Patent ID: 12219867

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that one embodiment of the present invention is not limited to the description below, and it is easily understood by those skilled in the art that modes and details of the present invention can be modified in various ways. The present invention should not be construed as being limited to the description in the embodiments given below.

Embodiment 1

In this embodiment, structure examples and application examples of a display device of one embodiment of the present invention are described with reference to drawings.

To fix a flexible display panel to part of a housing having a curved surface, a buffer plate formed of a member having a curved surface and metal is provided between the flexible display panel and the housing. For example, in a car, the housing is part of a dashboard, and the dashboard includes the mounted display panel in this specification. The dashboard means the whole interior components (including the meter and the display device) around the front of the driver's seat below the front window, and is also referred to as instrument panel.

FIG.1is a cross-sectional view illustrating an example of a member501having a curved surface provided with a display panel100.

The display device illustrated inFIG.1includes the member501having a curved surface, a buffer plate500, the display panel100, a flexible printed circuit board (FPC)112, a printed circuit board505, and guide portions502aand502b.

In the case where an organic resin film and an organic light-emitting element are respectively used for a substrate and a display element of the display panel100and the film thickness is reduced, the total thickness in a display region of the display panel100can be less than or equal to 1 mm.

In the case where a touch panel is provided so that the display panel100has a touch input function as well, the display panel100needs to be supported by the member501overlapping with the display panel100so that the user can touch the display panel. The member501for supporting the display panel100is formed of a hard material having repulsive force with respect to the finger touch. The use of such a material can prevent the display panel100from being broken by the finger touch.

The member501is formed using acrylic, polypropylene, polyvinyl chloride, polycarbonate, polyamide, or the like. Such organic resins are preferably used, in which case the weight of the display device can be reduced.

When the member501and the film of the display panel100are fixed to be in contact with each other, creases occur by a change in temperature due to difference in linear expansion coefficient of the materials.

FIG.16Ashows a cross-sectional perspective view of a sample in which the display panel100is bonded to be in contact with an acrylic flat plate20with a double-sided tape.FIGS.16B and16Cshow results of preservation test in which thermal shock is given.FIG.16Bis a photograph taken just after the display panel100is bonded to be in contact with the flat acrylic plate20.FIG.16Cis a photograph taken after preservation at 40° C. for 12 hours, after preservation at 0° C. for 12 hours, and after returning to the room temperature. As shown inFIG.16C, creases occur and the appearance is largely changed after the preservation test.

In view of the above results, in this embodiment, as illustrated inFIG.1, the buffer plate500is provided between the member501having a curved surface and the display panel100. Although not illustrated inFIG.1, a bonding layer such as a double-sided tape is provided between the member501and the buffer plate500.

The thickness of the buffer plate500is more than or equal to 0.1 mm and less than or equal to 2.5 mm. The mechanical treatment is preferably performed depending on the material to have a shape along the surface of the member501. In this embodiment, aluminum which is lightweight and inexpensive is used, and an aluminum plate having a thickness of 0.5 mm is used. With such a thickness, the aluminum plate can be flexible so that it can be formed into a shape along the curved surface of the member when bonded to the member501with a double-sided tape.

The buffer plate500can suppress occurrence of creases due to thermal shock as shown inFIG.16C. The buffer plate500formed using an aluminum plate can also be referred to as heat buffering plate and can disperse and equalize or dissipate heat generated by an element and the like of the display panel100. In the case where external force is applied from the outside, stress applied to the member501and the display panel100may be relieved with the buffer plate500.

If the member501is formed of the same metal material as the buffer plate500and the buffer plate is not provided, occurrence of creases due to thermal shock can be suppressed; however, the total weight of the member501is increased and the weight of the display device is increased.

In the case where the display device is incorporated in a car, the display device is fit into a frame which is fixed into another frame with a screw or the like for maintaining the rigidity of the car body, or the display device is fixed into a frame with a screw. In that case, if the weight of the display device is large, the load is concentrated on the frame to which the display device is fixed. For this reason, the weight of the display device including the member501is preferably small. In a car, the installation position needs to be considered to keep weight balance. Therefore, a lightweight display device using the flexible display panel is useful because there is no need to consider the installation position.

A region of the display panel100inFIG.1overlapping with the buffer plate has the center of curvature on the right side, which is a curved surface having a radius of curvature of greater than 700 mm. The other region has the center of curvature on the left side, which is a curved surface having a smaller radius of curvature. The curved surface having a smaller radius of curvature is supported by the guide portion502anot to have a radius of curvature of less than 5 mm. The display panel100can have enough reliability of display when the radius of curvature is greater than or equal to 5 mm.

In the display panel100inFIG.1, a terminal electrode120is electrically connected to a display element and the FPC112. The flat surface of the guide portion502boverlaps with a contact portion between the FPC112and the terminal electrode120. The display panel100and the FPC112are provided along the outer side of the guide portions502aand502b.

As illustrated inFIG.1, the display device in which the printed circuit board505provided with a driver IC506is provided on the rear side of the display panel100can be compact in size.

The guide portion502bis fixed to the guide portion502a. A flat portion of the guide portion502bmay be formed of a metal material. The guide portion502bmay have a portion in contact with the FPC112, and the contact portion is not necessarily rounded as inFIG.1because the FPC112is flexible. InFIG.1, the guide portion502bis fixed to the member501with a fastener504asuch as a bolt or screw.

The printed circuit board505includes an element group such as the driver IC506and is fixed to the member501with the fastener504band504c. The flat surfaces of the printed circuit board505and the member501are substantially parallel to each other. Note that the FPC112is connected to a connection portion503of the printed circuit board505. The power may be supplied to the display device through a connection cord from a power supply (e.g., a power generator or a secondary battery) of a vehicle. The printed circuit board505may be provided with a secondary battery, a wireless communication portion, or the like, and may have a system configuration for transmitting and receiving a video signal wirelessly.

The member501may have a chipped portion or a cavity for further reduction in weight. To further reduce the size, the member501may have a complex shape, specifically, a shape in which a region overlapping with a printed circuit board505hollowed out so that a distance between the printed circuit board505and the buffer plate500is reduced.

When the element provided for the printed circuit board505is a high-frequency circuit or the like, the buffer plate500preferably functions as an electric-field shielding film. The buffer plate500can reduce degradation in display quality of the display panel100due to noise from the high-frequency circuit. In order to reduce the influence of noise, the shortest distance between the printed circuit board and the organic light-emitting element is preferably 150 μm or more.

When a conductive plate is provided to be partly in contact with and overlap with a flexible film overlapping with the display region of the display panel, the degradation in display quality of the display panel100is reduced.

Therefore, the region of the buffer plate500overlapping with the display region of the display panel100is preferably at least the same as or larger than the area of the display region of the display panel100. If there is a portion where the display region of the display panel100does not overlap with the buffer plate500, a boundary might appear on the display by a difference in image displayed between them.

The cross-sectional shape of the member501is not particularly limited to the example inFIG.1as long as having a curved surface. For example, a cross-sectional shape of the member501illustrated inFIG.2may be used. Since the cross-sectional shape of the member501inFIG.2is different from that inFIG.1, the shapes of the buffer plate500and the display panel100are also different; however, other structures are the same, and thus the detailed description is omitted.

The member501inFIG.2has a smaller volume and lighter weight than the member501inFIG.1. In addition, in the member501inFIG.2, a region overlapping with the printed circuit board505is removed to achieve further reduction in weight. The member501having such a complex shape can be easily formed using a 3D printer or the like.

The display device described in this embodiment is effectively used in not only a vehicle but also a portable television receiver.

FIG.3Aillustrates an example of a portable television receiver5010.FIG.3Bis a cross-sectional view taken along a dotted line X-Y inFIG.3A. The portable television receiver5010includes a speaker5013, an LED lamp5014, operation keys5015, and a connection terminal5016. The portable television receiver5010can be set in a charger5017capable of transmitting and receiving signals as illustrated inFIG.3A. In addition to these components, the portable television receiver5010includes an antenna, a tuner, an image processing portion, a memory medium reading portion, a secondary battery, and the like.

Requirements for a portable television are a large screen, being lightweight, and wide variety of installation positions. A conventional portable television has a flat liquid crystal display panel using a glass substrate. In that case, the backlight having the same size as the glass substrate and a large base is needed, and thus the base becomes larger as the screen size increases to maintain balance.

It is difficult to install the television having a large base in a narrow position, for example, a shelf with a small width.

As illustrated inFIG.3B, the display element of this embodiment is an organic light-emitting element, and thus a backlight is not necessary. In addition, the ground surface side of the member501is wide and thus stable to maintain balance. The member501formed using an acrylic resin is lightweight. The display panel100is exposed to temperature shock when installed in a bathroom or the like; however, generation of creases or the like can be suppressed owing to the buffer plate500between the member501and the display panel100.

The curved screen of the display panel100is easily viewable for the user.

A liquid crystal panel is formed using a glass substrate and thus can be broken when it falls. In contrast, the display panel100described in this embodiment is safe because it is formed using a flexible film and thus is not broken when it falls and is safe. Furthermore, the curved surface has almost no contact with a flat floor or desk when the display panel100falls thereon.

The shape of the member501is adjusted appropriately, whereby the display device described in this embodiment can be reduced in size and weight and installed in various places such as the inside of a vehicle. Thus, the display device can be compact and stored in a narrow space.

Application examples in which the display device described in this embodiment is installed in a vehicle are described below.

FIG.4Aillustrates an example of installing a display device5002to a right-hand vehicle, but there is no particular limitation. In the case of a left-hand vehicle, the placement of the left and right is replaced.

FIG.4Aillustrates a dashboard5001, a handle5003, a windshield5004, and the like which are arranged around a driver's seat and a front passenger's seat.

The display device5002is arranged in a predetermined position in the dash board5001, specifically, around the driver, and is substantially T shape. The substantial T shape is preferable because a display region can be arranged in front of the driver's seat, in front of the front passenger's seat, and between the driver's seat and front passenger's seat in the car.FIG.4Aillustrates an example in which a plurality of display panels are combined into one display device5002and arranged on the curved or flat surface of the dashboard5001; however, one embodiment of the present invention is not limited to the example, and a plurality of display devices may be separately provided. The one display device5002illustrated inFIG.4Ahas a complex shape which includes a plurality of openings and does not include display regions in a handle connection portion, a display portion of a meter, a ventilation duct5006, and the like. It is an advantage of a flexible display panel to enable such a complex shape.

A plurality of cameras5005for shooting the situation on the rear side are provided outside the car. Although the camera5005is provided instead of a side mirror in the example ofFIG.4A, both the side mirror and the camera may be provided.

The camera5005can be a CCD camera or a CMOS camera, or an infrared camera may be combined to them. The infrared camera can detect or extract a living body such as a human or animal because as the temperature of the object increases, the output level increases.

An image taken with the camera5005can be output to the screen of the display device5002(one or some of the display regions5002a,5002b,5002c, and5002d). Note that the display device5002is broadly divided into the four display regions and is composed of four display panels. For example, the display region5002acorresponds to one display panel. In this embodiment, the display device illustrated inFIG.1is used for the display region5002b, and the display device illustrated inFIG.2is used for the display regions5002aand5002b.

The display device5002is mainly used for drive support. The situation on the rear side is taken at a wide angle of view in the horizontal direction by the camera5005, and the image is displayed so that the driver can see a blind area for avoiding an accident.

In the display regions5002a,5002b,5002c, and5002d, the use of a display system including a correction circuit having a function of correcting a video signal using artificial intelligence (AI) is preferable to display a seamless image in which a seam between adjacent display regions is inconspicuous. Specifically, a correction circuit capable of correcting a video image so that discontinuity of an image at the seam between the regions can be relieved by learning of an artificial neural network (ANN) is used. Inference (recognition) is made by the ANN after the learning, whereby a video signal is corrected to compensate for discontinuity of an image. This makes it possible to display the image in which a seam is inconspicuous, so that the quality of a high-resolution image can be improved.

Since the display device5002of the flexible display region5002dis flexible, the angle of a screen of part of the display region5002dcan be changed to an angle easy for the driver to see by bending a left-edge portion5002eusing a position adjuster. It is hard to see the edge of the display region5002dfor the driver due to the distance and viewing angle. However, the left-edge portion5002eof the display region5002dis bent to have an angle the driver can see at a position suitable for a display region where an image of a side mirror is displayed in the car, which is useful.

A distance image sensor may be provided over a roof or the like of the car to display an obtained image on the display device5002. As the distance image sensor, an image sensor or a light detection and ranging (LIDAR) is used. When an image obtained by a distance image sensor and an image obtained by a CCD camera are displayed on a large display area of a display device, more information can be provided to support the driver.

When the display device5002also displays map information, traffic information, television image, DVD image, and the like, more display panels are preferably combined to increase the display area of the display device. For example, map information can be displayed on a larger screen where the display regions5002a,5002b,5002c, and5002dare combined into one screen.

In the display regions5002a,5002b,5002c, and5002d, the image display regions are not particularly determined and can be freely changed to meet the driver's preference. For example, television image and DVD image are displayed in the display region5002don the left, map information is displayed in the display region5002bat the center position, meters are displayed in the display region5002con the right, audio information are displayed in the display region5002anear a transmission gear between the driver's seat and the front passenger's seat. Owing to the combination of a plurality of display panels, a fail-safe display device can be provided. For example, even when any one of the display panels is broken for any reason, display regions can be changed so that a display panel in the other region can be alternatively used.

The installation position is limited and there is dead space between the display panel and a curved surface of the interior car body, so that the in-car space is narrowed. Flexible display panels are preferably used for the display regions5002a,5002b,5002c, and5002d, since the display panels can be installed along the curved surface of the interior car body, so that the in-car space is hardly narrowed. Note that a flat display panel may be provided in combination with a flexible display panel as long as the in-car space is not narrowed so much. For example, the display region5002amay be a flat display panel. Alternatively, the display region5002athat the driver can reach may be a touch panel so that the driver can perform input operation.

Although an example of a vehicle is described in this embodiment, one embodiment of the present invention is not limited thereto and can be used as a display device around a cockpit in an aircraft, a digital signage mounted on a cylindrical column, or can be incorporated along a curved surface of the inner or outer wall of a house or building. As illustrated inFIG.4B, a display device8605may be provided around a handle bar of a bicycle (a motor scooter, for example). Three panels are combined into one T-shaped display device as the display device8605. A motor scooter8600illustrated inFIG.4Bincludes a secondary battery8602, side mirrors8601, and indicators8603. The secondary battery8602can supply electric power to the indicators8603. In the motor scooter8600illustrated inFIG.4B, the secondary battery8602can be held in a storage unit under seat8604. The secondary battery8602can be held in the storage unit under seat8604even with a small size. The secondary battery8602is detachable, can be carried indoors when charged, and be stored before the motorcycle is driven.

Embodiment 2

In this embodiment, a method for manufacturing the display panel100illustrated inFIG.1Aof one embodiment of the present invention will be described with reference toFIGS.5A to5F. The display panel100includes a display region101and a region110transmitting visible light that is adjacent to the display region101. In a region120, for example, a wiring electrically connected to the pixels included in the display region101is provided. In addition to the wiring, driver circuits (such as a scan line driver circuit and a signal line driver circuit) for driving the pixels may be provided. Furthermore, in the region120, a terminal electrically connected to the FPC112(also referred to as a connection terminal), a wiring electrically connected to the terminal, an IC chip, and the like may be provided.

First, as illustrated inFIG.5A, a separation layer233is formed over a formation substrate231. Then, plasma treatment is performed on a surface of the separation layer233(see the arrows indicated by dotted lines inFIG.5A). Note that in this specification, a layer formed over a separation layer may be referred to as a layer to be separated.

As the formation substrate231, a substrate having at least heat resistance high enough to withstand process temperature in a fabrication process is used. As the formation the substrate231, for example, a glass substrate, a quartz substrate, a sapphire substrate, a semiconductor substrate, a ceramic substrate, a metal substrate, or a plastic substrate can be used.

Note that it is preferable to use a large-sized glass substrate as the formation substrate231in terms of productivity. For example, a glass substrate having a size greater than or equal to the 3rd generation (550 mm×650 mm) and less than or equal to the 10th generation (2950 mm×3400 mm) or a glass substrate having a larger size than the 10th generation is preferably used.

In the case where a glass substrate is used as the formation substrate231, a base film is preferably formed between the formation substrate231and the separation layer233because contamination from the glass substrate can be prevented. Examples of the base film include insulating films such as a silicon oxide film, a silicon oxynitride film, a silicon nitride film, and a silicon nitride oxide film.

As the separation layer233, an inorganic material can be used. Examples of the inorganic material include a metal, an alloy, a compound, and the like that contain any of the following elements: tungsten, molybdenum, titanium, tantalum, niobium, nickel, cobalt, zirconium, zinc, ruthenium, rhodium, palladium, osmium, iridium, and silicon. A crystal structure of a layer containing silicon may be amorphous, microcrystal, or polycrystal. The separation layer233is preferably formed using a high-melting point metal material such as tungsten, titanium, or molybdenum, in which case the degree of freedom of the process for forming the layer to be separated can be increased.

In the case where the separation layer233has a single-layer structure, a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum is preferably formed. Note that the mixture of tungsten and molybdenum corresponds to an alloy of tungsten and molybdenum, for example.

The separation layer233can be formed by, for example, a sputtering method, a chemical vapor deposition (CVD) method (e.g., a plasma CVD method, a thermal CVD method, or a metal organic CVD (MOCVD) method), an atomic layer deposition (ALD) method, a coating method (e.g., a spin coating method, a droplet discharge method, or a dispensing method), a printing method, or an evaporation method.

The thickness of the separation layer233is greater than or equal to 1 nm and less than or equal to 1000 nm, preferably greater than or equal to 1 nm and less than or equal to 200 nm, further preferably greater than or equal to 10 nm and less than or equal to 100 nm.

In the case where the separation layer233is formed to have a stacked-layer structure including a layer containing tungsten and a layer containing an oxide of tungsten, the layer containing an oxide of tungsten may be formed as follows: the layer containing tungsten is formed first and an insulating film formed of an oxide is formed thereover, so that the layer containing an oxide of tungsten is formed at the interface between the tungsten layer and the insulating film.

Alternatively, the layer containing an oxide of tungsten may be formed by performing thermal oxidation treatment, oxygen plasma treatment, nitrous oxide (N2O) plasma treatment, treatment with a highly oxidizing solution such as ozone water, or the like on the surface of the layer containing tungsten. Plasma treatment or heat treatment can be performed in an atmosphere of oxygen, nitrogen, or nitrous oxide alone, or a mixed gas of any of these gasses and another gas.

Surface condition of the separation layer233is changed by the plasma treatment or heat treatment, whereby adhesion between the separation layer233and the insulating film formed later can be controlled. A case where plasma treatment is performed is described in this embodiment as an example.

Plasma treatment is preferably performed under an atmosphere containing nitrous oxide, further preferably under an atmosphere containing nitrous oxide and silane. Thus, an oxide layer of a material included in the separation layer233can be formed on the surface of the separation layer233. In particular, when plasma treatment is performed under an atmosphere containing silane, an oxide layer with a very small thickness can be formed. The oxide layer with an extremely small thickness is not easily observed in a cross-sectional observation image.

The oxide layer contains an oxide of the material contained in the separation layer. In the case where a metal is included in the separation layer233, the oxide layer contains an oxide of the metal contained in the separation layer233. The oxide layer preferably contains tungsten oxide, titanium oxide, or molybdenum oxide.

Next, as illustrated inFIG.5B, the first insulating layer205is formed over the separation layer233, and the second insulating layer207is formed over the first insulating layer205.

Each of the first insulating layer205and the second insulating layer207can be a single layer or a multilayer using a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon nitride oxide film, or the like.

Note that in this specification, “silicon oxynitride” contains more oxygen than nitrogen. Moreover, in this specification, “silicon nitride oxide” contains more nitrogen than oxygen.

The first insulating layer205preferably contains oxygen and silicon. The first insulating layer205preferably has a single-layer structure of a silicon oxide film or a silicon oxynitride film.

It is preferable that the first insulating layer205further contain hydrogen. The first insulating layer205has a function of releasing hydrogen in a later heating step. Hydrogen is released from the first insulating layer205by heating, whereby hydrogen is supplied to the oxide layer. The first insulating layer205may further have a function of releasing hydrogen and nitrogen in the later heating step. When nitrogen is released from the first insulating layer205by heating, nitrogen is supplied to the oxide layer.

The first insulating layer205preferably includes a region in which the hydrogen concentration measured by secondary ion mass spectrometry (SIMS) is greater than or equal to 1.0×1020atoms/cm3and less than or equal to 1.0×1022atoms/cm3, preferably greater than or equal to 5.0×1020atoms/cm3and less than or equal to 5.0×1021atoms/cm3.

The first insulating layer205preferably includes a region in which the nitrogen concentration measured by SIMS is greater than or equal to 5.0×1020atoms/cm3and less than or equal to 1.0×10 23 atoms/cm3, further preferably greater than or equal to 1.0×1021atoms/cm3and less than or equal to 5.0×1022atoms/cm3.

In particular, for the first insulating layer205, a silicon oxide film or a silicon oxynitride film is preferably formed by a plasma CVD method using a deposition gas containing a silane gas and a nitrous oxide gas, in which case a large amount of hydrogen and nitrogen can be contained in the film. In addition, the proportion of the silane gas in the deposition gas is preferably higher, in which case the amount of hydrogen released from the film in a later heating step is increased.

The second insulating layer207preferably contains nitrogen and silicon. The second insulating layer207preferably has a single-layer structure of a silicon nitride film or a silicon nitride oxide film or a stacked-layer structure including a silicon nitride film or a silicon nitride oxide film. In the case where the second insulating layer207has a stacked-layer structure, the second insulating layer207preferably further includes at least one of a silicon oxide film and a silicon oxynitride film.

The second insulating layer207has a function of blocking hydrogen released from the first insulating layer205in a later heating step. The second insulating layer207may be a film that can block hydrogen and nitrogen. The second insulating layer207can suppress supply of the hydrogen (and nitrogen) from the first insulating layer205to the element layer. In addition, the hydrogen (and nitrogen) can be supplied to the oxide layer efficiently. Another layer may be provided between the first insulating layer205and the second insulating layer207.

A silicon nitride film included in the second insulating layer207is preferably formed by a plasma CVD method using a deposition gas containing a silane gas, a nitrogen gas, and an ammonia gas.

The first insulating layer205and the second insulating layer207can be formed by a sputtering method, a plasma CVD method, a coating method, a printing method, or the like. For example, each of the first insulating layer205and the second insulating layer207is formed at a temperature higher than or equal to 250° C. and lower than or equal to 400° C. by a plasma CVD method, whereby each of the first insulating layer205and the second insulating layer207can be a dense film having an excellent moisture-resistant property. Note that each of the first insulating layer205and the second insulating layer207is preferably formed to have a thickness of greater than or equal to 10 nm and less than or equal to 3000 nm, further preferably greater than or equal to 200 nm and less than or equal to 1500 nm.

Next, the separation layer233, the first insulating layer205, and the second insulating layer207are heated. Note that the heat treatment may be performed after at least part of the element layer209is formed. For example, the heat treatment may be performed after the transistor is formed and before the display element is formed. In the case where a heating step is included in the process for fabricating the element layer209, the heating step may serve as the heat treatment.

By the heat treatment, hydrogen (and nitrogen) is released from the first insulating layer205to be supplied to the oxide layer. At this time, the second insulating layer207blocks the released hydrogen (and nitrogen); thus, hydrogen (and nitrogen) can be efficiently supplied to the oxide layer.

The oxide in the oxide layer is reduced by hydrogen supplied to the oxide layer, so that many kinds of oxides with different proportions of oxygen are mixed in the oxide layer. For example, in the case where tungsten is included in the separation layer, WO3formed by plasma treatment is reduced to generate WOx(2<x<3) and WO2with proportion of oxygen lower than that of WO3, leading to a state where WO3and the oxides with lower proportions of oxygen are mixed. The crystal structure of such a mixed metal oxide depends on the proportion of oxygen; thus, the mechanical strength of the oxide layer is reduced. As a result, the oxide layer is likely to be damaged inside; thus, the separability in a later separation step can be improved.

In addition, a compound containing nitrogen and a material in the separation layer is generated by supplying nitrogen to the oxide layer. Such a compound further reduces the mechanical strength of the oxide layer, so that the separability can be increased. In the case where a metal is included in the separation layer, a compound (a metal nitride) containing the metal and nitrogen is generated in the oxide layer. For example, in the case where tungsten is included in the separation layer, tungsten nitride is generated in the oxide layer.

As the amount of hydrogen supplied to the oxide layer is larger, WO3is more likely to be reduced, which facilitates the formation of the state where many kinds of oxides with different proportions of oxygen are mixed in the oxide layer. Therefore, the force required for the separation can be reduced. As the amount of nitrogen supplied to the oxide layer is larger, the mechanical strength of the oxide layer can be reduced and the force required for the separation can be reduced. The thickness of the first insulating layer205is preferably large for increase in the amount of released hydrogen (and nitrogen). On the other hand, it is preferable that the first insulating layer205has a small thickness because the productivity is increased.

The heat treatment may be performed at a temperature higher than or equal to the temperature at which hydrogen (and nitrogen) is released from the first insulating layer205and lower than or equal to the temperature at which the formation substrate231is softened. The heating is preferably performed at a temperature greater than or equal to the temperature at which the reduction of the metal oxide in the oxide layer with hydrogen occurs. The higher the temperature of the heat treatment is, the more hydrogen (and nitrogen) is released from the first insulating layer205; thus, the separability can be improved in later steps. Note that depending on heating time and heating temperature, the separability is unnecessarily increased so that separation occurs at an unintended timing. Thus, in the case where tungsten is used for the separation layer233, the heating temperature is higher than or equal to 300° C. and less than 700° C., preferably higher than or equal to 400° C. and less than 650° C., further preferably higher than or equal to 400° C. and less than or equal to 500° C.

Although the atmosphere in which the heat treatment is performed is not particularly limited and may be an air atmosphere, it is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere or a rare gas atmosphere.

Next, as illustrated inFIG.5C, the second insulating layer207in the region110that transmits visible light is removed. The second insulating layer207may be removed by a dry etching method, a wet etching method, or the like. Note that any of etching steps included in the fabrication processes of the element layer209and the insulating layer208, or the like may serve as the removal step of the second insulating layer207.

In one embodiment of the present invention, the second insulating layer207is provided over the entire surface of the separation layer233until the heat treatment is performed. After the heat treatment, the second insulating layer207in the region110that transmits visible light is removed. Accordingly, the separability in the region110that transmits visible light can be prevented from being lower than that in the other region. Thus, the separability of the entire display panel can be uniform. An influence of the structure of the region110that transmits visible light on the yield of the fabrication process of the display panel can be suppressed.

Next, as illustrated inFIG.5D, the element layer209, the insulating layer208, and the connection terminal223are formed over the second insulating layer207. The insulating layer208is formed to cover the display element included in the element layer209. It is preferable that an insulating layer included in the element layer209and the insulating layer208not be included in the region110that transmits visible light.

Next, a substrate235bonded to the formation substrate231in a later step is prepared. A separation layer237is formed over the substrate235. Then, plasma treatment is performed on a surface of the separation layer237(see the arrows indicated by dotted lines inFIG.5E).

Next, as illustrated inFIG.5F, a third insulating layer215is formed over the separation layer237, a fourth insulating layer217is formed over the third insulating layer215, and a functional layer219is formed over the fourth insulating layer217.

Note that heat treatment is performed after the fourth insulating layer217is formed and before part of the fourth insulating layer217is removed. The separation layer237, the third insulating layer215, and the fourth insulating layer217may be heated before the functional layer219is formed. Alternatively, the heat treatment may be performed after at least part of the functional layer219is formed. In the case where the process for fabricating the functional layer219includes a heating step, the heating step may serve as the heat treatment.

By the heat treatment, the separability in a later separation step can be improved.

Next, as illustrated inFIG.5G, the fourth insulating layer217in the region110that transmits visible light is removed. The fourth insulating layer217may be removed by a dry etching method, a wet etching, or the like. Note that any of etching steps included in the fabrication process of the functional layer219may serve as the removal step of the fourth insulating layer217.

In one embodiment of the present invention, the fourth insulating layer217is provided over the entire surface of the separation layer237until the heat treatment is performed. After the heat treatment, the fourth insulating layer217in the region110that transmits visible light is removed. Accordingly, the separability of the entire display panel can be uniform. An influence of the structure of the region110that transmits visible light on the yield of the fabrication process of the display panel can be suppressed.

Next, the formation substrate231and the substrate235are attached to each other by the bonding layer221(seeFIG.6A).

As the substrate235, various substrates that can be used as the formation substrate231can be used. A flexible substrate may be used. Alternatively, as the substrate235, a substrate provided with a functional element such as a semiconductor element (e.g., a transistor), a light-emitting element (e.g., an organic EL element), a liquid crystal element, or a sensor element, a color filter, and the like in advance may be used.

As the bonding layer221, a variety of curable adhesives such as a photocurable adhesive (e.g., an ultraviolet curable adhesive), a reactive curable adhesive, a thermosetting adhesive, and an anaerobic adhesive can be used. Alternatively, as the bonding layer221, an adhesive with which the substrate235and the first insulating layer205can be separated when necessary, such as a water-soluble resin, a resin soluble in an organic solvent, a resin that is capable of being plasticized upon irradiation with UV light, or the like may be used.

Then, the separation layer233is separated from the first insulating layer205.

For the separation, for example, the formation substrate231or the substrate235is fixed to a suction stage and a separation starting point is formed between the separation layer233and the first insulating layer205. The separation starting point may be formed by, for example, inserting a sharp instrument such as a knife between the layers. Alternatively, the separation starting point may be formed by irradiating part of the separation layer233with laser light to melt the part of the separation layer233. The separation starting point may be formed by dripping liquid (e.g., alcohol, water, or water containing carbon dioxide) onto an end portion of the separation layer233and the first insulating layer205so that the liquid penetrates into an interface between the separation layer233and the first insulating layer205by using capillary action.

Then, physical force (a separation process with a human hand or with a gripper, a separation process by rotation of a roller, or the like) is gently applied to the area where the separation starting point is formed in a direction substantially perpendicular to the bonded surfaces, so that separation can be caused without damage to the layer to be separated. For example, separation may be caused by attaching tape or the like to the formation substrate231or the substrate235and pulling the tape in the aforementioned direction, or separation may be caused by pulling an end portion of the formation substrate231or the substrate235with a hook-like member. Alternatively, separation may be caused by pulling an adhesive member or a member capable of vacuum suction attached to the back side of the formation substrate231or the substrate235.

Here, if separation is performed in such a manner that liquid containing water such as water or an aqueous solution is added to the separation interface and the liquid penetrates into the separation interface, the separability can be improved. Furthermore, an adverse effect of static electricity caused at separation on the functional element included in the layer to be separated (e.g., damage to a semiconductor element from static electricity) can be suppressed.

By the above method, the layer to be separated can be separated from the formation substrate231with a high yield.

After that, the substrate201is attached to the first insulating layer205with the bonding layer203inserted between (FIG.6B). The bonding layer203can be formed using a material for the bonding layer221. The substrate201can be formed using a material for the substrate235.

By using flexible substrates as the substrates201and235, a flexible display panel can be fabricated. Note that in the case where the substrate235functions as a temporary supporting substrate, the substrate235and the separation layer237are separated from the layer to be separated, and the separated layer may be attached to a substrate211(for example, a flexible substrate) using a bonding layer213.

As described above, in the method for manufacturing a display panel of one embodiment of the present invention, the heat treatment is performed while the first insulating layer205and the second insulating layer207are formed over the entire surface of the separation layer233; thus, the separability of the entire display panel can be uniformly increased. Furthermore, the second insulating layer207in the region110that transmits visible light is removed after the heat treatment, so that the reflectance in the region110that transmits visible light can be reduced.

Moreover, in the method for manufacturing a display panel of one embodiment of the present invention, a functional element is formed over a formation substrate, separated from the formation substrate, and then transferred to another substrate. Thus, there is almost no limitation on the temperature in formation steps of a functional element. Thus, a functional element with extremely high reliability that is manufactured through a high-temperature process can be manufactured over a flexible substrate with poor heat resistance with a high yield. Thus, a highly reliable flexible display panel can be obtained.

In this embodiment, a display panel employing a separate coloring method and having a top-emission structure is described as an example.

FIG.7Cis a cross-sectional view of a display panel370A employing a separate coloring method and having a top-emission structure.FIG.7Ccorresponds to cross-sectional views along dashed-dotted lines A1-A2and A3-A4in each ofFIGS.7A and7B.FIGS.7A and7Bshow top views of the display panel370A.

The display panel370A includes the substrate201, the bonding layer203, the insulating layer205, a plurality of transistors, a capacitor305, a conductive layer307, an insulating layer312, an insulating layer313, an insulating layer314, an insulating layer315, a light-emitting element304, a conductive layer355, a spacer316, a bonding layer317, the substrate211, the bonding layer213, and the insulating layer215.

The layers included in the region110transmitting visible light transmit visible light.FIG.14Cillustrates an example where the region110transmitting visible light includes the substrate201, the bonding layer203, the insulating layer205, a gate insulating layer311, the insulating layer312, the insulating layer313, the insulating layer314, the bonding layer317, the insulating layer215, the bonding layer213, and the substrate211. In this stacked-layer structure, the materials for the layers are preferably selected such that a difference in refractive index at each interface is minimized.

The driver circuit portion382includes a transistor301. The display portion381includes a transistor302and a transistor303.

Each transistor includes a gate, the gate insulating layer311, a semiconductor layer, a source, and a drain. The gate and the semiconductor layer overlap with each other with the gate insulating layer311provided therebetween. Part of the gate insulating layer311functions as a dielectric of the capacitor305. The conductive layer functioning as the source or the drain of the transistor302serves as one electrode of the capacitor305.

FIG.7Cshows a bottom gate transistor. The structure of the transistor may be different between the driver circuit portion382and the display portion381. The driver circuit portion382and the display portion381may each include a plurality of kinds of transistors.

The capacitor305includes a pair of electrodes and the dielectric therebetween. The capacitor305includes a conductive layer that is formed using the same material and the same step as the gate (the lower gate) of the transistor and a conductive layer that is formed using the same material and the same step as the source and the drain of the transistor.

A material through which impurities such as water and hydrogen do not easily diffuse is preferably used for at least one of the insulating layers312,313, and314. Diffusion of impurities from the outside into the transistors can be effectively inhibited, leading to improved reliability of the display panel. The insulating layer314functions as a planarization layer. In the example illustrated inFIG.7C, the insulating layer314is formed using an organic material and extends over the entire area of the display panel. Such a structure is preferable because the yield of the peeling process can be increased. Alternatively, a structure can be employed in which the insulating layer formed using an organic material is not placed in an end portion of the display panel. This structure can inhibit entry of impurities into the light-emitting element304.

The insulating layer205and the substrate201are attached to each other with the bonding layer203. The insulating layer215and the substrate211are attached to each other with the bonding layer213.

In the display portion381, the light-emitting element304is positioned between the insulating layer205and the insulating layer215. Entry of impurities into the light-emitting element304from the thickness direction of the display panel370A is suppressed. Similarly, a plurality of insulating layers covering the transistors are provided in the display portion381, and thus entry of impurities into the transistors is suppressed.

The light-emitting element304, the transistors, and the like are preferably provided between a pair of insulating films that are highly resistant to moisture, in which case entry of impurities such as water into these elements can be suppressed, leading to higher reliability of the display panel.

Examples of the insulating film highly resistant to moisture include a film containing nitrogen and silicon (e.g., a silicon nitride film and a silicon nitride oxide film) and a film containing nitrogen and aluminum (e.g., 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 highly resistant to moisture 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)].

In the case where the insulating layer314is formed using an organic material, impurities such as moisture might enter the light-emitting element304and the like from the outside of the display panel through the insulating layer314exposed at an end portion of the display panel. Deterioration of the light-emitting element304due to the entry of an impurity leads to deterioration of the display panel. Thus, as illustrated in a portion near a connection portion306inFIG.7C, it is preferable that an opening that reaches an inorganic film (here, the insulating layer313) be formed in the insulating layer314so that an impurity such as moisture entering from the outside of the display panel does not easily reach the light-emitting element304.

The light-emitting element304includes an electrode321, an EL layer322, and an electrode323. The light-emitting element304may include an optical adjustment layer324. The light-emitting element304emits light to the substrate211side.

The transistor, the capacitor, the wiring, and the like are provided to overlap with a light-emitting region of the light-emitting element304, whereby an aperture ratio of the display portion381can be increased.

One of the electrode321and the electrode323functions as an anode and the other functions as a cathode. When a voltage higher than the threshold voltage of the light-emitting element304is applied between the electrode321and the electrode323, holes are injected to the EL layer322from the anode side and electrons are injected to the EL layer322from the cathode side. The injected electrons and holes are recombined in the EL layer322and a light-emitting substance contained in the EL layer322emits light.

The electrode321is electrically connected to the source or the drain of the transistor303, directly or through another conductive layer. The electrode321functions as a pixel electrode and is provided for each light-emitting element304. Two adjacent electrodes321are electrically insulated from each other by the insulating layer315.

The EL layer322is a layer containing a light-emitting material. As the light-emitting element304, an organic EL element including an organic compound as a light-emitting material can be favorably used.

The EL layer322includes at least one light-emitting layer.

As a light-emitting material, a quantum dot can be used. A quantum dot is a semiconductor nanocrystal with a size of several nanometers and contains approximately 1×103to 1×106atoms. Since energy shift of quantum dots depends on their size, quantum dots made of the same substance emit light with different wavelengths depending on their size; thus, emission wavelengths can be easily adjusted by changing the size of quantum dots.

A quantum dot has an emission spectrum with a narrow peak, leading to emission with high color purity. In addition, a quantum dot is said to have a theoretical internal quantum efficiency of approximately 100%, and a quantum dot can be used as a light-emitting material to obtain a light-emitting element having high light emission efficiency. Furthermore, since a quantum dot that is an inorganic compound has high inherent stability, a light-emitting element that is favorable also in terms of lifetime can be obtained.

Examples of a material of a quantum dot include a Group 14 element in the periodic table, a Group 15 element in the periodic table, a Group 16 element in the periodic table, a compound of a plurality of Group 14 elements in the periodic table, a compound of an element belonging to any of Groups 4 to 14 in the periodic table and a Group 16 element in the periodic table, a compound of a Group 2 element in the periodic table and a Group 16 element in the periodic table, a compound of a Group 13 element in the periodic table and a Group 15 element in the periodic table, a compound of a Group 13 element in the periodic table and a Group 17 element in the periodic table, a compound of a Group 14 element in the periodic table and a Group 15 element in the periodic table, a compound of a Group 11 element in the periodic table and a Group 17 element in the periodic table, iron oxides, titanium oxides, spinel chalcogenides, and semiconductor clusters.

As examples of a material included in a quantum dot, cadmium selenide, cadmium sulfide, cadmium telluride, zinc sulfide, indium phosphide, lead selenide, lead sulfide, a compound of selenium, zinc, and cadmium, a compound of cadmium, selenium, and sulfur, and the like can be given. What is called an alloyed quantum dot, whose composition is represented by a given ratio, may be used. For example, an alloyed quantum dot of cadmium, selenium, and sulfur is a means effective in obtaining blue light because the emission wavelength can be changed by changing the content ratio of elements.

As the quantum dot, any of a core-type quantum dot, a core-shell quantum dot, a core-multishell quantum dot, and the like can be used. It is preferable to use a core-shell or core-multishell quantum dot because the quantum efficiency of light emission can be significantly improved. Examples of the material of a shell include zinc sulfide and zinc oxide.

Quantum dots have a high proportion of surface atoms and thus have high reactivity and easily cohere together. For this reason, it is preferable that a protective agent be attached to, or a protective group be provided at the surfaces of quantum dots. In this manner, cohesion of quantum dots can be prevented and solubility in a solvent can be increased. It can also reduce reactivity and improve electrical stability.

The range of size (diameter) of quantum dots is usually greater than or equal to 0.5 nm and less than or equal to 20 nm, preferably greater than or equal to 1 nm and less than or equal to 10 nm. The emission spectra are narrowed as the size distribution of the quantum dots gets smaller, and thus light can be obtained with high color purity. The shape of the quantum dots is not particularly limited and may be a spherical shape, a rod shape, a circular shape, or the like.

Even when a light-emitting layer is composed of quantum dots and made without a host material, the quantum dots enable light emission efficiency to be ensured; thus, a light-emitting element that is favorable in terms of a lifetime can be obtained. In the case where the light-emitting layer is composed of quantum dots, the quantum dots preferably have core-shell structures (including core-multishell structures).

The electrode323functions as a common electrode and is provided for a plurality of light-emitting elements304. A fixed potential is supplied to the electrode323.

Note that one embodiment of the present invention is not limited to the separate coloring method, and a color filter method, a color conversion method, a quantum dot method, and the like may be employed.

The light-emitting element304overlaps with the coloring layer325with the bonding layer317provided therebetween. The spacer316overlaps with the light-blocking layer326with the bonding layer317provided therebetween. AlthoughFIG.7Cillustrates the case where a space is provided between the light-emitting element304and the light-blocking layer326, the light-emitting element304and the light-blocking layer326may be in contact with each other. Although the spacer316is provided on the substrate201side in the structure illustrated inFIG.7C, the spacer316may be provided on the substrate211side (e.g., in a position closer to the substrate201than that of the light-blocking layer326).

The coloring layer is a colored layer that transmits light in a specific wavelength range. For example, a color filter that transmits light in a specific wavelength range, such as red, green, blue, or yellow light, can be used. Examples of materials that can be used for the coloring layer include a metal material, a resin material, and a resin material containing a pigment or dye.

The light-blocking layer is provided between the adjacent coloring layers. The light-blocking layer blocks light emitted from an adjacent light-emitting element to inhibit color mixture between adjacent light-emitting elements. Here, the coloring layer is provided such that its end portion overlaps with the light-blocking layer, whereby light leakage can be reduced. For the light-blocking layer, a material that blocks light from the light-emitting element can be used; for example, a black matrix can be formed using a metal material or a resin material containing pigment or dye. Note that it is preferable to provide the light-blocking layer in a region other than a pixel portion, such as a driver circuit, in which case undesired leakage of guided light or the like can be suppressed.

The connection portion306includes the conductive layer307and the conductive layer355. The conductive layer307and the conductive layer355are electrically connected to each other. The conductive layer307can be formed using the same material and the same step as those of the source and the drain of the transistor. The conductive layer355is electrically connected to an external input terminal through which a signal or a potential from the outside is transmitted to the driver circuit portion382. Here, an example in which an FPC373is provided as an external input terminal is shown. The FPC373and the conductive layer355are electrically connected to each other through a connector319.

As the connector319, any of various anisotropic conductive films (ACF), anisotropic conductive pastes (ACP), and the like can be used.

The transistors301,302, and303each include a gate, the gate insulating layer311, a semiconductor layer, a source, and a drain.FIG.9illustrates a bottom gate transistor.

A display panel may include an overcoat. The overcoat can prevent impurities and the like contained in the coloring layer325from being diffused into the light-emitting element304. The overcoat is formed using a material that transmits light emitted from the light-emitting element304. For example, it is possible to use an inorganic insulating film such as a silicon nitride film or a silicon oxide film, an organic insulating film such as an acrylic film or a polyimide film, or a stacked layer of an organic insulating film and an inorganic insulating film.

A flexible substrate is preferably used as each of the substrates201and211. For example, a material such as glass, quartz, a resin, a metal, an alloy, or a semiconductor thin enough to have flexibility can be used. The substrate through which light is extracted from the light-emitting element is formed using a material that transmits the light. For example, the thickness of the flexible substrate is preferably greater than or equal to 1 μm and less than or equal to 200 μm, further preferably greater than or equal to 1 μm and less than or equal to 100 μm, still further preferably greater than or equal to 10 μm and less than or equal to 50 μm, and particularly preferably greater than or equal to 10 μm and less than or equal to 25 μm. The thickness and hardness of the flexible substrate are set in the range where mechanical strength and flexibility can be balanced against each other. The flexible substrate may have a single-layer structure or a stacked-layer structure.

A resin, that has a specific gravity smaller than that of glass, is preferably used for the flexible substrate, in which case the display panel can be lightweight as compared with the case where glass is used.

The substrate is preferably formed using a material with high toughness. In that case, a display panel with high impact resistance that is less likely to be broken can be provided. For example, when a resin substrate or a thin metal or alloy substrate is used, the display panel can be lightweight and unlikely to be broken as compared with the case where a glass substrate is used.

A metal material and an alloy material, which have high thermal conductivity, are preferable because they can easily conduct heat to the whole substrate and accordingly can suppress a local temperature rise in the display panel. The thickness of a substrate using a metal material or an alloy material is preferably greater than or equal to 10 μm and less than or equal to 200 μm, further preferably greater than or equal to 20 μm and less than or equal to 50 μm.

There is no particular limitation on a material of the metal substrate or the alloy substrate, but it is preferable to use, for example, aluminum, copper, nickel, or a metal alloy such as an aluminum alloy or stainless steel. Examples of a material for a semiconductor substrate include silicon and the like.

Furthermore, when a material with high thermal emissivity is used for the substrate, increase of the surface temperature of the display panel can be suppressed, and breakage or a decrease in reliability of the display panel can be suppressed. For example, the substrate may have a stacked-layer structure of a metal substrate and a layer with high thermal emissivity (the layer can be formed using a metal oxide or a ceramic material, for example).

Examples of materials having flexibility and a light-transmitting property include polyester resins such as PET and PEN, a polyacrylonitrile resin, an acrylic resin, a polyimide resin, a polymethyl methacrylate resin, a PC resin, a PES resin, polyamide resins (such as nylon and aramid), a polysiloxane resin, a cycloolefin resin, a polystyrene resin, a polyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polypropylene resin, a PTFE resin, and an ABS resin. In particular, a material with a low coefficient of linear expansion is preferred, and for example, a polyamide imide resin, a polyimide resin, a polyamide resin, or PET can be suitably used. A substrate in which a fibrous body is impregnated with a resin, a substrate whose linear thermal expansion coefficient is reduced by mixing an inorganic filler with a resin, or the like can also be used.

The flexible substrate may have a stacked-layer structure in which at least one of a hard coat layer (e.g., a silicon nitride layer) by which a surface of the device is protected from damage, a layer for dispersing pressure (e.g., an aramid resin layer), and the like is stacked over a layer of any of the above-mentioned materials. A substrate that can be used as the protective substrate132may be used.

When a glass layer is used for the flexible substrate, a barrier property against water and oxygen can be improved and thus a highly reliable display panel can be provided.

For the bonding layer, various curable adhesives such as a photocurable adhesive (e.g., an ultraviolet curable adhesive), a reactive curable adhesive, a thermosetting adhesive, and an anaerobic adhesive can be used. Alternatively, an adhesive sheet or the like may be used.

Furthermore, the bonding layer may include a drying agent. For example, it is possible to use a substance that adsorbs moisture by chemical adsorption, such as oxide of an alkaline earth metal (e.g., calcium oxide or barium oxide). Alternatively, it is possible to use a substance that adsorbs moisture by physical adsorption, such as zeolite or silica gel. The drying agent is preferably included because entry of impurities such as moisture into the functional element can be suppressed, thereby improving the reliability of the display panel.

When a filler with a high refractive index or a light scattering member is contained in the bonding layer, the efficiency of light extraction from the light-emitting element can be improved. For example, titanium oxide, barium oxide, zeolite, or zirconium can be used.

As the light-emitting element, a self-luminous element can be used, and an element whose luminance is controlled by current or voltage is included in the category of the light-emitting element. For example, a light-emitting diode (LED), an organic EL element, an inorganic EL element, or the like can be used. Any of a variety of display elements can be used in the display panel of one embodiment of the present invention. For example, a liquid crystal element, an electrophoretic element, a display element using MEMS, or the like may be used.

The light-emitting element may be a top-emission, bottom-emission, or dual-emission light-emitting element. 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 light is not extracted.

The conductive film that transmits visible light can be formed using, for example, indium oxide, ITO, indium zinc oxide, zinc oxide (ZnO), or ZnO to which gallium is added. Alternatively, a film of 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; or a nitride of any of these metal materials (e.g., titanium nitride) can be formed thin so as to have a light-transmitting property. Alternatively, a stacked film of any of the above materials can be used as the conductive film. For example, a stacked film of ITO 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 that reflects visible light, 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.

Furthermore, lanthanum, neodymium, germanium, or the like may be added to the metal material or the alloy. Furthermore, an alloy containing aluminum (an aluminum alloy) such as an alloy of aluminum and titanium, an alloy of aluminum and nickel, an alloy of aluminum and neodymium, or an alloy of aluminum, nickel, and lanthanum (Al—Ni—La); or an alloy containing silver such as an alloy of silver and copper, an alloy of silver, palladium, and copper (also referred to as Ag—Pd—Cu or APC), or an alloy of silver and 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 on and in contact with an aluminum alloy film, oxidation of the aluminum alloy film can be suppressed. Examples of materials 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 film of silver and ITO or a stacked film of an alloy of silver and magnesium and ITO can be used.

Each of the electrodes can 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.

The EL layer322includes at least one light-emitting layer. The EL layer322may include a plurality of light-emitting layers. In addition to the light-emitting layer, the EL layer322can further include one or more layers containing any of 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.

For the EL layer322, either a low molecular compound or a high molecular compound can be used, and an inorganic compound may also be used. Each of the layers included in the EL layer322can be formed by any of the following methods: an evaporation method (including a vacuum evaporation method), a transfer method, a printing method, an inkjet method, a coating method, and the like.

The light-emitting element304may contain two or more kinds of light-emitting substances. Thus, for example, a light-emitting element that emits white light can be achieved. For example, light-emitting substances are selected so that two or more kinds of light-emitting substances emit complementary colors to obtain white light emission. A light-emitting substance that emits red (R) light, green (G) light, blue (B) light, yellow (Y) light, or orange (O) light or a light-emitting substance that emits light containing spectral components of two or more of R light, G light, and B light can be used, for example.

Moreover, the light-emitting element304may be a single element including one EL layer or a tandem element in which EL layers are stacked with a charge generation layer provided therebetween.

The structure of the transistors in the display panel is not particularly limited. For example, a planar transistor, a forward staggered transistor, or an inverted staggered transistor may be used. Atop-gate transistor or a bottom-gate transistor may be used. 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 an amorphous semiconductor or a semiconductor having crystallinity (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 semiconductor having crystallinity be used, in which case deterioration of the transistor characteristics can be suppressed.

A semiconductor material used for the semiconductor layer of the transistor is not particularly limited, and for example, a Group 14 element, a compound semiconductor, or an oxide semiconductor can be used. Typically, a semiconductor containing silicon, a semiconductor containing gallium arsenide, an oxide semiconductor containing indium, or the like can be used.

An oxide semiconductor is preferably used as a semiconductor where a channel of the transistor is formed. In particular, an oxide semiconductor having a wider band gap than silicon is preferably used. A semiconductor material having a wider band gap and a lower carrier density than silicon is preferably used because off-state current of the transistor can be reduced.

For example, the oxide semiconductor preferably contains at least indium (In) or zinc (Zn). Further preferably, the oxide semiconductor contains an oxide represented by an In-M-Zn oxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, Hf, or Nd).

A c-axis aligned crystalline oxide semiconductor (CAAC-OS) is preferably used as a semiconductor material for the transistors. Unlike an amorphous semiconductor, the CAAC-OS has few defect states, so that the reliability of the transistor can be improved. Moreover, since no grain boundary is observed in the CAAC-OS, a stable and uniform film can be formed over a large area, and stress that is caused by bending a flexible display device does not easily make a crack in a CAAC-OS film.

The CAAC-OS is a crystalline oxide semiconductor in which c-axes of crystals are oriented in a direction substantially perpendicular to the film surface. It has been found that oxide semiconductors have a variety of crystal structures other than a single-crystal structure. An example of such structures is a nano-crystal (nc) structure, which is an aggregate of nanoscale microcrystals. The crystallinity of a CAAC-OS structure is lower than that of a single-crystal structure and higher than that of an nc structure.

The CAAC-OS has c-axis alignment, its pellets (nanocrystals) are connected in an a-b plane direction, and the crystal structure has distortion. For this reason, the CAAC-OS can also be referred to as an oxide semiconductor including a c-axis-aligned a-b-plane-anchored (CAA) crystal.

An organic insulating material or an inorganic insulating material can be used for the insulating layers included in the display panel. Examples of resins include an acrylic resin, an epoxy resin, a polyimide resin, a polyamide resin, a polyimide-amide resin, a siloxane resin, a benzocyclobutene-based resin, and a phenol resin. Examples of inorganic insulating films include a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, a silicon nitride film, an aluminum oxide film, a hafnium oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, and a neodymium oxide film.

The conductive layers included in the display panel can each have a single-layer structure or a stacked-layer structure including any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten or an alloy containing any of these metals as its main component. Alternatively, a light-transmitting conductive material such as indium oxide, ITO, indium oxide containing tungsten, indium zinc oxide containing tungsten, indium oxide containing titanium, ITO containing titanium, indium zinc oxide, ZnO, ZnO to which gallium is added, or indium tin oxide containing silicon may be used. Alternatively, a semiconductor such as an oxide semiconductor or polycrystalline silicon whose resistance is lowered by containing an impurity element or the like, or silicide such as nickel silicide may be used. A film including graphene may be used as well. The film including graphene can be formed, for example, by reducing a film containing graphene oxide. A semiconductor such as an oxide semiconductor containing an impurity element may be used. Alternatively, the conductive layers may be formed using a conductive paste of silver, carbon, copper, or the like or a conductive polymer such as a polythiophene. A conductive paste is preferable because it is inexpensive. A conductive polymer is preferable because it is easily applied.

FIG.8is an example of a cross-sectional view of a display device including two display panels370A illustrated inFIG.7Cthat overlap with each other.

FIG.8illustrates the display region101a(corresponding to the display portion381inFIG.7C) and the region120athat blocks visible light (corresponding to the driver circuit portion382and the like inFIG.7C) of a lower display panel, and the display region101b(corresponding to the display portion381inFIG.7C) and the region110bthat transmits visible light (corresponding to the region110that transmits visible light inFIG.7C) of an upper display panel.

In the display device illustrated inFIG.8, the display panel positioned on the display surface side (upper side) includes the region110bthat transmits visible light adjacent to the display region101b. The display region101aof the lower display panel and the region110bthat transmits visible light of the upper display panel overlap with each other. Thus, a non-display region that appears between the display regions of the two display panels overlapping with each other can be reduced or even removed. Accordingly, a large display device in which a seam between display panels is less likely to be noticed by a user can be obtained.

The display device illustrated inFIG.8includes the light-transmitting layer103having a refractive index higher than that of air and transmitting visible light between the display region101aand the region110bthat transmits visible light. In that case, air can be prevented from entering between the display region101aand the region110bthat transmits visible light, so that the interface reflection due to a difference in refractive index can be reduced. In addition, display unevenness or luminance unevenness of the display device can be suppressed.

The light-transmitting layer103may overlap with the entire surface of the substrate211of the lower display panel or that of the substrate201of the upper display panel, or may overlap with only the display region101aand the region110bthat transmits visible light. In addition, the light-transmitting layer103may overlap with the region120athat blocks visible light.

For example, an attachment film in which attachment layers are provided on both surfaces of a base material can be used as the light-transmitting layer103.

The reflection of light in the region110bthat transmits visible light is suppressed. Thus, an area in which the two display panels overlap with each other (an overlapping area) is less likely to be seen by a user of the display device. Moreover, in the display in the display region101a, a difference in luminance between a portion seen through the region110bthat transmits visible light and a portion seen not through the region can be small.

<Example of Cross-Sectional Structure of Display Panel>

FIG.9is a cross-sectional view of a display panel370C employing a color filter method and having a top-emission structure.

The display panel370C is different from the display panel370A in that the EL layer is shared by a plurality of light-emitting elements, each transistor does not include a back gate, and a coloring layer325and a light-blocking layer326are provided.

In the display panel370D, the light-emitting element304emits light to the coloring layer325side.

Owing to the combination of a color filter (the coloring layer325) and a microcavity structure (the optical adjustment layer324), light with high color purity can be extracted from the display panel. The thickness of the optical adjustment layer324is varied depending on the color of the pixel.

The coloring layer is a colored layer that transmits light in a specific wavelength range. For example, a color filter that transmits light in a specific wavelength range, such as red, green, blue, or yellow light, can be used. Examples of materials that can be used for the coloring layer include a metal material, a resin material, and a resin material containing a pigment or dye.

The light-blocking layer is provided between the adjacent coloring layers. The light-blocking layer blocks light emitted from an adjacent light-emitting element to inhibit color mixture between adjacent light-emitting elements. Here, the coloring layer is provided such that its end portion overlaps with the light-blocking layer, whereby light leakage can be reduced. For the light-blocking layer, a material that blocks light from the light-emitting element can be used; for example, a black matrix can be formed using a metal material or a resin material containing a pigment or dye. Note that it is preferable to provide the light-blocking layer in a region other than a pixel portion, such as a driver circuit, in which case undesired leakage of guided light or the like can be suppressed.

A display panel may include an overcoat. The overcoat can prevent impurities and the like contained in the coloring layer325from being diffused into the light-emitting element304. The overcoat is formed using a material that transmits light emitted from the light-emitting element304. For example, it is possible to use an inorganic insulating film such as a silicon nitride film or a silicon oxide film, an organic insulating film such as an acrylic film or a polyimide film, or a stacked layer of an organic insulating film and an inorganic insulating film.

This embodiment can be freely combined with Embodiment 1.

Example 1

<Display Panel>

First, the display panel used in the display device in this example is described.

FIG.10Ais a schematic view of the display panel in this example. The display panel illustrated inFIG.10Awas an active matrix organic EL display that had the light-emitting portion250with a size of 13.5 inches diagonally, 1280×720 effective pixels, a resolution of 108 ppi, and an aperture ratio of 41.3%. The display panel includes a demultiplexer (DeMUX)253serving as a source driver. In addition, the display panel also included the scan driver255. Two sides of the light-emitting portion250are in contact with a region251transmitting visible light. A lead wiring257is provided along the other two sides.

A channel-etched transistor including a CAAC-OS was used as a transistor. Note that an In—Ga—Zn-based oxide was used for the oxide semiconductor.

As the light-emitting element, an organic EL element employing a separate coloring method and having a top-emission structure was used. The light-emitting element has a top emission structure combined with a color filter, where light generated by the light-emitting element is extracted to the outside of the display panel through the color filter.

FIG.10Bis a schematic view of a display device in which three display panels overlap with each other to have a T shape.FIG.10Cshows a cross-sectional schematic view taken along a dashed dotted line X-Y of the display device ofFIG.10B.

The display device in this example was formed by overlapping a plurality of display panels so that a non-display region between display regions was small. Specifically, the light-transmitting layer103was provided between the region251transmitting visible light of an upper display panel and the light-emitting portion250of a lower display panel.

A component that blocks visible light such as a lead wiring or a driver is not provided at all from an end portion of the light-emitting portion250to an end portion of the display panel along two sides of the display panel, and the region along two sides serves as the region251transmitting visible light. The width of the region251transmitting visible light of the display panel was approximately 5 mm. The thickness T of the region251that transmits visible light (also referred to as a thickness of one display panel) is very small, which is approximately 110 μm. Therefore, although the display device in this example had a region in which at most three display panels overlapped with each other, a step formed on the display surface side was extremely small; thus, a seam hardly stood out.

Each of the three display panels has flexibility. For example, as illustrate inFIG.10C, a region near an FPC373aof the lower display panel can be bent so that part of the lower display panel and part of the FPC373acan be placed under the light-emitting portion250of the upper display panel adjacent to the FPC373a. As a result, the FPC373acan be placed without physical interference with the rear surface of the upper display panel. In this way, another display panel can be provided on any one or more of the four sides of the display panel, whereby a large-sized display device is easily realized.

In this example, an attachment film including attachment layers on both surfaces of a base material was used as the light-transmitting layer103. With use of the attachment film, two display panels included in the display device can be detachably attached to each other. An attachment layer on one side of the light-transmitting layer103was attached to a substrate211a, and an attachment layer on the other side of the light-transmitting layer103was attached to a substrate201b.

InFIG.10B, the light-transmitting layer103includes not only a portion overlapping with the region251that transmits visible light, but also a portion overlapping with the light-emitting portion250. InFIG.10C, the light-transmitting layer103overlaps with the entire region251that transmits visible light from an end portion of the substrate201b, and also overlaps with part of a region155bcontaining a display element. Note that the light-transmitting layer103is not provided on a curved region of the display panel that is close to a region to which the FPC373ais connected illustrated inFIG.10C. However, the light-transmitting layer103may be provided on a curved portion of the display panel depending on the thickness or flexibility of the light-transmitting layer103.

Each of the display panels was formed by attaching a substrate and an element layer with a bonding layer. For example, as illustrated inFIG.10C, a substrate201a, the substrate211a, the substrate201b, and a substrate211bare attached to an element layer153a, the element layer153a, an element layer153b, and the element layer153brespectively, with a bonding layer157. The element layer153ahas a region155aincluding a display element and a region156aincluding a wiring electrically connected to the display element. Similarly, the element layer153bhas the region155bincluding a display element and a region156bincluding a wiring electrically connected to the display element.

As illustrated inFIG.10C, one of the three display panels is fixed to the member501having a curved surface with the buffer plate500provided therebetween.

In this example, a member, a guide portion, and the like that serve as part of a display device are designed, and flexible display panels are fixed to the member having a curved surface with a buffer plate provided therebetween. The curved surface of the member has a radius of curvature of 780 mm. As the buffer plate, a 0.5-mm-thick aluminum plate is used. In this example, one of the three display panels illustrated inFIG.10Bthat overlaps with the other two display panels on one side is fixed to a member having a curved surface with a buffer plate provided therebetween.FIG.15Ais a photograph showing an image displayed on the display panels.FIG.15Bis a photograph from an oblique angle. Note that a car navigation image is displayed on the display device shown inFIGS.15A and15B.

FIG.11is a side view of a design including a member which overlaps with a display panel, a guide portion, and the like.FIG.12Ais a rear view seen from the printed circuit board side.

InFIG.11andFIG.12A, four leg portions510are provided so that the display panel faces upward. InFIG.11andFIG.12A, explanation will be made using the same reference numerals for the portions that are common to those inFIG.1. Note that a display panel and an FPC are not illustrated inFIG.11andFIG.12A.

FIG.12Bis a photograph taken from the printed circuit board side in which the display panel and the FPC are connected to each other.FIG.13is a photograph taken from the side in which the display panel and the FPC are connected to each other.

FIG.14Ais a perspective view of the display panel whose display surface faces upward.FIG.14Bis a photograph taken from the above of the display panel in which four leg portions510are contact with the top surface of a desk.

FIG.14Cshows the results of a thermal shock preservation test.FIG.14Cis a photograph after preservation at 40° C. for 12 hours, returning to 0° C. for 12 hours, and preservation at room temperature. As shown inFIG.14C, no creases is caused after the preservation test and there is almost no change in the appearance.

An acrylic resin was used as the member501subjected to a preservation test. The same result was obtained when a glass epoxy resin was used instead of the acrylic resin under the same preservation test. It can be said that generation of creases is suppressed by the buffer plate500. Note that the acrylic resin is preferable for the member501because the weight and cost of the glass epoxy resin are higher than those of the acrylic resin.

A flexible display panel is mounted on a member having a curved surface and formed of an acrylic resin with a buffer plate provided therebetween, so that a kawara display composed of a plurality of flexible display panels can be achieved.

REFERENCE NUMERALS

20acrylic plate100display panel101adisplay region101bdisplay region103light-transmitting layer112FPC120terminal electrode120aregion132protective substrate153aelement layer153belement layer155aregion155bregion156aregion156bregion157bonding layer