panel (or a display device) with a touch sensor, or a display panel (or a display device) having a touch sensor function. A touch panel can include a display panel and a touch sensor panel. Alternatively, a touch panel can have a function of a touch sensor in the display panel or on the surface of the display panel.

In this specification and the like, a substrate of a touch panel on which a connector and an IC are mounted is referred to as a touch panel module, a display module, or simply a touch panel or the like in some cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the present invention and a fabrication method of the display device will be described.

The display device of one embodiment of the present invention includes light-emitting units emitting light of different colors. The light-emitting unit includes at least one light-emitting element. The light-emitting element includes a lower electrode, an upper electrode, and a layer containing a light-emitting compound (also referred to as a light-emitting layer or an EL layer) therebetween. As the light-emitting element, an electroluminescent element such as an organic EL element or an inorganic EL element is preferably used. Alternatively, a light-emitting diode (LED) may be used.

The light-emitting unit also includes an insulating layer overlapping with the light-emitting element and a reflective layer (also referred to as an optical adjustment layer) reflecting visible light through the insulating layer. Furthermore, it is preferable that the light-emitting element use a conductive film transmitting visible light as the lower electrode on the reflective layer side, and use a conductive film having a semi-transmissive property and a semi-reflective property as the upper electrode. The light-emitting unit has what is called a microcavity structure and intensifies light with a specific wavelength.

Two light-emitting elements provided in two light-emitting units that emit light of different colors are preferably light-emitting elements that emit white light and have similar structures. In this case, a structure can be employed in which the light-emitting layer and the upper electrode are shared by the two light-emitting elements, and the lower electrodes of the elements are electrically insulated from each other. Furthermore, the two light-emitting units differ in distance between the light-emitting element and the reflective layer. Thus, light with different wavelengths can be intensified and emitted.

In one embodiment of the present invention, reflective layers with different thicknesses are formed, an insulating layer is formed to cover these reflective layers, and then the top surface of the insulating layer is subjected to planarization treatment, whereby the insulating layer having different thicknesses over the respective reflective layers can be obtained. After that, the light-emitting elements overlapping with the respective reflective layers are formed over the planarized top surface of the insulating layer, whereby the light-emitting units that intensify different colors due to different optical distances (optical path lengths) can be formed separately.

That is, the display device of one embodiment of the present invention has a structure in which the reflective layers having different thicknesses are provided over a formation surface and the insulating layer whose top surface is subjected to planarization treatment is provided to cover the reflective layers. In the structure, the light-emitting elements can be provided over the insulating layer in the regions overlapping with the respective reflective layers. By the planarization treatment on the top surface of the insulating layer, a distance between the formation surface of the reflective layers (or the bottom surfaces of the reflective layers) and the top surface of the insulating layer becomes constant regardless of the thicknesses of the reflective layers. Thus, as the reflective layer is thicker, the insulating layer over the reflective layer is thinner; similarly, as the reflective layer is thinner, the insulating layer thereover is thicker. Thus, the thickness of the insulating layer positioned between the light-emitting element and the reflective layer can be adjusted by changing the thickness of the reflective layer. The reflective layer included in one embodiment of the present invention has a function of adjusting the optical distance (optical path length) by its thickness, and thus can be referred to as the optical adjustment layer.

Since the two light-emitting units have different distances between the light-emitting layer and the reflective layer, the light-emitting units intensify and emit light with different wavelengths. The difference in optical distance (also referred to as optical path length) between the light-emitting units is determined by the difference in the thickness of the reflective layer. Thus, the optical distances of the two light-emitting units can be adjusted accurately, which enables high-yield fabrication of a display device with high display quality, which has not only high color reproducibility but also reduced color unevenness between the light-emitting units.

In the light-emitting units exhibiting different colors, the light-emitting elements are each provided over the planarized top surface of the insulating layer. Thus, the light-emitting elements having the same structure are formed on the same plane within the light-emitting units emitting different colors, so that the level of a surface to which light is emitted (a light-emitting surface, specifically a top surface of the upper electrode) can be constant. This prevents a decrease in display quality due to different levels of the light-emitting surfaces, so that a display device with high color reproducibility and higher quality can be provided.

A structure may be employed in which one of the two light-emitting units does not include the insulating layer over the reflective layer. For example, the top surface of the insulating layer may be subjected to planarization treatment so that the top surface of the insulating layer and the top surface of the reflective layer are substantially aligned. When the planarization treatment for the insulating layer is performed in such a manner, the planarization treatment can be completed when the top surface of the reflective layer is exposed; thus, processing can be performed more accurately. In this case, a structure may be employed in which a layer containing a material different from that for the insulating layer and transmitting visible light is stacked over the reflective layer before the planarization treatment, and the top surface of the layer and the top surface of the insulating layer are substantially aligned after the planarization treatment. Thus, the top surface of the reflective layer is not exposed to the planarization treatment, so that a decrease in optical characteristics such as reflectance of the reflective layer can be prevented.

Furthermore, a structure may be employed in which an opening is provided in the insulating layer at a position overlapping with the reflective layer, and the lower electrode of the light-emitting element is embedded in the opening. In this case, planarization treatment is preferably performed so that the top surface of the insulating layer and the top surface of the lower electrode are substantially aligned. No step is generated in an end portion of the lower electrode in this case, so that the light-emitting layer and the upper electrode can be formed over a flat surface. Thus, the viewing angle characteristics, the aperture ratio, and the like can be improved.

In the display device of one embodiment of the present invention, the light-emitting units of different colors can be separately formed with extremely high accuracy. In addition, since no step is generated owing to the flat formation surface of the adjacent light-emitting elements, the light-emitting elements can be arranged at extremely high density. Thus, a display device with higher resolution than a conventional display device can be achieved. For example, the display device preferably has extremely high resolution in which pixels including one or more light-emitting elements (or light-emitting units) are arranged with a resolution greater than or equal to 2000 ppi, preferably greater than or equal to 3000 ppi, further preferably greater than or equal to 5000 ppi, still further preferably greater than or equal to 6000 ppi, and less than or equal to 20000 ppi or less than or equal to 30000 ppi.

Although description is made here using mainly two light-emitting units for easy description, light-emitting units exhibiting three primary colors or four or more colors are preferably provided. Specifically, the light-emitting units emitting light of red (R), green (G), and blue (B) can be included. Alternatively, a light-emitting unit emitting light of yellow (Y), cyan (C), magenta (M), white (W), or the like may be provided in addition to or instead of the above.

More specific structure examples and a fabrication method example will be described below with reference to drawings.

Structure Example 1

FIG.1is a schematic cross-sectional view illustrating a display device of one embodiment of the present invention. The display device includes a light-emitting unit120R, a light-emitting unit120G, and a light-emitting unit120B that exhibit different colors.

The light-emitting unit120R, the light-emitting unit120G, and the light-emitting unit120B each include a light-emitting element110. The light-emitting element110is provided over an insulating layer121having a light-transmitting property, and includes a conductive layer111functioning as a lower electrode, a conductive layer113functioning as an upper electrode, and an EL layer112that is sandwiched between the conductive layers and contains a light-emitting compound. The conductive layer111has a function of transmitting visible light, and the conductive layer113has a semi-transmissive property and a semi-reflective property with respect to visible light.

As the light-emitting element110, it is possible to use an electroluminescent element having a function of emitting light in accordance with current flowing into the EL layer112when a potential difference is applied between the conductive layer111and the conductive layer113. In particular, an organic EL element using a light-emitting organic compound is preferably used for the EL layer. In addition, the light-emitting element110is preferably an element emitting white light, which has two or more peaks in the visible light region of the emission spectrum.

Here, the EL layer112and the conductive layer113are provided in common for the light-emitting elements110provided in each of the light-emitting units. The conductive layer113functions as, for example, an electrode to which a common potential is applied. A potential for controlling the amount of light emitted from the light-emitting element110is independently applied to the conductive layers111provided in the light-emitting elements110. The conductive layers111function as pixel electrodes, for example.

In addition, inFIG.1, an insulating layer115is provided to cover an end portion of the conductive layer111. The insulating layer115has a function of preventing electrical short circuit between the conductive layer111and the conductive layer113because of a decrease in the thickness of the EL layer112due to a step in the end portion of the conductive layer111. As illustrated inFIG.1, for higher coverage with the EL layer112, an end portion of the insulating layer115positioned over the conductive layer111preferably has a tapered shape.

The light-emitting unit120R includes, in addition to the light-emitting element110, a reflective layer114R (also referred to as an optical adjustment layer) provided over a substrate101, and part of the insulating layer121positioned between the light-emitting element110and the reflective layer114R. Similarly, the light-emitting unit120G includes the light-emitting element110, a reflective layer114G, and part of the insulating layer121. The light-emitting unit120B includes the light-emitting element110, a reflective layer114B, and part of the insulating layer121.

A surface of the substrate101is the formation surface of the reflective layer114R, the reflective layer114G, the reflective layer114B, and the like. The substrate101has at least an insulating flat surface. As described later, a circuit board including a transistor, a wiring, or the like can also be used as the substrate101. Note that in the case of a display device employing a passive matrix method or a segment method, an insulating substrate such as a glass substrate can be used as the substrate101.

The insulating layer121is provided to cover the reflective layer114R, the reflective layer114G, and the reflective layer114B. A top surface of the insulating layer121is preferably subjected to planarization treatment to form a flat surface. In other words, processing is performed so that the top surface of the insulating layer121has substantially the same level regardless of the place. In addition, the processing is performed so that the distance between the insulating layer121and the formation surface of the reflective layer114R and the like (the top surface of the substrate101) is substantially constant regardless of the place.

Note that among the three reflective layers, the reflective layer114R has the smallest thickness and the reflective layer114B has the largest thickness. Thus, the insulating layer121positioned over the three reflective layers has the largest thickness in a portion overlapping with the reflective layer114R and has the smallest thickness in a portion overlapping with the reflective layer114B. Here, as illustrated inFIG.1, when the distances between top surfaces of the reflective layers and the bottom surface of the conductive layer113(i.e., an interface between the conductive layer113and the EL layer112) in the light-emitting units are referred to as a distance DR, a distance DG, and a distance DB, the distance DRis the largest and the distance DBis the smallest. The difference between the distance DR, the distance DG, and the distance DBcorresponds to the difference in optical distance (optical path length) in the light-emitting units.

The light-emitting unit120R has the longest optical path length among the three light-emitting units, and thus emits light R that is the intensified light with the longest wavelength. In contrast, the light-emitting unit120B has the shortest optical path length, and thus emits light B that is the intensified light with the shortest wavelength. The light-emitting unit120G emits light G that is the intensified light with the intermediate wavelength. For example, the light R is the intensified red light, the light G is the intensified green light, and the light B is the intensified blue light.

With such a structure, the light-emitting elements110need not be formed separately for different colors of the light-emitting units; thus, color display with high color reproducibility can be performed using elements with the same structure. Furthermore, since the EL layer112included in the light-emitting elements110need not be formed separately, the light-emitting elements110can be arranged at extremely high density. For example, a display device having resolution exceeding 5000 ppi can be achieved.

Structure Example 2

Structure examples of display devices provided with a substrate including a circuit element are described below.

Structure Example 2-1

FIG.2(A)is a schematic cross-sectional view of a display device100. The display device100includes, over the substrate101provided with a semiconductor circuit, the light-emitting unit120R, the light-emitting unit120G, and the light-emitting unit120B that are described in Structure Example 1.

The substrate101is a substrate provided with a circuit for driving the light-emitting units (also referred to as a pixel circuit) and a semiconductor circuit functioning as a driver circuit for driving the pixel circuit. More specific structure examples of the substrate101will be described later.

An insulating layer122is included between the substrate101and the insulating layer121. A top surface of the insulating layer122is the formation surface of the reflective layer114R, the reflective layer114G, and the reflective layer114B. The top surface of the insulating layer122is preferably flat.

The substrate101and the conductive layer111of the light-emitting element110are electrically connected to each other through a plug131a,a conductive layer132, and a plug131b. The plug131ais formed to be embedded in an opening provided in the insulating layer122. The conductive layer132is provided over the insulating layer122. In addition, the plug131bis formed to be embedded in an opening that is provided in the insulating layer121to reach the conductive layer132. The conductive layer111is provided in contact with a top surface of the plug131b.

FIG.2(A)illustrates an example in which the conductive layer132is formed by processing the same film as that for the reflective layer114B. Note that without limitation to this, the conductive layer132may be formed by processing the same film as that for the reflective layer114R or the reflective layer114G. Alternatively, the conductive layer132may be formed by stacking the same films as that for two or more of the reflective layer114R, the reflective layer114G, and the reflective layer114B.

In addition,FIG.2(A)illustrates an example in which the reflective layer114R, the reflective layer114G, and the reflective layer114B are not electrically connected to the substrate101and the conductive layer111. For example, the reflective layer114R, the reflective layer114G, and the reflective layer114B are electrically floating. Note that the reflective layer114R, the reflective layer114G, and the reflective layer114B may be electrically connected to the conductive layer132to have the same potential as the conductive layer111. Alternatively, a structure may be employed in which plugs that electrically connect the substrate101and each of the reflective layer114R, the reflective layer114G, and the reflective layer114B are provided in the insulating layer122to apply a constant potential.

Structure Example 2-2

FIG.2(B)is a schematic cross-sectional view of a display device100A. The display device100A is different from the display device100mainly in the structures of the reflective layer114G and the reflective layer114B.

The reflective layer114B has a stacked-layer structure in which a conductive layer141, a conductive layer142, and a conductive layer143are stacked in this order from the light-emitting element110side. The reflective layer114G has a stacked-layer structure in which the conductive layer141and the conductive layer142are stacked in this order from the light-emitting element110side. The reflective layer114R is formed of the conductive layer141.

A material with high reflectance with respect to visible light is preferably used for the conductive layer141, among the conductive layer141, the conductive layer142, and the conductive layer143. Although a material with lower reflectance than that for the conductive layer141may be used for the conductive layer142and the conductive layer143, the same material is preferably used because a processing apparatus can be shared.

In the example illustrated inFIG.2(B), the conductive layer132has the same stacked-layer structure as the reflective layer114B.

Note that the conductive layer142and the conductive layer143do not necessarily have a conducting property, and layers formed of an insulating film or a semiconductor film may be used instead of the conductive layers. In that case, only a layer having conductivity (e.g., the conductive layer141) can be used as the conductive layer132. Alternatively, a structure in which the plug131aand the plug131bare in contact with each other without the conductive layer132or a structure in which the conductive layer111and the substrate101are connected through one plug may be employed.

[Components]

{Light-Emitting Element and Light-Emitting Unit}

As a light-emitting element that can be used as the light-emitting element110, a self-luminous element can be used, and an element whose luminance is controlled by current or voltage is included in the category. For example, an LED, an organic EL element, an inorganic EL element, or the like can be used. In particular, an organic EL element is preferably used.

The light-emitting element has a top-emission structure, a bottom-emission structure, a dual-emission structure, or the like. A conductive film that transmits visible light is used as the electrode through which light is extracted. A conductive film that reflects visible light is preferably used as the electrode through which no light is extracted.

In one embodiment of the present invention, a top-emission light-emitting element in which light is emitted to the opposite side of the formation surface or a dual-emission light-emitting element can be particularly suitably used.

The EL layer112includes at least a light-emitting layer. In addition to the light-emitting layer, the EL layer112may further include layers containing a substance with a high hole-injection property, a substance with a high hole-transport property, a hole-blocking material, a substance with a high electron-transport property, a substance with a high electron-injection property, a substance with a bipolar property (a substance with a high electron- and hole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be used for the EL layer112, and an inorganic compound may also be contained. The layers that constitute the EL layer112can each be formed by a method such as an evaporation method (including a vacuum evaporation method), a transfer method, a printing method, an inkjet method, or a coating method.

When a voltage higher than the threshold voltage of the light-emitting element110is applied between a cathode and an anode, holes are injected to the EL layer112from the anode side and electrons are injected to the EL layer112from the cathode side. The injected electrons and holes are recombined in the EL layer112and a light-emitting substance contained in the EL layer112emits light.

In the case where a light-emitting element emitting white light is used as the light-emitting element110, the EL layer112preferably contains two or more kinds of light-emitting substances. A white emission can be obtained by selecting light-emitting substances so that two or more light-emitting substances emit light of complementary colors, for example. For example, it is preferable to contain two or more out of light-emitting substances emitting light of red (R), green (G), blue (B), yellow (Y), orange (O), and the like or light-emitting substances emitting light containing two or more of spectral components of R, G, and B. A light-emitting element whose emission spectrum has two or more peaks in the wavelength range of a visible light region (e.g., 350 nm to 750 nm) is preferably employed. An emission spectrum of a material having a peak in a yellow wavelength range preferably has spectral components also in green and red wavelength ranges.

The EL layer112preferably has a structure in which a light-emitting layer containing a light-emitting material emitting light of one color and a light-emitting layer containing a light-emitting material emitting light of another color are stacked. For example, the plurality of light-emitting layers in the EL layer112may be stacked in contact with each other or may be stacked with a region not including any light-emitting material therebetween. For example, between a fluorescent layer and a phosphorescent layer, a region that contains the same material as the fluorescent layer or phosphorescent layer (for example, a host material or an assist material) and no light-emitting material may be provided. This facilitates the fabrication of the light-emitting element and reduces the drive voltage.

The light-emitting element110may be a single element including one EL layer or a tandem element in which a plurality of EL layers are stacked with a charge generation layer therebetween.

The conductive film that can be used for the conductive layer111or the like and transmits visible light can be formed using, for example, indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added. Alternatively, a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium; an alloy containing any of these metal materials; a nitride of any of these metal materials (e.g., titanium nitride); or the like formed thin enough to have a light-transmitting property can be used. A stacked-layer film of any of the above materials can be used for the conductive layers. For example, a stacked-layer film of indium tin oxide and an alloy of silver and magnesium is preferably used, in which case conductivity can be increased. Further alternatively, graphene or the like may be used.

For the conductive film reflecting visible light that can be used for the reflective layers, for example, a metal material such as aluminum, gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or an alloy containing any of these metal materials can be used. Lanthanum, neodymium, germanium, or the like may be added to the above metal material or alloy. Alternatively, an alloy (an aluminum alloy) containing aluminum and titanium, nickel, or neodymium may be used. Alternatively, an alloy containing silver and copper, palladium, or magnesium may be used. An alloy containing silver and copper is preferable because of its high heat resistance. Furthermore, when a metal film or a metal oxide film is stacked in contact with an aluminum film or an aluminum alloy film, oxidation can be inhibited. Examples of a material for the metal film or the metal oxide film include titanium and titanium oxide. Alternatively, the above conductive film that transmits visible light and a film containing a metal material may be stacked. For example, a stacked-layer film of silver and indium tin oxide or a stacked-layer film of an alloy of silver and magnesium and indium tin oxide can be used.

As the conductive film having a semi-transmissive property and a semi-reflective property that can be used for the conductive layer113, the conductive film reflecting visible light formed to be thin enough to transmit visible light can be used. In addition, with the stacked-layer structure of the conductive film and the conductive film transmitting visible light, the conductivity and the mechanical strength can be increased. Furthermore, a conductive metal oxide film is preferably stacked over the conductive film reflecting visible light, in which case oxidization and corrosion of the conductive film reflecting visible light can be inhibited.

The conductive film having a semi-transmissive property and a semi-reflective property preferably has a reflectance with respect to visible light (e.g., the reflectance with respect to light having a specific wavelength within the range of 400 nm to 700 nm) of higher than or equal to 20% and lower than or equal to 80%, preferably higher than or equal to 40% and lower than or equal to 70%. The conductive film having reflectivity preferably has a reflectance with respect to visible light of higher than or equal to 40% and lower than or equal to 100%, further preferably higher than or equal to 70% and lower than or equal to 100%. The conductive film having light-transmitting property preferably has a reflectance with respect to visible light of higher than or equal to 0% and lower than or equal to 40%, further preferably higher than or equal to 0% and lower than or equal to 30%.

The electrodes included in the light-emitting elements and the light-emitting units may each be formed by an evaporation method or a sputtering method. Alternatively, a discharging method such as an inkjet method, a printing method such as a screen printing method, or a plating method may be used for the formation.

Note that the aforementioned light-emitting layer and layers containing a substance with a high hole-injection property, a substance with a high hole-transport property, a substance with a high electron-transport property, a substance with a high electron-injection property, a substance with a bipolar property, and the like may include an inorganic compound such as a quantum dot or a high molecular compound (e.g., an oligomer, a dendrimer, and a polymer). For example, when used for the light-emitting layer, the quantum dots can function as a light-emitting material.

Note that as the quantum dot material, a colloidal quantum dot material, an alloyed quantum dot material, a core-shell quantum dot material, a core quantum dot material, or the like can be used. A material containing elements belonging to Group 12 and Group 16, elements belonging to Group 13 and Group 15, or elements belonging to Group 14 and Group 16, may be used. Alternatively, a quantum dot material containing an element such as cadmium, selenium, zinc, sulfur, phosphorus, indium, tellurium, lead, gallium, arsenic, or aluminum may be used.

For the reflective layer included in each of the light-emitting units, the conductive film reflecting visible light is preferably used at least in a portion positioned on the side closest to the light-emitting element110.

In each of the light-emitting units, the optical distance between the surface of the reflective layer reflecting visible light and the conductive layer having a semi-transmissive property and a semi-reflective property with respect to visible light is preferably adjusted to be mλ/2 (m is a natural number) or in the vicinity thereof with respect to wavelength λ of light to be intensified.

To be exact, the above-described optical distance depends on a product of the physical distance between the reflective surface of the reflective layer and the reflective surface of the conductive layer having a semi-transmissive property and a semi-reflective property and the refractive index of a layer provided therebetween, and thus is difficult to adjust exactly. Thus, it is preferable to adjust the optical distance on the assumption that the surface of the reflective layer and the surface of the conductive layer having a semi-transmissive property and a semi-reflective property are each the reflective surface.

In each of the light-emitting units, a material with high transmitting property with respect to visible light is preferably used for the insulating layer121positioned between the reflective layer and the conductive layer111. For example, a single layer or stacked layers of an inorganic insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or a hafnium oxide film can be used. Using a material with a high refractive index (e.g., 1.4 or higher, preferably 1.5 or higher) for the insulating layer121can reduce the physical thickness and can increase the productivity.

Fabrication Method Example

An example of a fabrication method of the display device of one embodiment of the present invention will be described with reference to drawings. Description is made below using the display device100A described in Structure Example 2 as an example.

Note that thin films that form the display device (insulating films, semiconductor films, conductive films, or the like) can be formed by a sputtering method, a chemical vapor deposition (CVD) method, a vacuum evaporation method, a pulsed laser deposition (PLD) method, an atomic layer deposition (ALD) method, or the like. Examples of the CVD method include a plasma-enhanced chemical vapor deposition (PECVD) method and a thermal CVD method. In addition, as an example of the thermal CVD method, a metal organic chemical vapor deposition (MOCVD) method can be given.

Alternatively, thin films that form the display device (insulating films, semiconductor films, conductive films, or the like) can be formed by a method such as spin coating, dipping, spray coating, ink-jetting, dispensing, screen printing, offset printing, a doctor knife method, a slit coater, a roll coater, a curtain coater, and a knife coater.

When the thin films that form the display device are processed, a photolithography method or the like can be used. Besides, a nanoimprinting method, a sandblasting method, a lift-off method, or the like may be used for the processing of the thin films. Island-shaped thin films may be directly formed by a film formation method using a blocking mask such as a metal mask.

There are two typical examples of a photolithography method. In one of the methods, a resist mask is formed over a thin film that is to be processed, and the thin film is processed by etching or the like, so that the resist mask is removed. In the other method, after a photosensitive thin film is formed, exposure and development are performed, so that the thin film is processed into a desired shape.

For light for exposure in a photolithography method, for example, an i-line (with a wavelength of 365 nm), a g-line (with a wavelength of 436 nm), an h-line (with a wavelength of 405 nm), or combined light of any of them can be used. Besides, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Furthermore, exposure may be performed by liquid immersion light exposure technique. Furthermore, as the light used for the exposure, extreme ultra-violet (EUV) light or X-rays may be used. Furthermore, instead of the light used for the exposure, an electron beam can also be used. It is preferable to use extreme ultra-violet light, X-rays, or an electron beam because extremely minute processing can be performed. Note that in the case of performing exposure by scanning of a beam such as an electron beam, a photomask is unnecessary.

For etching of the thin film, a dry etching method, a wet etching method, a sandblast method, or the like can be used.

[Preparation for Substrate101]

As the substrate101, a substrate having at least heat resistance high enough to withstand the following heat treatment can be used. In the case where an insulating substrate is used as the substrate101, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate or the like can be used. Alternatively, a single crystal semiconductor substrate using silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate of silicon germanium or the like, a semiconductor substrate such as an SOI substrate, or the like can be used.

As the substrate101, it is particularly preferable to use the semiconductor substrate or the insulating substrate over which a semiconductor circuit including a semiconductor element such as a transistor is formed. The semiconductor circuit preferably forms a pixel circuit, a gate line driver circuit (a gate driver), a source line driver circuit (a source driver), or the like. In addition to the above, an arithmetic circuit, a memory circuit, or the like may be formed.

In this embodiment, a substrate including at least a pixel circuit is used as the substrate101.

[Formation of Insulating Layer122and Plug131a]

An insulating film to be the insulating layer122is formed over the substrate101. Next, an opening reaching the substrate101is formed in the insulating layer122in a position where the plug131ais to be formed. The opening is preferably an opening reaching an electrode or a wiring provided in the substrate101. Then, a conductive film is formed to fill the opening and planarization treatment is performed to expose a top surface of the insulating layer122. In this manner, the plug131aembedded in the insulating layer122can be formed (FIG.3(A)).

For the planarization treatment, a polishing method such as a chemical mechanical polishing (CMP) method or the like can be suitably used. Alternatively, dry etching treatment or plasma treatment may be used. Note that, polishing treatment, dry etching treatment, or plasma treatment may be performed a plurality of times, or these treatments may be performed in combination. In the case where the treatments are performed in combination, the order of steps is not particularly limited and may be set as appropriate depending on the roughness of the surface to be processed.

[Formation of Reflective Layer114R, Reflective Layer114G, Reflective Layer114B, and Conductive Layer132]

First, a conductive film143fto be the conductive layer143is formed over the insulating layer122. Next, a resist mask151is formed over the conductive film143f(FIG.3(B)). The resist mask151is formed in a portion to be the reflective layer114B later. Furthermore, the resist mask151is formed also in a portion covering a top surface of the plug131a.After that, the conductive film143fnot covered with the resist mask151is removed by etching, whereby the conductive layer143can be formed. After that, the resist mask151is removed.

Next, a conductive film142fto be the conductive layer142later is formed to cover the insulating layer122and the conductive layer143, and a resist mask152is formed over the conductive film142f(FIG.3(C)). The resist mask152is provided to cover a portion of the conductive film142foverlapping with the conductive layer143(including a portion to be the conductive layer132) and a portion to be the reflective layer114G later. After that, the conductive film142fis etched in a manner similar to the above, whereby the conductive layer142can be formed.

Next, a conductive film141fto be the conductive layer141later is formed to cover the insulating layer122and the conductive layer142, and a resist mask153is formed over the conductive film141f(FIG.3(D)). The resist mask153is provided to cover a portion of the conductive film141foverlapping with the conductive layer142and a portion to be the reflective layer114R later. After that, the conductive film141fis etched in a manner similar to the above, whereby the conductive layer141can be formed.

Through the above steps, the reflective layer114R, the reflective layer114G, the reflective layer114B, and the conductive layer132can be formed (FIG.3(E)).

Note that in the case where insulating films are used instead of the conductive film143fand the conductive film142f,a structure is employed in which the resist mask151and the resist mask152are not provided in a portion to be the conductive layer132so that the insulating films are not formed in the portion to be the conductive layer132.

Note that although the resist mask152is formed so that an end portion of the resist mask152and an end portion of the conductive layer143are aligned inFIG.3(C), these need not be aligned exactly. The resist mask152may be formed to cover the end portion of the conductive layer143. In that case, the conductive layer142to be formed has a shape covering the end portion of the conductive layer143. Note that the same applies to the positional relationship between the resist mask153and the conductive layer142.

[Formation of Insulating Layer121and Plug131b]

An insulating film121fto be the insulating layer121later is formed over the insulating layer122to cover the reflective layer114R, the reflective layer114G, the reflective layer114B, and the conductive layer132(FIG.4(A)).

Next, an opening reaching the conductive layer132is formed in the insulating film121f, and a conductive film131bfto be the plug131blater is formed to fill the opening (FIG.4(B)).

After that, planarization treatment is performed until a top surface of the insulating film121fis exposed and the insulating film121fover the reflective layer114B has a desired thickness, whereby the insulating layer121having a planarized top surface and the plug131bembedded in the insulating layer121can be formed (FIG.4(C)).

The thickness of the insulating film121fat least in a portion overlapping with the reflective layer114B is larger than the thickness of the insulating layer121that is to be formed after the planarization treatment. At this time, due to uneven shape of the top surface of the insulating film121f,part of the conductive film131bfmight remain over the top surface of the insulating film121fafter the planarization treatment. Thus, the insulating film121fis formed to have enough thickness in advance, and additional planarization treatment is performed after the top surface of the insulating film121fis exposed in the planarization treatment, whereby the remaining film of the conductive layer131bfcan be suitably removed.

In the planarization treatment, accurate processing is preferably performed so that a portion of the insulating layer121overlapping with the reflective layer114B has a desired thickness. For example, in the case of using a CMP method, polishing is performed first at a constant processing rate until the top surface of the insulating film121fis partly exposed. After that, polishing is performed under a condition with a lower processing rate until the insulating film121fhas a desired thickness, so that highly accurate processing can be performed.

Examples of a method for detecting the end of the polishing include an optical method in which the surface of the formation surface is irradiated with light and a change in the reflected light is detected; a physical method in which a change in the polishing resistance received by the processing apparatus from the formation surface is detected; and a method in which a magnetic line is applied to the formation surface and a change in the magnetic line due to the generated eddy current is used.

After the top surface of the insulating film121fis exposed, polishing treatment is performed under a condition with a low processing rate while the thickness of the insulating film121fis monitored by an optical method using a laser interferometer or the like, whereby the thickness of the insulating layer121can be controlled with high accuracy. Note that the polishing treatment may be performed a plurality of times until the insulating layer121has a desired thickness, as necessary.

[Formation of Conductive Layer111]

A conductive film is formed over the insulating layer121and the plug131band an unnecessary portion is removed by etching, whereby the conductive layer111electrically connected to the plug131bis formed.

[Formation of Insulating Layer115]

Next, an insulating film is formed to cover the conductive layer111and the insulating layer121, and an unnecessary portion is removed by etching, whereby the insulating layer115covering the end portion of the conductive layer111is formed (FIG.4(D)). The insulating layer115is processed to have an opening overlapping with the reflective layer114R, the reflective layer114G, or the reflective layer114B in a region overlapping with the conductive layer111.

In addition, the end portion of the insulating layer115over the conductive layer111is preferably processed into a tapered shape. The taper angle of the end portion of the insulating layer115(an angle between the formation surface and the end surface) is greater than 0° and less than or equal to 60°, preferably greater than or equal to 5° and less than or equal to 45°, further preferably greater than or equal to 5° and less than or equal to 30°.

The insulating layer115can be formed using an organic insulating film or an inorganic insulating film. In particular, in the case of a display device with ultra-high resolution (e.g., 2000 ppi or more), an inorganic insulating film is preferably used.

[Formation of EL Layer112and Conductive Layer113]

Next, the EL layer112and the conductive layer113are formed in this order over the conductive layer111and the insulating layer115, whereby the light-emitting element110is formed (FIG.4(E)).

The EL layer112includes at least a layer containing a light-emitting compound. A structure may be employed in which an electron-injection layer, an electron-transport layer, a charge-generation layer, a hole-transport layer, and a hole-injection layer are stacked in addition to the above. The EL layer112can be formed by, for example, a liquid phase method such as an evaporation method or an inkjet method.

The conductive layer113is formed to have a semi-transmissive property and a semi-reflective property with respect to visible light. For example, a metal film or an alloy film that is thin enough to transmit visible light can be used. Alternatively, a conductive film (e.g., a metal oxide film) may be stacked over such a film.

In the above manner, the light-emitting unit120R, the light-emitting unit120G, and the light-emitting unit120B that have different optical distances can be formed.

According to the above fabrication method example, the difference in optical distance among the light-emitting units can be precisely controlled by the thicknesses of the reflective layers; thus, chromaticity deviation in the light-emitting units is unlikely to occur, so that a display device having excellent color reproducibility and extremely high display quality can be fabricated easily.

The light-emitting element110and the reflective layers can be formed over an insulating layer with a planarized top surface. Furthermore, the lower electrode (the conductive layer111) of the light-emitting element110can be electrically connected to a pixel circuit or the like of the substrate101through a plug, so that an extremely minute pixel can be formed and accordingly a display device with extremely high resolution can be achieved. In addition, since the light-emitting element110can be placed to overlap with the pixel circuit or the driver circuit, a display device with a high aperture ratio (effective light-emitting area ratio) can be achieved.

Structure Example 3

A structure example of a display device whose structure is partly different from those of Structure Example 1 and Structure Example 2 will be described below.

Structure Example 3-1

FIG.5(A)is a schematic cross-sectional view of a display device100B.

The light-emitting unit120R included in the display device100B includes the reflective layer114R and a light-emitting element110R. The light-emitting element110R includes a conductive layer111R, the EL layer112, and the conductive layer113.

The reflective layer114R is electrically connected to the substrate101through the plug131a.In addition, an opening reaching the reflective layer114R is provided in the insulating layer121over the reflective layer114R, and the conductive layer111R is embedded in the opening. The top surface of the insulating layer121and a top surface of the conductive layer111R are each planarized so that no large step is formed at the boundary therebetween. The EL layer112is provided in contact with the top surface of the conductive layer111R and the top surface of the insulating layer121that are planarized, and the conductive layer113is provided over the EL layer112. Since the formation surface of the EL layer112is planarized in this manner, a structure may be employed in which the insulating layer115described in the above structure example is not provided, leading to a higher aperture ratio.

Here, since the reflective layer114R and the conductive layer111R are electrically connected to each other in the display device100B, a structure may be employed in which the conductive layer132and the plug131bincluded in the display device100A are not provided. Furthermore, since the top surface of the plug131ais planarized, a region overlapping with the plug131acan also be used as a light-emitting region of the light-emitting unit120R, leading to a higher aperture ratio.

The light-emitting unit120G includes a light-emitting element110G and the reflective layer114G. The light-emitting element110G includes a conductive layer111G, the EL layer112, and the conductive layer113. The light-emitting unit120G is similar to the light-emitting unit120R except for the structure of the reflective layer114G and the thickness of the conductive layer111G. In the reflective layer114G, the conductive layer141and the conductive layer142are stacked. Since the top surface of the conductive layer111G is planarized like the conductive layer111R, the conductive layer111G is formed to be thinner than the conductive layer111R by the thickness of the conductive layer142.

The light-emitting unit120B includes a light-emitting element110B and the reflective layer114B. The light-emitting element110B includes a conductive layer111B, the EL layer112, and the conductive layer113. The light-emitting unit120B is similar to the light-emitting unit120R and the light-emitting unit120G except for the structure of the reflective layer114B and the thickness of the conductive layer111B. In the reflective layer114B, the conductive layer141, the conductive layer142, and the conductive layer143are stacked. Since the top surface of the conductive layer111B is planarized like the conductive layer111R and the like, the conductive layer111B is formed to be thinner than the conductive layer111G by the thickness of the conductive layer143.

Structure Example 3-2

FIG.5(B)is a schematic cross-sectional view of a display device100C.

The light-emitting unit120R included in the display device100C includes the light-emitting element110, a reflective layer116R, and an insulating layer146R. The reflective layer116R includes the conductive layer141and a conductive layer144.

The conductive layer141of the reflective layer116R is provided over the insulating layer122and electrically connected to the plug131a.An opening reaching the conductive layer141is provided in the insulating layer121. The conductive layer144is provided in the opening of the insulating layer121and is provided along the top surface of the conductive layer144and a sidewall of the opening. In addition, the insulating layer146R is provided to be embedded in a region that is in the opening of the insulating layer121and surrounded by the conductive layer144. Top surfaces of the insulating layer121, the insulating layer146R, and the conductive layer144are each planarized.

The conductive layer111of the light-emitting element110included in the light-emitting unit120R is provided in contact with the top surfaces of the insulating layer121, the insulating layer146R, and the conductive layer144. That is, the conductive layer144and the conductive layer111are electrically connected to each other in an outer edge portion of the opening of the insulating layer121. With such a structure, the substrate101and the conductive layer111can be electrically connected to each other through the plug131a,the conductive layer141, and the conductive layer144. This enables a portion of the light-emitting unit120R overlapping with the plug131ato be used as a light-emitting region, leading to a higher aperture ratio.

The light-emitting unit120G is different from the light-emitting unit120R in including an insulating layer146G and a reflective layer116G instead of the insulating layer146R and the reflective layer116R. The reflective layer116G includes the conductive layer141, the conductive layer142, and the conductive layer144. The insulating layer146G is processed to have a thickness smaller than the insulating layer146R by the thickness of the conductive layer142.

The light-emitting unit120B is different from the light-emitting unit120R in including an insulating layer146B and a reflective layer116G instead of the insulating layer146R and the reflective layer116R. The reflective layer116G includes the conductive layer141, the conductive layer142, the conductive layer143, and the conductive layer144. The insulating layer146B is processed to have a thickness smaller than the insulating layer146R by the thicknesses of the conductive layer142and the conductive layer143.

Structure Example 4

A structure example of a display device whose structure is partly different from those of the above structure examples will be described below.

Structure Example 4-1

FIG.6(A)is a schematic cross-sectional view of a display device100D. The display device100D is different from the display device100A mainly in the structure of the light-emitting unit120B.

In the light-emitting unit120B, the top surface of the conductive layer141and the top surface of the insulating layer121are positioned on substantially the same plane. In addition, the insulating layer121is not positioned between the conductive layer111and the conductive layer141and these conductive layers are provided in contact with each other; thus, the conductive layer111and the conductive layer141are electrically connected to each other.

The plug131aprovided in the light-emitting unit120B is provided in contact with the conductive layer143. The substrate101and the conductive layer111are electrically connected to each other through the plug131a,the conductive layer143, the conductive layer142, and the conductive layer141. Thus, the conductive layer132is not necessarily provided in the light-emitting unit120B and the portion overlapping with the plug131acan be used as the light-emitting region, leading to a higher aperture ratio. In particular, in the case where the light-emitting unit120B is a light-emitting unit exhibiting blue, a light-emitting area emitting blue light with low luminosity factor can be made larger than light-emitting regions emitting the other colors, so that the display quality can be further increased and power consumption can be reduced.

In addition, with such a structure, a point of time when exposure of the conductive layer141is detected in the planarization treatment for the top surface of the insulating layer121can be the end of the planarization treatment. Thus, the thickness of the insulating layer121of the light-emitting unit120R or the light-emitting unit120G can be controlled accurately. Thus, chromaticity deviation due to optical distance deviation is unlikely to occur, leading to higher manufacturing yield.

The thicknesses of the conductive layers111can be the same in the light-emitting units. Since the display device100D has a structure in which the insulating layer121is not provided between the conductive layer111and the reflective layer114B in the light-emitting unit120B, the conductive layer111is preferably formed to be thicker than that of the display device100A described in Structure Example 2, for example. The thickness of the conductive layer111can be set in accordance with the optical distance of the light-emitting unit120B.

Structure Example 4-2

FIG.6(B)is a schematic cross-sectional view of a display device100E.

The light-emitting unit120R includes the light-emitting element110R, a conductive layer145, and the reflective layer114R. The light-emitting element110R includes the conductive layer111R, the EL layer112, and the conductive layer113.

The conductive layer141included in the reflective layer114R is provided over the insulating layer122to be in contact with the plug131a.The conductive layer145has a light-transmitting property and is provided over the conductive layer141. The insulating layer121has an opening reaching the conductive layer145. The conductive layer111R is provided to be embedded in the opening of the insulating layer121to be in contact with the conductive layer145. The top surface of the conductive layer111R and the top surface of the insulating layer121are planarized so that no step is formed at the boundary therebetween. The substrate101and the conductive layer111R are electrically connected to the plug131a,the conductive layer141, and the conductive layer145. In the light-emitting unit120R, a region overlapping with the plug131acan also be used as a light-emitting region.

The light-emitting unit120G includes the light-emitting element110G, the conductive layer145, and the reflective layer114G. The light-emitting element110G includes the conductive layer111G, the EL layer112, and the conductive layer113. The light-emitting unit120G has a structure similar to that of the light-emitting unit120R except that the reflective layer114G includes the conductive layer141and the conductive layer142. The conductive layer111G is formed to be thinner than the conductive layer111R by the thickness of the conductive layer142.

The light-emitting unit120B includes the light-emitting element110B, the conductive layer145, and the reflective layer114B. The light-emitting element110B is different from the light-emitting element110R and the light-emitting element110G in not including a conductive layer corresponding to the conductive layer111R or the conductive layer111G. That is, the light-emitting element110B includes the conductive layer145functioning as a lower electrode, the EL layer112, and the conductive layer113. In addition, in the light-emitting unit120B, a top surface of the conductive layer145is provided to be positioned on substantially the same plane as the top surface of the insulating layer121.

With such a structure, a point of time when exposure of the conductive layer145is detected in the planarization treatment for the top surface of the insulating layer121can be the end of the planarization treatment. Thus, the thickness of the conductive layer111R included in the light-emitting unit120R and the thickness of the conductive layer111G included in the light-emitting unit120B can be controlled accurately in the planarization treatment for the insulating layer121.

When each light-emitting unit has a structure in which the conductive layer145having a light-emitting property covers the top surface of the conductive layer141that forms the reflective surface, the top surface of the conductive layer141can be prevented from being exposed to etching at the time of formation of the opening of the insulating layer121and to planarization treatment at the time of the planarization treatment. This can prevent a decrease in emission efficiency of the light-emitting units due to decreased reflectance caused by the quality change, corrosion, or the like of the top surface of the conductive layer141. As the conductive layer145, a conductive metal oxide film can be used, for example.

Structure Example 5

A more specific example of the display device including a transistor will be described below.

Structure Example 5-1

FIG.7is a schematic cross-sectional view of a display device200A.

The display device200A includes the light-emitting unit120R, the light-emitting unit120G, the light-emitting unit120B, a capacitor240, a transistor210, and the like.

The transistor210is a transistor whose channel region is formed in a substrate201. As the substrate201, a semiconductor substrate such as a single crystal silicon substrate can be used. The transistor210includes part of the substrate201, a conductive layer211, a low-resistance region212, an insulating layer213, an insulating layer214, and the like. The conductive layer211functions as a gate electrode. The insulating layer213is positioned between the substrate201and the conductive layer211and functions as a gate insulating layer. The low-resistance region212is a region where the substrate201is doped with an impurity, and functions as one of a source and a drain. The insulating layer214is provided to cover a side surface of the conductive layer211and functions as a sidewall insulating layer.

In addition, an element isolation layer215is provided between two adjacent transistors210to be embedded in the substrate201.

Furthermore, an insulating layer261is provided to cover the transistor210, and the capacitor240is provided over the insulating layer261.

The capacitor240includes a conductive layer241, a conductive layer242, and an insulating layer243positioned therebetween. The conductive layer241functions as one electrode of the capacitor240, the conductive layer242functions as the other electrode of the capacitor240, and the insulating layer243functions as a dielectric of the capacitor240.

The conductive layer241is provided over the insulating layer261and is electrically connected to one of the source and the drain of the transistor210through a plug271embedded in the insulating layer261. The insulating layer243is provided to cover the conductive layer241. The conductive layer242is provided in a region overlapping with the conductive layer241with the insulating layer243therebetween.

The insulating layer122is provided to cover the capacitor240, and the light-emitting unit120R, the light-emitting unit120G, the light-emitting unit120B, the conductive layer132, and the like are provided over the insulating layer122. In the example shown here, the structure described in Structure Example 2-2 with reference toFIG.2(B)is used as the structures of the light-emitting unit120R, the light-emitting unit120G, the light-emitting unit120B, and the conductive layer132; however, there is no limitation and a variety of structures described above can be employed.

In the display device200A, an insulating layer161, an insulating layer162, and an insulating layer163are provided to cover the conductive layer113of the light-emitting element110. These three insulating layers each function as a protective layer that prevents diffusion of impurities such as water into the light-emitting element110. As the insulating layer161and the insulating layer163, it is preferable to use an inorganic insulating film with low moisture permeability, such as a silicon oxide film, a silicon nitride film, or an aluminum oxide film. As the insulating layer162, an organic insulating film having a high light-transmitting property can be used. Using an organic insulating film as the insulating layer162can reduce the influence of uneven shape below the insulating layer162, so that the formation surface of the insulating layer163can be a smooth surface. Accordingly, a defect such as a pinhole is unlikely to be generated in the insulating layer163, leading to higher moisture permeability of the protective layer. Note that the structure of the protective layer covering the light-emitting element110is not limited thereto, and a single layer or a two-layer structure may be employed or a stacked-layer structure of four or more layers may be employed.

A coloring layer165R overlapping with the light-emitting unit120R, a coloring layer165G overlapping with the light-emitting unit120G, and a coloring layer165B overlapping with the light-emitting unit120B are provided over the insulating layer163. For example, the coloring layer165R transmits red light, the coloring layer165G transmits green light, and the coloring layer165B transmits blue light. This can increase the color purity of light from the light-emitting units, so that a display device with higher display quality can be achieved. Furthermore, forming the coloring layers over the insulating layer163makes it easier to align the light-emitting units and the coloring layers than the case where the coloring layers are formed on a substrate202(described later) side, so that a display device with extremely high resolution can be achieved.

The display device200A includes the substrate202on the viewing side. The substrate202and the substrate201are bonded to each other with an adhesive layer164. As the substrate202, a substrate having a light-transmitting property such as a glass substrate, a quartz substrate, a sapphire substrate, or a plastic substrate can be used.

With such a structure, a display device with extremely high resolution and high display quality can be achieved.

Modification Example of Structure Example 5-1

A display device200B illustrated inFIG.8is different from the display device200A mainly in the structure of the capacitor.

The display device200B illustrated inFIG.8has a structure in which the reflective layer114R, the reflective layer114G, and the reflective layer114B each also serve as one electrode of a capacitor240A.

The reflective layer114R, the reflective layer114G, and the reflective layer114B are provided over the insulating layer243. The reflective layer114R, the reflective layer114G, and the reflective layer114B are each electrically connected to one of the source and the drain of the transistor210through the plug271, a conductive layer251a,and the plug131a.The conductive layer241is electrically connected to a conductive layer251bthrough a plug131c.

Such a structure can simplify the fabrication process compared to that for the display device200A, leading to a reduction in manufacturing cost.

Structure Example 5-2

FIG.9is a schematic cross-sectional view of a display device200C. The display device200C is different from the display device200A mainly in a transistor structure.

A transistor220is a transistor in which a metal oxide (also referred to as an oxide semiconductor) is used in a semiconductor layer where a channel is formed.

The transistor220includes a semiconductor layer221, a metal oxide layer222, an insulating layer223, a conductive layer224, a conductive layer225, an insulating layer226, a conductive layer227, and the like.

As a substrate201aover which the transistor220is provided, the above-described insulating substrate or semiconductor substrate can be used.

An insulating layer232is provided over the substrate201a.The insulating layer232functions as a barrier layer that prevents diffusion of impurities such as water and hydrogen from the substrate201ainto the transistor220and release of oxygen from the semiconductor layer221to the insulating layer232side. As the insulating layer232, it is preferable to use, for example, a film in which hydrogen and oxygen are unlikely to be diffused than in a silicon oxide film such as an aluminum oxide film, a hafnium oxide film, and a silicon nitride film.

The conductive layer227is provided over the insulating layer232, and the insulating layer226is provided to cover the conductive layer227. The conductive layer227functions as a first gate electrode of the transistor220, and part of the insulating layer226functions as a first gate insulating layer. For the insulating layer226at least in a portion in contact with the semiconductor layer221, an oxide insulating film such as a silicon oxide film is preferably used. In addition, a top surface of the insulating layer226is preferably planarized.

The semiconductor layer221is provided over the insulating layer226. The semiconductor layer221preferably includes a film of a metal oxide exhibiting semiconductor characteristics (also referred to as an oxide semiconductor). The material that can be suitably used for the semiconductor layer221is described in detail later.

The pair of conductive layers225is provided over and in contact with the semiconductor layer221, and functions as a source electrode and a drain electrode. The metal oxide layer222is provided to cover the top surface of the semiconductor layer221between the pair of conductive layers225. The metal oxide layer222preferably includes a metal oxide that can be used for the semiconductor layer221. The insulating layer223functioning as a second gate insulating layer and the conductive layer224functioning as a second gate electrode are provided to be stacked over the metal oxide layer222.

An insulating layer228is provided to cover the transistor220and the insulating layer261is provided over the insulating layer228. The insulating layer228functions as a barrier layer that prevents diffusion of impurities such as water and hydrogen from the insulating layer261or the like to the transistor220and release of oxygen from the semiconductor layer221. As the insulating layer228, an insulating film similar to the insulating layer232can be used.

The plug271electrically connected to the conductive layer225is provided to be embedded in the insulating layer261. Here, the plug271preferably includes a conductive layer271acovering a side surface of the opening of the insulating layer261and part of a top surface of the conductive layer225, and a conductive layer271bin contact with a top surface of the conductive layer271a.In this case, a conductive material in which hydrogen and oxygen are unlikely to be diffused is preferably used for the conductive layer271a.

Structure Example 5-3

FIG.10is a schematic cross-sectional view of a display device200D. The display device200D has a structure in which the transistor210whose channel is formed in the substrate201and the transistor220including a metal oxide in the semiconductor layer where the channel is formed are stacked.

The insulating layer261is provided to cover the transistor210and the conductive layer251is provided over the insulating layer261. In addition, an insulating layer262is provided to cover the conductive layer251and a conductive layer252is provided over the insulating layer262. The conductive layer251and the conductive layer252each function as a wiring. An insulating layer263and the insulating layer232are provided to cover the conductive layer252, and the transistor220is provided over the insulating layer232. An insulating layer265is provided to cover the transistor220, and the capacitor240is provided over the insulating layer265. The capacitor240and the transistor220are electrically connected to each other through a plug274.

The transistor220can be used as a transistor included in a pixel circuit. The transistor210can also be used as a transistor included in a pixel circuit or a transistor included in a driver circuit (a gate line driver circuit or a source line driver circuit) for driving the pixel circuit. The transistor210and the transistor220can also be used as transistors included in a variety of circuits such as an arithmetic circuit and a memory circuit.

With such a structure, not only the pixel circuit but also the driver circuit or the like can be formed directly under the light-emitting unit; thus, the display device can be downsized as compared with the case where the driver circuit is provided around a display region.

Structure Example 5-4

FIG.11is a schematic cross-sectional view of a display device200E. The display device200E is different from the display device200D mainly in that two transistors using an oxide semiconductor are stacked.

The display device200E includes a transistor230between the transistor210and the transistor220. The transistor230has a structure similar to that of the transistor220except that the first gate electrode is not included. Note that the transistor230may include a first gate electrode like the transistor220.

The insulating layer263and an insulating layer231are provided to cover the conductive layer252, and the transistor230is provided over the insulating layer231. The transistor230and the conductive layer252are electrically connected to each other through a plug273, a conductive layer253, and a plug272. An insulating layer264and the insulating layer232are provided to cover the conductive layer253, and the transistor220is provided over the insulating layer232.

The transistor220functions as, for example, a transistor for controlling current flowing through the light-emitting element110. The transistor230functions as a selection transistor for controlling the selection state of a pixel. The transistor210functions as a transistor included in a driver circuit for driving the pixel, for example.

When three or more layers in which a transistor is formed are stacked in this manner, the area occupied by the pixel can be further reduced and a high-resolution display device can be achieved.

[Components]

Components such as a transistor that can be used in the display device will be described below.

[Transistor]

The transistors each include a conductive layer functioning as the gate electrode, the semiconductor layer, a conductive layer functioning as the source electrode, a conductive layer functioning as the drain electrode, and an insulating layer functioning as the gate insulating layer.

Note that there is no particular limitation on the structure of the transistor included in the display device of one embodiment of the present invention. For example, a planar transistor, a staggered transistor, or an inverted staggered transistor may be used. A top-gate or a bottom-gate transistor structure may be employed. Gate electrodes may be provided above and below a channel.

There is no particular limitation on the crystallinity of a semiconductor material used for the transistors, and any of an amorphous semiconductor, a single crystal semiconductor, and a semiconductor having crystallinity other than single crystal (a microcrystalline semiconductor, a polycrystalline semiconductor, a single-crystal semiconductor, or a semiconductor partly including crystal regions) may be used. It is preferable that a single crystal semiconductor or a semiconductor having crystallinity be used, in which case deterioration of the transistor characteristics can be suppressed.

In particular, a transistor that uses a metal oxide film for a semiconductor layer where a channel is formed will be described below.

As a semiconductor material used for the transistors, a metal oxide whose energy gap is greater than or equal to 2 eV, preferably greater than or equal to 2.5 eV, further preferably greater than or equal to 3 eV can be used. A typical example thereof is a metal oxide containing indium, and for example, a CAC-OS described later or the like can be used.

A transistor with a metal oxide having a larger band gap and a lower carrier density than silicon has a low off-state current; therefore, charges stored in a capacitor that is series-connected to the transistor can be held for a long time.

The semiconductor layer can be, for example, a film represented by an In-M-Zn-based oxide that contains indium, zinc, and M (a metal such as aluminum, titanium, gallium, germanium, yttrium, zirconium, lanthanum, cerium, tin, neodymium, or hafnium).

In the case where the metal oxide contained in the semiconductor layer contains an In-M-Zn-based oxide, it is preferable that the atomic ratio of metal elements of a sputtering target used for forming a film of the In-M-Zn oxide satisfy In≥M and Zn≥M. The atomic ratio of metal elements in such a sputtering target is preferably, for example, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:3, In:M:Zn=4:2:4.1, In:M:Zn=5:1:6, In:M:Zn=5:1:7, or In:M:Zn=5:1:8. Note that the atomic ratio in the formed semiconductor layer varies from the above atomic ratio of metal elements of the sputtering target in a range of ±40%.

A metal oxide film with low carrier density is used as the semiconductor layer. For example, for the semiconductor layer, a metal oxide whose carrier density is lower than or equal to 1×1017/cm3, preferably lower than or equal to 1×1015/cm3, further preferably lower than or equal to 1×1013/cm3, still further preferably lower than or equal to 1×1011/cm3, even further preferably lower than 1×1013/cm3, and higher than or equal to 1×10−9/cm3can be used. Such a metal oxide is referred to as a highly purified intrinsic or substantially highly purified intrinsic metal oxide. The metal oxide has a low impurity concentration and a low density of defect states and can thus be referred to as a metal oxide having stable characteristics.

Note that, without limitation to those described above, an oxide semiconductor with an appropriate composition may be used in accordance with required semiconductor characteristics and electrical characteristics (e.g., field-effect mobility and threshold voltage) of the transistor. To obtain the required semiconductor characteristics of the transistor, it is preferable that the carrier density, the impurity concentration, the density of defect states, the atomic ratio between a metal element and oxygen, the interatomic distance, the density, and the like of the semiconductor layer be set to appropriate values.

When silicon or carbon, which is one of elements belonging to Group14, is contained in the metal oxide contained in the semiconductor layer, oxygen vacancies are increased in the semiconductor layer, and the semiconductor layer becomes n-type. Thus, the concentration of silicon or carbon (measured by secondary ion mass spectrometry) in the semiconductor layer is set to lower than or equal to 2×1018atoms/cm3, preferably lower than or equal to 2×1017atoms/cm3.

Alkali metal and alkaline earth metal might generate carriers when bonded to a metal oxide, in which case the off-state current of the transistor might be increased. Therefore, the concentration of alkali metal or alkaline earth metal of the semiconductor layer, which is measured by secondary ion mass spectrometry, is set to lower than or equal to 1×1018atoms/cm3, preferably lower than or equal to 2×1016atoms/cm3.

When nitrogen is contained in the metal oxide contained in the semiconductor layer, electrons serving as carriers are generated and the carrier density increases, so that the semiconductor layer easily becomes n-type. As a result, a transistor including a metal oxide that contains nitrogen is likely to be normally on. Hence, the concentration of nitrogen which is measured by secondary ion mass spectrometry is preferably set to lower than or equal to 5×1018atoms/cm3.

Oxide semiconductors are classified into a single crystal oxide semiconductor and a non-single-crystal oxide semiconductor. Examples of the non-single-crystal oxide semiconductor include a CAAC-OS (c-axis-aligned crystalline oxide semiconductor), a polycrystalline oxide semiconductor, an nc-OS (nanocrystalline oxide semiconductor), an amorphous-like oxide semiconductor (a-like OS), and an amorphous oxide semiconductor.

A CAC-OS (Cloud-Aligned Composite oxide semiconductor) may be used for a semiconductor layer of a transistor disclosed in one embodiment of the present invention.

The aforementioned non-single-crystal oxide semiconductor or CAC-OS can be suitably used for a semiconductor layer of a transistor disclosed in one embodiment of the present invention. As the non-single-crystal oxide semiconductor, the nc-OS or the CAAC-OS can be suitably used.

In one embodiment of the present invention, a CAC-OS is preferably used for a semiconductor layer of a transistor. The use of the CAC-OS allows the transistor to have high electrical characteristics or high reliability.

The semiconductor layer may be a mixed film including two or more of a region of a CAAC-OS, a region of a polycrystalline oxide semiconductor, a region of an nc-OS, a region of an a-like OS, and a region of an amorphous oxide semiconductor. The mixed film has, for example, a single-layer structure or a layered structure including two or more of the above regions in some cases.

<Composition of CAC-OS>

The composition of a CAC (Cloud-Aligned Composite)-OS that can be used in a transistor disclosed in one embodiment of the present invention will be described below.

A CAC-OS refers to one composition of a material in which elements constituting a metal oxide are unevenly distributed with a size greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size, for example. Note that a state in which one or more metal elements are unevenly distributed and regions including the metal element(s) are mixed with a size greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size in a metal oxide is hereinafter referred to as a mosaic pattern or a patch-like pattern.

Note that the metal oxide preferably contains at least indium. In particular, indium and zinc are preferably contained. In addition, one or more kinds selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like may be contained.

For example, CAC-OS in an In—Ga—Zn oxide (of the CAC-OS, an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) has a composition (hereinafter, referred to as cloud-like composition) in which materials are separated into indium oxide (hereinafter, InOX1(X1 is a real number greater than 0)) or indium zinc oxide (hereinafter, InX2ZnY2OZ2(X2, Y2, and Z2 are real numbers greater than 0)), and gallium oxide (hereinafter, GaOX3(X3 is a real number greater than 0)) or gallium zinc oxide (hereinafter, GaX4Zny4OZ4(X4, Y4, and Z4 are real numbers greater than 0)) to form a mosaic pattern, and InOX1or InX2ZnY2OZ2forming the mosaic pattern is evenly distributed in the film.

That is, the CAC-OS is a composite metal oxide having a composition in which a region including GaOX3as a main component and a region including InX2ZnY2OZ2or InOX1as a main component are mixed. Note that in this specification, for example, when the atomic ratio of In to an element M in a first region is greater than the atomic ratio of In to an element M in a second region, the first region is described as having higher In concentration than the second region.

Note that IGZO is a common name, which may specify a compound containing In, Ga, Zn, and O. Typical examples of IGZO include a crystalline compound represented by InGaO3(ZnO)m1(m1 is a natural number) and a crystalline compound represented by In(1+x0)Ga(1−x0)O3(ZnO)m0(−1≤x0≤1; m0 is a given number).

The above crystalline compounds have a single crystal structure, a polycrystalline structure, or a CAAC structure. Note that the CAAC structure is a crystal structure in which a plurality of IGZO nanocrystals have c-axis alignment and are connected in the a-b plane direction without alignment.

On the other hand, the CAC-OS relates to the material composition of a metal oxide. The CAC-OS refers to a composition in which, in the material composition containing In, Ga, Zn, and O, some regions that contain Ga as a main component and are observed as nanoparticles and some regions that contain In as a main component and are observed as nanoparticles are randomly dispersed in a mosaic pattern. Therefore, the crystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure including two or more films with different atomic compositions is not included. For example, a two-layer structure of a film containing In as a main component and a film containing Ga as a main component is not included.

A boundary between the region containing GaOX3as a main component and the region containing InX2ZnY2OZ2or InOX1as a main component is not clearly observed in some cases.

In the case where one or more kinds selected from aluminum, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like are contained instead of gallium, nanoparticle regions containing the selected metal element(s) as a main component(s) are observed in part of a CAC-OS and nanoparticle regions containing In as a main component are observed in part of the CAC-OS, and these nanoparticle regions are randomly dispersed to form a mosaic pattern in the CAC-OS.

The CAC-OS can be formed by a sputtering method under a condition where a substrate is not heated intentionally, for example. Moreover, in the case of forming the CAC-OS by a sputtering method, any one or more selected from an inert gas (typically, argon), an oxygen gas, and a nitrogen gas are used as a deposition gas. The flow rate of the oxygen gas to the total flow rate of the deposition gas in deposition is preferably as low as possible, for example, the flow rate of the oxygen gas is higher than or equal to 0% and lower than 30%, preferably higher than or equal to 0% and lower than or equal to 10%.

The CAC-OS is characterized in that a clear peak is not observed when measurement is conducted using a θ/2θ scan by an Out-of-plane method, which is an X-ray diffraction (XRD) measurement method. That is, it is found from X-ray diffraction measurement that no alignment in an a-b plane direction and a c-axis direction is observed in a measured region.

In an electron diffraction pattern of the CAC-OS which is obtained by irradiation with an electron beam with a probe diameter of 1 nm (also referred to as a nanometer-sized electron beam), a ring-like region with high luminance and a plurality of bright spots in the ring-like region are observed. Therefore, the electron diffraction pattern indicates that the crystal structure of the CAC-OS includes an nc (nano-crystal) structure with no alignment in the plan-view direction and the cross-sectional direction.

Moreover, for example, it can be checked by EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) that the CAC-OS in the In—Ga—Zn oxide has a composition in which regions including GaOX3as a main component and regions including InX2ZnY2OZ2or InOX1as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound in which metal elements are evenly distributed, and has characteristics different from those of the IGZO compound. That is, in the CAC-OS, regions containing GaOX3or the like as a main component and regions containing InX2ZnY2OZ2or InOX1as a main component are separated to form a mosaic pattern.

The conductivity of a region containing InX2ZnY2OZ2or InOX1as a main component is higher than that of a region containing GaOX3or the like as a main component. In other words, when carriers flow through the regions including InX2ZnY2OZ2or InOX1as a main component, the conductivity of a metal oxide is exhibited. Accordingly, when the regions including InX2ZnY2OZ2or InOX1as a main component are distributed in a metal oxide like a cloud, high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region containing GaOX3or the like as a main component is higher than that of a region containing InX2ZnY2OZ2or InOX1as a main component. In other words, when regions including GaOX3or the like as a main component are distributed in a metal oxide, leakage current can be suppressed and favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, the insulating property derived from GaOX3or the like and the conductivity derived from InX2ZnY2OZ2or InOX1complement each other, whereby high on-state current (Ion) and high field-effect mobility (μ) can be achieved.

A semiconductor element using a CAC-OS has high reliability. Thus, the CAC-OS is suitably used in a variety of semiconductor devices typified by a display.

Since a transistor including a CAC-OS in a semiconductor layer has high field-effect mobility and high driving capability, the use of the transistor in a driver circuit, typically a scan line driver circuit that generates a gate signal, enables a display device with a narrow frame width (also referred to as a narrow bezel) to be provided. Furthermore, with the use of the transistor in a signal line driver circuit that supplies a signal from a signal line of the display device (particularly in a demultiplexer connected to an output terminal of a shift register included in a signal line driver circuit), the display device connected to less number of wirings can be provided.

Furthermore, the transistor including a CAC-OS in the semiconductor layer does not need a laser crystallization step like a transistor including low-temperature polysilicon. Thus, the manufacturing cost of a display device can be reduced, even when the display device is formed using a large substrate. In addition, the transistor including a CAC-OS in the semiconductor layer is preferably used for a driver circuit and a display portion in a large display device having high resolution such as ultra-high definition (“4K resolution”, “4K2K”, and “4K”) or super high definition (“8K resolution”, “8K4K”, and “8K”), in which case writing can be performed in a short time and display defects can be reduced.

Alternatively, silicon may be used for a semiconductor in which a channel of a transistor is formed. As the silicon, amorphous silicon may be used but silicon having crystallinity is preferably used. For example, microcrystalline silicon, polycrystalline silicon, or single-crystal silicon are preferably used. In particular, polycrystalline silicon can be formed at a temperature lower than that for single crystal silicon and has higher field-effect mobility and higher reliability than amorphous silicon.

[Conductive Layer]

Examples of materials that can be used for conductive layers of a variety of wirings and electrodes and the like included in the display device in addition to a gate, a source, and a drain of a transistor include metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten and an alloy containing such a metal as its main component. A single-layer structure or stacked-layer structure including a film containing any of these materials can be used. For example, a single-layer structure of an aluminum film containing silicon, a two-layer structure in which an aluminum film is stacked over a titanium film, a two-layer structure in which an aluminum film is stacked over a tungsten film, a two-layer structure in which a copper film is stacked over a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is stacked over a titanium film, a two-layer structure in which a copper film is stacked over a tungsten film, a three-layer structure in which an aluminum film or a copper film is stacked over a titanium film or a titanium nitride film and a titanium film or a titanium nitride film is formed thereover, a three-layer structure in which an aluminum film or a copper film is stacked over a molybdenum film or a molybdenum nitride film and a molybdenum film or a molybdenum nitride film is formed thereover, and the like can be given. Note that an oxide such as indium oxide, tin oxide, or zinc oxide may be used. Copper containing manganese is preferably used because it increases controllability of a shape by etching.

[Insulating Layer]

Examples of an insulating material that can be used for the insulating layers include, in addition to a resin such as acrylic or epoxy and a resin having a siloxane bond, an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, or aluminum oxide.

The light-emitting element is preferably provided between a pair of insulating films with low water permeability. In that case, impurities such as water can be inhibited from entering the light-emitting element, and thus a decrease in device reliability can be inhibited.

Examples of the insulating film with low water permeability include a film containing nitrogen and silicon, such as a silicon nitride film and a silicon nitride oxide film, and a film containing nitrogen and aluminum, such as an aluminum nitride film. Alternatively, a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or the like may be used.

For example, the moisture vapor transmission rate of the insulating film with low water permeability is lower than or equal to 1×10−5[g/(m2·day)], preferably lower than or equal to 1×10−6[g/(m2·day)], further preferably lower than or equal to 1×10−7[g/(m2·day)], still further preferably lower than or equal to 1×10−8[g/(m2·day)].

Structure Example of Display Module

A structure example of a display module including the display device of one embodiment of the present invention will be described below.

FIG.12(A)is a schematic perspective view of a display module280. The display module280includes a display device200and an FPC290. Any of the display devices (the display device200A to the display device200E) described in Structure Example 5 can be used as the display device200.

The display module280includes the substrate201and the substrate202. A display portion281is also included on the substrate202side. The display portion281is a region of the display module280where an image is displayed and is a region where light emitted from pixels provided in a pixel portion284described later can be seen.

FIG.12(B)illustrates a perspective view schematically illustrating a structure on the substrate201side. The substrate201has a structure in which a circuit portion282, a pixel circuit portion283over the circuit portion282, and the pixel portion284over the pixel circuit portion283are stacked. In addition, a terminal portion285for connection to the FPC290is included in a portion not overlapping with the pixel portion284over the substrate201. The terminal portion285and the circuit portion282are electrically connected to each other through a wiring portion286formed of a plurality of wirings.

The pixel portion284includes a plurality of pixels284aarranged in a matrix. An enlarged view of one pixel284ais illustrated on the right side ofFIG.12(B). The pixel284aincludes the light-emitting unit120R, the light-emitting unit120G, and the light-emitting unit120B.

The pixel circuit portion283includes a plurality of pixel circuits283aarranged in a matrix. One pixel circuit283ais a circuit that controls light emission of three light-emitting units included in one pixel284a.One pixel circuit283amay be provided with three circuits each of which controls light emission of one light-emitting unit. For example, the pixel circuit283acan have a structure including at least one selection transistor, one current control transistor (driving transistor), and a capacitor for one light-emitting unit. In this case, a gate signal is input to a gate of the selection transistor and a source signal is input to one of a source and a drain thereof. Thus, an active-matrix display device is achieved.

The circuit portion282includes a circuit for driving the pixel circuits283ain the pixel circuit portion283. For example, a gate line driver circuit and a source line driver circuit are preferably included. In addition, an arithmetic circuit, a memory circuit, a power supply circuit, or the like may be included.

The FPC290functions as a wiring for supplying a video signal or a power supply potential to the circuit portion282from the outside. In addition, an IC may be mounted on the FPC290.

The display module280can have a structure in which the pixel circuit portion283, the circuit portion282, and the like are stacked below the pixel portion284; thus, the aperture ratio (the effective display area ratio) of the display portion281can be significantly high. For example, the aperture ratio of the display portion281can be greater than or equal to 40% and less than 100%, preferably greater than or equal to 50% and less than or equal to 95%, and further preferably greater than or equal to 60% and less than or equal to 95%. Furthermore, the pixels284acan be arranged extremely densely and thus the display portion281can have extremely high resolution. For example, the pixels284aare preferably arranged in the display portion281with a resolution greater than or equal to 2000 ppi, preferably greater than or equal to 3000 ppi, further preferably greater than or equal to 5000 ppi, still further preferably greater than or equal to 6000 ppi, and less than or equal to 20000 ppi or less than or equal to 30000 ppi.

Such a display module280has extremely high resolution, and thus can be suitably used for a device for VR such as a head-mounted display or a glasses-type device for AR. For example, even in the case of a structure in which the display portion of the display module280is seen through a lens, pixels of the extremely-high-resolution display portion281included in the display module280are prevented from being seen when the display portion is enlarged by the lens, so that display providing a high sense of immersion can be performed. Without limitation to the above, the display module280can also be suitably used for an electronic device having a relatively small display portion. For example, the display module280can be suitably used in a display portion of a wearable electronic device such as a smart watch.

At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate.

Embodiment 2

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

A display device illustrated inFIG.13(A)includes a pixel portion502, a driver circuit portion504, protection circuits506, and a terminal portion507. Note that a structure in which the protection circuits506are not provided may be employed.

The pixel portion502includes a plurality of pixel circuits501that drive a plurality of display elements arranged in X rows and Y columns (X and Y each independently represent a natural number of 2 or more).

The driver circuit portion504includes driver circuits such as a gate driver504athat outputs a scanning signal to gate lines GL_1to GL_X and a source driver504bthat supplies a data signal to data lines DL_1to DL_Y. The gate driver504aincludes at least a shift register. The source driver504bis formed using a plurality of analog switches, for example. Alternatively, the source driver504bmay be formed using a shift register or the like.

The terminal portion507refers to a portion provided with terminals for inputting power, control signals, image signals, and the like to the display device from external circuits.

The protection circuit506is a circuit that, when a potential out of a certain range is applied to a wiring to which the protection circuit506is connected, establishes continuity between the wiring and another wiring. The protection circuit506illustrated inFIG.13(A)is connected to a variety of wirings such as the scan lines GL that are wirings between the gate driver504aand the pixel circuits501and the data lines DL that are wirings between the source driver504band the pixel circuits501, for example.

The gate driver504aand the source driver504bmay be provided over the same substrate as the pixel portion502, or a substrate where a gate driver circuit or a source driver circuit is separately formed (e.g., a driver circuit board formed using a single crystal semiconductor film or a polycrystalline semiconductor film) may be mounted on the substrate by COG or TAB (Tape Automated Bonding).

In particular, the gate driver504aand the source driver504bare preferably placed below the pixel portion502.

The plurality of pixel circuits501illustrated inFIG.13(A)can have a configuration illustrated inFIG.13(B), for example.

The pixel circuit501illustrated inFIG.13(B)includes transistors552and554, a capacitor562, and a light-emitting element572. A data line DL_n, A scan line GL_m, a potential supply line VL_a, a potential supply line VL_b, and the like are connected to the pixel circuit501.

Note that a high power supply potential VDD is supplied to one of the potential supply line VL_a and the potential supply line VL_b, and a low power supply potential VSS is supplied to the other. Current flowing through the light-emitting element572is controlled in accordance with a potential applied to a gate of the transistor554, whereby the luminance of light emitted from the light-emitting element572is controlled.

At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate.

Embodiment 3

A pixel circuit including a memory for correcting gray levels displayed by pixels that can be used in one embodiment of the present invention and a display device including the pixel circuit will be described below.

[Circuit Configuration]

FIG.14(A)is a circuit diagram of a pixel circuit400. The pixel circuit400includes a transistor M1, a transistor M2, a capacitor C1, and a circuit401. A wiring S1, a wiring S2, a wiring G1, and a wiring G2are connected to the pixel circuit400.

In the transistor M1, a gate is connected to the wiring G1, one of a source and a drain is connected to the wiring S1, and the other is connected to one electrode of the capacitor C1. In the transistor M2, a gate is connected to the wiring G2, one of a source and a drain is connected to the wiring S2, and the other is connected to the other electrode of the capacitor C1and the circuit401.

The circuit401is a circuit including at least one display element. Any of a variety of elements can be used as the display element, and typically, a light-emitting element such as an organic EL element or an LED element can be used. In addition, a liquid crystal element, a MEMS (Micro Electro Mechanical Systems) element, or the like can also be used.

A node connecting the transistor M1and the capacitor C1is denoted as N1, and a node connecting the transistor M2and the circuit401is denoted as N2.

In the pixel circuit400, the potential of the node N1can be retained when the transistor M1is turned off The potential of the node N2can be retained when the transistor M2is turned off. When a predetermined potential is written to the node N1through the transistor M1with the transistor M2being in an off state, the potential of the node N2can be changed in accordance with displacement of the potential of the node N1owing to capacitive coupling through the capacitor C1.

Here, the transistor using an oxide semiconductor, which is described in Embodiment 1, can be used as one or both of the transistor M1and the transistor M2. Accordingly, owing to an extremely low off-state current, the potentials of the node N1and the node N2can be retained for a long time. Note that in the case where the period in which the potential of each node is retained is short (specifically, the case where the frame frequency is higher than or equal to 30 Hz, for example), a transistor using a semiconductor such as silicon may be used.

Driving Method Example

Next, an example of a method for operating the pixel circuit400is described with reference toFIG.14(B).FIG.14(B)is a timing chart of the operation of the pixel circuit400. Note that for simplification of description, the influence of various kinds of resistance such as wiring resistance, parasitic capacitance of a transistor, a wiring, or the like, the threshold voltage of the transistor, and the like is not taken into account here.

In the operation shown inFIG.14(B), one frame period is divided into a period T1and a period T2. The period T1is a period in which a potential is written to the node N2, and the period T2is a period in which a potential is written to the node N1.

[Period T1]

In the period T1, a potential for turning on the transistor is supplied to both the wiring G1and the wiring G2. In addition, a potential Vrefthat is a fixed potential is supplied to the wiring S1, and a first data potential Vwis supplied to the wiring S2.

The potential Vrefis supplied from the wiring S1to the node N1through the transistor M1. The first data potential Vwis supplied to the node N2through the transistor M2. Accordingly, a potential difference Vw−Vrefis retained in the capacitor C1.

[Period T2]

Next, in the period T2, a potential for turning on the transistor M1is supplied to the wiring G1, and a potential for turning off the transistor M2is supplied to the wiring G2. A second data potential Vdatais supplied to the wiring S1. The wiring S2may be supplied with a predetermined constant potential or brought into a floating state.

The second data potential Vdatais supplied to the node N1through the transistor M1. At this time, capacitive coupling due to the capacitor C1changes the potential of the node N2in accordance with the second data potential Vdataby a potential dV. That is, a potential that is the sum of the first data potential Vw and the potential dV is input to the circuit401. Note that although dV is shown as a positive value inFIG.14(B), dV may be a negative value. That is, the potential Vdatamay be lower than the potential Vref.

Here, the potential dV is roughly determined by the capacitance of the capacitor C1and the capacitance of the circuit401. When the capacitance of the capacitor C1is sufficiently larger than the capacitance of the circuit401, the potential dV is a potential close to the second data potential Vdata.

In the above manner, the pixel circuit400can generate a potential to be supplied to the circuit401including the display element, by combining two kinds of data signals; hence, a gray level can be corrected in the pixel circuit400.

The pixel circuit400can also generate a potential exceeding the maximum potential that can be supplied to the wiring S1and the wiring S2. For example, in the case of using a light-emitting element, high-dynamic range (HDR) display or the like can be performed. In the case of using a liquid crystal element, overdriving or the like can be achieved.

Application Example

A pixel circuit400EL illustrated inFIG.14(C)includes a circuit401EL. The circuit401EL includes a light-emitting element EL, a transistor M3, and the capacitor C2.

In the transistor M3, a gate is connected to the node N2and one electrode of the capacitor C2, one of a source and a drain is connected to a wiring supplied with a potential VH, and the other is connected to one electrode of the light-emitting element EL. The other electrode of the capacitor C2is connected to a wiring supplied with a potential Vcom. The other electrode of the light-emitting element EL is connected to a wiring supplied with a potential VL.

The transistor M3has a function of controlling a current to be supplied to the light-emitting element EL. The capacitor C2functions as a storage capacitor. The capacitor C2can be omitted when not needed.

Note that although the structure in which the anode side of the light-emitting element EL is connected to the transistor M3is described here, the transistor M3may be connected to the cathode side. In that case, the values of the potential VHand the potential VLcan be appropriately changed.

In the pixel circuit400EL, a large amount of current can flow through the light-emitting element EL when a high potential is applied to the gate of the transistor M3, which enables HDR display, for example. Moreover, a variation in the electrical characteristics of the transistor M3and the light-emitting element EL can be corrected by supply of a correction signal to the wiring S1or the wiring S2.

Note that the configuration is not limited to the circuits shown inFIG.14(C), and a configuration to which a transistor, a capacitor, or the like is further added may be employed.

At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate.

Embodiment 4

In this embodiment, structure examples of an electronic device for which the display device of one embodiment of the present invention is used will be described.

The display device and the display module of one embodiment of the present invention can be applied to a display portion of an electronic device or the like having a display function. Examples of such an electronic device include a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game machine, a portable information terminal, and an audio reproducing device, in addition to electronic devices with a relatively large screen, such as a television device, a laptop personal computer, a monitor device, digital signage, a pachinko machine, and a game machine.

In particular, the display device and the display module of one embodiment of the present invention can have a high resolution, and thus can be favorably used for an electronic device having a relatively small display portion. The display device and the display module can be favorably used for, for example, the following electronic devices: a watch-type or bracelet-type information terminal device (wearable device); and a wearable device worn on a head, such as a device for VR such as a head mounted display and a glasses-type device for AR.

FIG.15(A)is a perspective view of an electronic device700that is of a glasses type. The electronic device700includes a pair of display panels701, a pair of housings702, a pair of optical members703, a pair of temples704, and the like.

The electronic device700can project an image displayed on the display panel701onto a display region706of the optical member703. Since the optical members703have a light-transmitting property, a user can see images displayed on the display regions706, which are superimposed on transmission images seen through the optical members703. Thus, the electronic device700is an electronic device capable of AR display.

The housing702each include a camera705capable of taking an image of what lies in front thereof. Although not illustrated, one of the housings702is provided with a wireless receiver or a connector to which a cable can be connected, whereby a video signal or the like can be supplied to the housing702. Furthermore, when the housing702is provided with an acceleration sensor such as a gyroscope sensor, the orientation of the user's head can be detected and an image corresponding to the orientation can be displayed on the display region706. Moreover, the housing702is preferably provided with a battery, in which case charging can be performed with or without a wire.

Next, a method for projecting an image on the display region706of the electronic device700is described with reference toFIG.15(B). The display panel701, a lens711, and a reflective plate712are provided in the housing702. A reflective surface713functioning as a half mirror is provided in a portion corresponding to the display region706of the optical member703.

Light715emitted from the display panel701passes through the lens711and is reflected by the reflective plate712to the optical member703side. In the optical member703, the light715is fully reflected repeatedly by end surfaces the optical member703and reaches the reflective surface713, whereby an image is projected on the reflective surface713. Accordingly, the user can see both the light715reflected by the reflective surface713and transmitted light716transmitted through the optical member703(including the reflective surface713).

FIG.15shows an example in which the reflective plate712and the reflective surface713each have a curved surface. This can increase optical design flexibility and reduce the thickness of the optical member703, compared to the case where they have flat surfaces. Note that the reflective plate712and the reflective surface713may be flat.

The reflective plate712can use a component having a mirror surface, and preferably has high reflectivity. As the reflective surface713, a half mirror utilizing reflection of a metal film may be used, but the use of prism utilizing total reflection or the like can increase the transmittance of the transmitted light716.

Here, the housing702preferably includes a mechanism for adjusting the distance and angle between the lens711and the display panel701. This enables operations such as focus adjustment and zooming in/out of image. One or both of the lens711and the display panel701is preferably configured to be movable in the optical-axis direction, for example.

The housing702preferably includes a mechanism capable of adjusting the angle of the reflective plate712. The position of the display region706where images are displayed can be changed by changing the angle of the reflective plate712. Thus, the display region706can be placed at the most appropriate position in accordance with the position of the user's eye.

The display device or the display module of one embodiment of the present invention can be used for the display panel701. Thus, the electronic device700can perform display with extremely high resolution.

FIGS.16(A) and16(B)illustrate perspective views of an electronic device750that is of a goggle-type.FIG.16(A)is a perspective view illustrating the front surface, the top surface, and the left side surface of the electronic device750, andFIG.16(B)is a perspective view illustrating the back surface, the bottom surface, and the right side surface of the electronic device750.

The electronic device750includes a pair of display panels751, a housing752, a pair of temples754, a cushion755, a pair of lenses756, and the like. The pair of display panels751is positioned to be seen through the lenses756inside the housing752.

The electronic device750is an electronic device for VR. A user wearing the electronic device750can see an image displayed on the display panel751through the lens756. Furthermore, when the pair of display panels751displays different images, three-dimensional display using parallax can be performed.

An input terminal757and an output terminal758are provided on the back side of the housing752. To the input terminal757, a cable for supplying a video signal from a video output device or the like, power for charging a battery provided in the housing752, or the like can be connected. The output terminal758can function as, for example, an audio output terminal to which earphones, headphones, or the like can be connected. Note that in the case where audio data can be output by wireless communication or sound is output from an external video output device, the audio output terminal is not necessarily provided.

In addition, the housing752preferably includes a mechanism by which the left and right positions of the lens756and the display panel751can be adjusted to the optimal positions in accordance with the position of the user's eye. In addition, the housing752preferably includes a mechanism for adjusting focus by changing the distance between the lens756and the display panel751.

The display device or the display module of one embodiment of the present invention can be used for the display panel751. Thus, the electronic device750can perform display with extremely high resolution. This enables a user to feel high sense of immersion.

The cushion755is a portion in contact with the user's face (forehead, cheek, or the like). The cushion755is in close contact with the user's face, so that light leakage can be prevented, which increases the sense of immersion. A soft material is preferably used for the cushion755so that the cushion755is in close contact with the face of the user wearing the electronic device750. For example, a material such as silicone rubber, urethane, or sponge can be used. Furthermore, when a sponge or the like whose surface is covered with cloth, leather (natural leather or synthetic leather), or the like is used, a gap is unlikely to be generated between the user's face and the cushion755, whereby light leakage can be suitably prevented. Furthermore, using such a material is preferable because it has a soft texture and the user does not feel cold when wearing the device in a cold season, for example. The member in contact with user's skin, such as the cushion755or the temple754, is preferably detachable because cleaning or replacement can be easily performed.

At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate.

REFERENCE NUMERALS

100: display device,100A-E: display device,101: substrate,110: light-emitting element,110B: light-emitting element,110G: light-emitting element,110R: light-emitting element,111: conductive layer,111B: conductive layer,111G: conductive layer,111R: conductive layer,112: EL layer,113: conductive layer,114: reflective layer,114B: reflective layer,114G: reflective layer,114R: reflective layer,115: insulating layer,116G: reflective layer,116R: reflective layer,120B: light-emitting unit,120G: light-emitting unit,120R: light-emitting unit,121: insulating layer,121f: insulating film,122: insulating layer,131a: plug,131b: plug,131bf: conductive film,131c: plug,132: conductive layer,141: conductive layer,141f: conductive film,142: conductive layer,142f: conductive film,143: conductive layer,143f: conductive film,144: conductive layer,145: conductive layer,146B: insulating layer,146G: insulating layer,146R: insulating layer,151: resist mask,152: resist mask,153: resist mask,161: insulating layer,162: insulating layer,163: insulating layer,164: adhesive layer,165B: coloring layer,165G: coloring layer,165R: coloring layer,200: display device,200A-E: display device,201: substrate,201a: substrate,202: substrate,210: transistor,211: conductive layer,212: low-resistance region,213: insulating layer,214: insulating layer,215: element isolation layer,220: transistor,221: semiconductor layer,222: metal oxide layer,223: insulating layer,224: conductive layer,225: conductive layer,226: insulating layer,227: conductive layer,228: insulating layer,230: transistor,231: insulating layer,232: insulating layer,240: capacitor,240A: capacitor,241: conductive layer,242: conductive layer,243: insulating layer,251: conductive layer,251a: conductive layer,251b: conductive layer,252: conductive layer,253: conductive layer,261: insulating layer,262: insulating layer,263: insulating layer,264: insulating layer,265: insulating layer,271: plug,271a: conductive layer,271b: conductive layer,272: plug,273: plug,274: plug,280: display module,281: display portion,282: circuit portion,283: pixel circuit portion,283a: pixel circuit,284: pixel portion,284a: pixel,285: terminal portion,286: wiring portion,290: FPC