Patent Publication Number: US-2022238836-A1

Title: Display Device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One embodiment of the present invention relates to a display device. One embodiment of the present invention relates to a method for manufacturing a display device. 
     Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include a semiconductor device, a display device, a light-emitting apparatus, a power storage device, a memory device, an electronic device, a lighting device, an input device, an input/output device, a driving method thereof, and a manufacturing method thereof. A semiconductor device refers to a device that can function by utilizing semiconductor characteristics in general. 
     2. Description of the Related Art 
     In recent years, higher definition display panels have been demanded. Examples of devices that require high-definition display panels include a smartphone, a tablet terminal, and a laptop computer. Furthermore, higher definition has been required for a stationary display device such as a television device or a monitor device along with an increase in resolution. A device absolutely required to have a high-definition display panel is a device for virtual reality (VR) or augmented reality (AR). 
     Examples of the display device that can be used for a display panel include, typically, a liquid crystal display device, a light-emitting apparatus including a light-emitting element such as an organic electroluminescent (EL) element or a light-emitting diode (LED), and electronic paper performing display by an electrophoretic method or the like. 
     For example, an organic EL element basically has such a structure that a layer containing a light-emitting organic compound is provided between a pair of electrodes. By voltage application to this element, the light-emitting organic compound can emit light. A display device containing such an organic EL element needs no backlight which is necessary for a liquid crystal display device and the like and thus can have advantages such as thinness, lightweight, high contrast, and low power consumption. Patent Document 1, for example, discloses an example of a display device using an organic EL element. 
     Patent Document 2 discloses a display device using an organic EL device for VR. 
     REFERENCE 
     Patent Document 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2002-324673 
         [Patent Document 2] PCT International Publication No. 2018/087625 
       
    
     SUMMARY OF THE INVENTION 
     An object of one embodiment of the present invention is to provide a display device with high display quality. An object of one embodiment of the present invention is to provide a highly reliable display device. An object of one embodiment of the present invention is to provide a display device with low power consumption. An object of one embodiment of the present invention is to provide a display device that can easily achieve higher definition. An object of one embodiment of the present invention is to provide a display device with high display quality and high definition. An object of one embodiment of the present invention is to provide a display device with high contrast. 
     Another object of one embodiment of the present invention is to provide a display device with a novel structure or a method for manufacturing the display device. An object of one embodiment of the present invention is to provide a method for manufacturing the above display device with high yield. An object of one embodiment of the present invention is to alleviate at least one of problems of the conventional technique. 
     Note that the description of these objects does not preclude the existence of other objects. In one embodiment of the present invention, there is no need to achieve all these objects. Objects other than these can be derived from the description of the specification, the drawings, the claims, and the like. 
     One embodiment of the present invention is a display device including a first lower electrode, a first EL layer over the first lower electrode, a second lower electrode, a second EL layer over the second lower electrode, and an upper electrode over the first EL layer and the second EL layer. In addition, a first region where the first lower electrode is not provided is included below the first EL layer, and a second region where the second lower electrode is not provided is included below the second EL layer. In the first layer, the upper electrode is positioned not to be in contact with the first lower electrode. In the second region, the upper electrode is positioned not to be in contact with the second lower electrode. 
     Another embodiment of the present invention is a display device including a first lower electrode, a first EL layer over the first lower electrode, a second lower electrode, a second EL layer over the second lower electrode, and an upper electrode over the first EL layer and the second EL layer. The upper electrode is positioned to be apart from the first lower electrode in a first region below the first EL layer; and the upper electrode is positioned to be apart from the second lower electrode in a second region below the second EL layer. 
     Another embodiment of the present invention is a display device where the upper electrode in the first region includes a region overlapping with the first EL layer. 
     Another embodiment of the present invention is a display device including a common layer between the first EL layer and the upper electrode and between the second EL layer and the upper electrode. 
     Another embodiment of the present invention is a method for manufacturing a display device, which includes a step of forming a conductive film, a step of forming an EL film over the conductive film, a step of forming a sacrificial film over the EL film, a step of forming a protective film over the sacrificial film, a step of forming a resist over the protective film, a step of forming a stack of an EL layer, a sacrificial layer, and a protective layer with use of the resist as a mask, a step of forming a lower electrode with use of the stack as a mask, a step of removing the protective layer and the sacrificial layer, and a step of forming an upper electrode over the EL layer. The upper electrode is positioned to be apart from the lower electrode in a region below the EL layer. 
     Another embodiment of the present invention may be a light-emitting apparatus without a display function. Another embodiment of the present invention may be a photoelectric conversion device including a photoelectric conversion element such as a sensor. 
     According to one embodiment of the present invention, a display device with high display quality can be provided. Moreover, a highly reliable display device can be provided. Moreover, a display device with low power consumption can be provided. Moreover, a display device that can easily achieve higher definition can be provided. Moreover, a display device having high display quality and high definition can be provided. Moreover, a display device with high contrast can be provided. 
     According to another embodiment of the present invention, a display device with a novel structure or a method for manufacturing the display device can be provided. Moreover, a method for manufacturing the above display device with high yield can be provided. According to one embodiment of the present invention, at least one of problems of the conventional technique can be alleviated. 
     Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily have all these effects. Effects other than these can be derived from the description of the specification, the drawings, the claims, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  illustrate a structure example of a display device. 
         FIG. 2  illustrates a structure example of a display device. 
         FIGS. 3A to 3F  each illustrate a structure example of a display device. 
         FIGS. 4A to 4C  each illustrate a structure example of a display device. 
         FIGS. 5A to 5C  each illustrate a structure example of a display device. 
         FIGS. 6A to 6D  each illustrate a structure example of a display device. 
         FIGS. 7A to 7E  each illustrate a structure example of a display device. 
         FIGS. 8A to 8F  illustrate an example of a method for manufacturing a display device. 
         FIGS. 9A to 9C  illustrate an example of a method for manufacturing a display device. 
         FIG. 10  illustrates a structure example of a display device. 
         FIG. 11  is a perspective view illustrating an example of a display device. 
         FIG. 12A  is a cross-sectional view illustrating an example of a display device. 
         FIGS. 12B and 12C  are cross-sectional views each illustrating an example of a transistor. 
         FIG. 13  is a cross-sectional view illustrating an example of a display device. 
         FIG. 14  is a cross-sectional view illustrating an example of a display device. 
         FIGS. 15A and 15B  are perspective views illustrating an example of a display module. 
         FIG. 16  is a cross-sectional view illustrating an example of a display device. 
         FIG. 17  is a cross-sectional view illustrating an example of a display device. 
         FIG. 18  is a cross-sectional view illustrating an example of a display device. 
         FIGS. 19A to 19D  each illustrate a structure example of a light-emitting element. 
         FIGS. 20A and 20B  illustrate an example of an electronic device. 
         FIGS. 21A to 21D  each illustrate an example of an electronic device. 
         FIGS. 22A to 22F  illustrate examples of electronic devices. 
         FIGS. 23A to 23F  illustrate examples of electronic devices. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments will be described below with reference to the drawings. Note that the embodiments can be implemented with many different modes, and it will be readily understood by those skilled in the art that modes and details thereof can be changed in various ways without departing from the spirit and scope thereof. Therefore, the present invention should not be construed as being limited to the description of embodiments below. 
     Note that in structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and the description thereof is not repeated. The same hatching pattern is used for portions having similar functions, and the portions are not denoted by specific reference numerals in some cases. 
     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, the size, the layer thickness, or the region is not limited to the illustrated scale. 
     Note that in this specification and the like, ordinal numbers such as “first” and “second” are used in order to avoid confusion among components and do not limit the number of components. 
     In this specification and the like, the terms “film” and “layer” can be interchanged with each other. For example, in some cases, the terms “conductive layer” and “insulating layer” can be changed into “conductive film” and “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 stack 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 structure in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is attached to a substrate of a display panel, or a structure in which an integrated circuit (IC) is mounted on a substrate by a chip on glass (COG) method or the like is referred to as a display panel module or a display module, or simply referred to as a display panel or the like in some cases. 
     A light-emitting element of one embodiment of the present invention may include 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. 
     Note that the aforementioned 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. 
     The quantum dot material can be a colloidal quantum dot material, an alloyed quantum dot material, a core-shell quantum dot material, a core quantum dot material, or the like. The quantum dot containing elements belonging to Groups 12 and 16, elements belonging to Groups 13 and 15, or elements belonging to Groups 14 and 16, may be used. Alternatively, the quantum dot containing an element such as cadmium, selenium, zinc, sulfur, phosphorus, indium, tellurium, lead, gallium, arsenic, or aluminum may be used. 
     In this specification and the like, a device formed using a metal mask or a fine metal mask (FMM) may be referred to as a device having a metal mask (MM) structure. In this specification and the like, a device formed without using a metal mask or an FMM may be referred to as a device having a metal maskless (MML) structure. 
     In this specification and the like, a structure in which light-emitting layers in light-emitting devices of different colors (here, blue (B), green (G), and red (R)) are separately formed or separately patterned may be referred to as a side-by-side (SBS) structure. In this specification and the like, a light-emitting device capable of emitting white light may be referred to as a white light-emitting device. Note that a white light-emitting device that is combined with coloring layers (e.g., color filters) can be a light-emitting device of full-color display. 
     Structures of light-emitting devices can be classified roughly into a single structure and a tandem structure. A light-emitting device with a single structure includes one light-emitting unit between a pair of electrodes, and the light-emitting unit preferably includes one or more light-emitting layers. To obtain white light emission, two or more light-emitting layers that emit light of complementary colors are selected. For example, when emission colors of a first light-emitting layer and a second light-emitting layer are complementary colors, a light-emitting device can be configured to emit white light as a whole. The same applies to a light-emitting device including three or more light-emitting layers. 
     A light-emitting device with a tandem structure includes two or more light-emitting units between a pair of electrode, and each light-emitting unit preferably includes one or more light-emitting layers. To obtain white light emission, the structure is made so that light from light-emitting layers of the light-emitting units can be combined to be white light. Note that a structure for obtaining white light emission is similar to that in the case of a single structure. In the light-emitting device with a tandem structure, it is preferable that an intermediate layer such as a charge-generation layer be provided between the plurality of light-emitting units. 
     When the white light-emitting device (having a single structure or a tandem structure) and a light-emitting device having an SBS structure are compared to each other, the latter can have lower power consumption than the former. To reduce power consumption, a light-emitting device having an SBS structure is preferably used. Meanwhile, the white light-emitting device is preferable in terms of lower manufacturing cost or higher manufacturing yield because the manufacturing process of the white light-emitting device is simpler than that of a light-emitting device having an SBS structure. 
     Embodiment 1 
     In this embodiment, a structure example of a display device of one embodiment of the present invention and a method for manufacturing the display device will be described. 
     One embodiment of the present invention is a display device including a light-emitting element (also referred to as a light-emitting device). The display device includes at least two light-emitting elements which emit light of different colors. The light-emitting elements each include a pair of electrodes and an EL layer therebetween. As the light-emitting element, an electroluminescence element such as an organic EL element or an inorganic EL element can be used. Besides, a light-emitting diode (LED) can be used. The light-emitting element of one embodiment of the present invention is preferably an organic electroluminescence element (organic EL element). The two or more light-emitting elements emitting different colors include respective EL layers containing different materials. For example, three kinds of light-emitting elements emitting red (R), green (G), and blue (B) light are included, whereby a full-color display device can be achieved. 
     As a way of forming EL layers separately between light-emitting elements of different colors, an evaporation method using a shadow mask such as a metal mask is known. However, this method causes a deviation from the designed shape and position of an island-shaped organic film due to various influences such as the low accuracy of the metal mask position, the positional deviation between the metal mask and a substrate, a warp of the metal mask, and the vapor-scattering-induced expansion of outline of the deposited film; accordingly, it is difficult to achieve high definition and high aperture ratio of the display device. In addition, dust derived from a material attached to the metal mask in evaporation is generated in some cases. Such dust might cause defective patterning of the light-emitting element. In addition, a short circuit derived from the dust may occur. A cleaning step for removing the material attached to the metal mask is necessary. Thus, a measure has been taken for pseudo improvement in definition (also referred to pixel density). As a specific measure, a unique pixel arrangement such as a PenTile pattern has been employed. 
     In one embodiment of the present invention, fine patterning of an EL layer is performed without a shadow mask such as a metal mask. With the patterning, a high-definition display device with a high aperture ratio, which had been difficult to achieve, can be fabricated. Moreover, EL layers can be formed separately, which enables extremely clear images; thus, a display device with a high contrast and high display quality can be fabricated. 
     Here, a description is made on a case where EL layers in light-emitting elements of two colors are separately formed, for simplicity. First, a stack of a conductive film to be a pixel electrode (also referred to as lower electrode), a first EL film, and a first sacrificial film is formed. Next, a resist mask is formed over the first sacrificial film. Then, part of the first sacrificial film and part of the first EL film are etched using the resist mask, so that the first EL layer and a first sacrificial layer over the first EL layer are formed. 
     Next, a stack of a second EL film and a second sacrificial film is formed. Then, part of the second sacrificial film and part of the second EL film are etched using the resist mask, so that a second EL layer and a second sacrificial layer over the second EL layer are formed. Next, the pixel electrode is processed using the first sacrificial layer and the second sacrificial layer as a mask, so that a first pixel electrode overlapping with the first EL layer and a second pixel electrode overlapping with the second EL layer are formed. In this manner, the first EL layer and the second EL layer can be formed separately. Finally, the first sacrificial layer and second sacrificial layer are removed, and a common electrode (also referred to as upper electrode) is formed, whereby light-emitting elements of two colors can be formed separately. 
     Furthermore, by repeating the above-described steps, EL layers in light-emitting elements of three or more colors can be separately formed. Accordingly, a display device including light-emitting elements of three or more colors can be achieved. 
     In the case where an end portion of the pixel electrode is substantially aligned with an end portion of the EL layer and the case where the end portion of the pixel electrode is positioned on an outer side than the end portion of the EL layer, the common electrode and the pixel electrode are sometimes short-circuited when the common electrode is formed over the EL layer. 
     Thus, the display device of one embodiment of the present invention employs such a structure that a region without the pixel electrode is provided below the end portion of the EL layer, and the common electrode is positioned not to be in contact with the pixel electrode in the region. The common electrode and the pixel electrode are not electrically connected to each other as in the above manner, whereby a short circuit between the pixel electrode and the common electrode can be inhibited. 
     Moreover, in one embodiment of the present invention, the sacrificial layer is formed using a resist mask (also referred to as resist or photoresist), and the EL layer and the pixel electrode can be processed using the formed sacrificial layer. This means that a light-emitting element can be formed without use of different resist masks for processing the pixel electrode and processing of the EL layer. Thus, a margin between the end portions of the pixel electrode and the EL layer is not necessarily provided for forming a light-emitting element. With a reduction in the margin between the end portions, a light-emitting region can be extended, whereby the aperture ratio of the light-emitting element can be increased. Moreover, with a reduction in the margin between the end portions, a reduction in the pixel size is possible, whereby the display device can have higher definition. Furthermore, the number of uses of the resist masks can be reduced, whereby the process can be simplified. This enables a reduction in cost and an improvement in yield. 
     In the case where EL layers for different colors are adjacent to each other, it is difficult to set the distance between the EL layers adjacent to each other to be less than 10 μm with a formation method using a metal mask, for example. In contrast, with use of the above method in one embodiment of the present invention, the distance can be decreased to be less than or equal to 3 μm, less than or equal to 2 μm, or less than or equal to 1 μm. For example, with use of an exposure tool for LSI, the distance can be decreased to be less than or equal to 500 nm, less than or equal to 200 nm, less than or equal to 100 nm, or less than or equal to 50 nm. Accordingly, the area of a non-light-emitting region exiting between two light-emitting elements can be significantly reduced, and the aperture ratio can be close to 100%. For example, the aperture ratio may be higher than or equal to 50%, higher than or equal to 60%, higher than or equal to 70%, higher than or equal to 80%, or higher than or equal to 90%; that is, the aperture ratio lower than 100% can be achieved. 
     Furthermore, a pattern of the EL layer itself can be made extremely smaller than that in the case of using a metal mask. For example, in the case of using a metal mask for forming EL layers separately, a variation in the thickness of the pattern occurs between the center and the edge of the pattern. This causes a reduction in an effective area that can be used as a light-emitting region with respect to the whole pattern area. In contrast, in the manufacturing method of one embodiment of the present invention, a pattern is formed by processing a film deposited to have a uniform thickness, which enables a uniform thickness in the pattern. Thus, even in the fine pattern, almost the whole area can be used as a light-emitting region. Therefore, the above method makes it possible to obtain a high resolution display device with a high aperture ratio. 
     As described above, the above fabrication method enables a display device in which minute light-emitting elements are integrated; accordingly, it is not necessary to employ a unique pixel arrangement such as a PenTile pattern for pseudo improvement in the definition degree. Therefore, it is possible to achieve a display device employing what is called a stripe arrangement in which R, G, and B pixels are arranged in one direction and having definition higher than or equal to 500 ppi, higher than or equal to 1000 ppi, higher than or equal to 2000 ppi, higher than or equal to 3000 ppi, or higher than or equal to 5000 ppi. 
     Specific structure examples, fabrication method examples, and the like of the display device of one embodiment of the present invention are described below with reference to drawings. 
     Structure Example 1 of Display Device 
       FIG. 1A  is a schematic top view of a display device  100 A of one embodiment of the present invention. The display device  100 A includes a plurality of light-emitting elements  110 R exhibiting red, a plurality of light-emitting elements  110 G exhibiting green, and a plurality of light-emitting elements  110 B exhibiting blue. In  FIG. 1A , light-emitting regions of the light-emitting elements are denoted by R, G, and B to easily differentiate the light-emitting elements. 
     The light-emitting elements  110 R, the light-emitting elements  110 G, and the light-emitting elements  110 B are arranged in a matrix.  FIG. 1A  shows what is called a stripe arrangement, in which the light-emitting elements of the same color are arranged in one direction. Note that the arrangement of the light-emitting elements is not limited thereto; another arrangement such as a delta, zigzag, or PenTile pattern may also be used. 
     As each of the light-emitting elements  110 R,  110 G, and  110 B, an EL element such as an organic light-emitting diode (OLED) or a quantum-dot light-emitting diode (QLED) is preferably used. Examples of a light-emitting substance included in the EL element include a substance exhibiting fluorescence (fluorescent material), a substance exhibiting phosphorescence (phosphorescent material), an inorganic compound (e.g., quantum dot material), and a substance exhibiting thermally activated delayed fluorescence (a thermally activated delayed fluorescent (TADF) material). 
       FIG. 1B  and  FIG. 2  are each an example of a schematic cross-sectional view taken along dashed-dotted line A 1 -A 2  in  FIG. 1A , and show a structure in which light-emitting elements of different colors are adjacent to each other.  FIG. 1C  is an example of a schematic cross-sectional view taken along dashed-dotted line B 1 -B 2  and shows a structure in which light-emitting elements of the same color are adjacent to each other. 
     The light-emitting element  110 R includes a pixel electrode  111 R, an EL layer  112 R, and a common electrode  113 . The light-emitting element  110 G includes a pixel electrode  111 G, an EL layer  112 G, and the common electrode  113 . The light-emitting elements  110 B includes a pixel electrode  111 B, an EL layer  112 B, and the common electrode  113 . A light-emitting element  150 G includes a pixel electrode  151 G, an EL layer  152 G, and the common electrode  113 . 
     In the light-emitting element  110 R, the EL layer  112 R in included between the pixel electrode  111 R and the common electrode  113 . The EL layer  112 R contains a light-emitting organic compound that emits light with intensity at least in a red wavelength range. In the light-emitting elements  110 G, the EL layer  112 G is included between the pixel electrode  111 G and the common electrode  113 . The EL layer  112 G contains a light-emitting organic compound that emits light with intensity at least in a green wavelength range. In the light-emitting elements  110 B, the EL layer  112 B is included between the pixel electrode  111 B and the common electrode  113 . The EL layer  112 B contains a light-emitting organic compound that emits light with intensity at least in a blue wavelength range. Note that the light-emitting element  150 G is similar to the light-emitting elements  110 G. 
     The EL layer  112 R, the EL layer  112 G, and the EL layer  112 B each include a layer containing a light-emitting organic compound (light-emitting layer). The light-emitting layer may contain one or more kinds of compounds (a host material and an assist material) in addition to a light-emitting substance (guest material). As the host material and the assist material, one or more kinds of substances having a larger energy gap than the light-emitting substance (the guest material) can be used. As the host material and the assist material, compounds which form an exciplex are preferably used in combination. To form an exciplex efficiently, it is particularly preferable to combine a compound that easily accepts holes (hole-transport material) and a compound that easily accepts electrons (electron-transport material). 
     For the light-emitting element, either a low-molecular compound or a high-molecular compound can be used, and an inorganic compound (e.g., a quantum dot material) may also be used. 
     The EL layer  112 R, the EL layer  112 G, and the EL layer  112 B may each include one or more of an electron-injection layer, an electron-transport layer, a hole-injection layer, and a hole-transport layer in addition to the light-emitting layer. 
     The pixel electrode  111 R, the pixel electrode  111 G, and the pixel electrode  111 B are provided for respective light-emitting elements. The common electrode  113  is provided as a layer common to the light-emitting elements. A conductive film that transmits visible light is used for either the respective pixel electrodes or the common electrode  113 , and a reflective conductive film is used for the other. When the respective pixel electrodes are light-transmitting electrodes and the common electrode  113  is a reflective electrode, a bottom-emission display device is obtained. When the respective pixel electrodes are reflective electrodes and the common electrode  113  is a light-transmitting electrode, a top-emission display device is obtained. Note that when both the respective pixel electrodes and the common electrode  113  transmit light, a dual-emission display device can be obtained. 
     In addition, in the display device of one embodiment of the present invention, as illustrated in  FIG. 1B , the light-emitting element  110 R over a substrate  101  includes a region where the pixel electrode  111 R is not provided below the EL layer  112 R (as specific examples, see  FIGS. 3A to 3F , and the like). In the region, the common electrode  113  is preferably positioned not to be in contact with the pixel electrode  111 R. In other words, in the region, the common electrode  113  is preferably positioned to be apart from the pixel electrode  111 R. Furthermore, the common electrode  113  in the region preferably includes a region overlapping with the EL layer  112 R. With such a structure, a short circuit between the common electrode  113  and the pixel electrode  111 R can be prevented. 
     In  FIG. 1B , at least part of the end portion of the EL layer  112 R may protrude (also referred to stretch) toward the edge direction (also referred to as side-surface direction) more than the end portion of the pixel electrode  111 R. Furthermore, at least part of the end portion of the EL layer  112 R may be positioned outward from the end portion of the pixel electrode  111 R. Furthermore, the end portion of the pixel electrode  111 R may positioned inward from the end portion of the EL layer  112 R. 
     In addition, in  FIG. 1B , a top surface of the end portion of the pixel electrode  111 R is preferably in contact with the EL layer  112 R. 
     In the cross section, the end portion of the pixel electrode  111 R is preferably positioned on an inner side than the end portion of the EL layer  112 R. In the top view, the pixel electrode  111 R is preferably smaller than the EL layer  112 R. Furthermore, in the top view, the pixel electrode  111 R preferably includes a region positioned on an inner side than the EL layer  112 R. 
     A layer including a circuit and the like (described later) may be provided over the substrate  101 . In that case, the substrate  101  may be regarded as including the layer. The substrate  101  or the layer preferably has an insulating surface. The common electrode  113  preferably includes a region in contact with the substrate  101  (e.g., an insulating surface). 
     Although the above description is for one of end portions of the light-emitting element  110 R, the same structure can be applied to the other end portion of the light-emitting element  110 R, end portions of the light-emitting element  110 G, end portions of the light-emitting element  110 B, or end portions of the light-emitting element  150 G. 
       FIG. 2  illustrates a structure in which a common layer  114  is provided between the EL layer  112 R and the common electrode  113 . The common layer  114  corresponds to, for example, an electron-transport layer or an electron-injection layer, but is not limited thereto. Hereinafter, the structures illustrated in  FIGS. 1B and 1C  and  FIG. 2  are described in detail. 
     Enlarged views of the vicinity of one end portion of the light-emitting elements  110 R are exemplified in  FIG. 3A  to  FIG. 7E . Note that the description here uses only the vicinity of one end portion of the light-emitting element  110 R for simplicity; however, the same structure can be applied to the other end portion of the light-emitting element  110 R, end portions of the light-emitting element  110 G, end portions of the light-emitting element  110 B, or end portions of the light-emitting element  150 G. 
       FIG. 3A  illustrates an example of a structure including a region  200  where the pixel electrode  111 R is not provided below the end portion of the EL layer  112 R. In this structure, the common electrode  113  can be positioned to be led inwardly to a place under the EL layer  112 R. In other words, the region  200  includes a region where the EL layer  112 R overlaps with the common electrode  113 . In addition, in the region  200 , a gap (also referred to as a distance or a space) is preferably provided between the pixel electrode  111 R and the common electrode  113 . Note that the region  200  includes not only a region vertically under the EL layer  112 R but also a region positioned in the diagonally downward direction of the EL layer  112 R. 
       FIG. 3B  illustrates an example of a structure where the end portion of the EL layer  112 R has a tapered shape and the common electrode  113  is positioned to be aligned with the tapered shape. The end portion of the EL layer  112 R preferably has such a shape that a lower end portion protrudes more than an upper end portion. The region  200  includes a region where the EL layer  112 R does not overlap with the common electrode  113 , whereby the distance between the pixel electrode  111 R and the common electrode  113  can be increased. With this structure, the possibility of short circuit between the pixel electrode  111 R and the common electrode  113  can be reduced. Note that the end portion of the EL layer  112 R may have a structure in which the upper end portion protrudes more than the lower end portion. 
       FIG. 3C  illustrates a structure where the end portion of the pixel electrode  111 R has a tapered shape. The end portion of the pixel electrode  111 R preferably has such a shape that the upper end portion protrudes more than the lower end portion. For example, as illustrated in  FIG. 3C , in the case where a lower portion of the region  200  has a larger area where the common electrode  113  and the EL layer  112 R overlap with each other than an upper portion of the region  200 , the common electrode  113  can be favorably embedded in the region  200 . When the end portion of the pixel electrode  111 R has such a shape that the upper end portion protrudes more than the lower end portion, the possibility of short circuit between the pixel electrode  111 R and the common electrode  113  can be reduced even in the case where the common electrode  113  is favorably embedded in the region  200 . Note that the end portion of the pixel electrode  111 R may have such a structure that the lower end portion protrudes more than the upper end portion. 
       FIGS. 3D and 3E  each illustrate a structure in which both the end portion of the EL layer  112 R and the end portion of the pixel electrode  111 R have a tapered shape. In  FIG. 3D , both of the end portions have such a structure that the lower end portion protrudes more than the upper end portion. In  FIG. 3E , both of the end portions have such a structure that the upper end portion protrudes more than the lower end portion. 
       FIG. 3F  illustrates a structure in which a side surface of the EL layer  112 R has a region is not in contact with the common electrode  113 . In this case, a space (also referred to as a distance or a gap) between the EL layer  112 R and the common electrode  113  is preferably provided on the side surface of the EL layer  112 R. 
       FIG. 4A  illustrates a structure of the pixel electrode  111 R where the upper end portion and the lower end portion protrude more than a middle portion of a side surface. For example, as illustrated in  FIG. 4A , when the common electrode  113  in the middle portion of the region  200  is led more inwardly to a place under the EL layer  112 R than that in the upper and lower portions of the region  200 , such a structure enables the possibility of short circuit between the pixel electrode  111 R and the common electrode  113  to be reduced. The same effect can also be obtained when the middle portion of the region  200  has a larger area where the common electrode  113  and the EL layer  112 R overlap with each other than the upper and lower portions of the region  200 . 
       FIG. 4B  illustrates a structure of the region  200  where a recess portion is formed on a surface (e.g., insulating surface) of the substrate  101 , and the common electrode  113  is positioned in the recess portion. The recess portion can be provided in such a manner that part of the surface of the substrate  101  is etched to be thin. For example, when the substrate  101  in the region  200  has a partly tapered surface as illustrated in  FIG. 4B , a region where the EL layer  112 R overlaps with the common electrode  113  is from the end portion of the EL layer  112 R to the lower end portion of the tapered shape. With such a structure, the possibility of short circuit between the pixel electrode  111 R and the common electrode  113  can be reduced. In the region  200 , the distance between the EL layer  112 R and the substrate  101  may be larger than the thickness of the pixel electrode  111 R. 
       FIG. 4C  illustrates a structure where an insulating region  131  is provided between the pixel electrode  111 R and the common electrode  113  in the region  200 . The insulating region  131  may be formed by making the end portion of the pixel electrode  111 R have an insulating property or by providing an insulator additionally on the end portion of the pixel electrode  111 R. Furthermore, a structure in which the end portion of the pixel electrode  111 R is covered with an insulator may be employed. With such a structure, the possibility of short circuit between the pixel electrode  111 R and the common electrode  113  can be reduced. Note that a gap (also referred to as a distance or a space) may be provided between the insulating region  131  and the common electrode  113 . Moreover, a gap (also referred to as a distance or a space) may be provided between the insulating region  131  and the pixel electrode  111 R. 
       FIG. 5A  illustrates a structure including an optical adjustment layer  115 R between the pixel electrode  111 R and the EL layer  112 R. At least part of an end portion of the EL layer  112 R preferably protrudes in the edge direction more than end portions of the pixel electrode  111 R and the optical adjustment layer  115 R. Alternatively, not an optical adjustment layer but a layer having a different function can be arranged in a region between the pixel electrode  111 R and the EL layer  112 R. Note that a stacked body including the pixel electrode and the optical adjustment layer is referred to as a pixel electrode in some cases. 
       FIG. 5B  illustrates a structure where the optical adjustment layer  115 R has an upper end portion protruding more than a lower end portion, and the pixel electrode  111 R has a lower end portion protruding more than an upper end portion. The structure described with  FIG. 4A  can be applied to the structure in  FIG. 5B , and the same effect as that in  FIG. 4A  can be obtained. Note that the region  200  is not illustrated in some cases in  FIG. 5B  and the following drawings, considering the visibility of the drawings; the region is positioned below the EL layer  112 R. 
       FIG. 5C  illustrates a structure different from that in  FIG. 5A , in that the end portions of the EL layer  112 R and the pixel electrode  111 R protrude more than the end portion of the optical adjustment layer  115 R. 
       FIGS. 6A and 6B  each illustrate a structure where the end portions of the optical adjustment layer  115 R and the pixel electrode  111 R illustrated in  FIG. 5A  have tapered shapes. The taper angles of the optical adjustment layer  115 R and the pixel electrode  111 R may be the same or different from each other. When being formed using different materials, the optical adjustment layer  115 R and the pixel electrode  111 R preferably have different taper angles in terms of formation easiness.  FIG. 6A  shows a case where a taper angle θ 1  of the optical adjustment layer  115 R is smaller than a taper angle θ 2  of the pixel electrode  111 R.  FIG. 6B  shows a case where the taper angle of the optical adjustment layer  115 R is larger than the taper angle of the pixel electrode  111 R. Note that the taper angle indicates an angle formed by a lower side and an oblique side of a layer in a cross-sectional view. 
       FIG. 6C  illustrates a structure where a protective layer  121  is provided over the common electrode  113 . The protective layer  121  has a function of preventing diffusion of impurities such as water into each light-emitting element from above. 
       FIG. 6D  illustrates a structure in which the pixel electrode  111 R has a stacked structure. For example, a light-transmitting pixel electrode  111 R- 1  and a reflective pixel electrode  111 R- 2  can be stacked. In addition, the pixel electrode  111 R- 1  or the pixel electrode  111 R- 2  may have a tapered shape. 
       FIGS. 7A to 7E  illustrate specific examples of the structure including the common layer  114  illustrated in  FIG. 2 . The common layer  114  corresponds to, for example, an electron-transport layer or an electron-injection layer. 
       FIG. 7A  illustrates a structure where the common layer  114  is positioned between the EL layer  112 R and the common electrode  113 . The common layer  114  is also positioned to overlap with a surface (also referred to as a top surface) and a side surface of the EL layer  112 R. In other words, the common layer  114  on the tope surface and the side surface of the EL layer  112 R is positioned between the EL layer  112 R and the common electrode  113 . The common layer  114  in the region  200  is positioned between the common electrode  113  and the pixel electrode  111 R and the like. Furthermore, the common layer  114  may be positioned in contact with the substrate  101 . 
       FIG. 7B  illustrates a structure where the region  200  is not provided with the common layer  114  between the common electrode  113  and the pixel electrode  111 R and the like.  FIG. 7C  illustrates a structure where the common layer  114  is positioned to overlap with part of the side surface of the EL layer  112 R. 
       FIG. 7D  illustrates a structure where the thickness of the common layer  114  differs depending on portions, i.e., a portion overlapping with the top surface of the EL layer  112 R and a portion overlapping with the side surface of the EL layer  112 R. It is preferable that the thickness of the common layer  114  overlapping with the top surface be larger than that of the common layer  114  overlapping with the side surface because processing is facilitated in some cases. As illustrated in  FIG. 7E , the common layer  114  overlapping with the side surface of the EL layer  112 R may have such a structure that the thickness of the lower portion (close to the substrate  101 ) is smaller than that of the upper portion (far from the substrate  101 ). 
     The structures illustrated in  FIG. 5A  to  FIG. 7E  can be described with expression used for the description with  FIG. 1A  to  FIG. 3F  as appropriate. Similarly, in this specification, expression used for describing  FIG. 1A  to  FIG. 7E  can be used for description of the other drawings as appropriate. 
     As described above, the end portions of the light-emitting elements can have a variety of structures. The structures illustrated in the above drawings can be combined with each other as appropriate. For example, the structure in which the surface of the substrate  101  has a recess portion as illustrated in  FIG. 4B  may be combined with any of the structures in  FIG. 5A  to  FIG. 7E . Alternatively, the end portion of the optical adjustment layer  115 R as illustrated in  FIGS. 7A to 7E  may have a tapered shape as illustrated in  FIG. 6A  or  FIG. 6B . As described, a variety of structures in this specification is combined as appropriate, whereby the display device  100 A of one embodiment of the present invention can have a synergistic effect. 
     Example of Manufacturing Method of Display Device 
     An example of a method for manufacturing the display device of one embodiment of the present invention is described below with reference to the drawings. Here, description is made with use of the display device  100 A shown in the above structure example.  FIGS. 8A to 8F  are cross-sectional schematic views of steps in a manufacturing method of a display device described below. 
     Note that thin films included in the display device (e.g., insulating films, semiconductor films, or conductive films) can be formed by any of 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, and the like. Examples of the CVD method include a plasma-enhanced CVD (PECVD) method and a thermal CVD method. An example of a thermal CVD method includes a metal organic CVD (MOCVD) method. 
     Alternatively, thin films included in the display device (e.g., insulating films, semiconductor films, and conductive films) can be formed by a method such as spin coating, dipping, spray coating, ink-jetting, dispensing, screen printing, or offset printing or with a doctor knife, a slit coater, a roll coater, a curtain coater, or a knife coater. 
     When thin films included in the display device are processed, a photolithography method or the like can be used for the processing. Besides, a nanoimprinting method, a sandblasting method, a lift-off method, or the like may be used to process thin films. Alternatively, island-shaped thin films may be directly formed by a film formation method using a shielding mask such as a metal mask. 
     There are two typical examples of photolithography methods. In one of the methods, a resist mask is formed over a thin film that is to be processed, the thin film is processed by etching or the like, and then the resist mask is removed. In the other method, a photosensitive thin film is formed and then processed into a desired shape by light exposure and development. 
     As light for exposure in a photolithography method, it is possible to use light with the i-line (wavelength: 365 nm), light with the g-line (wavelength: 436 nm), light with the h-line (wavelength: 405 nm), or light in which the i-line, the g-line, and the h-line are mixed. Alternatively, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Exposure may be performed by liquid immersion exposure technique. As the light for exposure, extreme ultraviolet (EUV) light or X-rays may also be used. Furthermore, instead of the light used for the exposure, an electron beam can also be used. It is preferable to use EUV, X-rays, or an electron beam because extremely fine processing can be performed. Note that a photomask is not needed when exposure is performed by scanning with a beam such as an electron beam. 
     For etching of thin films, a dry etching method, a wet etching method, a sandblast method, or the like can be used. 
     [Preparation for Substrate  101 ] 
     The substrate  101  preferably has heat resistance high enough to withstand at least heat treatment performed later. As the substrate  101  having an insulating property, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, an organic resin substrate, or the like can be used. Alternatively, a semiconductor substrate can be used. For example, a single crystal semiconductor substrate or a polycrystalline semiconductor substrate of silicon, silicon carbide, or the like; a compound semiconductor substrate of silicon germanium or the like; an SOI substrate; or the like can be used. 
     As the substrate  101 , 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. The substrate  101  over which various circuits are formed preferably has an insulating surface. 
     [Formation of Conductive Film  111   f ] 
     Next, a conductive film  111   f  to be a pixel electrode  111  (the pixel electrode  111 R, the pixel electrode  111 G, and the pixel electrode  111 B) is formed over the substrate  101 . 
     In the case where a conductive film reflecting visible light is used as the pixel electrode, it is preferable to use a material (e.g., silver or aluminum) having reflectance as high as possible in the whole wavelength range of visible light. With such a material, both higher outcoupling efficiency of the light emitting element and higher color reproducibility can be obtained. Furthermore, a plurality of conductive films may be provided. For example, a reflective conductive film may be stacked over a light-transmitting conductive film. 
     [Formation of EL Film  112 Rf] 
     Next, an EL film  112 Rf that is to be the EL layer  112 R later is formed over the conductive film  111   f.    
     The EL film  112 Rf includes at least a film containing a light-emitting compound. A structure may be employed in which at least one of films functioning as an electron-injection layer, an electron-transport layer, a charge-generation layer, a hole-transport layer, and a hole-injection layer is stacked in addition to the above. The EL film  112 Rf can be formed by, for example, an evaporation method, a sputtering method, an inkjet method, or the like. Without limitation to this, the above-described film-formation method can be used as appropriate. 
     [Formation of Sacrificial Film  144   a ] 
     Next, a sacrificial film  144   a  is formed to cover the EL film  112 Rf. 
     As the sacrificial film  144   a , it is preferable to use a film highly resistant to etching treatment performed on various EL films such as the EL film  112 Rf, i.e., a film having high etching selectivity with respect to the EL film. Furthermore, as the sacrificial film  144   a , it is preferable to use a film having high etching selectivity with respect to a protective film such as a protective film  146   a  described later. Moreover, as the sacrificial film  144   a , it is preferable to use a film that can be removed by a wet etching method less likely to cause damage to the EL film. 
     The sacrificial film  144   a  can be formed using an inorganic film such as a metal film, an alloy film, a metal oxide film, a semiconductor film, or an inorganic insulating film, for example. 
     Alternatively, the sacrificial film  144   a  can be formed using a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, titanium, aluminum, yttrium, zirconium, or tantalum or an alloy material containing the metal material. It is particularly preferable to use a low-melting-point material such as aluminum or silver. 
     Alternatively, the sacrificial film  144   a  can be formed using a metal oxide such as an indium-gallium-zinc oxide (In-Ga—Zn oxide, also referred to as IGZO). Furthermore, the following material can be used: indium oxide, indium zinc oxide (In—Zn oxide), indium tin oxide (In—Sn oxide), indium titanium oxide (In—Ti oxide), indium tin zinc oxide (In—Sn—Zn oxide), indium titanium zinc oxide (In—Ti—Zn oxide), indium gallium tin zinc oxide (In—Ga—Sn—Zn oxide), or the like. Indium tin oxide containing silicon, or the like can also be used. 
     An element M (M is one or more of aluminum, silicon, boron, yttrium, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used instead of gallium. In particular, M is preferably one or more of gallium, aluminum and yttrium. 
     Alternatively, the sacrificial film  144   a  can be formed using an inorganic insulating material such as aluminum oxide, hafnium oxide, or silicon oxide. Use of an insulating material containing oxygen is preferable because damage to the EL film  112 Rf can be alleviated. 
     Note that a structure without the sacrificial film  144   a  can also be employed. The process can be simplified when the sacrificial film  144   a  is omitted. 
     [Formation of Protective Film  146   a ] 
     Next, the protective film  146   a  is formed over the sacrificial film  144   a.    
     The protective film  146   a  is a film used as a hard mask when the sacrificial film  144   a  is etched later. In a later step of processing the protective film  146   a , the sacrificial film  144   a  is exposed. Thus, the combination of films having high etching selectivity therebetween is selected for the sacrificial film  144   a  and the protective film  146   a . It is preferable to select a film that can be used for the protective film  146   a  depending on an etching condition of the sacrificial film  144   a  and an etching condition of the protective film  146   a.    
     For example, in the case where dry etching using a gas containing fluorine (also referred to as a fluorine-based gas) is performed for the etching of the protective film  146   a , the protective film  146   a  can be formed using silicon, silicon nitride, silicon oxide, tungsten, titanium, molybdenum, tantalum, tantalum nitride, an alloy containing molybdenum and niobium, an alloy containing molybdenum and tungsten, or the like. Here, a metal oxide film using IGZO, ITO, or the like is given as a film having high etching selectivity (that is, enabling low etching rate) in dry etching using the fluorine-based gas, and such a film can be used as the sacrificial film  144   a.    
     Without being limited to the above, a material of the protective film  146   a  can be selected from a variety of materials depending on etching conditions of the sacrificial film  144   a  and the protective film  146   a . For example, a material of the protective film  146   a  can be selected from the above-described films that can be used for the sacrificial film  144   a.    
     As the protective film  146   a , a nitride film can be used, for example. Specifically, a nitride such as silicon nitride, aluminum nitride, hafnium nitride, titanium nitride, tantalum nitride, tungsten nitride, gallium nitride, or germanium nitride can be used. 
     Alternatively, as the protective film  146   a , an organic film that can be used for the EL film  112 Rf or the like can be used. For example, the protective film  146   a  a can be formed using the same organic film that are used for the EL film  112 Rf, an EL film  112 Gf, or an EL film  112 Bf. Use of such an organic film for the protective film  146   a  is preferable because the same film-formation apparatus can be used for formation of the EL film  112 Rf or the like. 
     Note that a structure without the protective film  146   a  can be employed. The process can be simplified when the protective film  146   a  is omitted. 
     [Formation of Resist Mask  143   a ] Next, a resist mask  143   a  is formed over the protective film  146   a  ( FIG. 8A ). 
     For the resist mask  143   a , a resist material using a photosensitive resin such as a positive type resist material or a negative type resist material can be used. 
     On the assumption that the resist mask  143   a  is formed over the sacrificial film  144   a  without the protective film  146   a  therebetween, there is a risk of dissolving the EL film  112 Rf due to a solvent of the resist material if a defect such as a pinhole exists in the sacrificial film  144   a . Also in the case where the resist mask  143   a  is formed over the EL film  112 Rf without the sacrificial film  144   a , there is a similar risk of dissolving the EL film  112 Rf. Thus, with use of the sacrificial film  144   a  and the protective film  146   a , such a problem can be prevented. 
     [Etching of Protective Film  146   a ] 
     Next, part of the protective film  146   a  that is not covered with the resist mask  143   a  is removed by etching, so that an island-shaped or band-shaped protective layer  147   a  can be formed. 
     In the etching of the protective film  146   a , an etching condition with high selectively is preferably employed so that the sacrificial film  144   a  is not removed by the etching. Either wet etching or dry etching can be performed for the etching of the protective film  146   a . With use of dry etching, a reduction in a processing pattern of the protective film  146   a  can be inhibited. 
     [Removal of Resist Mask  143   a ] 
     Then, the resist mask  143   a  is removed. 
     The removal of the resist mask  143   a  can be performed by wet etching or dry etching. It is particularly preferable to perform dry etching (also referred to as plasma ashing) using an oxygen gas as an etching gas to remove the resist mask  143   a.    
     At this time, the removal of the resist mask  143   a  is performed in a state where the EL film  112 Rf is covered with the sacrificial film  144   a ; thus, the EL film  112 Rf is less likely to be affected by the removal. In particular, when the EL film  112 Rf is exposed to oxygen, the electrical characteristics of the light-emitting element are adversely affected in some cases. Therefore, it is preferable that the EL film  112 Rf be covered by the sacrificial film  144   a  when etching using an oxygen gas, such as plasma ashing, is performed. 
     [Etching of Sacrificial Film  144   a ] 
     Next, part of the protective layer  147   a  that is not covered with the sacrificial film  144   a  is removed with use of the protective layer  147   a  as a mask, so that an islands-shaped or band-shaped sacrificial layer  145   a  is formed. 
     Either wet etching or dray etching can be performed for the etching of the sacrificial film  144   a . With use of dry etching, a reduction in a processing pattern of the sacrificial film  144   a  can be inhibited. 
     [Etching of EL Film  112 Rf] 
     Next, part of the EL film  112 Rf that is not covered with the sacrificial layer  145   a  is removed by etching, so that an island-shaped or band-shaped EL layer  112 R is formed ( FIG. 8B ). 
     For the etching of the EL film  112 Rf, it is preferable to perform dry etching using an etching gas that does not contain oxygen as its main component. This is because the alteration of the EL film  112 Rf is inhibited, and a highly reliable display device can be achieved. Examples of the etching gas that does not contain oxygen as its main component include CF 4 , C 4 F 8 , SF 6 , CHF 3 , Cl 2 , H 2 O, BCl 3 , or a rare gas such as He. Alternatively, a mixed gas of the above gas and a dilution gas that does not contain oxygen can be used the etching gas. In the etching of the EL film  112 Rf, the protective layer  147   a  may be removed. 
     [Formation of EL Layer  112 G and EL Layer  112 B] 
     Next, the EL film  112 Gf that is to be the EL layer  112 G in a later step is formed over the sacrificial layer  145   a  and the exposed conductive film  111   f . For the EL film  112 Gf, the description of the EL film  112 Rf can be referred to. 
     Then, a sacrificial layer  144   b  is formed over the EL film  112 Gf, and a protective film  146   b  is formed over the sacrificial layer  144   b . For the sacrificial layer  144   b , the description of the sacrificial film  144   a  can be referred to. For the protective film  146   b , the description of the protective film  146   a  can be referred to. 
     Next, a resist mask  143   b  is formed over the protective film  146   b  ( FIG. 8C ). 
     Then, the protective film  146   b  is etched with use of the resist mask  143   b , so that a protective layer  147   b  is formed. After that, the resist mask  143   b  is removed. 
     Next, the sacrificial layer  144   b  and the EL film  112 Gf are each etched with use of the protective layer  147   b  as a mask, so that a sacrificial layer  145   b  and the EL layer  112 G are formed ( FIG. 8D ). 
     Next, the EL film  112 Bf that is to be the EL layer  112 B in a later step is formed over the sacrificial layer  145   a , the sacrificial layer  145   b , and the exposed conductive film  111   f . For the EL film  112 Bf, the description of the EL film  112 Rf can be referred to. 
     Next, a sacrificial layer  144   c  is formed over the EL film  112 Bf, and a protective film  146   c  is formed over the sacrificial layer  144   c . For the sacrificial layer  144   c , the description of the sacrificial film  144   a  can be referred to. For the protective film  146   c , the description of the protective film  146   a  can be referred to. 
     Next, a resist mask  143   c  is formed over the protective film  146   c  ( FIG. 8E ). 
     Then, the protective film  146   c  is etched with use of the resist mask  143   c , so that a protective layer  147   c  is formed. After that, the resist mask  143   c  is removed. 
     Next, the sacrificial layer  144   c  and the EL film  112 Bf are each etched with use of the protective layer  147   c  as a mask, so that a sacrificial layer  145   c  and the EL layer  112 B are formed ( FIG. 8F ). 
     [Formation of Pixel Electrodes  111 R,  111 G, and  111 B] 
     Next, part of the conductive film  111   f  that is not covered with the EL layer  112 R, the EL layer  112 G, the EL layer  112 B, the sacrificial layer  145   a , the sacrificial layer  145   b , the sacrificial layer  145   c , the protective layer  147   a , the protective layer  147   b , or the protective layer  147   c  is etched, so that the pixel electrode  111 R, the pixel electrode  111 G, and the pixel electrode  111 B are formed. 
     Note that at this time, the etching for forming the pixel electrode  111 R, the pixel electrode  111 G, and the pixel electrode  111 B is performed ( FIG. 9A ) so that each pixel electrode is not provided in a region below the end portion of the EL layer (the region  200  in  FIGS. 3A to 3F  and the like) as illustrated in  FIG. 1B . 
     Either wet etching or dry etching can be performed for the etching of the conductive film  111   f , and the etching condition is changed as appropriate, whereby processing into the shape illustrated in  FIG. 1B  is possible. Specifically, wet etching enables formation of a pixel electrode whose end portions are overetched (also referred to as side etched). Alternatively, when dry etching is performed, an etching gas that does not contain oxygen as its main component is used, whereby damage to an EL layer  112  (the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B) can be alleviated. With the combination of these methods as appropriate, the conductive film  111   f  can be processed into a desired shape. 
     Note that the etching of the conductive film  111   f  may be performed before the formation of the EL film  112 Rf and after the formation of the conductive film  111   f  illustrated in  FIG. 8A . In that case, when the side etching of the conductive film  111   f  is performed as described, damage to the EL layer  112  may be alleviated. 
     Furthermore, after the pixel electrode  111 R, the pixel electrode  111 G, and the pixel electrode  111 B are formed as described, the side surfaces of the pixel electrodes are altered, whereby an insulator may be formed on the side surfaces. For example, each of the side surfaces is oxidized to have a region containing oxygen. In this manner, an insulating region can be formed in the region  200  as illustrated in  FIG. 4C , and each of the pixel electrodes can be prevented from being in contact with the common electrode  113 . Note that an insulating layer may be formed on each side surface by a method other than the alteration of the side surface of the pixel electrode. 
     [Removal of Protective Layers  147   a  to  147   c  and Sacrificial Layers  145   a  to  145   c ] 
     Next, the protective layer  147   a , the protective layer  147   b , the protective layer  147   c , the sacrificial layer  145   a , the sacrificial layer  145   b , and the sacrificial layer  145   c  are removed, whereby top surfaces of the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B are exposed ( FIG. 9B ). 
     The protective layer  147   a , the protective layer  147   b , and the protective layer  147   c  can be removed by wet etching or dry etching. 
     The sacrificial layer  145   a , the sacrificial layer  145   b , and the sacrificial layer  145   c  can be removed by wet etching or dry etching. At this time, a method that causes damage to the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B as little as possible is preferably employed. In particular, a wet etching method is preferably used. For example, wet etching using a tetramethyl ammonium hydroxide (TMAH) solution, diluted hydrofluoric acid, oxalic acid, phosphoric acid, acetic acid, nitric acid, or a mixed solution thereof is preferably performed. With use of the conditions of wet etching, for example, damage to the insulating layer can be alleviated. 
     In this manner, the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B can be formed separately. 
     [Formation of Common Electrode  113 ] 
     Next, the common electrode  113  is formed to cover the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B ( FIG. 9C ). The common electrode  113  can be formed by a sputtering method or an evaporation method, for example. The deposition condition of the common electrode  113 , the shape or thickness of the EL layer, or the shape or thickness of the pixel electrode is changed as appropriate, whereby the common electrode  113  can be formed into the shape as illustrated in  FIG. 1B . 
     Through the above steps, the display device  100 A including the light-emitting element  110 R, the light-emitting element  110 G, and the light-emitting element  110 B as illustrated in  FIGS. 1B and 1C  can be manufactured. 
     Modification Example of Manufacturing Method 
     A modification example of the above-described manufacturing method example is described below. 
     [Formation of Protective Layer  121 ] 
     The protective layer  121  may be formed over the common electrode  113  in  FIG. 9C .  FIG. 6C  illustrates a detailed structure where the protective layer  121  is formed. The protective layer  121  has a function of preventing diffusion of impurities such as water into each light-emitting element from the above. 
     The protective layer  121  can have, for example, a single-layer structure or a stacked-layer structure at least including an inorganic insulating film. Examples of the inorganic insulating film include an oxide film or a nitride film such as a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, a silicon nitride film, an aluminum oxide film, an aluminum oxynitride film, or a hafnium oxide film. Alternatively, a semiconductor material such as indium gallium oxide or indium gallium zinc oxide may be used for the protective layer  121 . 
     As the protective layer  121 , a stacked film of an inorganic insulating film and an organic insulating film can be used. For example, a structure in which an organic insulating film is sandwiched between a pair of inorganic insulating films is preferable. Furthermore, it is preferable that the organic insulating film function as a planarization film. With this structure, the top surface of the organic insulating film can be flat, and accordingly, coverage with the inorganic insulating film over the organic insulating film is improved, leading to an improvement in barrier properties. Moreover, since the top surface of the protective layer  121  is flat, a preferable effect can be obtained; when a component (e.g., a color filter, an electrode of a touch sensor, a lens array, or the like) is provided above the protective layer  121 , the component is less affected by an uneven shape caused by the lower structure. 
     The protective layer  121  is preferably formed by a sputtering method, a PECVD method, or an ALD method. In particular, an ALD method is preferable because a film deposited by ALD has good step coverage and is less likely to cause a defect such as pinhole. The organic insulating film is preferably formed by an inkjet method because a uniform film can be formed in a desired area. 
     A layer (also referred to as a cap layer or as a protective layer) may be provided between the common electrode  113  and the protective layer  121 . The cap layer has a function of preventing light emitted from the light-emitting elements from being totally reflected by light. The cap layer is preferably formed using a material having a higher refractive index than the common electrode  113 . The cap layer can be formed using an organic substance or inorganic organic substance. The thickness of the cap layer is preferably larger than that of the common electrode  113 . The cap layer may have a function of preventing diffusion of impurities such as water from the above into each of the light-emitting elements. 
     [Formation of Common Layer  114 ] 
     The common layer  114  may be formed over the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B illustrated in  FIG. 9B .  FIGS. 7A to 7E  each illustrate a detailed structure where the common layer  114  is formed. 
     Like the common electrode  113 , the common layer  114  is provided across a plurality of light-emitting elements. The common layer  114  is provided to cover the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B. When the common layer  114  is included, the manufacturing process can be simplified, so that the manufacturing cost can be reduced. The common layer  114  and the common electrode  113  can be formed successively without a step such as etching performed between the formations of the common layers  114  and  113 . Thus, the interface between the common layer  114  and the common electrode  113  can be clean, and the light-emitting element can have favorable characteristics. 
     The common layer  114  is preferably in contact with one or more of the top surfaces of the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B. 
     Each of the EL layer  112 R, the EL layer  112 G, and the EL layer  112 B preferably includes at least a light-emitting layer containing a light-emitting material emitting one color. The common layer  114  preferably includes one or more of an electron-injection layer, an electron-transport layer, a hole-injection layer, and a hole-transport layer, for example. In the light-emitting element in which the pixel electrode serves as an anode and the common electrode serves as a cathode, a structure including the electron-injection layer or a structure including the electron-injection layer and the electron-transport layer can be used as the common layer  114 . 
     The common layer  114  can be formed by, for example, an evaporation method, a sputtering method, or an inkjet method. Without limitation to this, the above-described film-formation method can be used as appropriate. With control of the film-formation condition, the structure illustrated in any of  FIGS. 7A to 7E  can be formed. 
     [Formation of Optical Adjustment Layer  115 R] 
     A film that is to be the optical adjustment layer  115 R may be formed over the conductive film  111   f  in  FIG. 8A . In that case, in the step in  FIG. 9A , the conductive film  111   f  and the film to be the optical adjustment layer  115 R are etched to form a stack of the pixel electrode  111 R and the optical adjustment layer  115 R.  FIG. 5A  to  FIG. 7E  each illustrate a detailed structure where the optical adjustment layer  115 R is formed. 
     In the case where the thickness of the optical adjustment layer differs between the light-emitting elements, in each of the steps of  FIGS. 8A, 8C, and 8E , the film to be the optical adjustment layer is formed to have a desired thickness before the EL layer (e.g., the EL layer  112 R) is formed. Then, the film to be the optical adjustment layer may be etched together with the EL layer (e.g., the EL layer  112 R). After that, in the step of  FIG. 9A , the conductive film  111   f  and the optical adjustment layers can be subjected to side etching together. 
     An optical adjustment layer  115  (including the optical adjustment layer  115 R, an optical adjustment layer  115 G not illustrated, and an optical adjustment layer  115 B not illustrated) can make the optical path length in a microcavity structure different between the light-emitting elements, thereby increasing the intensity of light with a specific wavelength. Thus, a display device with high color purity can be achieved. 
     For example, with a layer transmitting visible light as the optical adjustment layer, the optical path lengths can vary between the light-emitting elements. For example, an optical adjustment layer  115  may be provided between the pixel electrode  111  and the EL layer  112 . As the optical adjustment layer  115 , a conductive material that transmits visible light can be used, for example. For example, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zinc oxide containing gallium, indium-tin oxide containing silicon, or an indium-zinc oxide containing silicon can be used. 
     The optical adjustment layer can be formed before the EL film  112 Rf is formed and after the conductive film to be the pixel electrodes ( 111 R,  111 G, or  111 B) is formed. The optical adjustment layers are formed to have different thicknesses, whereby the optical path length can differ between the light-emitting elements. The optical adjustment layers may be formed using conductive films with different thicknesses from each other or may have a single-layer structure, a two-layer structure, or a three-layer structure, in the order of thin thickness. 
     In the case where the optical adjustment layer  115  is not provided, the thickness of the EL layer  112  differs between the light-emitting elements, whereby a microcavity structure can be obtained. For example, the EL layer  112 R of the light-emitting element  110 R emitting light whose wavelength is longest can be made to have the largest thickness, and the EL layer  112 B of the light-emitting element  110 B emitting light whose wavelength is shortest can be made to have the smallest thickness. Without limitation to this, the thickness of the EL layer can be adjusted in consideration of the wavelength of light emitted by the light-emitting element, optical characteristics of the layer included in the light-emitting element, electrical characteristics of the light-emitting element, and the like. 
     Alternatively, the optical adjustment layer  115  may be combined with the EL layer  112  formed to have a different thickness depending on emitted colors. In that case, the optical adjustment layer  115  can have the same thickness between the light-emitting elements. An example in which this combination is employed is described below. 
     Structure Example 2 of Display Device 
       FIG. 10  illustrates a structure example of a display device using optical adjustment layers and EL layers whose thicknesses are different depending on emitted colors. 
     In a display device  100 B illustrated in  FIG. 10 , the light-emitting element  110 R includes the optical adjustment layer  115 R between the pixel electrode  111 R and the EL layer  112 R. The light-emitting element  110 G includes an optical adjustment layer  115 G between the pixel electrode  111 G and the EL layer  112 G. The light-emitting element  110 B includes an optical adjustment layer  115 B between the pixel electrode  111 B and the EL layer  112 B. With the optical adjustment layers, each optical path length can be adjusted. 
     Furthermore, the thickness of the EL layer  112  is differentiated between the light-emitting elements. In this manner, the optical path length can be optimized for each color, and an optical microcavity structure for each color can be obtained. In the structure illustrated here, the EL layer  112 R of the light-emitting element  110 R emitting light whose wavelength is longest is formed to have the largest thickness, and the EL layer  112 B of the light-emitting element  110 B emitting light whose wavelength is shortest is formed to have a smallest thickness. The manufacturing method example of the structure example 2 is as described above. 
     At least part of any of the structures, the structure examples, the manufacturing method examples, the drawings corresponding thereto, and the like described in this embodiment can be implemented in combination with any of the other structures, the other structure examples, the other manufacturing method examples, the other drawings corresponding thereto, and the like as appropriate. 
     Embodiment 2 
     In this embodiment, a structure example of a display device of one embodiment of the present invention will be described. 
     The display device in this embodiment can be a high-resolution display device or large-sized display device. Accordingly, the display device of this embodiment can be used for display portions of electronic devices such as a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game console, a smart phone, a wristwatch terminal, a tablet terminal, a portable information terminal, and an audio reproducing device, in addition to display portions of electronic devices with a relatively large screen, such as a television device, a desktop or laptop personal computer, a monitor of a computer or the like, digital signage, and a large game machine such as a pachinko machine. 
     [Display Device  400 A] 
       FIG. 11  is a perspective view of a display device  400 A, and  FIG. 12A  is a cross-sectional view of the display device  400 A. Note that as the display device, the display device  100 A, the display device  100 B, and display devices  400 A to  400 E, which are disclosed in this specification, can be employed as appropriate. 
     The display device  400 A has a structure where a substrate  452  and a substrate  451  are bonded to each other. In  FIG. 11 , the substrate  452  is denoted by a dashed line. 
     The display device  400 A includes a display portion  462 , a circuit  464  (also referred to as a circuit portion), a wiring  465 , and the like.  FIG. 11  illustrates an example in which an integrated circuit (IC)  473  and an FPC  472  are implemented on the display device  400 A. Thus, the structure illustrated in  FIG. 11  can be regarded as a display module including the display device  400 A, the IC, and the FPC. 
     As the circuit  464 , a scan line driver circuit can be used, for example. 
     The wiring  465  has a function of supplying a signal and power to the display portion  462  and the circuit  464 . The signal and power are input to the wiring  465  from the outside through the FPC  472  or from the IC  473 . 
       FIG. 11  illustrates an example in which the IC  473  is provided over the substrate  451  by a COG method, a chip on film (COF) method, or the like. An IC including a scan line driver circuit, a signal line driver circuit, or the like can be used as the IC  473 , for example. Note that the display devices  400 A to  400 C and the display module are not necessarily provided with an IC. The IC may be mounted on the FPC by a COF method or the like. 
       FIG. 12A  illustrates an example of cross sections of part of a region including the FPC  472 , part of the circuit  464 , part of the display portion  462 , and part of a region including an end portion of the display device  400 A. 
     The display device  400 A illustrated in  FIG. 12A  includes a transistor  201 , a transistor  205 , a light-emitting element  430   a  which emits red light, a light-emitting element  430   b  which emits green light, a light-emitting element  430   c  which emits blue light, and the like between the substrate  451  and the substrate  452 . 
     The light-emitting element described in Embodiment 1 or the like can be employed for the light-emitting element  430   a , the light-emitting element  430   b , and the light-emitting element  430   c . Specifically, the common layer  114  and the common electrode  113  can be positioned so as not to be in contact with the pixel electrodes  411   a  to  411   c  in a region below end portions of EL layers  416   a  to  416   c  in the light-emitting elements  430   a  to  430   c . The protective layer  121  is provided over the common electrode  113 . 
     In the case where a pixel of the display device includes three kinds of subpixels including light-emitting devices emitting different colors from each other, the three subpixels can be of three colors of R, G, and B or of three colors of yellow (Y), cyan (C), and magenta (M). In the case where four subpixels are included, the four subpixels can be of four colors of R, G, B, and white (W) or of four colors of R, G, B, and Y. 
     The protective layer  121  and the substrate  452  are bonded to each other with the adhesive layer  442 . A solid sealing structure, a hollow sealing structure, or the like can be employed to seal the light-emitting elements. 
     In the case of employing a hollow sealing structure, a region  443  surrounded by the substrate  452 , the adhesive layer  442 , and the substrate  451  includes a region filled with an inert gas (e.g., nitrogen or argon). The adhesive layer  442  may overlap with the light-emitting element. 
     In the case of employing a solid sealing structure, an adhesive layer may be provided in the region  443 . Alternatively, the adhesive layer  442  is not necessarily provided. 
     In the display device of one embodiment of the present invention, a gap (also referred to as a distance) is provided between the common electrode  113  and the substrate  452 . The gap includes a first gap in a region overlapping with the light-emitting element and a second gap in a region not overlapping with the light-emitting element (the region having the second gap is also referred to as a region between two light-emitting element). The second gap can be larger than the first gap. 
     Light from the light-emitting element is emitted toward the substrate  452 . For the substrate  452 , a material having a high visible-light-transmitting property is preferably used. 
     In addition, a circuit including the transistor is provided below the light-emitting element. The detailed description thereof is given below. 
     The transistor  201  and the transistor  205  are formed over the substrate  451 . These transistors can be fabricated using the same material in the same step. 
     An insulating layer  211 , an insulating layer  213 , an insulating layer  215 , and an insulating layer  214  are provided in this order over the substrate  451 . Part of the insulating layer  211  functions as a gate insulating layer of each transistor. Part of the insulating layer  213  functions as a gate insulating layer of each transistor. The insulating layer  215  is provided to cover the transistors. The insulating layer  214  is provided to cover the transistors and has a function of a planarization layer. Note that the number of gate insulating layers and the number of insulating layers covering the transistors are not limited and may each be one or two or more. 
     A material through which impurities such as water and hydrogen do not easily diffuse is preferably used for at least one of the insulating layers covering the transistors. This is because such an insulating layer can function as a barrier layer. Such a structure can effectively inhibit diffusion of impurities into the transistors from the outside and increase the reliability of a display device. 
     An inorganic insulating film is preferably used as each of the insulating layers  211 ,  213 , and  215 . As the inorganic insulating film, a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon nitride oxide film, an aluminum oxide film, or an aluminum nitride film can be used, for example. 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, a neodymium oxide film, or the like may be used. A stack including two or more of the above insulating films may also be used. 
     Here, an organic insulating film often has a lower barrier property than an inorganic insulating film. Therefore, the organic insulating film preferably has an opening in the vicinity of an end portion of the display device  400 A. This can inhibit entry of impurities from the end portion of the display device  400 A through the organic insulating film. Alternatively, the organic insulating film may be formed so that its end portion is positioned on the inner side compared to the end portion of the display device  400 A, to prevent the organic insulating film from being exposed at the end portion of the display device  400 A. 
     An organic insulating film is suitable for the insulating layer  214  functioning as a planarization layer. Examples of materials that can be used for the organic insulating film include an acrylic resin, a polyimide resin, an epoxy resin, a polyamide resin, a polyimide-amide resin, a siloxane resin, a benzocyclobutene-based resin, a phenol resin, and precursors of these resins. 
     In a region  228  illustrated in  FIG. 12A , an opening is formed in the insulating layer  214 , and the protective layer  121  is provided to cover the opening. This can inhibit entry of impurities into the display portion  462  from the outside through the insulating layer  214  even when an organic insulating film is used as the insulating layer  214 . Consequently, the reliability of the display device  400 A can be increased. 
     Each of the transistors  201  and  205 , includes a conductive layer  221  functioning as a gate, the insulating layer  211  functioning as a gate insulating layer, a conductive layer  222   a  and a conductive layer  222   b  functioning as a source and a drain, a semiconductor layer  231 , the insulating layer  213  functioning as a gate insulating layer, and a conductive layer  223  functioning as a gate. Here, a plurality of layers obtained by processing the same conductive film are shown with the same hatching pattern. The insulating layer  211  is positioned between the conductive layer  221  and the semiconductor layer  231 . The insulating layer  213  is positioned between the conductive layer  223  and the semiconductor layer  231 . 
     There is no particular limitation on the structure of the transistors included in the display device of this embodiment. For example, a planar transistor, a staggered transistor, or an inverted staggered transistor can be used. A top-gate transistor or a bottom-gate transistor can be used. Alternatively, gates may be provided above and below a semiconductor layer where a channel is formed. 
     The structure in which the semiconductor layer where a channel is formed is provided between two gates is used for the transistors  201  and  205 . The two gates may be connected to each other and supplied with the same signal to operate the transistor. Alternatively, the threshold voltage of the transistor may be controlled by applying a potential for controlling the threshold voltage to one of the two gates and a potential for driving to the other of the two gates. 
     There is no particular limitation on the crystallinity of a semiconductor material used in the transistor, 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) can be used. It is preferable to use a semiconductor having crystallinity, in which case deterioration of the transistor characteristics can be suppressed. 
     It is preferable that a semiconductor layer of a transistor contain a metal oxide (also referred to as an oxide semiconductor). That is, a transistor including a metal oxide in its channel formation region (hereinafter, also referred to as an OS transistor) is preferably used for the display device of this embodiment. Alternatively, a semiconductor layer of a transistor may contain silicon. Examples of silicon include amorphous silicon and crystalline silicon (e.g., low-temperature polysilicon or single crystal silicon). 
     The semiconductor layer preferably contains indium, M (M is one or more of gallium, aluminum, silicon, boron, yttrium, tin, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium), and zinc, for example. Specifically, M is preferably one or more of aluminum, gallium, yttrium, and tin. 
     It is particularly preferable that an oxide containing indium (In), gallium (Ga), and zinc (Zn) (also referred to as IGZO) be used as the semiconductor layer. 
     When the semiconductor layer is an In-M-Zn oxide, the atomic ratio of In is preferably greater than or equal to the atomic ratio of M in the In-M-Zn oxide. Examples of the atomic ratio of the metal elements in such an In-M-Zn oxide are In:M:Zn=1:1:1, 1:1:1.2, 2:1:3, 3:1:2, 4:2:3, 4:2:4.1, 5:1:3, 5:1:6, 5:1:7, 5:1:8, 6:1:6, and 5:2:5 and a composition in the vicinity of any of the above atomic ratios. Note that the vicinity of the atomic ratio includes ±30% of an intended atomic ratio. 
     For example, in the case of describing an atomic ratio of In:Ga:Zn=4:2:3 or a composition in the vicinity thereof, the case is included in which with the atomic proportion of In being 4, the atomic proportion of Ga is greater than or equal to 1 and less than or equal to 3 and the atomic proportion of Zn is greater than or equal to 2 and less than or equal to 4. In the case of describing an atomic ratio of In:Ga:Zn=5:1:6 or a composition in the vicinity thereof, the case is included in which with the atomic proportion of In being 5, the atomic proportion of Ga is greater than 0.1 and less than or equal to 2 and the atomic proportion of Zn is greater than or equal to 5 and less than or equal to 7. In the case of describing an atomic ratio of In:Ga:Zn=1:1:1 or a composition in the vicinity thereof, the case is included in which with the atomic proportion of In being 1, the atomic proportion of Ga is greater than 0.1 and less than or equal to 2 and the atomic proportion of Zn is greater than 0.1 and less than or equal to 2. 
     The transistor included in the circuit  464  and the transistor included in the display portion  462  may have the same structure or different structures. One structure or two or more kinds of structures may be employed for a plurality of transistors included in the circuit  464 . Similarly, one structure or two or more kinds of structures may be employed for a plurality of transistors included in the display portion  462 . 
     A connection portion is provided in a region of the substrate  451  where the substrate  452  does not overlap. In the connection portion, the wiring  465  is electrically connected to the FPC  472  through a conductive layer  466  and a connection layer  242 . An example is illustrated in which the conductive layer  466  has a stacked-layer structure of a conductive film obtained by processing the same conductive film as the pixel electrode and a conductive film obtained by processing the same conductive film as the optical adjustment layer. On a top surface of the connection portion, the conductive layer  466  is exposed. Thus, the connection portion and the FPC  472  can be electrically connected to each other through the connection layer  242 . 
     A light-blocking layer  417  is preferably provided on the surface of the substrate  452  on the substrate  451  side. A variety of optical members can be arranged on the outer surface of the substrate  452 . Examples of the optical members include a polarizing plate, a retardation plate, a light diffusion layer (e.g., a diffusion film), an anti-reflective layer, and a light-condensing film. Furthermore, an antistatic film preventing the attachment of dust, a water repellent film suppressing the attachment of stain, a hard coat film suppressing generation of a scratch caused by the use, an impact-absorbing layer, or the like may be arranged on the outer surface of the substrate  452 . 
     When the protective layer  121  covering the light-emitting element is provided, which prevents an impurity such as water from entering the light-emitting element. As a result, the reliability of the light-emitting element can be enhanced. 
     In the region  228  in the vicinity of the end portion of the display device  400 A, the insulating layer  215  and the protective layer  121  are preferably in contact with each other through an opening in the insulating layer  214 . In particular, the inorganic insulating film included in the insulating layer  215  and the inorganic insulating film included in the protective layer  121  are preferably in contact with each other. This can inhibit entry of impurities into the display portion  462  from the outside through the insulating layer  214  even when an organic insulating film is used as the insulating layer  214 . Consequently, the reliability of the display device  400 A can be enhanced. 
     For each of the substrates  451  and  452 , glass, quartz, ceramic, sapphire, a resin, a metal, an alloy, a semiconductor or the like can be used. The substrate on the side from which light from the light-emitting element is extracted is formed using a material which transmits the light. When the substrates  451  and  452  are formed using a flexible material, the flexibility of the display device can be increased. Furthermore, a polarizing plate may be used as the substrate  451  or the substrate  452 . 
     For each of the substrate  451  and the substrate  452 , any of the following can be used, for example: polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, an acrylic resin, a polyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, polyamide resins (e.g., 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 polytetrafluoroethylene (PTFE) resin, an ABS resin, and cellulose nanofiber. Glass that is thin enough to have flexibility may be used for one or both of the substrate  451  and the substrate  452 . 
     In the case where a circularly polarizing plate overlaps with the display device, a highly optically isotropic substrate is preferably used as the substrate included in the display device. A highly optically isotropic substrate has a low birefringence (in other words, a small amount of birefringence). 
     The absolute value of a retardation (phase difference) of a highly optically isotropic substrate is preferably less than or equal to 30 nm, further preferably less than or equal to 20 nm, still further preferably less than or equal to 10 nm. 
     Examples of the film having high optical isotropy include a triacetyl cellulose (TAC, also referred to as cellulose triacetate) film, a cycloolefin polymer (COP) film, a cycloolefin copolymer (COC) film, and an acrylic film. 
     When a film is used for the substrate and the film absorbs water, the shape of the display panel might be changed, e.g., creases are generated. Thus, for the substrate, a film with a low water absorption rate is preferably used. For example, the water absorption rate of the film is preferably 1% or lower, further preferably 0.1% or lower, still further preferably 0.01% or lower. 
     As the adhesive layer  442 , any of a variety of curable adhesives such as a reactive curable adhesive, a thermosetting curable adhesive, an anaerobic adhesive, and a photocurable adhesive such as an ultraviolet curable adhesive can be used. Examples of these adhesives include an epoxy resin, an acrylic resin, a silicone resin, a phenol resin, a polyimide resin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, and an ethylene vinyl acetate (EVA) resin. In particular, a material with low moisture permeability, such as an epoxy resin, is preferred. A two-component-mixture-type resin may be used. An adhesive sheet or the like may be used. 
     As the connection layer  242 , an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like can be used. 
     As materials for the gates, the source, and the drain of a transistor and conductive layers functioning as wirings and electrodes included in the display device, 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 can be used. A single-layer structure or a stacked-layer structure including a film containing any of these materials can be used. 
     As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide containing gallium, or graphene can be used. It is also possible to use a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium; or an alloy material containing any of these metal materials. Alternatively, a nitride of the metal material (e.g., titanium nitride) or the like may be used. Note that in the case of using the metal material or the alloy material (or the nitride thereof), the thickness is preferably set small enough to transmit light. Alternatively, a stacked film of any of the above materials can be used for the conductive layers. For example, a stacked film of indium tin oxide and an alloy of silver and magnesium is preferably used because conductivity can be increased. They can also be used for conductive layers such as wirings and electrodes included in the display device, and conductive layers (e.g., a conductive layer functioning as a pixel electrode or a common electrode) included in a light-emitting element. 
     Examples of insulating materials that can be used for the insulating layers include a resin such as an acrylic resin and an epoxy resin, and an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, and aluminum oxide. 
     In the case where any of the structures illustrated in  FIGS. 7B to 7E  is employed, the display device can have a structure in which the transistor  201  in the circuit  464  does not overlap with the common layer  114 . 
       FIGS. 12B and 12C  each illustrate a structure example of a transistor different from that in  FIG. 12A . 
     In  FIG. 12B , a transistor  202  includes the conductive layer  221  functioning as a gate, the insulating layer  211  functioning as a gate insulating layer, a semiconductor layer  231  including a channel formation region  231   i  and a pair of low-resistance regions  231   n , the conductive layer  222   a  connected to one of the low-resistance regions  231   n , the conductive layer  222   b  connected to the other low-resistance region  231   n , an insulating layer  225  functioning as a gate insulating layer, the conductive layer  223  functioning as a gate, and the insulating layer  215  covering the conductive layer  223 . The insulating layer  211  is positioned between the conductive layer  221  and the channel formation region  231   i . The insulating layer  225  is positioned between the conductive layer  223  and the channel formation region  231   i.    
     The conductive layer  222   a  and the conductive layer  222   b  are each connected to the corresponding low-resistance region  231   n  through openings provided in the insulating layer  225  and the insulating layer  215 . One of the conductive layers  222   a  and  222   b  serves as a source, and the other serves as a drain of the transistor  202 . 
       FIG. 12B  illustrates an example in which the insulating layer  225  covers a top and side surfaces of the semiconductor layer  231 . The conductive layer  222   a  and the conductive layer  222   b  are each connected to the corresponding low-resistance region  231   n  through openings provided in the insulating layer  225  and the insulating layer  215 . Furthermore, an insulating layer  218  covering the transistor  202  may be provided. 
     In a transistor  209  illustrated in  FIG. 12C , the insulating layer  225  overlaps with the channel formation region  231   i  of the semiconductor layer  231  and does not overlap with the low-resistance regions  231   n . The structure illustrated in  FIG. 12C  is obtained by processing the insulating layer  225  with the conductive layer  223  as a mask, for example. In  FIG. 12C , the insulating layer  215  is provided to cover the insulating layer  225  and the conductive layer  223 , and the conductive layer  222   a  and the conductive layer  222   b  are connected to the low-resistance regions  231   n  through the openings in the insulating layer  215 . Furthermore, an insulating layer  218  covering the transistor  209  may be provided. 
     [Display Device  400 B- 1 ] 
       FIG. 13  illustrates a structure example of a display device  400 B- 1 . The display device  400 B- 1  includes optical adjustment layers  415   a  to  415   c , and the EL layers  416   a  to  416   c  with different thicknesses depending on emitted colors. Specifically, the structure described in Embodiment 1 or the like can be used. 
     In addition, as illustrated in  FIG. 13 , a layer  414  may be provided in openings provided in the insulating layer  214  to be over the pixel electrodes  411   a ,  411   b , and  411   c . With the layer  414 , unevenness of surfaces where the optical adjustment layer  415   a , the optical adjustment layer  415   b , the optical adjustment layer  415   c , the EL layer  416   a , the EL layer  416   b , and the EL layer  416   c  are formed can be reduced, and coverage can be improved. The layer  414  can also be provided in the region including the FPC  472 . The layer  414  preferably has an insulating property. Alternatively, the layer  414  may be a conductive layer. Note that it is possible to employ a structure where the layer  414  is provided in the pixel portion but not provided in the connection portion or a structure where the layer  414  is provided in the connection portion but not provided in the pixel portion. 
       FIG. 13  shows a solid sealing structure in which an adhesive layer is provided in the region  443 . For the other components, the structures illustrated in  FIG. 12A to 12C  or the like may be employed as appropriate. 
     [Display Device  400 B- 2 ] 
       FIG. 14  illustrates a structure example of a display device  400 B- 2 . The display device  400 B- 2  has a structure where a substrate  453  and an insulating layer  212  are bonded to each other with an adhesive layer  455 . 
     As a method for manufacturing the display device  400 B- 2 , first, a formation substrate (not illustrated) is bonded to the substrate  452  provided with the light-blocking layer  417  are bonded to each other in region  443  with an adhesive layer. Here, the formation substrate is provided with the insulating layer  212 , the transistors  201  and  205 , the light-emitting elements  430   a  to  430   c , and the like. Then, the substrate  453  is attached to a surface exposed by separation of the formation substrate with use of the adhesive layer  455 , whereby the components formed over the formation substrate are transferred onto the substrate  453 . The substrate  453  and the substrate  452  are preferably flexible. Accordingly, the display device  400 B- 2  can be highly flexible. 
     The display device  400 B- 2  of one embodiment of the present invention can have a structure in which no partition layer is provided in a region between the light-emitting elements or a region above the driver circuit; thus, folding at the region can be facilitated. Such a region is preferably provided to overlap with a foldable region in the display device  400 B- 2 . For the other components, the structures illustrated in  FIG. 12A to 12C  or the like can be employed as appropriate. 
     At least part of any of the structures, the structure examples, the manufacturing method examples, the drawings corresponding thereto, and the like described in this embodiment can be implemented in combination with any of the other structures, the other structure examples, the other manufacturing method examples, the other drawings corresponding thereto, and the like as appropriate. 
     Embodiment 3 
     In this embodiment, a structure example of a display device different from the above will be described. 
     The display device in this embodiment can be a high-resolution display device. Thus, the display device in this embodiment can be used for display portions of information terminals (wearable devices) such as watch-type or bracelet-type information terminals and display portions of wearable devices capable of being worn on a head, such as a VR device such as a head mounted display and a glasses-type AR device. 
     [Display Module] 
       FIG. 15A  is a perspective view of a display module  280 . The display module  280  includes the display device  400 C and an FPC  290 . Note that as a display device included in the display module  280 , the display device  100 A, the display device  100 B, and the display devices  400 A to  400 E, which are disclosed in this specification, can be used as appropriate. 
     The display module  280  includes a substrate  291  and a substrate  292 . The display module  280  includes a display portion  281 . The display portion  281  is a region of the display module  280  where an image is displayed and is a region where light emitted from pixels provided in a pixel portion  284  described later can be seen. 
       FIG. 15B  is a perspective view schematically illustrating a structure on the substrate  291  side. Over the substrate  291 , a circuit portion  282 , a pixel circuit portion  283  over the circuit portion  282 , and the pixel portion  284  over the pixel circuit portion  283  are stacked. In addition, a terminal portion  285  for connection to the FPC  290  is included in a portion not overlapping with the pixel portion  284  over the substrate  291 . The terminal portion  285  and the circuit portion  282  are electrically connected to each other through a wiring portion  286  formed of a plurality of wirings. 
     The pixel portion  284  includes a plurality of pixels  284   a  arranged periodically. An enlarged view of one pixel  284   a  is illustrated on the right side in  FIG. 15B . The pixel  284   a  includes the light-emitting elements  430   a ,  430   b , and  430   c  whose emission colors are different from each other. The plurality of light-emitting elements are preferably arranged in a stripe pattern as illustrated in  FIG. 15B . Arrangement in a stripe pattern enables the light-emitting elements of one embodiment of the present invention to be arranged densely over the pixel circuit; thus, a high-resolution display device can be provided. Alternatively, a variety of kinds of patterns such as a delta pattern or a pentile pattern can be employed. 
     The pixel circuit portion  283  includes a plurality of pixel circuits  283   a  arranged periodically. 
     One pixel circuit  283   a  is a circuit that controls light emission from three light-emitting elements included in one pixel  284   a . One pixel circuit  283   a  may be provided with three circuits each of which controls light emission of one light-emitting element. For example, the pixel circuit  283   a  can include at least one selection transistor, one current control transistor (driving transistor), and a capacitor for one light-emitting element. 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 of the selection transistor. With such a structure, an active-matrix display device is achieved. 
     The circuit portion  282  includes a circuit for driving the pixel circuits  283   a  in the pixel circuit portion  283 . For example, one or both of a gate line driver circuit and a source line driver circuit are preferably included. In addition, at least one of an arithmetic circuit, a memory circuit, a power supply circuit, and the like may be included. 
     The FPC  290  serves as a wiring for supplying a video signal or a power supply potential to the circuit portion  282  from the outside. An IC may be mounted on the FPC  290 . 
     The display module  280  can have a structure in which one or both of the pixel circuit portion  283  and the circuit portion  282  are stacked below the pixel portion  284 ; thus, the aperture ratio (the effective display area ratio) of the display portion  281  can be significantly high. For example, the aperture ratio of the display portion  281  can 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 pixels  284   a  can be arranged extremely densely and thus the display portion  281  can have greatly high resolution. For example, the pixels  284   a  are preferably arranged in the display portion  281  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, further more 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 module  280  has 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 module  280  is seen through a lens, pixels of the extremely-high-resolution display portion  281  included in the display module  280  are 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 being limited thereto, the display module  280  can be suitably used for electronic devices including a relatively small display portion. For example, the display module  280  can be favorably used in a display portion of a wearable electronic device, such as a wrist watch. 
     [Display Device  400 C] 
     The display device  400 C illustrated in  FIG. 16  includes a substrate  301 , the light-emitting elements  430   a ,  430   b , and  430   c , a capacitor  240 , and a transistor  310 . 
     The substrate  301  corresponds to the substrate  291  illustrated in  FIGS. 15A and 15B . A stacked structure (layer  401 ) including the substrate  301  and the components thereover (up to an insulating layer  255 ) corresponds to the substrate  101  in Embodiment 1. 
     The transistor  310  is a transistor whose channel formation region is in the substrate  301 . As the substrate  301 , a semiconductor substrate such as a single crystal silicon substrate can be used, for example. The transistor  310  includes part of the substrate  301 , a conductive layer  311 , a low-resistance region  312 , an insulating layer  313 , and an insulating layer  314 . The conductive layer  311  functions as a gate electrode. The insulating layer  313  is positioned between the substrate  301  and the conductive layer  311  and functions as a gate insulating layer. The low-resistance region  312  is a region where the substrate  301  is doped with an impurity, and functions as one of a source and a drain. The insulating layer  314  is provided to cover a side surface of the conductive layer  311  and functions as an insulating layer. 
     An element isolation layer  315  is provided between two adjacent transistors  310  to be embedded in the substrate  301 . 
     Furthermore, an insulating layer  261  is provided to cover the transistor  310 , and the capacitor  240  is provided over the insulating layer  261 . 
     The capacitor  240  includes a conductive layer  241 , a conductive layer  245 , and an insulating layer  243  between the conductive layers  241  and  245 . The conductive layer  241  functions as one electrode of the capacitor  240 , the conductive layer  245  functions as the other electrode of the capacitor  240 , and the insulating layer  243  functions as a dielectric of the capacitor  240 . 
     The conductive layer  241  is provided over the insulating layer  261  and is embedded in an insulating layer  254 . The conductive layer  241  is electrically connected to one of the source and the drain of the transistor  310  through a plug  271  embedded in the insulating layer  261 . The insulating layer  243  is provided to cover the conductive layer  241 . The conductive layer  245  is provided in a region overlapping with the conductive layer  241  with the insulating layer  243  therebetween. 
     The insulating layer  255  is provided to cover the capacitor  240 , and the light-emitting element  430   a , the light-emitting element  430   b , the light-emitting element  430   c , and the like are provided over the insulating layer  255 . The protective layer  121  is provided over the light-emitting elements  430   a ,  430   b , and  430   c , and a substrate  420  is bonded to a top surface of the protective layer  121  with a resin layer  419 . The substrate  420  corresponds to the substrate  292  in  FIG. 15A . 
     The pixel electrode of the light-emitting element is electrically connected to one of the source and the drain of the transistor  310  through a plug  256  embedded in the insulating layer  255 , the conductive layer  241  embedded in the insulating layer  254 , and the plug  271  embedded in the insulating layer  261 . 
     [Display Device  400 D] 
     A display device  400 D illustrated in  FIG. 17  is different from the display device  400 C mainly in a structure of the transistor. Note that portions similar to those in the display device  400 C are not be described in some cases. 
     A transistor  320  contains a metal oxide (also referred to as an oxide semiconductor) in a semiconductor layer where a channel is formed. 
     The transistor  320  includes a semiconductor layer  321 , an insulating layer  323 , a conductive layer  324 , a pair of conductive layers  325 , an insulating layer  326 , and a conductive layer  327 . 
     A substrate  331  corresponds to the substrate  291  in  FIGS. 15A and 15B . A stacked structure (layer  401 ) including the substrate  331  and the components thereover (up to the insulating layer  255 ) corresponds to the substrate  101  in Embodiment 1. As the substrate  331 , an insulating substrate or a semiconductor substrate can be used. 
     An insulating layer  332  is provided over the substrate  331 . The insulating layer  332  functions as a barrier layer that prevents diffusion of impurities such as water or hydrogen from the substrate  331  side into the transistor  320  and release of oxygen from the semiconductor layer  321  to the substrate  331  side. As the insulating layer  332 , for example, a film in which hydrogen or oxygen is less likely to diffuse than in a silicon oxide film can be used. Examples of such a silicon oxide film include an aluminum oxide film, a hafnium oxide film, and a silicon nitride film. 
     The conductive layer  327  is provided over the insulating layer  332 , and the insulating layer  326  is provided to cover the conductive layer  327 . The conductive layer  327  functions as a first gate electrode of the transistor  320 , and part of the insulating layer  326  functions as a first gate insulating layer. An oxide insulating film such as a silicon oxide film is preferably used as at least part of the insulating layer  326  that is in contact with the semiconductor layer  321 . In addition, the top surface of the insulating layer  326  is preferably planarized. 
     The insulating layer  326  is provided over the semiconductor layer  321 . A metal oxide film having semiconductor characteristics (also referred to as an oxide semiconductor film) is preferably used as the semiconductor layer  321 . A material that can be used for the semiconductor layer  321  is described in detail later. 
     The pair of conductive layers  325  is provided on and in contact with the semiconductor layer  321 , and functions as a source electrode and a drain electrode of the transistor  320 . 
     An insulating layer  328  is provided to cover top and side surfaces of the pair of conductive layers  325 , a side surface of the semiconductor layer  321 , and the like, and an insulating layer  264  is provided over the insulating layer  328 . The insulating layer  328  functions as a barrier layer that prevents diffusion of impurities such as water or hydrogen from the interlayer insulating layer  264  and the like into the semiconductor layer  321  and release of oxygen from the semiconductor layer  321 . As the insulating layer  328 , an insulating film similar to the insulating layer  332  can be used. 
     An opening reaching the semiconductor layer  321  is provided in the insulating layers  328  and  264 . In the opening, the insulating layer  323  is provided to be in contact with side surfaces of the insulating layer  264 , the insulating layer  328 , and the conductive layer  325  and in contact with a top surface of the semiconductor layer  321 , and the conductive layer  324  is provided over the insulating layer  323  so as to fill the opening. The conductive layer  324  functions as a second gate electrode of the transistor  320 , and the insulating layer  323  functions as a second gate insulating layer. 
     The top surface of the conductive layer  324 , the top surface of the insulating layer  323 , and the top surface of the insulating layer  264  are planarized so that they are substantially level with each other, and insulating layers  329  and  265  are provided to cover these layers. 
     The insulating layers  264  and  265  each function as an interlayer insulating layer. The insulating layer  329  functions as a barrier layer that prevents diffusion of impurities such as water or hydrogen from the insulating layer  265  or the like to the transistor  320 . As the insulating layer  329 , an insulating film similar to the insulating layers  328  and  332  can be used. 
     A plug  274  electrically connected to one of the pair of conductive layers  325  is provided to be embedded in the insulating layers  265 ,  329 , and  264 . Here, the plug  274  preferably includes a conductive layer  274   a  that covers side surfaces of openings formed in the insulating layers  265 ,  329 ,  264 , and  328  and part of a top surface of the conductive layer  325 , and conductive layer  274   b  in contact with a top surface of the conductive layer  274   a . As the conductive layer  274   a , a conductive material in which hydrogen and oxygen are less likely to be diffused is preferably used. 
     The structure of the insulating layer  254  and the components thereover (up to the substrate  420 ) in the display device  400 D is similar to that of the display device  400 C. 
     [Display Device  400 E] 
     A display device  400 E illustrated in  FIG. 18  has a structure in which the transistor  310  whose channel is formed in the substrate  301  and the transistor  320  including a metal oxide in the semiconductor layer where the channel is formed are stacked. Note that portions similar to those of the display devices  400 C and  400 D are not described in some cases. 
     The insulating layer  261  is provided to cover the transistor  310 , and a conductive layer  251  is provided over the insulating layer  261 . The insulating layer  262  is provided so as to cover the conductive layer  251 , and a conductive layer  252  is provided over the insulating layer  262 . The conductive layers  251  and  252  each function as a wiring. An insulating layer  263  and the insulating layer  332  are provided to cover the conductive layer  252 , and the transistor  320  is provided over the insulating layer  332 . The insulating layer  265  is provided to cover the transistor  320 , and the capacitor  240  is provided over the insulating layer  265 . The capacitor  240  and the transistor  320  are electrically connected to each other through the plug  274 . 
     The transistor  320  can be used as a transistor included in the pixel circuit. The transistor  310  can be used as a transistor included in the pixel circuit or a transistor included in a driver circuit (one or both of a gate driver and a source driver) for driving the pixel circuit. The transistor  310  and the transistor  320  can 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 element; thus, the display device can be downsized as compared with the case where the driver circuit is provided around a display portion. 
     At least part of any of the structure examples, the drawings corresponding thereto, and the like described in this embodiment can be implemented in combination with any of the other structure examples, the other drawings corresponding thereto, and the like as appropriate. 
     Embodiment 4 
     In this embodiment, a light-emitting element (also referred to as light-emitting device) that can be used in the display device of one embodiment of the present invention will be described. 
     Structure Example of Light-Emitting Element 
     As illustrated in  FIG. 19A , the light-emitting element includes an EL layer  686  between a pair of electrodes (a lower electrode  672  and an upper electrode  688 ). The EL layer  686  can be formed of a plurality of layers such as a layer  4420 , a light-emitting layer  4411 , and a layer  4430 . The layer  4420  can include, for example, a layer containing a substance with a high electron-injection property (an electron-injection layer) and a layer containing a substance with a high electron-transport property (an electron-transport layer). The light-emitting layer  4411  contains a light-emitting compound, for example. The layer  4430  can include, for example, a layer containing a substance with a high hole-injection property (a hole-injection layer) and a layer containing a substance with a high hole-transport property (a hole-transport layer). 
     The structure including the layer  4420 , the light-emitting layer  4411 , and the layer  4430 , which is provided between a pair of electrodes, can function as a single light-emitting unit, and the structure in  FIG. 19A  is referred to as a single structure in this specification. 
       FIG. 19B  is a modification example of the EL layer  686  included in the light-emitting element illustrated in  FIG. 19A . Specifically, the light-emitting element illustrated in  FIG. 19B  includes a layer  4430 - 1  over the lower electrode  672 , a layer  4430 - 2  over the layer  4430 - 1 , the light-emitting layer  4411  over the layer  4430 - 2 , the layer  4420 - 1  over the light-emitting layer  4411 , the layer  4420 - 2  over the layer  4420 - 1 , and the upper electrode  688  over the layer  4420 - 2 . For example, when the lower electrode  672  functions as an anode and the upper electrode  688  functions as a cathode, the layer  4430 - 1  functions as a hole-injection layer, the layer  4430 - 2  functions as a hole-transport layer, the layer  4420 - 1  functions as an electron-transport layer, and the layer  4420 - 2  functions as an electron-injection layer. Alternatively, when the lower electrode  672  functions as a cathode and the upper electrode  688  functions as an anode, the layer  4430 - 1  functions as an electron-injection layer, the layer  4430 - 2  functions as an electron-transport layer, the layer  4420 - 1  functions as a hole-transport layer, and the layer  4420 - 2  functions as the hole-injection layer. With such a layered structure, carriers can be efficiently injected to the light-emitting layer  4411 , and the efficiency of the recombination of carriers in the light-emitting layer  4411  can be enhanced. 
     Note that the structure in which a plurality of light-emitting layers (light-emitting layers  4411 ,  4412 , and  4413 ) is provided between the layer  4420  and the layer  4430  as illustrated in  FIG. 19C  is another variation of the single structure. 
     The structure in which a plurality of light-emitting units (EL layers  686   a  and  686   b ) is connected in series with an intermediate layer (charge-generation layer)  4440  therebetween as illustrated in  FIG. 19D  is referred to as a tandem structure in this specification. In this specification and the like, the structure illustrated in  FIG. 19D  is referred to as a tandem structure; however, without being limited to this, a tandem structure may be referred to as a stack structure, for example. The tandem structure enables a light-emitting element capable of high luminance light emission. 
     Each of the structures illustrated  FIGS. 19C and 19D  may have a stacked structure in which each of the layer  4420  and the layer  4430  is formed with two or more layers as in the case of  FIG. 19B . 
     When the above single structure, the above tandem structure, and an SBS structure are compared in terms of the amount of power consumption, the ascending order is the SBS structure, the tandem structure, and the single structure. To reduce power consumption, the SBS structure is preferably used. Meanwhile, the single structure and the tandem structure are preferable in terms of lower manufacturing cost or higher manufacturing yield because the manufacturing processes of the single structure and the tandem structure are simpler than that of the SBS structure. 
     The emission color of the light-emitting element can be changed to red, green, blue, cyan, magenta, yellow, white, or the like depending on the material of the EL layer  686 . When the light-emitting element has a microcavity structure, the color purity can be further increased. 
     In the light-emitting element that emits white light, the light-emitting layer preferably contains two or more kinds of light-emitting substances. To obtain white light emission, the two or more kinds of light-emitting substances are selected so as to emit light of complementary colors. For example, the emission colors of first and second light-emitting layers are complementary, so that the light-emitting element can emit white light as a whole. This can be applied to a light-emitting element including three or more light-emitting layers. 
     The light-emitting layer preferably contains two or more selected from light-emitting substances that emit light of red (R), green (G), blue (B), yellow (Y), orange (O), and the like. A light-emitting substance that emits light of violet, bluish violet, yellowish blue, near infrared, and the like may be included. Alternatively, the light-emitting layer preferably contains two or more light-emitting substances that emit light containing two or more of spectral components of R, G, and B. 
     At least part of any of the structure examples, the drawings corresponding thereto, and the like described in this embodiment can be implemented in combination with any of the other structure examples, the other drawings corresponding thereto, and the like as appropriate. 
     Embodiment 5 
     Described in this embodiment is a metal oxide (also referred to as an oxide semiconductor) applicable to an OS transistor described in the above embodiment. 
     A metal oxide preferably contains at least indium or zinc. In particular, indium and zinc are preferably contained. In addition, aluminum, gallium, yttrium, tin, or the like is preferably contained. Furthermore, one or more elements selected from boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, cobalt, and the like may be contained. 
     The metal oxide can be formed by a sputtering method, a CVD method such as an MOCVD method, an ALD method, or the like. 
     &lt;Classification of Crystal Structure&gt; 
     Amorphous (including a completely amorphous structure), c-axis-aligned crystalline (CAAC), nanocrystalline (nc), cloud-aligned composite (CAC), single-crystal, and polycrystalline structures can be given as examples of a crystal structure of an oxide semiconductor. 
     A crystal structure of a film or a substrate can be analyzed with an X-ray diffraction (XRD) spectrum. For example, evaluation is possible using an XRD spectrum which is obtained by grazing-incidence XRD (GIXD) measurement. Note that a GIRD method is also referred to as a thin film method or a Seemann-Bohlin method. 
     For example, the peak of the XRD spectrum of the quartz glass substrate has a bilaterally symmetrical shape. On the other hand, the peak of the XRD spectrum of the IGZO film having a crystal structure has a bilaterally asymmetrical shape. The bilaterally asymmetrical peak shows the existence of crystal in the film or the substrate. In other words, the crystal structure of the film or the substrate cannot be regarded as “amorphous” unless it has a bilaterally symmetrical peak in the XRD spectrum. 
     The crystal structure of a film or a substrate can be analyzed with a diffraction pattern obtained by nanobeam electron diffraction (NBED) (also referred to as a nanobeam electron diffraction pattern). For example, a halo pattern is observed in the diffraction pattern of the quartz glass substrate, which indicates that the quartz glass substrate is in an amorphous state. Furthermore, not a halo pattern but a spot-like pattern is observed in the diffraction pattern of the IGZO film formed at room temperature. Thus, it is presumed that the IGZO film formed at room temperature is in an intermediate state, which is neither a crystal state nor an amorphous state, and it cannot be concluded that the IGZO film is in an amorphous state. 
     &lt;&lt;Oxide Semiconductor Structure&gt;&gt; 
     Oxide semiconductors might be classified in a manner different from the above-described one when classified in terms of the structure. Oxide semiconductors are classified into a single crystal oxide semiconductor and a non-single-crystal oxide semiconductor, for example. Examples of the non-single-crystal oxide semiconductor include the above-described CAAC and nc-OS. Other examples of the non-single-crystal oxide semiconductor include a polycrystalline oxide semiconductor, an amorphous-like oxide semiconductor (a-like OS), and an amorphous oxide semiconductor. 
     Next, the CAAC-OS, nc-OS, and a-like OS will be described in detail. 
     [CAAC-OS] 
     The CAAC-OS is an oxide semiconductor that has a plurality of crystal regions each of which has c-axis alignment in a particular direction. Note that the particular direction refers to the thickness direction of a CAAC-OS film, the normal direction of the surface where the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. The crystal region refers to a region having a periodic atomic arrangement. When an atomic arrangement is regarded as a lattice arrangement, the crystal region also refers to a region with a uniform lattice arrangement. The CAAC-OS has a region where a plurality of crystal regions are connected in the a-b plane direction, and the region has distortion in some cases. Note that distortion refers to a portion where the direction of a lattice arrangement changes between a region with a uniform lattice arrangement and another region with a uniform lattice arrangement in a region where a plurality of crystal regions are connected. That is, the CAAC-OS is an oxide semiconductor having c-axis alignment and having no clear alignment in the a-b plane direction. 
     Note that each of the plurality of crystal regions is formed of one or more fine crystals (crystals each of which has a maximum diameter of less than 10 nm). In the case where the crystal region is formed of one fine crystal, the maximum diameter of the crystal region is less than 10 nm. In the case where the crystal region is formed of a large number of fine crystals, the size of the crystal region may be approximately several tens of nanometers. 
     In the case of an In-M-Zn oxide (the element M is one or more of aluminum, gallium, yttrium, tin, titanium, and the like), the CAAC-OS tends to have a layered crystal structure (also referred to as a stacked-layer structure) in which a layer containing indium (In) and oxygen (hereinafter, an In layer) and a layer containing the element M, zinc (Zn), and oxygen (hereinafter, an (M,Zn) layer) are stacked. Indium and the element M can be replaced with each other. Therefore, indium may be contained in the (M,Zn) layer. In addition, the element M may be contained in the In layer. Note that Zn may be contained in the In layer. Such a layered structure is observed as a lattice image in a high-resolution transmission electron microscope (TEM) image, for example. 
     When the CAAC-OS film is subjected to structural analysis by out-of-plane XRD measurement with an XRD apparatus using θ/2θ scanning, for example, a peak indicating c-axis alignment is detected at or around 2θ=31°. Note that the position of the peak indicating c-axis alignment (the value of 2θ) may change depending on the kind, composition, or the like of the metal element contained in the CAAC-OS. 
     For example, a plurality of bright spots are observed in the electron diffraction pattern of the CAAC-OS film. Note that one spot and another spot are symmetric with respect to a spot of the incident electron beam which passes through a sample (also referred to as a direct spot). 
     When the crystal region is observed from the particular direction, a lattice arrangement in the crystal region is basically a hexagonal lattice arrangement; however, a unit lattice is not always a regular hexagon and is a non-regular hexagon in some cases. A pentagonal lattice arrangement, a heptagonal lattice arrangement, and the like are included in the distortion in some cases. Note that a clear grain boundary cannot be observed even in the vicinity of the distortion in the CAAC-OS. That is, formation of a grain boundary is inhibited by the distortion of a lattice arrangement. This is probably because the CAAC-OS can tolerate distortion owing to a low density of arrangement of oxygen atoms in the a-b plane direction, an interatomic bond distance changed by substitution of a metal atom, and the like. 
     A crystal structure in which a clear grain boundary is observed is what is called a polycrystal structure. It is highly probable that the grain boundary becomes a recombination center and traps carriers and thus decreases the on-state current and field-effect mobility of a transistor, for example. Thus, the CAAC-OS in which no clear grain boundary is observed is one of crystalline oxides having a crystal structure suitable for a semiconductor layer of a transistor. Note that Zn is preferably contained to form the CAAC-OS. For example, an In—Zn oxide and an In-Ga—Zn oxide are suitable because they can inhibit generation of a grain boundary as compared with an In oxide. 
     The CAAC-OS is an oxide semiconductor with high crystallinity in which no clear grain boundary is observed. Thus, in the CAAC-OS, a reduction in electron mobility due to the grain boundary is less likely to occur. Entry of impurities, formation of defects, or the like might decrease the crystallinity of an oxide semiconductor. This means that the CAAC-OS can be referred to as an oxide semiconductor having small amounts of impurities and defects (e.g., oxygen vacancies). Therefore, an oxide semiconductor including the CAAC-OS is physically stable. Accordingly, the oxide semiconductor including the CAAC-OS is resistant to heat and has high reliability. In addition, the CAAC-OS is stable with respect to high temperatures in the manufacturing process (i.e., thermal budget). Accordingly, the use of the CAAC-OS for the OS transistor can extend a degree of freedom of the manufacturing process. 
     [nc-OS] 
     In the nc-OS, a microscopic region (e.g., a region with a size greater than or equal to 1 nm and less than or equal to 10 nm, in particular, a region with a size greater than or equal to 1 nm and less than or equal to 3 nm) has a periodic atomic arrangement. In other words, the nc-OS includes a fine crystal. Note that the size of the fine crystal is, for example, greater than or equal to 1 nm and less than or equal to 10 nm, particularly greater than or equal to 1 nm and less than or equal to 3 nm; thus, the fine crystal is also referred to as a nanocrystal. There is no regularity of crystal orientation between different nanocrystals in the nc-OS. Hence, the orientation in the whole film is not observed. Accordingly, in some cases, the nc-OS cannot be distinguished from an a-like OS or an amorphous oxide semiconductor, depending on an analysis method. For example, when an nc-OS film is subjected to structural analysis by out-of-plane XRD measurement with an XRD apparatus using θ/2θ scanning, a peak indicating crystallinity is not observed. Furthermore, a halo pattern is shown in a selected-area electron diffraction pattern of the nc-OS film obtained using an electron beam having a probe diameter larger than the diameter of a nanocrystal (e.g., larger than or equal to 50 nm). Meanwhile, in some cases, a plurality of spots in a ring-like region with a direct spot as the center are observed in a nanobeam electron diffraction pattern of the nc-OS film obtained using an electron beam with a probe diameter nearly equal to or smaller than the diameter of a nanocrystal (e.g., 1 nm or larger and 30 nm or smaller). 
     [a-Like OS] 
     The a-like OS is an oxide semiconductor having a structure between those of the nc-OS and the amorphous oxide semiconductor. The a-like OS has a void or a low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and the CAAC-OS. Moreover, the a-like OS has higher hydrogen concentration than the nc-OS and the CAAC-OS. 
     &lt;&lt;Component of Oxide Semiconductor&gt;&gt; 
     Next, the CAC-OS will be described in detail. Note that the CAC-OS relates to the material composition. 
     [CAC-OS] 
     The CAC-OS has, for example, a composition in which elements included in a metal oxide are unevenly distributed. Materials including unevenly distributed elements each have 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 3 nm, or a similar size. Note that in the following description of a metal oxide, a state in which one or more types of metal elements are unevenly distributed and regions including the metal element(s) are mixed is referred to as a mosaic pattern or a patch-like pattern. 
     In addition, the CAC-OS has a composition in which materials are separated into a first region and a second region to form a mosaic pattern, and the first regions are distributed in the film. This composition is hereinafter also referred to as a cloud-like composition. That is, the CAC-OS is a composite metal oxide having a composition in which the first regions and the second regions are mixed. 
     Here, the atomic ratios of In, Ga, and Zn to a metal element included in a CAC-OS in an In-Ga—Zn oxide are expressed as [In], [Ga], and [Zn], respectively. For example, the first region in the CAC-OS in the In-Ga—Zn oxide has [In] higher than that in the composition of the CAC-OS film. Moreover, the second region of the CAC-OS in the In-Ga—Zn oxide has [Ga] higher than that in the composition of the CAC-OS film. Alternatively, for example, the first region has higher [In] and lower [Ga] than the second region. Moreover, the second region has higher [Ga] and lower [In] than the first region. 
     Specifically, the first region includes indium oxide, indium zinc oxide, or the like as its main component. The second region includes gallium oxide, gallium zinc oxide, or the like as its main component. That is, the first region can be referred to as a region containing In as its main component. The second region can be referred to as a region containing Ga as its main component. 
     Note that a clear boundary between the first region and the second region cannot be observed in some cases. 
     In a material composition of a CAC-OS in an In-Ga—Zn oxide that contains In, Ga, Zn, and O, regions containing Ga as a main component are observed in part of the CAC-OS and regions containing In as a main component are observed in part thereof. These regions are randomly dispersed to form a mosaic pattern. Thus, it is suggested that the CAC-OS has a structure in which metal elements are unevenly distributed. 
     The CAC-OS can be formed by a sputtering method under conditions where a substrate is not heated, for example. In the case of forming the CAC-OS by a sputtering method, one or more selected from an inert gas (typically, argon), an oxygen gas, and a nitrogen gas may be used as a deposition gas. The ratio of the flow rate of an oxygen gas to the total flow rate of the deposition gas at the time of film formation is preferably as low as possible, and for example, the flow ratio of an oxygen gas is preferably higher than or equal to 0% and less than 30%, further preferably higher than or equal to 0% and less than or equal to 10%. 
     For example, energy dispersive X-ray spectroscopy (EDX) is used to obtain EDX mapping, and according to the EDX mapping, the CAC-OS in the In-Ga—Zn oxide has a composition in which the regions containing In as a main component (the first regions) and the regions containing Ga as a main component (the second regions) are unevenly distributed and mixed. 
     Here, the first region has a higher conductivity than the second region. In other words, when carriers flow through the first region, the conductivity of a metal oxide is exhibited. Accordingly, when the first regions are distributed in a metal oxide as a cloud, high field-effect mobility (μ) can be achieved. 
     The second region has a higher insulating property than the first region. In other words, when the second regions are distributed in a metal oxide, leakage current can be inhibited. 
     Thus, in the case where a CAC-OS is used for a transistor, by the complementary function of the conducting function due to the first region and the insulating function due to the second region, the CAC-OS can have a switching function (on/off function). That is, the CAC-OS has a conducting function in part of the material and has an insulating function in another part of the material; as a whole, the CAC-OS has a function of a semiconductor. Separation of the conducting function and the insulating function can maximize each function. Accordingly, when a CAC-OS is used for a transistor, a high on-state current (I on ), a high field-effect mobility (μ), low leakage current, and favorable switching operation can be achieved. 
     A transistor including a CAC-OS is highly reliable. Thus, the CAC-OS is suitably used in a variety of semiconductor devices typified by a display device. 
     An oxide semiconductor can have any of various structures that show various different properties. Two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, the CAC-OS, an nc-OS, and the CAAC-OS may be included in an oxide semiconductor of one embodiment of the present invention. 
     &lt;Transistor Including Oxide Semiconductor&gt; 
     Next, a transistor including the above oxide semiconductor is described. 
     When the oxide semiconductor is used for a transistor, the transistor can have high field-effect mobility. In addition, the transistor can have high reliability. 
     An oxide semiconductor having a low carrier concentration is preferably used for the transistor. For example, the carrier concentration of an oxide semiconductor is lower than or equal to 1×10 17  cm −3 , preferably lower than or equal to 1×10 15  cm −3 , further preferably lower than or equal to 1×10 13  cm −3 , still further preferably lower than or equal to 1×10 11  cm −3 , yet further preferably lower than 1×10 10  cm −3 , and higher than or equal to 1×10 −9  cm −3 . In order to reduce the carrier concentration of an oxide semiconductor film, the impurity concentration in the oxide semiconductor film is reduced so that the density of defect states can be reduced. In this specification and the like, a state with a low impurity concentration and a low density of defect states is referred to as a highly purified intrinsic or substantially highly purified intrinsic state. Note that an oxide semiconductor having a low carrier concentration may be referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. 
     A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states and accordingly has a low density of trap states in some cases. 
     Charges trapped by the trap states in an oxide semiconductor take a long time to be released and may behave like fixed charges. A transistor whose channel formation region is formed in an oxide semiconductor having a high density of trap states has unstable electrical characteristics in some cases. 
     In order to obtain stable electrical characteristics of the transistor, it is effective to reduce the impurity concentration in the oxide semiconductor. In order to reduce the impurity concentration in the oxide semiconductor, the impurity concentration in a film that is adjacent to the oxide semiconductor is preferably reduced. Examples of impurities include hydrogen, nitrogen, alkali metal, alkaline earth metal, iron, nickel, and silicon. 
     &lt;Impurity&gt; 
     The influence of impurities in the oxide semiconductor is described. 
     When silicon or carbon, which is a Group 14 element, is contained in an oxide semiconductor, defect states are formed in the oxide semiconductor. Thus, the concentration of silicon or carbon in the oxide semiconductor and in the vicinity of an interface with the oxide semiconductor (the concentration measured by secondary ion mass spectrometry (SIMS)) is lower than or equal to 2×10 18  atoms/cm 3 , preferably lower than or equal to 2×10 17  atoms/cm 3 . 
     When the oxide semiconductor contains alkali metal or alkaline earth metal, defect states are formed and carriers are generated in some cases. Accordingly, a transistor including an oxide semiconductor that contains alkali metal or alkaline earth metal tends to have normally-on characteristics. Thus, the concentration of alkali metal or alkaline earth metal in the oxide semiconductor measured by SIMS is set lower than or equal to 1×10 18  atoms/cm 3 , and preferably lower than or equal to 2×10 16  atoms/cm 3 . 
     An oxide semiconductor containing nitrogen easily becomes n-type by generation of electrons serving as carriers and an increase in carrier concentration. Thus, a transistor using an oxide semiconductor that contains nitrogen is likely to be normally on. When nitrogen is contained in the oxide semiconductor, a trap state is sometimes formed. This might make the electrical characteristics of the transistor unstable. Thus, the concentration of nitrogen in the channel formation region using the oxide semiconductor, which is measured by SIMS, is lower than 5×10 19  atoms/cm 3 , preferably lower than or equal to 5×10 18  atoms/cm 3 , further preferably lower than or equal to 1×10 18  atoms/cm 3 , still further preferably lower than or equal to 5×10 17  atoms/cm 3 . 
     Hydrogen contained in an oxide semiconductor reacts with oxygen bonded to a metal atom to be water, and thus causes an oxygen vacancy in some cases. Entry of hydrogen into the oxygen vacancy generates an electron serving as a carrier in some cases. Furthermore, some hydrogen may react with oxygen bonded to a metal atom and generate an electron serving as a carrier. Thus, a transistor including an oxide semiconductor that contains hydrogen tends to have normally-on characteristics. For this reason, hydrogen in the oxide semiconductor is preferably reduced as much as possible. Specifically, the hydrogen concentration in the oxide semiconductor, which is measured by SIMS, is lower than 1×10 20  atoms/cm 3 , preferably lower than 1×10 19  atoms/cm 3 , further preferably lower than 5×10 18  atoms/cm 3 , still further preferably lower than 1×10 18  atoms/cm 3 . 
     When an oxide semiconductor with sufficiently reduced impurities is used for a channel formation region in a transistor, the transistor can have stable electrical characteristics. 
     At least part of this embodiment can be implemented in appropriate combination with any of the other embodiments described in this specification. 
     Embodiment 6 
     In this embodiment, electronic devices of one embodiment of the present invention will be described with reference to  FIGS. 20A and 20B, 21A to 21D, 22A to 22F, and 23A to 23F . 
     An electronic device in this embodiment includes the display device of one embodiment of the present invention. For the display device of one embodiment of the present invention, increases in resolution, definition, and sizes are easily achieved. Thus, the display device of one embodiment of the present invention can be used for display portions of a variety of electronic devices. 
     The display device of one embodiment of the present invention can be manufactured at low cost, which leads to a reduction in manufacturing cost of an electronic device. 
     Examples of the electronic devices include a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game console, 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 desktop or laptop personal computer, a monitor of a computer or the like, digital signage, and a large game machine such as a pachinko machine. 
     In particular, a display device 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. As such an electronic device, 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 can be given, for example. Examples of wearable devices includes a device for substitution reality (SR) and a device for mixed reality (MR). 
     The resolution of the display device of one embodiment of the present invention is preferably as high as HD (number of pixels: 1280×720), FHD (number of pixels: 1920×1080), WQHD (number of pixels: 2560×1440), WQXGA (number of pixels: 2560×1600), 4K2K (number of pixels: 3840×2160), or 8K4K (number of pixels: 7680×4320). In particular, resolution of 4K2K, 8K4K, or higher is preferable. Furthermore, the pixel density (definition) of the display device of one embodiment of the present invention is preferably higher than or equal to 300 ppi, further preferably higher than or equal to 500 ppi, still further preferably higher than or equal to 1000 ppi, still further preferably higher than or equal to 2000 ppi, still further preferably higher than or equal to 3000 ppi, still further preferably higher than or equal to 5000 ppi, and yet further preferably higher than or equal to 7000 ppi. With such a display device with high resolution and high definition, the electronic device can have higher realistic sensation, sense of depth, and the like in personal use such as portable use and home use. 
     The electronic device in this embodiment can be incorporated along a curved surface of an inside wall or an outside wall of a house or a building or the interior or the exterior of a car. 
     The electronic device in this embodiment may include an antenna. With the antenna receiving a signal, the electronic device can display an image, information, and the like on a display portion. When the electronic device includes an antenna and a secondary battery, the antenna may be used for contactless power transmission. 
     The electronic device in this embodiment may include a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, a chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, a smell, or infrared rays). 
     The electronic device in this embodiment can have a variety of functions. For example, the electronic device of one embodiment of the present invention can have a function of displaying a variety of data (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of executing a variety of software (programs), a wireless communication function, and a function of reading out a program or data stored in a recording medium. 
     An electronic device  6500  in  FIG. 20A  is a portable information terminal that can be used as a smartphone. 
     The electronic device  6500  includes a housing  6501 , a display portion  6502 , a power button  6503 , buttons  6504 , a speaker  6505 , a microphone  6506 , a camera  6507 , a light source  6508 , and the like. The display portion  6502  has a touch panel function. 
     The display device of one embodiment of the present invention can be used in the display portion  6502 . 
       FIG. 20B  is a schematic cross-sectional view including an end portion of the housing  6501  on the microphone  6506  side. 
     A protection member  6510  having a light-transmitting property is provided on a display surface side of the housing  6501 , and a display panel  6511 , an optical member  6512 , a touch sensor panel  6513 , a printed circuit board  6517 , a battery  6518 , and the like are provided in a space surrounded by the housing  6501  and the protection member  6510 . 
     The display panel  6511 , the optical member  6512 , and the touch sensor panel  6513  are fixed to the protection member  6510  with an adhesive layer (not illustrated). 
     Part of the display panel  6511  is folded back in a region outside the display portion  6502 , and an FPC  6515  is connected to the part that is folded back. An IC  6516  is mounted on the FPC  6515 . The FPC  6515  is connected to a terminal provided on the printed circuit board  6517 . 
     A flexible display of one embodiment of the present invention can be used as the display panel  6511 . Thus, an extremely lightweight electronic device can be achieved. Since the display panel  6511  is extremely thin, the battery  6518  with high capacity can be mounted while h the thickness of the electronic device is controlled. Moreover, a part of the display panel  6511  is folded back so that a connection portion with the FPC  6515  is provided on the back side of the pixel portion, whereby an electronic device with a narrow bezel can be achieved. 
       FIG. 21A  shows an example of a television device. In a television device  7100 , a display portion  7000  is incorporated in a housing  7101 . Here, the housing  7101  is supported by a stand  7103 . 
     The display device of one embodiment of the present invention can be used for the display portion  7000 . 
     Operation of the television device  7100  illustrated in  FIG. 21A  can be performed with an operation switch provided in the housing  7101  and a separate remote controller  7111 . Alternatively, the display portion  7000  may include a touch sensor, and the television device  7100  may be operated by touch on the display portion  7000  with a finger or the like. The remote controller  7111  may be provided with a display portion for displaying information output from the remote controller  7111 . With operation keys or a touch panel provided in the remote controller  7111 , channels and volume can be operated and videos displayed on the display portion  7000  can be operated. 
     Note that the television device  7100  has a structure in which a receiver, a modem, and the like are provided. A general television broadcast can be received with the receiver. When the television device is connected to a communication network with or without wires via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver or between receivers, for example) data communication can be performed. 
       FIG. 21B  illustrates an example of a laptop personal computer. The laptop personal computer  7200  includes a housing  7211 , a keyboard  7212 , a pointing device  7213 , an external connection port  7214 , and the like. In the housing  7211 , the display portion  7000  is incorporated. 
     The display device of one embodiment of the present invention can be used for the display portion  7000 . 
       FIGS. 21C and 21D  illustrate examples of digital signage. 
     Digital signage  7300  illustrated in  FIG. 21C  includes a housing  7301 , the display portion  7000 , a speaker  7303 , and the like. The digital signage  7300  can also include an LED lamp, an operation key (including a power switch or an operation switch), a connection terminal, a variety of sensors, a microphone, and the like. 
       FIG. 21D  is digital signage  7400  attached to a cylindrical pillar  7401 . The digital signage  7400  includes the display portion  7000  provided along a curved surface of the pillar  7401 . 
     The display device of one embodiment of the present invention can be used in the display portion  7000  illustrated in each of  FIGS. 21C and 21D . 
     A larger area of the display portion  7000  can increase the amount of data that can be provided at a time. The larger display portion  7000  attracts more attention, so that the effectiveness of the advertisement can be increased, for example. 
     The use of a touch panel in the display portion  7000  is preferable because in addition to display of a still image or a moving image on the display portion  7000 , intuitive operation by a user is possible. Moreover, for an application for providing information such as route information or traffic information, usability can be enhanced by intuitive operation. 
     As illustrated in  FIGS. 21C and 21D , it is preferable that the digital signage  7300  or the digital signage  7400  can work with an information terminal  7311  or an information terminal  7411  such as a smartphone a user has through wireless communication. For example, information of an advertisement displayed on the display portion  7000  can be displayed on a screen of the information terminal  7311  or the information terminal  7411 . By operation of the information terminal  7311  or the information terminal  7411 , display on the display portion  7000  can be switched. 
     It is possible to make the digital signage  7300  or the digital signage  7400  execute a game with use of the screen of the information terminal  7311  or the information terminal  7411  as an operation means (controller). Thus, an unspecified number of users can join in and enjoy the game concurrently. 
       FIG. 22A  is an external view of a camera  8000  to which a finder  8100  is attached. 
     The camera  8000  includes a housing  8001 , a display portion  8002 , operation buttons  8003 , a shutter button  8004 , and the like. Furthermore, a detachable lens  8006  is attached to the camera  8000 . Note that the lens  8006  and the housing  8001  may be integrated with each other in the camera  8000 . 
     Images can be taken with the camera  8000  at the press of the shutter button  8004  or the touch of the display portion  8002  serving as a touch panel. 
     The housing  8001  includes a mount including an electrode, so that the finder  8100 , a stroboscope, or the like can be connected to the housing. 
     The finder  8100  includes a housing  8101 , a display portion  8102 , a button  8103 , and the like. 
     The housing  8101  is attached to the camera  8000  by a mount for engagement with the mount of the camera  8000 . The finder  8100  can display a video received from the camera  8000  and the like on the display portion  8102 . 
     The button  8103  functions as a power supply button or the like. 
     A display device of one embodiment of the present invention can be used in the display portion  8002  of the camera  8000  and the display portion  8102  of the finder  8100 . Note that a finder may be incorporated in the camera  8000 . 
       FIG. 22B  is an external view of a head-mounted display  8200 . 
     The head-mounted display  8200  includes a mounting portion  8201 , a lens  8202 , a main body  8203 , a display portion  8204 , a cable  8205 , and the like. A battery  8206  is incorporated in the mounting portion  8201 . 
     The cable  8205  supplies electric power from the battery  8206  to the main body  8203 . The main body  8203  includes a wireless receiver or the like to receive image data and display it on the display portion  8204 . The main body  8203  includes a camera, and data on the movement of the eyeballs or the eyelids of the user can be used as an input means. 
     The mounting portion  8201  may include a plurality of electrodes capable of sensing current flowing accompanying with the movement of the user&#39;s eyeball at a position in contact with the user to recognize the user&#39;s sight line. The mounting portion  8201  may also have a function of monitoring the user&#39;s pulse with use of current flowing in the electrodes. The mounting portion  8201  may include sensors such as a temperature sensor, a pressure sensor, and an acceleration sensor so that the user&#39;s biological information can be displayed on the display portion  8204  and an image displayed on the display portion  8204  can be changed in accordance with the movement of the user&#39;s head. 
     A display device of one embodiment of the present invention can be used in the display portion  8204 . 
       FIGS. 22C to 22E  are external views of a head-mounted display  8300 . The head-mounted display  8300  includes the housing  8301 , the display portion  8302 , the band-like fixing member  8304 , and a pair of lenses  8305 . 
     A user can see display on the display portion  8302  through the lenses  8305 . The display portion  8302  is preferably curved because the user can feel high realistic sensation. Another image displayed in another region of the display portion  8302  is viewed through the lenses  8305 , so that three-dimensional display using parallax or the like can be performed. Note that the number of the display portions  8302  is not limited to one; two display portions  8302  may be provided for user&#39;s respective eyes. 
     The display device of one embodiment of the present invention can be used for the display portion  8302 . The display device of one embodiment of the present invention achieves extremely high resolution. For example, a pixel is not easily seen by the user even when the user sees display that is magnified by the use of the lenses  8305  as illustrated in  FIG. 22E . In other words, a video with a strong sense of reality can be seen by the user with use of the display portion  8302 . 
       FIG. 22F  is an external view of a google-type head-mounted display  8400 . The head-mounted display  8400  includes a pair of housings  8401 , a mounting portion  8402 , and a cushion  8403 . A display portion  8404  and a lens  8405  are provided in each of the pair of housings  8401 . Furthermore, when the pair of display portions  8404  display different images, three-dimensional display using parallax can be performed. 
     A display device of one embodiment of the present invention can be used in the display portion  8404 . 
     A user can see display on the display portion  8404  through the lens  8405 . The lens  8405  has a focus adjustment mechanism and can adjust the position according to the user&#39;s eyesight. The display portion  8404  is preferably a square or a horizontal rectangle. This can improve a realistic sensation. 
     The mounting portion  8402  preferably has flexibility and elasticity so as to be adjusted to fit the size of the user&#39;s face and not to slide down. In addition, part of the mounting portion  8402  preferably has a vibration mechanism functioning as a bone conduction earphone. Thus, audio devices such as an earphone and a speaker are not necessarily provided separately, and the user can enjoy images and sounds only when wearing the head-mounted display  8400 . Note that the housing  8401  may have a function of outputting sound data by wireless communication. 
     The mounting portion  8402  and the cushion  8403  are portions in contact with the user&#39;s face (forehead, cheek, or the like). The cushion  8403  is in close contact with the user&#39;s face, so that light leakage can be prevented, which increases the sense of immersion. The cushion  8403  is preferably formed using a soft material so that the head-mounted display  8400  is in close contact with the user&#39;s face when being worn by the user. For example, a material such as rubber, 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&#39;s face and the cushion  8403 , 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&#39;s skin, such as the cushion  8403  or the mounting portion  8402 , is preferably detachable because cleaning or replacement can be easily performed. 
     Electronic devices illustrated in  FIGS. 23A to 23F  include a housing  9000 , a display portion  9001 , a speaker  9003 , an operation key  9005  (including a power switch or an operation switch), a connection terminal  9006 , a sensor  9007  (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, a chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, a smell, or infrared rays), a microphone  9008 , and the like. 
     The electronic devices illustrated in  FIGS. 23A to 23F  have a variety of functions. For example, the electronic device can have a function of displaying a variety of information (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of executing a variety of software (programs), a wireless communication function, and a function of reading out a program or data stored in a recording medium. Note that the functions of the electronic devices are not limited thereto, and the electronic devices can have a variety of functions. The electronic devices may include a plurality of display portions. The electronic devices may each be provided with a camera or the like and have a function of taking a still image or a moving image, a function of storing the taken image in a storage medium (an external storage medium or a storage medium incorporated in the camera), a function of displaying the taken image on the display portion, or the like. 
     The display device of one embodiment of the present invention can be used for the display portion  9001 . 
     The electronic devices in  FIGS. 23A to 23F  are described in detail below. 
       FIG. 23A  is a perspective view showing a portable information terminal  9101 . For example, the portable information terminal  9101  can be used as a smartphone. Note that the portable information terminal  9101  may include the speaker  9003 , the connection terminal  9006 , the sensor  9007 , or the like. The portable information terminal  9101  can display characters and image information on its plurality of surfaces.  FIG. 23A  illustrates an example in which three icons  9050  are displayed. Furthermore, information  9051  indicated by dashed rectangles can be displayed on another surface of the display portion  9001 . Examples of the information  9051  include notification of reception of an e-mail, an SNS message, or an incoming call, the title and sender of an e-mail, an SNS message, or the like, the date, the time, remaining battery, and the reception strength of an antenna. Alternatively, the icon  9050  or the like may be displayed at the position where the information  9051  is displayed. 
       FIG. 23B  is a perspective view showing a portable information terminal  9102 . The portable information terminal  9102  has a function of displaying information on three or more surfaces of the display portion  9001 . Here, information  9052 , information  9053 , and information  9054  are displayed on different surfaces. For example, a user of the portable information terminal  9102  can check the information  9053  displayed such that it can be seen from above the portable information terminal  9102 , with the portable information terminal  9102  put in a breast pocket of his/her clothes. Thus, the user can see the display without taking out the portable information terminal  9102  from the pocket and decide whether to answer the call, for example. 
       FIG. 23C  is a perspective view illustrating a watch-type portable information terminal  9200 . For example, the portable information terminal  9200  can be used as a Smartwatch (registered trademark). The display surface of the display portion  9001  is curved, and an image can be displayed on the curved display surface. Mutual communication between the portable information terminal  9200  and, for example, a headset capable of wireless communication enables hands-free calling. With the connection terminal  9006 , the portable information terminal  9200  can perform mutual data transmission with another information terminal and charging. Note that the charging operation may be performed by wireless power feeding. 
       FIGS. 23D to 23F  are perspective views illustrating a foldable portable information terminal  9201 .  FIG. 23D  is a perspective view of an opened state of the portable information terminal  9201 ,  FIG. 23F  is a perspective view of a folded state thereof, and  FIG. 23E  is a perspective view of a state in the middle of change from one of  FIG. 23D  and  FIG. 23F  to the other. The portable information terminal  9201  is highly portable when folded. When the portable information terminal  9201  is opened, a seamless large display region is highly browsable. The display portion  9001  of the portable information terminal  9201  is supported by three housings  9000  joined together by hinges  9055 . For example, the display portion  9001  can be folded with a radius of curvature greater than or equal to 0.1 mm and less than or equal to 150 mm. 
     At least part of any of the structure examples, the drawings corresponding thereto, and the like described in this embodiment can be implemented in combination with any of the other structure examples, the other drawings corresponding thereto, and the like as appropriate. 
     This application is based on Japanese Patent Application Serial No. 2021-011450 filed with Japan Patent Office on Jan. 27, 2021, the entire contents of which are hereby incorporated by reference.