Patent Publication Number: US-2023162706-A1

Title: Display device and electronic device

Description:
TECHNICAL FIELD 
     The present invention relates to a display device and an electronic device. 
     Note that one embodiment of the present invention is not limited to the above technical field. The technical field of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a power storage device, an imaging device, a memory device, a processor, an electronic device, a system, a method for driving any of them, a method for manufacturing any of them, and a method for testing any of them. 
     BACKGROUND ART 
     In recent years, research and development have been extensively conducted on light-emitting elements utilizing electroluminescence (EL) used as display elements in a display region of a display device. As a basic structure of these light-emitting elements, a layer containing a light-emitting substance is provided between a pair of electrodes. Voltage is applied to the light-emitting element to obtain light emission from the light-emitting substance. 
     The light-emitting element is a self-luminous element; thus, a display device using the light-emitting elements has, in particular, advantages such as high visibility, no necessity of a backlight, and low power consumption. The display device using the light-emitting elements also has advantages in that it can be manufactured to be thin and lightweight and has high response speed. 
     A display device including the light-emitting elements can have flexibility; therefore, the use of a flexible substrate for the display device has been considered. 
     As a method for manufacturing a display device using a flexible substrate, a technique has been developed in which an oxide layer and a metal layer are formed between a substrate and a semiconductor element, the substrate is separated by utilizing weak adhesion of an interface between the oxide layer and the metal layer, and then the semiconductor element is transferred to another substrate (e.g., a flexible substrate) (Patent Document 1). 
     In some cases, over a light-emitting element that has been formed over a flexible substrate, another flexible substrate is provided in order to protect a surface of the light-emitting element or prevent entry of moisture or impurities from the outside. 
     The display device including a flexible substrate can be flexible. Thus, the substrate is preferably formed using a material with low elasticity, high degree of extensibility in stretching, high restorability after the stretch, and the like. Patent Document 2 discloses a structure body for electronics including a resin composition with high tensile stress relaxivity and excellent restorability after the stretch. 
     REFERENCES 
     Patent Document 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2003-174153 
         [Patent Document 2] Japanese Published Patent Application No. 2016-102669 
       
    
     DISCLOSURE OF INVENTION 
     In the case of a display device including a light-emitting element over a flexible substrate, the display device can be stretched in some cases depending on the material of the substrate. When the display device is stretched, the display device can be made to have a size different from a standard size in some cases. 
     However, there is a limit on the degree of elasticity of the flexible substrate; thus, excessive stretch might cause damage to the substrate. Even when the substrate is not damaged, a light-emitting element, a circuit element, a wiring, and the like provided over the substrate might be damaged. 
     Stretching the display device including the flexible substrate might lead to a decrease in the intensity of light emitted from each unit area of the display device. This is because the number of pixels per unit area (also referred to as resolution in some cases) of the stretched display device decreases. Thus, when the stretched display device is used, the quality of an image displayed on the display device is reduced in some cases. 
     An object of one embodiment of the present invention is to provide a novel display device that can be changed in shape. Another object of one embodiment of the present invention is to provide a novel display device having high display quality even with a change in its shape. Another object of one embodiment of the present invention is to provide an electronic device including the above-described display device. 
     Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like. 
     (1) One embodiment of the present invention is a display device whose aspect ratio can be changed. The display device includes a display region including a first unit and a second unit. The first unit and the second unit each include a light-emitting portion and a connection region. The connection region of the first unit is electrically connected to the connection region of the second unit. The display region has a function of changing an angle between the first unit and the second unit. 
     (2) Another embodiment of the present invention is the display device according to (1), including a driver region. The driver region includes a third unit. The third unit includes a driver circuit portion. The driver circuit portion has a function of driving the light-emitting portion of the first unit and the light-emitting portion of the second unit. The third unit of the driver region is parallel to one of the first unit and the second unit. 
     (3) Another embodiment of the present invention is the display device according to (1) or (2) in which a length in a first direction of the first unit is longer than a length in a second direction of the first unit. 
     (4) Another embodiment of the present invention is a display device whose aspect ratio can be changed. The display device includes a display region and a driver region. The display region includes a plurality of first units. The driver region includes a plurality of second units. The plurality of first units each include a connection region, and the plurality of second units each include a connection region. Some connection regions of the plurality of first units are electrically connected to some connection regions of the plurality of second units. The plurality of first units of the display region are parallel to each other. The plurality of second units of the driver region are parallel to each other. An angle between one first unit and one second unit which is connected to the first unit can be changed. 
     (5) Another embodiment of the present invention is the display device according to (4) in which the plurality of first units each include a light-emitting portion. At least one of the plurality of first units includes a driver circuit portion. The plurality of second units each include a driver circuit portion. At least one of the plurality of second units includes a light-emitting portion. 
     (6) Another embodiment of the present invention is a display device whose aspect ratio can be changed. The display device includes a display region. The display region includes a first unit and a second unit. The first unit and the second unit each include a light-emitting portion. The second unit overlaps with a first region of the first unit. The display region has a function of changing an area of the first region. 
     (7) Another embodiment of the present invention is the display device according to (6), including a driver region. The driver region includes a third unit and a fourth unit. The third unit has a function of driving the light-emitting portion of the first unit. The fourth unit has a function of driving the light-emitting portion of the second unit. The fourth unit overlaps with a first region of the third unit. The driver region has a function of changing an area of the first region of the third unit. 
     (8) Another embodiment of the present invention is the display device according to (7), including a first insulator and a second insulator. The first unit and the third unit are each covered with the first insulator. The second unit and the fourth unit are each covered with the second insulator. The second insulator is positioned over the first insulator. The first insulator and the second insulator have elasticity. 
     (9) Another embodiment of the present invention is the display device according to (6), including a third unit and a first insulator. The third unit has a function of driving the light-emitting portions of the first unit and the second unit. The first unit, the second unit, and the third unit are each covered with the first insulator. The first insulator has elasticity. 
     (10) Another embodiment of the present invention is the display device according to any one of (1) to (3) and (5) to (9), in which the light-emitting portions each include a light-emitting element. 
     (11) Another embodiment of the present invention is an electronic device including the display device according to any one of (1) to (10). 
     According to one embodiment of the present invention, a novel display device that can be changed in shape can be provided. According to another embodiment of the present invention, a novel display device having high display quality even with a change in its shape can be provided. According to another embodiment of the present invention, an electronic device including the above-described display device can be provided. 
     Note that the descriptions of these effects do not disturb the existence of other effects. One embodiment of the present invention does not necessarily achieve all the effects. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the accompanying drawings: 
         FIGS.  1 A,  1 B,  1 C ,  1 D 1 , and  1 D 2  illustrate examples of display devices; 
         FIGS.  2 A to  2 C  illustrate an example of constituting the display device in FIGS.  1 D 1  and  1 D 2 ; 
         FIGS.  3 A to  3 C  are a top view and cross-sectional views of part of a display device; 
         FIGS.  4 A and  4 B  are cross-sectional views illustrating an example of a shaft; 
         FIGS.  5 A and  5 B  are each a perspective view illustrating an example of a conductor included in a shaft; 
         FIG.  6    is a cross-sectional view illustrating an example of a shaft; 
         FIGS.  7 A and  7 B  are a perspective view and a cross-sectional view illustrating an example of a shaft; 
         FIGS.  8 A,  8 B ,  8 C 1 ,  8 C 2 ,  8 D 1 ,  8 D 2 , and  8 E illustrate examples of display devices; 
         FIGS.  9 A to  9 C  illustrate an example of a display device and an example of constituting the display device; 
       FIGS.  10 A 1 ,  10 A 2 ,  10 B 1 , and  10 B 2  illustrate examples of electronic devices; 
         FIGS.  11 A and  11 B  illustrate examples of electronic devices; 
         FIGS.  12 A ,  12 B 1 , and  12 B 2  are schematic views illustrating examples of display regions; 
       FIGS.  13 A 1  and  13 A 2  are each a schematic view illustrating an example of a display region; 
         FIGS.  14 A ,  14 B 1 , and  14 B 2  are schematic views illustrating examples of display regions; 
         FIGS.  15 A ,  15 B 1 , and  15 B 2  are a schematic view and cross-sectional views illustrating examples of display regions; 
         FIGS.  16 A ,  16 B 1 , and  16 B 2  are a schematic view and cross-sectional views illustrating examples of display regions; 
         FIGS.  17 A and  17 B  are schematic views illustrating examples of a display device; 
         FIGS.  18 A ,  18 B 1 , and  18 B 2  are a schematic view and cross-sectional views illustrating examples of display devices; 
         FIGS.  19 A to  19 C  are cross-sectional views illustrating an example of a method for manufacturing a display device; 
         FIGS.  20 A and  20 B  are cross-sectional views illustrating an example of a method for manufacturing a display device; 
         FIGS.  21 A and  21 B  are cross-sectional views illustrating an example of a method for manufacturing a display device; 
         FIG.  22    is a cross-sectional view illustrating an example of a method for manufacturing a display device; 
         FIG.  23    is a cross-sectional view illustrating an example of a method for manufacturing a display device; 
         FIGS.  24 A and  24 B  are cross-sectional views illustrating an example of a method for manufacturing a display device; 
         FIGS.  25 A to  25 D  illustrate examples of electronic devices; 
         FIGS.  26 A and  26 B  illustrate examples of electronic devices; 
         FIGS.  27 A to  27 D  illustrate structures of light-emitting elements; 
         FIGS.  28 A to  28 C  illustrate light-emitting devices; 
         FIG.  29    is a cross-sectional view illustrating an example of a sample; and 
         FIGS.  30 A to  30 D  are each a photograph of a sample. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     (Notes on the Description in this Specification and the Like) 
     First, notes on the description of structures in the following embodiments and example are described. 
     &lt;Notes on One Embodiment of the Present Invention Described in Embodiments and Example&gt; 
     One embodiment of the present invention can be constituted by appropriately combining the structure described in an embodiment with any of the structures described in the other embodiments and Example. In addition, in the case where a plurality of structure examples are described in one embodiment, some of the structure examples can be combined as appropriate. 
     Note that what is described (or part thereof) in an embodiment can be applied to, combined with, or replaced with another content in the same embodiment and/or what is described (or part thereof) in another embodiment or other embodiments. 
     Note that in each embodiment and example, a content described in the embodiment and example is a content described with reference to a variety of diagrams or a content described with text in the specification. 
     Note that by combining a diagram (or part thereof) described in one embodiment or one example with another part of the diagram, a different diagram (or part thereof) described in the embodiment or example, and/or a diagram (or part thereof) described in another embodiment, other embodiments, or an example, much more diagrams can be formed. 
     &lt;Notes on Ordinal Numbers&gt; 
     In this specification and the like, ordinal numbers such as first, second, and third are used in order to avoid confusion among components. Thus, the terms do not limit the number or order of components. In this specification and the like, for example, a “first” component in one embodiment can be referred to as a “second” component in other embodiments or claims. Furthermore, in this specification and the like, for example, a “first” component in one embodiment can be omitted in other embodiments or claims. 
     &lt;Notes on the Description for Drawings&gt; 
     Embodiments and Example are described with reference to drawings. However, the embodiments and the example can be implemented with various modes. It is readily appreciated by those skilled in the art that modes and details can be changed in various ways without departing from the spirit and scope of the present invention. Thus, the present invention should not be interpreted as being limited to the description of the embodiments and example. Note that in the structures of the invention in the embodiments and example, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and the description of such portions is not repeated. 
     In this specification and the like, the terms for explaining arrangement, such as “over” and “under,” are used for convenience to describe the positional relation between components with reference to drawings. Furthermore, the positional relation between components is changed as appropriate in accordance with a direction in which the components are described. Therefore, the terms for explaining arrangement are not limited to those used in this specification and may be changed to other terms as appropriate depending on the situation. 
     The term “over” or “under” does not necessarily mean that a component is placed directly over or directly under and directly in contact with another component. For example, the expression “electrode B over insulating layer A” does not necessarily mean that the electrode B is on and in direct contact with the insulating layer A and can mean the case where another component is provided between the insulating layer A and the electrode B. 
     In drawings, the size, the layer thickness, or the region is determined arbitrarily for description convenience. Therefore, the size, the layer thickness, or the region is not limited to the illustrated scale. Note that the drawings are schematically shown for clarity, and embodiments of the present invention are not limited to shapes or values shown in the drawings. For example, the following can be included: variation in signal, voltage, or current due to noise or difference in timing. 
     In drawings such as perspective views, some components might not be illustrated for clarity of the drawings. 
     In the drawings, the same components, components having similar functions, components formed of the same material, or components formed at the same time are denoted by the same reference numerals in some cases, and the description thereof is not repeated in some cases. 
     &lt;Notes on Expressions that can be Rephrased&gt; 
     In this specification and the like, the terms “one of a source and a drain” (or a first electrode or a first terminal) and “the other of the source and the drain” (or a second electrode or a second terminal) are used to describe the connection relation of a transistor. This is because a source and a drain of a transistor are interchangeable depending on the structure, operation conditions, or the like of the transistor. Note that the source or the drain of the transistor can also be referred to as a source (or drain) terminal, a source (or drain) electrode, or the like as appropriate depending on the situation. In this specification and the like, two terminals except a gate are sometimes referred to as a first terminal and a second terminal or as a third terminal and a fourth terminal. In this specification and the like, in the case where a transistor has two or more gates (this structure is referred to as a multi-gate structure in some cases), these gates are referred to as a first gate and a second gate in some cases. Note that a “bottom gate” is a terminal that is formed before a channel formation region in manufacture of a transistor, and a “top gate” is a terminal that is formed after a channel formation region in manufacture of a transistor. 
     In addition, in this specification and the like, the term such as an “electrode” or a “wiring” does not limit a function of the component. For example, an “electrode” is used as part of a “wiring” in some cases, and vice versa. Furthermore, the term “electrode” or “wiring” can also mean a combination of a plurality of “electrodes” and “wirings” formed in an integrated manner. 
     In this specification and the like, “voltage” and “potential” can be replaced with each other. The term “voltage” refers to a potential difference from a reference potential. When the reference potential is a ground potential, for example, “voltage” can be replaced with “potential”. The ground potential does not necessarily mean 0 V. Potentials are relative values, and the potential applied to a wiring or the like is changed depending on the reference potential, in some cases. 
     In this specification and the like, the terms “film” and “layer” can be interchanged with each other depending on the case or circumstances. For example, the term “conductive layer” can be changed into the term “conductive film” in some cases. Moreover, the term “insulating film” can be changed into the term “insulating layer” in some cases, or can be replaced with a word not including the term “film” or “layer” depending on the case or circumstances. For example, the term “conductive layer” or “conductive film” can be changed into the term “conductor” in some cases. Furthermore, for example, the term “insulating layer” or “insulating film” can be changed into the term “insulator” in some cases. 
     In this specification and the like, the terms “wiring”, “signal line”, “power supply line”, and the like can be interchanged with each other depending on circumstances or conditions. For example, the term “wiring” can be changed into the term such as “signal line” or “power supply line” in some cases. The term such as “signal line” or “power supply line” can be changed into the term “wiring” in some cases. The term such as “power supply line” can be changed into the term such as “signal line” in some cases. The term such as “signal line” can be changed into the term such as “power supply line” in some cases. The term “potential” that is applied to a wiring can be changed into the term “signal” or the like depending on circumstances or conditions. Inversely, the term “signal” or the like can be changed into the term “potential” in some cases. 
     &lt;Notes on Definitions of Terms&gt; 
     Definitions of the terms that will be mentioned in the following embodiments and example are described below. 
     &lt;&lt;Impurity in Semiconductor&gt;&gt; 
     An impurity in a semiconductor refers to, for example, elements other than the main components of a semiconductor layer. For example, an element with a concentration of lower than 0.1 atomic % is an impurity. When an impurity is contained, the density of states (DOS) may be formed in a semiconductor, the carrier mobility may be decreased, or the crystallinity may be decreased. In the case where the semiconductor is an oxide semiconductor, examples of an impurity that changes characteristics of the semiconductor include Group 1 elements, Group 2 elements, Group 13 elements, Group 14 elements, Group 15 elements, and transition metals other than the main components of the semiconductor; specifically, there are hydrogen (included in water), lithium, sodium, silicon, boron, phosphorus, carbon, and nitrogen, for example. When the semiconductor is an oxide semiconductor, oxygen vacancies may be formed by entry of impurities such as hydrogen, for example. Furthermore, when the semiconductor is a silicon layer, examples of an impurity that changes the characteristics of the semiconductor include oxygen, Group 1 elements except hydrogen, Group 2 elements, Group 13 elements, and Group 15 elements. 
     &lt;&lt;Transistor&gt;&gt; 
     In this specification, a transistor is an element having at least three terminals of a gate, a drain, and a source. The transistor has a channel formation region between the drain (a drain terminal, a drain region, or a drain electrode) and the source (a source terminal, a source region, or a source electrode). Voltage is applied between the gate and the source, whereby current can flow between the source and the drain. 
     Furthermore, functions of a source and a drain might be switched when a transistor of opposite polarity is employed or a direction of current flow is changed in circuit operation, for example. Therefore, the terms “source” and “drain” can be switched in this specification and the like. 
     &lt;&lt;Switch&gt;&gt; 
     In this specification and the like, a switch is conducting (on state) or not conducting (off state) to determine whether current flows therethrough or not. Alternatively, a switch has a function of selecting and changing a current path. 
     Examples of a switch include an electrical switch and a mechanical switch. That is, any element can be used as a switch as long as it can control current, without limitation to a certain element. 
     Examples of the electrical switch include a transistor (e.g., a bipolar transistor or a MOS transistor), a diode (e.g., a PN diode, a PIN diode, a Schottky diode, a metal-insulator-metal (MIM) diode, a metal-insulator-semiconductor (MIS) diode, or a diode-connected transistor), and a logic circuit in which such elements are combined. 
     In the case of using a transistor as a switch, an “on state” of the transistor refers to a state in which a source electrode and a drain electrode of the transistor are electrically short-circuited. Furthermore, an “off state” of the transistor refers to a state in which the source electrode and the drain electrode of the transistor are electrically cut off. In the case where a transistor operates just as a switch, the polarity (conductivity type) of the transistor is not particularly limited to a certain type. 
     An example of a mechanical switch is a switch formed using a micro electro mechanical systems (MEMS) technology, such as a digital micromirror device (DMD). Such a switch includes an electrode that can be moved mechanically, and operates by controlling conduction and non-conduction in accordance with movement of the electrode. 
     &lt;&lt;Connection&gt;&gt; 
     In this specification and the like, when it is described that X and Y are connected, the case where X and Y are electrically connected, the case where X and Y are functionally connected, and the case where X and Y are directly connected are included therein. Accordingly, without being limited to a predetermined connection relation, for example, a connection relation other than that shown in a drawing or text is also possible. 
     Here, X, Y, and the like each denote an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer). 
     For example, in the case where X and Y are electrically connected, one or more elements that enable an electrical connection between X and Y (e.g., a switch, a transistor, a capacitor, an inductor, a resistor, a diode, a display element, a light-emitting element, or a load) can be connected between X and Y. Note that the switch is controlled to be turned on or off. That is, a switch is conducting or not conducting (is turned on or off) to determine whether current flows therethrough or not. 
     For example, in the case where X and Y are functionally connected, one or more circuits that enable functional connection between X and Y (e.g., a logic circuit such as an inverter, a NAND circuit, or a NOR circuit; a signal converter circuit such as a DA converter circuit, an AD converter circuit, or a gamma correction circuit; a potential level converter circuit such as a power source circuit (e.g., a step-up converter or a step-down converter) or a level shifter circuit for changing the potential level of a signal; a voltage source; a current source; a switching circuit; an amplifier circuit such as a circuit that can increase signal amplitude, the amount of current, or the like, an operational amplifier, a differential amplifier circuit, a source follower circuit, or a buffer circuit; a signal generation circuit; a memory circuit; and/or a control circuit) can be connected between X and Y. For example, even when another circuit is interposed between X and Y, X and Y are functionally connected when a signal output from Xis transmitted to Y. 
     Note that when it is explicitly described that X and Y are electrically connected, the case where X and Y are electrically connected (i.e., the case where X and Y are connected with another element or another circuit provided therebetween), the case where X and Y are functionally connected (i.e., the case where X and Y are functionally connected with another circuit provided therebetween), and the case where X and Y are directly connected (i.e., the case where X and Y are connected without another element or another circuit provided therebetween) are included therein. That is, the explicit expression “X and Y are electrically connected” is the same as the explicit simple expression “X and Y are connected”. 
     For example, any of the following expressions can be used for the case where a source (or a first terminal or the like) of a transistor is electrically connected to X through (or not through) Z 1  and a drain (or a second terminal or the like) of the transistor is electrically connected to Y through (or not through) Z 2 , or the case where a source (or a first terminal or the like) of a transistor is directly connected to one part of Z 1  and another part of Z 1  is directly connected to X while a drain (or a second terminal or the like) of the transistor is directly connected to one part of Z 2  and another part of Z 2  is directly connected to Y. 
     The expressions include, for example, “X, Y, a source (or a first terminal or the like) of a transistor, and a drain (or a second terminal or the like) of the transistor are electrically connected to each other, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are electrically connected to each other in this order”, “a source (or a first terminal or the like) of a transistor is electrically connected to X, a drain (or a second terminal or the like) of the transistor is electrically connected to Y, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are electrically connected to each other in this order”, and “X is electrically connected to Y through a source (or a first terminal or the like) and a drain (or a second terminal or the like) of a transistor, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are provided to be connected in this order”. When the connection order in a circuit configuration is defined by an expression similar to the above examples, a source (or a first terminal or the like) and a drain (or a second terminal or the like) of a transistor can be distinguished from each other to specify the technical scope. Note that these expressions are examples and there is no limitation on the expressions. Here, X, Y, Z 1 , and Z 2  each denote an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer). 
     Even when independent components are electrically connected to each other in a circuit diagram, one component has functions of a plurality of components in some cases. For example, when part of a wiring also functions as an electrode, one conductive film functions as the wiring and the electrode. Thus, “electrical connection” in this specification includes in its category such a case where one conductive film has functions of a plurality of components. 
     &lt;&lt;Parallel and Perpendicular&gt;&gt; 
     In this specification, the term “parallel” indicates that the angle formed between two straight lines is greater than or equal to −10° and less than or equal to 10°, and accordingly also includes the case where the angle is greater than or equal to −5° and less than or equal to 5°. The term “substantially parallel” indicates that the angle formed between two straight lines is greater than or equal to −30° and less than or equal to 30°. The term “perpendicular” indicates that the angle formed between two straight lines is greater than or equal to 80° and less than or equal to 100°, and accordingly also includes the case where the angle is greater than or equal to 85° and less than or equal to 95°. The term “substantially perpendicular” indicates that the angle formed between two straight lines is greater than or equal to 60° and less than or equal to 120°. 
     Embodiment 1 
     In this embodiment, a display device disclosed in one embodiment of the present invention is described. 
     &lt;Structure Example&gt; 
       FIGS.  1 A,  1 B, and  1 C  illustrate a display unit, a driver circuit unit, and a support unit, respectively, that are included in the display device of one embodiment of the present invention. A display unit  80  illustrated in  FIG.  1 A  includes a light-emitting portion  81 , a connection region  82 , and a support  83 . A driver circuit unit  90  illustrated in  FIG.  1 B  includes a driver circuit portion  91 , a connection region  92 , and a support  93 . A support unit  70  illustrated in  FIG.  1 C  includes a connection region  72  and a support  73 . 
     The light-emitting portion  81  of the display unit  80  includes a light-emitting element and a pixel circuit. Examples of the light-emitting element include a transmissive liquid crystal element, an organic EL element, an inorganic EL element, and a nitride semiconductor light-emitting diode. Instead of the light-emitting element, a reflective liquid crystal element, an electrophoretic element, or the like can be used. The pixel circuit is a circuit for making the light-emitting element emit light. A terminal electrically connected to the circuit is included in the connection region  82 . 
     Note that the light-emitting portion  81  may be a pixel including a plurality of light-emitting elements. For example, the plurality of light-emitting elements may emit light of three colors of red (R), green (G), and blue (B), or four colors of red (R), green (G), blue (B), and white (W). Alternatively, the plurality of light-emitting elements may emit light of some of red (R), green (G), blue (B), white (W), cyan (C), yellow (Y), magenta (M), and the like in combination as necessary. The light-emitting portion  81  of the display unit  80  is not necessarily the pixel including the plurality of light-emitting elements, and may be a subpixel including a light-emitting element emitting light of any one of the above colors, for example. 
     The driver circuit portion  91  of the driver circuit unit  90  has a function of driving the pixel circuit included in the display unit  80  to make the light-emitting element emit light. For the driver circuit portion  91 , a source driver circuit, a gate driver circuit, or the like can be used. A terminal electrically connected to the driver circuit portion  91  is included in the connection region  92 . 
     The connection regions  72 ,  82 , and  92  are provided so that each unit can be electrically connected to other units. Note that a method for connecting the units to each other is described later. 
     FIG.  1 D 1  illustrates the display device of one embodiment of the present invention. A display device  100  is functionally divided into a display region  101 , a driver region  102 A, and a driver region  102 B. 
     The display region  101  includes a plurality of display units  80 . The driver region  102 A includes a plurality of driver circuit units  90 . The driver region  102 B includes a plurality of driver circuit units  90  that are different from those in the driver region  102 A. The display device  100  also includes the support unit  70 . In FIGS.  1 D 1  and  1 D 2 , the support unit  70  is not included in the display region  101 , the driver region  102 A, nor the driver region  102 B. 
     The units are connected to each other with a shaft  60  passing through the connection regions of the units. Thus, the units include openings for the shaft  60  in the connection regions. For example, in a region  105   a , one shaft  60  passes through the connection regions  82  of four display units  80 , whereby the four display units  80  are connected to one another. For another example, in a region  105   b , one shaft  60  passes through the connection regions  82  of two display units  80  and the connection regions  92  of two driver circuit units  90 , whereby the two display units  80  and the two driver circuit units  90  are connected to one another. Note that the shaft  60  is a structure body for electrically connecting the units to each other; the details of the shaft  60  are described later. 
     As described above, for the driver circuit portion  91  included in the driver circuit unit  90 , a source driver circuit, a gate driver circuit, or the like can be used. Thus, the plurality of driver circuit units  90  included in the driver region  102 A can constitute one of the source driver circuit and the gate driver circuit by being electrically connected to each other with the shaft  60 . In addition, the plurality of driver circuit units  90  included in the driver region  102 B can constitute the other of the source driver circuit and the gate driver circuit by being electrically connected to each other with the shaft  60 . 
     The support unit  70  has a function of maintaining the structure of the display device  100 . In FIG.  1 D 1 , one of the connection regions  72  of the support unit  70  is connected to the connection region  92  of the driver circuit unit  90  in the driver region  102 A with the shaft  60 , and the other of the connection regions  72  of the support unit  70  is connected to the connection region  92  of the driver circuit unit  90  in the driver region  102 B with the shaft  60 . Note that the support unit  70  may be provided with a wiring, a circuit, an element, or the like. In that case, the connection region  72  of the support unit  70  is electrically connected to the connection region  92  of the driver circuit unit  90  with the shaft  60 . In the case where the display device  100  does not need the support unit  70 , the support unit  70  may be omitted from the components of the display device  100 . 
     Note that the display unit, the driver circuit unit, and the support unit are each rotatable on the shaft  60  in the connection region. For example, although an angle θ between the dotted line X 1 -X 2  and the dotted line X 1 -X 3  is 45° in the display device  100  in FIG.  1 D 1 , the units may be rotated until the angle θ becomes 30° to change the shape of the display device  100  as illustrated in FIG.  1 D 2 . In that case, the display device  100  in FIG.  1 D 1  is stretched by approximately 1.2 times in the x direction and approximately 0.71 times in the y direction to have the shape in FIG.  1 D 2 . That is, by changing the angle θ, the aspect ratio of the display device  100  can be changed. In the case where the display device  100  is stretched as much as possible, the display device  100  is configured so that the units are movable in the range of the angle θ of approximately 10° to 80°. Depending on the shape of the display unit  80 , the range of the angle θ becomes narrower than or wider than the above-described range of 10° to 80°. 
     Note that because of the structure of the display device  100 , some of the plurality of driver circuit units  90  included in the driver region  102 A and the driver region  102 B are parallel to some of the display units  80  included in the display region  101 . 
     As described above, the display device  100  in FIG.  1 D 1  that is formed using the plurality of display units  80 , the plurality of driver circuit units  90 , and the support unit  70  can be a stretchable display device. 
     &lt;Configuration Method&gt; 
     Next, a method for connecting the units to each other to form the display device  100  in FIG.  1 D 1  is described. 
       FIGS.  2 A to  2 C  illustrate an example of the method for connecting the units to each other. Only the display unit  80  is described in this example; however, depending on circumstances or conditions or as needed, the display unit may be replaced with the driver circuit unit or the support unit. 
     [Step  1 ] 
       FIG.  2 A  illustrates a display unit group  85  combining four display units  80  (display units  80   a ,  80   b ,  80   c , and  80   d ). The display unit  80   a  includes a region where one of the two connection regions  82  of the display unit  80   a  overlaps with one of the two connection regions  82  of the display unit  80   b , and a region where the other of the two connection regions  82  of the display unit  80   a  overlaps with one of the two connection regions  82  of the display unit  80   c . The display unit  80   d  includes a region where one of the two connection regions  82  of the display unit  80   d  overlaps with the other of the two connection regions  82  of the display unit  80   b , and a region where the other of the two connection regions  82  of the display unit  80   d  overlaps with the other of the two connection regions  82  of the display unit  80   c . Note that in the display unit group  85  in  FIGS.  2 A to  2 C , the display unit  80   a  and the display unit  80   d  are provided on the lower side, and the display unit  80   b  and the display unit  80   c  are provided on the upper side. 
     [Step  2 ] 
     Next, four display unit groups  85  are provided so that the connection regions  82  of the four display unit groups  85  overlap with the connection regions  82  of the display unit group  85  in  FIG.  2 A  (see  FIG.  2 B ). Then, the shafts  60  are provided in the overlapping connection regions  82  to connect four display units to each other. In order to avoid complexity of description, the display unit group  85  in  FIG.  2 A  is indicated by a different hatching pattern from the other display unit groups  85  in  FIG.  2 B . 
     [Step  3 ] 
     After that, another four display unit groups  85  are provided under connection regions  82   a ,  82   b ,  82   c ,  82   d ,  82   e ,  82   f ,  82   g , and  82   h  in  FIG.  2 B  and electrically connected to the connection regions with the shafts  60 . Specifically, one of the four display unit groups  85  is provided under the connection regions  82   a  and  82   b  and electrically connected thereto with shafts  60   a  and  60   b ; one of the remaining three display unit groups  85  is provided under the connection regions  82   c  and  82   d  and electrically connected thereto with shafts  60   c  and  60   d ; one of the remaining two display unit groups  85  is provided under the connection regions  82   e  and  82   f  and electrically connected thereto with shafts  60   e  and  60   f ; and the remaining display unit group  85  is provided under the connection regions  82   g  and  82   h  and electrically connected thereto with shafts  60   g  and  60   h  (see  FIG.  2 C ). Note that in order to avoid complexity of description, in  FIG.  2 C , the display unit group  85  in  FIG.  2 A  and the display unit groups  85  newly electrically connected to the connection regions in Step  3  are indicated by different hatching patterns from the other display unit groups  85 . That is, in  FIG.  2 C , the hatching patterns of the display unit groups  85  on the upper side are not changed, whereas the hatching patterns of the display unit groups  85  on the lower side are changed. 
     As described above, the display device can be configured by connecting the adjacent display unit groups  85  to each other so that one of them is positioned on the upper side and the other is positioned on the lower side. 
     Note that in the case where no display unit groups  85  are provided adjacent to the display unit groups  85  (e.g., when no display unit groups  85  are newly provided in a region  106  in  FIG.  2 C ), the display units are electrically connected to each other with shafts  61  passing through the connection regions  82  in the region  106 . For another example, when no display unit groups  85  are provided adjacent to the display unit groups  85  in a region other than the region  106 , the display units are electrically connected to each other with the shafts  61  passing through the connection regions in the region. 
     Next, a cross section of the display device formed by the above-described method is described. 
       FIG.  3 A  illustrates a region  101   a  in  FIG.  2 C .  FIG.  3 B  is a cross-sectional view taken along the dashed-dotted line A 1 -A 2  in  FIG.  3 A , and  FIG.  3 C  is a cross-sectional view taken along the dashed-two dotted line B 1 -B 2  in  FIG.  3 A . The shafts  60   e  to  60   h , a shaft  60   i , and the shafts  61  that have a function of connecting the display units  80  to each other are also illustrated in  FIGS.  3 B and  3 C . 
     In the region  101   a , display unit groups  85 A,  85 B, and  85 C are electrically connected to each other so that the display unit group  85 B is positioned on the upper side and the display unit groups  85 A and  85 C are positioned on the lower side. As illustrated in  FIGS.  3 B and  3 C , the display unit group  85 B is positioned above the display unit groups  85 A and  85 C. 
     Next, the shafts  60   e  to  60   i  (collectively referred to as the shaft  60 ) and a method for electrically connecting the shaft  60  to the display units  80  are described. Here, a region  101   b  and the shaft  60   h  in  FIG.  3 B  are described in detail, for example. In the following detailed description, the shaft  60   h  can be replaced by the shaft  60   e ,  60   f ,  60   g , or  60   i , for example. For the shafts  61 , refer to the following description of the shaft  60   h.    
       FIG.  4 A  illustrates the details of the region  101   b .  FIG.  4 B  is a cross-sectional view of the shaft  60   h  taken along the dashed-dotted line C 1 -C 2  in  FIG.  4 A . 
     The display unit group  85 B includes a display unit  80 [ 1 ] and a display unit  80 [ 2 ]. The display unit group  85 C includes a display unit  80 [ 3 ] and a display unit  80 [ 4 ]. In  FIG.  4 A , the display unit  80 [ 1 ] includes wirings  86   b , and the display unit  80 [ 4 ] includes wirings  86   c . The wirings  86   b  are electrically connected to respective conductors  41  to  44 . The wirings  86   c  are electrically connected to the respective conductors  41  to  44 . 
     The shaft  60   h  includes the conductors  41  to  44  and conductors  45  to  48 . 
     In the cross-sectional view in  FIG.  4 B , the conductor  41  is positioned in the center of the shaft  60   h . The conductors  42  to  48  are positioned concentrically around the conductor  41  (the center of the shaft  60   h ). 
     The conductor  41  has a structure illustrated in a perspective view in  FIG.  5 A . The conductor  41  includes a disk  41   a , a column  41   b , and a disk  41   c . The column  41   b  is provided on the center portions of the disks  41   a  and  41   c . One of the wirings  86   b  is electrically connected to the conductor  41  by contact with a side surface of the disk  41   a . One of the wirings  86   c  is electrically connected to the conductor  41  by contact with a side surface of the disk  41   c.    
     The conductor  44  has a structure illustrated in a perspective view in  FIG.  5 B . The conductor  44  includes a disk  44   a  having a circular hole, a hollow cylinder  44   b , and a disk  44   c  having a circular hole. The circular hole of the disk  44   a , the circular hole of the disk  44   c , and the hollow of the cylinder  44   b  have the same size. The disk  44   c  is provided on the bottom base of the cylinder  44   b  so that the circular hole of the disk  44   c  is aligned with the hollow of the cylinder  44   b . The disk  44   a  is provided on the upper base of the cylinder  44   b  so that the circular hole of the disk  44   a  is aligned with the hollow of the cylinder  44   b . One of the wirings  86   b  is electrically connected to the conductor  44  by contact with a side surface of the disk  44   a . One of the wirings  86   c  is electrically connected to the conductor  44  by contact with a side surface of the disk  44   c.    
     For the structures of the conductors  42 ,  43 , and  45  to  48 , refer to the description of the conductor  44 . 
     In  FIG.  4 A , the conductor  42  has a function of electrically connecting one of the wirings  86   b  to one of the wirings  86   c . The conductor  43  has a function of electrically connecting another one of the wirings  86   b  to another one of the wirings  86   c . Although not illustrated, the conductors  45  to  48  have functions of electrically connecting wirings included in the display unit  80 [ 2 ] to wirings included in the display unit  80 [ 3 ]. 
     When the conductors included in the shaft  60  have the structures illustrated in  FIGS.  4 A and  4 B  and  FIGS.  5 A and  5 B , the units can be electrically connected to each other with the shaft  60 . 
       FIGS.  4 A and  4 B  illustrate one example of the structure of the shaft  60   h , and one embodiment of the present invention is not limited to this example. For example, the shaft  60   h  may have a structure in  FIG.  6    instead of the structure in  FIGS.  4 A and  4 B . In the structure illustrated in  FIG.  6   , the wirings  86   b  are in contact with the respective conductors  41  to  44 , and the wirings  86   c  are in contact with the respective conductors  41  to  44 . Similarly, the wirings included in the display unit  80 [ 2 ] are in contact with the respective conductors  45  to  48 , and the wirings included in the display unit  80 [ 3 ] are in contact with the respective conductors  45  to  48  (the contacts between the wirings and the conductors  45  to  48  are not illustrated in  FIG.  6   ). Note that the conductors are positioned on the wirings at the upper side of the shaft  60   h  and the wirings are positioned on the conductors at the lower side of the shaft  60   h . This structure can reduce the contact resistance between the wirings included in the display units and the conductors included in the shaft  60   h.    
     Alternatively, the shaft  60   h  may include, for example, codes formed of a ductile and malleable conductor covered with an insulator such as rubber, instead of the conductors  41  to  48 . The shaft having such a structure is illustrated in  FIGS.  7 A and  7 B  as a shaft  60 A.  FIG.  7 A  is a perspective view of the shaft  60 A including the codes in place of the conductors  41  to  48 .  FIG.  7 B  is a cross-sectional view of the shaft  60 A taken along the planes Y 1 -Y 2  in  FIG.  7 A . 
     In  FIG.  7 A , the shaft  60 A includes openings  69   b [ 1 ],  69   b [ 2 ],  69   c [ 1 ], and  69   c [ 2 ] for connecting the codes to the wirings (e.g., the wirings  86   b  and  86   c ) included in the display units. Note that the movable range of the display units depends on the lengths of the openings in the circumferential direction; the longer the lengths of the openings in the circumferential direction are, the wider the movable range of the display units is. 
       FIG.  7 B  illustrates a structure example of the region  101   b  including the shaft  60 A in  FIG.  7 A . The shaft  60 A includes codes  51  to  54 . The codes  51  to  54  are used in place of the conductors  41  to  44  in  FIGS.  4 A and  4 B  and  FIG.  6   . That is, the codes  51  to  54  have functions of electrically connecting the wirings  86   b  to the wirings  86   c  through the openings  69   b [ 1 ] and  69   c [ 2 ]. The codes  51  to  54  have ductility and malleability to be highly resistant to bending and thus can withstand the movement of the units connected to each other. 
     The above-described connection method makes it possible to obtain the display device  100  in FIG.  1 D 1 . 
     &lt;Modification Example&gt; 
     One embodiment of the present invention is not limited to the display device  100  in FIG.  1 D 1 . Depending on the circumstances or conditions or as needed, the components of the display device  100  can be changed as appropriate. 
     For example, instead of the display unit  80  in  FIG.  1 A , a display unit  80 A in  FIG.  8 A  whose light-emitting portion is larger than the light-emitting portion  81  of the display unit  80  may be used. The display unit  80 A includes a light-emitting portion  81 A, the connection region  82 , and a support  83 A. The light-emitting portion  81 A of the display unit  80 A has a larger light-emitting area than the light-emitting portion  81  of the display unit  80 . With an increase in the light-emitting area of the light-emitting portion  81 A, the area of the support  83 A is increased in the display unit  80 A. 
       FIG.  8 B  illustrates a display device  100 A including the display unit  80 A in place of the display unit  80  of the display device  100  illustrated in FIG.  1 D 1 . The use of the display unit  80 A enables the display device  100 A to have a larger light-emitting area. Thus, the display device  100 A can have a smaller non-display region (a region other than the light-emitting portion  81 ) than the display device  100 , resulting in an increase in the emission luminance of the display device  100 A. 
     Here, the case where the size of the support  83 A of the display unit  80 A is increased as much as possible is described. FIG.  8 C 1 , FIG.  8 D 1 , and  FIG.  8 E  illustrate a display unit group  86  combining four display units  80 , a display unit group  86 A combining four display units  80 A, and a display unit group  86 B combining four display units  80 B, respectively. In the display unit group  86 B, the display units  80 B have such large supports that the opposite display units  80 B are in contact with each other. 
     In this specification and the like, as an index of the size of the display unit, the distance between the center of the shaft in one of the connection regions and the center of the shaft in the other of the connection regions in the display unit is defined as a length in a first direction. In addition, the width of the display unit in the direction perpendicular to the first direction of the display unit is defined as a length in a second direction. 
     The distance between the two connection regions of each of the display unit  80  in FIG.  8 C 1 , the display unit  80 A in FIG.  8 D 1 , and the display unit  80 B in  FIG.  8 E  (hereinafter, referred to as the length in the first direction) is referred to as L. The lengths in the second direction of the display unit  80  in FIG.  8 C 1 , the display unit  80 A in FIG.  8 D 1 , and the display unit  80 B in  FIG.  8 E  are referred to as W 1 , W 2 , and W 3 , respectively. Note that W 2  is longer than W 1 , and W 3  is longer than W 2 . The size of the support of the display unit  80 B is as large as possible; thus, W 3  is the maximum value in the display unit group  86 B composed of the display units  80 B. 
     The opposite display units  80 B are in contact with each other in the display unit group  86 B in  FIG.  8 E ; thus, the length L in the first direction of the display unit  80 B is the same as the length W 3  in the second direction of the display unit  80 B. 
     In the display unit  80  in FIG.  8 C 1 , the center of the shaft in one of the connection regions is referred to as Z 1 , and the center of the shaft in the other of the connection regions is referred to as Z 3 . In the display unit group  86  in FIG.  8 C 1 , the center of the shaft in the connection region that is diagonally opposite to Z 1  is referred to as Z 2 . Similarly, in the display unit  80 A in FIG.  8 D 1 , the center of the shaft in one of the connection regions is referred to as Z 1 , and the center of the shaft in the other of the connection regions is referred to as Z 3 . In the display unit group  86 A in FIG.  8 D 1 , the center of the shaft in the connection region that is diagonally opposite to Z 1  is referred to as Z 2 . Similarly, in the display unit  80 B in  FIG.  8 E , the center of the shaft in one of the connection regions is referred to as Z 1 , and the center of the shaft in the other of the connection regions is referred to as Z 3 . In the display unit group  86 B in  FIG.  8 E , the center of the shaft in the connection region that is diagonally opposite to Z 1  is referred to as Z 2 . In each of FIGS.  8 C 1 ,  8 D 1 , and  8 E, an angle between the dotted line Z 1 -Z 2  and the dotted line Z 1 -Z 3  is referred to as B. 
     The display unit group  86  in FIG.  8 C 1  is changed in shape such that θ has the minimum value, so that the display unit group  86  has a shape in FIG.  8 C 2 . An angle between the dotted line Z 1 -Z 3  and the dotted line Z 1 -Z 2  at this time is referred to as ϕ 1 . The display unit group  86 A in FIG.  8 D 1  is changed in shape such that θ has the minimum value, so that the display unit group  86 A has a shape in FIG.  8 D 2 . An angle between the dotted line Z 1 -Z 3  and the dotted line Z 1 -Z 2  at this time is referred to as ϕ 2 . Note that the angle ϕ 1  is smaller than the angle ϕ 2 . 
     Note that in FIGS.  8 C 2  and  8 D 2 , the dotted line Z 1 -Z 3  and the dotted line Z 1 -Z 2  are extended to clearly show the angle ϕ 1  and the angle ϕ 2 . 
     When the second direction length W 1  of the display unit  80  in the display unit group  86  is increased, the shape of the display unit group  86  becomes close to that of the display unit group  86 A. That is, the increased second direction length of the display unit increases the minimum value in the range of the angle θ. For the same reason, the increased second direction length of the display unit reduces the maximum value in the range of the angle θ. In other words, the increased second direction length of the display unit narrows the range of the angle θ in the display unit group including the display unit. 
     The display unit group  86 B in  FIG.  8 E  cannot be changed in shape by reducing the angle θ because the opposite display units  80 B are in contact with each other. 
     Accordingly, in the case where the display device  100 A is formed using the display unit whose light-emitting portion and support are larger than the light-emitting portion  81  and the support  83  of the display unit  80 , the length in the second direction of the display unit needs to be shorter than the length in the first direction of the display unit. 
     A plurality of units in  FIGS.  9 A and  9 B  may be used instead of the units in  FIGS.  1 A to  1 C , for example. 
     A region  100   a  in  FIG.  9 A  includes one support unit  70  and a plurality of units  30 . Note that not all the units  30  have the same length and some of the units  30  have different lengths from the others, and the support unit  70  and each of the plurality of units  30  are parallel to each other. Each of the units  30  includes the light-emitting portion  81  and a connection region  32 . Some of the units  30  include one or two driver circuit portions  91 , and the others do not include the driver circuit portion  91 . 
     A region  100   b  in  FIG.  9 B  includes a plurality of units  31 . Note that not all the units  31  have the same length and some of the units  31  have different lengths from the others, and the plurality of units  31  are parallel to each other. Each of the units  31  includes the driver circuit portion  91  and the connection region  32 . Some of the units  31  include the light-emitting portion  81 , and the others do not include the light-emitting portion  81 . 
     A display device  100 B in  FIG.  9 C  can be obtained in such a manner that the connection regions  32  of the units  31  in  FIG.  9 B  are provided to overlap with the connection regions  32  of the support unit  70  and the units  30  in  FIG.  9 A , and the connection regions  32  are connected to each other with shafts  62 . Such a structure enables the display device  100 B to change its shape so as to be the display device  100  in FIG.  1 D 2  (this change is not illustrated), as in the display device  100  in FIG.  1 D 1 . Although the display device  100  in FIG.  1 D 1  includes four units overlapping with one another as in  FIGS.  3 B and  3 C , the display device  100 B includes two units overlapping with each other and thus can be stored in a thin housing or the like. 
     In the above description, the support unit  70  is described as a component of the display device  100 B; however, the display device  100 B does not necessarily include the support unit  70 . 
     Note that this embodiment can be combined with other embodiments and/or an example in this specification as appropriate. 
     Embodiment 2 
     In this embodiment, examples of electronic devices each including the display device  100  in Embodiment 1 are described. 
     Application Example 1 
     FIGS.  10 A 1  and  10 A 2  each illustrate a signboard  6002  provided on the roof of a building  6001 . The signboard  6002  is supported by steel frames  6003  provided on the roof of the building  6001 . 
     Here, the case where the signboard  6002  includes the display device  100  in Embodiment 1 is described. The signboard  6002  in FIG.  10 A 1  that includes the display device  100  can change its shape so as to be a signboard  6002 A in FIG.  10 A 2 . Accordingly, the aspect ratio of the signboard can be freely changed depending on the contents displayed on the signboard. 
     Application Example 2 
     FIGS.  10 B 1  and  10 B 2  each illustrate an example of a small-sized digital signage that can be easily transferred. A digital signage  6100  in FIG.  10 B 1  includes a display portion  6101 , a structure body  6102 , and casters  6103 . The structure body  6102  has a structure supporting the display portion  6101  and a structure provided with the casters  6103 . The digital signage  6100  can be transferred by rolling the casters  6103 . 
     Here, the case where the display portion  6101  includes the display device  100  in Embodiment 1 is described. The display portion  6101  in FIG.  10 B 1  that includes the display device  100  can change its shape so as to be a display portion  6101 A in FIG.  10 B 2 . Accordingly, the aspect ratio of the display portion can be freely changed depending on the contents displayed on the display portion. 
     Application Example 3 
       FIGS.  11 A and  11 B  each illustrate an example of a digital signage that can be attached to a wall.  FIG.  11 A  illustrates a digital signage  6200 A attached to a wall  6201 . 
     Here, the case where the digital signage  6200 A includes the display device  100  in Embodiment 1 is described. The digital signage  6200 A in  FIG.  11 A  that includes the display device  100  can change its shape so as to be a digital signage  6200 B in  FIG.  11 B . Accordingly, the aspect ratio of the digital signage can be freely changed depending on the contents displayed on the digital signage. 
     Note that this embodiment can be combined with other embodiments and/or an example in this specification as appropriate. 
     Embodiment 3 
     In this embodiment, a display device of one embodiment of the present invention that is different from the display device  100  in Embodiment 1 is described. 
     &lt;Structure Example&gt; 
       FIG.  12 A  illustrates a structure example of a display unit included in the display device of one embodiment of the present invention. A display unit  250  includes a circuit  251 , and the circuit  251  includes a light-emitting portion  252 . 
     The circuit  251  is a circuit for making the light-emitting portion  252  emit light. A selection signal, a data signal, or the like input to the circuit  251  through a wiring (not illustrated in  FIG.  12 A ) enables the light-emitting portion  252  to emit light. 
     For the light-emitting portion  252 , a transmissive liquid crystal element, an organic EL element, an inorganic EL element, a nitride semiconductor light-emitting diode, or the like can be used. Instead of the light-emitting portion  252 , a reflective liquid crystal element, an electrophoretic element, or the like can be used. 
     The light-emitting portion  252  may include a plurality of kinds of light-emitting elements. For example, the plurality of light-emitting elements may emit light of three colors of red (R), green (G), and blue (B), or four colors of red (R), green (G), blue (B), and white (W). Alternatively, the plurality of light-emitting elements may emit light of some of red (R), green (G), blue (B), white (W), cyan (C), yellow (Y), magenta (M), and the like in combination as necessary. The light-emitting portion  252  of the display unit  250  does not necessarily include the plurality of kinds of light-emitting elements, and may include one kind of light-emitting element. For example, the light-emitting portion may emit light of any one of the above colors. 
     The display unit  250  in  FIGS.  12 A ,  12 B 1 , and  12 B 2  may be replaced with a pixel. In the case where the pixel is used instead of the display unit  250  in this embodiment, the display unit  250 , the circuit  251 , and the light-emitting portion  252  may be replaced with a pixel, a pixel circuit, and a light-emitting element, respectively. 
     Note that although the display unit  250  in  FIGS.  12 A ,  12 B 1 , and  12 B 2  has a square shape, one embodiment of the present invention is not limited thereto. For example, the display unit  250  may have a circular shape, an elliptical shape, a shape with a curve, a polygonal shape, or the like. In addition, the light-emitting portion  252  does not necessarily have a square shape, but may have a circular shape, an elliptical shape, a shape with a curve, a polygonal shape, or the like. 
     FIG.  12 B 1  illustrates a structure example of a display region in the display device of one embodiment of the present invention. A display region  260 A has a stacked structure of two layers each including a plurality of display units  250 . In FIG.  12 B 1 , the plurality of display units  250  in an upper layer of the two layers are referred to as display units  250   a , and the plurality of display units  250  in a lower layer of the two layers are referred to as display units  250   b . To avoid complexity of description, wirings connected to the display units  250   a  and the display units  250   b  are not illustrated in FIG.  12 B 1 . 
     Note that the display region  260 A includes an elastic and light-transmitting insulator  240 . In this specification and the like, an elastic material refers to a material that can expand and contract and has high restorability. In addition, a light-transmitting material refers to a material with high transmittance. The insulator  240  has a two-layer structure of the upper layer and the lower layer. The upper layer of the insulator  240  covers all the display units  250   a  and the lower layer of the insulator  240  covers all the display units  250   b . In the insulator  240 , the upper layer and the lower layer may be formed using the same material or different materials. In addition, in the insulator  240 , the upper layer and/or the lower layer may be formed using a combination of a plurality of materials. Alternatively, the insulator  240  may be formed using one elastic and light-transmitting material. 
     The area of the display region  260 A can be increased by stretching the elastic and light-transmitting insulator  240 . For example, the stretch of the insulator  240  in directions of arrows enables the display region  260 A in FIG.  12 B 1  to change its shape so as to be a display region  260 B in FIG.  12 B 2 . 
     The insulator  240  can be formed using, for example, vinyl chloride, a polyurethane resin, silicone, or rubber. 
     The display region  260 A in FIG.  12 B 1  is stretched in the directions of the arrows, whereby gaps between the adjacent display units  250   a  in the upper layer of the display region  260 A are increased. Note that in the case where the display region  260 A including only the display units  250   a  as pixels is stretched so as to be the display region  260 B, the gaps between the adjacent display units  250   a  are increased, leading to a reduction in resolution of the display region  260 B. 
     Thus, the plurality of display units  250   b  are provided in the lower layer in addition to the display units  250   a  in the upper layer in the display region  260 A, as illustrated in FIG.  12 B 1 . With such a structure, when the display region  260 A is stretched to be the display region  260 B, the light-emitting portions  252  of the display units  250   b  appear on the display surface side of the display region  260 B. That is, the light-emitting regions of the display units  250   b  in the lower layer are increased by stretching the display region  260 A to be the display region  260 B, which prevents a reduction in display quality of the display region  260 B. Note that the upper layer and the lower layer of the insulator  240  are preferably formed using materials with different degrees of elasticity. The degrees of elasticity of the materials included in the upper layer and the lower layer are optimized, so that the light-emitting portions  252  of the display units  250   b  can overlap with the gaps between the adjacent display units  250   a  when the display region  260 A is stretched to be the display region  260 B. 
     As illustrated in FIG.  12 B 1 , each of the display units  250   b  in the lower layer of the display region  260 A is preferably provided to overlap with parts of the four display units  250   a  in the upper layer of the display region  260 A. The display region  260 A having such a structure enables each of the display units  250   b  to be positioned in the largest gap between the adjacent display units  250   a  in the upper layer when the display region  260 A is stretched to be the display region  260 B. 
     Note that the positions of the display units  250   b  in the lower layer of the display region  260 A are not limited to those in the display region  260 A in FIG.  12 B 1 . For example, in the case where the display region is stretched in predetermined directions, the structure of a display region  261 A in FIG.  13 A 1  can be employed. The display region  261 A has a structure in which each of the display units  250   b  is provided in the lower layer of the display region  261 A to overlap with parts of the two display units  250   a  in the upper layer. The insulator  240  in such a structure is stretched in the directions of the arrows, whereby the display region  261 A in FIG.  13 A 1  can be a display region  261 B in FIG.  13 A 2 . 
     Alternatively, for example, a display unit  255  in  FIG.  14 A  may be used as each of the pixels provided in the lower layer of the display region. The display unit  255  is smaller than the display unit  250  (display units  250   a  and  250   b ), and includes a circuit  256  including a light-emitting portion  257 . FIG.  14 B 1  illustrates a display region including the display units  255  in the lower layer. A display region  262 A has a structure in which a plurality of display units  255  in the lower layer overlap with parts of the display units  250   a  in the upper layer. Specifically, the display region  262 A has the structure in which some of the display units  255  in the lower layer overlap with two adjacent display units  250   a  in the upper layer, and the others in the lower layer overlap with the four display units  250   a  arranged in adjacent two rows and two columns in the upper layer. The insulator  240  in such a structure is stretched in the directions of the arrows, whereby the display region  262 A in FIG.  14 B 1  can be a display region  262 B in FIG.  14 B 2 . Note that owing to the use of the display units  255 , the display region  262 A can include more pixels in the lower layer than the display region  260 A. Thus, the light-emitting area of the display region  262 B obtained by stretching the display region  262 A can be larger than that of the display region  260 B obtained by stretching the display region  260 A. Accordingly, a decrease in resolution is less caused in the display region  262 A than in the display region  260 A by the stretch. 
     Next, an example of the electrical connection between the plurality of display units  250  included in the display region  260 A ( 260 B) and lead wirings is described. 
       FIG.  15 A  illustrates an example of the electrical connection between the display units  250  (display units  250   a  and  250   b ) and the wirings in the display region  260 A ( 260 B). Note that the wirings in the display region  260 B are illustrated in  FIG.  15 A  to clearly show the electrical connection between the display units  250  (display units  250   a  and  250   b ) and the wirings. 
     The display region  260 A ( 260 B) includes a plurality of signal lines and a plurality of gate lines. Note that in  FIG.  15 A , a signal line SLa[ 1 ], a signal line SLa[ 2 ], a signal line SLb[ 1 ], a signal line SLb[ 2 ], a gate line GLa[ 1 ], a gate line GLa[ 2 ], a gate line GLb[ 1 ], and a gate line GLb[ 2 ] are illustrated, and reference numerals of the other wirings are omitted. In this specification, the signal lines SLa[ 1 ] and SLa[ 2 ] are collectively referred to as a signal line SLa, the signal lines SLb[ 1 ] and SLb[ 2 ] are collectively referred to as a signal line SLb, the gate lines GLa[ 1 ] and GLa[ 2 ] are collectively referred to as a gate line GLa, and the gate lines GLb[ 1 ] and GLb[ 2 ] are collectively referred to as a gate line GLb. Each of the signal line SLa, the signal line SLb, the gate line GLa, and the gate line GLb in  FIG.  15 A  may include a plurality of wirings. For example, each of the signal line SLa[ 1 ] and the gate line GLa[ 1 ] is not composed of one wiring but may be composed of a plurality of wirings. In some cases, the wirings referred to as the signal lines can be replaced with the wirings referred to as the gate lines as appropriate. 
     The signal line SLa and the gate line GLa are electrically connected to the plurality of display units  250   a  included in the upper layer of the display region  260 A ( 260 B). The signal line SLb and the gate line GLb are electrically connected to the plurality of display units  250   b  included in the lower layer of the display region  260 A ( 260 B). 
     FIG.  15 B 1  is a cross-sectional view of the display region  260 A in  FIG.  15 A , and FIG.  15 B 2  is a cross-sectional view of the display region  260 B in  FIG.  15 A . FIG.  15 B 1  shows cross sections taken along the dashed-dotted lines P 1 -P 2  and P 3 -P 4  in the display region  260 A in  FIG.  15 A . FIG.  15 B 2  shows cross sections taken along the dashed-dotted lines P 1 -P 2  and P 3 -P 4  in the display region  260 B obtained by stretching the display region  260 A in  FIG.  15 A . Note that the cross section taken along the dashed-dotted line P 1 -P 2  shows only the upper layer of the display region  260 A ( 260 B), and the cross section taken along the dashed-dotted line P 3 -P 4  shows only the lower layer of the display region  260 A ( 260 B). 
     That is, the signal line SLa is electrically connected to the display units  250   a  and thus is included in the upper layer, and the signal line SLb is electrically connected to the display units  250   b  and thus is included in the lower layer. In addition, the signal lines SLa and SLb are formed using an elastic conductive material, which enables the display region  260 A in FIG.  15 B 1  to be stretched to be the display region  260 B in FIG.  15 B 2 . When the display region  260 A in FIG.  15 B 1  is stretched to be the display region  260 B in FIG.  15 B 2 , the gaps between the adjacent display units  250   a  are increased, resulting in an increase in the light-emitting areas of the light-emitting elements of the display units  250   b  overlapping with parts of the gaps between the adjacent display units  250   a.    
     Similarly, the gate lines GLa and GLb are formed using an elastic conductive material, which enables the display region  260 A to be stretched to be the display region  260 B. 
     A wiring routing way in the display region  260 A ( 260 B) is not limited to the way described using the display region  260 A ( 260 B) in  FIGS.  15 A ,  15 B 1 , and  15 B 2 . For example, one of a plurality of signal lines SLa in the upper layer and one of a plurality of signal lines SLb in the lower layer may be combined into one wiring.  FIG.  16 A  illustrates an example of a display region in such a case. In the display region  260 A ( 260 B) in  FIG.  16 A , the signal lines SLa[ 1 ] and SLb[ 1 ] are combined into one signal line SL[ 1 ], and the signal lines SLa[ 2 ] and SLb[ 2 ] are combined into one signal line SL[ 2 ]. Note that also in the signal lines not shown with reference numerals in  FIG.  16 A , one of the signal lines SLa in the upper layer and one of the signal lines SLb in the lower layer are combined into one wiring. In this specification, the signal lines included in the display region  260 A ( 260 B) in  FIGS.  16 A ,  16 B 1 , and  16 B 2  are collectively referred to as a signal line SL. Note that a combined wiring in this paragraph means a wiring formed using one wiring or a wiring formed using a plurality of wirings. 
     FIG.  16 B 1  is a cross-sectional view of the display region  260 A in  FIG.  16 A , and FIG.  16 B 2  is a cross-sectional view of the display region  260 B in  FIG.  16 A . FIG.  16 B 1  is the cross-sectional view taken along the dashed-dotted line Q 1 -Q 2  in the display region  260 A in  FIG.  16 A . FIG.  16 B 2  is the cross-sectional view taken along the dashed-dotted line Q 1 -Q 2  in the display region  260 B obtained by stretching the display region  260 A in  FIG.  16 A . 
     In  FIG.  16 A , the signal line SL electrically connects the display units  250   a  in the upper layer to the display units  250   b  in the lower layer as illustrated in FIGS.  16 B 1  and  16 B 2 . 
     The signal line SL is formed using an elastic conductive material, which enables the display region  260 A in FIG.  16 B 1  to be stretched to be the display region  260 B in FIG.  16 B 2 . When the display region  260 A in FIG.  16 B 1  is stretched to be the display region  260 B in FIG.  16 B 2 , the gaps between the adjacent display units  250   a  are increased, resulting in an increase in the light-emitting areas of the light-emitting elements of the display units  250   b  overlapping with parts of the gaps between the adjacent display units  250   a.    
     Similarly, the gate lines GLa and GLb are formed using an elastic conductive material, which enables the display region  260 A to be stretched to be the display region  260 B. The gate lines GLa and GLb can be combined into one wiring (not illustrated) as in the signal line SL. 
     Next, an example of a driver circuit for driving the display region  260 A ( 260 B) is described. 
       FIG.  17 A  illustrates a display device  300  including a display region  260 . The display device  300  includes a driver region  270  and a driver region  280  in addition to the display region  260 . Here, the driver region  270  functions as a source driver for driving the display region  260 , and the driver region  280  functions as a gate driver for driving the display region  260 . 
     For another example, the display device  300  may have a structure in which the driver region  270  functions as a gate driver for driving the display region  260  and the driver region  280  functions as a source driver for driving the display region  260 . 
     The driver region  270  includes a plurality of driver circuit units  271 . Some of the plurality of driver circuit units  271  are electrically connected to the display units  250   a  through the signal line SLa, and the others are electrically connected to the display units  250   b  through the signal line SLb. The plurality of driver circuit units  271  have a function of supplying a signal for an image to be displayed on the display region  260  to the display region  260  through the signal lines SLa and SLb. 
     The plurality of driver circuit units  271  are aligned in a line, and the adjacent driver circuit units  271  are electrically connected to each other with a wiring  272 . Note that the number of wirings  272  may be one, or two or more. 
     The driver region  280  includes a plurality of driver circuit units  281 . Some of the plurality of driver circuit units  281  are electrically connected to the display units  250   a  through the gate line GLa, and the others are electrically connected to the display units  250   b  through the gate line GLb. The plurality of driver circuit units  281  have a function of supplying a selection signal to pixels included in the display region  260  through the gate lines GLa and GLb. 
     The plurality of driver circuit units  281  are aligned in a line, and the adjacent driver circuit units  281  are electrically connected to each other with a wiring  282 . Note that the number of wirings  282  may be one, or two or more. 
     The wirings  272  and  282  are formed using an elastic conductive material as in the signal lines SLa and SLb and the gate lines GLa and GLb. Accordingly, the elastic wirings  272  and  282  increase the gaps between the adjacent driver circuit units  271  and the gaps between the adjacent driver circuit units  281 . Thus, the display device  300  in  FIG.  17 A  can have the shape in  FIG.  17 B  when stretched. 
     Although the driver region  270  includes the plurality of driver circuit units  271  in  FIG.  17 A , one embodiment of the present invention is not limited thereto. For example, the driver region  270  may include one driver circuit unit  271  (not illustrated). Similarly, although the driver region  280  includes the plurality of driver circuit units  281  in  FIG.  17 A , the driver region  280  may include one driver circuit unit  281  (not illustrated). 
     In the case where the circuit area of the driver circuit unit  271  and/or the driver circuit unit  281  becomes large, the driver region  270  and/or the driver region  280  may have a two-layer structure as in the display region  260 . Specifically, in the driver region having the two-layer structure, the adjacent driver circuit units may partly overlap with each other. 
     A driver region  270 A and a driver region  280 A in a display device  300 A in  FIG.  18 A  each have a two-layer structure. The driver region  270 A includes a plurality of driver circuit units  271 A, and the driver region  280 A includes a plurality of driver circuit units  281 A. The driver circuit units  271 A in the upper layer of the driver region  270 A are electrically connected to the display units  250   a  through the signal line SLa, and the driver circuit units  271 A in the lower layer of the driver region  270 A are electrically connected to the display units  250   b  through the signal line SLb. Similarly, the driver circuit units  281 A in the upper layer of the driver region  280 A are electrically connected to the display units  250   a  through the gate line GLa, and the driver circuit units  281 A in the lower layer of the driver region  280 A are electrically connected to the display units  250   b  through the gate line GLb. 
     FIG.  18 B 1  is a cross-sectional view taken along the dashed-dotted line R 1 -R 2  in  FIG.  18 A . As described above, in the driver region  270 A, the adjacent driver circuit units  271 A partly overlap with each other. In addition, the adjacent driver circuit units  271 A are electrically connected to each other with the elastic wiring  272 . 
     Note that when the display device  300 A is stretched, the cross section taken along the dashed-dotted line R 1 -R 2  in FIG.  18 B 1  changes to that in FIG.  18 B 2 . With the driver region  270 A having the two-layer structure and the elastic wiring  272  illustrated in FIG.  18 B 1 , the display device  300 A can be stretched even when the circuit area of the driver circuit unit  271  is large. 
     For the description of stretching the driver region  280 A, refer to the description of stretching the driver region  270 A. 
     The structure examples described in this embodiment can be combined with each other as appropriate. 
     &lt;Manufacturing Method Example&gt; 
     Next, an example of a method for manufacturing the display region  260 A is described with reference to  FIGS.  19 A to  19 C ,  FIGS.  20 A and  20 B ,  FIGS.  21 A and  21 B ,  FIG.  22   , and  FIG.  23   . 
     First, an insulator  321  is formed over a substrate  311  (see  FIG.  19 A ). 
     The substrate  311  can be formed using any of a variety of materials such as glass, quartz, a resin, a metal, an alloy, and a semiconductor. When the substrate  311  is formed using a flexible material, any of the above-described materials that is thin enough to be flexible may be used, for example. 
     The insulator  321  can be used as a barrier layer that prevents diffusion of impurities contained in the substrate  311  into a transistor and a display element formed later. For example, the insulator  321  preferably prevents moisture and the like contained in the substrate  311  from diffusing into the transistor and the display element in a heating step performed in the manufacturing process of the display region  260 A. Thus, the insulator  321  preferably has a high barrier property. 
     For the insulator  321 , an inorganic insulating film such as 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. Alternatively, 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. It is particularly preferable that a silicon nitride film be formed over the substrate  311  and a silicon oxide film be formed over the silicon nitride film. 
     The inorganic insulating film is preferably formed at high temperatures because the film can have higher density and a higher barrier property as the deposition temperature becomes higher. The deposition temperature of the insulator  321  is preferably lower than or equal to the upper temperature limit of the substrate  311 . 
     After the insulator  321  is formed over the substrate  311 , a circuit, a wiring, and the like are formed over the insulator  321  (see  FIG.  19 B ). In  FIG.  19 B , a transistor  401  is formed over the substrate  311 . 
     There is no particular limitation on the structure of the transistor in the display region  260 A. For example, a planar transistor, a staggered transistor, or an inverted staggered transistor may be used. A top-gate transistor or a bottom-gate transistor may also be used. Gate electrodes may be provided above and below a channel. 
     Described here is the case where a bottom-gate transistor including a metal oxide  350  is formed as the transistor  401 . The metal oxide  350  can function as a semiconductor layer of the transistor  401 . Note that the metal oxide described here can function as an oxide semiconductor. 
     In this embodiment, an oxide semiconductor is used as a semiconductor of the transistor. The oxide semiconductor is a semiconductor material having a wider band gap and a lower carrier density than silicon; thus, the off-state current of a transistor including the oxide semiconductor in a channel formation region can be reduced. 
     The transistor  401  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     Here, a specific example of a method for forming the transistor  401  is described. 
     First, a conductor  341  is formed over the insulator  321 . The conductor  341  can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. 
     The substrate temperature during the formation of the conductive film is preferably higher than or equal to room temperature and lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 300° C. 
     The conductors included in the display region  260 A can each have a single-layer structure or a stacked-layer structure including any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten or an alloy containing any of these metals as its main component. Alternatively, a light-transmitting conductive material such as indium oxide, indium tin oxide (ITO), indium oxide containing tungsten, indium zinc oxide containing tungsten, indium oxide containing titanium, ITO containing titanium, indium zinc oxide, zinc oxide (ZnO), ZnO containing gallium, or ITO containing silicon may be used. Alternatively, a semiconductor such as an oxide semiconductor or polycrystalline silicon whose resistance is lowered by adding an impurity element, for example, or silicide such as nickel silicide may be used. A film including graphene may be used as well. The film including graphene can be formed, for example, by reducing a film including graphene oxide. A semiconductor such as an oxide semiconductor containing an impurity element may be used. Alternatively, the conductors may be formed using a conductive paste of silver, carbon, copper, or the like or a conductive polymer such as a polythiophene. A conductive paste is preferable because it is inexpensive. A conductive polymer is preferable because it is easily applied. 
     Then, an insulator  322  is formed over the conductor  341  and the insulator  321 . For the material that can be used for the insulator  322 , refer to the description of the inorganic insulating film that can be used for the insulator  321 . 
     The insulator  322  is formed at a temperature lower than or equal to the upper temperature limit of the substrate  311 . The insulator  322  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     Next, the metal oxide  350  is formed over the insulator  322  to overlap with part of the conductor  341 . The metal oxide  350  can be formed in the following manner: a metal oxide film is formed, a resist mask is formed, the metal oxide film is etched, and the resist mask is removed. 
     The substrate temperature during the formation of the metal oxide film is preferably lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 200° C., still further preferably higher than or equal to room temperature and lower than or equal to 130° C. 
     The metal oxide film can be formed using one or both of an inert gas and an oxygen gas. Note that there is no particular limitation on the flow ratio of oxygen (the partial pressure of oxygen) in the step of forming the metal oxide film. In the case where a transistor having high field-effect mobility is obtained, the flow ratio of oxygen (the partial pressure of oxygen) in the step of forming the metal oxide film is preferably higher than or equal to 0% and lower than or equal to 30%, further preferably higher than or equal to 5% and lower than or equal to 30%, still further preferably higher than or equal to 7% and lower than or equal to 15%. 
     The metal oxide film preferably contains at least indium or zinc. In particular, indium and zinc are preferably contained. 
     The energy gap of the metal oxide is preferably 2 eV or more, further preferably 2.5 eV or more, and still further preferably 3 eV or more. The use of such a metal oxide having a wide energy gap leads to a reduction in off-state current of a transistor. 
     The metal oxide film can be formed by a sputtering method. Alternatively, a PLD method, a PECVD method, a thermal CVD method, an ALD method, a vacuum evaporation method, or the like may be used. 
     Then, a conductor  342   a  and a conductor  342   b  are formed over the insulator  322  and the metal oxide  350 . Note that part of the conductor  342   a  and/or part of the conductor  342   b  may be included in a region overlapping with the metal oxide  350 . The conductors  342   a  and  342   b  can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. 
     Note that during the processing for forming the conductor  342   a  and the conductor  342   b , the metal oxide  350  might be partly etched to be thin in a region not covered by the resist mask. 
     The substrate temperature during the formation of the conductive film is preferably higher than or equal to room temperature and lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 300° C. 
     In the above manner, the transistor  401  can be fabricated. In the transistor  401 , part of the conductor  341  functions as a gate, part of the insulator  322  functions as a gate insulating layer, the conductor  342   a  functions as one of a source and a drain, and the conductor  342   b  functions as the other of the source and the drain. 
     A conductor  343  is formed over the insulator  322 . The conductor  343  can be formed at the same time as the conductors  342   a  and  342   b . In the case where the conductor  343  is formed using a material different from that of the conductors  342   a  and  342   b , the conductor  343  may be formed independently of the conductors  342   a  and  342   b . The conductor  343  functions as a wiring electrically connecting a display unit, an element, a circuit, and the like to each other. Part of the conductor  343  also functions as a terminal that transmits and receives an electrical signal to and from the outside. 
     Next, an insulator  323  that covers the transistor  401  is formed. The insulator  323  can be formed in a manner similar to that of the insulator  321 . 
     It is preferable to use an oxide insulating film formed in an oxygen-containing atmosphere, such as a silicon oxide film or a silicon oxynitride film, for the insulator  323 . An insulating film with low oxygen diffusibility and oxygen permeability, such as a silicon nitride film, is preferably stacked over the silicon oxide film or the silicon oxynitride film. The oxide insulating film formed in an oxygen-containing atmosphere can easily release a large amount of oxygen by heating. When a stack including such an oxide insulating film that releases oxygen and such an insulating film with low oxygen diffusibility and oxygen permeability is heated, oxygen can be supplied to the metal oxide  350 . As a result, oxygen vacancies in the metal oxide  350  can be filled and defects at the interface between the metal oxide  350  and the insulator  323  can be repaired, leading to a reduction in defect levels. Accordingly, an extremely highly reliable display device can be manufactured. 
     Then, an insulator  324  is formed over the insulator  323 . The display element is formed on the insulator  324  in a later step; thus, the insulator  324  preferably functions as a planarization layer. For the insulator  324 , refer to the description of the organic insulating film or the inorganic insulating film that can be used for the insulator  321 . 
     The insulator  324  is formed at a temperature lower than or equal to the upper temperature limit of the substrate  311 . The insulator  324  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     Next, an opening  361  reaching the conductor  342   b  and an opening  362  reaching the conductor  343  are formed in the insulators  323  and  324  (see  FIG.  19 C ). 
     Then, a conductor  344   a  is formed over the insulator  324  and the conductor  342   b  through the opening  361 . Part of the conductor  344   a  functions as a pixel electrode of a light-emitting element  370  described later. The conductor  344   a  can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. 
     Concurrently with the conductor  344   a , a conductor  344   b  is formed over the conductor  343  through the opening  362 . Note that the conductor  344   b  is not necessarily formed. 
     The substrate temperature during the formation of the conductive film is preferably higher than or equal to room temperature and lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 300° C. 
     An insulator  325  that covers an end portion of the conductor  344   a  is formed. For the insulator  325 , refer to the description of the inorganic insulating film that can be used for the insulator  321 . Alternatively, the insulator  325  can be formed using an organic insulating film. 
     The insulator  325  is formed at a temperature lower than or equal to the upper temperature limit of the substrate  311 . The insulator  325  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     Next, the light-emitting element  370  is formed over the formation substrate in  FIG.  19 C  (see  FIG.  20 A ). 
     For formation of the light-emitting element  370 , first, an EL layer  371  is formed over the conductor  344   a  and the insulator  325 . 
     The EL layer  371  can be formed by an evaporation method, a coating method, a printing method, a discharge method, or the like. In the case where the EL layer  371  is formed for each individual pixel, an evaporation method using a shadow mask such as a metal mask, an ink-jet method, or the like can be used. In the case of sharing the EL layer  371  by some pixels, an evaporation method not using a metal mask can be used. 
     Either a low molecular compound or a high molecular compound can be used for the EL layer  371 , and an inorganic compound may also be used. 
     Note that for the details of the EL layer  371 , refer to the description of an EL layer  1103  in Embodiment 5. 
     Next, a conductor  345  is formed over the insulator  325  and the EL layer  371 . Part of the conductor  345  functions as a common electrode of the light-emitting element  370 . 
     The conductor  345  can be formed by an evaporation method, a sputtering method, or the like. 
     The conductor  345  is formed at a temperature that is lower than or equal to the upper temperature limit of the substrate  311  and lower than or equal to the upper temperature limit of the EL layer  371 . The conductor  345  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     As the conductor  345 , a light-transmitting conductor is used. Examples of the light-transmitting conductor include metal oxides such as indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide, indium oxide-tin oxide containing titanium, indium titanium oxide, and indium oxide containing tungsten oxide and zinc oxide. As the conductor  345 , indium tin oxide is particularly preferable. 
     In the above manner, the light-emitting element  370  can be formed. In the light-emitting element  370 , the conductor  344   a  part of which functions as a pixel electrode, the EL layer  371 , and the conductor  345  part of which functions as a common electrode are stacked. Note that a top-emission light-emitting element is formed as the light-emitting element  370  here. 
     Next, an insulator  326  is formed to cover the conductor  345 . The insulator  326  functions as a protective layer that prevents diffusion of impurities such as water into the light-emitting element  370 . The light-emitting element  370  is sealed with the insulator  326 . After the conductor  345  is formed, the insulator  326  is preferably formed without exposure to the air. 
     The insulator  326  is formed at a temperature that is lower than or equal to the upper temperature limit of the substrate  311  and lower than or equal to the upper temperature limit of the light-emitting element  370 . The insulator  326  is preferably formed at a temperature lower than the temperature of the heat treatment. 
     The insulator  326  preferably includes an inorganic insulating film with a high barrier property that can be used for the insulator  321 , for example. A stack including an inorganic insulating film and an organic insulating film can also be used. 
     The insulator  326  can be formed by an ALD method, a sputtering method, or the like. An ALD method and a sputtering method are preferable because a film can be formed at low temperatures. An ALD method is preferable because the coverage with the insulator  326  is improved. 
     A structure where the components up to the insulator  326  are formed over the substrate  311  corresponds to the display unit  250 . 
     To describe an example of a method for manufacturing the display region  260 A having a two-layer structure below, the display unit  250  in the lower layer is referred to as the display unit  250   b , and the display units  250  in the upper layer are referred to as a display unit  250   a [ 1 ] and a display unit  250   a [ 2 ]. 
     The display unit  250   b  is provided over a support substrate  301  (see  FIG.  20 B ). The substrate  311  is bonded to the support substrate  301  preferably with an adhesive resin layer or the like. Note that the resin layer is not illustrated in  FIG.  20 B . The support substrate  301  is included in the insulator  240 . 
     The support substrate  301  is formed using an elastic material. For example, the support substrate  301  can be formed using a thermosetting elastomer, a thermoplastic elastomer, or the like. 
     Next, a conductor  380  is formed over the conductor  344   b  and the support substrate  301  (see  FIG.  21 A ). The conductor  380  corresponds to the signal line, the gate line, or the like described in the structure examples. 
     The conductor  380  preferably has elasticity. The conductor  380  can be formed using a conductive paste of silver, carbon, copper, or the like, a conductive polymer such as polythiophene, or the like. 
     Then, a protective layer  390  is formed over the support substrate  301  and the display unit  250   b  over the substrate  311  (see  FIG.  21 B ). Note that the protective layer  390  is included in the insulator  240 . 
     As the protective layer  390 , a light-transmitting and elastic insulator is used. For example, the protective layer  390  can be formed using vinyl chloride, a polyurethane resin, or the like. In addition to a light-transmitting property and elasticity, the protective layer  390  preferably has adhesiveness for bonding the support substrate  301  to the display unit  250   b.    
     Next, a substrate  302  is provided over the protective layer  390  (see  FIG.  22   ). The substrate  302  is formed using a light-transmitting and elastic material. In addition, the degrees of elasticity of the substrate  302  and the support substrate  301  are preferably different from each other. Note that the substrate  302  is included in the insulator  240 . 
     Then, the display units  250   a [ 1 ] and  250   a [ 2 ], which can be formed in a manner similar to that of the display unit  250   b , are formed over the substrate  302  (see  FIG.  23   ). The display units  250   a [ 1 ] and  250   a [ 2 ] each include a transistor, a light-emitting element, and a wiring as in the display unit  250   b.    
     The display units  250   a [ 1 ] and  250   a [ 2 ] are preferably formed over the substrate  302  so that part of the light-emitting element  370  of the display unit  250   b  overlaps with part of the gap between the display units  250   a [ 1 ] and  250   a [ 2 ]. 
     After the formation of the display units  250   a [ 1 ] and  250   a [ 2 ], a conductor  381  is formed as a wiring in a manner similar to that of the conductor  380  electrically connected to the display unit  250   b . For materials that can be used for the conductor  381 , refer to the description of the materials that can be used for the conductor  380 . 
     After the formation of the conductor  381 , a protective layer  391  is formed over the display units  250   a [ 1 ] and  250   a [ 2 ], the conductor  381 , and the substrate  302  in a manner similar to that of the protective layer  390  formed over the display unit  250   b . Note that the materials that can be used for the protective layer  391  preferably have the degree of elasticity different from that of elasticity of the materials that can be used for the protective layer  390 . The protective layer  391  is included in the insulator  240 . 
     After the formation of the protective layer  391 , a substrate  303  is provided over the protective layer  391  in a manner similar to that of the substrate  302  provided over the protective layer  390 . The substrate  303  is formed using a light-transmitting and elastic material. In addition, the degrees of elasticity of the substrate  303 , the support substrate  301 , and the substrate  302  are preferably different from each other. Note that the substrate  303  is included in the insulator  240 . In the example of a method for manufacturing the display region  260 A, the substrate  303  is not necessarily provided. 
     Through the above steps, the display region  260 A can be manufactured. 
     The display regions  261 A and  262 A can be manufactured in a manner similar to that of the display region  260 A by referring to the above-described manufacturing method example. 
     Although the display unit  250  is formed over the support substrate  301  in this manufacturing method example, a method for manufacturing the display device of one embodiment of the present invention is not limited thereto. 
     For example, before the transistor  401 , the light-emitting element  370 , and the like are formed, the substrate  311  may be provided over the support substrate  301 . In this case, the deposition temperature of the insulators, conductors, metal oxides, and the like included in the display unit  250  and the temperature of the heat treatment performed on the transistor  401  and the like are preferably lower than the upper temperature limits of the support substrate  301  and the substrate  311 . For another example, instead of the substrate  311  provided over the support substrate  301 , an insulator formed by a sputtering method, a pulsed laser deposition (PLD) method, a plasma-enhanced chemical vapor deposition (PECVD) method, a thermal CVD method, an atomic layer deposition (ALD) method, a vacuum evaporation method, or the like may be used. In that case, the insulator may be formed using a material different from that of the insulator  321  and stacked with the insulator  321 ; alternatively, the insulators may be formed using the same material as the insulator  321  and successively formed. 
     For example, one embodiment of the present invention may employ a manufacturing method in which the display unit  250  is formed over a polyimide film or the like that is provided over the substrate  311  in advance by application of polyimide or the like as an organic film, and the display unit  250  is separated from the polyimide film and transferred to the support substrate  301 . After the display unit  250  is transferred to the support substrate  301 , the conductor  380  and the protective layer  390  may be formed. Instead of the organic film such as a polyimide film, an inorganic film such as a tungsten film can be used, in some cases.  FIG.  24 A  illustrates a step of providing the display unit  250 , which is separated from the organic film or the inorganic film, over the support substrate  301 . In some cases, the residue of the organic film or the inorganic film are attached to the insulator  321  on the bottom surface of the display unit  250  separated from the organic film or the inorganic film. 
     After the display unit  250  is separated by the above-described method, the display unit  250  may be transferred to a flexible substrate  315  and then the substrate  315  may be bonded to the support substrate  301  (see  FIG.  24 B ). In that case, the circuit  251  is positioned on the substrate  315 ; thus, the substrate  315  is preferably formed using a material with low elasticity, which prevents the circuit  251  from being damaged (e.g., a crack) by the stretch of the substrate  315 . 
     With this method, the display unit  250  is formed over the substrate provided with the polyimide film or the like; thus, the heat treatment for forming the display unit  250  does not need to be performed on the support substrate  301  and the substrate  315  to which the display unit  250  is transferred. That is, the temperatures of the heat treatment performed on the insulators, conductors, and metal oxides included in the display unit  250  are not limited to the upper temperature limits of the support substrate  301  and the substrate  315  to which the display unit  250  is transferred. The support substrate  301  can be formed using a material with low heat resistance because the support substrate  301  is not affected by the heat treatment for forming the display unit  250 . 
     The manufacturing method example described in this embodiment enables a display device whose display quality does not degrade even when the area of the display region is increased by the stretch. 
     Note that this embodiment can be combined with other embodiments and/or an example in this specification as appropriate. 
     Embodiment 4 
     In this embodiment, examples of electronic devices each including the display device  300  in Embodiment 3 are described. 
     Example 1 
       FIG.  25 A  illustrates an electronic device including the display device  300 . An electronic device  7000  can be used as an information terminal or electronic paper, for example. The electronic device  7000  includes the display device  300  and thus can be stretched by pulling with fingers  7001 , as illustrated in  FIG.  25 A . Owing to its elasticity, the electronic device  7000  can be attached to a structure body having a curved surface or the like. When the electronic device  7000  including the display device  300  as a light-emitting device is attached to a structure body having a curved surface or the like, the electronic device  7000  can be used as a lighting device. 
     Example 2 
       FIG.  25 B  illustrates a smart watch which is one of wearable terminals. The smart watch includes a housing  5901 , a display portion  5902 , operation buttons  5903 , an operator  5904 , a band  5905 , and the like. The display device  300  can be used for the display portion  5902  of the smart watch. When the display portion  5902  has a convex surface, for example, the stretched display device  300  is attached to the convex surface, whereby the convex display portion  5902  can be obtained. 
     Example 3 
       FIG.  25 C  illustrates clothing to which the display device  300  is attached. Clothing  5801  includes a display portion  5802  and the like. The display device  300  can be used for the display portion  5802 . Since the display device  300  can be stretched, the display device  300  can be attached to the elastic clothing  5801 . In addition, the display portion  5802  can be used as a lighting device. 
       FIG.  25 C  illustrates an example in which the display portion  5802  is attached to a chest portion of the clothing  5801 ; however, one embodiment of the present invention is not limited to this example. For example, the display portion  5802  may be attached to a sleeve portion, a belly portion, a back portion, and the like. Although the clothing  5801  in  FIG.  25 C  is a shirt, the clothing  5801  can also be clothes such as a jacket, underwear, and pants, accessories such as shoes, a hat, and a wristband, and the like. 
     Example 4 
       FIG.  25 D  illustrates a windshield and its vicinity inside a car, which is one of moving vehicles. The display device  300  can be used for display panels  5701 ,  5702 , and  5703  attached to a dashboard, a display panel  5704  attached to a pillar, and the like illustrated in  FIG.  25 D . 
     The display panels  5701  to  5703  can display a variety of kinds of information such as navigation information, a speedometer, a tachometer, a mileage, a fuel meter, a gearshift indicator, and air-condition setting. The content, layout, or the like of the display on the display panels can be changed freely to suit the user&#39;s preferences, so that the design can be improved. The display panels  5701  to  5703  can also be used as lighting devices. 
     The display panel  5704  can compensate for the view obstructed by the pillar (blind areas) by showing an image taken by an imaging unit provided for the car body. That is, showing an image taken by an imaging unit provided on the outside of the car body leads to elimination of blind areas and enhancement of safety. In addition, showing an image so as to compensate for the area which a driver cannot see makes it possible for the driver to confirm safety easily and comfortably. The display panel  5704  can also be used as a lighting device. 
     Example 5 
       FIGS.  26 A and  26 B  each illustrate an example of a digital signage that can be attached to a wall.  FIG.  26 A  illustrates a digital signage  6300 A attached to a wall  6301 . 
     Here, the case where the digital signage  6300 A includes the display device  300  in Embodiment 3 is described. The digital signage  6300 A in  FIG.  26 A  that includes the display device  300  can change its shape so as to be a digital signage  6300 B in  FIG.  26 B  by the stretch. The digital signage  6200 A in  FIGS.  11 A and  11 B  in Embodiment 2 can be stretched in the vertical direction or the horizontal direction, and the aspect ratio of the digital signage  6300 A ( 6300 B) in  FIGS.  26 A and  26 B  can be freely changed depending on the contents displayed on the digital signage. 
     Note that this embodiment can be combined with other embodiments and/or an example in this specification as appropriate. 
     Embodiment 5 
     In this embodiment, light-emitting elements that can be used for the display units in Embodiment 1 are described with reference to  FIGS.  27 A to  27 D . 
     &lt;Basic Structure of Light-Emitting Element&gt; 
     A basic structure of a light-emitting element will be described.  FIG.  27 A  illustrates a light-emitting element including, between a pair of electrodes, an EL layer having a light-emitting layer. Specifically, the EL layer  1103  is provided between a first electrode  1101  and a second electrode  1102 . 
       FIG.  27 B  illustrates a light-emitting element that has a stacked-layer structure (tandem structure) in which a plurality of EL layers (two EL layers  1103   a  and  1103   b  in  FIG.  27 B ) are provided between a pair of electrodes and a charge-generation layer  1104  is provided between the EL layers. With the use of such a tandem light-emitting element, a light-emitting device which can be driven at low voltage with low power consumption can be obtained. 
     The charge-generation layer  1104  has a function of injecting electrons into one of the EL layers ( 1103   a  or  1103   b ) and injecting holes into the other of the EL layers ( 1103   b  or  1103   a ) when voltage is applied between the first electrode  1101  and the second electrode  1102 . Thus, when voltage is applied in  FIG.  27 B  such that the potential of the first electrode  1101  is higher than that of the second electrode  1102 , the charge-generation layer  1104  injects electrons into the EL layer  1103   a  and injects holes into the EL layer  1103   b.    
     Note that in terms of light extraction efficiency, the charge-generation layer  1104  preferably has a property of transmitting visible light (specifically, the charge-generation layer  1104  has a visible light transmittance of 40% or more). The charge-generation layer  1104  functions even when it has lower conductivity than the first electrode  1101  or the second electrode  1102 . 
       FIG.  27 C  illustrates a stacked-layer structure of the EL layer  1103  in the light-emitting element which can be used in the display device of one embodiment of the present invention. In this case, the first electrode  1101  is regarded as functioning as an anode. The EL layer  1103  has a structure in which a hole-injection layer  1111 , a hole-transport layer  1112 , a light-emitting layer  1113 , an electron-transport layer  1114 , and an electron-injection layer  1115  are stacked in this order over the first electrode  1101 . Even in the case where a plurality of EL layers are provided as in the tandem structure illustrated in  FIG.  27 B , the layers in each EL layer are sequentially stacked from the anode side as described above. When the first electrode  1101  is a cathode and the second electrode  1102  is an anode, the stacking order is reversed. 
     The light-emitting layer  1113  included in the EL layers ( 1103 ,  1103   a , and  1103   b ) contains an appropriate combination of a light-emitting substance and a plurality of substances, so that fluorescence or phosphorescence of a desired emission color can be obtained. The light-emitting layer  1113  may have a stacked-layer structure having different emission colors. In that case, the light-emitting substance and other substances are different between the stacked light-emitting layers. Alternatively, the plurality of EL layers ( 1103   a  and  1103   b ) in  FIG.  27 B  may exhibit their respective emission colors. Also in that case, the light-emitting substance and other substances are different between the light-emitting layers. 
     In the light-emitting element of one embodiment of the present invention, for example, a micro optical resonator (microcavity) structure in which the first electrode  1101  is a reflective electrode and the second electrode  1102  is a transflective electrode can be employed in  FIG.  27 C , whereby light emission from the light-emitting layer  1113  in the EL layer  1103  can be resonated between the electrodes and light emission obtained through the second electrode  1102  can be intensified. 
     Note that when the first electrode  1101  of the light-emitting element is a reflective electrode having a structure in which a reflective conductive material and a light-transmitting conductive material (transparent conductive film) are stacked, optical adjustment can be performed by controlling the thickness of the transparent conductive film. Specifically, when the wavelength of light obtained from the light-emitting layer  1113  is λ, the distance between the first electrode  1101  and the second electrode  1102  is preferably adjusted to around mλ/2 (m is a natural number). 
     To amplify desired light (wavelength: X) obtained from the light-emitting layer  1113 , the optical path length from the first electrode  1101  to a region where the desired light is obtained in the light-emitting layer  1113  (light-emitting region) and the optical path length from the second electrode  1102  to the region where the desired light is obtained in the light-emitting layer  1113  (light-emitting region) are preferably adjusted to around (2m′+1)λ/4 (m′ is a natural number). Here, the light-emitting region means a region where holes and electrons are recombined in the light-emitting layer  1113 . 
     By such optical adjustment, the spectrum of specific monochromatic light obtained from the light-emitting layer  1113  can be narrowed and light emission with high color purity can be obtained. 
     In that case, the optical path length between the first electrode  1101  and the second electrode  1102  is, to be exact, the total thickness from a reflective region in the first electrode  1101  to a reflective region in the second electrode  1102 . However, it is difficult to exactly determine the reflective regions in the first electrode  1101  and the second electrode  1102 ; thus, it is assumed that the above effect can be sufficiently obtained wherever the reflective regions may be set in the first electrode  1101  and the second electrode  1102 . Furthermore, the optical path length between the first electrode  1101  and the light-emitting layer  1113  emitting the desired light is, to be exact, the optical path length between the reflective region in the first electrode  1101  and the light-emitting region in the light-emitting layer  1113  emitting the desired light. However, it is difficult to precisely determine the reflective region in the first electrode  1101  and the light-emitting region in the light-emitting layer emitting the desired light; thus, it is assumed that the above effect can be sufficiently obtained wherever the reflective region and the light-emitting region may be set in the first electrode  1101  and the light-emitting layer emitting the desired light. 
     The light-emitting element in  FIG.  27 C  has a microcavity structure, so that light (monochromatic light) with different wavelengths can be extracted even if the same EL layer is used. Thus, separate coloring for obtaining a plurality of emission colors (e.g., R, G, and B) is not necessary. Therefore, high resolution can be easily achieved. Note that a combination with coloring layers (color filters) is also possible. Furthermore, emission intensity of light with a specific wavelength in the front direction can be increased, whereby power consumption can be reduced. 
     In the light-emitting element of one embodiment of the present invention, at least one of the first electrode  1101  and the second electrode  1102  is a light-transmitting electrode (e.g., a transparent electrode or a transflective electrode). In the case where the light-transmitting electrode is a transparent electrode, the transparent electrode has a visible light transmittance of higher than or equal to 40%. In the case where the light-transmitting electrode is a transflective electrode, the transflective electrode has a visible light reflectance of higher than or equal to 20% and lower than or equal to 80%, and preferably higher than or equal to 40% and lower than or equal to 70%. These electrodes preferably have a resistivity of 1×10 −2  Ωcm or less. 
     Furthermore, when one of the first electrode  1101  and the second electrode  1102  is a reflective electrode in the light-emitting element of one embodiment of the present invention, the visible light reflectance of the reflective electrode is higher than or equal to 40% and lower than or equal to 100%, and preferably higher than or equal to 70% and lower than or equal to 100%. This electrode preferably has a resistivity of 1×10 −2  Ω/cm or less. 
     &lt;Specific Structure and Fabrication Method of Light-Emitting Element&gt; 
     Specific structures and specific fabrication methods of light-emitting elements of embodiments of the present invention will be described. Here, a light-emitting element having the tandem structure in  FIG.  27 B  and a microcavity structure will be described with reference to  FIG.  27 D . In the light-emitting element in  FIG.  27 D , the first electrode  1101  is formed as a reflective electrode and the second electrode  1102  is formed as a transflective electrode. Thus, a single-layer structure or a stacked-layer structure can be formed using one or more kinds of desired electrode materials. Note that the second electrode  1102  is formed after formation of the EL layer  1103   b , with the use of a material selected as described above. For fabrication of these electrodes, a sputtering method or a vacuum evaporation method can be used. 
     &lt;&lt;First Electrode and Second Electrode&gt;&gt; 
     As materials used for the first electrode  1101  and the second electrode  1102 , any of the following materials can be used in an appropriate combination as long as the functions of the electrodes described above can be fulfilled. For example, a metal, an alloy, an electrically conductive compound, a mixture of these, and the like can be appropriately used. Specifically, an In—Sn oxide (also referred to as ITO), an In—Si—Sn oxide (also referred to as ITSO), an In—Zn oxide, an In—W—Zn oxide, or the like can be used. In addition, it is possible to use a metal such as aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), or neodymium (Nd) or an alloy containing an appropriate combination of any of these metals. It is also possible to use a Group 1 element or a Group 2 element in the periodic table, which is not described above (e.g., lithium (Li), cesium (Cs), calcium (Ca), or strontium (Sr)), a rare earth metal such as europium (Eu) or ytterbium (Yb), an alloy containing an appropriate combination of any of these elements, graphene, or the like. 
     In the light-emitting element in  FIG.  27 D , when the first electrode  1101  is an anode, a hole-injection layer  1111   a  and a hole-transport layer  1112   a  of the EL layer  1103   a  are sequentially stacked over the first electrode  1101  by a vacuum evaporation method. After the EL layer  1103   a  and the charge-generation layer  1104  are formed, a hole-injection layer  1111   b  and a hole-transport layer  1112   b  of the EL layer  1103   b  are sequentially stacked over the charge-generation layer  1104  in a similar manner. 
     &lt;&lt;Hole-Injection Layer and Hole-Transport Layer&gt;&gt; 
     The hole-injection layers ( 1111   a  and  1111   b ) inject holes from the first electrode  1101  that is an anode to the EL layers ( 1103   a  and  1103   b ) and each contain a material with a high hole-injection property. 
     As examples of the material with a high hole-injection property, transition metal oxides such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide can be given. Alternatively, it is possible to use any of the following materials: phthalocyanine-based compounds such as phthalocyanine (abbreviation: H 2 Pc) and copper phthalocyanine (abbreviation: CuPc); aromatic amine compounds such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) and N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-diphenyl-(1,1′-biphenyl)-4,4′-diamine (abbreviation: DNTPD); high molecular compounds such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (abbreviation: PEDOT/PSS); and the like. 
     Alternatively, as the material with a high hole-injection property, a composite material containing a hole-transport material and an acceptor material (an electron-accepting material) can also be used. In that case, the acceptor material extracts electrons from the hole-transport material, so that holes are generated in the hole-injection layers ( 1111   a  and  1111   b ) and the holes are injected into the light-emitting layers ( 1113   a  and  1113   b ) through the hole-transport layers ( 1112   a  and  1112   b ). Note that each of the hole-injection layers ( 1111   a  and  1111   b ) may be formed to have a single-layer structure using a composite material containing a hole-transport material and an acceptor material (electron-accepting material), or a stacked-layer structure in which a layer including a hole-transport material and a layer including an acceptor material (electron-accepting material) are stacked. 
     The hole-transport layers ( 1112   a  and  1112   b ) transport the holes, which are injected from the first electrode  1101  by the hole-injection layers ( 1111   a  and  1111   b ), to the light-emitting layers ( 1113   a  and  1113   b ). Note that the hole-transport layers ( 1112   a  and  1112   b ) each contain a hole-transport material. It is particularly preferable that the HOMO level of the hole-transport material included in the hole-transport layers ( 1112   a  and  1112   b ) be the same as or close to that of the hole-injection layers ( 1111   a  and  1111   b ). 
     Examples of the acceptor material used for the hole-injection layers ( 1111   a  and  1111   b ) include an oxide of a metal belonging to any of Groups 4 to 8 of the periodic table. Specifically, molybdenum oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, tungsten oxide, manganese oxide, and rhenium oxide can be given. Among these, molybdenum oxide is especially preferable since it is stable in the air, has a low hygroscopic property, and is easy to handle. Alternatively, organic acceptors such as a quinodimethane derivative, a chloranil derivative, and a hexaazatriphenylene derivative can be used. Specifically, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F 4 -TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN), and the like can be used. 
     The hole-transport materials used for the hole-injection layers ( 1111   a  and  1111   b ) and the hole-transport layers ( 1112   a  and  1112   b ) are preferably substances with a hole mobility of greater than or equal to 10 −6  cm 2 /Vs. Note that other substances may be used as long as the substances have a hole-transport property higher than an electron-transport property. 
     Preferred hole-transport materials are π-electron rich heteroaromatic compounds (e.g., carbazole derivatives and indole derivatives) and aromatic amine compounds, examples of which include compounds having an aromatic amine skeleton, such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn), N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine (abbreviation: PCBiF), N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine (abbreviation: PCBASF), 4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA); compounds having a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), 3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP), 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA); compounds having a thiophene skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and compounds having a furan skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). 
     A high molecular compound such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can also be used. 
     Note that the hole-transport material is not limited to the above examples and may be one of or a combination of various known materials when used for the hole-injection layers ( 1111   a  and  1111   b ) and the hole-transport layers ( 1112   a  and  1112   b ). 
     Next, in the light-emitting element in  FIG.  27 D , the light-emitting layer  1113   a  is formed over the hole-transport layer  1112   a  of the EL layer  1103   a  by a vacuum evaporation method. After the EL layer  1103   a  and the charge-generation layer  1104  are formed, the light-emitting layer  1113   b  is formed over the hole-transport layer  1112   b  of the EL layer  1103   b  by a vacuum evaporation method. 
     &lt;&lt;Light-Emitting Layer&gt;&gt; 
     The light-emitting layers ( 1113   a  and  1113   b ) each contain a light-emitting substance. Note that as the light-emitting substance, a substance whose emission color is blue, violet, bluish violet, green, yellowish green, yellow, orange, red, or the like is appropriately used. When the plurality of light-emitting layers ( 1113   a  and  1113   b ) are formed using different light-emitting substances, different emission colors can be exhibited (for example, complementary emission colors are combined to achieve white light emission). Furthermore, a stacked-layer structure in which one light-emitting layer contains two or more kinds of light-emitting substances may be employed. 
     The light-emitting layers ( 1113   a  and  1113   b ) may each contain one or more kinds of organic compounds (a host material and an assist material) in addition to a light-emitting substance (guest material). As the one or more kinds of organic compounds, one or both of the hole-transport material and the electron-transport material described in this embodiment can be used. 
     There is no particular limitation on light-emitting substances that can be used for the light-emitting layers ( 1113   a  and  1113   b ), and a light-emitting substance that converts singlet excitation energy into light emission in the visible light range or a light-emitting substance that converts triplet excitation energy into light emission in the visible light range can be used. Examples of the light-emitting substance are given below. 
     As an example of the light-emitting substance that converts singlet excitation energy into light emission, a substance that emits fluorescence (fluorescent material) can be given. Examples of the substance that emits fluorescence include a pyrene derivative, an anthracene derivative, a triphenylene derivative, a fluorene derivative, a carbazole derivative, a dibenzothiophene derivative, a dibenzofuran derivative, a dibenzoquinoxaline derivative, a quinoxaline derivative, a pyridine derivative, a pyrimidine derivative, a phenanthrene derivative, and a naphthalene derivative. A pyrene derivative is particularly preferable because it has a high emission quantum yield. Specific examples of the pyrene derivative include N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N′-bis(dibenzofuran-2-yl)-N,N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6FrAPrn), N,N′-bis(dibenzothiophen-2-yl)-N,N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6ThAPrn), N,N′-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-6-amine] (abbreviation: 1,6BnfAPrn), N,N′-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-02), and N,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-03). 
     In addition, it is possible to use 5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation: PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine (abbreviation: PAPP2BPy), N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine (abbreviation: YGA2S), 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), 4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), 4-[4-(10-phenyl-9-anthryl)phenyl]-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPBA), perylene, 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP), N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), or the like. 
     As examples of a light-emitting substance that converts triplet excitation energy into light emission, a substance that emits phosphorescence (phosphorescent material) and a thermally activated delayed fluorescence (TADF) material that exhibits thermally activated delayed fluorescence can be given. 
     Examples of a phosphorescent material include an organometallic complex, a metal complex (platinum complex), and a rare earth metal complex. These substances exhibit the respective emission colors (emission peaks) and thus, any of them is appropriately selected according to need. 
     As examples of a phosphorescent material which emits blue or green light and whose emission spectrum has a peak wavelength at greater than or equal to 450 nm and less than or equal to 570 nm, the following substances can be given. 
     For example, organometallic complexes having a 4H-triazole skeleton, such as tris {2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp) 3 ]), tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Mptz) 3 ]), tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPrptz-3b) 3 ]), and tris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPr5btz) 3 ]); organometallic complexes having a 1H-triazole skeleton, such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Mptz1-mp) 3 ]) and tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Prptzl-Me) 3 ]); organometallic complexes having an imidazole skeleton, such as fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpmi) 3 ]) and tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: [Ir(dmpimpt-Me) 3 ]); organometallic complexes in which a phenylpyridine derivative having an electron-withdrawing group is a ligand, such as bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III) tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III) picolinate (abbreviation: Flrpic), bis{2-[3′, 5 ′-bis(trifluoromethyl)phenyl]pyridinato-N,C 2′ }iridium(III) picolinate (abbreviation: [Ir(CF 3 ppy) 2 (pic)]), and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III) acetylacetonate (abbreviation: FIr(acac)); and the like can be given. 
     As examples of a phosphorescent material which emits green or yellow light and whose emission spectrum has a peak wavelength at greater than or equal to 495 nm and less than or equal to 590 nm, the following substances can be given. 
     For example, organometallic iridium complexes having a pyrimidine skeleton, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm) 3 ]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm) 3 ]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm) 2 (acac)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm) 2 (acac)]), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(nbppm) 2 (acac)]), (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(mpmppm) 2 (acac)]), (acetylacetonato)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III) (abbreviation: [Ir(dmppm-dmp) 2 (acac)]), and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm) 2 (acac)]); organometallic iridium complexes having a pyrazine skeleton, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-Me) 2 (acac)]) and (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-iPr) 2 (acac)]); organometallic iridium complexes having a pyridine skeleton, such as tris(2-phenylpyridinato-N,C 2′ )iridium(III) (abbreviation: [Ir(ppy) 3 ]), bis(2-phenylpyridinato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(ppy) 2 (acac)]), bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation: [Ir(bzq) 2 (acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation: [Ir(bzq) 3 ]), tris(2-phenylquinolinato-N,C 2′ )iridium(III) (abbreviation: [Ir(pq) 3 ]), and bis(2-phenylquinolinato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(pq) 2 (acac)]); organometallic complexes such as bis(2,4-diphenyl-1,3-oxazolato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(dpo) 2 (acac)]), bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C 2′ }iridium(III) acetylacetonate (abbreviation: [Ir(p-PF-ph) 2 (acac)]), and bis(2-phenylbenzothiazolato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(bt) 2 (acac)]); and rare earth metal complexes such as tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: [Tb(acac) 3 (Phen)]) can be given. 
     As examples of a phosphorescent material which emits yellow or red light and whose emission spectrum has a peak wavelength at greater than or equal to 570 nm and less than or equal to 750 nm, the following substances can be given. 
     For example, organometallic complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm) 2 (dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm) 2 (dpm)]), and bis[4,6-di(naphthalen-1-yl)pyrimidinato] (dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm) 2 (dpm)]); organometallic complexes having a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr) 2 (acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr) 2 (dpm)]), bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ 2 O,O′)iridium(III) (abbreviation: [Ir(dmdppr-P) 2 (dibm)]), bis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,2,6,6-tetramethyl-3,5-heptanedionato-κ 2 O,O′)iridium(III) (abbreviation: [Ir(dmdppr-dmCP) 2 (dpm)]), (acetylacetonato)bis[2-methyl-3-phenylquinoxalinato-N,C 2′ ]iridium(III) (abbreviation: [Ir(mpq) 2 (acac)]), (acetylacetonato)bis(2,3-diphenylquinoxalinato-N,C 2′ )iridium(III) (abbreviation: [Ir(dpq) 2 (acac)]), and (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: [Ir(Fdpq) 2 (acac)]); organometallic complexes having a pyridine skeleton, such as tris(1-phenylisoquinolinato-N,C 2′ )iridium(III) (abbreviation: [Ir(piq) 3 ]) and bis(1-phenylisoquinolinato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(piq) 2 (acac)]); platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (abbreviation: [PtOEP]); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: [Eu(DBM) 3 (Phen)]) and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: [Eu(TTA) 3 (Phen)]) can be given. 
     As the organic compounds (the host material and the assist material) used in the light-emitting layers ( 1113   a  and  1113   b ), one or more kinds of substances having a larger energy gap than the light-emitting substance (the guest material) are used. 
     When the light-emitting substance is a fluorescent material, it is preferable to use an organic compound that has a high energy level in a singlet excited state and has a low energy level in a triplet excited state. For example, an anthracene derivative or a tetracene derivative is preferably used. Specific examples include 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), 6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan (abbreviation: 2mBnfPPA), 9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene (abbreviation: FLPPA), 5,12-diphenyltetracene, and 5,12-bis(biphenyl-2-yl)tetracene. 
     In the case where the light-emitting substance is a phosphorescent material, an organic compound having triplet excitation energy (energy difference between a ground state and a triplet excited state) which is higher than that of the light-emitting substance is preferably selected. In that case, it is possible to use a zinc- or aluminum-based metal complex, an oxadiazole derivative, a triazole derivative, a benzimidazole derivative, a quinoxaline derivative, a dibenzoquinoxaline derivative, a dibenzothiophene derivative, a dibenzofuran derivative, a pyrimidine derivative, a triazine derivative, a pyridine derivative, a bipyridine derivative, a phenanthroline derivative, an aromatic amine, a carbazole derivative, and the like. 
     Specific examples include metal complexes such as tris(8-quinolinolato)aluminum(III) (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq 3 ), bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq 2 ), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); heterocyclic compounds such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBphen), and 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11); and aromatic amine compounds such as NPB, TPD, and BSPB. 
     In addition, condensed polycyclic aromatic compounds such as anthracene derivatives, phenanthrene derivatives, pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chrysene derivatives can be used. Specifically, 9,10-diphenylanthracene (abbreviation: DPAnth), N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine (abbreviation: DPhPA), YGAPA, PCAPA, N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine (abbreviation: PCAPBA), 2PCAPA, 6,12-dimethoxy-5,11-diphenylchrysene, DBC1, 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 9,9′-bianthryl (abbreviation: BANT), 9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS), 9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2), 1,3,5-tri(1-pyrenyl)benzene (abbreviation: TPB3), or the like can be used. 
     In the case where a plurality of organic compounds are used for the light-emitting layers ( 1113   a  and  1113   b ), it is preferable to use compounds that form an exciplex in combination with each other. In that case, although any of various organic compounds can be used in an appropriate combination, in order 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). As the hole-transport material and the electron-transport material, specifically, any of the materials described in this embodiment can be used. 
     The TADF material is a material that can up-convert a triplet excited state into a singlet excited state (i.e., reverse intersystem crossing is possible) using a little thermal energy and efficiently exhibits light emission (fluorescence) from the singlet excited state. The TADF is efficiently obtained under the condition where the difference in energy between the triplet excited level and the singlet excited level is greater than or equal to 0 eV and less than or equal to 0.2 eV, preferably greater than or equal to 0 eV and less than or equal to 0.1 eV. Note that “delayed fluorescence” exhibited by the TADF material refers to light emission having the same spectrum as normal fluorescence and an extremely long lifetime. The lifetime is 10 −6  seconds or longer, preferably 10 −3  seconds or longer. 
     Examples of the TADF material include fullerene, a derivative thereof, an acridine derivative such as proflavine, and eosin. Other examples include a metal-containing porphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of the metal-containing porphyrin include a protoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Proto IX)), a mesoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Meso IX)), a hematoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (abbreviation: SnF 2 (Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (abbreviation: SnF 2 (OEP)), an etioporphyrin-tin fluoride complex (abbreviation: SnF 2 (Etio I)), and an octaethylporphyrin-platinum chloride complex (abbreviation: PtCl 2 OEP). 
     Alternatively, a heterocyclic compound having a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation: ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviation: DMAC-DPS), or 10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation: ACRSA) can be used. Note that a substance in which the π-electron rich heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring is particularly preferable because both the donor property of the π-electron rich heteroaromatic ring and the acceptor property of the π-electron deficient heteroaromatic ring are increased and the energy difference between the singlet excited state and the triplet excited state becomes small. 
     Note that when a TADF material is used, the TADF material can be combined with another organic compound. 
     Then, in the light-emitting element in  FIG.  27 D , an electron-transport layer  1114   a  is formed over the light-emitting layer  1113   a  of the EL layer  1103   a  by a vacuum evaporation method. After the EL layer  1103   a  and the charge-generation layer  1104  are formed, an electron-transport layer  1114   b  is formed over the light-emitting layer  1113   b  of the EL layer  1103   b  by a vacuum evaporation method. 
     &lt;&lt;Electron-Transport Layer&gt;&gt; 
     The electron-transport layers ( 1114   a  and  1114   b ) transport the electrons, which are injected from the second electrode  1102  by the electron-injection layers ( 1115   a  and  1115   b ), to the light-emitting layers ( 1113   a  and  1113   b ). Note that the electron-transport layers ( 1114   a  and  1114   b ) each contain an electron-transport material. It is preferable that the electron-transport materials included in the electron-transport layers ( 1114   a  and  1114   b ) be substances with an electron mobility of higher than or equal to 1×10 −6  cm 2 /Vs. Note that other substances may also be used as long as the substances have an electron-transport property higher than a hole-transport property. 
     Examples of the electron-transport material include metal complexes having a quinoline ligand, a benzoquinoline ligand, an oxazole ligand, and a thiazole ligand; an oxadiazole derivative; a triazole derivative; a phenanthroline derivative; a pyridine derivative; and a bipyridine derivative. In addition, a π-electron deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound can also be used. 
     Specifically, it is possible to use metal complexes such as Alq 3 , tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq 3 ), bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq 2 ), BAlq, bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(II) (abbreviation: Zn(BOX) 2 ), and bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ) 2 ), heteroaromatic compounds such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), OXD-7, 3-(4′-tert-butylphenyl)-4-phenyl-5-(4″-biphenyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs), and quinoxaline derivatives and dibenzoquinoxaline derivatives such as 2[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDB q-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDB q-II). 
     Alternatively, a high molecular compound such as poly(2,5-pyridinediyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)] (abbreviation: PF-BPy) can be used. 
     Each of the electron-transport layers ( 1114   a  and  1114   b ) is not limited to a single layer, but may be a stack of two or more layers each containing any of the above substances. 
     Next, in the light-emitting element in  FIG.  27 D , the electron-injection layer  1115   a  is formed over the electron-transport layer  1114   a  of the EL layer  1103   a  by a vacuum evaporation method. Subsequently, the EL layer  1103   a  and the charge-generation layer  1104  are formed, the components up to the electron-transport layer  1114   b  of the EL layer  1103   b  are formed, and then the electron-injection layer  1115   b  is formed thereover by a vacuum evaporation method. 
     &lt;&lt;Electron-Injection Layer&gt;&gt; 
     The electron-injection layers ( 1115   a  and  1115   b ) each contain a substance having a high electron-injection property. The electron-injection layers ( 1115   a  and  1115   b ) can each be formed using an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF 2 ), or lithium oxide (LiO x ). A rare earth metal compound like erbium fluoride (ErF 3 ) can also be used. Electride may also be used for the electron-injection layers ( 1115   a  and  1115   b ). Examples of the electride include a substance in which electrons are added at high concentration to calcium oxide-aluminum oxide. Any of the substances for forming the electron-transport layers ( 1114   a  and  1114   b ), which are given above, can also be used. 
     A composite material in which an organic compound and an electron donor (donor) are mixed may also be used for the electron-injection layers ( 1115   a  and  1115   b ). Such a composite material is excellent in an electron-injection property and an electron-transport property because electrons are generated in the organic compound by the electron donor. The organic compound here is preferably a material excellent in transporting the generated electrons; specifically, for example, the electron-transport materials for forming the electron-transport layers ( 1114   a  and  1114   b ) (e.g., a metal complex or a heteroaromatic compound) can be used. As the electron donor, a substance showing an electron-donating property with respect to the organic compound may be used. Preferable examples are an alkali metal, an alkaline earth metal, and a rare earth metal. Specifically, lithium, cesium, magnesium, calcium, erbium, ytterbium, and the like can be given. Furthermore, an alkali metal oxide and an alkaline earth metal oxide are preferable, and a lithium oxide, a calcium oxide, a barium oxide, and the like can be given. Alternatively, a Lewis base such as magnesium oxide can be used. Further alternatively, an organic compound such as tetrathiafulvalene (abbreviation: TTF) can be used. 
     In the case where light obtained from the light-emitting layer  1113   b  is amplified, for example, the optical path length between the second electrode  1102  and the light-emitting layer  1113   b  is preferably less than one fourth of the wavelength λ of light emitted from the light-emitting layer  1113   b . In that case, the optical path length can be adjusted by changing the thickness of the electron-transport layer  1114   b  or the electron-injection layer  1115   b.    
     &lt;&lt;Charge-Generation Layer&gt;&gt; 
     The charge-generation layer  1104  has a function of injecting electrons into the EL layer  1103   a  and injecting holes into the EL layer  1103   b  when voltage is applied between the first electrode (anode)  1101  and the second electrode (cathode)  1102 . The charge-generation layer  1104  may have either a structure in which an electron acceptor (acceptor) is added to a hole-transport material or a structure in which an electron donor (donor) is added to an electron-transport material. Alternatively, both of these structures may be stacked. Note that forming the charge-generation layer  1104  by using any of the above materials can suppress an increase in drive voltage caused by the stack of the EL layers. 
     In the case where the charge-generation layer  1104  has a structure in which an electron acceptor is added to a hole-transport material, any of the materials described in this embodiment can be used as the hole-transport material. As the electron acceptor, it is possible to use 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F 4 -TCNQ), chloranil, and the like. In addition, oxides of metals that belong to Group 4 to Group 8 of the periodic table can be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide, or the like is used. 
     In the case where the charge-generation layer  1104  has a structure in which an electron donor is added to an electron-transport material, any of the materials described in this embodiment can be used as the electron-transport material. As the electron donor, it is possible to use an alkali metal, an alkaline earth metal, a rare earth metal, metals that belong to Groups 2 and 13 of the periodic table, or an oxide or carbonate thereof. Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like is preferably used. Alternatively, an organic compound such as tetrathianaphthacene may be used as the electron donor. 
     &lt;&lt;Substrate&gt;&gt; 
     The light-emitting element described in this embodiment can be formed over any of a variety of substrates. Note that the type of the substrate is not limited to a certain type. Examples of the substrate include a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper including a fibrous material, and a base material film. 
     Examples of the glass substrate include a barium borosilicate glass substrate, an aluminoborosilicate glass substrate, and a soda lime glass substrate. Examples of the flexible substrate, the attachment film, and the base material film include plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyether sulfone (PES); a synthetic resin such as acrylic; polypropylene; polyester; polyvinyl fluoride; polyvinyl chloride; polyamide; polyimide; aramid; epoxy; an inorganic vapor deposition film; and paper. 
     For fabrication of the light-emitting element in this embodiment, a vacuum process such as an evaporation method or a solution process such as a spin coating method or an ink-jet method can be used. When an evaporation method is used, a physical vapor deposition method (PVD method) such as a sputtering method, an ion plating method, an ion beam evaporation method, a molecular beam evaporation method, or a vacuum evaporation method, a chemical vapor deposition method (CVD method), or the like can be used. Specifically, the functional layers (the hole-injection layers ( 1111   a  and  1111   b ), the hole-transport layers ( 1112   a  and  1112   b ), the light-emitting layers ( 1113   a  and  1113   b ), the electron-transport layers ( 1114   a  and  1114   b ), the electron-injection layers ( 1115   a  and  1115   b )) included in the EL layers and the charge-generation layer  1104  of the light-emitting element can be formed by an evaporation method (e.g., a vacuum evaporation method), a coating method (e.g., a dip coating method, a die coating method, a bar coating method, a spin coating method, or a spray coating method), a printing method (e.g., an ink-jet method, screen printing (stencil), offset printing (planography), flexography (relief printing), gravure printing, or micro-contact printing), or the like. 
     Note that materials that can be used for the functional layers (the hole-injection layers ( 1111   a  and  1111   b ), the hole-transport layers ( 1112   a  and  1112   b ), the light-emitting layers ( 1113   a  and  1113   b ), the electron-transport layers ( 1114   a  and  1114   b ), and the electron-injection layers ( 1115   a  and  1115   b )) that are included in the EL layers ( 1103   a  and  1103   b ) and the charge-generation layer  1104  in the light-emitting element described in this embodiment are not limited to the above materials, and other materials can be used in combination as long as the functions of the layers are fulfilled. For example, a high molecular compound (e.g., an oligomer, a dendrimer, or a polymer), a middle molecular compound (a compound between a low molecular compound and a high molecular compound with a molecular weight of 400 to 4000), an inorganic compound (e.g., a quantum dot material), or the like can be used. The quantum dot may be a colloidal quantum dot, an alloyed quantum dot, a core-shell quantum dot, a core quantum dot, or the like. 
     The structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments or the example in this specification. 
     Embodiment 6 
     In this embodiment, a light-emitting device of one embodiment of the present invention is described. Note that a light-emitting device illustrated in  FIG.  28 A  is an active-matrix light-emitting device in which transistors (FETs)  1202  are electrically connected to light-emitting elements ( 1203 R,  1203 G,  1203 B, and  1203 W) over a first substrate  1201 . The light-emitting elements ( 1203 R,  1203 G,  1203 B, and  1203 W) include a common EL layer  1204  and each have a microcavity structure in which the optical path length between electrodes is adjusted depending on the emission color of the light-emitting element. The light-emitting device is a top-emission light-emitting device in which light is emitted from the EL layer  1204  through color filters ( 1206 R,  1206 G, and  1206 B) formed on a second substrate  1205 . 
     The light-emitting device illustrated in  FIG.  28 A  is fabricated such that a first electrode  1207  functions as a reflective electrode and a second electrode  1208  functions as a transflective electrode. Note that description in any of the other embodiments can be referred to as appropriate for electrode materials for the first electrode  1207  and the second electrode  1208 . 
     In the case where the light-emitting element  1203 R functions as a red light-emitting element, the light-emitting element  1203 G functions as a green light-emitting element, the light-emitting element  1203 B functions as a blue light-emitting element, and the light-emitting element  1203 W functions as a white light-emitting element in  FIG.  28 A , for example, a gap between the first electrode  1207  and the second electrode  1208  in the light-emitting element  1203 R is adjusted to have an optical path length  1211 R, a gap between the first electrode  1207  and the second electrode  1208  in the light-emitting element  1203 G is adjusted to have an optical path length  1211 G, and a gap between the first electrode  1207  and the second electrode  1208  in the light-emitting element  1203 B is adjusted to have an optical path length  1211 B as illustrated in  FIG.  28 B . Note that optical adjustment can be performed in such a manner that a conductive layer  1210 R is stacked over the first electrode  1207  in the light-emitting element  1203 R and a conductive layer  1210 G is stacked over the first electrode  1207  in the light-emitting element  1203 G as illustrated in  FIG.  28 B . 
     The second substrate  1205  is provided with the color filters ( 1206 R,  1206 G, and  1206 B). Note that the color filters each transmit visible light in a specific wavelength range and blocks visible light in the other wavelength ranges. Thus, as illustrated in  FIG.  28 A , the color filter  1206 R that transmits only light in the red wavelength range is provided in a position overlapping with the light-emitting element  1203 R, whereby red light emission can be obtained from the light-emitting element  1203 R. Furthermore, the color filter  1206 G that transmits only light in the green wavelength range is provided in a position overlapping with the light-emitting element  1203 G, whereby green light emission can be obtained from the light-emitting element  1203 G. Moreover, the color filter  1206 B that transmits only light in the blue wavelength range is provided in a position overlapping with the light-emitting element  1203 B, whereby blue light emission can be obtained from the light-emitting element  1203 B. Note that the light-emitting element  1203 W can emit white light without a color filter. Note that a black layer (black matrix)  1209  may be provided at an end portion of each color filter. The color filters ( 1206 R,  1206 G, and  1206 B) and the black layer  1209  may be covered with an overcoat layer formed using a transparent material. 
     Although the light-emitting device in  FIG.  28 A  has a structure in which light is extracted from the second substrate  1205  side (top emission structure), a structure in which light is extracted from the first substrate  1201  side where the FETs  1202  are formed (bottom emission structure) may be employed as illustrated in  FIG.  28 C . In the case of a bottom-emission light-emitting device, the first electrode  1207  is formed as a transflective electrode and the second electrode  1208  is formed as a reflective electrode. As the first substrate  1201 , a substrate having at least a light-transmitting property is used. As illustrated in  FIG.  28 C , color filters ( 1206 R′,  1206 G′, and  1206 B) are provided so as to be closer to the first substrate  1201  than the light-emitting elements ( 1203 R,  1203 G, and  1203 B) are. 
     In  FIG.  28 A , the light-emitting elements are the red light-emitting element, the green light-emitting element, the blue light-emitting element, and the white light-emitting element; however, the light-emitting elements that can be used in the display device of one embodiment of the present invention are not limited to the above, and a yellow light-emitting element or an orange light-emitting element may be used. Note that description in any of the other embodiments can be referred to as appropriate for materials that are used for the EL layers (a light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, a charge-generation layer, and the like) to fabricate each of the light-emitting elements. In that case, a color filter needs to be appropriately selected depending on the emission color of the light-emitting element. 
     With the above structure, a light-emitting device including light-emitting elements that exhibit a plurality of emission colors can be fabricated. 
     This embodiment can be implemented in an appropriate combination with any of the other embodiments and an example in this specification. 
     Example 1 
     In this example, a sample including a glass substrate over an elastic support substrate is described. 
       FIG.  29    schematically illustrates a sample in which substrates  503  are provided over a support substrate  501  at intervals MMT. Note that the support substrate  501  and each of the substrates  503  correspond to the support substrate  301  and the display unit  250   b  in the manufacturing method example in Embodiment 3 described with reference to  FIG.  20 B , respectively. 
     Adhesives  502  are positioned in regions where the substrates  503  overlap with the support substrate  501 . The adhesives  502  are used for bonding the substrates  503  onto the support substrate  501 . 
       FIG.  30 A  is a photograph of a sample in which a silicone rubber sheet (KS05000, produced by Kyowa Industries, Inc.) was used as the support substrate  501 , Super X No. 8008 (produced by CEMEDINE Co., Ltd.) was used as each of the adhesives  502 , and glass substrates (AN100, produced by Asahi Glass Co., Ltd.) were used as the substrates  503 . The substrates  503  were each processed into 10 mm square and provided in a matrix of four rows and three columns over the support substrate  501  with an interval MMT of 10 mm. 
       FIG.  30 B  is an image of the sample in  FIG.  30 A  stretched in the s direction.  FIG.  30 C  is an image of the sample in  FIG.  30 A  stretched in the t direction.  FIG.  30 D  is an image of the sample in  FIG.  30 A  stretched in the u direction. Note that  FIGS.  30 B to  30 D  each show the sample stretched by 10 mm or more and 20 mm or less with the hands of an experimenter. 
     The sample in  FIG.  30 A  formed using the above-described materials can be stretched without the separation of the substrates  503  from the support substrate  501  as shown in  FIGS.  30 B to  30 D . 
     Note that the structures described in this example can be used in combination with any of the structures described in the other embodiments as appropriate. 
     REFERENCE NUMERALS 
     SLa[ 1 ]: signal line, SLa[ 2 ]: signal line, SLb[ 1 ]: signal line, SLb[ 2 ]: signal line, SL[ 1 ]: signal line, SL[ 2 ]: signal line, GLa[ 1 ]: gate line, GLa[ 2 ]: gate line, GLb[ 1 ]: gate line, GLb[ 2 ]: gate line,  30 : unit,  31 : unit,  32 : connection region,  41 : conductor,  41   a : disk,  41   b : column,  41   c : disk,  42 : conductor,  43 : conductor,  44 : conductor,  44   a : disk,  44   b : cylinder,  44   c : disk,  45 : conductor,  46 : conductor,  47 : conductor,  48 : conductor,  51 : code,  52 : code,  53 : code,  54 : code,  60 : shaft,  60 A: shaft,  60   a : shaft,  60   b : shaft,  60   c : shaft,  60   d : shaft,  60   e : shaft,  60   f : shaft,  60   g : shaft,  60   h : shaft,  60   i : shaft,  61 : shaft,  62 : shaft,  69   b [ 1 ]: opening,  69   b [ 2 ]: opening,  69   c [ 1 ]: opening,  69   c [ 2 ]: opening,  70 : support unit,  72 : connection region,  73 : support,  80 : display unit,  80 A: display unit,  80 B: display unit,  80   a : display unit,  80   b : display unit,  80   c : display unit,  80   d : display unit,  81 : display portion,  81 A: display portion,  82 : connection region,  82   a : connection region,  82   b : connection region,  82   c : connection region,  82   d : connection region,  82   e : connection region,  82   f : connection region,  82   g : connection region,  82   h : connection region,  83 : support,  83 A: support,  85 : display unit group,  85 A: display unit group,  85 B: display unit group,  85 C: display unit group,  86 : display unit group,  86 A: display unit group,  86 B: display unit group,  80 [ 1 ]: display unit,  80 [ 2 ]: display unit,  80 [ 3 ]: display unit,  80 [ 4 ]: display unit,  86   b : wiring,  86   c : wiring,  90 : driver circuit unit,  91 : driver circuit portion,  92 : connection region,  93 : support,  100 : display device,  100   a : region,  100   b : region,  100 A: display device,  100 B: display device,  101 : display region,  101   a : region,  101   b : region,  102 A: driver region,  102 B: driver region,  105   a : region,  105   b : region,  106 : region,  240 : insulator,  250 : display unit,  250   a : display unit,  250   a [ 1 ]: display unit,  250   a [ 2 ]: display unit,  250   b : display unit,  251 : circuit,  252 : light-emitting portion,  255 : display unit,  256 : circuit,  260 : display region,  260 A: display region,  260 B: display region,  261 A: display region,  261 B: display region,  262 A: display region,  262 B: display region,  270 : driver region,  270 A: driver region,  271 : driver circuit unit,  272 : wiring,  280 : driver region,  280 A: driver region,  281 : driver circuit unit,  282 : wiring,  301 : support substrate,  302 : substrate,  303 : substrate,  311 : substrate,  315 : substrate,  321 : insulator,  322 : insulator,  323 : insulator,  324 : insulator,  325 : insulator,  326 : insulator,  341 : conductor,  342   a : conductor,  342   b : conductor,  343 : conductor,  344   a : conductor,  344   b : conductor,  345 : conductor,  350 : metal oxide,  361 : opening,  362 : opening,  370 : light-emitting element,  380 : conductor,  381 : conductor,  390 : protective layer,  391 : protective layer,  401 : transistor,  501 : support substrate,  502 : adhesive,  503 : substrate,  1101 : electrode,  1102 : electrode,  1103 : EL layer,  1103   a : EL layer,  1103   b : EL layer,  1104 : charge-generation layer,  1111 : hole-injection layer,  1111   a : hole-injection layer,  1111   b : hole-injection layer,  1112 : hole-transport layer,  1112   a : hole-transport layer,  1112   b : hole-transport layer,  1113 : light-emitting layer,  1113   a : light-emitting layer,  1113   b : light-emitting layer,  1114 : electron-transport layer,  1114   a : electron-transport layer,  1114   b : electron-transport layer,  1115 : electron-injection layer,  1115   a : electron-injection layer,  1115   b : electron-injection layer,  1201 : substrate,  1202 : FET,  1203 R: light-emitting element,  1203 G: light-emitting element,  1203 B: light-emitting element,  1203 W: light-emitting element,  1204 : EL layer,  1205 : substrate,  1206 R: color filter,  1206 R′: color filter,  1206 G: color filter,  1206 G′: color filter,  1206 B: color filter,  1206 B′: color filter,  1207 : electrode,  1208 : electrode,  1209 : black layer,  1210 R: conductive layer,  1210 G: conductive layer,  1211 R: optical path length,  1211 G: optical path length,  1211 B: optical path length,  5701 : display panel,  5702 : display panel,  5703 : display panel,  5704 : display panel,  5801 : clothing,  5802 : display portion,  5901 : housing,  5902 : display portion,  5903 : operation button,  5904 : operator,  5905 : band,  6001 : building,  6002 : signboard,  6002 A: signboard,  6003 : steel frame,  6100 : digital signage,  6101 : display portion,  6102 : structure body,  6103 : caster,  6200 A: digital signage,  6200 B: digital signage,  6201 : wall,  6300 A: digital signage,  6300 B: digital signage  6301 : wall,  7000 : electronic device, and  7001 : finger. 
     This application is based on Japanese Patent Application Serial No. 2016-248914 filed with Japan Patent Office on Dec. 22, 2016 and Japanese Patent Application Serial No. 2017-159979 filed with Japan Patent Office on Aug. 23, 2017, the entire contents of which are hereby incorporated by reference.