US20180145096A1 - Display device and electronic device - Google Patents

Abstract

A liquid crystal display device with high aperture ratio is provided. The liquid crystal display device includes a first conductive layer, a second conductive layer, and a liquid crystal element where a liquid crystal layer is positioned between a third conductive layer and a fourth conductive layer. The first to fourth conductive layers transmit visible light and include a region where the first to fourth conductive layers overlap with each other. The second conductive layer is positioned between the first conductive layer and the third conductive layer. An insulating layer is positioned between the first conductive layer and the second conductive layer. An insulating layer is positioned between the second conductive layer and the third conductive layer. Therefore, two capacitors each including the second conductive layer as an electrode are stacked. The two capacitors transmit light and overlap with the liquid crystal element; thus, aperture ratio can be increased.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention
• One embodiment of the present invention relates to a liquid crystal display device and an electronic device.
• Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention include a semiconductor device, a display device, a light-emitting device, a power storage device, a storage device, an electronic device, a lighting device, an input device (e.g., a touch sensor), an input/output device (e.g., a touch panel), a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
• In recent years, attention has been drawn to a technique in which, instead of a silicon semiconductor, a metal oxide exhibiting semiconductor characteristics is used for transistors. For example, Patent Documents 1 and 2 disclose techniques in which a transistor is manufactured using zinc oxide or an In-Ga-Zn-based oxide as a metal oxide and the transistor is used as a switching element or the like of a pixel of a display device.
REFERENCESPatent Documents
• Patent Document 1: Japanese Published Patent Application No. 2007-123861
• Patent Document 2: Japanese Published Patent Application No. 2007-096055
SUMMARY OF THE INVENTION
• A display device that includes a liquid crystal element or a light-emitting element can display a high-resolution image when the number of pixels per unit area is increased. In the case of an active display element, a pixel needs to include a display element, a transistor, a capacitor, a wiring, and the like.
• When the number of pixels per unit area is increased, area occupied by components that do not transmit light is relatively large in the pixel. That is, aperture ratio is decreased. Thus, in a transmissive liquid crystal element or the like, the light intensity of a backlight needs to be increased to display a clear image, and power consumption is increased.
• In addition, when pixel area is significantly decreased, it becomes difficult to design a horizontal electric field-mode liquid crystal element where a comb-shape electrode is positioned in a horizontal direction. Thus, it also becomes difficult to increase a manufacturing yield.
• An object of one embodiment of the present invention is to provide a liquid crystal display device with high aperture ratio. Another object of one embodiment of the present invention is to provide a low-power liquid crystal display device. Another object of one embodiment of the present invention is to provide a high-resolution liquid crystal display device. Another object of one embodiment of the present invention is to provide a highly reliable liquid crystal display device.
• The description of these objects does not disturb the existence of other objects. One embodiment of the present invention does not necessarily achieve all the objects. Other objects can be derived from the description of the specification, the drawings, and the claims.
• One embodiment of the present invention relates to a liquid crystal display device that includes a capacitor transmitting visible light.
• One embodiment of the present invention is a display device that includes a first conductive layer, a second conductive layer, and a liquid crystal element. The first conductive layer is a region where a source electrode or a drain electrode of a transistor extends. The liquid crystal element includes a third conductive layer, a liquid crystal layer, and a fourth conductive layer. The liquid crystal layer is positioned between the third conductive layer and the fourth conductive layer. The first to fourth conductive layers transmit visible light. The first to fourth conductive layers include a region where the first to fourth conductive layers overlap with each other. The second conductive layer is positioned between the first conductive layer and the third conductive layer. A first insulating layer is positioned between the first conductive layer and the second conductive layer. A second insulating layer is positioned between the second conductive layer and the third conductive layer. The second conductive layer includes a first opening portion. The first insulating layer and the second insulating layer include a second opening portion. The second opening portion is positioned inside the first opening portion. The third conductive layer is electrically connected to the first conductive layer through the second opening portion.
• Another embodiment of the present invention is a display device that includes a first conductive layer, a second conductive layer, and a liquid crystal element. The first conductive layer is a region where a semiconductor layer of a transistor extends. The liquid crystal element includes a third conductive layer, a liquid crystal layer, and a fourth conductive layer. The liquid crystal layer is positioned between the third conductive layer and the fourth conductive layer. The first to fourth conductive layers transmit visible light. The first to fourth conductive layers include a region where the first to fourth conductive layers overlap with each other. The second conductive layer is positioned between the first conductive layer and the third conductive layer. A first insulating layer is positioned between the first conductive layer and the second conductive layer. A second insulating layer is positioned between the second conductive layer and the third conductive layer. The second conductive layer includes a first opening portion. The first insulating layer and the second insulating layer include a second opening portion. The second opening portion is positioned inside the first opening portion. The third conductive layer is electrically connected to the first conductive layer through the second opening portion.
• The second conductive layer is a common electrode. The first conductive layer, the second conductive layer, and the first insulating layer can function as a first capacitor. The second conductive layer, the third conductive layer, and the second insulating layer can function as a second capacitor.
• The first to fourth conductive layers can each include a metal oxide.
• The transistor includes a fifth conductive layer functioning as a gate electrode. The fifth conductive layer may include a metal oxide that transmits visible light.
• The fifth conductive layer may include a region overlapping with the first to fourth conductive layers.
• The transistor preferably includes a metal oxide in a semiconductor layer where a channel is formed.
• Note that in this specification, in some cases, the display device includes any of the following modules in its category: a module in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is attached to a display portion; a module in which a printed wiring board is provided on the tip of a TCP; and a module having an integrated circuit (IC) directly mounted by chip on glass (COG) on a substrate over which a display element is formed.
• One embodiment of the present invention can provide a liquid crystal display device with high aperture ratio. One embodiment of the present invention can provide a low-power liquid crystal display device. One embodiment of the present invention can provide a high-resolution liquid crystal display device. One embodiment of the present invention can provide a highly reliable liquid crystal display device.
• Note that the description of these effects does not disturb the existence of other effects. One embodiment of the present invention does not necessarily achieve all the effects. Other effects can be derived from the description of the specification, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the accompanying drawings:
• FIG. 1 is a perspective view illustrating a pixel;
• FIG. 2 is a perspective view illustrating the pixel;
• FIGS. 3A to 3C are a top view and cross-sectional views illustrating the pixel;
• FIGS. 4A and 4B are perspective views illustrating a pixel;
• FIGS. 5A to 5C are a top view and cross-sectional views illustrating the pixel;
• FIG. 6 is a perspective view illustrating a pixel;
• FIG. 7 is a perspective view illustrating the pixel;
• FIGS. 8A to 8C are a top view and cross-sectional views illustrating the pixel;
• FIG. 9 is a perspective view illustrating a pixel;
• FIG. 10 is a perspective view illustrating the pixel;
• FIGS. 11A to 11C are a top view and cross-sectional views illustrating the pixel;
• FIGS. 12A and 12B are top views illustrating the pixels;
• FIG. 13 is a perspective view illustrating a display device;
• FIGS. 14A and 14B are perspective views illustrating a touch panel and an input device;
• FIGS. 15A and 15B are cross-sectional views illustrating the display device;
• FIGS. 16A and 16B are cross-sectional views illustrating the display device;
• FIGS. 17A and 17B are cross-sectional views illustrating the display device;
• FIG. 18 illustrates pixel layout;
• FIGS. 19A to 19C illustrate examples of an operation mode; and
• FIGS. 20A to 20F each illustrate an example of an electronic device.
DETAILED DESCRIPTION OF THE INVENTION
• Embodiments will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description. It will be readily appreciated by those skilled in the art that modes and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. The present invention therefore should not be construed as being limited to the following description of the embodiments.
• In structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and the description thereof is not repeated. The same hatching pattern is applied to portions having similar functions, and the portions are not particularly denoted by reference numerals in some cases.
• The position, size, range, or the like of each component illustrated in the drawings is not accurately represented in some cases for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like disclosed in the drawings.
• The terms “film” and “layer” can be interchanged with each other depending on circumstances or conditions. For example, the term “conductive layer” can be changed into the term “conductive film.” The term “insulating film” can be changed into the term “insulating layer,” for example.
• In this specification and the like, a metal oxide means an oxide of metal in a broad sense. A metal oxide is classified into an oxide insulator, an oxide conductor (including a transparent oxide conductor), an oxide semiconductor (also simply referred to as an OS), and the like. For example, a metal oxide used for a semiconductor layer of a transistor is called an oxide semiconductor in some cases. That is, an OS transistor is a transistor including a metal oxide or an oxide semiconductor.
• In this specification and the like, a metal oxide including nitrogen is also called a metal oxide in some cases. Moreover, a metal oxide including nitrogen may be called a metal oxynitride.
Embodiment 1
• In this embodiment, a display device in one embodiment of the present invention is described.
• The display device in one embodiment of the present invention includes a first conductive layer, a second conductive layer, and a liquid crystal element. In the liquid crystal element, a liquid crystal layer is positioned between a third conductive layer and a fourth conductive layer.
• The first to fourth conductive layers transmit visible light and include a region where the first to fourth conductive layers overlap with each other. The second conductive layer is positioned between the first conductive layer and the third conductive layer.
• An insulating layer is positioned between the first conductive layer and the second conductive layer. An insulating layer is positioned between the second conductive layer and the third conductive layer. Therefore, two capacitors each including the second conductive layer as an electrode are stacked.
• The two capacitors transmit light and overlap with the liquid crystal element; thus, aperture ratio can be increased and the power consumption of the display device can be reduced. In addition, the display device can have higher resolution.
• FIG. 1 is a perspective view illustrating main components provided in a pixel of a liquid crystal display device in one embodiment of the present invention.FIG. 2 is a development view of the perspective view in a vertical direction. Note thatFIG. 1 andFIG. 2 do not illustrate insulating layers and the like for clarity.
• Apixel10aincludes awiring31, awiring32, atransistor21, aconductive layer42, and aconductive layer43.
• Here, thewiring31 functions as a scan line. Thewiring32 functions as a signal line. Thewirings31 and32 each preferably include a low-resistance metal layer to prevent signal delay.
• Part of thewiring31 and a region where thewiring31 extends function as a gate of thetransistor21. Characteristics of thetransistor21 might be varied by irradiation with light depending on a material used for a channel region of thetransistor21. The use of a metal layer with a high light-blocking property for thewiring31 can suppress irradiation of the channel region with light such as external light or light from a backlight. Thus, the reliability of thetransistor21 can be increased.
• Thetransistor21 is a bottom-gate transistor, which includes asemiconductor layer25, aconductive layer41a, and aconductive layer41b.
• Theconductive layer41afunctions as one of a source and a drain. Theconductive layer41ais electrically connected to thewiring32.
• Theconductive layer41bfunctions as the other of the source and the drain. In addition, theconductive layer41bfunctions as one electrode or the other electrode of a capacitor.
• Theconductive layer42 functions as one electrode or the other electrode of a capacitor. In addition, theconductive layer42 is a common electrode, which also functions as a capacitor line.
• Theconductive layer43 functions as a pixel electrode of a liquid crystal element. In addition, theconductive layer43 functions as one electrode or the other electrode of a capacitor.
• Theconductive layer42 includes an openingportion42b. In addition, in the openingportion42b, theconductive layer41bis electrically connected to theconductive layer43.
• A first insulating layer (not illustrated inFIG. 1 andFIG. 2) is positioned between theconductive layers41band42. Thus, it is possible to form acapacitor26 that includes theconductive layers41band42 as electrodes and the first insulating layer as a dielectric.
• A second insulating layer (not illustrated inFIG. 1 andFIG. 2) is positioned between theconductive layers42 and43. Thus, it is possible to form acapacitor27 that includes theconductive layers42 and43 as electrodes and the second insulating layer as a dielectric.
• FIG. 3A is a top view of thepixel10a. As illustrated inFIG. 3A, theconductive layers41b,42, and43 are positioned to include a region where theconductive layers41b,42, and43 overlap with each other in a region excluding thewirings31 and32.
• Here, in one embodiment of the present invention, theconductive layers41b,42, and43, the first insulating layer, and the second insulating layer are each formed using a material that transmits visible light. Thus, a region where theconductive layer43 that also functions as the pixel electrode of the liquid crystal element, thecapacitor26, and thecapacitor27 overlap with each other transmits light. Consequently, the aperture ratio of thepixel10acan be increased.
• FIG. 3B is a cross-sectional view that corresponds to a cross section taken along a line segment A1-A2 inFIG. 3A.FIG. 3C is a cross-sectional view that corresponds to a cross section taken along a line segment A3-A4 inFIG. 3A. Note thatFIGS. 3B and 3C illustrate cross sections of asubstrate71, asubstrate72, aliquid crystal element75, acoloring layer65, a light-blockinglayer66, and the like that are not illustrated inFIG. 2.
• Theliquid crystal element75 is a transmissive liquid crystal element and operates in a vertical electric field mode. Theliquid crystal element75 can include theconductive layer43, analignment film61, aliquid crystal layer63, analignment film62, and aconductive layer64.
• An insulating layer is positioned between components as needed. An insulatinglayer51 positioned between thewiring31 and thesemiconductor layer25 functions as a gate insulating film of thetransistor21. An insulatinglayer52 and an insulatinglayer53 provided over theconductive layer41bfunction as a protective film and a planarization film, respectively. In addition, an insulatinglayer55 that is positioned between thecoloring layer65 and the light-blockinglayer66, and the common electrode functions as a protective film and a planarization film. Note that the insulating layers are just examples, and other insulating layers may be provided. Alternatively, it may be possible not to provide some of the insulating layers.
• Here, a region where theconductive layer41b, the insulatinglayer52, the insulatinglayer53, and theconductive layer42 overlap with each other functions as thecapacitor26. A region where theconductive layer42, an insulatinglayer54, and theconductive layer43 overlap with each other functions as thecapacitor27. In other words, the liquid crystal display device in one embodiment of the present invention includes stacked capacitors where one electrode is used common.
• When the number of pixels per unit area is increased, pixel area is inevitably decreased; thus, the capacitance of a capacitor formed in a pixel is decreased. Thus, a reduction of a function of holding an image signal occurs. In one embodiment of the present invention, a region where thecapacitors26 and27 overlap with each other is provided as a stacked structure; however, thecapacitors26 and27 are connected to each other in parallel because one electrode is used common. Consequently, the capacitance can be increased compared to the case where one of the capacitors is provided, so that the reduction of the function of holding an image signal can be suppressed.
• Furthermore, thecapacitor26 that includes theconductive layers41band42 and thecapacitor27 that includes theconductive layers42 and43 transmit visible light.
• Thus, when the light from the backlight is delivered from thesubstrate71 side, the light is emitted in a direction indicated by dashed arrows. The light from the backlight also penetrates the openingportion42b.
• As illustrated inFIGS. 3B and 3C, the light from the backlight may be emitted to the outside through thecoloring layer65. When the light from the backlight is emitted through thecoloring layer65, the light can be colored with a desired color. The color of thecoloring layer65 can be selected from red (R), green (G), blue (B), cyan (C), magenta (M), yellow (Y), or the like. Note that the light from the backlight may be delivered from thesubstrate72 side.
• As described above, the use of the structure in one embodiment of the present invention can provide a liquid crystal display device with high aperture ratio. Therefore, a clear image can be displayed without an increase in the intensity of the light from the backlight, and the power consumption of the liquid crystal display device can be reduced.
• The liquid crystal display device in one embodiment of the present invention may include apixel10billustrated in a perspective view ofFIG. 4A.
• FIG. 4B is a perspective view illustrating thetransistor21 and thewiring31 in thepixel10b. Thepixel10bdiffers from thepixel10ain the structure of a conductive layer functioning as the gate of thetransistor21.
• In thepixel10a, the region where thewiring31 extends is used as the gate, whereas in thepixel10b, aconductive layer33 that transmits visible light is used as the gate. Therefore, the area of thewiring31 that blocks light can be reduced.
• FIG. 5A is a top view of thepixel10b.FIG. 5B is a cross-sectional view that corresponds to a cross section taken along a line segment B1-B2 inFIG. 5A.FIG. 5C is a cross-sectional view that corresponds to a cross section taken along a line segment B3-B4 inFIG. 5A.
• In thepixel10b, a region where theconductive layer33 and other components overlap with each other also transmits light in a region excluding thewirings31 and32. For example, a contact portion of thesemiconductor layer25 of thetransistor21 and theconductive layer41band a channel portion of thetransistor21 can transmit light. Accordingly, the aperture ratio of thepixel10bcan be higher than that of thepixel10a. Note that thesemiconductor layer25 of thetransistor21 can be formed using a material that transmits visible light, regardless of a pixel structure.
• Note thatFIGS. 4A and 4B andFIG. 5A illustrate a structure where electrical connection is established by formation of thewiring31 over theconductive layer33; however, theconductive layer33 may be formed over thewiring31.
• Furthermore, the liquid crystal display device in one embodiment of the present invention may include apixel10cillustrated in perspective views ofFIG. 6 andFIG. 7. Thepixel10chas a structure similar to those of thepixels10aand10bexcept for a transistor structure.
• Thepixel10cincludes a self-aligned top-gate transistor. Atransistor22 includes thesemiconductor layer25, theconductive layer41a, theconductive layer41b, and aconductive layer34.
• Theconductive layer41afunctions as one of a source and a drain. Theconductive layer41bfunctions as the other of the source and the drain. In addition, theconductive layer41bfunctions as one electrode or the other electrode of a capacitor. Theconductive layer34 functions as a gate.
• FIG. 8A is a top view of thepixel10c.FIG. 8B is a cross-sectional view that corresponds to a cross section taken along a line segment C1-C2 inFIG. 8A.FIG. 8C is a cross-sectional view that corresponds to a cross section taken along a line segment C3-C4 inFIG. 8A.
• In thepixel10c, a region where thesemiconductor layer25 and other components overlap with each other also transmits light in a region excluding thewirings31 and32 and theconductive layer34. Accordingly, the aperture ratio can be increased. Note that although theconductive layer34 can be formed using a low-resistance material such as metal, theconductive layer34 may be replaced with theconductive layer34bthat transmits visible light, as illustrated inFIG. 12A. This structure can further increase the aperture ratio.
• Note that as illustrated inFIG. 8B, in the case of a top-gate transistor, it is preferable to provide an insulatinglayer56 between thesubstrate71 and thesemiconductor layer25. The shielding effect of the insulatinglayer56 can prevent diffusion of an impurity from thesubstrate71 to thesemiconductor layer25. In addition, when an oxide semiconductor is used for thesemiconductor layer25, excess oxygen in the insulatinglayer56 and aprotective film57 can fill oxygen vacancies in thesemiconductor layer25, so that the reliability of the transistor can be increased.
• Furthermore, the liquid crystal display device in one embodiment of the present invention may include apixel10dinFIG. 9 andFIG. 10. Thepixel10dhas a structure similar to that of thepixel10cexcept that thesemiconductor layer25 has a different shape and that theconductive layers41aand41bare not included.
• In thetransistor22, thesemiconductor layer25 includes aregion25bthat functions as one of a source and a drain and aregion25cthat functions as the other of the source and the drain.
• In thetransistor22 included in thepixel10c, theconductive layer41athat functions as one of the source and the drain is connected to theregion25b. In contrast, in thetransistor22 included in thepixel10d, theregion25bis directly connected to thewiring32.
• Furthermore, in thetransistor22 included in thepixel10c, theconductive layer41bthat functions as the other of the source and the drain is connected to theregion25c, and theconductive layer41bfunctions as the electrode of thecapacitor26. In contrast, in thetransistor22 included in thepixel10d, theregion25cextends to function as the electrode of thecapacitor26.
• As a result, steps and the like for forming theconductive layers41aand41bcan be omitted, so that manufacturing cost can be reduced.
• FIG. 11A is a top view of thepixel10d.FIG. 11B is a cross-sectional view that corresponds to a cross section taken along a line segment D1-D2 inFIG. 11A.FIG. 11C is a cross-sectional view that corresponds to a cross section taken along a line segment D3-D4 inFIG. 11A.
• As in thepixel10c, in thepixel10d, a region where thesemiconductor layer25 and other components overlap with each other also transmits light in a region excluding thewirings31 and32 and theconductive layer34. Accordingly, the aperture ratio can be increased. Note that theconductive layer34 may be replaced with theconductive layer34bthat transmits visible light, as illustrated inFIG. 12B. This structure can further increase the aperture ratio.
• Since thepixel10ddoes not include theconductive layer41b, thepixel10dhas higher transmittance in an opening portion than thepixel10c.
• As illustrated inFIG. 11B, thesemiconductor layer25 includes aregion25athat functions as a channel formation region, theregion25bthat functions as one of the source and the drain, and theregion25cthat functions as the other of the source and the drain. Theregions25band25care low-resistance regions that can be formed by formation of oxygen vacancies with introduction of impurities into thesemiconductor layer25 by plasma treatment, doping treatment, or the like using theconductive layer34 as a mask.
• Materials described below can be used for the transistors, wirings, capacitors, and the like. Note that these materials can also be used for semiconductor layers and conductive layers that transmit visible light in other structure examples described in this embodiment.
• The semiconductor layer of the transistor can be formed using a light-transmitting semiconductor material. Examples of the light-transmitting semiconductor material include a metal oxide and an oxide semiconductor. The oxide semiconductor preferably contains at least indium. In particular, indium and zinc are preferably contained. In addition, one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, or the like may be contained.
• The conductive layer of the transistor can be formed using a light-transmitting conductive material. The light-transmitting conductive material preferably contains one or more elements selected from indium, zinc, or tin. Specific examples of the light-transmitting conductive material include an In oxide, an In-Sn oxide (also referred to as indium tin oxide or ITO), an In-Zn oxide, an In-W oxide, an In-W-Zn oxide, an In-Ti oxide, an In-Sn-Ti oxide, an In-Sn-Si oxide, a Zn oxide, and a Ga-Zn oxide.
• The conductive layer of the transistor may be formed using an oxide semiconductor that includes an impurity element and has reduced resistance. The oxide semiconductor with the reduced resistance can be regarded as an oxide conductor (OC).
• For example, to form an oxide conductor, oxygen vacancies are formed in an oxide semiconductor and then hydrogen is added to the oxygen vacancies, so that a donor level is formed in the vicinity of the conduction band. The oxide semiconductor having the donor level has increased conductivity and becomes a conductor.
• An oxide semiconductor has a large energy gap (e.g., an energy gap of larger than or equal to 2.5 eV) and thus transmits visible light. As described above, an oxide conductor is an oxide semiconductor having a donor level in the vicinity of the conduction band. Therefore, the influence of absorption due to the donor level is small in an oxide conductor, and the oxide conductor has a light-transmitting property comparable to that of an oxide semiconductor.
• The oxide conductor preferably contains one or more metal elements contained in the semiconductor layer of the transistor. When two or more layers included in the transistor are formed using oxide semiconductors containing the same metal element, the same manufacturing apparatus (e.g., deposition apparatus or processing apparatus) can be used in two or more steps and manufacturing cost can thus be reduced.
• The structure of the pixel included in the liquid crystal display device described in this embodiment enables efficient use of light emitted from a backlight unit. Thus, an excellent liquid crystal display device with lower power consumption can be provided.
• Next, the liquid crystal display device in this embodiment is described with reference toFIG. 13.FIG. 13 is a perspective view of adisplay device100A. Part of thedisplay device100A is enlarged. Note that for clarity, thesubstrate72 is indicated by a dashed line inFIG. 13, and components such as apolarizing plate67 are not illustrated inFIG. 13.
• Thedisplay device100A includes adisplay portion162 and adriver circuit portion164. AnFPC172 and anIC173 are mounted on thedisplay device100A.
• Thedisplay portion162 includes a plurality of pixels and has a function of displaying images. A pixel includes a plurality of subpixels. Note that althoughFIG. 13 illustrates thepixel10aas a subpixel, the subpixel may be thepixel10b, thepixel10c, or thepixel10d.
• For example, a subpixel exhibiting red, a subpixel exhibiting green, and a subpixel exhibiting blue can form one pixel, which leads to full-color display in thedisplay portion162. Note that the color exhibited by subpixels is not limited to red (R), green (G), and blue (B). A pixel may be composed of subpixels that exhibit colors of white (W), yellow (Y), magenta (M), or cyan (C), for example. In this specification and the like, a subpixel is simply described as a pixel in some cases.
• Thedisplay device100A may include either or both a scan line driver circuit and a signal line driver circuit. Alternatively, thedisplay device100A may include neither the scan line driver circuit nor the signal line driver circuit. When thedisplay device100A includes a sensor such as a touch sensor, thedisplay device100A may include a sensor driver circuit. In an example described in this embodiment, a scan line driver circuit is included as thedriver circuit portion164. The scan line driver circuit has a function of outputting a scan signal to a scan line included in thedisplay portion162.
• In thedisplay device100A, theIC173 is mounted on thesubstrate71 by a mounting method such as COG. TheIC173 includes, for example, one or more of a signal line driver circuit, a scan line driver circuit, and a sensor driver circuit.
• TheFPC172 is electrically connected to thedisplay device100A. Through theFPC172, signals and power are supplied from the outside to theIC173 and thedriver circuit portion164. In addition, a signal from theIC173 can be output to the outside through theFPC172.
• An IC may be mounted on theFPC172. For example, an IC including one or more of a signal line driver circuit, a scan line driver circuit, and a sensor driver circuit may be mounted on theFPC172.
• Signals and power are supplied to thedisplay portion162 and thedriver circuit portion164 through awiring165. The signals and power are input to thewiring165 from theIC173 or from the outside through theFPC172.
• Furthermore, aninput device167 can be provided over thesubstrate72. Thedisplay device100A with theinput device167 can function as a touch panel.
• There is no particular limitation on a sensor element included in the touch panel in one embodiment of the present invention. Note that a variety of sensors that can sense proximity or touch of a sensing target such as a finger or a stylus can be used as the sensor element.
• For example, a variety of types such as a capacitive type, a resistive type, a surface acoustic wave type, an infrared type, an optical type, and a pressure-sensitive type can be used for the sensor.
• In this embodiment, a touch panel including a capacitive sensor element is described as an example.
• Examples of the capacitive sensor element include a surface capacitive sensor element and a projected capacitive sensor element. Examples of the projected capacitive sensor element include a self-capacitive sensor element and a mutual capacitive sensor element. The use of a mutual capacitive type is preferable because multiple points can be sensed simultaneously.
• The touch panel in one embodiment of the present invention can have any of a variety of structures, including a structure in which a display device and a sensor element that are separately formed are attached to each other and a structure in which an electrode and the like included in a sensor element are provided on either or both a substrate supporting a display element and a counter substrate.
• FIGS. 14A and 14B illustrate an example of the touch panel.FIG. 14A is a perspective view of atouch panel350A.FIG. 14B is a perspective schematic view of theinput device167. Note thatFIGS. 14A and 14B illustrate only main components for clarity.
• Thetouch panel350A has a structure in which a display device and a sensor element that are separately formed are attached to each other.
• Thetouch panel350A includes theinput device167 and thedisplay device100A that overlap with each other.
• Theinput device167 includes asubstrate163, anelectrode127, anelectrode128, a plurality ofwirings137, a plurality ofwirings138, and a plurality ofwirings139. For example, theelectrode127 can be electrically connected to thewiring137 or139. In addition, theelectrode128 can be electrically connected to thewiring139. AnFPC172bis electrically connected to each of the plurality ofwirings137 and the plurality ofwirings138. AnIC173bcan be provided on theFPC172b.
• Alternatively, a touch sensor may be positioned between thesubstrates71 and72 in thedisplay device100A. In the case where a touch sensor is positioned between thesubstrates71 and72, an optical touch sensor including a photoelectric conversion element as well as a capacitive touch sensor may be used.
• FIG. 15A is a cross-sectional view illustrating thedisplay portion162, thedriver circuit portion164, and thewiring165. Note that althoughFIG. 15A illustrates an example in which thepixel10ainFIG. 1,FIG. 2, andFIGS. 3A to 3C is used, a similar structure is obtained when thepixel10binFIGS. 4A and 4B andFIGS. 5A to 5C is used.
• As illustrated inFIG. 15A, thedisplay device100A includes thesubstrate71, thetransistor21, thetransistor22, theliquid crystal element75, thealignment film61, thealignment film62, aconnection portion68, anadhesive layer73, thecoloring layer65, the light-blockinglayer66, the insulatinglayer55, thesubstrate72, a polarizing plate130, and the like.
• Theliquid crystal element75 that is a transmissive liquid crystal element and operates in a vertical electric field mode is provided in thedisplay portion162. Theliquid crystal element75 includes theconductive layer43 that functions as a pixel electrode, theconductive layer64 that functions as a common electrode, and theliquid crystal layer63. Alignment of theliquid crystal layer63 can be controlled with an electric field generated between theconductive layers43 and64. Theliquid crystal layer63 is positioned between thealignment films61 and62.
• A liquid crystal material is classified into a positive liquid crystal material with positive dielectric anisotropy (Δε) and a negative liquid crystal material with negative dielectric anisotropy. Both of the materials can be used in one embodiment of the present invention, and an optimal liquid crystal material can be used depending on the mode and design to be used.
• Theliquid crystal element75 can employ a variety of modes. For example, a liquid crystal element using a vertical alignment (VA) mode, a twisted nematic (TN) mode, an in-plane switching (IPS) 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, an electrically controlled birefringence (ECB) mode, a VA-IPS mode, a guest-host mode, or the like can be used.
• Furthermore, thedisplay device100A may include a normally black liquid crystal element, for example, a transmissive liquid crystal element using a VA mode. Examples of the VA mode include a multi-domain vertical alignment (MVA) mode, a patterned vertical alignment (PVA) mode, and an advanced super view (ASV) mode.
• The liquid crystal element controls transmission and non-transmission of light by optical modulation action of liquid crystal. The optical modulation action of the liquid crystal is controlled by an electric field applied to the liquid crystal (including a horizontal electric field, a vertical electric field, and 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. Such a liquid crystal material exhibits a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, or the like depending on conditions.
• As thedisplay device100A is a transmissive liquid crystal display device, a conductive material that transmits visible light is used for both theconductive layers43 and64. A conductive material that transmits visible light can be used for one or more conductive layers included in thetransistor21. Thus, at least part of a region where thetransistor21 is provided can be used as an effective display region.
• For example, a material containing one or more elements selected from indium (In), zinc (Zn), or tin (Sn) is preferably used for the conductive material that transmits visible light. Specific examples include indium oxide, indium tin oxide (ITO), indium zinc oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide containing silicon oxide (ITSO), zinc oxide, and zinc oxide containing gallium. Note that a film containing graphene can be used as well. The film containing graphene can be formed, for example, by reducing a film containing graphene oxide.
• It is preferable to use an oxide conductive layer that is one embodiment of a metal oxide for one or more of theconductive layer33, theconductive layer34, theconductive layer41a, theconductive layer41b, theconductive layer42, theconductive layer43, and theconductive layer64 included in thedisplay portion162. The oxide conductive layer preferably contains one or more metal elements contained in thesemiconductor layer25 of thetransistor21. For example, the oxide conductive layer preferably contains indium and is further preferably an In-M-Zn oxide (M is Al, Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf) film.
• It is preferable to use an oxide semiconductor that is one embodiment of a metal oxide for one or more of theconductive layer33, theconductive layer34, theconductive layer41a, theconductive layer41b, theconductive layer42, theconductive layer43, and theconductive layer64. When two or more layers included in the display device are formed using oxide semiconductors containing the same metal element, the same manufacturing apparatus (e.g., deposition apparatus or processing apparatus) can be used in two or more steps and manufacturing cost can thus be reduced.
• The oxide semiconductor is a semiconductor material whose resistance can be controlled by oxygen vacancies in the film of the semiconductor material and/or the concentration of impurities such as hydrogen or water in the film of the semiconductor material. Thus, the resistivity of the oxide conductive layer can be controlled by selecting treatment for increasing oxygen vacancies and/or impurity concentration in an oxide semiconductor layer or treatment for reducing oxygen vacancies and/or impurity concentration in an oxide semiconductor layer.
• Note that such an oxide conductor layer formed using an oxide semiconductor layer can be referred to as an oxide semiconductor layer having high carrier density and low resistivity, an oxide semiconductor layer having conductivity, or an oxide semiconductor layer having high conductivity.
• In addition, manufacturing cost can be reduced by forming the oxide semiconductor layer and the oxide conductive layer using the same metal element. For example, manufacturing cost can be reduced by using a metal oxide target with the same metal composition. An etching gas or an etchant used for processing of the oxide semiconductor layer can also be used for processing of the oxide conductive layer. Note that even when the oxide semiconductor layer and the oxide conductive layer have the same metal elements, the metal elements have different compositions in some cases. For example, in some cases, metal elements in the film desorb during the manufacturing process of the display device, which results in different metal compositions.
• In thedisplay device100A, thecoloring layer65 and the light-blockinglayer66 are provided over theliquid crystal layer63. It is preferable to provide the insulatinglayer55 between thecoloring layer65 and the light-blockinglayer66, and theliquid crystal layer63. The insulatinglayer55 can suppress diffusion of impurities contained in thecoloring layer65, the light-blockinglayer66, and the like into theliquid crystal layer63 and functions as a planarization film.
• Thesubstrates71 and72 are attached to each other by theadhesive layer73. Theliquid crystal layer63 is sealed in a region surrounded by thesubstrates71 and72 and theadhesive layer73.
• Note that when thedisplay device100A functions as a transmissive liquid crystal display device, two polarizing plates are provided so that thedisplay portion162 is positioned between the two polarizing plates.FIGS. 15A and 15B illustrate thepolarizing plate67 on thesubstrate72 side. Light from a backlight provided outside a polarizing plate on thesubstrate71 side enters thedisplay portion162 through the polarizing plate. At this time, the alignment of theliquid crystal layer63 is controlled with voltage applied between theconductive layers43 and64, so that optical modulation of light can be controlled. In other words, the intensity of light emitted through thepolarizing plate67 can be controlled. Furthermore, thecoloring layer65 absorbs light of wavelengths other than a specific wavelength range from incident light, so that red (R), blue (B), or green (G) light is emitted, for example.
• A circularly polarizing plate can be used as the polarizing plate, for example. As the circularly polarizing plate, for example, a stack including a linear polarizing plate and a quarter-wave retardation plate can be used. With the circularly polarizing plate, the viewing angle dependence of display of the display device can be reduced.
• Theliquid crystal element75 may be driven in a guest-host liquid crystal mode. When the guest-host liquid crystal mode is used, either one or both the polarizing plates are not necessarily required. Since light absorption due to the polarizing plate can be reduced, light extraction efficiency is increased and the display device can perform bright display.
• Thedriver circuit portion164 includes atransistor23. Thetransistor23 includes aconductive layer37 that functions as a gate, a gate insulating film, a semiconductor layer, aconductive layer35, and aconductive layer36. One of theconductive layers35 and36 functions as a source, and the other of theconductive layers35 and36 functions as a drain.
• The transistor included in thedriver circuit portion164 does not necessarily have a function of transmitting visible light. Therefore, a low-resistance metal layer or the like can be used for theconductive layers36 and37.
• In theconnection portion68, thewiring165 is connected to aconductive layer44, and theconductive layer44 is connected to aconnector45. That is, in theconnection portion68, thewiring165 is electrically connected to theFPC172 through theconductive layer44 and theconnector45. With this structure, signals and power can be supplied from theFPC172 to thewiring165.
• Thetransistors21 and22 may have the same structure or different structures. That is, the transistors included in thedriver circuit portion164 and the transistors included in thedisplay portion162 may have the same structure or different structures. In addition, thedriver circuit portion164 may include transistors having a plurality of structures. Thedisplay portion162 may include transistors having a plurality of structures.
• Note that althoughFIG. 15A illustrates a structure where one gate is provided for a channel formation region of the transistor, two gates formed using theconductive layers35 and38 may be provided so that a channel formation region is positioned between the two gates, as in the case of thetransistor23 inFIG. 15B.
• Different potentials can be supplied to theconductive layers35 and38. Alternatively, theconductive layers35 and38 may be electrically connected to each other. The structure in the former case is effective in controlling the threshold voltage of the transistor.
• A transistor that includes two gates electrically connected to each other 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, 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 suppress display unevenness even in a display device in which the number of wirings is increased because of an increase in size or resolution. In addition, the use of such a structure allows manufacture of a highly reliable transistor.
• Note that in the case where thepixel10binFIGS. 4A and 4B andFIGS. 5A to 5C includes theconductive layer38, theconductive layer38 is preferably formed using a material that transmits visible light.
• FIG. 16A is a cross-sectional view of thedisplay device100A where the structure of thepixel10cinFIG. 6,FIG. 7, andFIGS. 8A to 8C is employed.FIG. 17A is a cross-sectional view of thedisplay device100A where the structure of thepixel10dinFIG. 9,FIG. 10, andFIGS. 11A to 11C is employed. Thedriver circuit portion164 includes atransistor24.
• The transistor included in thedriver circuit portion164 does not necessarily have a function of transmitting visible light. Therefore, a low-resistance metal layer or the like can be used for theconductive layers36 and37.
• FIG. 16B andFIG. 17B are cross-sectional views where each of thetransistors22 and24 includes two gate electrodes.
• Note that in the case where thepixel10cinFIG. 12A and thepixel10dinFIG. 12B each include theconductive layer38, theconductive layer38 is preferably formed using a material that transmits visible light.
• FIG. 18 is a top view illustrating an example of arrangement where thepixels10aare used as subpixels. InFIG. 18, R, G, and B represent examples of colors of thecoloring layer65 provided over the subpixels. It is preferable to arrange the pixels while inverting pixel layout row by row so that the viewing angle dependence can be reduced. Note that similar arrangement is applicable to thepixels10b,10c, and10d.
• Next, the details of materials and the like that can be used for components of the display device in this embodiment are described. Note that description of the components already described is omitted in some cases. Materials described below can be used as appropriate for a display device, a touch panel, and components thereof to be described later.
<Substrates71 and72>
• There are no large limitations on the material of the substrate used in the display device in one embodiment of the present invention; a variety of substrates can be used. For example, a glass substrate, a quartz substrate, a sapphire substrate, a semiconductor substrate, a ceramic substrate, a metal substrate, a plastic substrate, or the like can be used.
• The weight and thickness of the display device can be reduced by using a thin substrate. Furthermore, a flexible display device can be obtained by using a substrate that is thin enough to have flexibility.
• The display device in one embodiment of the present invention is manufactured by forming a transistor and the like over a manufacture substrate and then transferring the transistor and the like on another substrate. The use of the manufacture substrate enables the following: formation of a transistor with favorable characteristics; formation of a transistor with low power consumption; manufacture of a durable display device, addition of heat resistance to the display device, a reduction of the weight of the display device, or a reduction of the thickness of the display device. Examples of a substrate to which a transistor is transferred include, in addition to the substrate over which the transistor can be formed, a paper substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), and the like), a leather substrate, and a rubber substrate.
<Transistors21,22,23, and24>
• Each transistor included in the display device in one embodiment of the present invention may have a top-gate structure or a bottom-gate structure. Gate electrodes may be provided above and below a channel. A semiconductor material used for the transistor is not particularly limited, and an oxide semiconductor, silicon, or germanium can be used, for example.
• There is no particular limitation on the crystallinity of the semiconductor material used for the transistor, and an amorphous semiconductor or a crystalline semiconductor (a microcrystalline semiconductor, a polycrystalline semiconductor, a single-crystal semiconductor, or a semiconductor partly including crystal regions) may be used. The use of a crystalline semiconductor is preferable because degradation of transistor characteristics can be reduced.
• For example, aGroup 14 element, a compound semiconductor, or an oxide semiconductor can be used for the semiconductor layer. Typically, a semiconductor including silicon, a semiconductor including gallium arsenide, an oxide semiconductor including indium, or the like can be used for the semiconductor layer.
• An oxide semiconductor is preferably used for a semiconductor where a channel of a transistor is formed. In particular, the use of an oxide semiconductor with a larger bandgap than that of silicon is preferable. The use of a semiconductor material with a larger bandgap than that of silicon and low carrier density is preferable because off-state current of the transistor can be reduced.
• The use of such an oxide semiconductor makes it possible to provide a highly reliable transistor with a small change in electrical characteristics.
• Charge accumulated in a capacitor through the transistor can be retained for a long time because of low off-state current of the transistor. The use of such a transistor in pixels allows a driver circuit to stop while the gray level of an image displayed is maintained. As a result, a display device with extremely low power consumption can be obtained.
• Thetransistors21,22,23, and24 preferably each include an oxide semiconductor layer that is highly purified to suppress formation of oxygen vacancies. Accordingly, the off-state current of the transistor can be made low. Therefore, an electrical signal such as an image signal can be held for a long time, and a writing interval can be set long in an on state. Consequently, the frequency of refresh operation can be reduced, which leads to an effect of reducing power consumption.
• In thetransistors21,22,23, and24, comparatively high field-effect mobility can be obtained, so that high-speed operation is possible. The use of such transistors capable of high-speed operation in the display device enables formation of the transistor in the display portion and the transistor in the driver circuit portion over the same substrate. This means that a semiconductor device separately formed using a silicon wafer or the like does not need to be used as the driver circuit, which enables a reduction in the number of components in the display device. In addition, by using the transistor capable of high-speed operation in the pixel portion, a high-quality image can be provided.
<Insulating Layer>
• An organic insulating material or an inorganic insulating material can be used as an insulating material that can be used for each insulating layer, a spacer, or the like included in the display device. Examples of the organic insulating material include an acrylic resin, an epoxy resin, a polyimide resin, a polyamide resin, a polyimide amide resin, a siloxane resin, a benzocyclobutene-based resin, and a phenol resin. Examples of an inorganic insulating layer include a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, a silicon nitride film, an aluminum oxide film, a hafnium oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, and a neodymium oxide film.
<Conductive Layer>
• For a gate, a source, and a drain of a transistor and a conductive layer such as a wiring or an electrode included in the display device, a single-layer structure or a stacked structure including any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten, or an alloy containing any of these metals as its main component can be used. For example, a two-layer structure in which a titanium film is stacked over an aluminum film; a two-layer structure in which a titanium film is stacked over a tungsten film; a two-layer structure in which a copper film is stacked over a molybdenum film; a two-layer structure in which a copper film is stacked over an alloy film containing molybdenum and tungsten; a two-layer structure in which a copper film is stacked over an alloy film containing copper, magnesium, and aluminum; 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 that order; 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 that order; or the like can be employed. For example, in the case where the conductive layer has a three-layer structure, it is preferable that each of first and third layers be a film formed using titanium, titanium nitride, molybdenum, tungsten, an alloy containing molybdenum and tungsten, an alloy containing molybdenum and zirconium, or molybdenum nitride, and that a second layer be a film formed using a low-resistance material such as copper, aluminum, gold, silver, or an alloy containing copper and manganese. Note that a light-transmitting conductive material such as ITO, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or ITSO may be used.
• Note that an oxide conductive layer may be formed by controlling the resistivity of the oxide semiconductor.
<Adhesive Layer73>
• A curable resin such as a thermosetting resin, a photocurable resin, or a two-component type curable resin can be used for theadhesion layer73. For example, an acrylic resin, a urethane resin, an epoxy resin, or a siloxane resin can be used.
<Connector45>
• As theconnector45, for example, an anisotropic conductive film (ACF) or an anisotropic conductive paste (ACP) can be used.
<Coloring Layer65>
• Thecoloring layer65 is a colored layer that transmits light in a specific wavelength range. Examples of a material that can be used for thecoloring layer65 include a metal material, a resin material, and a resin material containing a pigment or dye.
<Light-Blocking Layer66>
• The light-blockinglayer66 is positioned between adjacent coloring layers65 for different colors. A black matrix formed using, for example, a metal material or a resin material containing a pigment or dye can be used as the light-blockinglayer66. Note that it is preferable to provide the light-blockinglayer66 also in a region other than thedisplay portion162, such as thedriver circuit portion164, because leakage of guided light or the like can be inhibited.
• Note that thin films included in the display device (e.g., insulating films, semiconductor films, or conductive films) can be formed by any of sputtering, chemical vapor deposition (CVD), vacuum deposition, pulsed laser deposition (PLD), atomic layer deposition (ALD), or the like. Examples of CVD include plasma-enhanced CVD (PECVD) and thermal CVD. Examples of thermal CVD include metal organic CVD (MOCVD).
• Alternatively, the thin films included in the display device (e.g., the insulating films, semiconductor films, or conductive films) can be formed by a method such as spin coating, dipping, spray coating, inkjet printing, dispensing, screen printing, or offset printing, or with a doctor knife, a slit coater, a roll coater, a curtain coater, or a knife coater.
• The thin films included in the display device can be processed using photolithography or the like. Alternatively, island-shaped thin films may be formed by a deposition method using a blocking mask. Alternatively, the thin films may be processed by nano-imprinting, sandblasting, lift-off, or the like. Examples of photolithography include a method in which a resist mask is formed over a thin film to be processed, the thin film is processed by etching or the like, and the resist mask is removed, and a method in which a photosensitive thin film is formed, and the photosensitive thin film is exposed to light and developed to be processed in a desired shape.
• As light for exposure in photolithography, light with an i-line (with a wavelength of 365 nm), light with a g-line (with a wavelength of 436 nm), light with an h-line (with a wavelength of 405 nm), and light in which the i-line, the g-line, and the h-line are mixed can be used. Alternatively, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Exposure may be performed by an immersion exposure technique. As light for exposure, extreme ultraviolet light (EUV), X-rays, or the like can be used. An electron beam can be used instead of light for exposure. It is preferable to use EUV, X-rays, or an electron beam because extremely fine processing can be performed. Note that when exposure is performed by scanning of a beam such as an electron beam, a photomask is not needed.
• For etching of the thin film, dry etching, wet etching, sandblasting, or the like can be used.
• As a result, it is possible to manufacture a liquid crystal display device with high aperture ratio and low power consumption.
• This embodiment can be combined with any of the other embodiments as appropriate.
Embodiment 2
• In this embodiment, an operation mode that can be employed in the display device in one embodiment of the present invention is described with reference toFIGS. 19A to 19C.
• A normal driving mode with normal frame frequency (typically, higher than or equal to 60 Hz and lower than or equal to 240 Hz) and an idling stop (IDS) driving mode with low frame frequency are described below.
• Note that the IDS driving mode refers to a method in which after image data is written, rewriting of image data is stopped. This increases the interval between writing of image data and subsequent writing of image data, so that power that would be consumed by writing of image data in that interval can be reduced. The IDS driving mode can be performed at frame frequency that is 1/100 to 1/10 of the normal driving mode, for example. A still image is displayed by the same video signals in consecutive frames. Thus, the IDS driving mode is particularly effective when displaying a still image. When an image is displayed using IDS driving, power consumption is reduced, image flickering is suppressed, and eyestrain can be reduced.
• FIGS. 19A to 19C are a circuit diagram of a pixel circuit and timing charts illustrating the normal driving mode and the IDS driving mode. Note that inFIG. 19A, aliquid crystal element501 and apixel circuit506 electrically connected to theliquid crystal element501 are illustrated. In thepixel circuit506 inFIG. 19A, a signal line SL, a gate line GL, a transistor M1 connected to the signal line SL and the gate line GL, and a capacitor C_SLCconnected to the transistor M1 are illustrated.
• The transistor M1 might become a leakage path of data D₁. Thus, the off-state current of the transistor M1 is preferably as low as possible. A transistor including a metal oxide in a semiconductor layer where a channel is formed is preferably used as the transistor M1. A metal oxide having at least one of an amplification function, a rectification function, and a switching function can be referred to as a metal oxide semiconductor or an oxide semiconductor (abbreviated to an OS). As a typical example of a transistor, a transistor including an oxide semiconductor in a semiconductor layer where a channel is formed (such a transistor is also referred to as an OS transistor) is described below. The OS transistor has extremely low leakage current in an off state (off-state current) compared to a transistor including polycrystalline silicon or the like. Note that a node to which a pixel electrode of theliquid crystal element501, one of a source and a drain of the transistor M1, and the capacitor C_SLCare connected is referred to as a node ND1. Charge supplied to the node ND1 can be retained for a long time when the OS transistor is used as the transistor M1.
• In the circuit diagram inFIG. 19A, theliquid crystal element501 also becomes a leakage path of the data D₁. Therefore, to perform IDS driving appropriately, the resistivity of theliquid crystal element501 is preferably higher than or equal to 1.0×10¹⁴Ω·cm.
• Note that for example, an In-Ga-Zn oxide or an In-Zn oxide can be suitably used for a channel region of the OS transistor. The In-Ga-Zn oxide can typically have an atomic ratio of In:Ga:Zn=4:2:4.1 or a neighborhood thereof.
• FIG. 19B is a timing chart showing waveforms of signals supplied to the signal line SL and the gate line GL in the normal driving mode. In the normal driving mode, normal frame frequency (e.g., 60 Hz) is used for operation. Periods T₁to T₃are shown inFIG. 19B. A scan signal is supplied to the gate line GL in each frame period and the data D₁is written from the signal line SL to theliquid crystal element501 and the capacitor C_SLC. This operation is performed both to write the same data D₁in the periods T₁to T₃and to write different data in the periods T₁to T_3.
• In contrast,FIG. 19C is a timing chart showing waveforms of signals supplied to the signal line SL and the gate line GL in the IDS driving mode. In the IDS driving, low frame frequency (e.g., 1 Hz) is used for operation. One frame period is denoted by a period T₁and includes a data writing period Tw and a data retention period T_RET. In the IDS driving mode, a scan signal is supplied to the gate line GL and the data D₁of the signal line SL is written in the period T_W, the gate line GL is fixed to low-level voltage in the period T_RET, and the transistor M1 is turned off so that the written data D₁is retained. Note that the low frame frequency may be higher than or equal to 0.1 Hz and lower than 60 Hz, for example.
• The IDS driving mode can reduce power consumption.
• This embodiment can be combined with any of the other embodiments as appropriate.
Embodiment 3
• A metal oxide that can be used for a semiconductor layer of a transistor disclosed in one embodiment of the present invention is described in this embodiment. Note that when a metal oxide is used for a semiconductor layer of a transistor, the metal oxide may be referred to as an oxide semiconductor.
• An oxide semiconductor is classified into a single crystal oxide semiconductor and a non-single-crystal oxide semiconductor. Examples of a non-single-crystal oxide semiconductor include a c-axis aligned crystalline oxide semiconductor (CAAC-OS), a polycrystalline oxide semiconductor, a nanocrystalline oxide semiconductor (nc-OS), an amorphous-like oxide semiconductor (a-like OS), and an amorphous oxide semiconductor.
• A cloud-aligned composite oxide semiconductor (CAC-OS) may be used for the semiconductor layer of the transistor disclosed in one embodiment of the present invention.
• Note that the non-single-crystal oxide semiconductor or the CAC-OS can be suitably used for the semiconductor layer of the transistor disclosed in one embodiment of the present invention. In addition, the nc-OS or the CAAC-OS can be suitably used as the non-single-crystal oxide semiconductor.
• Note that in one embodiment of the present invention, the CAC-OS is preferably used for the semiconductor layer of the transistor. The use of the CAC-OS can provide high electrical characteristics or high reliability of the transistor.
• Details of the CAC-OS are described below.
• The CAC-OS or a CAC metal oxide has a conducting function in part of a material and has an insulating function in another part of the material; as a whole, the CAC-OS or the CAC metal oxide functions as a semiconductor. In the case where the CAC-OS or the CAC metal oxide is used for a channel formation region of a transistor, the conducting function is to allow electrons (or holes) serving as carriers to flow, and the insulating function is to not allow electrons serving as carriers to flow. By the complementary action of the conducting function and the insulating function, the CAC-OS or the CAC metal oxide can have a switching function (on/off function). In the CAC-OS or the CAC metal oxide, separation of the functions can maximize each function.
• The CAC-OS or the CAC metal oxide includes conductive regions and insulating regions. The conductive regions have the conducting function, and the insulating regions have the insulating function. In some cases, the conductive regions and the insulating regions in the material are separated at the nanoparticle level. In some cases, the conductive regions and the insulating regions are unevenly distributed in the material. The conductive regions are observed to be coupled in a cloud-like manner with their boundaries blurred in some cases.
• Furthermore, in the CAC-OS or the CAC metal oxide, the conductive regions and the insulating regions each have a size of greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 0.5 nm and less than or equal to 3 nm and are dispersed in the material in some cases.
• The CAC-OS or the CAC metal oxide includes components having different bandgaps. For example, the CAC-OS or the CAC metal oxide includes a component having a wide gap due to an insulating region and a component having a narrow gap due to a conductive region. In the case of such a composition, carriers mainly flow in the component having a narrow gap. The component having a narrow gap complements the component having a wide gap, and carriers also flow in the component having a wide gap in conjunction with the component having a narrow gap. Therefore, in the case where the CAC-OS or the CAC metal oxide is used for a channel formation region of a transistor, high current drive capability in the on state of the transistor, that is, high on-state current and high field-effect mobility, can be obtained.
• In other words, a CAC-OS or a CAC-metal oxide can be called a matrix composite or a metal matrix composite.
• The CAC-OS has, for example, a composition in which elements included in a metal oxide are unevenly distributed. Materials including unevenly distributed elements each have a size of greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size. Note that in the following description of a metal oxide, a state in which one or more metal elements are unevenly distributed in regions each having a size of greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size and the regions including the one or more metal elements are mixed is referred to as a mosaic pattern or a patch-like pattern.
• Note that the metal oxide preferably contains at least indium. In particular, indium and zinc are preferably contained. In addition, one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, or the like may be contained.
• As an example of the CAC-OS, an In-Ga-Zn oxide with the CAC composition (such an In-Ga-Zn oxide may be particularly referred to as CAC-IGZO) is described. The CAC-IGZO has a composition with a mosaic pattern in which materials are separated into indium oxide (InO_X1, where X1 is a real number greater than 0) or indium zinc oxide (In_X2Zn_Y2O_Z2, where X2, Y2, and Z2 are each a real number greater than 0) and gallium oxide (GaO_X3, where X3 is a real number greater than 0) or gallium zinc oxide (Ga_X4Zn_Y4O_Z4, where X4, Y4, and Z4 are each a real number greater than 0), for example. Furthermore, InO_X1or In_X2Zn_Y2O_Z2forming the mosaic pattern is evenly distributed in the film. This composition is also referred to as a cloud-like composition.
• That is, the CAC-OS is a composite metal oxide with a composition in which a region including GaO_X3as a main component and a region including In_X2Zn_Y2O_Z2or InO_X1as a main component are mixed. Note that in this specification, for example, when the atomic ratio of In to an element M in a first region is higher than the atomic ratio of In to the element M in a second region, the first region has higher In concentration than the second region.
• Note that a compound containing In, Ga, Zn, and O is also commonly known as IGZO. Typical examples of IGZO include a crystalline compound represented by InGaO₃(ZnO)_m1(m1 is a natural number) and a crystalline compound represented by In_(1+x0)Ga_(1−x0)O₃(ZnO)_m0(−1≤x0≤1; m0 is a given number).
• The crystalline compound has a single crystal structure, a polycrystalline structure, or a CAAC structure. Note that the CAAC structure is a crystal structure in which a plurality of IGZO nanocrystals have c-axis alignment and are connected in the a-b plane direction without alignment.
• In contrast, the CAC-OS relates to the material composition of a metal oxide. In part of the material composition of a CAC-OS containing In, Ga, Zn, and O, nanoparticle regions including Ga as a main component and nanoparticle regions including In as a main component are observed. These nanoparticle regions are randomly dispersed in a mosaic pattern. Therefore, the crystal structure is a secondary element for the CAC-OS.
• Note that the CAC-OS does not include a stacked structure of two or more films with different compositions. For example, a two-layer structure of a film including In as a main component and a film including Ga as a main component is not included.
• A boundary between the region including GaO_X3as a main component and the region including In_X2Zn_Y2O_Z2or InO_X1as a main component is not clearly observed in some cases.
• In part of the composition of a CAC-OS that contains, instead of gallium, one or more metal elements selected from aluminum, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, or the like, nanoparticle regions including the one or more metal elements as a main component and nanoparticle regions including In as a main component are observed. These nanoparticle regions are randomly dispersed in a mosaic pattern.
• The CAC-OS can be formed by sputtering under a condition where a substrate is not heated intentionally, for example. In the case where the CAC-OS is formed by sputtering, one or more gases selected from an inert gas (typically, argon), an oxygen gas, or a nitrogen gas may be used as a deposition gas. The percentage of the oxygen gas flow rate in the total flow rate of the deposition gas at the time of deposition is preferably as low as possible; for example, the percentage of the oxygen gas flow rate is preferably higher than or equal to 0% and lower than 30%, more preferably higher than or equal to 0% and lower than or equal to 10%.
• The CAC-OS is characterized in that no clear peak is observed in measurement using θ/2θ scan by an out-of-plane method, which is an X-ray diffraction (XRD) measurement method. That is, X-ray diffraction shows no alignment in the a-b plane direction and the c-axis direction in a measured region.
• In an electron diffraction pattern of the CAC-OS that is obtained by irradiation with an electron beam with a probe diameter of 1 nm (also referred to as a nanometer-sized electron beam), a ring-like region with high luminance and a plurality of bright spots in the ring-like region are observed. Therefore, the electron diffraction pattern indicates that the crystal structure of the CAC-OS includes a nanocrystal (nc) structure with no alignment in the plan-view direction and the cross-sectional direction.
• For example, energy dispersive X-ray spectroscopy (EDX) is used to obtain EDX mapping, and according to the EDX mapping, the CAC-OS of the In-Ga-Zn oxide has a composition in which the region including GaO_X3as a main component and the region including In_X2Zn_Y2O_Z2or InO_X1as a main component are unevenly distributed and mixed.
• The CAC-OS has a structure and characteristics different from those of an IGZO compound in which metal elements are evenly distributed. That is, in the CAC-OS, regions including GaO_X3or the like as a main component and regions including In_X2Zn_Y2O_Z2or InO_X1as a main component are phase-separated from each other in a mosaic pattern.
• The conductivity of the region including In_X2Zn_Y2O_Z2or InO_X1as a main component is higher than that of the region including GaO_X3or the like as a main component. In other words, when carriers flow through the region including In_X2Zn_Y2O_Z2or InO_X1as a main component, the oxide semiconductor exhibits conductivity. Accordingly, when the regions including In_X2Zn_Y2O_Z2or InO_X1as a main component are distributed in the oxide semiconductor like a cloud, high field-effect mobility (μ) can be achieved.
• In contrast, the insulating property of the region including GaO_X3or the like as a main component is higher than that of the region including In_X2Zn_Y2O_Z2or InO_X1as a main component. In other words, when the regions including GaO_X3or the like as a main component are distributed in the oxide semiconductor, leakage current can be reduced and favorable switching operation can be achieved.
• Accordingly, when a CAC-OS is used for a semiconductor element, the insulating property derived from GaO_X3or the like and the conductivity derived from In_X2Zn_Y2O_Z2or InO_X1complement each other, so that high on-state current and high field-effect mobility (μ) can be achieved.
• A semiconductor element including a CAC-OS has high reliability. Thus, the CAC-OS is suited for a variety of semiconductor devices typified by a display.
• This embodiment can be combined with any of the other embodiments as appropriate.
Embodiment 4
• Examples of an electronic device that can use the display device in one embodiment of the present invention include display devices, personal computers, image storage devices or image reproducing devices provided with storage media, cellular phones, game machines (including portable game machines), portable data terminals, e-book readers, cameras such as video cameras and digital still cameras, goggle-type displays (head mounted displays), navigation systems, audio reproducing devices (e.g., car audio players and digital audio players), copiers, facsimiles, printers, multifunction printers, automated teller machines (ATM), and vending machines.FIGS. 20A to 20F illustrate specific examples of these electronic devices.
• FIG. 20A illustrates a digital camera, which includes ahousing961, ashutter button962, amicrophone963, aspeaker967, adisplay portion965,operation keys966, azoom lever968, alens969, and the like. The display device in one embodiment of the present invention can be used for thedisplay portion965.
• FIG. 20B illustrates a wrist-watch-type information terminal, which includes ahousing931, adisplay portion932, awristband933,operation buttons935, awinder936, acamera939, and the like. Thedisplay portion932 may be a touch panel. The display device in one embodiment of the present invention can be used for thedisplay portion932.
• FIG. 20C illustrates an example of a cellular phone, which includes ahousing951, adisplay portion952, anoperation button953, anexternal connection port954, aspeaker955, amicrophone956, acamera957, and the like. Thedisplay portion952 of the cellular phone includes a touch sensor. Operations such as making a call and inputting text can be performed by touch on thedisplay portion952 with a finger, a stylus, or the like. The display device in one embodiment of the present invention can be used for thedisplay portion952.
• FIG. 20D illustrates a portable data terminal, which includes a housing911, adisplay portion912, acamera919, and the like. A touch panel function of thedisplay portion912 enables input and output of information. The display device in one embodiment of the present invention can be used for thedisplay portion912.
• FIG. 20E is a television, which includes ahousing971, adisplay portion973, anoperation key974,speakers975, acommunication connection terminal976, anoptical sensor977, and the like. Thedisplay portion973 includes a touch sensor that enables input operation. The display device in one embodiment of the present invention can be used for thedisplay portion973.
• FIG. 20F illustrates an information processing terminal, which includes ahousing901, adisplay portion902, adisplay portion903, asensor904, and the like. Thedisplay portions902 and903 are formed using one display panel and flexible. Thehousing901 is also flexible, can be used in a bent state as illustrated inFIG. 20F, and can be used in a flat plate-like shape like a tablet terminal. Thesensor904 can sense the shape of thehousing901, and for example, it is possible to switch display on thedisplay portions902 and903 when thehousing901 is bent. The display device in one embodiment of the present invention can be used for thedisplay portions902 and903.
• This embodiment can be combined with any of the other embodiments as appropriate.
• This application is based on Japanese Patent Application Serial No. 2016-227337 filed with Japan Patent Office on Nov. 23, 2016, the entire contents of which are hereby incorporated by reference.

Claims (16)

What is claimed is:

1. A display device comprising:

a first conductive layer;

a second conductive layer;

a liquid crystal element including a third conductive layer, a fourth conductive layer, and a liquid crystal layer therebetween;

a first insulating layer between the first and second conductive layers; and

a second insulating layer between the second and third conductive layers,

wherein:

the first conductive layer includes a region where a source or drain electrode of a transistor extends,

the first to fourth conductive layers transmit visible light,

the first to fourth conductive layers include a region where the first to fourth conductive layers overlap with each other,

the second conductive layer includes a first opening portion,

the first and second insulating layers include a second opening portion,

the second opening portion is inside the first opening portion, and

the third conductive layer is electrically connected to the first conductive layer through the second opening portion.

2. The display device according toclaim 1, wherein:

the second conductive layer functions as a common electrode,

the first and second conductive layers, and the first insulating layer function as a first capacitor, and

the second and third conductive layers, and the second insulating layer function as a second capacitor.

3. The display device according toclaim 1, wherein the first to fourth conductive layers each contain a metal oxide.

4. The display device according toclaim 1, wherein:

the transistor includes a fifth conductive layer functioning as a gate electrode, and

the fifth conductive layer transmits visible light.

5. The display device according toclaim 4, wherein the fifth conductive layer includes a region overlapping with the first to fourth conductive layers.

6. The display device according toclaim 4, wherein the fifth conductive layer contains a metal oxide.

7. The display device according toclaim 1, wherein the transistor contains a metal oxide in a channel formation region.

8. An electronic device comprising the display device according toclaim 1 and an input device overlapping with a display portion.

9. A display device comprising:

a first conductive layer;

a second conductive layer;

a liquid crystal element including a third conductive layer, a fourth conductive layer, and a liquid crystal layer therebetween;

a first insulating layer between the first and second conductive layers; and

a second insulating layer between the second and third conductive layers,

wherein:

the first conductive layer includes a region where a semiconductor layer of a transistor extends,

the first to fourth conductive layers transmit visible light,

the first to fourth conductive layers include a region where the first to fourth conductive layers overlap with each other,

the second conductive layer includes a first opening portion,

the first and second insulating layers include a second opening portion,

the second opening portion is inside the first opening portion, and

the third conductive layer is electrically connected to the first conductive layer through the second opening portion.

10. The display device according toclaim 9, wherein:

the second conductive layer functions as a common electrode,

the first and second conductive layers, and the first insulating layer function as a first capacitor, and

the second and third conductive layers, and the second insulating layer function as a second capacitor.

11. The display device according toclaim 9, wherein the first to fourth conductive layers each contain a metal oxide.

12. The display device according toclaim 9, wherein:

the transistor includes a fifth conductive layer functioning as a gate electrode, and

the fifth conductive layer transmits visible light.

13. The display device according toclaim 12, wherein the fifth conductive layer includes a region overlapping with the first to fourth conductive layers.

14. The display device according toclaim 12, wherein the fifth conductive layer contains a metal oxide.

15. The display device according toclaim 9, wherein the transistor contains a metal oxide in a channel formation region.

16. An electronic device comprising the display device according toclaim 9 and an input device overlapping with a display portion.

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