Patent Publication Number: US-2022236569-A1

Title: Composite Device

Description:
TECHNICAL FIELD 
     One embodiment of the present invention relates to a display device. One embodiment of the present invention relates to a sensor device. One embodiment of the present invention relates to an image capturing device. 
     Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include a semiconductor device, a display device, a light-emitting 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. A semiconductor device generally means a device that can function by utilizing semiconductor characteristics. 
     BACKGROUND ART 
     A device for virtual reality (VR) or augmented reality (AR) has been actively developed in recent years. 
     Examples of a display device that can be used for a display panel include, typically, a liquid crystal display device, a light-emitting device including a light-emitting element such as an organic EL (Electro Luminescence) element or a light-emitting diode (LED), and electronic paper performing display by an electrophoretic method or the like. 
     For example, the basic structure of an organic EL element is a structure in which a layer containing a light-emitting organic compound is provided between a pair of electrodes. By applying a voltage to this element, light emission can be obtained from the light-emitting organic compound. A display device using such an organic EL element does not need a backlight that is necessary for a liquid crystal display device and the like; thus, a thin, lightweight, high-contrast, and low-power display device can be achieved. Patent Document 1, for example, discloses an example of a display device using an organic EL element. 
     REFERENCE 
     Patent Document 
     [Patent Document 1] Japanese Published Patent Application No. 2002-324673 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Since a device for VR or AR is worn on a human body, a small and lightweight device is preferable for the VR or AR device. However, when the device is used for a long time in an environment with no power supply, a battery having large capacitance needs to be mounted, which makes it difficult to reduce the size or weight of the device. In addition, an increase in power consumption caused by an increase in functions of the device requires a battery having larger capacitance. 
     In recent years, because of a rise in health awareness, a device with which a health condition is grasped and monitored in daily life has been required. For example, medical devices targeted at individuals, such as a hemadynamometer and an electrocardiograph, have been reduced in size and price. Furthermore, functions of information terminals such as a smartphone and a tablet have been increased by addition of a function of managing obtained data, or the like. In contrast, people who are not very conscious of health feel that such daily measurement is troublesome in many cases; thus, polarization between people who take care of their health and people who do not do it tends to occur. 
     One object of one embodiment of the present invention is to provide an electronic device having reduced power consumption. Another object is to provide a multifunction electronic device that facilitates a reduction in weight or size. Another object is to provide an electronic device that facilitates management of health condition. Another object is to provide an electronic device in which an image having enhanced reality can be displayed. Another object is to provide a novel display device, a novel sensor device, a novel electronic device, a novel composite device, or the like. 
     Note that the description of these objects does not preclude the existence of other objects. One embodiment of the present invention does not have to achieve all these objects. Objects other than these can be derived from the description of the specification, the drawings, the claims, and the like. 
     Means for Solving the Problems 
     One embodiment of the present invention is a composite device including a sensor device and a display device. The sensor device includes a first communication portion and a sensor portion and can be worn on a human body. The display device includes a display portion, a second communication portion, and a control portion. The first communication portion has a function of transmitting a signal including information obtained by the sensor portion. The second communication portion has a function of receiving the signal. The control portion has a function of returning from a resting state in accordance with the signal. The control portion has a function of generating first image data on the basis of the information and outputting the first image data to the display portion. The display portion has a function of displaying an image on the basis of the first image data. 
     In the above, the sensor device is preferably configured to be able to be worn on an eyeball. In the above, the sensor device is preferably configured to be able to be attached to (worn on) skin. Alternatively, the sensor device is preferably configured to be able to be worn on a wrist, a finger, or an arm. Alternatively, the sensor device is preferably fixed to clothes. 
     In the above, the sensor portion preferably has a function of detecting one or more of a blood sugar level, a heart rate, a blood pressure, a body temperature, a degree of oxygen saturation, and a neutral fat concentration. 
     In the above, in the display portion, the pixel density is preferably higher than or equal to 1000 ppi and less than or equal to 10000 ppi, and the number of pixels in a scan line direction or a signal line direction is preferably greater than or equal to 2000 and less than or equal to 10000. 
     In the above, the display device preferably includes an image capturing portion. In that case, the control portion preferably has a function of generating the first image data on the basis of the information included in the signal and second image data input from the image capturing portion and outputting the first image data to the display portion. 
     Effect of the Invention 
     According to one embodiment of the present invention, an electronic device having reduced power consumption can be provided. Alternatively, a multifunction electronic device that facilitates a reduction in weight or size can be provided. Alternatively, an electronic device that facilitates management of health condition can be provided. Alternatively, an electronic device in which an image having enhanced reality can be displayed can be provided. Alternatively, a novel display device, a novel sensor device, a novel electronic device, a novel composite device, or the like can be provided. 
     Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not have to have all of these effects. Effects other than these can be derived from the description of the specification, the drawings, the claims, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are diagrams illustrating a structure example of a composite device. 
         FIG. 2  is a diagram illustrating an operation example of a display device. 
         FIG. 3A  to  FIG. 3E  are diagrams illustrating structure examples of a sensor device. 
         FIG. 4A  to  FIG. 4C  are diagrams illustrating examples of an image. 
         FIG. 5A  and  FIG. 5B  are diagrams illustrating a structure example of a composite device. 
         FIG. 6A  and  FIG. 6B  are diagrams illustrating a structure example of an electronic device. 
         FIG. 7A  and  FIG. 7B  are diagrams illustrating a structure example of an electronic device. 
         FIG. 8A  and  FIG. 8B  are diagrams illustrating a structure example of a display panel. 
         FIG. 9A  and  FIG. 9B  are diagrams illustrating structure examples of a display module. 
         FIG. 10  is a diagram illustrating a structure example of a semiconductor device. 
         FIG. 11  is a diagram illustrating a structure example of a semiconductor device. 
         FIG. 12  is a diagram illustrating a structure example of a semiconductor device. 
         FIG. 13  is a diagram illustrating a structure example of a semiconductor device. 
         FIG. 14A  to  FIG. 14C  are diagrams illustrating a structure example of a semiconductor device. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments are described with reference to the drawings. Note that the embodiments can be implemented in many different modes, and it is readily understood by those skilled ion the art that modes and details thereof can be changed in various ways without departing from the spirit and scope thereof. Thus, the present invention should not be construed as being limited to the following description of the embodiments. 
     Note that in structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and a description thereof is not repeated. Furthermore, the same hatch pattern is used for the 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, they are not limited to the illustrated scale. 
     Note that in this specification and the like, the ordinal numbers such as “first” and “second” are used in order to avoid confusion among components and do not limit the number. 
     Embodiment 1 
     In this embodiment, a display device and a sensor device of one embodiment of the present invention and a composite device including them are described with reference to drawings. 
     [Structure Example of Composite Device] 
       FIG. 1A  illustrates a schematic diagram of a composite device  10 . The composite device  10  includes a display device  11  and a sensor device  12 . 
     The display device  11  includes a control portion  21 , a display portion  22 , an image capturing portion  23 , and a lens  24 . The sensor device  12  includes a sensor portion  31  and a communication portion  32 . 
     The display device  11  preferably has a structure that can be worn on a head of a human body. For example, the display device  11  can be used as a glasses-type display device or a goggle-type display device. Furthermore, a structure in which an image is recognized by one eye may be employed. 
     The sensor device  12  preferably has a structure that can be worn on a human body.  FIG. 1A  illustrates an example in which the sensor device  12  can be worn on an eyeball of a human body. The sensor device  12  illustrated in  FIG. 1A  can also be used as a contact lens. Note that the structure of the sensor device  12  is not limited to this and can have various modes. 
     The display portion  22  included in the display device  11  includes a plurality of pixels and has a function of displaying images. The pixel includes one or more of display elements. A variety of display elements such as a light-emitting element, a liquid crystal element, a microcapsule, an electrophoretic element, an electrowetting element, an electrofluidic element, an electrochromic element, and a MEMS element can be used as the display element. 
     In particular, the use of a light-emitting element as the display element included in the display portion  22  can obtain high contrast, and thus an image with a strong sense of reality can be displayed. As the light-emitting element, an organic EL element, an LED element, an inorganic EL element, or the like can be used. In particular, an organic EL element is preferably used. 
     Examples of the LED element include a macro LED (also referred to as a huge LED), a mini LED, a micro LED, and the like in descending order in size. Here, an LED chip whose one side size is larger than 1 mm is called a macro LED, an LED chip whose one side size is larger than 100 μm and smaller than or equal to 1 mm is called a mini LED, and an LED chip whose one side size is smaller than or equal to 100 μm is called a micro LED. It is particularly preferable to use a micro LED as an LED element applied to the pixel. The use of a micro LED can achieve an extremely high-resolution display device. 
     The display portion  22  preferably has higher resolution. The pixel density of the display portion  22  can be higher than or equal to 1000 ppi and less than or equal to 50000 ppi, preferably higher than or equal to 2000 ppi and less than or equal to 20000 ppi, further preferably higher than or equal to 3000 ppi and less than or equal to 10000 ppi, still further preferably higher than or equal to 5000 ppi and less than or equal to 10000 ppi. Typically, the pixel density can be higher than or equal to 4500 ppi and less than or equal to 5500 ppi, higher than or equal to 5500 ppi and less than or equal to 6500 ppi, or higher than or equal to 6500 ppi and less than or equal to 7500 ppi. 
     Moreover, the display portion  22  preferably has higher definition. The number of pixels in the display portion  22  in the scan line direction or the signal line direction is, for example, greater than or equal to 1000 and less than or equal to 20000, preferably greater than or equal to 2000 and less than or equal to 10000, further preferably greater than or equal to 3000 and less than or equal to 10000. When two display portions  22  are provided for a left eye and a right eye, the shape of the display region can be close to a regular square (the ratio of the lateral length to the longitudinal length is greater than or equal to 0.8 and less than or equal to 1.2). In contrast, when one display region is used for a right eye and a left eye, the shape of the display region is preferably a laterally-long rectangle (e.g., the ratio of the lateral length to the longitudinal length is greater than or equal to 1.5 and less than or equal to 5.0). Furthermore, the display portion  22  may meet the standard of television whose aspect ratio is 16:9, and in that case, the display portion  22  can have the definition of the FHD standard, the 4K2K standard, or the 8K4K standard. 
     Moreover, as the display portion  22 , what is called a see-through panel, which transmits external light, may be used. Accordingly, the display device  11  can be used as a device for AR. In that case, the display device  11  may have a structure without the image capturing portion  23 . 
     The image capturing portion  23  is provided in a position at which an image of what lies in front of the image capturing portion  23  can be taken when the display device  11  is worn. The image taken by the image capturing portion  23  can be displayed on the display portion  22  through the control portion  21 . 
     As the image capturing portion  23 , a camera can be favorably used. An image capturing element included in the image capturing portion  23  preferably has higher definition. In particular, the image capturing element preferably includes pixels whose number is the same as or greater than the number of pixels included in the display portion  22 . 
     The control portion  21  has a function of generating an image signal S 1  and outputting the image signal S 1  to the display portion  22 . The control portion  21  has a function of controlling the operation of the image capturing portion  23  and obtaining an image signal S 2  input from the image capturing portion  23 . The control portion  21  has a function of receiving a signal  33  supplied from the sensor device  12  and generating the image signal S 1  output to the display portion  22  on the basis of information included in the signal  33 . 
     For example, the control portion  21  can display an image taken by the image capturing portion  23  on the display portion  22  with almost no delay on the basis of image data that is included in the image signal S 2  and taken by the image capturing portion  23 . Furthermore, the control portion  21  can synthesize an image formed on the basis of information obtained by the sensor device  12  and an image included in the image signal S 2  and can display the synthesized image on the display portion  22 . Accordingly, what is called AR display or MR (Mixed Reality) display can be performed. 
     The sensor device  12  includes the sensor portion  31  and the communication portion  32 . The sensor device  12  can transmit information obtained by the sensor portion  31  to the control portion  21  in the display device  11  through the communication portion  32 . 
     The sensor portion  31  can include a sensor that can obtain various kinds of biological information. For example, for the sensor portion, a contact-type sensor that is in contact with a human body, an optical sensor using light, an electric sensor that uses an electron signal from a human body, a sensor that can obtain a constituent or a property of body fluids (e.g., a lachrymal fluid or sweat), or the like can be used. 
     For example, the sensor device  12  illustrated in  FIG. 1A  can measure the concentration of salinity, glucose, or the like from a lachrymal fluid by the sensor portion  31 . For example, from the concentration of glucose measured by the sensor portion  31 , a user&#39;s blood sugar level can be estimated. 
     The communication portion  32  has a function of transmitting the signal  33  including information obtained by the sensor portion  31  to the display device  11 . The communication portion  32  can have a structure including an antenna, a signal generation circuit, a modulation circuit, or the like. 
       FIG. 1A  illustrates an eyeball  41  of a user. Here, for easy understanding, a space is illustrated between the eyeball  41  and the sensor device  12 ; however, the sensor device  12  can be worn to be in contact with the eyeball  41 , in practice. 
     The lens  24  is provided between the display portion  22  and the sensor device  12  and has a function of focus adjustment. Note that a structure in which the lens  24  is not provided may be employed in the case where focus adjustment is not necessary because a sufficient distance is provided between the display portion  22  and the eyeball  41  or the case where the sensor device  12  has a function of focus adjustment, for example. 
     The user can see an image displayed on the display portion  22  through the sensor device  12  and the lens  24 . 
     When the user wears the display device  11  on his/her head and wears the sensor device  12  on the eyeball  41 , the communication distance between a communication portion  25  and the communication portion  32  becomes extremely small. Thus, power needed for communication can be extremely low, so that the power consumption of the composite device  10  can be reduced. Furthermore, since power needed for communication is low, the influence of communication radio waves on health can be small enough to be ignored. 
       FIG. 1B  is a block diagram of the composite device  10 . 
     The control portion  21  includes the communication portion  25  and an image generation portion  26 . To the control portion  21 , the image signal S 2  is input from the image capturing portion  23  and the signal  33  is input from the sensor device  12 . Furthermore, an image signal S 0  may be input from the outside. Moreover, the image signal S 1  is output from the control portion  21  to the display portion  22 . 
     The communication portion  25  has a function of receiving the signal  33  transmitted from the sensor device  12  and outputting data included in the signal to the image generation portion  26 . The communication portion  25  can have a structure including an antenna, a demodulation circuit, or the like, for example. 
     Note that in the case where the communication portion  25  and the communication portion  32  have a structure that enables mutual communication, each of them may include a demodulation circuit and a modulation circuit. 
     The communication portion  25  preferably has a function of switching to a state where operation is stopped (also referred to as a resting state) in a period during which the signal  33  is not input. In that case, the control portion  21  has a function of returning the communication portion  25  from the resting state on the basis of the input of the signal  33 . Bringing the communication portion  25  including an analog circuit into the resting state in a period during which operation is not necessary can reduce the power consumption of the control portion  21  considerably. Furthermore, the display device  11  can be reduced in size and weight. 
       FIG. 2  is a schematic timing chart showing the operation of the signal  33  and the communication portion  25 . One signal of the signal  33  has a pulse signal  33   a  and a signal  33   b  including data. As shown in  FIG. 2 , as the signal  33  transmitted from the communication portion  32 , a set of the pulse signal  33   a  and the signal  33   b  is output intermittently. 
     The operation of the communication portion  25  is roughly divided into three: a returning operation  25   a,  a processing operation  25   b,  and a resting operation  25   c,  and the three forms one set. When the control portion  21  receives the pulse signal  33   a,  the control portion  21  controls the communication portion  25  to execute the returning operation  25   a.  The communication portion  25  is made to return from the resting state by the returning operation  25   a.  After the returning operation  25   a,  the communication portion  25  demodulates the received signal  33   b,  generates data, and outputs the data to the image generation portion  26  in the processing operation  25   b.  After the output, the resting operation  25   c  is performed, and then the communication portion  25  is brought into the resting state. 
     Here, in  FIG. 2 , an operation period T act  and a resting period T off  are shown. As the resting period T off  with respect to the operation period T act  is longer, the power consumption can be reduced. For example, sampling frequencies needed for monitoring a change of biological information of a human can be less than or equal to 10 Hz, less than or equal to 5 Hz, less than or equal to 1 Hz, or less than or equal to 0.1 Hz, and thus the receiving frequencies of the signal  33  can be substantially equal to the sampling frequencies. Furthermore, the operation period T act  can be an extremely short time (e.g., several ten microseconds to several ten milliseconds), and thus the communication portion  25  can be in the resting state in most of the period. 
     When data included in the signal  33  is input from the communication portion  25 , the image generation portion  26  illustrated in  FIG. 1B  has a function of generating image data on the basis of the input data and synthesizing an image data formed on the basis of the image data and image data included in the image signal S 2  input from the image capturing portion  23 . The control portion  21  generates the image signal S 1  including the synthesized image data and outputs the image signal S 1  to the display portion  22 . 
     Furthermore, in the case where the image signal S 0  is input from the outside, the image generation portion  26  may have a function of synthesizing an image data formed on the basis of image data included in the image signal S 0  and image data generated on the basis of the data included in the signal  33   
     Moreover, the image generation portion  26  may have a function of synthesizing an image data formed on the basis of image data included in the image signal S 1 , the image data included in the image signal S 0 , and the image data generated on the basis of the data included in the signal  33 . 
     [Sensor Device] 
     Although the structure that can be worn on an eyeball of a human body is described in the above, a variety of embodiments can be used for the sensor device  12 . Other examples of the sensor device  12  are described below. 
       FIG. 3A  illustrates the sensor device  12  that is attached to skin.  FIG. 3A  illustrates a state where the sensor device  12  is attached on an arm  42 . The sensor device  12  includes the sensor portion  31  and the communication portion  32  each having a chip form. The exterior of the sensor device  12  is preferably a thin sheet-like member and preferably has flexibility or elasticity. The sensor device  12  can have a structure including an adhesive on the side of a surface in contact with the skin. 
       FIG. 3B  illustrates the sensor device  12  that can wrap around the arm  42  (wrist). The sensor device  12  includes at least the sensor portion  31  and the communication portion  32 . Furthermore, the sensor device  12  illustrated in  FIG. 3B  may include an information display portion, and for example, the sensor device  12  may function as a wrist-watch type information terminal. 
       FIG. 3C  illustrates the sensor device  12  that can be worn on a finger  43 . The sensor device  12  illustrated in  FIG. 3C  includes at least the sensor portion  31  and the communication portion  32 . The sensor device  12  may include an information display portion, and for example, the sensor device  12  may function as a ring type information terminal. Furthermore, the sensor device  12  may be an input device that has a structure including a gyroscope sensor or the like and thus uses gestures. 
       FIG. 3D  illustrates the sensor device  12  that can be worn on an upper arm  44  of a user  40 . The sensor device  12  includes at least the sensor portion  31  and the communication portion  32 . The sensor device  12  preferably has a cylindrical exterior made of a material having elasticity or an exterior having a shape in which part of a cylinder is lacking (that is, the cross-sectional shape is a schematic C shape). 
       FIG. 3E  illustrates the sensor device  12  that is fixed to the inner side of clothes  45  of the user  40 . The sensor device  12  includes at least the sensor portion  31  and the communication portion  32 . When the user  40  wears the clothes  45  on the innermost side, part of the sensor device  12  is preferably in contact with the skin. Even when the user  40  wears another clothes on the inner side of the clothes  45 , it is preferable that the sensor device  12  can obtain the user&#39;s biological information through the other clothes. Note that the sensor device  12  may be fixed to the outer side of the clothes  45  or inside the clothes  45 . 
     Here, the sensor device  12  preferably has a function of detecting at least one of a blood sugar level, a heart rate, a pulse, a blood pressure, a body temperature, a degree of oxygen saturation, and a neutral fat concentration. As described above, the blood sugar level can be estimated by measuring the concentration of glucose in a body fluid. 
     Moreover, reflectivity of an artery (arteriole) with respect to infrared light or visible light is changed in accordance with a change of a degree of blood oxygen saturation; thus, optical measurement of the artery can be performed. By obtaining this change over time, i.e., temporal modulation of a degree of blood oxygen saturation, information on the pulse wave can be obtained. Thus, the user&#39;s heart rate can be measured. Furthermore, with infrared light or visible light, the neutral fat concentration in blood, the glucose concentration in blood or a corium, or the like can be detected. 
     When a structure in which an electrode in contact with the skin is provided is used for the sensor portion  31 , an electrocardiogram can be measured. 
     The blood pressure can be calculated from a difference in timing of two pulsations of the electrocardiogram and the pulse wave (a period of pulse wave propagation time), for example. A high blood pressure results in a short pulse wave propagation time, whereas a low blood pressure results in a long pulse wave propagation time. The body conditions of the user can be estimated from a relationship between the heart rate and the blood pressure that are calculated from the electrocardiogram and the pulse wave. For example, when both the heart rate and the blood pressure are high, it can be estimated that the user is nervous or excited, whereas when both the heart rate and the blood pressure are low, it can be estimated that the user is relaxed. When the state where the blood pressure is low and the heart rate is high is continued, the user might suffer from a heart disease or the like. 
     Note that it is preferable to provide a means of obtaining other biological information for the sensor device  12  or the display device  11 . Examples of such biological information include internal biological information on an electrocardiogram, a blood pressure, a body temperature, and the like and superficial biological information on facial expression, a complexion, a pupil, and the like. In addition, information on the number of steps taken, exercise intensity, a height difference in a movement, and a meal (e.g., calorie intake and nutrients) are important for health care. The use of a plurality of kinds of biological information and the like enables complex management of physical conditions, leading to not only daily health management but also early detection of injuries and diseases. 
     The sensor device  12  may include a GPS (Global Positioning System) with which position information can be obtained. The sensor device  12  may have a function of electronic payment. 
     [Example of Image] 
     Examples of images that can be shown to a user by the composite device  10  are described below. 
       FIG. 4A  illustrates an example of an image  50   a  that is reflected on the field of vision of the user at meals. In the image  50   a,  image information  51   a  is superimposed on an actual image taken by the image capturing portion  23 . In the image information  51   a  illustrated in  FIG. 4A , an icon image that represents a blood sugar level (an image resembling a cube sugar), a comment for warning the user of a high blood sugar level, and an estimated blood sugar level are shown (CAUTION!! 140 mg/dL). The user notices that his/her blood sugar level is high from the image information  51   a,  and can take actions such as eating less, canceling the order of a dessert, or ordering a drink for inhibiting an increase in the blood sugar level. 
       FIG. 4B  illustrates an example of an image  50   b  that is reflected on the field of vision of the user who is hiking. Image information  51   b  is shown in the image  50   b.  In the image information  51   b,  an icon image that represents a heart rate (an image resembling a heart), a comment for warning the user of a high heart rate, and an estimated heart rate are shown (CAUTION!! 130 bpm). The user can notice that his/her heart rate is high from the image information  51   b,  and can take actions such as taking a rest or walking slowly. 
       FIG. 4C  illustrates an example of an image  50   c  that is reflected on the field of vision of the user who calls his/her subordinate and is reprimanding him/her. Image information  51   c  is shown in the image  50   c.  In the image information  51   c,  an icon image that represents a blood pressure (an image resembling a heart and an electrocardiogram), a comment for warning the user of a high blood pressure, and an estimated blood pressure are shown (CAUTION!! 160 mmHg). The user can notice that he or she is extremely excited from the image information  51   c,  and can take actions such as breathing deeply to quell his/her anger or reconsidering a way of communicating with his/her subordinate. 
     Although the examples in which the comments for warning the user are illustrated are shown in the above, display for urging the user to do a specific action may be performed. For example, in the situation shown in  FIG. 4C , a comment for urging the user to breathe deeply, an animation image, or the like may be shown. 
     MODIFICATION EXAMPLE 
     Modification examples of the above structure example are described below. 
       FIG. 5A  is a schematic diagram of the composite device  10   a,  and  FIG. 5B  is a block diagram of the composite device  10   a.    
     The composite device  10   a  includes the sensor device  12   a  having a function of displaying an image and an information processing device  13 . 
     The sensor device  12   a  includes a display portion  34  in addition to the sensor portion  31  and the communication portion  32 . The display portion  34  has a function of displaying an image. As the display portion  34 , a see-through display can be favorably used. 
     The communication portion  32  has a function of transmitting the signal  33  including information obtained by the sensor portion  31  to the information processing device  13 . Furthermore, the communication portion  32  has a function of demodulating a signal  27  received from the information processing device  13  and outputting an image signal included in the signal  27  to the display portion  34 . 
     The display portion  34  can display an image on the basis of the image signal input from the communication portion  32 . 
     The information processing device  13  includes the control portion  21 . The control portion  21  includes the communication portion  25  and the image generation portion  26 . 
     The communication portion  25  has a function of receiving the signal  33  transmitted from the sensor device  12   a  and outputting data included in the signal to the image generation portion  26 . Moreover, the communication portion  25  has a function of transmitting the signal  27 , which is input from the image generation portion  26  and includes the image signal S 1 , to the sensor device  12   a.    
     When data included in the signal  33  is input from the communication portion  25 , the image generation portion  26  has a function of generating the image signal S 1  on the basis of the input data and outputting the image signal S 1  to the communication portion  25 . 
     The user can see an image displayed on the display portion  34  in a state where the image is superimposed on a transmission image that is transmitted through the sensor device  12   a.  The composite device  10   a  can show AR display to the user. Alternatively, a structure in which the display portion  34  does not transmit light may be employed to show VR display to the user. 
     With such a structure, the structure of the composite device  10   a  can be extremely simple. Furthermore, since the information processing device  13  is easily reduced in size and weight, the information processing device  13  can be put into a pocket or a bag. In that case, the composite device  10   a  does not bother the user since a device worn on a head is not required. 
     At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate. 
     Embodiment 2 
     In this embodiment, structure examples of electronic devices each of which includes a display device and can be used for the composite device of one embodiment of the present invention are described. 
       FIG. 6A  is a perspective view of an electronic device  900  that is of a glasses type. The electronic device  900  includes a pair of display panels  901 , a pair of housings (a housing  902   a  and a housing  902   b ), a pair of optical members  903 , a pair of mounting portions  904 , and the like. 
     The electronic device  900  can project an image displayed on the display panel  901  onto a display region  906  of the optical member  903 . Since the optical members  903  have a light-transmitting property, a user can see images displayed on the display regions  906 , which are superimposed on transmission images seen through the optical members  903 . Thus, the electronic device  900  is an electronic device capable of AR display. 
     One housing  902   a  is provided with a camera  905  capable of capturing an image of what lies in front thereof. Furthermore, the housing  902   a  includes a wireless communication device  907 , and a video signal or the like can be supplied to the housing  902   a  and the housing  902   b.  Instead of or in addition to the wireless communication device  907 , a connector that can be connected to a cable for supplying a video signal or a power supply potential may be provided. Furthermore, when the housing  902   a  or the housing  902   b  is provided with an acceleration sensor such as a gyroscope sensor, the orientation of the user&#39;s head can be detected and an image corresponding to the orientation can be displayed on the display region  906 . Moreover, the housing  902   a  or the housing  902   b  is preferably provided with a battery, in which case charging can be performed with or without a wire. 
     Furthermore, the housing  902   b  includes a processor  908 . The processor  908  has a function of controlling the components of the electronic device  900 , such as the camera  905 , the wireless communication device  907 , and the pair of display panels  901 , a function of generating an image, and the like. The processor  908  may have a function of generating a synthesized image for AR display. 
     Data communication with an external device can be performed by the wireless communication device  907 . For example, when data transmitted from the outside is output to the processor  908 , the processor  908  can generate image data for AR display on the basis of the transmitted data. Examples of the data transmitted from the outside include, in addition to image data, data including biological information transmitted from a biological sensor device or the like. 
     Next, a method for projecting an image on the display region  906  of the electronic device  900  is described with reference to  FIG. 6B . The display panel  901 , a lens  911 , and a reflective plate  912  are provided in a housing  902  (the housing  902   a  and the housing  902   b ). A reflective surface  913  functioning as a half mirror is provided in a portion corresponding to the display region  906  of the optical member  903 . 
     Light  915  emitted from the display panel  901  passes through the lens  911  and is reflected by the reflective plate  912  to the optical member  903  side. In the optical member  903 , the light  915  is fully reflected repeatedly by end surfaces of the optical member  903  and reaches the reflective surface  913 , whereby an image is projected on the reflective surface  913 . Accordingly, the user can see both the light  915  reflected by the reflective surface  913  and transmitted light  916  that has passed through the optical member  903  (including the reflective surface  913 ). 
       FIG. 6B  shows an example in which a surface of the reflective plate  912  and the reflective surface  913  each have a curved surface. This can increase optical design flexibility and reduce the thickness of the optical member  903 , compared to the case where they have flat surfaces. Note that the surface of the reflective plate  912  and the reflective surface  913  may have flat surfaces. 
     The reflective plate  912  can use a component having a mirror surface, and preferably has high reflectivity. As the reflective surface  913 , a half mirror utilizing reflection of a metal film may be used, but the use of a prism utilizing total reflection or the like can increase the transmittance of the transmitted light  916 . 
     Here, the housing  902  preferably includes a mechanism for adjusting the distance and angle between the lens  911  and the display panel  901 . This enables focus adjustment, zooming in/out of an image, or the like. One or both of the lens  911  and the display panel  901  are configured to be movable in the optical-axis direction, for example. 
     The housing  902  preferably includes a mechanism capable of adjusting the angle of the reflective plate  912 . The position of the display region  906  where images are displayed can be changed by changing the angle of the reflective plate  912 . Thus, the display region  906  can be placed at the optimal position in accordance with the position of the user&#39;s eye. 
     The display device or the display module of one embodiment of the present invention can be used for the display panel  901 . Thus, the electronic device  900  can perform display with extremely high resolution. 
       FIG. 7A  and  FIG. 7B  illustrate perspective views of a goggle-type electronic device  950 .  FIG. 7A  is a perspective view illustrating the front surface, the top surface, and the left side surface of the electronic device  950 , and  FIG. 7B  is a perspective view illustrating the back surface, the bottom surface, and the right side surface of the electronic device  950 . 
     The electronic device  950  includes a pair of display panels  951 , a housing  952 , a pair of mounting portions  954 , a cushion  955 , a pair of lenses  956 , and the like. The pair of display panels  951  is positioned to be seen through the lenses  956  inside the housing  952 . 
     The electronic device  950  is an electronic device for VR. A user wearing the electronic device  950  can see an image displayed on the display panels  951  through the lenses  956 . Furthermore, when the pair of display panels  951  displays different images, three-dimensional display using parallax can be performed. Furthermore, the housing  952  included in the electronic device  950  may be provided with a waterproof function so that the electronic device  950  can be used also in the water. In that case, it is preferable to make the housing  952  have a streamlined shape, in which case water resistance can be reduced and thus the user can swim faster. 
     An input terminal  957  and an output terminal  958  are provided on the back surface side of the housing  952 . To the input terminal  957 , a cable for supplying a video signal from a video output device or the like, power for charging a battery provided in the housing  952 , or the like can be connected. The output terminal  958  can function as, for example, an audio output terminal to which earphones, headphones, or the like can be connected. Note that in the case where audio data can be output by wireless communication or sound is output from an external video output device, the audio output terminal is not necessarily provided. 
     The housing  952  is provided with a camera  959  capable of taking an image of what lies in front thereof. The electronic device  950  can display an image taken by the camera  959  or a synthesized image using the image. The electronic device  950  can perform AR display and MR display in addition to VR display. 
     Furthermore, a processor  961  and a wireless communication device  962  are provided in the housing  952 . The processor  961  can control the components of the electronic device  950 , such as a pair of display panels  951 , the camera  959 , the wireless communication device  962 , and the like. In addition, the processor  961  can form an image to be displayed on the display panel  951 . 
     Furthermore, data communication with an external device can be performed by the wireless communication device  962 . For example, when data transmitted from the outside is output to the processor  961 , the processor  961  can generate image data for VR display, AR display, or MR display on the basis of the transmitted data. Examples of the data transmitted from the outside include, in addition to image data, data including biological information transmitted from a biological sensor device or the like. 
     In addition, the housing  952  preferably includes a mechanism by which the left and right positions of the lenses  956  and the display panels  951  can be adjusted to the optimal positions in accordance with the positions of the user&#39;s eyes. In addition, a mechanism for adjusting focus by change in the distance between the lens  956  and the display panel  951  is preferably included. 
     The display device or the display module of one embodiment of the present invention can be used for the display panel  951 . Thus, the electronic device  950  can perform display with extremely high resolution. This enables a user to feel high sense of immersion. 
     The cushion  955  is a portion in contact with the user&#39;s face (forehead, cheek, or the like). The cushion  955  is in close contact with the user&#39;s face, so that light leakage can be prevented, which further increases the sense of immersion. A soft material is preferably used for the cushion  955  so that the cushion  955  is in close contact with the user&#39;s face when the user wears the electronic device  950 . For example, a material such as rubber, silicone rubber, urethane, or sponge can be used. Furthermore, when a sponge or the like whose surface is covered with cloth, leather (natural leather or synthetic leather), or the like is used, a gap is unlikely to be generated between the user&#39;s face and the cushion  955 , whereby light leakage can be suitably prevented. Furthermore, using such a material is preferable because it has a soft texture and the user does not feel cold when wearing the device in a cold season, for example. The member in contact with user&#39;s skin, such as the cushion  955  or the mounting portion  954 , is preferably detachable, in which case cleaning or replacement can be easily performed. 
     At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate. 
     Embodiment 3 
     In this embodiment, a structure example of a display panel that can be applied to the composite device according to one embodiment of the present invention is described. The display panel described below as an example can have extremely high resolution and thus can be favorably used for a display device or a display portion included in a sensor device. 
     [Pixel Structure Example] 
     An example of a pixel layout suitable for a high-resolution display panel is described below. 
     For example, a structure shown below enables a display device where pixels including light-emitting elements are arranged in a display region at a resolution (pixel density) higher than or equal to 1000 ppi and less than or equal to 50000 ppi, preferably higher than or equal to 2000 ppi and less than or equal to 20000 ppi, further preferably higher than or equal to 3000 ppi and less than or equal to 10000 ppi, still further preferably higher than or equal to 5000 ppi and less than or equal to 10000 ppi. Typically, the pixel density can be higher than or equal to 4500 ppi and less than or equal to 5500 ppi, higher than or equal to 5500 ppi and less than or equal to 6500 ppi, or higher than or equal to 6500 ppi and less than or equal to 7500 ppi 
     [Structure Example of Pixel Circuit] 
       FIG. 8A  shows an example of a circuit diagram of a pixel unit  70 . The pixel unit  70  is composed of two pixels (a pixel  70   a  and a pixel  70   b ). In addition, the pixel unit  70  is connected to a wiring  91   a,  a wiring  91   b,  a wiring  92   a,  a wiring  92   b,  a wiring  92   c,  a wiring  92 d, a wiring  93   a,  a wiring  93   b,  a wiring  93   c  and the like. 
     The pixel  70   a  includes a subpixel  71   a,  a subpixel  72   a,  and a subpixel  73   a.  The pixel  70   b  includes a subpixel  71   b,  a subpixel  72   b,  and a subpixel  73   b.  The subpixel  71   a,  the subpixel  72   a,  and the subpixel  73   a  include a pixel circuit  81   a,  a pixel circuit  82   a,  and a pixel circuit  83   a,  respectively. The subpixel  71   b,  the subpixel  72   b,  and the subpixel  73   b  include a pixel circuit  81   b,  a pixel circuit  82   b,  and a pixel circuit  83   b,  respectively. 
     Each subpixel includes the pixel circuit and a display element  60 . For example, the subpixel  71   a  includes the pixel circuit  81   a  and the display element  60 . A light-emitting element such as an organic EL element is used here as the display element  60 . 
     The wiring  91   a  and the wiring  91   b  each have a function as a scan line (also referred to as a gate line). The wiring  92   a,  the wiring  92   b,  the wiring  92   c,  and the wiring  92 d each have a function as a signal line (also referred to as a source line or a data line). The wiring  93   a,  the wiring  93   b,  and the wiring  93   c  each have a function of supplying a potential to the display element  60 . 
     The pixel circuit  81   a  is electrically connected to the wiring  91   a,  the wiring  92   a,  and the wiring  93   a.  The pixel circuit  82   a  is electrically connected to the wiring  91   b,  the wiring  92 d, and the wiring  93   a.  The pixel circuit  83   a  is electrically connected to the wiring  91   a,  the wiring  92   b,  and the wiring  93   b.  The pixel circuit  81   b  is electrically connected to the wiring  91   b,  the wiring  92   a,  and the wiring  93   b.  The pixel circuit  82   b  is electrically connected to the wiring  91   a,  the wiring  92   c,  and the wiring  93   c.  The pixel circuit  83   b  is electrically connected to the wiring  91   b,  the wiring  92   b,  and the wiring  93   c.    
     With the structure shown in  FIG. 8A  in which two gate lines are connected to one pixel, the number of source lines can be conversely reduced by half as compared with that in stripe arrangement. As a result, the number of ICs used as source driver circuits can be reduced by half and the number of components can be reduced. 
     One wiring functioning as a signal line is preferably connected to pixel circuits corresponding to the same color. For example, when a signal with an adjusted potential is supplied to the wiring to correct for variation in luminance between pixels, the correction value may greatly vary between colors. Thus, when pixel circuits connected to one signal line are pixel circuits corresponding to the same color, the correction can be performed easily. 
     In addition, each pixel circuit includes a transistor  61 , a transistor  62 , and a capacitor  63 . In the pixel circuit  81   a,  for example, a gate of the transistor  61  is electrically connected to the wiring  91   a,  one of a source and a drain of the transistor  61  is electrically connected to the wiring  92   a,  and the other of the source and the drain is electrically connected to a gate of the transistor  62  and one electrode of the capacitor  63 . One of a source and a drain of the transistor  62  is electrically connected to one electrode of the display element  60 , and the other of the source and the drain is electrically connected to the other electrode of the capacitor  63  and the wiring  93   a.  The other electrode of the display element  60  is electrically connected to a wiring to which a potential V 1  is applied. 
     Note that, as shown in  FIG. 8A , the other pixel circuits are similar to the pixel circuit  81   a  except that any of the wiring to which the gate of the transistor  61  is connected, the wiring to which the one of the source and the drain of the transistor  61  is connected, and the wiring to which the other electrode of the capacitor  63  is connected is different between the pixel circuit  81   a  and the other pixel circuits. 
     In  FIG. 8A , the transistor  61  serves as a selection transistor. The transistor  62  is in a series connection with the display element  60  and has a function of controlling a current flowing into the display element  60 . The capacitor  63  has a function of holding the potential of a node connected to the gate of the transistor  62 . Note that the capacitor  63  does not have to be intentionally provided in the case where an off-state leakage current of the transistor  61 , a leakage current through the gate of the transistor  62 , and the like are extremely small. 
     The transistor  62  preferably includes a first gate and a second gate electrically connected to each other as shown in  FIG. 8A . This structure with the two gates can increase the amount of current that the transistor  62  can carry. Such a structure is particularly preferable for a high-resolution display device because the amount of current can be increased without increasing the size, the channel width in particular, of the transistor  62 . 
     Note that the transistor  62  may have one gate. This structure eliminates the need for forming the second gate and thus can simplify the process as compared with the above structure. The transistor  61  may have two gates. This structure enables a reduction in size of each transistor. A first gate and a second gate of each transistor can be electrically connected to each other. Alternatively, one gate may be electrically connected to a different wiring. In this case, threshold voltages of the transistors can be controlled by varying potentials that are applied to the wirings. 
     One of a pair of electrodes of the display element  60  that is electrically connected to the transistor  62  corresponds to a pixel electrode.  FIG. 8A  shows a structure where an electrode of the display element  60  that is electrically connected to the transistor  62  is a cathode and the opposite electrode is an anode. This structure is particularly effective when the transistor  62  is an n-channel transistor. That is, when the transistor  62  is on, the potential applied by the wiring  93   a  is a source potential; accordingly, the amount of current flowing into the transistor  62  can be constant regardless of variation or change in resistance of the display element  60 . Alternatively, a p-channel transistor may be used as a transistor of the pixel circuit. 
     [Structure Example of Display Element] 
       FIG. 8B  is a schematic top view illustrating an example of a layout of display elements.  FIG. 8B  is a schematic top view of two pixel units. 
     The pixel  70   a  includes a display element R 1 , a display element G 1 , and a display element B 1 . The pixel  70   b  includes a display element R 2 , a display element G 2 , and a display element B 2 . The display element R 1  and the display element R 2  exhibit a red color, the display element G 1  and the display element G 2  exhibit a green color, and the display element B 1  and the display element B 2  exhibit a blue color. 
     As the arrangement of the display element R 1  and the display element R 2 , they are arranged in a zigzag line in the longitudinal direction. Similarly, the display element G 1  and the display element G 2  are also arranged in a zigzag line, and the display element B 1  and the display element B 2  are also arranged in a zigzag line. With such a structure, the viewing angle dependence is improved, which brings an effect that deviation of chromaticity or luminance is less likely to occur when the device is seen from an oblique direction with respect to the display surface. 
     The above is the description of the structure examples of the pixels. 
     [Structure Example of Display Module] 
     A structure example of a display module of one embodiment of the present invention is described below. 
       FIG. 9A  is a schematic perspective view of a display module  280 . The display module  280  includes a display device  200  and an FPC  290 . 
     The display module  280  includes the substrate  201  and the substrate  202 . A display portion  281  is also included on the substrate  202  side. The display portion  281  is a region of the display module  280  where an image is displayed and is a region where light emitted from pixels provided in a pixel portion  284  described later can be seen. 
       FIG. 9B  illustrates a perspective view schematically illustrating a structure on the substrate  201  side. The substrate  201  has a structure in which a circuit portion  282 , a pixel circuit portion  283  over the circuit portion  282 , and the pixel portion  284  over the pixel circuit portion  283  are stacked. In addition, a terminal portion  285  for connection to the FPC  290  is included in a portion not overlapping with the pixel portion  284  over the substrate  201 . The terminal portion  285  and the circuit portion  282  are electrically connected to each other through a wiring portion  286  formed of a plurality of wirings. 
     The pixel portion  284  includes a plurality of pixels  284   a  arranged in a matrix. An enlarged view of one pixel  284   a  is illustrated on the right side of  FIG. 9B . The pixel  284   a  includes the display element R 1 , the display element G 1 , the display element B 1 , the display element R 2 , the display element G 2 , and the display element B 2 . The pixel  284   a  corresponds to the pixel unit  70  that is described above with reference to  FIG. 8A  and  FIG. 8B  as an example. 
     The pixel circuit portion  283  includes a plurality of pixel circuits  283   a  arranged in a matrix. One pixel circuit  283   a  is a circuit that controls light emission of six display elements included in one pixel  284   a.  One pixel circuit  283   a  may be provided with six circuits for controlling light emission of respective display elements. For example, the pixel circuit  283   a  for one display element can include at least one selection transistor, one current control transistor (driving transistor), and a capacitor. In this case, a gate signal is input to a gate of the selection transistor and a source signal is input to one of a source and a drain thereof. With such a structure, an active-matrix display device is achieved. 
     The circuit portion  282  includes a circuit for driving the pixel circuits  283   a  in the pixel circuit portion  283 . For example, a gate line driver circuit and a source line driver circuit are preferably included. In addition, an arithmetic circuit, a memory circuit, a power supply circuit, or the like may be included. 
     The FPC  290  functions as a wiring for supplying a video signal or a power supply potential to the circuit portion  282  from the outside. In addition, an IC may be mounted on the FPC  290 . 
     The display module  280  can have a structure in which the pixel circuit portion  283 , the circuit portion  282 , and the like are stacked below the pixel portion  284 ; thus, the aperture ratio (the effective display area ratio) of the display portion  281  can be significantly high. For example, the aperture ratio of the display portion  281  can be greater than or equal to 40% and less than 100%, preferably greater than or equal to 50% and less than or equal to 95%, and further preferably greater than or equal to 60% and less than or equal to 95%. Furthermore, the pixels  284   a  can be arranged extremely densely and thus the display portion  281  can have extremely high resolution. For example, in the display portion  281 , the pixels  284   a  are preferably arranged with a resolution (pixel density) higher than or equal to 1000 ppi and less than or equal to 50000 ppi, preferably higher than or equal to 2000 ppi and less than or equal to 20000 ppi, further preferably higher than or equal to 3000 ppi and less than or equal to 10000 ppi, still further preferably higher than or equal to 5000 ppi and less than or equal to 10000 ppi. Typically, the pixel density can be higher than or equal to 4500 ppi and less than or equal to 5500 ppi, higher than or equal to 5500 ppi and less than or equal to 6500 ppi, or higher than or equal to 6500 ppi and less than or equal to 7500 ppi. 
     Such a display module  280  has extremely high resolution, and thus can be suitably used for a device for VR such as a head-mounted display or a glasses-type device for AR. For example, even in the case of a structure in which the display portion of the display module  280  is seen through a lens, pixels of the extremely-high-resolution display portion  281  included in the display module  280  are prevented from being seen when the display portion is enlarged by the lens, so that display providing a high sense of immersion can be performed. Without limitation to the above, the display module  280  can also be suitably used for an electronic device having a relatively small display portion. For example, the display module  280  can also be suitably used for a display portion of a wearable electronic device such as a wrist-watch type electronic device. 
     At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate. 
     Embodiment 4 
     In this embodiment, an example of a CPU to which the composite system of one embodiment of the present invention can be applied is described. The CPU described below as an example can be favorably used especially for a control portion included in a display device. 
     &lt;Structure of CPU&gt; 
     A semiconductor device  5400  shown in  FIG. 10  includes a CPU core  5401 , a power management unit  5421 , and a peripheral circuit  5422 . The power management unit  5421  includes a power controller  5402  and a power switch  5403 . The peripheral circuit  5422  includes a cache  5404  including a cache memory, a bus interface (BUS I/F)  5405 , and a debug interface (Debug I/F)  5406 . The CPU core  5401  includes a data bus  5423 , a control unit  5407 , a PC (program counter)  5408 , a pipeline register  5409 , a pipeline register  5410 , an ALU (Arithmetic logic unit)  5411 , and a register file  5412 . Data is transmitted between the CPU core  5401  and the peripheral circuit  5422  such as the cache  5404  via the data bus  5423 . 
     The semiconductor device (cell) can be used for many logic circuits typified by the power controller  5402  and the control unit  5407 . The semiconductor device (cell) can be used particularly for all logic circuits that can be constituted using standard cells. Accordingly, the semiconductor device  5400  can be small. The semiconductor device  5400  can have reduced power consumption. The semiconductor device  5400  can have a higher operating speed. The semiconductor device  5400  can have a smaller power supply voltage variation. 
     When p-channel Si transistors and the transistor described in the above embodiment which includes an oxide semiconductor (preferably an oxide containing In, Ga, and Zn) in a channel formation region are used in the semiconductor device (cell) and the semiconductor device (cell) is used in the semiconductor device  5400 , the semiconductor device  5400  can be small. The semiconductor device  5400  can have reduced power consumption. The semiconductor device  5400  can have a higher operating speed. Particularly when the Si transistors are only p-channel ones, the manufacturing cost can be reduced. 
     The control unit  5407  has functions of decoding and executing instructions contained in a program such as input applications by controlling the overall operations of the PC  5408 , the pipeline register  5409 , the pipeline register  5410 , the ALU  5411 , the register file  5412 , the cache  5404 , the bus interface  5405 , the debug interface  5406 , and the power controller  5402 . 
     The ALU  5411  has a function of performing a variety of arithmetic operations such as four arithmetic operations and logic operations. 
     The cache  5404  has a function of temporarily storing frequently used data. The PC  5408  is a register having a function of storing an address of an instruction to be executed next. Note that although not shown in  FIG. 10 , the cache  5404  is provided with a cache controller for controlling the operation of the cache memory. 
     The pipeline register  5409  has a function of temporarily storing instruction data. 
     The register file  5412  includes a plurality of registers including a general-purpose register and can store data that is read from the main memory, data obtained as a result of arithmetic operations in the ALU  5411 , or the like. 
     The pipeline register  5410  has a function of temporarily storing data used for arithmetic operations in the ALU  5411 , data obtained as a result of arithmetic operations in the ALU  5411 , or the like. 
     The bus interface  5405  functions as a path for data between the semiconductor device  5400  and various devices outside the semiconductor device  5400 . The debug interface  5406  functions as a path of a signal for inputting an instruction to control debugging to the semiconductor device  5400 . 
     The power switch  5403  has a function of controlling supply of a power supply voltage to various circuits included in the semiconductor device  5400  other than the power controller  5402 . The above various circuits belong to several different power domains. The power switch  5403  controls whether the power supply voltage is supplied to the various circuits in the same power domain. In addition, the power controller  5402  has a function of controlling the operation of the power switch  5403 . 
     The semiconductor device  5400  having the above structure can perform power gating. An example of the power gating operation sequence is described. 
     First, by the CPU core  5401 , timing for stopping the supply of the power supply voltage is set in a register of the power controller  5402 . Then, an instruction of starting power gating is sent from the CPU core  5401  to the power controller  5402 . Then, various registers and the cache  5404  included in the semiconductor device  5400  start data saving. Then, the power switch  5403  stops the supply of the power supply voltage to the various circuits included in the semiconductor device  5400  other than the power controller  5402 . Then, an interrupt signal is input to the power controller  5402 , whereby the supply of the power supply voltage to the various circuits included in the semiconductor device  5400  is started. Note that a counter may be provided in the power controller  5402  to be used to determine the timing of starting the supply of the power supply voltage regardless of input of an interrupt signal. Next, the various registers and the cache  5404  start data restoration. Then, execution of an instruction is resumed in the control unit  5407 . 
     Such power gating can be performed in the whole processor or one or a plurality of logic circuits included in the processor. Furthermore, power supply can be stopped even for a short time. Consequently, power consumption can be reduced at a fine spatial or temporal granularity. 
     In performing power gating, data retained by the CPU core  5401  or the peripheral circuit  5422  is preferably saved in a short time. In that case, the power can be turned on or off in a short time, and an effect of saving power becomes significant. 
     In order that the data retained by the CPU core  5401  or the peripheral circuit  5422  be saved in a short time, the data is preferably saved in a flip-flop circuit itself (referred to as a flip-flop circuit capable of backup operation). Furthermore, the data is preferably saved in an SRAM cell itself (referred to as an SRAM cell capable of backup operation). The flip-flop circuit and SRAM cell that are capable of backup operation preferably include transistors including an oxide semiconductor (preferably an oxide containing In, Ga, and Zn) in a channel formation region. Consequently, the transistor has a low off-state current; thus, the flip-flop circuit and SRAM cell that are capable of backup operation can retain data for a long time without power supply. When the transistor has a high switching speed, the flip-flop circuit and SRAM cell that are capable of backup operation can save and restore data in a short time in some cases. 
     An example of the flip-flop circuit capable of backup operation is described with reference to  FIG. 11 . 
     A semiconductor device  5500  shown in  FIG. 11  is an example of the flip-flop circuit capable of backup operation. The semiconductor device  5500  includes a first memory circuit  5501 , a second memory circuit  5502 , a third memory circuit  5503 , and a read circuit  5504 . As a power supply voltage, a potential difference between a potential V 1  and a potential V 2  is supplied to the semiconductor device  5500 . One of the potential V 1  and the potential V 2  is at a high level, and the other is at a low level. An example of the structure of the semiconductor device  5500  when the potential V 1  is at a low level and the potential V 2  is at a high level is described below. 
     The first memory circuit  5501  has a function of retaining data when a signal D including the data is input in a period during which the power supply voltage is supplied to the semiconductor device  5500 . Furthermore, the first memory circuit  5501  outputs a signal Q including the retained data in the period during which the power supply voltage is supplied to the semiconductor device  5500 . On the other hand, the first memory circuit  5501  cannot retain data in a period during which the power supply voltage is not supplied to the semiconductor device  5500 . That is, the first memory circuit  5501  can be referred to as a volatile memory circuit. 
     The second memory circuit  5502  has a function of reading the data retained in the first memory circuit  5501  to store (or save) it. The third memory circuit  5503  has a function of reading the data retained in the second memory circuit  5502  to store (or save) it. The read circuit  5504  has a function of reading the data retained in the second memory circuit  5502  or the third memory circuit  5503  to store (or restore) it in the first memory circuit  5501 . 
     In particular, the third memory circuit  5503  has a function of reading the data retained in the second memory circuit  5502  to store (or save) it even in the period during which the power supply voltage is not supplied to the semiconductor device  5500 . 
     As shown in  FIG. 11 , the second memory circuit  5502  includes a transistor  5512  and a capacitor  5519 . The third memory circuit  5503  includes a transistor  5513 , a transistor  5515 , and a capacitor  5520 . The read circuit  5504  includes a transistor  5510 , a transistor  5518 , a transistor  5509 , and a transistor  5517 . 
     The transistor  5512  has a function of charging and discharging the capacitor  5519  in accordance with data retained in the first memory circuit  5501 . The transistor  5512  is desirably capable of charging and discharging the capacitor  5519  at a high speed in accordance with data retained in the first memory circuit  5501 . Specifically, the transistor  5512  desirably contains crystalline silicon (preferably polycrystalline silicon, further preferably single crystal silicon) in a channel formation region. 
     The conduction state or the non-conduction state of the transistor  5513  is determined in accordance with the charge retained in the capacitor  5519 . The transistor  5515  has a function of charging and discharging the capacitor  5520  in accordance with the potential of a wiring  5544  when the transistor  5513  is in a conduction state. It is desirable that the off-state current of the transistor  5515  be extremely low. Specifically, the transistor  5515  desirably contains an oxide semiconductor (preferably an oxide containing In, Ga, and Zn) in a channel formation region. 
     Specific connection relations between the elements are described. One of a source and a drain of the transistor  5512  is connected to the first memory circuit  5501 . The other of the source and the drain of the transistor  5512  is connected to one electrode of the capacitor  5519 , a gate of the transistor  5513 , and a gate of the transistor  5518 . The other electrode of the capacitor  5519  is connected to a wiring  5542 . One of a source and a drain of the transistor  5513  is connected to the wiring  5544 . The other of the source and the drain of the transistor  5513  is connected to one of a source and a drain of the transistor  5515 . The other of the source and the drain of the transistor  5515  is connected to one electrode of the capacitor  5520  and a gate of the transistor  5510 . The other electrode of the capacitor  5520  is connected to a wiring  5543 . One of a source and a drain of the transistor  5510  is connected to a wiring  5541 . The other of the source and the drain of the transistor  5510  is connected to one of a source and a drain of the transistor  5518 . The other of the source and the drain of the transistor  5518  is connected to one of a source and a drain of the transistor  5509 . The other of the source and the drain of the transistor  5509  is connected to one of a source and a drain of the transistor  5517  and the first memory circuit  5501 . The other of the source and the drain of the transistor  5517  is connected to a wiring  5540 . Although a gate of the transistor  5509  is connected to a gate of the transistor  5517  in  FIG. 11 , the gate of the transistor  5509  is not necessarily connected to the gate of the transistor  5517 . 
     As the transistor  5515 , a transistor using an oxide semiconductor can be used. Because of the low off-state current of the transistor  5515 , the semiconductor device  5500  can retain data for a long time without power supply. The favorable switching characteristics of the transistor  5515  allow the semiconductor device  5500  to perform high-speed backup and recovery. 
     At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate. 
     Embodiment 5 
     In this embodiment, a structure example of a semiconductor device that can be used for the display device or the sensor device included in the composite device of one embodiment of the present invention is described. The semiconductor device described below can be particularly used for the control portion included in the display device. The semiconductor device described below can be used not only for the control portion but also for an image capturing portion, a sensor portion or the communication portion included in the sensor device, or the like. 
     A semiconductor device in  FIG. 12  includes a transistor  300 , a transistor  500 , and a capacitor  800 .  FIG. 14A  is a cross-sectional view of the transistor  500  in the channel length direction,  FIG. 14B  is a cross-sectional view of the transistor  500  in the channel width direction, and  FIG. 14C  is a cross-sectional view of the transistor  300  in the channel width direction. 
     The transistor  500  is a transistor including a metal oxide in its channel formation region (an OS transistor). Since the off-state current of the transistor  500  is low, when the transistor  500  is used as an OS transistor included in the semiconductor device, written data can be retained for a long time. 
     The semiconductor device described in this embodiment includes the transistor  300 , the transistor  500 , and the capacitor  800 , as shown in  FIG. 12 . The transistor  500  is provided above the transistor  300 , and the capacitor  800  is provided above the transistor  300  and the transistor  500 . 
     The transistor  300  is provided over a substrate  311  and includes a conductor  316 , an insulator  315 , a semiconductor region  313  that is part of the substrate  311 , and a low-resistance region  314   a  and a low-resistance region  314   b  each functioning as a source region or a drain region. Note that the transistor  300  can be used as the transistor included in the memory, for example. 
     As shown in  FIG. 14C , in the transistor  300 , a top surface and a side surface in the channel width direction of the semiconductor region  313  are covered with the conductor  316  with the insulator  315  therebetween. Such a Fin-type transistor  300  can have an increased effective channel width, and thus have improved on-state characteristics. In addition, since contribution of an electric field of a gate electrode can be increased, the off-state characteristics of the transistor  300  can be improved. 
     Note that the transistor  300  can be either a p-channel transistor or an n-channel transistor. 
     A region of the semiconductor region  313  where a channel is formed, a region in the vicinity thereof, the low-resistance region  314   a  and the low-resistance region  314   b  each functioning as a source region or a drain region, and the like preferably contain a semiconductor such as a silicon-based semiconductor, and preferably contain single crystal silicon. Alternatively, the regions may be formed using a material containing Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), or the like. A structure may be used in which silicon whose effective mass is controlled by applying stress to the crystal lattice and changing the lattice spacing is used. Alternatively, the transistor  300  may be an HEMT (High Electron Mobility Transistor) with the use of GaAs and GaAlAs, or the like. 
     The low-resistance region  314   a  and the low-resistance region  314   b  contain an element which imparts n-type conductivity, such as arsenic or phosphorus, or an element which imparts p-type conductivity, such as boron, in addition to the semiconductor material used for the semiconductor region  313 . 
     For the conductor  316  functioning as a gate electrode, a semiconductor material such as silicon containing the element which imparts n-type conductivity, such as arsenic or phosphorus, or the element which imparts p-type conductivity, such as boron, or a conductive material such as a metal material, an alloy material, or a metal oxide material can be used. 
     Note that since the work function of a conductor depends on the material of the conductor, the threshold voltage of the transistor can be adjusted by selecting the material of the conductor. Specifically, it is preferable to use a material such as titanium nitride or tantalum nitride for the conductor. Moreover, in order to ensure both conductivity and embeddability, it is preferable to use stacked layers of metal materials such as tungsten and aluminum for the conductor, and it is particularly preferable to use tungsten in terms of heat resistance. 
     Note that the transistor  300  shown in  FIG. 12  is an example and the structure is not limited thereto; an appropriate transistor is used in accordance with a circuit structure or a driving method. For example, when the semiconductor device is composed of only OS transistors, the transistor  300  has a structure similar to that of the transistor  500  using an oxide semiconductor, as shown in  FIG. 13 . Note that the details of the transistor  500  are described later. 
     An insulator  320 , an insulator  322 , an insulator  324 , and an insulator  326  are stacked sequentially and provided to cover the transistor  300 . 
     For the insulator  320 , the insulator  322 , the insulator  324 , and the insulator  326 , silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like is used, for example. 
     Note that in this specification, silicon oxynitride refers to a material that contains oxygen at a higher proportion than nitrogen, and silicon nitride oxide refers to a material that contains nitrogen at a higher proportion than oxygen. Furthermore, in this specification, aluminum oxynitride refers to a material that contains oxygen at a higher proportion than nitrogen, and aluminum nitride oxide refers to a material that contains nitrogen at a higher proportion than oxygen. 
     The insulator  322  may have a function of a planarization film for planarizing a level difference caused by the transistor  300  or the like provided below the insulator  322 . For example, a top surface of the insulator  322  may be planarized by planarization treatment using a chemical mechanical polishing (CMP) method or the like to improve planarity. 
     In addition, for the insulator  324 , it is preferable to use a film having a barrier property that prevents diffusion of hydrogen or impurities from the substrate  311 , the transistor  300 , or the like into a region where the transistor  500  is provided. 
     For the film having a barrier property against hydrogen, silicon nitride formed by a CVD method can be used, for example. Here, diffusion of hydrogen to a semiconductor element including an oxide semiconductor, such as the transistor  500 , degrades the characteristics of the semiconductor element in some cases. Therefore, a film that inhibits hydrogen diffusion is preferably used between the transistor  500  and the transistor  300 . The film that inhibits hydrogen diffusion is specifically a film from which a small amount of hydrogen is released. 
     The amount of released hydrogen can be analyzed by thermal desorption spectroscopy (TDS) or the like, for example. The amount of hydrogen released from the insulator  324  that is converted into hydrogen atoms per area of the insulator  324  is less than or equal to 10×10 15  atoms/cm 2 , preferably less than or equal to 5×10 15  atoms/cm 2 , in the TDS analysis in a film-surface temperature range of 50° C. to 500° C., for example. 
     Note that the dielectric constant of the insulator  326  is preferably lower than that of the insulator  324 . For example, the dielectric constant of the insulator  326  is preferably lower than 4, further preferably lower than 3. The dielectric constant of the insulator  326  is, for example, preferably 0.7 times or less, further preferably 0.6 times or less the dielectric constant of the insulator  324 . When a material with a low dielectric constant is used as an interlayer film, the parasitic capacitance generated between wirings can be reduced. 
     In addition, a conductor  328 , a conductor  330 , and the like that are connected to the capacitor  800  or the transistor  500  are embedded in the insulator  320 , the insulator  322 , the insulator  324 , and the insulator  326 . Note that the conductor  328  and the conductor  330  each have a function of a plug or a wiring. Furthermore, a plurality of conductors functioning as plugs or wirings are collectively denoted by the same reference numeral in some cases. Moreover, in this specification and the like, a wiring and a plug connected to the wiring may be a single component. That is, there are cases where part of a conductor functions as a wiring and part of a conductor functions as a plug. 
     As a material for each of the plugs and wirings (the conductor  328 , the conductor  330 , and the like), a single layer or a stacked layer of a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material can be used. It is preferable to use a high-melting-point material that has both heat resistance and conductivity, such as tungsten or molybdenum, and it is preferable to use tungsten. Alternatively, it is preferable to form the plugs and wirings with a low-resistance conductive material such as aluminum or copper. The use of a low-resistance conductive material can reduce wiring resistance. 
     A wiring layer may be provided over the insulator  326  and the conductor  330 . For example, in  FIG. 12 , an insulator  350 , an insulator  352 , and an insulator  354  are stacked sequentially and provided. Furthermore, a conductor  356  is formed in the insulator  350 , the insulator  352 , and the insulator  354 . The conductor  356  has a function of a plug or a wiring that is connected to the transistor  300 . Note that the conductor  356  can be provided using a material similar to those for the conductor  328  and the conductor  330 . 
     Note that for example, as the insulator  350 , like the insulator  324 , an insulator having a barrier property against hydrogen is preferably used. Furthermore, the conductor  356  preferably contains a conductor having a barrier property against hydrogen. In particular, the conductor having a barrier property against hydrogen is formed in an opening of the insulator  350  having a barrier property against hydrogen. With this structure, the transistor  300  and the transistor  500  can be separated by a barrier layer, so that diffusion of hydrogen from the transistor  300  into the transistor  500  can be inhibited. 
     Note that for the conductor having a barrier property against hydrogen, tantalum nitride is preferably used, for example. In addition, the use of a stack including tantalum nitride and tungsten, which has high conductivity, can inhibit diffusion of hydrogen from the transistor  300  while the conductivity of a wiring is kept. In that case, a structure is preferable in which a tantalum nitride layer having a barrier property against hydrogen is in contact with the insulator  350  having a barrier property against hydrogen. 
     A wiring layer may be provided over the insulator  354  and the conductor  356 . For example, in  FIG. 12 , an insulator  360 , an insulator  362 , and an insulator  364  are stacked sequentially and provided. Furthermore, a conductor  366  is formed in the insulator  360 , the insulator  362 , and the insulator  364 . The conductor  366  has a function of a plug or a wiring. Note that the conductor  366  can be provided using a material similar to those for the conductor  328  and the conductor  330 . 
     Note that for example, as the insulator  360 , like the insulator  324 , an insulator having a barrier property against hydrogen is preferably used. Furthermore, the conductor  366  preferably contains a conductor having a barrier property against hydrogen. In particular, the conductor having a barrier property against hydrogen is formed in an opening portion of the insulator  360  having a barrier property against hydrogen. With this structure, the transistor  300  and the transistor  500  can be separated by a barrier layer, so that diffusion of hydrogen from the transistor  300  into the transistor  500  can be inhibited. 
     A wiring layer may be provided over the insulator  364  and the conductor  366 . For example, in  FIG. 12 , an insulator  370 , an insulator  372 , and an insulator  374  are stacked sequentially and provided. Furthermore, a conductor  376  is formed in the insulator  370 , the insulator  372 , and the insulator  374 . The conductor  376  has a function of a plug or a wiring. Note that the conductor  376  can be provided using a material similar to those for the conductor  328  and the conductor  330 . 
     Note that for example, as the insulator  370 , like the insulator  324 , an insulator having a barrier property against hydrogen is preferably used. Furthermore, the conductor  376  preferably contains a conductor having a barrier property against hydrogen. In particular, the conductor having a barrier property against hydrogen is formed in an opening portion of the insulator  370  having a barrier property against hydrogen. With this structure, the transistor  300  and the transistor  500  can be separated by a barrier layer, so that diffusion of hydrogen from the transistor  300  into the transistor  500  can be inhibited. 
     A wiring layer may be provided over the insulator  374  and the conductor  376 . For example, in  FIG. 12 , an insulator  380 , an insulator  382 , and an insulator  384  are stacked sequentially and provided. Furthermore, a conductor  386  is formed in the insulator  380 , the insulator  382 , and the insulator  384 . The conductor  386  has a function of a plug or a wiring. Note that the conductor  386  can be provided using a material similar to those for the conductor  328  and the conductor  330 . 
     Note that for example, as the insulator  380 , like the insulator  324 , an insulator having a barrier property against hydrogen is preferably used. Furthermore, the conductor  386  preferably contains a conductor having a barrier property against hydrogen. In particular, the conductor having a barrier property against hydrogen is formed in an opening portion of the insulator  380  having a barrier property against hydrogen. With this structure, the transistor  300  and the transistor  500  can be separated by a barrier layer, so that diffusion of hydrogen from the transistor  300  into the transistor  500  can be inhibited. 
     Although the wiring layer including the conductor  356 , the wiring layer including the conductor  366 , the wiring layer including the conductor  376 , and the wiring layer including the conductor  386  are described above, the semiconductor device of this embodiment is not limited thereto. Three or less wiring layers that are similar to the wiring layer including the conductor  356  may be provided, or five or more wiring layers that are similar to the wiring layer including the conductor  356  may be provided. 
     An insulator  510 , an insulator  512 , an insulator  514 , and an insulator  516  are stacked sequentially and provided over the insulator  384 . A substance having a barrier property against oxygen or hydrogen is preferably used for any of the insulator  510 , the insulator  512 , the insulator  514 , and the insulator  516 . 
     For example, for the insulator  510  and the insulator  514 , it is preferable to use a film having a barrier property that prevents diffusion of hydrogen or impurities from the substrate  311 , a region where the transistor  300  is provided, or the like into the region where the transistor  500  is provided. Therefore, a material similar to that for the insulator  324  can be used. 
     For the film having a barrier property against hydrogen, silicon nitride formed by a CVD method can be used, for example. Here, diffusion of hydrogen to a semiconductor element including an oxide semiconductor, such as the transistor  500 , degrades the characteristics of the semiconductor element in some cases. Therefore, a film that inhibits hydrogen diffusion is preferably used between the transistor  500  and the transistor  300 . The film that inhibits hydrogen diffusion is specifically a film from which a small amount of hydrogen is released. 
     In addition, for the film having a barrier property against hydrogen, a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide is preferably used for the insulator  510  and the insulator  514 , for example. 
     In particular, aluminum oxide has an excellent blocking effect that prevents the passage of both oxygen and impurities such as hydrogen and moisture, which are factors of a change in electrical characteristics of the transistor. Accordingly, aluminum oxide can prevent mixing of impurities such as hydrogen and moisture into the transistor  500  in a manufacturing process and after manufacturing of the transistor. In addition, release of oxygen from the oxide included in the transistor  500  can be inhibited. Therefore, aluminum oxide is suitably used for a protective film of the transistor  500 . 
     In addition, for the insulator  512  and the insulator  516 , a material similar to that for the insulator  320  can be used, for example. Furthermore, when a material with a comparatively low dielectric constant is used for these insulators, parasitic capacitance generated between wirings can be reduced. A silicon oxide film, a silicon oxynitride film, or the like can be used for the insulator  512  and the insulator  516 , for example. 
     Furthermore, a conductor  518 , a conductor included in the transistor  500  (a conductor  503  for example), and the like are embedded in the insulator  510 , the insulator  512 , the insulator  514 , and the insulator  516 . Note that the conductor  518  has a function of a plug or a wiring that is connected to the capacitor  800  or the transistor  300 . The conductor  518  can be provided using a material similar to those for the conductor  328  and the conductor  330 . 
     In particular, the conductor  518  in a region in contact with the insulator  510  and the insulator  514  is preferably a conductor having a barrier property against oxygen, hydrogen, and water. With this structure, the transistor  300  and the transistor  500  can be separated by a layer having a barrier property against oxygen, hydrogen, and water; thus, diffusion of hydrogen from the transistor  300  into the transistor  500  can be inhibited. 
     The transistor  500  is provided above the insulator  516 . 
     As shown in  FIG. 14A  and  FIG. 14B , the transistor  500  includes the conductor  503  positioned to be embedded in the insulator  514  and the insulator  516 ; an insulator  522  positioned over the insulator  516  and the conductor  503 ; an insulator  524  positioned over the insulator  522 ; an oxide  530   a  positioned over the insulator  524 ; an oxide  530   b  positioned over the oxide  530   a;  an oxide  530   c  positioned over the oxide  530   b;  a conductor  542   a  and a conductor  542   b  positioned apart from each other over the oxide  530   c;  an insulator  580  that is positioned over the conductor  542   a  and the conductor  542   b  and is provided with an opening formed to overlap with a region between the conductor  542   a  and the conductor  542   b;  an insulator  550  positioned on a bottom and a side surface of the opening; and a conductor  560  positioned on a formation surface of the insulator  550 . 
     In addition, as shown in  FIG. 14A  and  FIG. 14B , an insulator  544  is preferably positioned between the insulator  580  and the oxide  530   a,  the oxide  530   b,  the conductor  542   a,  and the conductor  542   b.  Furthermore, as shown in  FIG. 14A  and  FIG. 14B , the conductor  560  preferably includes a conductor  560   a  provided inside the insulator  550  and a conductor  560   b  provided to be embedded inside the conductor  560   a.  Moreover, as shown in  FIG. 14A  and  FIG. 14B , an insulator  574  is preferably positioned over the insulator  580 , the conductor  560 , and the insulator  550 . 
     Note that in the following description, the oxide  530   a,  the oxide  530   b,  and the oxide  530   c  are sometimes collectively referred to as an oxide  530 . 
     Note that although a structure of the transistor  500  in which three layers of the oxide  530   a,  the oxide  530   b,  and the oxide  530   c  are stacked in a region where a channel is formed and its vicinity is shown, the present invention is not limited thereto. For example, a single layer of the oxide  530   b,  a two-layer structure of the oxide  530   b  and the oxide  530   a,  a two-layer structure of the oxide  530   b  and the oxide  530   c,  or a stacked-layer structure of four or more layers may be employed. Furthermore, although the conductor  560  is shown to have a stacked-layer structure of two layers in the transistor  500 , the present invention is not limited thereto. For example, the conductor  560  may have a single-layer structure or a stacked-layer structure of three or more layers. Moreover, the transistor  500  shown in  FIG. 12  and  FIG. 14A  is an example and the structure is not limited thereto; an appropriate transistor is used in accordance with a circuit configuration or a driving method. 
     Here, the conductor  560  functions as a gate electrode of the transistor, and the conductor  542   a  and the conductor  542   b  each function as a source electrode or a drain electrode. As described above, the conductor  560  is formed to be embedded in the opening of the insulator  580  and the region between the conductor  542   a  and the conductor  542   b.  The positions of the conductor  560 , the conductor  542   a,  and the conductor  542   b  with respect to the opening of the insulator  580  are selected in a self-aligned manner. That is, in the transistor  500 , the gate electrode can be positioned between the source electrode and the drain electrode in a self-aligned manner. Therefore, the conductor  560  can be formed without an alignment margin, resulting in a reduction in the area occupied by the transistor  500 . Accordingly, miniaturization and high integration of the semiconductor device can be achieved. 
     In addition, since the conductor  560  is formed in the region between the conductor  542   a  and the conductor  542   b  in a self-aligned manner, the conductor  560  does not have a region overlapping with the conductor  542   a  or the conductor  542   b.  Thus, parasitic capacitance formed between the conductor  560  and each of the conductor  542   a  and the conductor  542   b  can be reduced. As a result, the switching speed of the transistor  500  can be improved, and the transistor  500  can have high frequency characteristics. 
     The conductor  560  sometimes functions as a first gate (also referred to as top gate) electrode. In addition, the conductor  503  sometimes functions as a second gate (also referred to as bottom gate) electrode. In that case, the threshold voltage of the transistor  500  can be controlled by changing a potential applied to the conductor  503  independently of a potential applied to the conductor  560 . In particular, the threshold voltage of the transistor  500  can be higher than 0 V and the off-state current can be reduced by applying a negative potential to the conductor  503 . Thus, a drain current at the time when a potential applied to the conductor  560  is 0 V can be lower in the case where a negative potential is applied to the conductor  503  than in the case where a negative potential is not applied to the conductor  503 . 
     The conductor  503  is positioned to overlap with the oxide  530  and the conductor  560 . Thus, in the case where potentials are applied to the conductor  560  and the conductor  503 , an electric field generated from the conductor  560  and an electric field generated from the conductor  503  are connected, so that a channel formation region formed in the oxide  530  can be covered. In this specification and the like, a transistor structure in which a channel formation region is electrically surrounded by electric fields of a first gate electrode and a second gate electrode is referred to as a surrounded channel (S-channel) structure. 
     In addition, the conductor  503  has a structure similar to that of the conductor  518 ; a conductor  503   a  is formed in contact with an inner wall of an opening in the insulator  514  and the insulator  516 , and a conductor  503   b  is formed on the inner side. Note that although the transistor  500  having a structure in which the conductor  503   a  and the conductor  503   b  are stacked is shown, the present invention is not limited thereto. For example, the conductor  503  may be provided as a single layer or to have a stacked-layer structure of three or more layers. 
     Here, for the conductor  503   a,  a conductive material that has a function of inhibiting diffusion of impurities such as a hydrogen atom, a hydrogen molecule, a water molecule, and a copper atom (through which the impurities are less likely to pass) is preferably used. Alternatively, it is preferable to use a conductive material that has a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom, an oxygen molecule, and the like) (through which oxygen is less likely to pass). Note that in this specification, a function of inhibiting diffusion of impurities or oxygen means a function of inhibiting diffusion of any one or all of the impurities and oxygen. 
     For example, when the conductor  503   a  has a function of inhibiting diffusion of oxygen, a reduction in conductivity of the conductor  503   b  due to oxidation can be inhibited. 
     In addition, in the case where the conductor  503  also functions as a wiring, a conductive material with high conductivity that contains tungsten, copper, or aluminum as its main component is preferably used for the conductor  503   b.  Note that the conductor  503   b  is shown as a single layer but may have a stacked-layer structure, for example, a stack of the above conductive material and titanium or titanium nitride. 
     The insulator  522 , the insulator  524 , and the insulator  550  have a function of a gate insulating film. 
     Here, as the insulator  524  and the insulator  550  that are in contact with the oxide  530 , an insulator that contains oxygen more than oxygen in the stoichiometric composition is preferably used. That is, an excess-oxygen region is preferably formed in the insulator  524  and the insulator  550 . When such an insulator containing excess oxygen is provided in contact with the oxide  530 , oxygen vacancies in the oxide  530  can be reduced and the reliability of the transistor  500  can be improved. 
     As the insulator including an excess-oxygen region, specifically, an oxide material that releases part of oxygen by heating is preferably used. An oxide that releases oxygen by heating is an oxide film in which the amount of released oxygen converted into oxygen atoms is greater than or equal to 1.0×10 18  atoms/cm 3 , preferably greater than or equal to 1.0×10 19  atoms/cm 3 , further preferably greater than or equal to 2.0×10 19  atoms/cm 3  or greater than or equal to 3.0×10 20  atoms/cm 3  in TDS (Thermal Desorption Spectroscopy) analysis. Note that the temperature of the film surface in the TDS analysis is preferably in a range of higher than or equal to 100° C. and lower than or equal to 700° C., or higher than or equal to 100° C. and lower than or equal to 400° C. 
     In addition, in the case where the insulator  524  includes an excess-oxygen region, it is preferable that the insulator  522  have a function of inhibiting diffusion of oxygen (e.g., an oxygen atom, an oxygen molecule, or the like) (through which oxygen is less likely to pass). 
     When the insulator  522  has a function of inhibiting diffusion of oxygen or impurities, oxygen contained in the oxide  530  is not diffused into the insulator  516  side, which is preferable. Furthermore, the conductor  503  can be inhibited from reacting with oxygen contained in the insulator  524  or the oxide  530 . 
     For the insulator  522 , a single layer or stacked layers of an insulator containing what is called a high-k material such as aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO 3 ), or (Ba,Sr)TiO 3  (BST) are preferably used, for example. As miniaturization and high integration of transistors progress, a problem such as leakage current might arise because of a thinner gate insulating film. When a high-k material is used for an insulator functioning as the gate insulating film, a gate potential during transistor operation can be reduced while the physical thickness is maintained. 
     It is particularly preferable to use an insulator containing an oxide of one or both of aluminum and hafnium, which is/are an insulating material having a function of inhibiting diffusion of impurities, oxygen, and the like (through which oxygen is less likely to pass). Aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like is preferably used as the insulator containing an oxide of one or both of aluminum and hafnium. In the case where the insulator  522  is formed using such a material, the insulator  522  functions as a layer that inhibits release of oxygen from the oxide  530  and mixing of impurities such as hydrogen from the periphery of the transistor  500  into the oxide  530 . 
     Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to these insulators, for example. Alternatively, these insulators may be subjected to nitriding treatment. The insulator over which silicon oxide, silicon oxynitride, or silicon nitride is stacked may be used. 
     Note that in the transistor  500  in  FIG. 14A  and  FIG. 14B , the insulator  522  and the insulator  524  are shown as the second gate insulating film having a stacked-layer structure of two layers; however, the second gate insulating film may be a single layer or may have a stacked-layer structure of three or more layers. In such cases, without limitation to a stacked-layer structure formed of the same material, a stacked-layer structure formed of different materials may be employed. 
     In the transistor  500 , a metal oxide functioning as an oxide semiconductor is preferably used as the oxide  530  including the channel formation region. For example, as the oxide  530 , a metal oxide such as an In-M-Zn oxide (the element M is one kind or a plurality of kinds selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like) is preferably used. The In-M-Zn oxide that can be used as the oxide  530  is particularly preferably a CAAC-OS or a CAC-OS described later. Furthermore, as the oxide  530 , an In—Ga oxide or an In—Zn oxide may be used. 
     The metal oxide functioning as the channel formation region in the oxide  530  has a band gap of more than or equal to 2 eV, preferably more than or equal to 2.5 eV. With the use of a metal oxide having such a wide bandgap, the off-state current of the transistor can be reduced. 
     When the oxide  530  includes the oxide  530   a  under the oxide  530   b,  it is possible to inhibit diffusion of impurities into the oxide  530   b  from the components formed below the oxide  530   a.  Moreover, including the oxide  530   c  over the oxide  530   b  makes it possible to inhibit diffusion of impurities into the oxide  530   b  from the components formed above the oxide  530   c.    
     Note that the oxide  530  preferably has a stacked-layer structure of a plurality of oxide layers that differ in the atomic ratio of metal atoms. Specifically, the atomic ratio of the element M to the constituent elements in the metal oxide used as the oxide  530   a  is preferably higher than the atomic ratio of the element M to the constituent elements in the metal oxide used as the oxide  530   b.  In addition, the atomic ratio of the element M to In in the metal oxide used as the oxide  530   a  is preferably higher than the atomic ratio of the element M to In in the metal oxide used as the oxide  530   b.  Furthermore, the atomic ratio of In to the element M in the metal oxide used as the oxide  530   b  is preferably higher than the atomic ratio of In to the element M in the metal oxide used as the oxide  530   a.  Moreover, a metal oxide that can be used as the oxide  530   a  or the oxide  530   b  can be used as the oxide  530   c.    
     In addition, the energy of the conduction band minimum of each of the oxide  530   a  and the oxide  530   c  is preferably higher than the energy of the conduction band minimum of the oxide  530   b.  In other words, the electron affinity of each of the oxide  530   a  and the oxide  530   c  is preferably smaller than the electron affinity of the oxide  530   b.    
     Here, the energy level of the conduction band minimum gradually changes at junction portions of the oxide  530   a,  the oxide  530   b,  and the oxide  530   c.  In other words, the energy level of the conduction band minimum at the junction portions of the oxide  530   a,  the oxide  530   b,  and the oxide  530   c  continuously changes or is continuously connected. To change the energy level gradually, the densities of defect states in mixed layers formed at an interface between the oxide  530   a  and the oxide  530   b  and an interface between the oxide  530   b  and the oxide  530   c  is preferably made low. 
     Specifically, when the oxide  530   a  and the oxide  530   b  or the oxide  530   b  and the oxide  530   c  contain a common element (as a main component) in addition to oxygen, a mixed layer with a low density of defect states can be formed. For example, in the case where the oxide  530   b  is an In—Ga—Zn oxide, an In—Ga—Zn oxide, a Ga—Zn oxide, gallium oxide, or the like is preferably used as the oxide  530   a  and the oxide  530   c.    
     At this time, the oxide  530   b  serves as a main carrier path. When the oxide  530   a  and the oxide  530   c  have the above structures, the densities of defect states at the interface between the oxide  530   a  and the oxide  530   b  and the interface between the oxide  530   b  and the oxide  530   c  can be made low. Thus, the influence of interface scattering on carrier conduction is small, and the transistor  500  can have a high on-state current. 
     The conductor  542   a  and the conductor  542   b  functioning as the source electrode and the drain electrode are provided over the oxide  530   c.  For the conductor  542   a  and conductor  542   b,  it is preferable to use a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, and lanthanum; an alloy containing the above metal element; an alloy containing a combination of the above metal element; or the like. For example, it is preferable to use tantalum nitride, titanium nitride, tungsten, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, an oxide containing lanthanum and nickel, or the like. In addition, tantalum nitride, titanium nitride, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, and an oxide containing lanthanum and nickel are preferable because they are oxidation-resistant conductive materials or materials that retain their conductivity even after absorbing oxygen. Furthermore, a metal nitride film of tantalum nitride or the like is preferable because it has a barrier property against hydrogen or oxygen. 
     In addition, although the conductor  542   a  and the conductor  542   b  each having a single-layer structure are shown in  FIG. 14A  and  FIG. 14B , a stacked-layer structure of two or more layers may be employed. For example, it is preferable to stack a tantalum nitride film and a tungsten film. Alternatively, a titanium film and an aluminum film may be stacked. Alternatively, a two-layer structure where an aluminum film is stacked over a tungsten film, a two-layer structure where a copper film is stacked over a copper-magnesium-aluminum alloy film, a two-layer structure where a copper film is stacked over a titanium film, or a two-layer structure where a copper film is stacked over a tungsten film may be employed. 
     Other examples include a three-layer structure where a titanium film or a titanium nitride film is formed, an aluminum film or a copper film is stacked over the titanium film or the titanium nitride film, and a titanium film or a titanium nitride film is formed over the aluminum film or the copper film; and a three-layer structure where a molybdenum film or a molybdenum nitride film is formed, an aluminum film or a copper film is stacked over the molybdenum film or the molybdenum nitride film, and a molybdenum film or a molybdenum nitride film is formed over the aluminum film or the copper film. Note that a transparent conductive material containing indium oxide, tin oxide, or zinc oxide may be used. 
     In addition, as shown in  FIG. 14A , a region  543   a  and a region  543   b  are sometimes formed as low-resistance regions at an interface between the oxide  530  and the conductor  542   a  (the conductor  542   b ) and in the vicinity of the interface. In that case, the region  543   a  functions as one of a source region and a drain region, and the region  543   b  functions as the other of the source region and the drain region. Furthermore, the channel formation region is formed in a region between the region  543   a  and the region  543   b.    
     When the conductor  542   a  (the conductor  542   b ) is provided to be in contact with the oxide  530 , the oxygen concentration in the region  543   a  (the region  543   b ) sometimes decreases. In addition, a metal compound layer that contains the metal contained in the conductor  542   a  (the conductor  542   b ) and the component of the oxide  530  is sometimes formed in the region  543   a  (the region  543   b ). In such a case, the carrier density of the region  543   a  (the region  543   b ) increases, and the region  543   a  (the region  543   b ) becomes a low-resistance region. 
     The insulator  544  is provided to cover the conductor  542   a  and the conductor  542   b  and inhibits oxidation of the conductor  542   a  and the conductor  542   b.  At this time, the insulator  544  may be provided to cover a side surface of the oxide  530  and to be in contact with the insulator  524 . 
     A metal oxide containing one kind or two or more kinds selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, neodymium, lanthanum, magnesium, and the like can be used as the insulator  544 . Alternatively, silicon nitride oxide, silicon nitride, or the like can be used as the insulator  544 . 
     It is particularly preferable to use an insulator containing an oxide of one or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate), as the insulator  544 . In particular, hafnium aluminate has higher heat resistance than a hafnium oxide film. Therefore, hafnium aluminate is preferable because it is less likely to be crystallized by heat treatment in a later step. Note that the insulator  544  is not an essential component when the conductor  542   a  and the conductor  542   b  are oxidation-resistant materials or do not significantly lose their conductivity even after absorbing oxygen. Design is appropriately set in consideration of required transistor characteristics. 
     When the insulator  544  is included, diffusion of impurities such as water and hydrogen contained in the insulator  580  into the oxide  530   b  through the oxide  530   c  and the insulator  550  can be inhibited. Furthermore, oxidation of the conductor  560  due to excess oxygen contained in the insulator  580  can be inhibited. 
     The insulator  550  functions as a first gate insulating film. Like the insulator  524 , the insulator  550  is preferably formed using an insulator that contains excess oxygen and releases oxygen by heating. 
     Specifically, silicon oxide containing excess oxygen, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, or porous silicon oxide can be used. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. 
     Furthermore, to efficiently supply excess oxygen contained in the insulator  550  to the oxide  530 , a metal oxide may be provided between the insulator  550  and the conductor  560 . The metal oxide preferably inhibits diffusion of oxygen from the insulator  550  to the conductor  560 . Providing the metal oxide that inhibits diffusion of oxygen inhibits diffusion of excess oxygen from the insulator  550  to the conductor  560 . That is, a reduction in the amount of excess oxygen supplied to the oxide  530  can be inhibited. Moreover, oxidation of the conductor  560  due to excess oxygen can be inhibited. As the metal oxide, a material that can be used as the insulator  544  is used. 
     Note that the insulator  550  may have a stacked-layer structure like the second gate insulating film. As miniaturization and high integration of transistors progress, a problem such as leakage current might arise because of a thinner gate insulating film. For that reason, when the insulator functioning as the gate insulating film has a stacked-layer structure of a high-k material and a thermally stable material, a gate potential during transistor operation can be reduced while the physical thickness is maintained. Furthermore, the stacked-layer structure can be thermally stable and have a high dielectric constant. 
     Although the conductor  560  that functions as the first gate electrode and has a two-layer structure is shown in  FIG. 14A  and  FIG. 14B , a single-layer structure or a stacked-layer structure of three or more layers may be employed. 
     As the conductor  560   a,  it is preferable to use a conductive material having a function of inhibiting diffusion of impurities such as a hydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, a nitrogen molecule, a nitrogen oxide molecule (N 2 O, NO, NO 2 , and the like), and a copper atom. Alternatively, it is preferable to use a conductive material having a function of inhibiting diffusion of oxygen (e.g., at least one of an oxygen atom and an oxygen molecule). When the conductor  560   a  has a function of inhibiting diffusion of oxygen, it is possible to inhibit a reduction in conductivity of the conductor  560   b  due to oxidation caused by oxygen contained in the insulator  550 . As a conductive material having a function of inhibiting diffusion of oxygen, for example, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used. For the conductor  560   a,  the oxide semiconductor that can be used as the oxide  530  can be used. In that case, when the conductor  560   b  is deposited by a sputtering method, the conductor  560   a  can have a reduced electrical resistance value to be a conductor. Such a conductor can be referred to as an OC (Oxide Conductor) electrode. 
     In addition, a conductive material containing tungsten, copper, or aluminum as its main component is preferably used for the conductor  560   b.  Furthermore, the conductor  560   b  also functions as a wiring and thus a conductor having high conductivity is preferably used as the conductor  560   b.  For example, a conductive material containing tungsten, copper, or aluminum as its main component can be used. Moreover, the conductor  560   b  may have a stacked-layer structure, for example, a stacked-layer structure of the above conductive material and titanium or titanium nitride. 
     The insulator  580  is provided over the conductor  542   a  and the conductor  542   b  with the insulator  544  therebetween. The insulator  580  preferably includes an excess-oxygen region. For example, the insulator  580  preferably contains silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, porous silicon oxide, resin, or the like. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In particular, silicon oxide and porous silicon oxide are preferable because an excess-oxygen region can be easily formed in a later step. 
     The insulator  580  preferably includes an excess-oxygen region. When the insulator  580  that releases oxygen by heating is provided in contact with the insulator  550 , oxygen in the insulator  580  can be efficiently supplied to the oxide  530  through the insulator  550 . Note that the concentration of impurities such as water or hydrogen in the insulator  580  is preferably reduced. 
     The opening of the insulator  580  is formed to overlap with the region between the conductor  542   a  and the conductor  542   b.  Accordingly, the conductor  560  is formed to be embedded in the opening of the insulator  580  and the region between the conductor  542   a  and the conductor  542   b.    
     The gate length needs to be short for miniaturization of the semiconductor device, but it is necessary to prevent a reduction in conductivity of the conductor  560 . When the conductor  560  is made thick to achieve this, the conductor  560  might have a shape with a high aspect ratio. In this embodiment, the conductor  560  is provided to be embedded in the opening of the insulator  580 ; thus, even when the conductor  560  has a shape with a high aspect ratio, the conductor  560  can be formed without collapsing during the process. 
     The insulator  574  is preferably provided in contact with a top surface of the insulator  580 , a top surface of the conductor  560 , and a top surface of the insulator  550 . When the insulator  574  is deposited by a sputtering method, excess-oxygen regions can be provided in the insulator  550  and the insulator  580 . Accordingly, oxygen can be supplied from the excess-oxygen regions to the oxide  530 . 
     For example, a metal oxide containing one kind or two or more kinds selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like can be used as the insulator  574 . 
     In particular, aluminum oxide has a high barrier property, and even a thin aluminum oxide film having a thickness of greater than or equal to 0.5 nm and less than or equal to 3.0 nm can inhibit diffusion of hydrogen and nitrogen. Accordingly, aluminum oxide deposited by a sputtering method serves as an oxygen supply source and can also have a function of a barrier film against impurities such as hydrogen. 
     In addition, an insulator  581  functioning as an interlayer film is preferably provided over the insulator  574 . As in the insulator  524  or the like, the concentration of impurities such as water or hydrogen in the insulator  581  is preferably reduced. 
     Furthermore, a conductor  540   a  and a conductor  540   b  are positioned in openings formed in the insulator  581 , the insulator  574 , the insulator  580 , and the insulator  544 . The conductor  540   a  and the conductor  540   b  are provided to face each other with the conductor  560  therebetween. The structures of the conductor  540   a  and the conductor  540   b  are similar to a structure of a conductor  546  and a conductor  548  that are described later. Furthermore, as illustrated in  FIG. 14A , an insulator having a function of a barrier film against impurities such as hydrogen may be provided between the sidewall of the opening and the conductor  540   a  or the conductor  540   b.    
     An insulator  582  is provided over the insulator  581 . A substance having a barrier property against oxygen or hydrogen is preferably used for the insulator  582 . Therefore, a material similar to that for the insulator  514  can be used for the insulator  582 . For the insulator  582 , a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide is preferably used, for example. 
     In particular, aluminum oxide has an excellent blocking effect that prevents the passage of both oxygen and impurities such as hydrogen and moisture which are factors of a change in electrical characteristics of the transistor. Accordingly, aluminum oxide can prevent mixing of impurities such as hydrogen and moisture into the transistor  500  in a manufacturing process and after manufacturing of the transistor. In addition, release of oxygen from the oxide included in the transistor  500  can be inhibited. Therefore, aluminum oxide is suitably used for a protective film of the transistor  500 . 
     In addition, an insulator  586  is provided over the insulator  582 . For the insulator  586 , a material similar to that for the insulator  320  can be used. Furthermore, when a material with a comparatively low dielectric constant is used for these insulators, parasitic capacitance generated between wirings can be reduced. A silicon oxide film, a silicon oxynitride film, or the like can be used for the insulator  586 , for example. 
     Furthermore, the conductor  546 , the conductor  548 , and the like are embedded in the insulator  522 , the insulator  524 , the insulator  544 , the insulator  580 , the insulator  574 , the insulator  581 , the insulator  582 , and the insulator  586 . 
     The conductor  546  and the conductor  548  have functions of plugs or wirings that are connected to the capacitor  800 , the transistor  500 , or the transistor  300 . The conductor  546  and the conductor  548  can be provided using materials similar to those for the conductor  328  and the conductor  330 . 
     Next, the capacitor  800  is provided above the transistor  500 . The capacitor  800  includes a conductor  810 , a conductor  820 , and an insulator  830 . 
     In addition, a conductor  812  may be provided over the conductor  546  and the conductor  548 . The conductor  812  has a function of a plug or a wiring that is connected to the transistor  500 . The conductor  810  has a function of an electrode of the capacitor  800 . The conductor  812  and the conductor  810  can be formed at the same time. 
     For the conductor  812  and the conductor  810 , a metal film containing an element selected from molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, and scandium; a metal nitride film containing any of the above elements as its component (a tantalum nitride film, a titanium nitride film, a molybdenum nitride film, or a tungsten nitride film); or the like can be used. Alternatively, it is possible to use a conductive material such as indium tin oxide, 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 indium tin oxide to which silicon oxide is added. 
     Although the conductor  812  and the conductor  810  each having a single-layer structure are shown in  FIG. 12 , the structure is not limited thereto; a stacked-layer structure of two or more layers may be employed. For example, between a conductor having a barrier property and a conductor having high conductivity, a conductor that is highly adhesive to the conductor having a barrier property and the conductor having high conductivity may be formed. 
     The conductor  820  is provided so as to overlap with the conductor  810  with the insulator  830  positioned therebetween. The conductor  820  can be formed using a conductive material such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material that has both heat resistance and conductivity, such as tungsten or molybdenum, and it is particularly preferable to use tungsten. In addition, in the case where the conductor is formed concurrently with another component such as a conductor, Cu (copper), Al (aluminum), or the like, which is a low-resistance metal material, is used. 
     An insulator  840  is provided over the conductor  820  and the insulator  830 . The insulator  840  can be provided using a material similar to that for the insulator  320 . The insulator  840  may function as a planarization film that covers an uneven shape thereunder. 
     With the use of this structure, a change in electrical characteristics can be inhibited and reliability can be improved in a semiconductor device using a transistor including an oxide semiconductor. Alternatively, a memory device, an arithmetic device, or the like using a transistor including an oxide semiconductor can be miniaturized or highly integrated. 
     [Metal Oxide] 
     A metal oxide that can be used for the semiconductor layer (the oxide  530 ) where the channel of the transistor is formed is described below. 
     Note that in this specification and the like, a metal oxide containing nitrogen is also collectively referred to as a metal oxide in some cases. A metal oxide containing nitrogen may be referred to as a metal oxynitride. For example, a metal oxide containing nitrogen, such as zinc oxynitride (ZnON), may be used for the semiconductor layer. 
     Note that in this specification and the like, “CAAC (c-axis aligned crystal)” or “CAC (Cloud-Aligned Composite)” might be stated. Note that CAAC refers to an example of a crystal structure, and CAC refers to an example of a function or a material composition. 
     For example, a CAC (Cloud-Aligned Composite)-OS(Oxide Semiconductor) can be used for the semiconductor layer. 
     A CAC-OS or a CAC-metal oxide has a conducting function in part of the material and has an insulating function in another part of the material; as a whole, the CAC-OS or the CAC-metal oxide has a function of a semiconductor. Note that in the case where the CAC-OS or the CAC-metal oxide is used in an active layer of a transistor, the conducting function is a function that allows electrons (or holes) serving as carriers to flow, and the insulating function is a function that does not allow electrons serving as carriers to flow. By the complementary action of the conducting function and the insulating function, a switching function (On/Off function) can be given to the CAC-OS or the CAC-metal oxide. In the CAC-OS or the CAC-metal oxide, separation of the functions can maximize each function. 
     Furthermore, the CAC-OS or the CAC-metal oxide includes conductive regions and insulating regions. The conductive regions have the above-described conducting function, and the insulating regions have the above-described insulating function. Furthermore, in some cases, the conductive regions and the insulating regions in the material are separated at the nanoparticle level. Furthermore, in some cases, the conductive regions and the insulating regions are unevenly distributed in the material. Furthermore, in some cases, the conductive regions are observed to be coupled in a cloud-like manner with their boundaries blurred. 
     Furthermore, in the CAC-OS or the CAC-metal oxide, the conductive regions and the insulating regions each have a size greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 0.5 nm and less than or equal to 3 nm, and are dispersed in the material, in some cases. 
     Furthermore, 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 the insulating region and a component having a narrow gap due to the conductive region. In the case of the structure, when carriers flow, carriers mainly flow in the component having a narrow gap. Furthermore, 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 above-described CAC-OS or CAC-metal oxide is used in a channel formation region of a transistor, high current driving capability in an on state of the transistor, that is, a high on-state current and high field-effect mobility can be obtained. 
     In other words, the CAC-OS or the CAC-metal oxide can also be referred to as a matrix composite or a metal matrix composite. 
     Oxide semiconductors (metal oxides) can be classified into a single crystal oxide semiconductor and a non-single-crystal oxide semiconductor. Examples of a non-single-crystal oxide semiconductor include a CAAC-OS (c-axis aligned crystalline oxide semiconductor), a polycrystalline oxide semiconductor, an nc-OS (nanocrystalline oxide semiconductor), an amorphous-like oxide semiconductor (a-like OS), and an amorphous oxide semiconductor. 
     The CAAC-OS has c-axis alignment, a plurality of nanocrystals are connected in the a-b plane direction, and its crystal structure has distortion. Note that the distortion refers to a portion where the direction of a lattice arrangement changes between a region with a regular lattice arrangement and another region with a regular lattice arrangement in a region where the plurality of nanocrystals are connected. 
     The nanocrystal is basically a hexagon but is not always a regular hexagon and is a non-regular hexagon in some cases. Furthermore, a pentagonal or heptagonal lattice arrangement, for example, is included in the distortion in some cases. Note that it is difficult to observe a clear crystal grain boundary (also referred to as grain boundary) even in the vicinity of distortion in the CAAC-OS. That is, formation of a crystal grain boundary is found to be inhibited by the distortion of a lattice arrangement. This is because the CAAC-OS can tolerate distortion owing to a low density of arrangement of oxygen atoms in the a-b plane direction, an interatomic bond length changed by substitution of a metal element, and the like. 
     Furthermore, the CAAC-OS tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium and oxygen (hereinafter, In layer) and a layer containing the element M, zinc, and oxygen (hereinafter, (M,Zn) layer) are stacked. Note that indium and the element M can be replaced with each other, and when the element M in the (M,Zn) layer is replaced with indium, the layer can also be referred to as an (In,M,Zn) layer. Furthermore, when indium in the In layer is replaced with the element M, the layer can be referred to as an (In,M) layer. 
     The CAAC-OS is a metal oxide with high crystallinity. On the other hand, a clear crystal grain boundary cannot be observed in the CAAC-OS; thus, it can be said that a reduction in electron mobility due to the crystal grain boundary is less likely to occur. Entry of impurities, formation of defects, or the like might decrease the crystallinity of a metal oxide; thus, it can be said that the CAAC-OS is a metal oxide that has small amounts of impurities and defects (e.g., oxygen vacancies (also referred to as V O )). Thus, a metal oxide including a CAAC-OS is physically stable. Therefore, the metal oxide including a CAAC-OS is resistant to heat and has high reliability. 
     In the nc-OS, a microscopic region (e.g., a region with a size greater than or equal to 1 nm and less than or equal to 10 nm, in particular, a region with a size greater than or equal to 1 nm and less than or equal to 3 nm) has a periodic atomic arrangement. Furthermore, there is no regularity of crystal orientation between different nanocrystals in the nc-OS. Thus, the orientation in the whole film is not observed. Accordingly, the nc-OS cannot be distinguished from an a-like OS or an amorphous oxide semiconductor by some analysis methods. 
     Note that indium-gallium-zinc oxide (hereinafter referred to as IGZO) that is a kind of metal oxide containing indium, gallium, and zinc has a stable structure in some cases by being formed of the above-described nanocrystals. In particular, crystals of IGZO tend not to grow in the air and thus, a stable structure is obtained when IGZO is formed of smaller crystals (e.g., the above-described nanocrystals) rather than larger crystals (here, crystals with a size of several millimeters or several centimeters). 
     An a-like OS is a metal oxide having a structure between those of the nc-OS and an amorphous oxide semiconductor. The a-like OS includes a void or a low-density region. That is, the a-like OS has low crystallinity as compared with the nc-OS and the CAAC-OS. 
     An oxide semiconductor (metal oxide) can have various structures which show different properties. Two or more of the amorphous oxide semiconductor, the polycrystalline oxide semiconductor, the a-like OS, the nc-OS, and the CAAC-OS may be included in an oxide semiconductor of one embodiment of the present invention. 
     A metal oxide film that functions as a semiconductor layer can be formed using either or both of an inert gas and an oxygen gas. Note that there is no particular limitation on the flow rate ratio of oxygen (the partial pressure of oxygen) at the time of forming the metal oxide film. However, to obtain a transistor having high field-effect mobility, the flow rate ratio of oxygen (the partial pressure of oxygen) at the time of forming the metal oxide film is preferably higher than or equal to 0% and lower than or equal to 30%, further preferably higher than or equal to 5% and lower than or equal to 30%, still further preferably higher than or equal to 7% and lower than or equal to 15%. 
     The energy gap of the metal oxide is preferably 2 eV or more, further preferably 2.5 eV or more, still further preferably 3 eV or more. With the use of a metal oxide having such a wide energy gap, the off-state current of the transistor can be reduced. 
     The substrate temperature during the formation of the metal oxide film is preferably lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 200° C., still further preferably higher than or equal to room temperature and lower than or equal to 130° C. The substrate temperature at the time of depositing the metal oxide film is preferably room temperature because productivity can be increased. 
     The metal oxide film can be formed by a sputtering method. Alternatively, for example, a PLD method, a PECVD method, a thermal CVD method, an ALD method, or a vacuum evaporation method may be used. 
     At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate. 
     REFERENCE NUMERALS 
     R 1 , R 2 , G 1 , G 2 , B 1 , B 2 : display element, S 0 , S 1 , S 2 : image signal,  10 ,  10   a:  composite device,  11 : display device,  12 ,  12   a:  sensor device,  13 : information processing device,  21 : control portion,  22 : display portion,  23 : image capturing portion,  24 : lens,  25 : communication portion,  25   a:  returning operation,  25   b:  processing operation,  25   c:  resting operation,  26 : image generation portion,  27 : signal,  31 : sensor portion,  32 : communication portion,  33 : signal,  33   a:  pulse signal,  33   b:  signal,  34 : display portion,  40 : user,  41 : eyeball,  42 : arm,  43 : finger,  44 : upper arm,  45 : clothes,  50   a,    50   b,    50   c:  image,  51   a,    51   b,    51   c:  image information