Patent Publication Number: US-11029796-B2

Title: Touch panel

Description:
This application is a continuation of U.S. application Ser. No. 15/807,218, filed on Nov. 8, 2017 is a continuation of U.S. application Ser. No. 15/070,241, filed on Mar. 15, 2016 (now U.S. Pat. No. 9,817,536 issued Nov. 14, 2017) which are all incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One embodiment of the present invention relates to an input device. One embodiment of the present invention relates to a display device. One embodiment of the present invention relates to an input/output device. One embodiment of the present invention relates to a touch panel. 
     Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, an electronic device, a lighting device, an input device, an input/output device, a driving method thereof, and a manufacturing method thereof. 
     In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A semiconductor element such as a transistor, a semiconductor circuit, an arithmetic device, and a memory device are each an embodiment of a semiconductor device. An imaging device, a display device, a liquid crystal display device, a light-emitting device, an input device, an input/output device, an electro-optical device, a power generation device (including a thin film solar cell, an organic thin film solar cell, and the like), and an electronic device may each include a semiconductor device. 
     2. Description of the Related Art 
     In recent years, a display device provided with a touch sensor as a position-input device has been in practical use. A display device provided with a touch sensor is called a touch panel, a touch screen, or the like (hereinafter also referred to simply as a touch panel). For example, a smartphone and a tablet terminal are examples of a portable information terminal provided with a touch panel. 
     As one of display devices, there is a liquid crystal display device provided with a liquid crystal element. For example, an active matrix liquid crystal display device, in which pixel electrodes are arranged in a matrix and transistors are used as switching elements connected to respective pixel electrodes, has attracted attention. 
     For example, an active matrix liquid crystal display device including transistors, in which metal oxide is used for a channel formation region, as switching elements connected to respective pixel electrodes is already known (Patent Documents 1 and 2). 
     It is known that an active matrix liquid crystal display device is classified into two major types: transmissive type and reflective type. 
     In a transmissive liquid crystal display device, a backlight such as a cold cathode fluorescent lamp is used, and a state in which light from the backlight is transmitted through liquid crystal and output to the outside of the liquid crystal display device or a state in which light is not output is selected using optical modulation action of liquid crystal, whereby bright and dark images are displayed. Furthermore, those displays are combined to display an image. 
     In a reflective liquid crystal display device, a state in which external light, in other words, incident light is reflected at a pixel electrode and output to the outside of the device or a state in which incident light is not output to the outside of the device is selected using optical modulation action of liquid crystal, whereby bright and dark images are displayed. Furthermore, those displays are combined to display an image. Compared to the transmissive liquid crystal display device, the reflective liquid crystal display device has the advantage of low power consumption since the backlight is not used. 
     REFERENCE 
     Patent Document 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2007-123861 
         [Patent Document 2] Japanese Published Patent Application No. 2007-096055 
       
    
     SUMMARY OF THE INVENTION 
     What is desirable is a touch panel in which a display panel is provided with a function of inputting data with a finger, a stylus, or the like touching a screen as a user interface. 
     Furthermore, it is demanded that an electronic appliance using a touch panel is reduced in thickness and weight. Therefore, a touch panel itself is required to be reduced in thickness and weight. 
     For example, in a touch panel, a touch sensor can be provided on the viewer side (the display surface side) of a display panel. 
     In a touch panel where a capacitive touch sensor is provided so as to overlap with the display surface side of a display panel, when the distance between a pixel or a wiring of the display panel and an electrode or a wiring of the touch sensor is reduced, the touch sensor is likely to be influenced by noise caused when the display panel is driven by the touch sensor, which results in a reduction of the detection sensitivity of the touch panel in some cases. 
     One object of one embodiment of the present invention is to provide a thin touch panel. Another object is to provide a touch panel with high visibility. Another object is to provide a lightweight touch panel. Another object is to provide a touch panel with low power consumption. 
     Another object is to provide a novel input device. Another object is to provide a novel input/output device. 
     One embodiment of the present invention is a touch panel including a first substrate, a first conductive layer, a second conductive layer, a third conductive layer, a fourth conductive layer, and a liquid crystal layer. The third conductive layer is over the first substrate. The fourth conductive layer is apart from the third conductive layer on the same plane. The liquid crystal layer is positioned above the third conductive layer. The second conductive layer is positioned above the liquid crystal layer. The first conductive layer is positioned above the second conductive layer. The first conductive layer has a function of blocking visible light and has a mesh shape including a plurality of openings. The second conductive layer has a function of transmitting visible light and includes a portion overlapping with the first conductive layer, a portion overlapping with the third conductive layer, and a portion overlapping with the fourth conductive layer. The third conductive layer and the fourth conductive layer each have a function of reflecting visible light. The third conductive layer includes a portion overlapping with one of the plurality of openings. The fourth conductive layer includes a portion overlapping with another one of the plurality of openings. Part of the first conductive layer is between the third conductive layer and the fourth conductive layer in a plan view. 
     In the above, it is preferable that the second conductive layer function as a common electrode and the third conductive layer and the fourth conductive layer each function as a pixel electrode. 
     Another embodiment of the present invention is a touch panel including a first substrate, a first conductive layer, a second conductive layer, a third conductive layer, a fourth conductive layer, a fifth conductive layer, and a liquid crystal layer. The fifth conductive layer is over the first substrate. The third conductive layer is positioned above the fifth conductive layer. The fourth conductive layer is apart from the third conductive layer on the same plane. The liquid crystal layer is positioned above the third conductive layer. The second conductive layer is positioned above the liquid crystal layer. The first conductive layer is positioned above the second conductive layer. The first conductive layer has a function of blocking visible light and has a mesh shape including a plurality of openings. The second conductive layer has a function of transmitting visible light and includes a portion overlapping with the first conductive layer, a portion overlapping with the third conductive layer, and a portion overlapping with the fourth conductive layer. The third conductive layer and the fourth conductive layer each have a function of reflecting visible light. The third conductive layer includes a portion overlapping with one of the plurality of openings. The third conductive layer and the fourth conductive layer, or the fifth conductive layer has a function of reflecting visible light. Part of the first conductive layer is between the third conductive layer and the fourth conductive layer in a plan view. The third conductive layer has a comb-like shape. The one of the plurality of openings, the third conductive layer, and the fifth conductive layer overlap with one another in a region. The one of the plurality of openings and the fifth conductive layer overlap with each other and do not overlap with the third conductive layer in a region. 
     Another embodiment of the present invention is a touch panel including a first substrate, a first conductive layer, a second conductive layer, a third conductive layer, a fourth conductive layer, a fifth conductive layer, and a liquid crystal layer. The fifth conductive layer is positioned over the first substrate. The third conductive layer is positioned between the fifth conductive layer and the first substrate. The fourth conductive layer is apart from the third conductive layer on the same plane. The liquid crystal layer is positioned above the fifth conductive layer. The second conductive layer is positioned above the liquid crystal layer. The first conductive layer is positioned above the second conductive layer. The first conductive layer has a function of blocking visible light and has a mesh shape including a plurality of openings. The second conductive layer has a function of transmitting visible light and includes a portion overlapping with the first conductive layer, a portion overlapping with the third conductive layer, and a portion overlapping with the fourth conductive layer. The third conductive layer includes a portion overlapping with one of the plurality of openings. The fourth conductive layer includes a portion overlapping with another one of the plurality of openings. The third conductive layer and the fourth conductive layer, or the fifth conductive layer has a function of reflecting visible light. Part of the first conductive layer is between the third conductive layer and the fourth conductive layer in a plan view. The fifth conductive layer has a comb-like shape. The one of the plurality of openings, the third conductive layer, and the fifth conductive layer overlap with one another in a region. The one of the plurality of openings and the fifth conductive layer overlap with each other and do not overlap with the third conductive layer in a region. 
     In the above, it is preferable that one of the third conductive layer and the fifth conductive layer function as a pixel electrode, and the other function as a common electrode. Alternatively, it is preferable that the third conductive layer and the fourth conductive layer each function as a pixel electrode and the fifth conductive layer function as a common electrode. 
     The second conductive layer is preferably electrically connected to a terminal supplied with a constant potential. 
     In the above, a second substrate is preferably above the first conductive layer. At this time, the first conductive layer and the second conductive layer are preferably formed over the second substrate: 
     In the above, it is preferable that a first coloring layer and a second coloring layer be positioned above the third conductive layer, the first coloring layer include a region overlapping with the one of the plurality of openings, and the second coloring layer include a region overlapping with the another one of the plurality of openings. 
     In the above, the first conductive layer preferably includes a portion overlapping with at least one of the first coloring layer and the second coloring layer. 
     In the above, it is preferable that a spacer be provided above the third conductive layer and below the second conductive layer and include a portion overlapping with the first conductive layer. 
     In the above, it is preferable that a transistor be between the liquid crystal layer and the first substrate, one of a source and a drain of the transistor be electrically connected to the third conductive layer, and the transistor include a semiconductor layer containing an oxide semiconductor. 
     In this case, the transistor preferably includes a first gate electrode and a second gate electrode. It is preferable that the first gate electrode be positioned below the semiconductor layer, the second gate electrode be positioned above the semiconductor layer, and the second gate electrode, the semiconductor layer, and the third conductive layer overlap with one another in a region. Moreover, in this case, the second gate electrode and the semiconductor layer preferably contain the same metal element. 
     According to one embodiment of the present invention, a thin touch panel can be provided. Alternatively, a touch panel with high visibility can be provided. Alternatively, a lightweight touch panel can be provided. Alternatively, a touch panel with low power consumption can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show a structure example of a touch panel module of an embodiment. 
         FIG. 2  shows a structure example of a touch panel module of an embodiment. 
         FIG. 3  shows a structure example of a touch panel module of an embodiment. 
         FIG. 4  shows a structure example of a touch panel module of an embodiment. 
         FIG. 5  shows a structure example of a touch panel module of an embodiment. 
         FIG. 6  shows a structure example of a touch panel module of an embodiment. 
         FIG. 7  shows a structure example of a touch panel module of an embodiment. 
         FIG. 8  shows a structure example of a touch panel module of an embodiment. 
         FIGS. 9A to 9C  show structure examples of a touch sensor of an embodiment. 
         FIGS. 10A to 10C  show structure examples of a touch sensor of an embodiment. 
         FIGS. 11A and 11B  show structure examples of a touch sensor of an embodiment. 
         FIGS. 12A to 12G  show structure examples of a touch panel of an embodiment. 
         FIGS. 13A and 13B  are a block diagram and a timing chart of a touch sensor of an embodiment. 
         FIG. 14  is a circuit diagram of a touch sensor of an embodiment. 
         FIGS. 15A and 15B  each illustrate a pixel provided with a touch sensor of an embodiment. 
         FIGS. 16A and 16B  illustrate operation of a touch sensor and a pixel of an embodiment. 
         FIG. 17  illustrates a display module of an embodiment. 
         FIGS. 18A to 18H  each illustrate an electronic device of an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments will be described in detail with reference to drawings. Note that the present invention is not limited to the description below, and it is easily understood by those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. Accordingly, the present invention should not be interpreted as being limited to the content of the embodiments below. 
     Note that in the structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and description of such portions is not repeated. Furthermore, the same hatching pattern is applied to portions having similar functions, and the portions are not especially denoted by reference numerals in some cases. 
     Note that in each drawing described in this specification, the size, the layer thickness, or the region of each component is exaggerated for clarity in some cases. Therefore, embodiments of the present invention are not limited to such a scale. 
     Note that in this specification and the like, ordinal numbers such as “first”, “second”, and the like are used in order to avoid confusion among components and do not limit the number. 
     Note that the terms “film” and “layer” can be interchanged with each other in some cases. For example, in some cases, the term “conductive film” can be used instead of the term “conductive layer,” and the term “insulating layer” can be used instead of the term “insulating film.” 
     Embodiment 1 
     In this embodiment, a structure example of an input device (a touch sensor) of one embodiment of the present invention, and a structure example of an input/output device (a touch panel) including the input device of one embodiment of the present invention and a display device (a display panel) are described with reference to drawings. 
     In the description below, a capacitive touch sensor is used as the touch sensor of one embodiment of the present invention. 
     Note that in this specification and the like, a touch panel has a function of displaying or outputting an image or the like on or to a display surface and a function as a touch sensor capable of detecting contact or proximity of an object such as a finger or a stylus on or to the display surface. Therefore, the touch panel is an embodiment of an input/output device. 
     In this specification and the like, a structure in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is attached to a substrate of a touch panel, or a structure in which an integrated circuit (IC) is directly mounted on a substrate by a chip on glass (COG) method is referred to as a touch panel module or simply referred to as a touch panel in some cases. 
     A capacitive touch sensor that can be used for one embodiment of the present invention includes a pair of conductive layers. A capacitor is formed in the pair of conductive layers. The capacitance of the pair of conductive layers changes when an object touches or gets close to the pair of conductive layers. Utilizing this effect, detection can be conducted. 
     Examples of the capacitive touch sensor are a surface capacitive touch sensor and a projected capacitive touch sensor. Examples of a projected capacitive touch sensor are a self-capacitive touch sensor and a mutual capacitive touch sensor. The use of a mutual capacitive touch sensor is preferable because multiple points can be detected simultaneously. 
     It is preferable that a pair of conductive layers included in the touch sensor each have an opening. It is more preferable that the pair of conductive layers have a mesh shape having a plurality of openings. It is preferable that the opening and a display element overlap with each other. Such a structure enables extraction of light emitted from the display element to the outside through the opening, and therefore, the pair of conductive layers included in the touch sensor do not necessarily have a light-transmitting property. That is, a material such as metal or alloy that has lower resistance than a light-transmitting conductive material can be used as a material for the pair of conductive layers included in the touch sensor. This reduces the influence of detection signal delay or the like and increases the detection sensitivity of the touch panel. Furthermore, such a structure can be applied to large-sized display devices such as televisions as well as portable devices. 
     Furthermore, it is preferable that the pair of conductive layers included in the touch sensor be provided to overlap with a region between two display elements in a plan view. In this case, it is more preferable that a material blocking visible light be used for the pair of conductive layers. Such a structure allows the pair of conductive layers to function as a light-blocking layer for preventing color mixture between adjacent pixels. Thus, it is not necessary to provide a black matrix or the like as a light-blocking layer and the manufacturing process can be simplified, which leads to high yield, low manufacturing cost, and the like. Moreover, by applying such a touch sensor, a touch panel having high visibility can be obtained. 
     Furthermore, the pair of conductive layers included in the touch sensor are provided in a region other than an optical path of light from the display element; thus, moire is not generated in principle. Here, moire means interference fringes generated in the case where two or more regular patterns overlap with each other. As a result, a touch panel having extremely high display quality can be obtained. 
     As a display element in a touch panel of one embodiment of the present invention, a variety of display elements, for example, a liquid crystal element, an optical element utilizing micro electro mechanical systems (MEMS), a light-emitting element such as an organic electroluminescence (EL) element or a light-emitting diode (LED), and an electrophoretic element can be used. 
     Here, a reflective liquid crystal display device including a liquid crystal element as a display element is preferably used for the touch panel. A reflective liquid crystal display device consumes much lower power than a transmissive liquid crystal display device. 
     Moreover, it is preferable that the pair of conductive layers included in the touch sensor be provided between a pair of substrates included in the touch panel. In particular, it is preferable that the conductive layer included in the touch sensor have a plurality of openings. Such a conductive layer can have a smaller surface area. Therefore, electrical noise in driving of the display element is hardly transmitted to the conductive layer as compared with the case where a light-transmitting conductive film without openings is used as the conductive layer included in the touch sensor, for example. In other words, even when both a display element and a conductive film included in the touch sensor are provided between the pair of substrates, high detection sensitivity can be achieved. As a result, a thin touch panel having high detection sensitivity can be provided. 
     Furthermore, it is more preferable that a conductive layer capable of supplying a constant potential be provided between a circuit for driving a display element and the pair of conductive layers included in the touch sensor. Such a conductive layer can function as a shield layer. Specifically, the conductive layer can prevent transmission of noise from the circuit for driving the display element to the touch sensor. The conductive layer can also prevent transmission of noise in driving of the touch sensor to the display element, the circuit for driving the display element, a wiring included in the circuit, or the like. Therefore, the display element and the touch sensor can be driven at the same time or can be driven not in synchronization without taking measures, for example, without preventing influence of noise by driving the display element and the touch sensor at different timings. As a result, a smooth moving image can be displayed by, for example, increasing the drive frequency (also referred to as frame rate) of the display element. Furthermore, the sensing accuracy can be increased by, for example, increasing the drive frequency of the touch sensor. Moreover, the drive frequency of the display element and the drive frequency of the touch sensor each can be freely set. For example, by providing a period during which one or both of the drive frequencies are low depending on conditions, power consumption can be reduced. 
     With the use of a reflective liquid crystal display device for the touch panel, a structure without a backlight can be employed. Thus, by providing a conductive film included in a touch sensor and a reflective liquid crystal element between a pair of substrates, a touch panel whose thickness is synergistically reduced can be provided. 
     A more specific structure example of one embodiment of the present invention is described below with reference to drawings. 
     [Structure Example] 
       FIG. 1A  is a schematic perspective view of a touch panel module  10  of one embodiment of the present invention.  FIG. 1B  is a schematic perspective view of the touch panel module  10  in which a pair of substrates are separated. In the touch panel module  10 , a substrate  31  and a substrate  21  are attached to each other. The touch sensor  22  is provided on the substrate  21  side. 
     The substrate  21  is provided with an FPC  41 . Furthermore, the touch sensor  22  is provided on a surface on the display panel  30  side of the substrate  21 . The touch sensor  22  includes a conductive layer  23 , a conductive layer  24 , a conductive layer  25 , and the like. Furthermore, the touch sensor  22  includes a wiring  29  which electrically connects these conductive layers to the FPC  41 . The FPC  41  has a function of supplying a signal from the outside to the touch sensor  22 . Furthermore, the FPC  41  has a function of outputting a signal from the touch sensor  22  to the outside. Note that the substrate without the FPC  41  is simply referred to as a touch panel. 
     Note that the substrate  21  over which the touch sensor  22  is formed also can be used alone as a touch sensor substrate or a touch sensor module. For example, such a substrate can be attached to the display surface side of the display panel to form a touch panel. 
     The touch sensor  22  includes a plurality of conductive layers  23 , a plurality of conductive layers  24 , and a plurality of conductive layers  25 . Each of the conductive layers  23  has a shape extending in one direction. The plurality of conductive layers  23  are arranged in a direction crossing the extending direction. Each of the conductive layers  24  is positioned between two adjacent conductive layers  23 . Each of the conductive layers  25  electrically connects two conductive layers  24  adjacent in the direction crossing the extending direction of the conductive layers  23 . That is, the plurality of conductive layers  24  arranged in the direction crossing the extending direction of the conductive layers  23  are electrically connected to each other with the plurality of conductive layers  25 . 
     Here, there is a region where the conductive layer  23  and the conductive layer  25  overlap with each other. An insulating layer is provided between the conductive layer  23  and the conductive layer  25 . 
     A capacitor is formed in the conductive layers  23  and  24  adjacent to each other. For example, in the case of employing a projected capacitive driving method, one of the conductive layers  23  and  24  can be used as a transmission-side electrode, and the other thereof can be used as a reception-side electrode. 
     Note that here, the plurality of conductive layers  24  are electrically connected to each other with the conductive layer  25 . Alternatively, it is possible to employ a structure in which the conductive layer  24  has a shape extending in one direction like the conductive layer  23 , an insulating layer is provided between the conductive layer  23  and the conductive layer  24 , and the conductive layer  25  is not provided. In this case, the conductive layer  23  and the conductive layer  24  partly overlap with each other. 
     Note that, for example, a low-resistance material is preferably used as a material of conductive films such as the conductive layer  23 , the conductive layer  24 , and the conductive layer  25 , i.e., a wiring and an electrode in the touch panel. As an example, metal such as silver, copper, or aluminum may be used. Alternatively, a metal nanowire including a number of conductors with an extremely small width (for example, a diameter of several nanometers) may be used. Examples of such a metal nanowire include an Ag nanowire, a Cu nanowire, and an Al nanowire. In the case of using an Ag nanowire, light transmittance of 89% or more and a sheet resistance of 40 ohm/square or more and 100 ohm/square or less can be achieved. Note that because such a metal nanowire provides high transmittance, the metal nanowire may be used for an electrode of the display element, e.g., a pixel electrode or a common electrode. 
     A display portion  32  is provided over the substrate  31 . The display portion  32  includes a plurality of pixels  33  arranged in a matrix. Each pixel  33  preferably includes a plurality of sub-pixel circuits. Each sub-pixel circuit is electrically connected to a display element. A circuit  34  electrically connected to the pixel  33  in the display portion  32  is preferably provided over the substrate  31 . For example, a circuit functioning as a gate driver circuit can be used as the circuit  34 . An FPC  42  has a function of supplying a signal from the outside to at least one of the display portion  32  and the circuit  34 . An IC functioning as a source driver circuit is preferably mounted on the substrate  31  or the FPC  42 . The IC can be mounted on the substrate  31  by a COG method. Alternatively, the FPC  42 , a TAB, a TCP, or the like on which an IC is mounted can be attached to the substrate  31 . 
     The touch panel module of one embodiment of the present invention can output positional information based on the change in capacitance by the touch sensor  22  at the time of a touch motion. Furthermore, the display portion  32  can display an image. 
     [Cross-Sectional Structure Example] 
     A cross-sectional structure example of the touch panel module  10  is described below with reference to drawings. The touch panel module  10  described below as an example is a module in which a reflective liquid crystal element is used as a display element. 
     [Cross-Sectional Structure Example 1] 
       FIG. 2  is a schematic cross-sectional view of the touch panel module  10 .  FIG. 2  illustrates cross sections of a region including the FPC  42 , a region including the circuit  34 , a region including the display portion  32 , a region including the FPC  41 , and the like in  FIG. 1A . 
     The substrate  21  and the substrate  31  are attached to each other with an adhesive layer  141 . A region surrounded by the substrate  21 , the substrate  31 , and the adhesive layer  141  is filled with a liquid crystal  112 . A polarizing plate  130  is provided on an outer surface of the substrate  21 . 
     The touch sensor  22  including the conductive layer  23  and the conductive layer  24 , a connection portion  101 , a wiring  29 , a display element  60 , a transistor  201 , a transistor  202 , a capacitor  203 , a connection portion  204 , a wiring  35 , and the like are provided between the substrate  31  and the substrate  21 . 
     Insulating layers such as an insulating layer  211 , an insulating layer  212 , an insulating layer  213 , and an insulating layer  214  are provided over the substrate  31 . Part of the insulating layer  211  functions as a gate insulating layer of each transistor, and another portion thereof functions as a dielectric of the capacitor  203 . The insulating layer  212 , the insulating layer  213 , and the insulating layer  214  are provided to cover each transistor, the capacitor  203 , and the like. The insulating layer  214  functions as a planarization layer. Note that an example where the three insulating layers, the insulating layers  212 ,  213 , and  214 , are provided to cover the transistors and the like is described here; however, the present invention is not limited to this example, and four or more insulating layers, a single insulating layer, or two insulating layers may be provided. The insulating layer  214  functioning as a planarization layer is not necessarily provided when not needed. 
     A conductive layer  221 , a conductive layer  222 , a conductive layer  223 , a semiconductor layer  231 , a conductive layer  111 , and the like are provided over the substrate  31 . Here, a plurality of layers obtained by processing the same conductive film are denoted by the same reference numeral in some cases. 
     The conductive layer  221  can be used for a gate electrode of each transistor, one electrode of the capacitor  203 , a wiring, or the like. The conductive layer  222  can be used for a source electrode or a drain electrode of each transistor, one electrode of a capacitor, a wiring, or the like. The conductive layer  223  can be used for another gate electrode of each transistor, a wiring, or the like. The semiconductor layer  231  can be used for a semiconductor layer of a transistor or the like. 
       FIG. 2  illustrates an example of cross sections of a sub-pixel  33 R and parts of a sub-pixel  33 G and a sub-pixel  33 B which are adjacent to the sub-pixel  33 R in the display portion  32 . For example, the sub-pixel  33 R is a sub-pixel exhibiting a red color, the sub-pixel  33 G is a sub-pixel exhibiting a green color, and the sub-pixel  33 B is a sub-pixel exhibiting a blue color; thus, full-color display can be achieved. The sub-pixel  33 R includes, for example, the transistor  202 , the capacitor  203 , the display element  60 , and a coloring layer  131 R. Here, the sub-pixel circuit includes the transistor  202 , the capacitor  203 , a wiring, and the like. 
       FIG. 2  illustrates an example of the circuit  34  in which the transistor  201  is provided. 
     In the example illustrated in  FIG. 2 , the transistors  201  and  202  each have a structure in which the semiconductor layer  231  where a channel is formed is provided between two gate electrodes (conductive layers  221  and  223 ). Such transistors can have higher field-effect mobility and thus have higher on-state current than other transistors. Consequently, a circuit capable of high-speed operation can be obtained. Furthermore, the area occupied by a circuit portion can be reduced. The use of the transistor having high on-state current can reduce signal delay in wirings and can reduce display unevenness even in a display panel or a touch panel in which the number of wirings is increased because of increase in size or resolution. 
     It is preferable that the conductive layer  111  be provided to overlap with the semiconductor layer  231  of the transistor  202  as illustrated in  FIG. 2  because the aperture ratio of the sub-pixels can be increased. In this case, the conductive layer  223  is preferably provided between the conductive layer  111  and the semiconductor layer  231 . The conductive layer  223  prevents influence of the electric field of the conductive layer  111  on the semiconductor layer  231 , and a malfunction is suppressed. In the case where the conductive layer  223  is not provided, the semiconductor layer  231  and the conductive layer  111  are preferably provided not to overlap with each other as illustrated in  FIG. 3 , for example. 
     Note that the transistor included in the circuit  34  and the transistor included in the display portion  32  may have the same structure. A plurality of transistors included in the circuit  34  may have the same structure or different structures. A plurality of transistors included in the display portion  32  may have the same structure or different structures. 
     A material through which impurities such as water or hydrogen do not easily diffuse is preferably used for at least one of the insulating layers  212  and  213  which cover the transistors. That is, the insulating layer  212  or the insulating layer  213  can function as a barrier film. Such a structure can effectively suppress diffusion of the impurities into the transistors from the outside, and a highly reliable touch panel can be provided. 
     The conductive layer  111  is provided over the insulating layer  214 . The conductive layer  111  is electrically connected to one of a source and a drain of the transistor  202  through an opening formed in the insulating layer  214 , the insulating layer  213 , the insulating layer  212 , and the like. The conductive layer  111  is also electrically connected to one electrode of the capacitor  203 . 
     The conductive layer  23 , the conductive layer  24 , the conductive layer  25 , the wiring  29 , an insulating layer  121 , an overcoat  123 , a spacer  124 , a coloring layer  131 G, the coloring layer  131 R, a coloring layer  131 B, a conductive layer  113 , and the like are provided on the substrate  31  side of the substrate  21 . 
     In  FIG. 2 , a cross section of an intersection of the conductive layer  23  and the conductive layer  24  is illustrated. The conductive layer  23  and the conductive layer  24  are provided on the same plane. The insulating layer  121  is provided between the conductive layer  25  and the conductive layers  23  and  24 . Part of the conductive layer  25  overlaps with the conductive layer  23 . The two conductive layers  24  between which the conductive layer  23  is provided are electrically connected to the conductive layer  25  through openings provided in the insulating layer  121 . 
     The coloring layer  131 R and the like are provided on the substrate  31  side of the insulating layer  121 . The overcoat  123  is provided to cover the coloring layer  131 R and the like. The conductive layer  113  is provided on the substrate  31  side of the overcoat  123 . 
     In  FIG. 2 , the display element  60  includes the conductive layer  111 , part of the conductive layer  113 , and the liquid crystal  112  sandwiched therebetween. 
     Alignment films for controlling alignment of the liquid crystal  112  may be provided on surfaces of the conductive layers  111  and  113 , the insulating layer  214 , and the like which are in contact with the liquid crystal  112 . 
     In the structure of  FIG. 2 , the conductive layer  23  is provided not to overlap with the display element  60 . In other words, the conductive layer  23  is provided so that the display element  60  overlaps with an opening in the conductive layer  23 . In still other words, the conductive layer  23  is provided to overlap with a region between the two conductive layers  111  of two adjacent sub-pixels. Although an example of the conductive layer  23  is described here, it is preferable that the conductive layer  24  and the conductive layer  25  be also provided not to overlap with the display element  60 . 
     In the display element  60 , the conductive layer  111  has a function of reflecting visible light, and the conductive layer  113  has a function of transmitting visible light. By having such a structure, the display element  60  can be a reflective liquid crystal element. Light which enters from the polarizing plate  130  side and is polarized by the polarizing plate  130 , for example, passes through the substrate  21  and the conductive layer  113 , is reflected by the conductive layer  111 , passes through the conductive layer  113  and the substrate  21  again, and then reaches the polarizing plate  130 . In this case, alignment of the liquid crystal  112  is controlled with a voltage that is applied between the conductive layers  111  and  113 , and thus optical modulation of light can be controlled. That is, the intensity of light emitted through the polarizing plate  130  can be controlled. Light other than one in a particular wavelength region of the incident light is absorbed by the coloring layer  131 R, and thus, reflected light, i.e., emitted light, is red light, for example. As the polarizing plate  130 , a circularly polarizing plate can be used, for example. An example of a circularly polarizing plate is a stack including a linear polarizing plate and a quarter-wave retardation plate. 
     Here, as for the display element  60 , a pair of electrodes are provided in the thickness direction of the touch panel module  10  and an electric field is applied to the liquid crystal  112  in the thickness direction. The arrangement of the electrodes is not limited thereto, and a method in which an electric field is applied in a direction perpendicular to the thickness direction may be employed. 
     Liquid crystal elements using a variety of modes can be used as the liquid crystal element which can be used for the display element  60 . For example, a liquid crystal element using a vertical alignment (VA) mode, a twisted nematic (TN) mode, an in-plane switching (IPS) mode, a fringe field switching (FFS) mode, an axially symmetric aligned micro-cell (ASM) mode, an optically compensated birefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, or the like can be used. 
     Furthermore, a normally black liquid crystal display device, for example, a transmissive liquid crystal display device using a vertical alignment (VA) mode may be used as the touch panel module  10 . Some examples are given as the vertical alignment mode; for example, a multi-domain vertical alignment (MVA) mode, a patterned vertical alignment (PVA) mode, or an advanced super view (ASV) mode can be used. 
     The liquid crystal element controls transmission or non-transmission of light utilizing an optical modulation action of liquid crystal. Note that optical modulation action of liquid crystal is controlled by an electric field applied to the liquid crystal (including a horizontal electric field, a vertical electric field, or an oblique electric field). As the liquid crystal used for the liquid crystal element, thermotropic liquid crystal, low-molecular liquid crystal, high-molecular liquid crystal, polymer dispersed liquid crystal (PDLC), ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or the like can be used. These liquid crystal materials exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, or the like depending on conditions. 
     As the liquid crystal material, either of a positive liquid crystal and a negative liquid crystal may be used, and an appropriate liquid crystal material can be used depending on the mode or design to be used. 
     Here, the conductive layer  113  can be used as a common electrode, and the conductive layer  111  can be used as a pixel electrode. 
     In  FIG. 2 , the conductive layer  113  is provided to overlap with the conductive layers  23  to  25  and the like. By applying a common potential, a ground potential, or an arbitrary constant potential to the conductive layer  113 , electrical noise generated to the substrate  31  side when the conductive layers  23  to  25  are driven can be blocked. Furthermore, electrical noise generated to the substrate  21  side when the sub-pixel circuit provided on the substrate  31  side is driven can be blocked. 
     The connection portion  204  is provided in a region near an end portion of the substrate  31 . The connection portion  204  is electrically connected to the FPC  42  through a connection layer  242 .  FIG. 2  illustrates an example of the connection portion  204  formed by stacking part of the wiring  35  and the conductive layer  223 . The connection portion  101  is provided in a region near an end portion of the substrate  21 . The connection portion  101  is electrically connected to the FPC  41  through a connection layer  241 . In the example of the structure illustrated in  FIG. 2 , the connection portion  101  is formed by stacking part of the wiring  29 , a conductive layer formed by processing the conductive film used for forming the conductive layer  25 , and a conductive layer formed by processing the conductive film used for forming the conductive layer  113 . 
     In  FIG. 2 , a cross-sectional structure of an intersection of the conductive layer  221  functioning as a wiring and the conductive layer  222  functioning as a wiring is illustrated as an example. The conductive layer  221  can be used as one or both of a wiring functioning as a scan line and a wiring functioning as a capacitor line, and the conductive layer  222  can be used as a wiring functioning as a signal line, for example. 
     A substrate with which an object to be sensed, such as a finger or a stylus, is to be in contact may be provided above the polarizing plate  130 . In that case, a protective layer (such as a ceramic coat) is preferably provided over the substrate. The protective layer can be formed using an inorganic insulating material such as silicon oxide, aluminum oxide, yttrium oxide, or yttria-stabilized zirconia (YSZ). Alternatively, tempered glass may be used for the substrate. The tempered glass which can be used here is one that has been subjected to physical or chemical treatment by an ion exchange method, a thermal tempering method, or the like and has a surface to which compressive stress has been added. 
     The overcoat  123  has a function of preventing impurities such as a pigment included in the coloring layer  131 R or the like from diffusing into the liquid crystal  112 . 
     The spacer  124  is provided over the conductive layer  113  and has a function of keeping a certain distance between the substrate  21  and the substrate  31 . Although  FIG. 2  illustrates an example where the spacer  124  is not in contact with structures (e.g., the conductive layer  111  and the insulating layer  214 ) on the substrate  31  side, the spacer  124  may be in contact with them. Moreover,  FIG. 2  illustrates an example where the spacer  124  is provided on the substrate  21  side; however, the spacer  124  may be provided on the substrate  31  side. For example, the spacer  124  may be provided between the two conductive layers  111  of the two adjacent sub-pixels. Alternatively, a particulate spacer may be used as the spacer  124 . Although a material such as silica can be used for the particulate spacer, an elastic material such as an organic resin or rubber is preferably used. In some cases, the particulate spacer may be vertically crushed. 
     It is preferable that the spacer  124  and the conductive layer  23  (or the conductive layer  24  or  25 ) be provided to overlap with each other as illustrated in  FIG. 2 . In such a structure, the spacer  124  is not provided in a portion where the display element  60  is provided, in which case absorption, refraction, or diffusion of light due to the spacer  124  does not occur, for example; thus, the light-extraction efficiency can be improved. 
     In the touch panel module  10  of one embodiment of the present invention, the conductive layers  23  to  25  can function as light-blocking layers for suppressing color mixture between adjacent sub-pixels. For that reason, a material which blocks visible light is preferably used for the conductive layers  23  to  25 . Alternatively, a material reflecting visible light may be used. A structure in which a layer containing a material which reflects visible light and a layer absorbing at least part of visible light in a position closer to the substrate  31  than that of the former layer are stacked is preferable because light reaching the conductive layer  23  or the like of light reflected by the conductive layer  111  is prevented from being reflected to the substrate  31  side again. 
     It is preferable that end portions of two adjacent coloring layers overlap with each other to further overlap with the conductive layer  23  or the like as illustrated in  FIG. 4 , for example. In  FIG. 4 , the conductive layer  23 , an end portion of the coloring layer  131 G, and an end portion of the coloring layer  131 R overlap with one another in the vicinity of a boundary between the sub-pixel  33 G and the sub-pixel  33 R. The conductive layer  23 , an end portion of the coloring layer  131 R, and an end portion of the coloring layer  131 B are provided to overlap with one another in the vicinity of a boundary between the sub-pixel  33 R and the sub-pixel  33 B. Such a structure does not require additionally providing a layer absorbing visible light, which leads to lower manufacturing cost. Although only one coloring layer may overlap with the conductive layer  23  or the like, visible light can be more effectively absorbed when two or more coloring layers overlap with the conductive layer  23 . 
     The above is the description of Cross-sectional Structure Example 1. 
     [Cross-Sectional Structure Example 2] 
     A cross-sectional structure example of the touch panel module  10  that includes a liquid crystal element having a mode different from that in Cross-sectional Structure Example 1 is described below. Note that descriptions of the portions already described are omitted and different portions are described below. 
       FIG. 5  illustrates an example where the display element  60  is a liquid crystal element using an FFS mode. The display element  60  includes a conductive layer  151 , a liquid crystal  152 , and a conductive layer  153 . 
     The conductive layer  153  is provided over the insulating layer  214 . The insulating layer  215  is provided to cover the conductive layer  153 , and the conductive layer  151  is provided over the insulating layer  215 . The conductive layer  151  is electrically connected to one of a source and a drain of the transistor  202  through an opening provided in the insulating layers  212  to  215 . 
     The top surface shape of the conductive layer  151  is a comb-like shape or has a slit. The conductive layer  153  is provided to overlap with the conductive layer  151 . There is a portion where the conductive layer  151  is not provided over the conductive layer  153  in a region overlapping with the coloring layer  131 R and the like. 
     In the structure illustrated in  FIG. 5 , the conductive layer  151  functions as a pixel electrode, and the conductive layer  153  functions as a common electrode. Note that the conductive layer  151  which is provided in an upper layer and whose top surface shape is a comb-like shape or has a slit may function as a common electrode, and the conductive layer  153  provided in a lower layer may function as a pixel electrode. In this case, the conductive layer  153  may be electrically connected to one of the source and the drain of the transistor  202 . 
     Even in the case of a horizontal electric field mode such as an FFS mode or an IPS mode, the conductive layer  113  can function as a shield layer for suppressing the adverse effect of noise. In this case, a constant potential which does not influence switching of the liquid crystal  152  may be supplied to the conductive layer  113 . For example, a ground potential, a common potential, or an arbitrary constant potential can be used. The conductive layer  153  and the conductive layer  113  may be set at the same potential, for example. 
     One or both of the conductive layers  151  and  153  can be formed using a material that reflects visible light. When both of them are formed using a material that reflects visible light, the aperture ratio can be increased. The conductive layer  153  may be formed using a material that reflects visible light and the conductive layer  151  may be formed using a material that transmits visible light. 
     Alternatively, in the case of employing a horizontal electric field mode, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. A blue phase is one of liquid crystal phases, which is generated just before a cholesteric phase changes into an isotropic phase while temperature of cholesteric liquid crystal is increased. Since the blue phase appears only in a narrow temperature range, a liquid crystal composition in which several weight percent or more of a chiral material is mixed is used for the liquid crystal layer in order to improve the temperature range. The liquid crystal composition which includes liquid crystal exhibiting a blue phase and a chiral material has a short response time and optical isotropy. In addition, the liquid crystal composition which includes liquid crystal exhibiting a blue phase and a chiral material has a small viewing angle dependence. An alignment film does not need to be provided and rubbing treatment is thus not necessary; accordingly, electrostatic discharge damage caused by the rubbing treatment can be prevented and defects and damage of the liquid crystal display device in the manufacturing process can be reduced. 
       FIG. 6  illustrates an example where the conductive layer  223  is not provided in the structure in  FIG. 5 . In the case where the conductive layer  153  is used as a common electrode, the conductive layer  153  is preferably provided between the semiconductor layer  231  of the transistor  202  and the conductive layer  151  as illustrated in  FIG. 6 . Thus, an electric field of the conductive layer  151  can be prevented from affecting the semiconductor layer  231 . 
     The above is the description of Cross-sectional Structure Example 2. 
     [Cross-Sectional Structure Example 3] 
     A cross-sectional structure example of the touch panel module  10  including a touch sensor having a structure different from those in Cross-sectional Structure Examples 1 and 2 is described below. Note that descriptions of the portions already described are omitted and different portions are described below. 
     The touch panel module in  FIG. 7  is different from that in  FIG. 5  in that a conductive layer  125  is provided instead of the conductive layer  25  and an insulating layer  122  is provided. 
     The conductive layer  125  in  FIG. 7  is formed using a conductive material including a metal oxide. 
     Among the light-transmitting conductive materials which are described later, metal oxides can be used, for example. 
     Alternatively, a low-resistance oxide semiconductor is preferably included. In particular, in the case where an oxide semiconductor is used for a semiconductor layer of a transistor in the touch panel module  10 , an oxide semiconductor whose resistivity is lower than that of the oxide semiconductor is preferably used for the conductive layer  125 . 
     The resistivity of the conductive layer  125  can be reduced, for example, by a method for controlling the resistivity of an oxide semiconductor which is described later. 
     In this case, an insulating layer containing much hydrogen is preferably used as the insulating layer  122  covering the conductive layer  125 . In particular, the insulating layer  122  preferably includes an insulating film containing silicon nitride. 
     The use of a conductive metal oxide or a low-resistance oxide semiconductor for the conductive layer  125  suppresses oxidation of its surface, so that the touch panel module  10  having high reliability can be provided. 
     The above is the description of Cross-sectional structure example 3. 
     [Cross-Sectional Structure Example 4] 
       FIG. 8  illustrates an example of a touch panel of one embodiment of the present invention that includes a top-gate transistor. 
     A touch panel module in  FIG. 8  is different from that in  FIG. 5  mainly in structures of the transistors  301  and  302 . Since structures other than the transistor structures are almost the same as those in  FIG. 5 , the same portions are denoted by the same reference numerals and detailed descriptions of common portions are omitted. 
       FIG. 8  illustrates an example where the display element  60  is a liquid crystal element using an FFS mode. The display element  60  includes the conductive layer  151 , the liquid crystal  152 , and the conductive layer  153 . 
     The transistors  301  and  302  each include a semiconductor layer over a buffer layer  300 , an insulating layer functioning as a gate insulating layer, a conductive layer functioning as a gate electrode and overlapping with the semiconductor layer with the gate insulating layer provided therebetween, an insulating layer covering the conductive layer functioning as the gate electrode, a conductive layer functioning as a source electrode, and a conductive layer functioning as a drain electrode. A region of the semiconductor layer which does not overlap with the gate electrode preferably has lower resistance than a channel formation region overlapping with the gate electrode. 
     In the case of using an oxide semiconductor layer, an impurity element (a rare gas, nitrogen, phosphorus, boron, hydrogen, or the like) is preferably added to a semiconductor layer not overlapping with the gate electrode so that the region of the semiconductor layer not overlapping with the gate electrode has lower resistance than the channel formation region. Helium, argon, or the like can be used as the rare gas. To add impurities, a method using plasma, an ion implantation method, or the like can be used. An ion implantation method is preferable because impurity elements can be added using the gate electrode as a mask to reduce the resistance of part of the oxide semiconductor layer. 
     The capacitor  203  includes the conductive layer functioning as the gate electrode, the conductive layer functioning as the source electrode or the drain electrode, and an insulating layer provided therebetween as a dielectric. The connection portion  204  is formed by stacking part of the wiring  35  and the conductive layer  223 . The conductive layer  223  is formed by a sputtering method in an atmosphere containing an oxygen gas, and thus, oxygen or excess oxygen is added to the insulating layer  212  over which the conductive layer  223  is formed. Furthermore, excess oxygen fills oxygen vacancies in the oxide semiconductor layers in the transistors  301  and  302 ; thus, a highly reliable transistor can be provided. In the case where excess oxygen is supplied to one or both of the insulating layer  212  and the oxide semiconductor layer, the insulating layer  213  is preferably formed using a material capable of suppressing penetration of oxygen. 
     The buffer layer  300  is formed using an insulating material such as silicon oxide or metal oxide. As the metal oxide used for the buffer layer  300 , an oxide containing one or more of aluminum, indium, gallium, zinc, and the like is used. For the buffer layer  300 , a material through which impurities such as water and hydrogen are hardly diffused is preferably used. In other words, the buffer layer  300  can function as a barrier film. Such a structure can effectively suppress diffusion of the impurities into the transistors  301  and  302  from the outside, and thus, a highly reliable touch panel can be provided. 
     [Components] 
     The above-mentioned components are described below. 
     [Substrate] 
     A substrate having a flat surface can be used as the substrate included in the touch panel. The substrate on the side from which light from the display element is extracted is formed using a material that transmits the light. For example, a material such as glass, quartz, ceramics, sapphire, or an organic resin can be used. 
     The weight and thickness of the touch panel can be decreased by using a thin substrate. A flexible touch panel can be obtained by using a substrate that is thin enough to have flexibility. 
     As the glass, for example, non-alkali glass, barium borosilicate glass, aluminoborosilicate glass, or the like can be used. 
     Examples of a material that has flexibility and transmits visible light include flexible glass, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, a polystyrene resin, a polyamide imide resin, a polyvinyl chloride resin, and a polytetrafluoroethylene (PTFE). In particular, a material whose thermal expansion coefficient is low is preferable, and for example, a polyamide imide resin, a polyimide resin, or PET can be suitably used. A substrate in which a glass fiber is impregnated with an organic resin or a substrate whose thermal expansion coefficient is reduced by mixing an organic resin with an inorganic filler can also be used. A substrate using such a material is lightweight, and accordingly a touch panel using this substrate can also be lightweight. 
     Since it is not necessary for the substrate through which light emission is not extracted to have a light-transmitting property, a metal substrate, a ceramic substrate, a semiconductor substrate, or the like can be used as well as the above-described substrates. A metal material and an alloy material, which have high thermal conductivity, is preferable because they can easily conduct heat to the whole sealing substrate and accordingly can prevent a local temperature rise in the touch panel. To obtain flexibility and bendability, the thickness of a metal substrate is preferably greater than or equal to 10 μm and less than or equal to 200 μm, more preferably greater than or equal to 20 μm and less than or equal to 50 μm. 
     Although there is no particular limitation on a material of a metal substrate, it is favorable to use, for example, a metal such as aluminum, copper, and nickel, an aluminum alloy, or an alloy such as stainless steel. 
     It is preferable to use a substrate subjected to insulation treatment, e.g., a metal substrate whose surface is oxidized or provided with an insulating film. An insulating film may be formed by, for example, a coating method such as a spin-coating method and a dipping method, an electrodeposition method, an evaporation method, or a sputtering method. An oxide film may be formed over the substrate surface by an anodic oxidation method, exposing to or heating in an oxygen atmosphere, or the like. 
     A hard coat layer (e.g., a silicon nitride layer) by which a touch panel surface is protected from damage, a layer (e.g., an aramid resin layer) that can disperse pressure, or the like may be stacked over the flexible substrate. Furthermore, to suppress a decrease in lifetime of the display element due to moisture and the like, an insulating film with low water permeability may be stacked over the flexible substrate. For example, an inorganic insulating material such as silicon nitride, silicon oxynitride, aluminum oxide, or aluminum nitride can be used. 
     The substrate may be formed by stacking a plurality of layers. When a glass layer is used, a barrier property against water and oxygen can be improved and thus a highly reliable touch panel can be provided. 
     A substrate in which a glass layer, an adhesive layer, and an organic resin layer are stacked from the side closer to the display element can be used, for example. The thickness of the glass layer is greater than or equal to 20 μm and less than or equal to 200 μm, preferably greater than or equal to 25 μm and less than or equal to 100 μm. With such a thickness, the glass layer can have both a high barrier property against water and oxygen and a high flexibility. The thickness of the organic resin layer is greater than or equal to 10 μm and less than or equal to 200 μm, preferably greater than or equal to 20 μm and less than or equal to 50 μm. Providing such an organic resin layer, occurrence of a crack or a break in the glass layer can be suppressed and mechanical strength can be improved. With the substrate that includes such a composite material of a glass material and an organic resin, a highly reliable flexible touch panel can be provided. 
     [Transistor] 
     The transistor includes a conductive layer functioning as the gate electrode, the semiconductor layer, a conductive layer functioning as the source electrode, a conductive layer functioning as the drain electrode, and an insulating layer functioning as the gate insulating layer. The above description is that of the case where a bottom-gate transistor is used. 
     Note that there is no particular limitation on the structure of the transistor included in the touch panel of one embodiment of the present invention. For example, a forward staggered transistor or an inverted staggered transistor may be used. A top-gate transistor or a bottom-gate transistor may be used. There is no particular limitation on a semiconductor material that is used for the transistor, and for example, an oxide semiconductor, silicon, or germanium can be used. 
     There is no particular limitation on the crystallinity of a semiconductor material used for the transistors, and an amorphous semiconductor or a semiconductor having crystallinity (a microcrystalline semiconductor, a polycrystalline semiconductor, a single-crystal semiconductor, or a semiconductor partly including crystal regions) may be used. It is preferable that a semiconductor having crystallinity be used, in which case deterioration of the transistor characteristics can be suppressed. 
     As a semiconductor material for the semiconductor layer of the transistor, an element of Group 14, a compound semiconductor, or an oxide semiconductor can be used, for example. Typically, a semiconductor containing silicon, a semiconductor containing gallium arsenide, an oxide semiconductor containing indium, or the like can be used. 
     In particular, an oxide semiconductor having a wider band gap than silicon is preferably used. A semiconductor material having a wider band gap and a lower carrier density than silicon is preferably used because off-state leakage current of the transistor can be reduced. 
     For example, at least indium (In) or zinc (Zn) is preferably included as the oxide semiconductor. More preferably, an In-M-Zn-based oxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf) is included. 
     As the semiconductor layer, it is particularly preferable to use an oxide semiconductor film including a plurality of crystal parts whose c-axes are aligned substantially perpendicular to a surface on which the semiconductor layer is formed or the top surface of the semiconductor layer and in which a grain boundary is not observed between adjacent crystal parts. 
     There is no grain boundary in such an oxide semiconductor; therefore, generation of a crack in an oxide semiconductor film which is caused by stress when a display panel is bent is prevented. Therefore, such an oxide semiconductor can be preferably used for a flexible touch panel which is used in a bent state, or the like. 
     Moreover, the use of such an oxide semiconductor with crystallinity for the semiconductor layer makes it possible to provide a highly reliable transistor in which a change in the electrical characteristics is suppressed. 
     A transistor with an oxide semiconductor whose band gap is larger than the band gap of silicon can hold charges stored in a capacitor that is series-connected to the transistor for a long time, owing to the low off-state current of the transistor. When such a transistor is used for a pixel, operation of a driver circuit can be stopped while a gray scale of an image displayed in each display region is maintained. As a result, a display device with extremely low power consumption can be obtained. 
     The semiconductor layer preferably includes, for example, a film represented by an In-M-Zn oxide that contains at least indium, zinc, and M (a metal such as Al, Ti, Ga, Y, Zr, La, Ce, Sn, or Hf). In order to reduce variations in electrical characteristics of the transistor including the oxide semiconductor, the oxide semiconductor preferably contains a stabilizer in addition to indium, zinc, and M. 
     Examples of the stabilizer, including metals that can be used as M, are gallium, tin, hafnium, aluminum, and zirconium. As another stabilizer, lanthanoid such as lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium can be given. 
     As an oxide semiconductor included in the semiconductor layer, any of the following can be used, for example: an In—Ga—Zn-based oxide, an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, and an In—Hf—Al—Zn-based oxide. 
     Note that here, for example, an “In—Ga—Zn-based oxide” means an oxide containing In, Ga, and Zn as its main components, and there is no limitation on the ratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metal element in addition to In, Ga, and Zn. 
     The semiconductor layer and the conductive layer may include the same metal elements contained in the above oxides. The use of the same metal elements for the semiconductor layer and the conductive layer can reduce the manufacturing cost. For example, when metal oxide targets with the same metal composition are used, the manufacturing cost can be reduced, and the same etching gas or the same etchant can be used in processing the semiconductor layer and the conductive layer. Note that even when the semiconductor layer and the conductive layer include the same metal elements, they have different compositions in some cases. For example, a metal element in a film is released during the manufacturing process of the transistor and the capacitor, which might result in different metal compositions. 
     In the case where the semiconductor layer is an In-M-Zn oxide, the proportions of In and M when the summation of In and M is assumed to be 100 atomic % are preferably as follows: the atomic percentage of In is higher than 25 atomic % and the atomic percentage of M is lower than 75 atomic %, more preferably, the atomic percentage of In is higher than 34 atomic % and the atomic percentage of M is lower than 66 atomic %. 
     The energy gap of the semiconductor layer is 2 eV or more, preferably 2.5 eV or more, more preferably 3 eV or more. With the use of an oxide semiconductor having such a wide energy gap, the off-state current of the transistor can be reduced. 
     The thickness of the semiconductor layer is greater than or equal to 3 nm and less than or equal to 200 nm, preferably greater than or equal to 3 nm and less than or equal to 100 nm, more preferably greater than or equal to 3 nm and less than or equal to 50 nm. 
     In the case where the semiconductor layer contains an In-M-Zn oxide (M represents Al, Ga, Y, Zr, La, Ce, or Nd), it is preferable that the atomic ratio of metal elements of a sputtering target used for forming a film of the In-M-Zn oxide satisfy In M and Zn≥M. As the atomic ratio of metal elements of such a sputtering target, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, and In:M:Zn=3:1:2 are preferable. Note that the atomic ratio of metal elements in the formed semiconductor layer varies from the above atomic ratio of metal elements of the sputtering target within a range of ±40% as an error. 
     An oxide semiconductor film with low carrier density is used as the semiconductor layer. For example, the semiconductor layer is an oxide semiconductor with low carrier density (specifically, lower than or equal to 1×10 17 /cm 3 , preferably lower than or equal to 1×10 15 /cm 3 , more preferably lower than or equal to 1×10 13 /cm 3 , still more preferably lower than or equal to 1×10 11 /cm 3 , even more preferably lower than 1×10 10 /cm 3 , and higher than or equal to 1×10 −9 /cm 3 ). Such an oxide semiconductor is referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. The oxide semiconductor has low impurity concentration and a low density of defect states and can thus be referred to as an oxide semiconductor having stable characteristics. 
     Note that, without limitation to those described above, a material with an appropriate composition may be used depending on required semiconductor characteristics and electrical characteristics (e.g., field-effect mobility and threshold voltage) of a transistor. To obtain the required semiconductor characteristics of the transistor, it is preferable that the carrier density, the impurity concentration, the defect density, the atomic ratio between a metal element and oxygen, the interatomic distance, the density, and the like of the semiconductor layer be set to appropriate values. 
     When silicon or carbon that is one of elements belonging to Group 14 is contained in the semiconductor layer, oxygen vacancies are increased in the semiconductor layer, and the semiconductor layer becomes n-type. Thus, the concentration of silicon or carbon (measured by secondary ion mass spectrometry (SIMS)) in the semiconductor layer is lower than or equal to 2×10 18  atoms/cm 3 , preferably lower than or equal to 2×10 17  atoms/cm 3 . 
     An alkali metal and an alkaline earth metal might generate carriers when bonded to an oxide semiconductor, in which case the off-state current of the transistor might be increased. Therefore, the concentration of alkali metal or alkaline earth metal of the semiconductor layer, which is measured by SIMS, is lower than or equal to 1×10 18  atoms/cm 3 , preferably lower than or equal to 2×10 16  atoms/cm 3 . 
     When nitrogen is contained in the semiconductor layer, electrons serving as carriers are generated and the carrier density increases, so that the semiconductor layer easily becomes n-type. Thus, a transistor including an oxide semiconductor which contains nitrogen is likely to be normally on. For this reason, the concentration of nitrogen which is measured by SIMS is preferably set to, for example, lower than or equal to 5×10 18  atoms/cm 3 . 
     The semiconductor layer may have, for example, a non-single crystal structure. Examples of the non-single crystal structure include a c-axis aligned crystalline oxide semiconductor (CAAC-OS), a polycrystalline structure, a microcrystalline structure, and an amorphous structure. Among the non-single crystal structures, the amorphous structure has the highest density of defect states, whereas CAAC-OS has the lowest density of defect states. 
     The semiconductor layer may have an amorphous structure, for example. The oxide semiconductor film having an amorphous structure has disordered atomic arrangement and no crystalline component, for example. Alternatively, the oxide film having an amorphous structure has, for example, an absolutely amorphous structure and no crystal part. 
     Note that the semiconductor layer may be a mixed film including two or more of the following: a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure. The mixed film includes, for example, two or more of a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure in some cases. The mixed film may have a stacked-layer structure of two or more of the following: a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure. 
     Alternatively, silicon is preferably used as a semiconductor in which a channel of a transistor is formed. Although amorphous silicon may be used as silicon, silicon having crystallinity is particularly preferable. For example, microcrystalline silicon, polycrystalline silicon, single-crystal silicon, or the like is preferably used. In particular, polycrystalline silicon can be formed at a lower temperature than single-crystal silicon and has higher field effect mobility and higher reliability than amorphous silicon. When such a polycrystalline semiconductor is used for a pixel, the aperture ratio of the pixel can be improved. Even in the case of a high-definition display panel, a gate driver circuit and a source driver circuit can be formed over a substrate over which the pixels are formed, and the number of components of an electronic device can be reduced. 
     [Conductive Layer] 
     As a gate, a source, and a drain of a transistor, and a wiring or an electrode included in a touch panel, any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten, or an alloy containing any of these metals as its main component can be used. A single-layer structure or multi-layer structure including a film containing any of these materials can be used. For example, the following structures can be given: a single-layer structure of an aluminum film containing silicon, a two-layer structure in which an aluminum film is stacked over a titanium film, a two-layer structure in which an aluminum film is stacked over a tungsten film, a two-layer structure in which a copper film is stacked over a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is stacked over a titanium film, a two-layer structure in which a copper film is stacked over a tungsten film, a three-layer structure in which a titanium film or a titanium nitride film, an aluminum film or a copper film, and a titanium film or a titanium nitride film are stacked in this order, and a three-layer structure in which a molybdenum film or a molybdenum nitride film, an aluminum film or a copper film, and a molybdenum film or a molybdenum nitride film are stacked in this order. Note that an oxide such as indium oxide, tin oxide, or zinc oxide may be used. Copper containing manganese is preferably used because controllability of a shape by etching is increased. 
     As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added, or graphene can be used. Alternatively, a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium, or an alloy material containing any of these metal materials can be used. Alternatively, a nitride of the metal material (e.g., titanium nitride) or the like may be used. In the case of using the metal material or the alloy material (or the nitride thereof), the thickness is set small enough to be able to transmit light. Alternatively, a stack of any of the above materials can be used as the conductive layer. For example, a stacked film of indium tin oxide and an alloy of silver and magnesium is preferably used because the conductivity can be increased. 
     Alternatively, for the conductive layer, an oxide semiconductor similar to that of the semiconductor layer is preferably used. In that case, it is preferable that the conductive layer be formed to have a lower electric resistance than a region in the semiconductor layer where a channel is formed. 
     For example, such a conductive layer can be used as the conductive layer  223  functioning as the second gate electrode of the transistor. Alternatively, it can be used as another light-transmitting conductive layer. 
     &lt;Method for Controlling Resistivity of Oxide Semiconductor&gt; 
     An oxide semiconductor film that can be used as each of the semiconductor layer and the conductive layer includes a semiconductor material whose resistivity can be controlled by oxygen vacancies in the film and/or the concentration of impurities such as hydrogen or water in the film. Thus, treatment to be performed on the semiconductor layer and the conductive layer is selected from the following to control the resistivity of each of the oxide semiconductor films: treatment for increasing oxygen vacancies and/or impurity concentration and treatment for reducing oxygen vacancies and/or impurity concentration. 
     Specifically, plasma treatment is performed on the oxide semiconductor film used as the conductive layer to increase oxygen vacancies and/or impurities such as hydrogen or water in the oxide semiconductor film, so that the oxide semiconductor film can have a high carrier density and low resistivity. Furthermore, an insulating film containing hydrogen is formed in contact with the oxide semiconductor film to diffuse hydrogen from the insulating film containing hydrogen to the oxide semiconductor film, so that the oxide semiconductor film can have a high carrier density and low resistivity. 
     The semiconductor layer that functions as the channel region of the transistor is not in contact with the insulating films containing hydrogen. With the use of an insulating film containing oxygen, in other words, an insulating film capable of releasing oxygen for at least one of the insulating films, oxygen can be supplied to the semiconductor layer. The semiconductor layer to which oxygen is supplied has high resistivity because oxygen vacancies in the film or at the interface are compensated. Note that as the insulating film capable of releasing oxygen, a silicon oxide film or a silicon oxynitride film can be used, for example. 
     In order to reduce the resistivity of the oxide semiconductor film, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, or the like can be employed to inject hydrogen, boron, phosphorus, or nitrogen into the oxide semiconductor film. 
     In order to reduce the resistivity of the oxide semiconductor film, plasma treatment may be performed on the oxide semiconductor film. For the plasma treatment, a gas containing at least one of a rare gas (He, Ne, Ar, Kr, or Xe), hydrogen, and nitrogen is typically used. Specifically, plasma treatment in an Ar atmosphere, plasma treatment in a mixed gas atmosphere of Ar and hydrogen, plasma treatment in an ammonia atmosphere, plasma treatment in a mixed gas atmosphere of Ar and ammonia, plasma treatment in a nitrogen atmosphere, or the like can be employed. 
     In the oxide semiconductor film subjected to the plasma treatment, an oxygen vacancy is formed in a lattice from which oxygen is released (or in a portion from which oxygen is released). This oxygen vacancy can cause carrier generation. When hydrogen is supplied from an insulating film that is in the vicinity of the oxide semiconductor film (specifically, an insulating film that is in contact with the lower surface or the upper surface of the oxide semiconductor film), and hydrogen is bonded to the oxygen vacancy, an electron serving as a carrier might be generated. 
     The oxide semiconductor film in which oxygen vacancies are compensated with oxygen and the hydrogen concentration is reduced can be referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film. Here, the term “substantially intrinsic” refers to a state where an oxide semiconductor film has a carrier density of lower than 8×10 11 /cm 3 , preferably lower than 1×10 11 /cm 3 , more preferably lower than 1×10 10 /cm 3 . A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has few carrier generation sources and can thus have a low carrier density. The highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states and can accordingly have a low density of trap states. 
     The highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has an extremely low off-state current; even when an element has a channel width of 1×10 6  μm and a channel length of 10 μm, the off-state current can be lower than or equal to the measurement limit of a semiconductor parameter analyzer, i.e., lower than or equal to 1×10 −13  A, at a voltage (drain voltage) between a source electrode and a drain electrode ranging from 1 V to 10 V. Accordingly, the transistor in which the channel region is formed in the semiconductor layer that is a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film can have a small variation in electrical characteristics and high reliability. 
     For example, an insulating film containing hydrogen, in other words, an insulating film capable of releasing hydrogen, typically, a silicon nitride film, is used as the insulating film in contact with the oxide semiconductor film used as the conductive layer, whereby hydrogen can be supplied to the conductive layer. The hydrogen concentration of the insulating film capable of releasing hydrogen is preferably higher than or equal to 1×10 22  atoms/cm 3 . Such an insulating film is formed in contact with the conductive layer, whereby hydrogen can be effectively contained in the conductive layer. In this manner, the resistivity of the oxide semiconductor film can be controlled by changing the structure of insulating films in contact with the semiconductor layer and the conductive layer. 
     Hydrogen contained in the oxide semiconductor film reacts with oxygen bonded to a metal atom to be water, and in addition, an oxygen vacancy is formed in a lattice from which oxygen is released (or in a portion from which oxygen is released). Due to entry of hydrogen into the oxygen vacancy, an electron serving as a carrier is generated in some cases. Furthermore, bonding of part of hydrogen to oxygen bonded to a metal atom causes generation of an electron serving as a carrier in some cases. Accordingly, the conductive layer formed in contact with the insulating film containing hydrogen is an oxide semiconductor film that has a higher carrier density than the semiconductor layer. 
     In the semiconductor layer where the channel region of the transistor is formed, it is preferable to reduce hydrogen as much as possible. Specifically, in the semiconductor layer, the hydrogen concentration which is measured by SIMS is set to lower than or equal to 2×10 20  atoms/cm 3 , preferably lower than or equal to 5×10 19  atoms/cm 3 , more preferably lower than or equal to 1×10 19  atoms/cm 3 , more preferably lower than 5×10 18  atoms/cm 3 , more preferably lower than or equal to 1×10 18  atoms/cm 3 , more preferably lower than or equal to 5×10 17  atoms/cm 3 , more preferably lower than or equal to 1×10 16  atoms/cm 3 . 
     The conductive layer is an oxide semiconductor film that has a higher hydrogen concentration and/or a larger number of oxygen vacancies (i.e., a lower resistivity) than the semiconductor layer. The hydrogen concentration in the conductive layer is higher than or equal to 8×10 19  atoms/cm 3 , preferably higher than or equal to 1×10 20  atoms/cm 3 , more preferably higher than or equal to 5×10 20  atoms/cm 3 . The hydrogen concentration in the conductive layer is greater than or equal to 2 times, preferably greater than or equal to 10 times the hydrogen concentration in the semiconductor layer. The resistivity of the conductive layer is preferably greater than or equal to 1×10 −8  times and less than 1×10 −1  times the resistivity of the semiconductor layer. The resistivity of the conductive layer is typically higher than or equal to 1×10 −3  Ω/cm and lower than 1×10 4  Ωcm, preferably higher than or equal to 1×10 −3  Ωcm and lower than 1×10 −1  Ωcm. 
     [Insulating Layer] 
     Examples of an insulating material that can be used for the insulating layers, the overcoat, the spacer, and the like include a resin such as acrylic or epoxy resin, a resin having a siloxane bond, and an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, or aluminum oxide. 
     [Adhesive Layer] 
     For the adhesive layers, a curable resin such as a heat curable resin, a photocurable resin, or a two-component type curable resin can be used. For example, an acrylic resin, a urethane resin, an epoxy resin, or a resin having a siloxane bond such as silicone can be used. 
     [Connection Layer] 
     As the connection layers, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like can be used. 
     [Coloring Layer] 
     As examples of a material that can be used for the coloring layers, a metal material, a resin material, and a resin material containing a pigment or dye can be given. 
     The above is the description of each of the components. 
     [Structural Example of Touch Sensor] 
     Next, a structure example of the touch sensor  22  which can be used for the touch panel module  10  of one embodiment of the present invention is described with reference to drawings. 
       FIG. 9A  is a schematic top view (schematic plan view) of part of the touch sensor  22 .  FIG. 9B  is an enlarged schematic top view of a region surrounded by dashed-dotted line in  FIG. 9A . 
     As shown in  FIGS. 9A and 9B , it is preferable that the conductive layer  23  be partly narrowed so that the width of a portion crossing the conductive layer  25  is small. Thus, the capacitance of the capacitor  11  can be reduced. In the case of using a self-capacitive touch sensor, the detection sensitivity can be increased more as the capacitance of the capacitor  11  is smaller. 
     Furthermore, between the conductive layer  23  and the conductive layer  24  which are adjacent to each other, a conductive layer  26  which is electrically insulated from these conductive layers  23  and  24  may be provided. The conductive layer  26  can suppress the formation of a thin portion of the touch sensor  22 . For example, in the case where the conductive layer  23  and the conductive layer  24  are formed over the same flat surface, the conductive layer  26  formed in a manner similar to that of the conductive layer  23  and the conductive layer  24  can increase coverage of a thin film formed after the formation of these conductive layers; thus, a surface can be planarized. Furthermore, owing to the uniform thickness of the touch sensor  22 , luminance unevenness of light emitted from the pixels through the touch sensor  22  can be reduced, so that the touch panel can achieve high display quality. 
       FIG. 9C  shows the case where the conductive layer  23  and the conductive layer  24  are formed over different flat surfaces and the conductive layer  25  is not provided. At this time, the conductive layer  26  may be formed over the flat surface over which the conductive layer  23  or the conductive layer  24  is formed, or may be formed over a flat surface different from the flat surface over which the conductive layer  23  or the conductive layer  24  is formed. Note that the conductive layer  26  is not necessarily provided if not necessary. 
       FIG. 10A  shows an example of a circuit diagram of the touch sensor  22  including a plurality of conductive layers  23  and a plurality of conductive layers  24 . In  FIG. 10A , six conductive layers  23  and six conductive layers  24  are shown for simplicity, but the number of the conductive layers  23  and the number of the conductive layers  24  are not limited thereto. 
     One capacitor  11  is formed between one of the conductive layers  23  and one of the conductive layers  24 . Therefore, capacitors  11  are arranged in a matrix. 
     In the case of a projected self-capacitive type, a pulse voltage is applied to each of the conductive layers  23  and  24  so that the conductive layers  23  and  24  are scanned, and the value of a current flowing in the conductive layer  23  or the conductive layer  24  at this time is sensed. The amount of current is changed when an object approaches, and therefore, positional information of the object can be obtained by sensing the difference between the values. In the case of a projected mutual-capacitive type, a pulse voltage is applied to one of the conductive layers  23  and  24  so that one of the conductive layers  23  and  24  is scanned, and a current flowing in the other is sensed to obtain positional information of the object. 
     Each of the conductive layers  23  and  24  preferably has a lattice shape or a mesh shape having a plurality of openings.  FIG. 10B  shows an example of a top surface shape of part of the conductive layer  23 . 
     The conductive layer  23  shown in  FIG. 10B  has a lattice shape in which a distance P 1  is provided in a lateral direction and a distance P 2  is provided in a longitudinal direction. The distance P 1  and the distance P 2  are almost the same in  FIG. 10B , but may be different from each other. For example, the distance P 2  in a longitudinal direction may be larger than the distance P 1  in a lateral direction as shown in  FIG. 10C , or the distance P 2  in a longitudinal direction may be smaller than the distance P 1  in a lateral direction. The same can be said for the conductive layer  24 . 
     The aperture ratio of the conductive layer  23  or the conductive layer  24  (the proportion of the opening area in the conductive layer  23  or the conductive layer  24  per unit area) is preferably higher than or equal to 20% and lower than 100%, more preferably higher than or equal to 30% and lower than 100%, still more preferably higher than or equal to 50% and lower than 100% in a region. 
     The aperture ratio can be easily calculated from the distance P 1 , the distance P 2 , and the width of the conductive layer. Alternatively, when a region R is assumed to be a periodic unit in  FIG. 10B , the aperture ratio can be calculated from the ratio of the area of the region R to the area of the conductive layer  23  included in the region R. Here, the region R is a periodic unit of a periodic pattern of the conductive layer  23 . By arranging regions R longitudinally and laterally in a periodic manner, the pattern of the conductive layer  23  can be formed. 
     In each of the conductive layer  23  and the conductive layer  24 , the line width of a lattice is preferably greater than or equal to 50 nm and less than or equal to 100 μm, more preferably greater than or equal to 1 μm and less than or equal to 50 μm, still more preferably greater than or equal to 1 μm and less than or equal to 20 μm. The lattice having such a narrow line width allows adjacent pixels to be close to each other in the case where the opening overlaps with the pixel as described later. Consequently, the touch panel can have higher resolution and higher aperture ratio. 
       FIG. 11A  is an enlarged schematic top view of a boundary portion between the conductive layer  23  and the conductive layer  24 . 
     Each of the conductive layers  23  and  24  preferably has a lattice shape (also referred to as a mesh shape). That is, each of the conductive layers  23  and  24  preferably has a plurality of openings (an opening  23   a  and an opening  24   a ). When the opening and the pixel are provided to overlap with each other as described later, light emitted from the display element in the pixel is not blocked by the conductive layer  23  and the conductive layer  24 , or a reduction in the luminance of light due to the transmission through the conductive layer  23  and the conductive layer  24  does not occur. As a result, the touch sensor  22  can be used in the touch panel without a reduction in the aperture ratio of the pixel and the light extraction efficiency. It is preferable that the conductive layer  25  similarly have a shape not overlapping with the pixel. 
     As shown in  FIG. 11A , an opening  22   a  surrounded by part of the conductive layer  23  and part of the conductive layer  24  may be formed in the boundary portion. Such a structure can significantly reduce the distance between the conductive layer  23  and the conductive layer  24  and can increase capacitance therebetween. In particular, in the case of using a mutual capacitive type, the distance between the two conductive layers is preferably reduced to increase capacitance therebetween. 
       FIG. 11B  is an enlarged schematic top view of an intersection of the conductive layers  23  and  24 . An example where the two adjacent conductive layers  24  are electrically connected to each other with the conductive layer  25  is shown here. Although not illustrated in the drawing, the insulating layer  121  is provided between the conductive layer  25  and the conductive layers  23  and  24 . The conductive layers  24  and  25  are electrically connected to each other through an opening provided in the insulating layer  121 . The conductive layers  23  and  25  partly overlap with each other with the insulating layer  121  provided therebetween. 
     [Arrangement Example of Opening of Conductive Layer and Pixel] 
       FIGS. 12A to 12G  are schematic views each showing the positional relationship between a pixel, sub-pixels included in the pixel, and the conductive layer  23  which are seen from the display surface side. Note that although the conductive layer  23  is shown in  FIGS. 12A to 12G  as an example, the same applies to the conductive layer  24  and the conductive layer  25 . 
     In the example shown in  FIG. 12A , the pixel  33  includes a sub-pixel  33 R, a sub-pixel  33 G, and a sub-pixel  33 B. For example, the sub-pixel  33 R, the sub-pixel  33 G, and the sub-pixel  33 B have a function of expressing red color, green color, and blue color, respectively. Note that the number and the colors of the sub-pixels included in the pixel  33  are not limited thereto. 
     The sub-pixels included in the pixel  33  each have a display element. The above-described reflective liquid crystal element can be used as the display element. Besides the reflective liquid crystal element, examples of the display element include light-emitting elements such as organic EL elements; transmissive or semi-transmissive liquid crystal elements; display elements (electronic ink) that perform display by an electrophoretic method, an electronic liquid powder (registered trademark) method, or the like; MEMS shutter display elements; and optical interference type MEMS display elements. The sub-pixel may have a transistor, a capacitor, a wiring that electrically connects the transistor and the capacitor, and the like in addition to the display element. 
     In the structure shown in  FIG. 12A , each of a plurality of openings in the conductive layer  23  is provided to overlap with the three sub-pixels, i.e., the sub-pixel  33 R, the sub-pixel  33 G, and the sub-pixel  33 B. In this manner, the opening in the conductive layer  23  is preferably provided to overlap with one sub-pixel. 
     As shown in  FIG. 12A , it is preferable that there is no gap between the conductive layer  23  and each sub-pixel because light leakage from the sub-pixels can be suppressed. For example, the conductive layer  23  is provided to overlap with an end portion of the coloring layer of a sub-pixel or an end portion of a pixel electrode; thus, the conductive layer  23  can be provided so that such a gap is not formed. Furthermore, with such a structure, a surface area of the conductive layer  23  can be increased, so that wiring resistance of the conductive layer  23  can be reduced and the detection sensitivity can be increased. 
       FIG. 12B  illustrates a structure where the conductive layer  23  is provided between two adjacent sub-pixels exhibiting different colors. Since color mixture does not occur between two adjacent sub-pixels exhibiting the same color, a structure including a portion where the conductive layer  23  is not provided therebetween as illustrated in  FIG. 12B  may be employed. 
       FIGS. 12C and 12D  each show an example where the pixel  33  further includes a sub-pixel  33 Y in the structure shown in  FIGS. 12A and 12B . For example, a pixel capable of expressing yellow color can be used for the sub-pixel  33 Y. Instead of the sub-pixel  33 Y, a pixel capable of expressing white color may be used. When the pixel  33  includes sub-pixels of more than three colors, power consumption can be reduced. 
     In the examples shown in  FIGS. 12A to 12D , sub-pixels of each color are arranged in a stripe pattern. Alternatively, as shown in  FIG. 12E , sub-pixels of two colors may be alternated in one direction, for example. 
     Furthermore, the sub-pixels included in the pixel  33  may differ in size (e.g., the area of a region contributing to display). For example, the size of the sub-pixel of blue color with a relatively low luminosity factor can be set large, whereas the size of the sub-pixel of green or red color with a relatively high luminosity factor can be set small. 
       FIGS. 12F and 12G  each show an example where the size of the sub-pixel  33 B is larger than the size of the sub-pixel  33 R and the size of the sub-pixel  33 G. In the examples shown here, the sub-pixel  33 R and the sub-pixel  33 G are alternated. However, sub-pixels of each color may be arranged in a stripe pattern as shown in  FIG. 12A  and other drawings, and may have different sizes from each other. 
     Note that although the positional relationship between the conductive layer  23  and the sub-pixels is described here, the same applies to the conductive layer  24  and the conductive layer  25 . That is, in the touch panel of one embodiment of the present invention, the opening  23   a  in the conductive layer  23  overlaps with one or more sub-pixels in a region and the opening  24   a  in the conductive layer  24  overlaps with one or more of the other sub-pixels in a region. Since each sub-pixel includes the display element as described above, it can be said that the opening  23   a  and the opening  24   a  each have a region overlapping with one or more display elements. 
     At least part of this embodiment can be implemented in combination with any of the embodiments described in this specification as appropriate. 
     Embodiment 2 
     In this embodiment, examples of a driving method of an input device or an input/output device of one embodiment of the present invention are described with reference to drawings. 
     [Example of Sensing Method of Sensor] 
       FIG. 13A  is a block diagram illustrating the structure of a mutual capacitive touch sensor.  FIG. 13A  illustrates a pulse voltage output circuit  601  and a current sensing circuit  602 . Note that in  FIG. 13A , six wirings X 1  to X 6  represent electrodes  621  to which a pulse voltage is applied, and six wirings Y 1  to Y 6  represent electrodes  622  that sense changes in current.  FIG. 13A  also illustrates a capacitor  603  that is formed where electrodes  621  and  622  overlap with each other. Note that functional replacement between the electrodes  621  and  622  is possible. 
     The pulse voltage output circuit  601  is a circuit for sequentially applying a pulse voltage to the wirings X 1  to X 6 . By application of a pulse voltage to the wirings X 1  to X 6 , an electric field is generated between the electrodes  621  and  622  of the capacitor  603 . When the electric field between the electrodes is shielded, for example, a change occurs in mutual capacitance of the capacitor  603 . The approach or contact of an object can be sensed by utilizing this change. 
     The current sensing circuit  602  is a circuit for sensing changes in current flowing through the wirings Y 1  to Y 6  that are caused by the change in capacitance in the capacitor  603 . No change in current value is sensed in the wirings Y 1  to Y 6  when there is no approach or contact of an object, whereas a decrease in current value is sensed when capacitance is decreased owing to the approach or contact of an object. Note that an integrator circuit or the like is used for sensing of current values. 
       FIG. 13B  is a timing chart showing input and output waveforms in the mutual capacitive touch sensor illustrated in  FIG. 13A . In  FIG. 13B , detection of an object is performed in all the rows and columns in one frame period.  FIG. 13B  shows a period when an object is not detected (not touched) and a period when an object is detected (touched). Sensed current values of the wirings Y 1  to Y 6  are shown as waveforms of voltage values. 
     A pulse voltage is sequentially applied to the wirings X 1  to X 6 , and waveforms of the wirings Y 1  to Y 6  change in accordance with the pulse voltage. When there is no proximity or contact of an object, the waveforms of the wirings Y 1  to Y 6  change in accordance with changes in the voltages of the wirings X 1  to X 6 . The current value is decreased at the point of approach or contact of the object and accordingly the waveform of the voltage value changes. 
     By sensing a change in mutual capacitance in this manner, proximity or contact of an object can be sensed. 
     It is preferable that the pulse voltage output circuit  601  and the current sensing circuit  602  be mounted on a substrate in a housing of an electronic appliance or on the touch panel in the form of an IC. In the case where the touch panel has flexibility, parasitic capacitance might be increased in a bent portion of the touch panel, and the influence of noise might be increased. In view of this, it is preferable to use an IC to which a driving method less influenced by noise is applied. For example, it is preferable to use an IC to which a driving method capable of increasing a signal-noise ratio (SN ratio) is applied. 
     Although  FIG. 13A  is a passive matrix type touch sensor in which only the capacitor  603  is provided at the intersection portion of wirings as a touch sensor, an active matrix type touch sensor including a transistor and a capacitor may be used.  FIG. 14  is a sensor circuit included in an active matrix type touch sensor. 
     The sensor circuit includes the capacitor  603  and transistors  611 ,  612 , and  613 . A signal G 2  is input to a gate of the transistor  613 . A voltage VRES is applied to one of a source and a drain of the transistor  613 , and one electrode of the capacitor  603  and a gate of the transistor  611  are electrically connected to the other of the source and the drain of the transistor  613 . One of a source and a drain of the transistor  611  is electrically connected to one of a source and a drain of the transistor  612 , and a voltage VSS is applied to the other of the source and the drain of the transistor  611 . A signal G 1  is input to a gate of the transistor  612 , and a wiring ML is electrically connected to the other of the source and the drain of the transistor  612 . The voltage VSS is applied to the other electrode of the capacitor  603 . 
     Next, the operation of the sensor circuit will be described. First, a potential for turning on the transistor  613  is supplied as the signal G 2 , and a potential with respect to the voltage VRES is thus applied to the node n connected to the gate of the transistor  611 . Then, a potential for turning off the transistor  613  is applied as the signal G 2 , whereby the potential of the node n is maintained. 
     Then, capacitance of the capacitor  603  changes owing to the approach or contact of an object such as a finger, and accordingly the potential of the node n is changed from VRES. 
     In reading operation, a potential for turning on the transistor  612  is supplied as the signal G 1 . A current flowing through the transistor  611 , that is, a current flowing through the wiring ML is changed in accordance with the potential of the node n. By sensing this current, the approach or contact of an object can be detected. 
     It is preferable that the transistors  611 ,  612 , and  613  each include an oxide semiconductor in a semiconductor layer where a channel is formed. In particular, such a transistor is preferably used as the transistor  613  so that the potential of the node n can be held for a long time and the frequency of operation of resupplying VRES to the node n (refresh operation) can be reduced. 
     [Structure Example of in-Cell Touch Panel] 
     Although the examples where the electrodes in the touch sensor are formed over a substrate different from a substrate where the display element and the like are provided are described above, one or both of the pair of electrodes in the touch sensor may be formed over the substrate where the display element and the like are provided. 
     A structure example of a touch panel incorporating the touch sensor into a display portion including a plurality of pixels is described below. Here, an example where a liquid crystal element is used as a display element provided in the pixel is shown. 
       FIG. 15A  is an equivalent circuit diagram of part of a pixel circuit provided in the display portion of the touch panel in this structure example. 
     Each pixel includes at least a transistor  3503  and a liquid crystal element  3504 . In addition, a gate of the transistor  3503  is electrically connected to a wiring  3501 , and one of a source and a drain of the transistor  3503  is electrically connected to a wiring  3502 . 
     The pixel circuit includes a plurality of wirings extending in the X direction (e.g., a wiring  3510 _ 1  and a wiring  3510 _ 2 ) and a plurality of wirings extending in the Y direction (e.g., a wiring  3511 ). These wirings are provided to intersect with each other, and capacitance is formed therebetween. 
     Among the pixels provided in the pixel circuit, electrodes on one side of the liquid crystal elements of some pixels adjacent to each other are electrically connected to each other to form one block. The block is classified into two types: an island-shaped block (e.g., a block  3515 _ 1  or a block  3515 _ 2 ) and a linear block (e.g., a block  3516 ) extending in the Y direction. Note that only part of the pixel circuit is illustrated in  FIGS. 15A and 15B , but actually, these two kinds of blocks are repeatedly arranged in the X direction and the Y direction. 
     The wiring  3510 _ 1  (or the wiring  3510 _ 2 ) extending in the X direction is electrically connected to the island-shaped block  3515 _ 1  (or the block  3515 _ 2 ). Although not illustrated, the wiring  3510 _ 1  extending in the X direction is electrically connected to a plurality of island-shaped blocks  3515 _ 1  which are provided discontinuously along the X direction with the linear blocks therebetween. Furthermore, the wiring  3511  extending in the Y direction is electrically connected to the linear block  3516 . 
       FIG. 15B  is an equivalent circuit diagram illustrating the connection between a plurality of wirings  3510  extending in the X direction and the plurality of wirings  3511  extending in the Y direction. An input voltage or a common potential can be input to each of the wirings  3510  extending in the X direction. Furthermore, a ground potential can be input to each of the wirings  3511  extending in the Y direction, or the wirings  3511  can be electrically connected to the sensing circuit. 
     Operation of the above-described touch panel is described with reference to  FIGS. 16A and 16B . 
     Here, one frame period is divided into a writing period and a sensing period. The writing period is a period in which image data is written to a pixel, and the wirings  3501  (also referred to as gate lines or scan lines) illustrated in  FIG. 15A  are sequentially selected. On the other hand, the sensing period is a period in which sensing is performed by a touch sensor, and the wirings  3510  extending in the X direction are sequentially selected and an input voltage is input. 
       FIG. 16A  is an equivalent circuit diagram in the writing period. In the writing period, a common potential is input to both the wiring  3510  extending in the X direction and the wiring  3511  extending in the Y direction. 
       FIG. 16B  is an equivalent circuit diagram at a certain point of time in the sensing period. In the sensing period, each of the wirings  3511  extending in the Y direction is electrically connected to the sensing circuit. An input voltage is input to the wirings  3510  extending in the X direction which are selected, and a common potential is input to the wirings  3510  extending in the X direction which are not selected. 
     Note that the driving method described here can be applied to not only an in-cell touch panel but also the above-described touch panels, and can be used in combination with the method described in the driving method example. 
     It is preferable that a period in which an image is written and a period in which sensing is performed by a touch sensor be separately provided as described above. Thus, a decrease in sensitivity of the touch sensor caused by noise generated when data is written to a pixel can be suppressed. 
     At least part of this embodiment can be implemented in combination with any of the other embodiments described in this specification as appropriate. 
     Embodiment 3 
     In this embodiment, a display module and electronic devices that include the display device of one embodiment of the present invention or a display system will be described with reference to  FIG. 17  and  FIGS. 18A to 18H . 
     In a display module  8000  illustrated in  FIG. 17 , a touch panel  8004  connected to an FPC  8003 , a frame  8009 , a printed board  8010 , and a battery  8011  are provided between an upper cover  8001  and a lower cover  8002 . 
     The touch panel module of one embodiment of the present invention can be used for, for example, the touch panel  8004 . 
     The shapes and sizes of the upper cover  8001  and the lower cover  8002  can be changed as appropriate in accordance with the size of the touch panel  8004 . 
     The touch panel  8004  can be a resistive touch panel or a capacitive touch panel and may be formed so as to overlap with a display panel. Alternatively, a counter substrate (sealing substrate) of the touch panel  8004  can have a touch panel function. Further alternatively, a photosensor may be provided in each pixel of the touch panel  8004  to form an optical touch panel. 
     In the case of a transmissive liquid crystal element, a backlight  8007  may be provided as illustrated in  FIG. 17 . The backlight  8007  includes a light source  8008 . Although the light source  8008  is provided over the backlight  8007  in  FIG. 17 , one embodiment of the present invention is not limited to this structure. For example, a structure in which the light source  8008  is provided at an end portion of the backlight  8007  and a light diffusion plate is further provided may be employed. Note that the backlight  8007  need not be provided in the case where a self-luminous light-emitting element such as an organic EL element is used or in the case where a reflective panel or the like is employed. 
     The frame  8009  protects the display panel  8006  and functions as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed board  8010 . The frame  8009  can also function as a radiator plate. 
     The printed board  8010  is provided with a power supply circuit and a signal processing circuit for outputting a video signal and a clock signal. As a power source for supplying power to the power supply circuit, an external commercial power source or a power source using the battery  8011  provided separately may be used. The battery  8011  can be omitted in the case of using a commercial power source. 
     The display module  8000  may be additionally provided with a component such as a polarizing plate, a retardation plate, or a prism sheet. 
       FIGS. 18A to 18H  illustrate electronic devices. These electronic devices can include a housing  5000 , a display portion  5001 , a speaker  5003 , an LED lamp  5004 , operation keys  5005  (including a power switch or an operation switch), a connection terminal  5006 , a sensor  5007  (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), a microphone  5008 , and the like. 
       FIG. 18A  illustrates a mobile computer, which can include a switch  5009 , an infrared port  5010 , and the like in addition to the above components.  FIG. 18B  illustrates a portable image reproducing device provided with a recording medium (e.g., a DVD reproducing device), which can include a second display portion  5002 , a recording medium read portion  5011 , and the like in addition to the above components.  FIG. 18C  illustrates a goggle-type display, which can include the second display portion  5002 , a support  5012 , an earphone  5013 , and the like in addition to the above components.  FIG. 18D  illustrates a portable game machine, which can include the recording medium read portion  5011  and the like in addition to the above components.  FIG. 18E  illustrates a digital camera which has a television reception function and can include an antenna  5014 , a shutter button  5015 , an imaging portion  5016 , and the like in addition to the above components.  FIG. 18F  illustrates a portable game machine, which can include the second display portion  5002 , the recording medium read portion  5011 , and the like in addition to the above components.  FIG. 18G  illustrates a portable television receiver, which can include a charger  5017  capable of transmitting and receiving signals, and the like in addition to the above components.  FIG. 18H  illustrates a wrist-watch-type information terminal, which can include a band  5018 , a clasp  5019 , and the like in addition to the above components. The display portion  5001  mounted in the housing  5000  serving as a bezel includes a non-rectangular display region. The display portion  5001  can display an icon  5020  indicating time, another icon  5021 , and the like. 
     The electronic devices illustrated in  FIGS. 18A to 18H  can have a variety of functions, for example, a function of displaying a variety of information (e.g., a still image, a moving image, and a text image) on a display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of controlling processing with a variety of software (programs), a wireless communication function, a function of being connected to a variety of computer networks with a wireless communication function, a function of transmitting and receiving a variety of data with a wireless communication function, and a function of reading a program or data stored in a recording medium and displaying the program or data on a display portion. Furthermore, the electronic device including a plurality of display portions can have a function of displaying image information mainly on one display portion while displaying text information mainly on another display portion, a function of displaying a three-dimensional image by displaying images where parallax is considered on a plurality of display portions, or the like. Furthermore, the electronic device including an imaging portion can have a function of photographing a still image, a function of photographing a moving image, a function of automatically or manually correcting a photographed image, a function of storing a photographed image in a recording medium (an external recording medium or a recording medium incorporated in a camera), a function of displaying a photographed image on the display portion, or the like. Note that functions that can be provided for the electronic devices illustrated in  FIGS. 18A to 18H  are not limited to the above, and the electronic devices can have a variety of functions. 
     The electronic devices described in this embodiment are characterized by including a display portion for displaying some sort of information. The display device described in the above embodiment can be employed for the display portion. 
     At least part of this embodiment can be implemented in combination with any of the other embodiments described in this specification as appropriate. 
     This application is based on Japanese Patent Application serial no. 2015-053631 filed with Japan Patent Office on Mar. 17, 2015, the entire contents of which are hereby incorporated by reference.