Liquid crystal display device

Abstract

To provide a liquid crystal display device capable of minimizing reduction in image display functionality and sufficiently reducing power consumption, and to provide a method of driving the liquid crystal display device.SOLUTION: In a liquid crystal display device, the liquid crystal is reset to the initial state before turning off the power by applying a fixed potential to a capacitive element to eliminate a potential difference between electrodes of the capacitive element (thereby making capacitance almost zero) such that no electric field is applied to the liquid crystal. Turning off the power after displaying an initial state screen prevents continued application of an unnecessary electric field to the liquid crystal in the Off state and allows the liquid crystal to be in the stable initial state, which prevents aging of the liquid crystal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a driving method for a liquid crystal display device and a liquid crystal display device.

Background Art

[0002] There is attention being paid to the technology of forming a thin film transistor (TFT) using a semiconductor thin film formed on a substrate having an insulating surface. The thin film transistor is widely applied to electronic devices such as integrated circuits (ICs) and image display devices ( display devices).

[0003] Examples of electrical devices using thin film transistors include mobile devices such as mobile phones and notebook personal computers. For such portable electronic devices, the problem of power consumption that affects the continuous operation time is significant. Also, for large-sized television devices that are becoming larger, it is important to suppress the increase in power consumption associated with the increase in size.

[0004] In a display device, when rewriting the image data input to a pixel, even if the image data for a continuous period is the same, an operation of rewriting the same image data again is performed. As a result, even for the same image data, by performing the operation of writing the image data multiple times, the power consumption increases. In order to suppress such an increase in power consumption of the display device, for example, in a still image display, after scanning the screen once and writing the image data, a pause period longer than the scanning period is provided as a non-scanning period (see, for example, Patent Document 1 and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Document

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in a display method where the screen is scanned once, after writing the image data, a pause period longer than the scanning period is provided to continuously display a still image, an arbitrary voltage remains applied to the liquid crystal, resulting in a problem that the liquid crystal deteriorates and the image display function deteriorates. Also, if the image data remains, there is a risk that the image data remains on the screen even after the power of the display device is turned off. Therefore, in a liquid crystal display device, one of the problems is to suppress the deterioration of the image display function as described above. Another problem is to provide a liquid crystal display device capable of achieving low power consumption and a driving method for the liquid crystal display device.

[0008]

[0009]

[0010]

Means for Solving the Problems

[0010] The liquid crystal display device operates when the power supply starts and becomes inoperative when the power supply stops. In this specification, the state where power is supplied to the liquid crystal display device (power-on state) is referred to as the on state, and the state where the power supply is stopped (power-off state) is referred to as the off state. A control signal that turns on the display device is called a start signal, and a control signal that turns it off is called a stop signal. and so on.

[0011] The liquid crystal elements provided in the liquid crystal display device are composed of a pixel electrode, a common electrode, and liquid crystal provided between these electrodes. By applying different potentials to the pixel electrode and the common electrode respectively, a voltage is applied to the liquid crystal element. When a voltage is applied to the liquid crystal element, an electric field is formed, the electric field acts on the liquid crystal, and the liquid crystal responds to display an image. On the other hand, when the same potential is applied to the pixel electrode and the common electrode, no potential difference is generated between the electrodes, so no voltage is applied to the liquid crystal element either. Therefore, no electric field is formed in the liquid crystal element, no electric field acts on the liquid crystal, and the liquid crystal does not respond. In this specification, such a state where no electric field is applied (non-response state) of the liquid crystal is called the initial state (liquid crystal initial state). The liquid crystal in the liquid crystal initial state, in a display device that has become on state upon receiving a start signal, is subjected to an electric field and responds to display an image, and in a display device that has become off state upon receiving a stop signal, returns to the initial state. and so on.

[0012] and so on. and so on. and so on. and so on.

[0013] The liquid crystal display device disclosed in this specification has a pixel configuration that stores charges in a capacitive element and holds the voltage applied to the liquid crystal element by these charges to hold the display image. In the on state of such a liquid crystal display device, the switching element electrically connected to the capacitive element and the liquid crystal element is preferably a semiconductor element with a low current value (off current value) in the off state. If it is a semiconductor element with a low off current value, it is difficult for charges to leak from the capacitive element through the semiconductor element. and so on.

[0014] and so on. and so on. and so on. and so on.

[0015] and so on. <, it can hold the voltage applied to the liquid crystal element for a long time. Therefore, it can be a liquid crystal display device with high holding characteristics of the displayed image. It can be a display device.

[0016] On the other hand, in a pixel where the power supply is stopped and it is in the off state, for the liquid crystal in the responsive state to which an electric field is applied to return to the initial state, the charge held in the capacitive element needs to be completely discharged through the semiconductor element. Since an electric field continues to be applied to the liquid crystal while the charge in the capacitive element is being discharged, especially if that time is long, it will accelerate the deterioration of the liquid crystal. Also, since the liquid crystal is responding and the image is being held while the charge is being discharged, especially in the case of a reflective liquid crystal display device that uses external light as a light source, the image will remain even after the power is turned off (appearing as an afterimage to the human eye), resulting in a deterioration of the display quality. Continuously applying an unnecessary electric field to the liquid crystal in the off state where no image is being displayed in this way may lead to a decrease in the image display function and reliability of the liquid crystal display device. In the liquid crystal display device disclosed in this specification, before turning off the power supply, in order to prevent an electric field from being applied to the liquid crystal, a fixed potential is input to the capacitive element to eliminate the potential difference between the electrodes of the capacitive element (making the capacitance almost zero), and the liquid crystal is set to the initial state. In this specification, the image represented by the liquid crystal in the initial state is called the initial state image. The initial state image is, for example, a full - white screen in the case of a normally - white liquid crystal display device and a full - black screen in the case of a normally - black liquid crystal display device. In the case of a normally - white liquid crystal display device, it can also be a single - color screen by a color filter and a light source.

[0017]

[0018]

[0019] ​​​​​​​​​If the power is turned off after the initial state image is displayed, unnecessary electric fields will not continue to be applied in the off state of the liquid crystal, and it can be in a stable initial state. Also, since an initialization image such as an all-white screen or an all-black screen is displayed and then turned off, it is possible to prevent information of the image immediately before power-off from leaking to others due to the display of afterimages or the like on the screen.

[0020] Also, since an initialization image such as an all-white screen or an all-black screen is displayed and then turned off, it is possible to prevent information of the image immediately before power-off from leaking to others due to the display of afterimages or the like on the screen. Also, since an initialization image such as an all-white screen or an all-black screen is displayed and then turned off, it is possible to prevent information of the image immediately before power-off from leaking to others due to the display of afterimages or the like on the screen. Can be prevented.

[0021] Therefore, it is possible to provide a liquid crystal display device that maintains a long and good image display function and has high security. Can be done.

[0022] One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source.

[0023] One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source to the driving circuit section. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source to the driving circuit section. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source to the driving circuit section. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source to the driving circuit section. One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section, causes a liquid crystal of a liquid crystal element to respond to display an image on a screen provided with a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element, supplies a stop signal by a stop means, writes a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, sets the responded liquid crystal to a non-responsive state, displays an initial state image on the screen, and stops the supply of the power potential from the power source to the driving circuit section.

[0024] One form of the driving method of the liquid crystal display device disclosed in this specification supplies a power potential from a power source to a driving circuit section and a back Supply a power potential to the light unit, and a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element are provided on the screen, causing the liquid crystal of the liquid crystal element to respond to display an image, and a stop signal is supplied by the stop means to stop the supply of the power potential from the power supply to the backlight unit, and a fixed potential is written to the capacitive elements of the plurality of pixels by the stop signal, causing the responsive liquid crystal to become non-responsive and displaying an initial state image on the screen, and stopping the supply of the power potential from the power supply to the drive circuit unit.

[0025] One aspect of the driving method of the liquid crystal display device disclosed in this specification is to supply a power potential from the power supply to the drive circuit unit and the back light unit, and a plurality of pixels including a capacitive element, a liquid crystal element, and a semiconductor element are provided on the screen, causing the liquid crystal of the liquid crystal element to respond to display an image, and a stop signal is supplied by the stop means, writing a fixed potential to the capacitive elements of the plurality of pixels by the stop signal, and causing the responsive liquid crystal to become non-responsive and displaying an initial state image on the screen, and stopping the supply of the power potential from the power supply to the drive circuit unit and the backlight unit thereof.

[0026] In the above configuration, a transistor including an oxide semiconductor layer can be used as the semiconductor element that is electrically connected to the capacitive element and the liquid crystal element and functions as a switching element.

Advantages of the Invention

[0027] Before setting the liquid crystal display device to the off state, a fixed potential is written so that no voltage is applied to the liquid crystal element, and an initialization image is displayed. This prevents deterioration of the liquid crystal element, maintains a long-term good image display function, and can also enhance security. Therefore, in the liquid crystal display device, it is possible to achieve higher reliability and lower power consumption.

[0028] become possible.​

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that its form and details can be variously changed. Also, the present invention is not construed to be limited to the description content of the embodiments shown below.

[0031] (Embodiment 1) In this embodiment, one form of a liquid crystal display device and a driving method of the liquid crystal display device will be described with reference to FIGS. 1 and 2. This will be described using FIGS. 1 and 2.

[0032] The liquid crystal display device according to this embodiment will be described with reference to the flowchart of FIG. 1.

[0033] As shown in FIG. 1, it is assumed that an image A is displayed on the display screen of the liquid crystal display device. When a display image by supplying a new image signal is not required (at the end of use), a stop means is selected. When the stop means is selected, a stop signal is input, and a fixed potential is written to the capacitive elements of all pixels. By writing a fixed potential to the capacitive elements, the potential difference between the electrodes of the capacitive elements is eliminated (making the capacitance almost zero), and the liquid crystal in the responsive state is set to the initial non-responsive state. Therefore, an initial state image S displayed by the liquid crystal in the initial state is displayed on the display screen. The initial state image S is, for example, a full white screen in the case of a normally white liquid crystal display device, and a full black screen in the case of a normally black liquid crystal display device. Also, in the case of a normally white liquid crystal display device, it can be a single-color screen by a color filter or a light source. By writing a fixed potential to the capacitive elements, the potential difference between the electrodes of the capacitive elements is eliminated (making the capacitance almost zero), and the liquid crystal in the responsive state is set to the initial non-responsive state. Thus, the initial state image S displayed by the liquid crystal in the initial state is displayed on the display screen. The initial state image S is, for example, a full white screen in the case of a normally white liquid crystal display device, and a full black screen in the case of a normally black liquid crystal display device. Also, in the case of a normally white liquid crystal display device, it can be a single-color screen by a color filter or a light source. By writing a fixed potential to the capacitive elements, the potential difference between the electrodes of the capacitive elements is eliminated (making the capacitance almost zero), and the liquid crystal in the responsive state is set to the initial non-responsive state. Therefore, the initial state image S displayed by the liquid crystal in the initial state is displayed on the display screen. The initial state image S is, for example, a full white screen in the case of a normally white liquid crystal display device, and a full black screen in the case of a normally black liquid crystal display device. Also, in the case of a normally white liquid crystal display device, it can be a single-color screen by a color filter or a light source. After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Therefore, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state. After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Thus, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state. After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Therefore, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state. In addition, since it becomes the off state after displaying an initialization image such as a full white screen or a full black screen, it is possible to prevent information of the image immediately before power-off from leaking to others due to an afterimage or the like being displayed on the screen.

[0034] After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Therefore, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state. After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Thus, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state. After the initial state image S is displayed, the power supply is stopped and the supply of the power potential to the display panel is stopped, and the liquid crystal display device is set to the off state. Therefore, the liquid crystal can be in a stable initial state without unnecessary electric fields being continuously applied in the off state.

[0035] In addition, since it becomes the off state after displaying an initialization image such as a full white screen or a full black screen, it is possible to prevent information of the image immediately before power-off from leaking to others due to an afterimage or the like being displayed on the screen. In addition, since it becomes the off state after displaying an initialization image such as a full white screen or a full black screen, it is possible to prevent information of the image immediately before power-off from leaking to others due to an afterimage or the like being displayed on the screen. In addition, since it becomes the off state after displaying an initialization image such as a full white screen or a full black screen, it is possible to prevent information of the image immediately before power-off from leaking to others due to an afterimage or the like being displayed on the screen.

[0036] Therefore, it is possible to provide a liquid crystal display device that maintains a long and good image display function and has high security. This can be achieved.

[0037] Each component of the liquid crystal display device 100 according to this embodiment will be described with reference to the block diagram of FIG. 2. The liquid crystal display device 100 includes a power supply 116, a stop means 117, a display control circuit 113, and a display panel 1 20. In the case of a transmissive liquid crystal display device or a transflective liquid crystal display device, a backlight unit may be further provided together with a light source. This is advisable.

[0038] An image signal (image signal Data) is supplied to the liquid crystal display device 100 from an externally connected device. Note that the power supply potentials (high power supply potential Vdd, low power supply potential Vss, and common potential Vco m) are supplied by turning on the power supply 116 of the liquid crystal display device to start power supply, and the control signals (start pulse SP and clock signal CK) are supplied by the display control circuit 113. In addition, the supply of the power supply potentials (high power supply potential Vdd, low power supply potential Vss, and common potential Vc om) is stopped under the control of the stop means 117. After displaying the initial state image, the power supply 116 is turned off to stop the supply of the power supply potential to the display panel. This is done by the control of the stop means 117. After displaying the initial state image, the power supply 116 is turned off to stop the supply of the power supply potential to the display panel. After that, the power supply 116 is turned off to stop the supply of the power supply potential to the display panel.

[0039] Note that the high power supply potential Vdd is a potential higher than the reference potential, and the low power supply potential Vss is a potential equal to or lower than the reference potential. It is desirable that both the high power supply potential Vdd and the low power supply potential Vss are potentials at which the transistor can operate. The difference between the high power supply potential Vdd and the low power supply potential Vss is sometimes referred to as the power supply voltage.

[0040] The common potential Vcom serves as a reference with respect to the potential of the image signal Data supplied to the pixel electrode. A fixed potential is sufficient, and as an example, it may be a ground potential.

[0041] The image signal Data is appropriately inverted according to dot inversion driving, source line inversion driving, gate line inversion driving, frame inversion driving, etc., and is input to the liquid crystal display device 100. Further, when the image signal Data is an analog signal, it may be configured to be converted into a digital signal via an A / D converter or the like and supplied to the liquid crystal display device 100.

[0042] In the present embodiment, a common potential Vcom, which is a fixed potential, is applied from the power supply 116 to one of the common electrode 128 and the electrodes of the capacitor element 210 via the display control circuit 113.

[0043] The display control circuit 113 is a circuit that supplies a display panel image signal (Data), a control signal (specifically, a start pulse SP, a clock signal CK, etc.), and power supply potentials (a high power supply potential Vdd, a low power supply potential Vss, and a common potential Vcom) to the display panel 120.

[0044] The display panel 120 has a configuration in which liquid crystal elements 215 are sandwiched between a pair of substrates (a first substrate and a second substrate), and a drive circuit section 121 and a pixel section 122 are provided on the first substrate. Further, a common connection portion (also referred to as a common contact) and a common electrode 128 (also referred to as a common electrode or a counter electrode) are provided on the second substrate. The common connection portion electrically connects the first substrate and the second substrate, and the common connection portion may be provided on the first substrate.

[0045] A plurality of gate lines 124 (scanning lines) and source lines 125 (signal lines) are provided in the pixel section 122. ​​​​​​​is provided, and a plurality of pixels 123 are surrounded by a gate line 124 and a source line 125 to form a matrix pattern. In the display panel exemplified in the present embodiment, the gate line 124 extends from the gate line driving circuit 121A, and the source line 125 extends from the source line driving circuit 121B.

[0046] The pixel 123 also has a transistor 214 as a switching element, a capacitor element 210 connected to the transistor 214, and a liquid crystal element 215.

[0047] The liquid crystal element 215 is an element that controls the transmission or non - transmission of light by the optical modulation action of liquid crystal. The optical modulation action of liquid crystal is controlled by the electric field applied to the liquid crystal. The direction of the electric field applied to the liquid crystal varies depending on the liquid crystal material, driving method, and electrode structure, and can be appropriately selected . For example, when using a driving method of applying an electric field in the thickness direction of the liquid crystal layer (so - called longitudinal direction), a structure may be adopted in which a pixel electrode is provided on the first substrate and a common electrode is provided on the second substrate so as to sandwich the liquid crystal . Also, when using a driving method of applying an electric field in the in - plane direction of the substrate (so - called horizontal electric field) to the liquid crystal, a structure may be adopted in which a pixel electrode and a common electrode are provided on the same surface with respect to the liquid crystal . Also, the pixel electrode and the common electrode may have various opening patterns. In the present embodiment, as long as it is an element that controls the transmission or non - transmission of light by the optical modulation action , the liquid crystal material, driving method, and electrode structure are not particularly limited . Also, the pixel electrode and the common electrode may have a shape with various opening patterns. In the present embodiment, as long as it is an element that controls the transmission or non - transmission of light by the optical modulation action , the liquid crystal material, driving method, and electrode structure are not particularly limited .

[0048] The transistor 214 has a gate electrode connected to one of the plurality of gate lines 124 provided in the pixel portion 122, and one of the source electrode or the drain electrode is connected to one of the plurality of source lines 125 . It is connected to one of them, and the other of the source electrode or the drain electrode is connected to one electrode of the capacitor element 210 and one electrode (pixel electrode) of the liquid crystal element 215.

[0049] For the transistor 214, it is preferable to use a transistor with a low off-current. When the transistor 214 is in the off state, the liquid crystal element 215 connected to the transistor 214 with a low off-current and the charges stored in the capacitor element 210 are less likely to leak through the transistor 214 and can hold the written state for a long time before the transistor 214 turns off.

[0050] With such a configuration, the capacitor element 210 can hold the voltage applied to the liquid crystal element 215. Also, the electrode of the capacitor element 210 may be configured to be connected to a separately provided capacitor line.

[0051] The drive circuit unit 121 includes a gate line drive circuit 121A and a source line drive circuit 121B. The gate line drive circuit 121A and the source line drive circuit 121B are drive circuits for driving the pixel unit 1 22 having a plurality of pixels, and have a shift register circuit (also referred to as a shift register).

[0052] Note that the gate line drive circuit 121A and the source line drive circuit 121B may be formed on the same substrate as the pixel unit 122, or may be formed on a different substrate.

[0053] Note that a high power supply potential Vdd, a low power supply potential Vss, a start pulse SP, a clock signal CK, and an image signal Data, which are controlled by the display control circuit 113, are supplied to the drive circuit unit 121.

[0054] ​​​​ The terminal portion 126 is an input terminal that supplies a predetermined signal (high power supply potential Vdd, low power supply potential Vss, start pulse SP, clock signal CK, image signal Data, common potential Vc om, etc.) output by the display control circuit 113 to the drive circuit portion 121.

[0055] The common electrode 128 is electrically connected to the common potential line that supplies the common potential Vcom controlled by the display control circuit 113 at the common connection portion.

[0056] As a specific example of the common connection portion, electrical connection between the common electrode 128 and the common potential line can be achieved by interposing conductive particles coated with a metal thin film on an insulating sphere. In addition, the common connection portion may be configured to be provided at a plurality of locations within the display panel 120.

[0057] Further, the liquid crystal display device may have a photometry circuit. The liquid crystal display device provided with the photometry circuit can detect the brightness of the environment where the liquid crystal display device is placed. As a result, the display control circuit 113 to which the photometry circuit is connected can control the driving method of light sources such as a backlight and a s idle light according to the signal input from the photometry circuit.

[0058] In the case of performing color display, display can be achieved by combining color filters. In addition, other optical films (polarizing film, retardation film, anti-reflection film, etc.) can also be combined and used. Light sources such as a backlight used in the case of a transmissive liquid crystal display device or a transflective liquid crystal display device can be selected and combined according to the use of the liquid crystal display device 100, and a cold cathode tube, a light emitting diode (LED), etc. can be used. A surface light source may be configured using a plurality of LED light sources, or a plurality of electroluminescence (EL) light sources, etc. As the surface light source, three or more types of LEDs may be used, or white light-emitting LEDs may be used. Note that when adopting the sequential addition color mixing method (field sequential method) of color display by arranging RGB light-emitting diodes, etc. in the backlight and performing color display by time division, a color filter may not be provided in some cases.

[0059] As described above, in the on state where the liquid crystal display device is powered on and power is supplied, low power consumption can be achieved by using a semiconductor element with a low off-current. Furthermore, by writing an initialization image representing a fixed potential so that a voltage is not applied to the liquid crystal element before setting it to the off state, deterioration of the liquid crystal element can be prevented, a good image display function can be maintained for a long time, and security can also be enhanced. Therefore, it is possible to provide a liquid crystal display device with higher reliability and achieved low power consumption, and a driving method for the liquid crystal display device.

[0060]

[0061] (Embodiment 2) In this embodiment, a driving method for a liquid crystal display device that can further reduce power consumption by combining with Embodiment 1 is shown. Parts that are the same as or have the same functions as those in Embodiment 1, and processes can be performed in the same manner as in Embodiment 1, and repeated explanations are omitted. Also, detailed explanations of the same locations are omitted.

[0062] The liquid crystal display device combines moving images and still images and displays them on the screen. A moving image is recognized by a human eye as a moving image by rapidly switching a plurality of different images corresponding to a plurality of frames. ​​​​​​​​refers to an image. Specifically, the image is switched 60 times (60 frames) or more per second so that there is little flicker and it is recognized as a moving image by the human eye. On the other hand, a still image, unlike a moving image and a partial moving image, even if a plurality of images corresponding to a plurality of frame periods for time division are switched at high speed and operated, refers to an image that does not change between consecutive frame periods, for example, the nth frame and the (n + 1)th frame.

[0063] The liquid crystal display device according to the present invention can use different display modes, namely, a moving image display mode and a still image display mode, when the image is moving during moving image display and when the image is stationary during still image display, respectively. In this specification, the image displayed during still image display is also referred to as a still image.

[0064] When the image signals of consecutive frames are different (for example, in the first consecutive frame and the second frame, the first image signal of the first frame is different from the second image signal of the second frame) during moving image display, a display mode in which the image signal is written for each frame is used. On the other hand, when the image signals of consecutive frames are the same (for example, in the first consecutive frame and the second frame, the first image signal of the first frame is the same as the second image signal of the second frame) during still image display, a new image signal is not written, and a display mode is used in which the voltages of the pixel electrode and the common electrode to which a voltage is applied to the liquid crystal element are made to float (floating) to hold the voltage applied to the liquid crystal element and display the still image without supplying a new potential.

[0065] The liquid crystal display device in the present embodiment, and the moving image display mode and still image display The mode switching will be described with reference to FIGS. 3 to 6 and 11. FIG.

[0066] Each component of a liquid crystal display device 200 according to this embodiment will be described with reference to the block diagram of FIG. The liquid crystal display device 200 is a transmissive liquid crystal display device that displays images by using the transmission and non-transmission of light in pixels. The display device is an example of a semi-transmissive liquid crystal display device, and includes an image processing circuit 110, a power supply 116, a stop The display device includes a stopper 117, a display panel 120, and a backlight unit 130. In the case of the display device, the backlight unit 130 can be omitted because external light is used as the light source. Cut.

[0067] The liquid crystal display device 200 receives an image signal (image signal Data) from a connected external device. In addition, the power supply potentials (high power supply potential Vdd, low power supply potential Vss, and common potential Vco m) is supplied by turning on the power supply 116 of the liquid crystal display device to start the power supply, The control signals (start pulse SP and clock signal CK) are generated by the display control circuit 113. In addition, the power supply potentials (high power supply potential Vdd, low power supply potential Vss, and common potential Vc om) is stopped by the control of the stop means 117, and the initial state image is displayed. Thereafter, the power supply 116 is turned off to stop the supply of the power supply potential to the display panel.

[0068] In addition, if the image signal data is an analog signal, it is converted to digital form via an A / D converter, etc. The signal is converted into a digital signal and supplied to the image processing circuit 110 of the liquid crystal display device 200. For example, when detecting a difference between image signals later, detection can be easily performed, which is preferable.

[0069] The configuration of the image processing circuit 110 and the procedure for processing signals by the image processing circuit 110 are described below. Do it.

[0070] The image processing circuit 110 includes a memory circuit 111, a comparison circuit 112, a display control circuit 113, and a selection circuit 115. The image processing circuit 110 generates a display panel image signal and a backlight signal from the input digital image signal Data. The display panel image signal is an image signal for controlling the display panel 120, and the backlight signal is a signal for controlling the backlight unit 130. Also, a signal for controlling the common electrode 128 is output to the switching element 127.

[0071] The memory circuit 111 has a plurality of frame memories for storing image signals related to a plurality of frames. The number of frame memories included in the memory circuit 111 is not particularly limited, and any element capable of storing image signals related to a plurality of frames may be used. The frame memory may be configured using a storage element such as, for example, DRAM (Dynamic Random Access Memory) , SRAM (Static Random Access Memory), etc.

[0072] The frame memory only needs to be configured to store an image signal for each frame period, and the number of frame memories is not particularly limited. Also, the image signals in the frame memories are selectively read out by the comparison circuit 112 and the display control circuit 113. Note that the frame memory 111b in the figure conceptually illustrates a memory area for one frame.

[0073] One of these frame memories is set to the initial state where the liquid crystal shown in Embodiment 1 is in a non-responsive state. It is possible to store the image signal of the initial state image (for example, a display of an all-white screen or an all-black screen). The image signal of the initial state image receives an input of a stop signal and is read out by the display control circuit 113 and written to the screen. The comparison circuit 112 selectively reads out the image signals of consecutive frame periods stored in the storage circuit 111, compares them pixel by pixel between consecutive frames of the image signals, and is a circuit for detecting differences. The comparison circuit 112 selectively reads out the image signals of consecutive frame periods stored in the storage circuit 111, compares them pixel by pixel between consecutive frames of the image signals, and is a circuit for detecting differences.

[0074] The comparison circuit 112 selectively reads out the image signals of consecutive frame periods stored in the storage circuit 111, compares them pixel by pixel between consecutive frames of the image signals, and is a circuit for detecting differences. The comparison circuit 112 selectively reads out the image signals of consecutive frame periods stored in the storage circuit 111, compares them pixel by pixel between consecutive frames of the image signals, and is a circuit for detecting differences. The comparison circuit 112 selectively reads out the image signals of consecutive frame periods stored in the storage circuit 111, compares them pixel by pixel between consecutive frames of the image signals, and is a circuit for detecting differences.

[0075] In this embodiment, the operations of the display control circuit 113 and the selection circuit 115 are determined based on the presence or absence of differences in the image signals between frames. When the comparison circuit 112 detects a difference in any pixel between frames (when there is a difference), the comparison circuit 112 determines that the image signal is not a signal for a still image and determines that the consecutive frame periods in which the difference is detected are periods for displaying a moving image. In this embodiment, the operations of the display control circuit 113 and the selection circuit 115 are determined based on the presence or absence of differences in the image signals between frames. When the comparison circuit 112 detects a difference in any pixel between frames (when there is a difference), the comparison circuit 112 determines that the image signal is not a signal for a still image and determines that the consecutive frame periods in which the difference is detected are periods for displaying a moving image. In this embodiment, the operations of the display control circuit 113 and the selection circuit 115 are determined based on the presence or absence of differences in the image signals between frames. When the comparison circuit 112 detects a difference in any pixel between frames (when there is a difference), the comparison circuit 112 determines that the image signal is not a signal for a still image and determines that the consecutive frame periods in which the difference is detected are periods for displaying a moving image. In this embodiment, the operations of the display control circuit 113 and the selection circuit 115 are determined based on the presence or absence of differences in the image signals between frames. When the comparison circuit 112 detects a difference in any pixel between frames (when there is a difference), the comparison circuit 112 determines that the image signal is not a signal for a still image and determines that the consecutive frame periods in which the difference is detected are periods for displaying a moving image. In this embodiment, the operations of the display control circuit 113 and the selection circuit 115 are determined based on the presence or absence of differences in the image signals between frames. When the comparison circuit 112 detects a difference in any pixel between frames (when there is a difference), the comparison circuit 112 determines that the image signal is not a signal for a still image and determines that the consecutive frame periods in which the difference is detected are periods for displaying a moving image.

[0076] On the other hand, when no difference is detected in all pixels as a result of comparing the image signals in the comparison circuit 112 (when there is no difference), the consecutive frame periods in which no difference is detected are determined to be periods for displaying a still image. That is, the comparison circuit 112 determines whether the image signal is an image signal for displaying a moving image or an image signal for displaying a still image by detecting the presence or absence of differences in the image signals of consecutive frame periods. On the other hand, when no difference is detected in all pixels as a result of comparing the image signals in the comparison circuit 112 (when there is no difference), the consecutive frame periods in which no difference is detected are determined to be periods for displaying a still image. That is, the comparison circuit 112 determines whether the image signal is an image signal for displaying a moving image or an image signal for displaying a still image by detecting the presence or absence of differences in the image signals of consecutive frame periods. On the other hand, when no difference is detected in all pixels as a result of comparing the image signals in the comparison circuit 112 (when there is no difference), the consecutive frame periods in which no difference is detected are determined to be periods for displaying a still image. That is, the comparison circuit 112 determines whether the image signal is an image signal for displaying a moving image or an image signal for displaying a still image by detecting the presence or absence of differences in the image signals of consecutive frame periods. On the other hand, when no difference is detected in all pixels as a result of comparing the image signals in the comparison circuit 112 (when there is no difference), the consecutive frame periods in which no difference is detected are determined to be periods for displaying a still image. That is, the comparison circuit 112 determines whether the image signal is an image signal for displaying a moving image or an image signal for displaying a still image by detecting the presence or absence of differences in the image signals of consecutive frame periods. On the other hand, when no difference is detected in all pixels as a result of comparing the image signals in the comparison circuit 112 (when there is no difference), the consecutive frame periods in which no difference is detected are determined to be periods for displaying a still image. That is, the comparison circuit 112 determines whether the image signal is an image signal for displaying a moving image or an image signal for displaying a still image by detecting the presence or absence of differences in the image signals of consecutive frame periods.

[0077] Note that the criterion for detecting "there is a difference" by the comparison may be set such that when the magnitude of the difference exceeds a certain level, it is determined that there is a difference. Note that the criterion for detecting "there is a difference" by the comparison may be set such that when the magnitude of the difference exceeds a certain level, it is determined that there is a difference. The difference detected by the circuit 112 may be set to make a determination based on the absolute value of the difference.

[0078] Also, in the present embodiment, the comparison circuit 112 provided inside the liquid crystal display device 200 detects the difference between the image signals in consecutive frame periods to determine whether the image is a moving image or a still image. However, it may be configured to supply a signal indicating whether it is a moving image or a still image from the outside.

[0079] The selection circuit 115 is configured to provide a plurality of switches formed of transistors, for example. When the comparison circuit 112 detects a difference between consecutive frames, that is, when the image is a moving image , it selects a moving image signal from the frame memory in the memory circuit 111 and outputs it to the display control circuit 113.

[0080] When the selection circuit 115 does not detect a difference between consecutive frames by the comparison circuit 112, that is, when the image is a still image, it does not output an image signal from the frame memory in the memory circuit 111 to the display control circuit 113. By adopting a configuration in which the image signal is not output from the frame memory to the display control circuit 113, the power consumption of the liquid crystal display device can be reduced.

[0081] In the liquid crystal display device of the present embodiment, the operation in which the comparison circuit 112 determines that the image signal is for still image display is the still image display mode, and the operation in which the comparison circuit 112 determines that the image signal is for moving image display is the moving image display mode.

[0082] The display control circuit 113 supplies the image signal selected by the selection circuit 115 to the display panel 120, as well as control signals (specifically, control signals such as a start pulse SP and a clock signal CK).​​​ or a signal for controlling the switching between start and stop), a power supply potential (a high power supply potential Vdd, a low power supply potential Vss, and a common potential Vcom), and supplies a backlight control signal (specifically, a signal for the backlight control circuit 131 to control the lighting and extinguishing of the backlight) to the backlight unit 130. It is a circuit that

[0083] Note that the image processing circuit exemplified in this embodiment may have a display mode switching function. The display mode switching function is a function for switching between a moving image display mode and a still image display mode by a user of the liquid crystal display device selecting the operation mode of the liquid crystal display device manually or using an external connection device.

[0084] The selection circuit 115 can also output an image signal to the image display control circuit 113 according to a signal input from the display mode switching circuit.

[0085] For example, when the mode switching signal is input from the display mode switching circuit to the selection circuit 115 while operating in the still image display mode, even if the comparison circuit 112 does not detect the difference between the image signals in consecutive frame periods, the selection circuit 115 can execute a mode in which the input image signal is sequentially output to the display control circuit 113, that is, the moving image display mode. Also, when the mode switching signal is input from the display mode switching circuit to the selection circuit 115 while operating in the moving image display mode, even if the comparison circuit 112 detects the difference between the image signals in consecutive frame periods, the selection circuit 115 can execute a mode in which only the signal of the selected one-frame image signal is output, that is, the still image display mode. Therefore ​​​​​​​​​​​, when the liquid crystal display device of the present embodiment is operating in the video display mode, among the images corresponding to a plurality of frames for time division, the image corresponding to one frame is displayed as a still image. .

[0086] Further, the liquid crystal display device may have a photometry circuit. The liquid crystal display device provided with the photometry circuit can detect the brightness of the environment where the liquid crystal display device is placed. As a result, the display control circuit 113 to which the photometry circuit is connected can control the driving method of a light source such as a backlight according to the signal input from the photometry circuit.

[0087] For example, when it is determined by the detection of the photometry circuit that the liquid crystal display device is being used in a dim environment, the display control circuit 113 controls to increase the light intensity of the backlight 132 to ensure good visibility of the display screen. On the contrary, when it is determined that the liquid crystal display device is being used under extremely bright external light (for example, direct sunlight outdoors), the display control circuit 113 controls to suppress the light intensity of the backlight 132 and reduce the power consumed by the backlight 132.

[0088] The backlight unit 130 has a backlight control circuit 131 and a backlight 132. The backlight 132 can be selected and combined according to the use of the liquid crystal display device 200, and a cold cathode tube, a light emitting diode (LED), etc. can be used. In the case of performing color display, display can be achieved by combining a color filter. For the backlight 132, for example, a white light emitting element (for example, an LED) can be arranged. Note that RGB light emitting diodes or the like can be arranged on the backlight 132, and color display can be performed by time division sequential addition color mixing. ​​​​​​​​​​​​​When the field sequential method is adopted, there is a case where a color filter is not provided. There is also a backlight control circuit 131 to which a backlight signal for controlling the backlight and a power supply potential are supplied from the display control circuit 113.

[0089] In this embodiment, the display panel 120 has a switching element 127 in addition to the pixel portion 122. In this embodiment, the display panel 120 has a first substrate and a second substrate, and a drive circuit portion 121, a pixel portion 122, and a switching element 127 are provided on the first substrate.

[0090] Further, the pixel 123 has a transistor 214 as a switching element, a capacitor element 210 connected to the transistor 214, and a liquid crystal element 215 (see FIG. 3).

[0091] It is preferable to use a transistor with a low off-current for the transistor 214. When the transistor 214 is in the off state, the liquid crystal element 215 connected to the transistor 214 with a low off-current and the charge stored in the capacitor element 210 are difficult to leak through the transistor 214, and the state written before the transistor 214 becomes the off state can be held for a long time.

[0092] In this embodiment, the liquid crystal is controlled by a vertical electric field formed by a common electrode provided on a second substrate facing a pixel electrode provided on the first substrate.

[0093] As an example of the liquid crystal applied to the liquid crystal element, nematic liquid crystal, cholesteric liquid crystal, smectic liquid crystal, discotic liquid crystal, thermotropic liquid crystal, lyotropic liquid crystal, low molecular weight ​​​​​​​​​​Liquid crystal, polymer liquid crystal, polymer dispersed liquid crystal (PDLC), ferroelectric liquid crystal, antiferroelectric liquid crystal, main chain type Examples include liquid crystal, side chain type polymer liquid crystal, banana type liquid crystal, etc.

[0094] Also, as an example of the driving method of liquid crystal, there are TN (Twisted Nematic) mode, STN (Super Twisted Nematic) mode, OCB (Optica lly Compensated Birefringence) mode, ECB (El ectrically Controlled Birefringence) mode, FLC (Ferroelectric Liquid Crystal) mode, AFL C (AntiFerroelectric Liquid Crystal) mode, P DLC (Polymer Dispersed Liquid Crystal) mode PNLC (Polymer Network Liquid Crystal) mode guest-host mode, etc.

[0095] The switching element 127 supplies the common potential Vcom to the common electrode 128 according to the control signal output by the display control circuit 113. As the switching element 127, a transistor can be used. One of the gate electrode and the source electrode or the drain electrode of the transistor is connected to the display control circuit 113, and the common potential Vcom is supplied from the display control circuit 113 to one of the source electrode or the drain electrode via the terminal portion 1 26, and the other is connected to the common electrode 128. Note that the switching element 127 may be formed on the same substrate as the drive circuit portion 121, or the pixel portion 122, or may be formed on a different substrate. It may be either.

[0096] By using a transistor with a low off-current as the switching element 127, it is possible to suppress the phenomenon in which the voltage applied to both terminals of the liquid crystal element 215 decreases over time.

[0097] The common connection portion electrically connects the terminal connected to the source electrode or drain electrode of the switching element 127 and the common electrode 128.

[0098] One of the source electrode or drain electrode of the switching element 127 using a transistor, which is one aspect of the switching element, is connected to the other electrode of the capacitor element 210 that is not connected to the transistor 214 and the other electrode of the liquid crystal element 215. The other of the source electrode or drain electrode of the switching element 127 is connected to the terminal 126B. Also, the gate electrode of the switching element 127 is connected to the terminal 126A.

[0099] Next, the state of the signal supplied to the pixel will be described using the equivalent circuit diagram of the liquid crystal display device shown in FIG. 3 and the timing chart shown in FIG. 4.

[0100] FIG. 4 shows the clock signal GCK and the start pulse GSP that the display control circuit 113 supplies to the gate line drive circuit 121A. Also, FIG. 4 shows the clock signal SCK and the start pulse SSP that the display control circuit 113 supplies to the source line drive circuit 121B. Note that, in order to explain the output timing of the clock signal, the waveform of the clock signal is shown as a simple rectangular wave in FIG. 4.

[0101] Also, FIG. 4 shows the potential of the source line (Data line) 125, the potential of the pixel electrode, the potential of the terminal 126A, the potential of the terminal 126B, and the potential of the common electrode. ​​​​​​​​​​​​

[0102] In FIG. 4, period 1401 corresponds to a period for writing an image signal for displaying a video. During period 1401, the image signal and the common potential are supplied to each pixel and the common electrode of pixel section 122. It operates as such.

[0103] Also, period 1402 corresponds to a period for displaying a still image. During period 1402, the supply of the image signal to each pixel of pixel section 122 and the common potential to the common electrode will be stopped. Note that in the period 1402 shown in FIG. 4, the configuration of supplying each signal so as to stop the operation of the drive circuit section is shown. Therefore, it is preferable to adopt a configuration in which deterioration of the still image is prevented by periodically writing an image signal according to the length of period 1402 and the refresh rate. First, the timing chart in period 1401 will be described. In period 1401, a constant clock signal is supplied as the clock signal GCK, and a pulse corresponding to the vertical synchronization frequency is supplied as the start pulse GSP. Also, in period 1401, a constant clock signal is supplied as the clock signal SCK, and a pulse corresponding to one gate selection period is supplied as the start pulse SSP.

[0104]

[0105]

[0106] Also, the image signal Data is supplied to each pixel of each row via the source line 125, and the potential of the source line 125 is supplied to the pixel electrode according to the potential of the gate line 124.

[0107] ​​​​​​​​​​On the one hand, period 1402 is a period for displaying a still image. Next, the timing chart in period 1402 will be described. In period 1402, the clock signal GCK, the start pulse G SP, the clock signal SCK, and the start pulse SSP all stop. Also, during period 14 02, the image signal Data supplied to the source line 125 stops. During period 1402 when the clock signal GCK and the start pulse GSP both stop, the transistor 21 4 becomes non-conductive and the potential of the pixel electrode becomes a floating state.

[0108] Also, the display control circuit 113 supplies a potential to the terminal 126A of the switching element 127 to make the switching element 127 non-conductive, making the potential of the common electrode a floating state.

[0109] In period 1402, the electrodes at both ends of the liquid crystal element 215, that is, the pixel electrode and the common electrode, have their potentials in a floating state, and a still image can be displayed without newly supplying a potential. Moreover, by stopping the clock signals and start pulses supplied to the gate line driving circuit 121A and the source line driving circuit 121B, power consumption can be reduced.

[0110] In particular, by using transistors with low off-currents for the transistor 214 and the switching element 127, the phenomenon of the voltage applied to both terminals of the liquid crystal element 215 decreasing over time can be suppressed. Next, the operation of the display control circuit during the period of switching from a moving image to a still image (period 1403 in FIG. 4) and the period of switching from a still image to a moving image (period 1404 in FIG. 4) will be described with reference to FIG. 5(A).

[0111] Specifically, by using transistors with low off-currents for the transistor 214 and the switching element 127, the phenomenon of the voltage applied to both terminals of the liquid crystal element 215 decreasing over time can be suppressed. Moreover, by stopping the clock signals and start pulses supplied to the gate line driving circuit 121A and the source line driving circuit 121B, power consumption can be reduced. Next, the operation of the display control circuit during the period of switching from a moving image to a still image (period 1403 in FIG. 4) and the period of switching from a still image to a moving image (period 1404 in FIG. 4) will be described with reference to FIG. 5(A).

[0112] Next, the operation of the display control circuit during the period of switching from a moving image to a still image (period 1403 in FIG. 4), and the period of switching from a still image to a moving image (period 1404 in FIG. 4) will be described with reference to FIG. 5(A). Next, the operation of the display control circuit during the period of switching from a moving image to a still image (period 1403 in FIG. 4), and the period of switching from a still image to a moving image (period 1404 in FIG. 4) will be described with reference to FIG. 5(A). , it will be described with reference to (B). FIGS. 5(A) and (B) show the high power supply potential Vdd, the clock signal (here GCK), the start pulse signal (here GSP), and the potential of terminal 126A.

[0113] The operation of the display control circuit during the period 1403 when switching from video to still image is shown in FIG. 5(A). The display control circuit stops the start pulse GSP (E1 in FIG. 5(A), the first step) . Next, after the start pulse signal GSP stops and the pulse output reaches the last stage of the shift register, a plurality of clock signals GCK are stopped (E2 in FIG. 5(A), the second step). Next, the high power supply potential Vdd of the power supply is changed to the low power supply potential Vss (E3 in FIG. 5(A), the third step). Next, the potential of terminal 126A is set to a potential at which the switching element 127 is non-conductive (E4 in FIG. 5(A), the fourth step).

[0114] With the above procedure, the signal supplied to the drive circuit unit 121 can be stopped without causing malfunction of the drive circuit unit 12 1. Malfunctions during the switching from video to still image generate noise, and since the noise is retained as a still image, a liquid crystal display device equipped with a display control circuit with few malfunctions can display a still image with little image degradation.

[0115] Next, the operation of the display control circuit during the period 1404 when switching from still image to video is shown in FIG. 5(B). The display control circuit sets the potential of terminal 126A to a potential at which the switching element 127 is conductive (S1 in FIG. 5(B), the first step). Next, the power supply voltage is changed from the low power supply potential Vss to the high power supply potential Vdd (S2 in FIG. 5(B), the second step). Next, the clock signal After applying a high potential to the GCK terminal, a plurality of clock signals GCK are supplied (Fig. 5( B), S3, the third step). Next, a start pulse signal GSP is supplied (Fig. 5(B ), S4, the fourth step).

[0116] With the above procedure, the supply of the drive signal to the drive circuit unit 121 can be restarted without causing malfunction of the drive circuit unit 121 . By appropriately returning the potential of each wiring in order during video display, the drive circuit unit can be driven without malfunction .

[0117] Also, Fig. 6 schematically shows the writing frequency of the image signal for each frame period during the period 601 for displaying a video or the period 602 for displaying a still image . In Fig. 6, "W" represents the writing period of the image signal, and "H" represents the period for holding the image signal . Also, in Fig. 6, the period 603 represents one frame period, but it may be another period .

[0118] Thus, in the configuration of the liquid crystal display device according to the present embodiment, the image signal of the still image displayed in the period 602 is written in the period 604, and the image signal written in the period 604 is held in another period of the period 6 02 .

[0119] The liquid crystal display device exemplified in the present embodiment can reduce the writing frequency of the image signal during the period of displaying a still image. As a result, power consumption can be reduced when displaying a still image .

[0120] Also, when a still image is displayed by rewriting the same image a plurality of times, if the switching of the image is visible, a person may feel eye fatigue. The liquid crystal display device of the present embodiment ​​​Since the writing frequency of the signal is reduced, it also has the effect of reducing eye fatigue.

[0121] In particular, in the liquid crystal display device of the present embodiment, by applying a transistor with a low off-current to each pixel and the switching element of the common electrode, the period (time) during which the voltage can be held by the holding capacitor can be lengthened. As a result, it becomes possible to significantly reduce the writing frequency of the image signal, and it has a remarkable effect on reducing power consumption when displaying a still image and reducing eye fatigue. Also, when the stop means 117 is selected in the liquid crystal display device 200 of the present embodiment, a stop signal is input, and a fixed potential is written to the capacitive elements 210 of all pixels. By writing a fixed potential to the capacitive element 210, the potential difference between the electrodes of the capacitive element 210 is eliminated, and the liquid crystal in the response state is set to the initial state of the non-response state.

[0122] Therefore, an initial state image of the liquid crystal in the initial state is displayed on the display screen. After displaying the initial state image, the power supply 116 is stopped and the supply of the power potential to the display panel 120 is stopped, and the liquid crystal display device 200 is turned off. Therefore, the liquid crystal does not continue to be applied with an unnecessary electric field in the off state, and can be in a stable initial state. As described above, in the on state where the liquid crystal display device is turned on and power is supplied, the moving image display mode and the still image display mode are appropriately selected by the image signals of consecutive frames to reduce power consumption, and a fixed potential is written before turning off the state so that no voltage is applied to the liquid crystal element, and an initialization image is displayed to prevent deterioration of the liquid crystal element, and a good image display can be obtained for a long time.

[0123]

[0124] ​​​​​​​​​It is possible to maintain the function and enhance the security at the same time.

[0125] Therefore, it is possible to provide a liquid crystal display device that achieves higher reliability and lower power consumption, and a driving method of the liquid crystal display device.

[0126] (Embodiment 3) In this embodiment, an example of a transistor applicable to the liquid crystal display device disclosed in this specification is shown. The structure of the transistor applicable to the liquid crystal display device disclosed in this specification is not particularly limited, and for example, a staggered or planar type of top gate structure or bottom gate structure can be used. Also, the transistor may have a single gate structure in which one channel formation region is formed, a double gate structure in which two channel formation regions are formed, or a triple gate structure in which three channel formation regions are formed. Further, a dual gate type having two gate electrode layers disposed via a gate insulating layer above and below the channel region may also be used. FIGS. 7(A) to (D) show an example of the cross-sectional structure of the transistor. Note that the transistors shown in FIGS. 7(A) to (D) use an oxide semiconductor as the semiconductor. The merit of using an oxide semiconductor is that high mobility and low off-current can be obtained by a relatively simple and low-temperature process. Of course, other semiconductors may also be used. The transistor 410 shown in FIG. 7(A) is one of the thin film transistors having a bottom gate structure, and is also called an inverted staggered thin film transistor.

[0127] On a substrate 400 having an insulating surface, a gate electrode layer 401, a gate insulating layer 402, an oxide semiconductor layer 403, a source electrode layer 405a, and a drain electrode layer 40 are provided for the transistor 410.

[0128] ​​​​​It includes 5b. Also, an insulating film that covers the transistor 410 and is laminated on the oxide semiconductor layer 403 407 is provided. A protective insulating layer 409 is further formed on the insulating film 407 .

[0129] The transistor 420 shown in FIG. 7(B) is one of the bottom gate structures called channel protection type (also called channel stop type ). It is also called an inverted staggered type thin film transistor

[0130] The transistor 420 includes a gate electrode layer 401, a gate insulating layer 402, an oxide semiconductor layer 403, an insulating layer 427 that functions as a channel protection layer covering the channel formation region of the oxide semiconductor layer 403, a source electrode layer 405a, and a drain electrode layer 405b on a substrate 400 having an insulating surface. Also, a protective insulating layer 409 covering the transistor 420 is formed . .

[0131] The transistor 430 shown in FIG. 7(C) is a bottom gate type thin film transistor. On the substrate 400 which is a substrate having an insulating surface, it includes a gate electrode layer 401, a gate insulating layer 402, a source electrode layer 405a, a drain electrode layer 405b, and an oxide semiconductor layer 403. Also , an insulating film 407 that covers the transistor 430 and is in contact with the oxide semiconductor layer 403 is provided . A protective insulating layer 409 is further formed on the insulating film 407

[0132] In the transistor 430, the gate insulating layer 402 is provided in contact with the substrate 400 and the gate electrode layer 40 1. The source electrode layer 405a and the drain electrode layer 405b are provided in contact with the gate insulating layer 402. Then, the gate insulating layer 402 and the source electrode layer 40 5a. An oxide semiconductor layer 403 is provided on the drain electrode layer 405b.

[0133] The transistor 440 shown in FIG. 7(D) is one of the thin-film transistors having a top-gate structure. The transistor 440 includes an insulating layer 437, an oxide semiconductor layer 403, a source electrode layer 405a, a drain electrode layer 405b, a gate insulating layer 402, and a gate electrode layer 401 on a substrate 400 having an insulating surface. Wiring layers 436a and 436b are respectively in contact with and electrically connected to the source electrode layer 405a and the drain electrode layer 405b.

[0134] In this embodiment, as described above, an oxide semiconductor layer 403 is used as the semiconductor layer. Examples of the oxide semiconductor used for the oxide semiconductor layer 403 include quaternary metal oxides such as In-Sn-Ga-Zn-O, ternary metal oxides such as In-Ga-Zn-O, In-Sn-Zn-O, In-Al-Zn-O, Sn-Ga-Zn-O, Al-Ga-Zn-O, Sn-Al-Zn-O, binary metal oxides such as In-Zn-O, Sn-Zn-O, Al-Zn-O, Zn-Mg-O, Sn-Mg-O, In-Mg-O, In-O, Sn-O, Zn-O, etc. Further, the above oxide semiconductor may contain SiO2. Here, for example, an In-Ga-Zn-O-based oxide semiconductor is an oxide containing at least In, Ga, and Zn, and its composition ratio is not particularly limited. In addition, elements other than In, Ga, and Zn may be included.

[0135] Further, a thin film represented by the chemical formula InMO3(ZnO)m (m>0) can be used for the oxide semiconductor layer 403. Here, M is selected from Ga, Al, Mn, and Co. ​ or a plurality of metal elements. For example, as M, there are Ga, Ga and Al, Ga and Mn, or Ga and Co, etc. and the like.

[0136] Transistors 410, 420, 430, and 440 using the oxide semiconductor layer 403 can reduce the current value (off-current value) in the off state. Therefore, the holding time of an electrical signal such as an image signal can be lengthened, and in the power-on state, the writing interval can also be set longer. Therefore, since the frequency of the refresh operation can be reduced, the effect of suppressing power consumption is achieved. Also, since transistors 410, 420, 430, and 440 using the oxide semiconductor layer 403 can obtain a relatively high field-effect mobility, high-speed driving is possible. Therefore, by using such transistors in the pixel portion of a liquid crystal display device, a high-quality image can be provided. Also, since the transistors can be separately fabricated for the drive circuit portion or the pixel portion on the same substrate, the number of components of the liquid crystal display device can be reduced.

[0137] There is no significant limitation on the substrate that can be used for the substrate 400 having an insulating surface, but a glass substrate such as barium borosilicate glass or aluminoborosilicate glass is used.

[0138] In transistors 410, 420, and 430 having a bottom gate structure, an insulating film serving as an underlayer film may be provided between the substrate and the gate electrode layer. The underlayer film has a function of preventing the diffusion of impurity elements from the substrate and can be formed by a laminated structure of one or a plurality of films selected from a silicon nitride film, a silicon oxide film, a silicon oxynitride film, or a silicon nitride oxide film.

[0139]

[0140] The material of the gate electrode layer 401 can be formed of a single layer or laminated using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, scandium, or an alloy material mainly composed of these.

[0141] The gate insulating layer 402 can be formed of a single layer or laminated using the plasma CVD method, sputtering method, etc., to form a silicon oxide layer, silicon nitride layer, silicon oxynitride layer, silicon nitride oxide layer, aluminum oxide layer, nitride aluminum layer, aluminum oxynitride layer, aluminum nitride oxide layer, or hafnium oxide layer. For example, as the first gate insulating layer, a silicon nitride layer (SiNy (y >0)) with a film thickness of 50 nm or more and 200 nm or less is formed by the plasma CVD method, and a silicon oxide layer (SiOx (x>0)) with a film thickness of 5 nm or more and 3 00 nm or less is laminated on the first gate insulating layer to form a gate insulating layer with a total film thickness of 200 nm .

[0142] As the conductive film used for the source electrode layer 405a and the drain electrode layer 405b, for example, elements selected from Al , Cr, Cu, Ta, Ti, Mo, W, or an alloy composed of the above-mentioned elements, or an alloy film formed by combining the above-mentioned elements can be used. Also, a high melting point metal layer such as Ti, Mo, W can be laminated on one or both of the lower side and the upper side of a metal layer such as Al, Cu. Further, by using an Al material added with an element (such as Si, Nd, Sc) that prevents the generation of hillocks and whiskers generated in the Al film, the heat resistance can be improved.

[0143] ​​​​​The wiring layers 436a and 43 6b connected to the source electrode layer 405a and the drain electrode layer 405b can also be made of the same material as the source electrode layer 405a and the drain electrode layer 405b. It can be used.

[0144] In addition, as the conductive film that becomes the source electrode layer 405a, the drain electrode layer 405b (including the wiring layer formed of the same layer), it may be formed of a conductive metal oxide. As the conductive metal oxide, indium oxide (In2O3), tin oxide (SnO2), zinc oxide (ZnO ), indium tin oxide alloy (In2O3―SnO2, abbreviated as ITO), indium zinc oxide alloy (In2O3―ZnO), or those obtained by adding silicon oxide to these metal oxide materials can be used.

[0145] The insulating films 407, 427, and 437 can typically be inorganic insulating films such as a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or an aluminum oxynitride film. It can be used.

[0146] The protective insulating layer 409 can be an inorganic insulating film such as a silicon nitride film, an aluminum nitride film, a silicon oxynitride film, or an aluminum oxynitride film. It can be used.

[0147] In addition, a planarizing insulating film may be formed on the protective insulating layer 409 to reduce surface irregularities caused by the transistor. As the planarizing insulating film, organic materials such as polyimide, acrylic, benzocyclobutene can be used. In addition to the above organic materials, low dielectric constant materials (low -k materials) and the like can be used. Note that a planarizing insulating film may be formed by laminating a plurality of insulating films formed of these materials. ​​​​​​​

[0148] Thus, in this embodiment, by using a transistor including an oxide semiconductor layer having a low off-current value, a liquid crystal display device with low power consumption can be provided.

[0149] (Embodiment 4) This embodiment will be described in detail with reference to FIG. 8 for an example of a transistor including an oxide semiconductor layer and a manufacturing method. The same parts or parts having similar functions and processes as those in the above embodiment can be carried out in the same manner as in the above embodiment, and repeated descriptions will be omitted. Also, detailed descriptions of the same locations will be omitted.

[0150] Examples of the cross-sectional structure of the transistor are shown in FIGS. 8(A) to (E). The transistor 510 shown in FIGS. 8(A) to (E) is an inverted staggered thin film transistor having the same bottom gate structure as the transistor 410 shown in FIG. 7(A).

[0151] The oxide semiconductor used for the semiconductor layer in this embodiment is an i-type (intrinsic) oxide semiconductor, or an oxide semiconductor that is extremely close to i-type (intrinsic), by removing hydrogen, which is an n-type impurity, from the oxide semiconductor and purifying it so that it contains as few impurities as possible other than the main components of the oxide semiconductor. That is, instead of adding impurities to make it i-type, impurities such as hydrogen and water are removed as much as possible, resulting in a highly purified i-type (intrinsic semiconductor) or approaching it. Therefore, the oxide semiconductor layer included in the transistor 510 is an oxide semiconductor layer that has been highly purified and electrically i-type (intrinsic).

[0152] In addition, in the highly purified oxide semiconductor, the carriers are extremely few (close to zero), and the The carrier concentration is less than 1×1014 / cm3, preferably less than 1×1012 / cm3, more preferably less than 1×1011 / cm3. That is.

[0153] Since the number of carriers in the oxide semiconductor is extremely small, the off-current of the transistor can be reduced. The smaller the off-current, the more preferable.

[0154] Specifically, the thin film transistor including the above-described oxide semiconductor layer has an off-current density of 10 aA / μm (1×10-17 A / μm) or less at room temperature for a channel width of 1 μm. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less.

[0155] By using the transistor having an extremely small current value (off-current value) in the off state as the transistor in the element portion of Embodiment 1, the refresh operation in the still image region can be performed with a small number of write times of image data. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less.

[0156] In addition, the transistor 510 including the above-described oxide semiconductor layer has almost no temperature dependence of the on-current, and the off-current also remains very small. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less.

[0157] Hereinafter, the process of manufacturing the transistor 510 on the substrate 505 will be described with reference to FIGS. 8(A) to (E). That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less.

[0158] First, after forming a conductive film on the substrate 505 having an insulating surface, the gate electrode layer 511 is formed by a first photolithography process. Note that the resist mask may be formed by an inkjet method. That is, it can be made 1 aA / μm (1×10-18 A / μm) or less, and further 10 zA / μm (1×10-20 A / μm) or less. When the resist mask is formed by an inkjet method, the use of a photomask can be omitted. Therefore, the manufacturing cost can be reduced.

[0159] As the substrate 505 having an insulating surface, a substrate similar to the substrate 400 shown in Embodiment 3 can be used. In this embodiment, a glass substrate is used as the substrate 505.

[0160] An insulating film serving as an underlayer film may be provided between the substrate 505 and the gate electrode layer 511. The underlayer film has a function of preventing the diffusion of impurity elements from the substrate 505, and is made of one or more films selected from a silicon nitride film, a silicon oxide film, a silicon oxynitride film, or a silicon nitride oxide film, and can be formed by a laminated structure.

[0161] Also, the material of the gate electrode layer 511 can be formed as a single layer or by lamination using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, scandium, or an alloy material mainly composed of these.

[0162] Next, a gate insulating layer 507 is formed on the gate electrode layer 511. The gate insulating layer 507 can be formed as a single layer or by lamination using a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a silicon nitride oxide layer, an aluminum oxide layer, an aluminum nitride layer, an aluminum oxynitride layer, an aluminum nitride oxide layer, or a hafnium oxide layer by a plasma CVD method, a sputtering method, or the like.

[0163] In this embodiment, an impurity-removed, i-type or substantially i-type oxide semiconductor is used. Such a highly purified oxide semiconductor is extremely sensitive to interface states and interface charges, so the interface between the oxide semiconductor layer and the gate insulating layer is important. Therefore, a gate insulating layer in contact with a highly purified oxide semiconductor is required to have high quality.

[0164] For example, a high-density plasma CVD method using microwaves (e.g., a frequency of 2.45 GHz) is preferable because it can form a high-quality insulating layer with high breakdown voltage in a dense manner. When a highly purified oxide semiconductor and a high-quality gate insulating layer are in close contact, interface states can be reduced and interface characteristics can be improved. This is because the interface states can be reduced and the interface characteristics can be made good.

[0165] Of course, other film formation methods such as sputtering and plasma CVD can be applied as long as a high-quality insulating layer can be formed as the gate insulating layer. Also, an insulating layer whose film quality and interface characteristics with the oxide semiconductor are modified by heat treatment after film formation may be used. In any case, not only should the film quality as the gate insulating layer be good, but it is sufficient if it can reduce the interface state density with the oxide semiconductor and form a good interface.

[0166] Further, in order to minimize the inclusion of hydrogen, hydroxyl groups, and moisture in the gate insulating layer 507 and the oxide semiconductor film 530, as a pretreatment for forming the oxide semiconductor film 530, the substrate 505 on which the gate electrode layer 511 is formed in the preheating chamber of the sputtering apparatus, or the substrate 505 on which up to the gate insulating layer 507 is formed is preheated to desorb and exhaust impurities such as hydrogen and moisture adsorbed on the substrate 505. It is preferable that the exhaust means provided in the preheating chamber is a cryopump. Note that this preheating process can be omitted. Also, this preheating may be similarly performed on the substrate 505 on which the source electrode layer 515a and the drain electrode layer 515b are formed before forming the insulating layer 516.

[0167] Next, an oxide semiconductor film 530 with a film thickness of 2 nm or more and 200 nm or less, preferably 5 nm or more and 30 nm or less is formed on the gate insulating layer 507 (see Fig. 8(A)).

[0168] Note that before forming the oxide semiconductor film 530 by sputtering, argon gas is introduced to perform reverse sputtering to generate plasma, and powdery substances (also called particles or dust) adhering to the surface of the gate insulating layer 507 are preferably removed. Reverse sputtering is a method in which a voltage is applied to the substrate side using an RF power source in an argon atmosphere without applying a voltage to the target side to form plasma near the substrate and modify the surface. Note that nitrogen, helium, oxygen, etc. may be used instead of the argon atmosphere.

[0169] As the oxide semiconductor used for the oxide semiconductor film 530, a quaternary metal oxide shown in Embodiment 3 or a ternary metal oxide, a binary metal oxide, an In-O system, an Sn-O system, a Zn-O system, etc. Any oxide semiconductor can be used. Further, SiO2 may be included in the above oxide semiconductor. In this embodiment, an In-Ga-Zn-O-based oxide target is used to form the film by sputtering for the oxide semiconductor film 530. The cross-sectional view at this stage corresponds to Fig. 8(A). Also, the oxide semiconductor film 530 can be formed by sputtering in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

[0170] As a target for producing the oxide semiconductor film 530 by sputtering, for example, as a composition ratio, In2O3:Ga2O3:ZnO = 1:1:1 [mole ratio] is used. It is possible. Additionally, other than this, In2O3:Ga2O3:ZnO = 1:1:2 [molar ratio], or a target having a composition ratio of In2O3:Ga2O3:ZnO = 1:1:4 [molar ratio] may also be used. The filling rate of the oxide target is 90% or more and 100% or less, preferably 95% or more and 99.9% or less. By using a metal oxide target with a high filling rate, the formed oxide semiconductor film becomes a dense film.

[0171] For the oxide semiconductor film 530, when forming the film, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl groups, or hydrogen compounds have been removed.

[0172] Hold the substrate in a film formation chamber maintained in a reduced pressure state, and set the substrate temperature to 100°C or higher and 600°C or lower, preferably 200°C or higher and 400°C or lower. By forming the film while heating the substrate, the impurity concentration in the formed oxide semiconductor film can be reduced. Also, the damage caused by sputtering is reduced. Then, while removing the residual moisture in the film formation chamber, introduce a sputtering gas from which hydrogen and moisture have been removed, and form an oxide semiconductor film 530 on the substrate 505 using the above target. To remove the residual moisture in the film formation chamber, it is preferable to use an adsorption-type vacuum pump, for example, a cryopump, an ion pump, or a titanium sublimation pump. Also, as the exhaust means, a turbo molecular pump with a cold trap added may be used. The film formation chamber evacuated using a cryopump has, for example, compounds containing hydrogen atoms, water (H2 O), etc. (more preferably compounds containing carbon atoms as well) exhausted, so the concentration of impurities contained in the oxide semiconductor film formed in the film formation chamber can be reduced.

[0173] As an example of film formation conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa , and the conditions under an atmosphere of a direct current (DC) power supply of 0.5 kW and oxygen (oxygen flow rate ratio 100%) are applied . Note that when using a pulsed DC power supply, it is preferable because powdery substances (also called particles, debris) generated during film formation can be reduced and the film thickness distribution becomes uniform .

[0174] Next, the oxide semiconductor film 530 is processed into island-shaped oxide semiconductor layers by a second photolithography process . Also, a resist mask for forming the island-shaped oxide semiconductor layer may be formed by an inkjet method . When the resist mask is formed by the inkjet method, since a photomask is not used, the manufacturing cost can be reduced .

[0175] Also, when forming a contact hole in the gate insulating layer 507, the process can be performed simultaneously during the processing of the oxide semiconductor film 530 .

[0176] Note that the etching of the oxide semiconductor film 530 here may be either dry etching or wet etching, or both may be used. For example, as an etching solution used for wet etching of the oxide semiconductor film 530, a solution obtained by mixing phosphoric acid, acetic acid, and nitric acid, etc. can be used . Also, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used . .

[0177] Next, a first heat treatment is performed on the oxide semiconductor layer. By this first heat treatment, dehydration or dehydrogenation of the oxide semiconductor layer can be performed. The temperature of the first heat treatment is 400°C or higher and 750°C or lower, or 400°C or higher and less than the strain point of the substrate . Here, the substrate is introduced into an electric furnace which is one of the heat treatment apparatuses, and the oxide semiconductor layer is heated to 450°C in a nitrogen atmosphere . . After performing a heat treatment for 1 hour, without exposure to the atmosphere, re-mixing of water and hydrogen into the oxide semiconductor layer is prevented to obtain an oxide semiconductor layer 531 (see FIG. 8(B)). Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used.

[0178] Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used. Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may also be used. For example, an RTA (Rapid Thermal Anneal) apparatus such as a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The LRTA apparatus is an apparatus that heats the object to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs a heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas such as argon or an inert gas that does not react with the object to be treated by the heat treatment, such as nitrogen, is used.

[0179] For example, as the first heat treatment, the substrate may be moved and placed in an inert gas heated to a high temperature of 650°C or higher and 700°C or lower, heated for several minutes, and then removed from the inert gas heated to a high temperature by moving the substrate to perform GRTA. For example, as the first heat treatment, the substrate may be moved and placed in an inert gas heated to a high temperature of 650°C or higher and 700°C or lower, heated for several minutes, and then removed from the inert gas heated to a high temperature by moving the substrate to perform GRTA. For example, as the first heat treatment, the substrate may be moved and placed in an inert gas heated to a high temperature of 650°C or higher and 700°C or lower, heated for several minutes, and then removed from the inert gas heated to a high temperature by moving the substrate to perform GRTA.

[0180] Note that in the first heat treatment, it is preferable that nitrogen or an inert gas such as helium, neon, or argon does not contain water, hydrogen, etc. Alternatively, the purity of nitrogen or an inert gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or higher. Note that in the first heat treatment, it is preferable that nitrogen or an inert gas such as helium, neon, or argon does not contain water, hydrogen, etc. Alternatively, the purity of nitrogen or an inert gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or higher. Note that in the first heat treatment, it is preferable that nitrogen or an inert gas such as helium, neon, or argon does not contain water, hydrogen, etc. Alternatively, the purity of nitrogen or an inert gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or higher. Preferably, it is 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less).

[0181] Also, after heating the oxide semiconductor layer in the first heat treatment, high-purity oxygen gas, high-purity N2O gas, or ultra-dry air (dew point of -40 °C or less, preferably -60 °C or less) may be introduced into the same furnace. It is preferable that water, hydrogen, etc. are not contained in the oxygen gas or N2O gas. Alternatively, the purity of the oxygen gas or N2O gas introduced into the heat treatment apparatus is preferably 6N or more, more preferably 7N or more (that is, the impurity concentration in the oxygen gas or N2O gas is 1 ppm or less, preferably 0.1 ppm or less). By the action of the oxygen gas or N2O gas, the oxygen that has simultaneously decreased due to the step of removing impurities by dehydration or dehydrogenation treatment is supplied, thereby purifying the oxide semiconductor layer and making it electrically i-type (intrinsic).

[0182] Also, the first heat treatment of the oxide semiconductor layer can also be performed on the oxide semiconductor film 530 before processing it into an island-shaped oxide semiconductor layer. In that case, after the first heat treatment, the substrate is taken out from the heating apparatus, and a photolithography process is performed.

[0183] In addition, the first heat treatment can be performed in any of the following cases: after forming the source electrode layer and the drain electrode layer on the oxide semiconductor layer, or after forming an insulating layer on the source electrode layer and the drain electrode layer, as long as it is after the formation of the oxide semiconductor layer.

[0184] Also, when forming a contact hole in the gate insulating layer 507, the process may be performed before or after performing the first heat treatment on the oxide semiconductor film 530. ​​​​

[0185] Also, by forming the oxide semiconductor layer in two steps and performing heat treatment in two steps, regardless of the material of the base member being an oxide, a nitride, a metal, etc., an oxide semiconductor layer having a thick crystal region (single crystal region), that is, a crystal region with c-axis orientation perpendicular to the film surface can be formed. For example, a first oxide semiconductor film with a thickness of 3 nm or more and 15 nm or less is formed, and a first heat treatment is performed at 450°C or more and 850°C or less, preferably 550°C or more and 750°C or less, in an atmosphere of nitrogen, oxygen, noble gas, or dry air, to form a first oxide semiconductor film having a crystal region (including plate-like crystals) in the region including the surface. Then, a second oxide semiconductor film thicker than the first oxide semiconductor film is formed, and a second heat treatment is performed at 450°C or more and 850°C or less, preferably 600°C or more and 700°C or less. Using the first oxide semiconductor film as a seed for crystal growth, crystal growth is performed upward to crystallize the entire second oxide semiconductor film, and as a result, an oxide semiconductor layer having a thick crystal region may be formed. Next, a conductive film that will become the source electrode layer and the drain electrode layer (including wirings formed of the same layer) is formed on the gate insulating layer 507 and the oxide semiconductor layer 531. As the conductive film used for the source electrode layer and the drain electrode layer, the materials used for the source electrode layer 405a and the drain electrode layer 405b shown in Embodiment 3 can be used. A resist mask is formed on the conductive film by a third photolithography process, and after selectively etching to form the source electrode layer 515a and the drain electrode layer 515b, the resist mask is removed (see FIG. 8(C)).

[0186]

[0187]

[0188] ​​​​​​​​​​​​​ For the exposure during resist mask formation in the third photolithography process, it is advisable to use ultraviolet light, KrF laser light, or ArF laser light. The channel length L of the transistor formed later is determined by the distance between the lower ends of the adjacent source electrode layers and the lower ends of the drain electrode layers on the oxide semiconductor layer 531. When performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. During the etching of the conductive film, the oxide semiconductor layer 531 is etched and separated. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased. Note that when performing exposure with a channel length L of less than 25 nm, it is advisable to perform the exposure during resist mask formation in the third photolithography process using extreme ultraviolet light with a wavelength as short as several nm to several tens of nm. Exposure with extreme ultraviolet light has high resolution and a large depth of focus. Therefore, it is also possible to set the channel length L of the transistor formed later to be 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased.

[0189] Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process. Moreover, in order to reduce the number of photomasks and the number of processes used in the photolithography process, the etching process may be performed using a resist mask formed by a multi-tone mask, which is an exposure mask in which the transmitted light has multiple intensities. The resist mask formed using the multi-tone mask has a shape with multiple film thicknesses, and the shape can be further deformed by performing etching. Therefore, it can be used in multiple etching processes for processing different patterns. Thus, a resist mask corresponding to at least two or more different patterns can be formed using a single multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, making it possible to simplify the process.

[0190] During the etching of the conductive film, the oxide semiconductor layer 531 is etched and separated. It is desirable to optimize the etching conditions so as not to cause this. It is difficult to obtain a condition in which the oxide semiconductor layer 531 is etched without being etched at all. During etching of the conductive film, the oxide semiconductor layer 531 is only partially etched, and a groove is formed. In some cases, the oxide semiconductor layer may have a recess (concave portion).

[0191] In this embodiment, a Ti film is used as the conductive film, and an In-Ga- Since a Zn-O-based oxide semiconductor was used, ammonia hydrogen peroxide (AH) was used as an etchant for the conductive film. A mixture of ammonia, water, and hydrogen peroxide is used.

[0192] Then, a plasma treatment is performed using a gas such as N2O, N2, or Ar to remove the exposed Water or the like adsorbed on the surface of the oxide semiconductor layer may be removed by the plasma treatment. In this case, the insulating layer 5, which is a protective insulating film that is in contact with a part of the oxide semiconductor layer without being exposed to the air, is formed. Form 16.

[0193] The insulating layer 516 has a thickness of at least 1 nm. The insulating layer 516 can be formed by using a method that does not mix impurities such as hydrogen. When hydrogen is contained in the oxide semiconductor layer, the hydrogen penetrates into the oxide semiconductor layer, or the hydrogen penetrates into the oxide semiconductor layer. Oxygen is extracted from the layer, and the back channel of the oxide semiconductor layer becomes low-resistance (n-type). Therefore, the insulating layer 516 should be as thin as possible. It is important that the deposition process does not use hydrogen, resulting in a hydrogen-free film.

[0194] In this embodiment, a silicon oxide film having a thickness of 200 nm is formed as the insulating layer 516 by sputtering. It is used for film formation. The substrate temperature during film formation may be from room temperature to 300 °C, and in this embodiment, it is 100 °C. Film formation of the silicon oxide film by sputtering can be performed in an inert gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of an inert gas and oxygen. Also, a silicon oxide target or a silicon target can be used as the target. For example, silicon oxide can be formed by sputtering in an atmosphere containing oxygen using a silicon target. The insulating layer 516 formed in contact with the oxide semiconductor layer does not contain impurities such as moisture, hydrogen ions, and OH−, and an inorganic insulating film that blocks these from entering from the outside is used. Typically, a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or an aluminum oxynitride film is used. To remove residual moisture in the film formation chamber of the insulating layer 516 in the same manner as during the film formation of the oxide semiconductor film 530, it is preferable to use an adsorption type vacuum pump (such as a cryopump). The concentration of impurities contained in the insulating layer 516 formed in the film formation chamber evacuated using a cryopump can be reduced. Also, as an exhaust means for removing residual moisture in the film formation chamber of the insulating layer 516, a turbo molecular pump with a cold trap added may be used. When forming the insulating layer 516, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl groups, or hydrides have been removed as the sputtering gas. Next, a second heat treatment (preferably at 200 °C or higher and 400 °C or lower, for example, 250 °C or higher and 350 °C or lower) is performed in an inert gas atmosphere or an oxygen gas atmosphere. For example, in a nitrogen atmosphere

[0195]

[0196]

[0197] ​​​​​​​​​​​​​ Perform a second heat treatment at 250°C for 1 hour in an atmosphere. When the second heat treatment is performed, a part of the oxide semiconductor layer (channel formation region) is heated in contact with the insulating layer 516.

[0198] By going through the above steps, the oxide semiconductor film is subjected to the first heat treatment to intentionally remove impurities such as hydrogen, moisture, hydroxyl groups, or hydrides (also referred to as hydrogen compounds) from the oxide semiconductor layer, and at the same time, oxygen, which is one of the main component materials constituting the oxide semiconductor that would otherwise decrease due to the impurity removal process, can be supplied. Therefore, the oxide semiconductor layer is purified to a high purity and electrically becomes i-type (intrinsic).

[0199] The transistor 510 is formed through the above steps (see FIG. 8(D)).

[0200] Also, when using a silicon oxide layer containing many defects for the insulating layer 516, hydrogen, moisture, hydroxyl groups, or hydrides and other impurities contained in the oxide semiconductor layer are diffused into the oxide insulating layer by the heat treatment after the formation of the silicon oxide layer, and the effect of further reducing the impurities contained in the oxide semiconductor layer is achieved.

[0201] A protective insulating layer 506 may be further formed on the insulating layer 516. For example, a silicon nitride film is formed using the RF sputtering method. The RF sputtering method is preferable as a film formation method for the protective insulating layer because of its good mass productivity. The protective insulating layer uses an inorganic insulating film that does not contain impurities such as moisture and blocks these from entering from the outside, and a silicon nitride film, an aluminum nitride film, etc. are used. In this embodiment, the protective insulating layer 506 is formed using a silicon nitride film (see FIG. 8(E)).

[0202] In this embodiment, as the protective insulating layer 506, the substrate 505 formed up to the insulating layer 516 is heated to a temperature of 100°C or higher and 400°C or lower, and sputtering gas containing high-purity nitrogen from which hydrogen and moisture have been removed is introduced, and a silicon nitride film is formed using a silicon semiconductor target. In this case as well, similar to the insulating layer 516, it is preferable to form the protective insulating layer 506 while removing residual moisture in the processing chamber.

[0203] After the formation of the protective insulating layer 506, a heat treatment may be further performed in the atmosphere at 100°C or higher and 200°C or lower for 1 hour or more and 30 hours or less. This heat treatment may be performed while maintaining a constant heating temperature, or may be performed by repeating multiple times the temperature increase from room temperature to a heating temperature of 100°C or higher and 200°C or lower and the temperature decrease from the heating temperature to room temperature.

[0204] Thus, by using the transistor including the highly purified oxide semiconductor layer manufactured using this embodiment, the current value (off-current value) in the off state can be made lower. Therefore, the holding time of an electrical signal such as an image signal can be lengthened, and the writing interval can also be set longer. Therefore, the frequency of the refresh operation can be made lower, so that the effect of suppressing power consumption can be enhanced.

[0205] In addition, since the transistor including the highly purified oxide semiconductor layer can obtain a high field-effect mobility, it can be driven at high speed. Therefore, by using the transistor in the pixel portion of the liquid crystal display device, a high-quality image can be provided. Also, since the transistor can be used to separately manufacture a drive circuit portion or a pixel portion on the same substrate, the number of components of the liquid crystal display device can be reduced. ​​​​​​​​​

[0206] This embodiment can be implemented in appropriate combination with the configurations described in other embodiments. It is.

[0207] (Embodiment 5) The liquid crystal display device disclosed in this specification can be applied to various electronic devices (including gaming machines). Examples of electronic devices include, for example, television devices (also referred to as TVs or television receivers), monitors for computers, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game machines, portable information terminals, audio playback devices, and large gaming machines such as pachinko machines. In this embodiment, examples of electronic devices equipped with the liquid crystal display device described in the above embodiment will be described.

[0208] FIG. 9(A) shows an electronic book (also referred to as an E-book), which can have a housing 9630, a display unit 9631, operation keys 9632, a solar cell 9633, and a charge / discharge control circuit 9634. The electronic book shown in FIG. 9(A) can have functions such as displaying various information (such as still images, moving images, and text images), displaying a calendar, date, or time on the display unit, operating or editing the information displayed on the display unit, controlling processing by various software (programs), and the like. Note that in FIG. 9(A), an example of the charge / discharge control circuit 9634 shows a configuration having a battery 9635 and a DCDC converter (hereinafter abbreviated as a converter) 9636. By applying the liquid crystal display device shown in any of Embodiments 1 to 4 to the display unit 9631, a better image display function can be maintained for a longer time, and security​​​​​​ It can be an e - book with high performance and low power consumption.

[0209] By adopting the configuration shown in Fig. 9(A), when using a transflective or reflective liquid crystal display device as the display unit 9631, it is expected to be used under relatively bright conditions, and power generation by the solar cell 9633 and charging of the battery 9635 can be efficiently performed, which is preferable. Note that the solar cell 9633 can be appropriately provided in the empty space (front or back surface) of the housing 9630, so that a configuration for efficiently charging the battery 9635 can be achieved, which is preferable. When using a lithium - ion battery as the battery 9635, there are advantages such as miniaturization.

[0210] Also, the configuration and operation of the charge - discharge control circuit 9634 shown in Fig. 9(A) will be illustrated with a block diagram in Fig. 9(B). Fig. 9(B) shows the solar cell 9633, the battery 9635, the converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631. The battery 9635, the converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the parts of the charge - discharge control circuit 9634.

[0211] First, an example of the operation when power is generated by the solar cell 9633 due to external light will be described. The power generated by the solar cell is stepped up or down by the converter 9636 to obtain a voltage for charging the battery 9635. When the power from the solar cell 9 633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the required voltage for the display unit 9631. Also, for the display unit 9631 ​​When not displaying the battery, turn SW1 off and SW2 on to power the battery. The charging may be performed in the above-mentioned manner.

[0212] Next, an example of operation when external light does not generate power by the solar cell 9633 will be described. The power stored in the Battery 9635 is converted by turning on the switch SW3. The voltage is increased or decreased by the power supply 9637. Power will be drawn from Lee 9635.

[0213] Although the solar cell 9633 is shown as an example of a charging means, the battery may be charged by other means. It may be configured to charge the Terry 9635. It may also be configured to charge the Terry 9635 in combination with other charging means. This may also be configured.

[0214] FIG. 10A shows a notebook personal computer, which includes a main body 3001 and a housing 300 2, a display unit 3003, a keyboard 3004, etc. By applying the liquid crystal display device shown in any one of the above to 4 to the display portion 3003, A notebook-type personal computer that maintains good image display capabilities, is highly secure, and consumes low power. The computer may be a null computer.

[0215] FIG. 10B shows a portable digital assistant (PDA), which includes a display unit 3023 and a display unit 3024 on a main body 3021. An external interface 3025 and operation buttons 3024 are provided. The liquid crystal display device according to any one of the first to fourth embodiments includes a stylus 3022. By applying a display device to the display unit 3023, it is possible to provide higher convenience, higher security, and lower It can be used as a power-efficient personal digital assistant (PDA).

[0216] Figure 10(C) shows an example of an e-book. For example, the e-book 2700 is composed of two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are integrated by a shaft portion 2711 and can perform an opening and closing operation about the shaft portion 2711. With such a configuration, it is possible to perform operations similar to those of a paper book. A display unit 2705 is incorporated in the housing 2701, and a display unit 2707 is incorporated in the housing 2703. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. With a configuration of displaying different screens, for example, text can be displayed on the right display unit (display unit 2705 in FIG. 10(C)), and an image can be displayed on the left display unit (display unit 2707 in FIG. 10(C)). By applying the liquid crystal display device shown in any one of Embodiments 1 to 4 to the display unit 2705 and the display unit 2707, it is possible to obtain an e-book 2700 that maintains a better image display function for a longer time, has high security, and low power consumption. In FIG. 10(C), an example in which the housing 2701 is provided with an operation unit and the like is shown. For example, in the housing 2701, a power supply 2721, operation keys 2723, a speaker 2725, and the like are provided. The operation keys 2723 can be used to turn the page. In addition, a configuration may be adopted in which a keyboard, a pointing device, or the like is provided on the same surface as the display unit of the housing. Further, a configuration may be adopted in which external connection terminals (such as earphone terminals, USB terminals, etc.), a recording medium insertion portion, and the like are provided on the back surface or side surface of the housing. Furthermore, the e-book 2700 may have a function as an electronic dictionary.

[0217]

[0218] ​ It may also be configured as described above.

[0219] Also, the e - book 2700 may be configured to be able to wirelessly transmit and receive information. By wireless means, it is possible to purchase and download desired book data and the like from an e - book server. This is also possible.

[0220] FIG. 10(D) shows a mobile phone, which is composed of two casings, a casing 2800 and a casing 2801. The casing 2801 is provided with a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, an external connection terminal 2808, etc. Also, the casing 2800 is provided with a solar battery cell 2810 for charging the portable information terminal, an external memory slot 2811, etc. Also, the antenna is built inside the casing 2801. By applying the liquid crystal display device shown in any of Embodiments 1 to 4 to the display panel 2802, it is possible to maintain a better image display function for a longer time, and to obtain a mobile phone with high security, high usability, and low power consumption.

[0221] Also, the display panel 2802 is provided with a touch panel, and a plurality of operation keys 2805 shown by dotted lines in FIG. 10(D) are displayed. Note that a boost circuit for boosting the voltage output by the solar battery cell 2810 to the voltage required for each circuit is also installed. The display direction of the display panel 2802 changes appropriately according to the usage form. Also, since the camera lens 2807 is provided on the same surface as the display panel

[0222] 2802, a video phone is possible. The speaker 2803 and the microphone 2804 are not limited to voice calls, but also support video phones, ​​​It is possible to record, play back, etc. Further, the housing 2800 and the housing 2801 can be slid and changed from the unfolded state as shown in Fig. 10(D) to an overlapping state, enabling miniaturization suitable for portability.

[0223] The external connection terminal 2808 can be connected to various cables such as an AC adapter and a USB cable, enabling charging and data communication with a personal computer, etc. Also, by inserting a recording medium into the external memory slot 2811, it is possible to handle the storage and transfer of a larger amount of data.

[0224] In addition to the above functions, it may also be equipped with an infrared communication function, a television reception function, etc.

[0225] Fig. 10(E) shows a digital video camera, which is composed of a main body 3051, a display section (A) 3057, an eyepiece section 3053, an operation switch 3054, a display section (B) 3055, a battery 3056, etc. By applying the liquid crystal display device shown in any of Embodiments 1 to 4 to the display section (A) 3057 and the display section (B) 3055, it is possible to obtain a digital video camera that maintains a better image display function for a longer time, has high security, and consumes low power.

[0226] Fig. 10(F) shows an example of a television device. The television device 9600 has a display section 9603 incorporated in a housing 9601. The display section 9603 can display video. Also, here, a configuration is shown in which the housing 9601 is supported by a stand 9605. By applying the liquid crystal display device shown in any of Embodiments 1 to 4 to the display section 96 03, ​​​​​​​​​By applying it to 03, a longer and better image display function can be maintained, and the security can also be enhanced. Moreover, a television apparatus with low power consumption can be obtained.

[0227] The operation of the television apparatus 9600 can be performed by operation switches provided on the housing 9601 or a separate remote control device. Further, the remote control device may be configured to include a display unit for displaying information output from the remote control device.

[0228] Note that the television apparatus 9600 is configured to include a receiver, a modem, and the like. The receiver can receive more general television broadcasts, and further, by connecting to a communication network via a modem, either wired or wirelessly, one-way (from the sender to the receiver) or two-way (between the sender and the receiver, or between receivers, etc.) information communication can also be performed.

[0229] This embodiment can be implemented in appropriate combination with the configurations described in other embodiments.

Example

[0230] In this example, the display states of a liquid crystal display device that displays an initialization image before turning off and a liquid crystal display device that is turned off while displaying an image before the off state are compared as a comparative example. The results are shown.

[0231] Figures 12(A) and 13(A) (Figures 12(A) and 13(A) are the same photograph) show screens on which images in the on state before the off state are displayed. Note that the images in Figures 12(A) and 13(A ) are black and white checkered patterns, and the switching element of the pixel is an oxide with a low off-current. A transistor using an oxide semiconductor layer (In-Ga-Zn-O layer) was applied. The liquid crystal display device of this example is a transmissive liquid crystal display device, and light is supplied by a backlight. In this example, even after the power potential to the display panel including the drive circuit section and the pixel section is stopped with the liquid crystal display device in the off state, the backlight continues to light so that the display state of the screen can be seen. The liquid crystal display device of this example is a normally white liquid crystal display device, and the initial state of the liquid crystal is a white display by transmitting the light from the backlight.

[0232] Before the display device shown in Fig. 12(B) is turned off, a fixed potential is written to the capacitive element, and after the liquid crystal is returned to the initial state, when the power potential to the display panel including the drive circuit section and the pixel section is stopped, the display screen immediately after the off state is shown. The display screen shows the initial state image of the all-white screen displayed in the initial state of the liquid crystal. Therefore, it can be seen that the liquid crystal is in a stable initial state without an electric field applied in the off state.

[0233] On the other hand, as a comparative example in Fig. 13(B), when the liquid crystal display device is turned off while displaying the lattice pattern display image shown in Fig. 13(A) and the supply of the power potential to the display panel is stopped, the display screen immediately after the off state is shown. In Fig. 13(B), the checkerboard pattern image displayed in the on state immediately before the off can be faintly confirmed, and it can be seen that an electric field continues to be applied to the liquid crystal even after the off. Applying an electric field to the liquid crystal like this for such an unnecessary time causes deterioration of the liquid crystal and leads to a decrease in the image display function and reliability of the liquid crystal display device.

[0234] As can be understood from the above, a fixed potential is applied so that no voltage is applied to the liquid crystal element before setting it to the off state. By displaying a write initialization image for the positions, deterioration of the liquid crystal elements can be prevented, and long-term good image display function can be maintained, and security can also be enhanced.

[0235] Therefore, it becomes possible to provide a liquid crystal display device achieving higher reliability and lower power consumption, and a driving method of the liquid crystal display device.

Explanation of Signs

[0236] 100 Liquid crystal display device 110 Image processing circuit 111 Memory circuit 111b Frame memory 112 Comparison circuit 113 Display control circuit 115 Selection circuit 116 Power supply 117 Stop means 120 Display panel 121 Driving circuit section 121A Gate line driving circuit 121B Source line driving circuit 122 Pixel section 123 Pixel 124 Gate line 125 Source line 126 Terminal section 126A Terminal 126B Terminal 127 Switching element 128 Common electrode 130 Backlight section 131 Backlight control circuit 132 Backlight 200 Liquid crystal display device 210 Capacitive element 214 Transistor 215 Liquid crystal element 400 Substrate 401 Gate electrode layer 402 Gate insulating layer 403 Oxide semiconductor layer ​405a Source electrode layer 405b Drain electrode layer 407 Insulating film 409 Protective insulating layer 410 Transistor 420 Transistor 427 Insulating layer 430 Transistor 436a Wiring layer 436b Wiring layer 437 Insulating layer 440 Transistor 505 Substrate 506 Protective insulating layer 507 Gate insulating layer 510 Transistor 511 Gate electrode layer 515a Source electrode layer 515b Drain electrode layer 516 Insulating layer 530 Oxide semiconductor film 531 Oxide semiconductor layer 601 Period 602 Period 603 Period 604 Period 1401 Period 1402 Period 1403 Period 1404 Period 2700 E-book 2701 Housing 2703 Housing 2705 Display unit 2707 Display unit 2711 Shaft portion 2721 Power supply 2723 Operation key 2725 Speaker 2800 Housing 2801 Housing 2802 Display panel 2803 Speaker 2804 Microphone 2805 Operation key 2806 Pointing device Camera lens 2807 External connection terminal 2808 Solar cell 2810 External memory slot 2811 Main body 3001 Housing 3002 Display unit 3003 Keyboard 3004 Main body 3021 Stylus 3022 Display unit 3023 Operation button 3024 External interface 3025 Main body 3051 Eyepiece 3053 Operation switch 3054 Display unit (B) 3055 Battery 3056 Display unit (A) 3057 Television apparatus 9600 Housing 9601 Display unit 9603 Stand 9605 Housing 9630 Display unit 9631 Operation key 9632 Solar cell 9633 Charge and discharge control circuit 9634 Battery 9635 Converter 9636 Converter 9637

Claims

1. A liquid crystal display device having a moving image display mode and a still image display mode, comprising a plurality of pixels in which an image signal is written into a capacitive element through a channel formation region of a transistor, wherein in the still image display mode, the frequency at which the image signal is written into the pixel is lower than that in the moving image display mode. Each of the pixels has a first conductive layer, a first insulating layer having a region above the first conductive layer and containing nitrogen and silicon, a second insulating layer having a region above the first insulating layer and containing oxygen and silicon, an oxide semiconductor layer having a region above the second insulating layer, a third insulating layer having a region above the oxide semiconductor layer and containing oxygen and silicon, and a fourth insulating layer having a region above the third insulating layer and containing nitrogen and silicon. The oxide semiconductor layer has a channel formation region of the transistor. The oxide semiconductor layer has a first oxide semiconductor layer and a second oxide semiconductor layer provided in contact with an upper surface of the first oxide semiconductor layer and having a larger film thickness than the first oxide semiconductor layer. The first oxide semiconductor layer contains In, Ga, and Zn. The second oxide semiconductor layer contains In, Ga, and Zn. The second oxide semiconductor layer has crystals oriented such that the c-axis is perpendicular to the surface of the second oxide semiconductor layer. The ratio of the c-axis oriented crystals in the second oxide semiconductor layer is larger than the ratio of the c-axis oriented crystals in the first oxide semiconductor layer. The first conductive layer has a region functioning as a gate electrode layer of the transistor. The first insulating layer has a region in contact with an upper surface of the first conductive layer. The second insulating layer has a region in contact with an upper surface of the first insulating layer. The oxide semiconductor layer has a region in contact with an upper surface of the second insulating layer. The third insulating layer has a region in contact with an upper surface of the oxide semiconductor layer. The fourth insulating layer has a region overlapping the oxide semiconductor layer via the third insulating layer. The third insulating layer has a region in contact with an upper surface of the second insulating layer. The liquid crystal display device.

2. A liquid crystal display device having a moving image display mode and a still image display mode, comprising a plurality of pixels in which an image signal is written into a capacitive element through a channel formation region of a transistor, wherein in the still image display mode, the frequency at which the image signal is written into the pixel is lower than that in the moving image display mode. The pixel is a first conductive layer, a first insulating layer having a region above the first conductive layer and containing nitrogen and silicon, a second insulating layer having a region above the first insulating layer and containing oxygen and silicon, an oxide semiconductor layer having a region above the second insulating layer, a third insulating layer having a region above the oxide semiconductor layer and containing oxygen and silicon, a fourth insulating layer having a region above the third insulating layer and containing nitrogen and silicon, a fifth insulating layer having a region above the fourth insulating layer and containing an organic material, and the oxide semiconductor layer has a channel formation region of the transistor, the oxide semiconductor layer has a first oxide semiconductor layer and a second oxide semiconductor layer provided in contact with the upper surface of the first oxide semiconductor layer and having a larger film thickness than the first oxide semiconductor layer, the first oxide semiconductor layer has In, Ga, and Zn, the second oxide semiconductor layer has In, Ga, and Zn, the second oxide semiconductor layer has a crystal oriented such that the c-axis takes a direction perpendicular to the surface of the second oxide semiconductor layer, the ratio of the c-axis oriented crystal in the second oxide semiconductor layer is larger than the ratio of the c-axis oriented crystal in the first oxide semiconductor layer, the first conductive layer has a region functioning as a gate electrode layer of the transistor, the first insulating layer has a region in contact with the upper surface of the first conductive layer, the second insulating layer has a region in contact with the upper surface of the first insulating layer, the oxide semiconductor layer has a region in contact with the upper surface of the second insulating layer, the third insulating layer has a region in contact with the upper surface of the oxide semiconductor layer, the fourth insulating layer has a region overlapping the oxide semiconductor layer via the third insulating layer, the third insulating layer has a region in contact with the upper surface of the second insulating layer, a liquid crystal display device.

3. having a moving image display mode and a still image display mode, having a plurality of pixels in which an image signal is written into a capacitive element via a channel formation region of a transistor, the still image display mode is a liquid crystal display device in which the frequency at which the image signal is written into the pixel is lower than that in the moving image display mode, the pixel is a first conductive layer, a first insulating layer having a region above the first conductive layer and containing nitrogen and silicon, a second insulating layer having a region above the first insulating layer and containing oxygen and silicon, An oxide semiconductor layer having a region above the second insulating layer; A third insulating layer having a region above the oxide semiconductor layer and containing oxygen and silicon; A fourth insulating layer having a region above the third insulating layer and containing nitrogen and silicon; The oxide semiconductor layer has a channel formation region of the transistor; The oxide semiconductor layer includes a first oxide semiconductor layer and a second oxide semiconductor layer provided in contact with the upper surface of the first oxide semiconductor layer and having a larger film thickness than the first oxide semiconductor layer; The first oxide semiconductor layer contains In, Ga, and Zn; The second oxide semiconductor layer contains In, Ga, and Zn; The second oxide semiconductor layer has a crystal oriented such that the c-axis is perpendicular to the surface of the second oxide semiconductor layer; The ratio of the c-axis oriented crystal in the second oxide semiconductor layer is larger than the ratio of the c-axis oriented crystal in the first oxide semiconductor layer; The first conductive layer has a region that functions as a gate electrode layer of the transistor; The first insulating layer has a region in contact with the upper surface of the first conductive layer; The second insulating layer has a region in contact with the upper surface of the first insulating layer; The oxide semiconductor layer has a region in contact with the upper surface of the second insulating layer; The third insulating layer has a region in contact with the upper surface of the oxide semiconductor layer; The fourth insulating layer has a region overlapping the oxide semiconductor layer via the third insulating layer; The third insulating layer has a region in contact with the upper surface of the second insulating layer; The first insulating layer has a region with a film thickness of 50 nm or more and 200 nm or less; The second insulating layer has a region with a film thickness of 5 nm or more and 300 nm or less; The oxide semiconductor layer has a region with a film thickness of 2 nm or more and 200 nm or less; The third insulating layer has a region with a film thickness of 1 nm or more, a liquid crystal display device.

4. Having a moving image display mode and a still image display mode; Having a plurality of pixels in which an image signal is written into a capacitive element via a channel formation region of a transistor; The still image display mode is a liquid crystal display device in which the frequency at which the image signal is written into the pixel is lower than that in the moving image display mode; The pixel is A first conductive layer; A first insulating layer having a region above the first conductive layer and containing nitrogen and silicon; A second insulating layer having a region above the first insulating layer and containing oxygen and silicon; An oxide semiconductor layer having a region above the second insulating layer; A third insulating layer having a region above the oxide semiconductor layer and containing oxygen and silicon; A fourth insulating layer having a region above the third insulating layer and containing nitrogen and silicon; A fifth insulating layer having a region above the fourth insulating layer and containing an organic material, and having; The oxide semiconductor layer has a channel formation region of the transistor; The oxide semiconductor layer has a first oxide semiconductor layer and a second oxide semiconductor layer provided in contact with the upper surface of the first oxide semiconductor layer and having a larger film thickness than the first oxide semiconductor layer; The first oxide semiconductor layer has In, Ga, and Zn; The second oxide semiconductor layer has In, Ga, and Zn; The second oxide semiconductor layer has a crystal oriented such that the c-axis takes a direction perpendicular to the surface of the second oxide semiconductor layer; The ratio of the c-axis oriented crystal in the second oxide semiconductor layer is larger than the ratio of the c-axis oriented crystal in the first oxide semiconductor layer; The first conductive layer has a region functioning as a gate electrode layer of the transistor; The first insulating layer has a region in contact with the upper surface of the first conductive layer; The second insulating layer has a region in contact with the upper surface of the first insulating layer; The oxide semiconductor layer has a region in contact with the upper surface of the second insulating layer; The third insulating layer has a region in contact with the upper surface of the oxide semiconductor layer; The fourth insulating layer has a region overlapping the oxide semiconductor layer via the third insulating layer; The third insulating layer has a region in contact with the upper surface of the second insulating layer; The first insulating layer has a region having a film thickness of 50 nm or more and 200 nm or less; The second insulating layer has a region having a film thickness of 5 nm or more and 300 nm or less; The oxide semiconductor layer has a region having a film thickness of 2 nm or more and 200 nm or less; The third insulating layer has a region having a film thickness of 1 nm or more, a liquid crystal display device.

5. In any one of Claims 1 to 4, In a cross-sectional view in the channel length direction of the transistor, the width of the oxide semiconductor layer is larger than the width of the first conductive layer, a liquid crystal display device.

6. In any one of Claims 1 to 5, The fourth insulating layer has a region overlapping the second insulating layer via the third insulating layer without passing through the oxide semiconductor layer, a liquid crystal display device.

7. In any one of claims 1 to 6, a third conductive layer having a region in contact with the upper surface of the oxide semiconductor layer, wherein the third conductive layer has a region overlapping with the first conductive layer, a liquid crystal display device.

8. In any one of claims 1 to 7, one of the source electrode layer or the drain electrode layer of the transistor is electrically connected to one electrode of the liquid crystal element and one electrode of the capacitor element, a liquid crystal display device.

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