Liquid crystal display device

Abstract

To provide a liquid crystal display device capable of suppressing reduction in image display function and sufficiently reducing power consumption, and to provide a method of driving the liquid crystal display device.SOLUTION: In the liquid crystal display device, in order to prevent application of an electric field on a liquid crystal before power is turned off, a fixed potential is input to a capacitive element to eliminate a potential difference between the electrodes of the capacitive element (sets capacity almost to zero), and the liquid crystal is set to an initial state. When power is stopped after an initial state image is displayed, the liquid crystal, in an off state, is stably kept in the initial state without any continued application of unnecessary electric fields. Thus, deterioration of the liquid crystal is prevented.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Techniques for forming thin film transistors (TFTs) using semiconductor thin films formed on substrates having insulating surfaces have attracted attention. Thin film transistors are widely applied to electronic devices such as integrated circuits (ICs) and image display devices (display devices). Thin film transistors are widely used in electronic devices such as mobile devices such as mobile phones and notebook personal computers. However, 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. In a display device, when rewriting 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 an operation of writing the image data a plurality of times, the power consumption increases. 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 technique of providing a pause period longer than the scanning period as a non-scanning period has been reported (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003]

[0004]

[0005]

Prior Art Documents

[0006]

Patent Documents

[0006] [Non-Patent Document 1] K. Tsuda et al. IDW'02 Proc., p.295-298 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, after scanning the screen once and writing the image data, there is a pause longer than the scanning period. In a display method that continuously displays a still image for a set period of time, an arbitrary voltage is applied to the liquid crystal. This can lead to the LCD degrading, resulting in a decrease in image display capabilities. Furthermore, if image data remains, the display will still display images even after the power to the display device has been turned off. There is a risk that image data may remain on the surface.

[0008] Therefore, the challenge in liquid crystal display devices is to suppress the degradation of image display functionality as described above. Let it be one.

[0009] Furthermore, we propose a liquid crystal display device that can reduce power consumption, and a method for driving the liquid crystal display device. One of the objectives is to provide it. [Means for solving the problem]

[0010] Liquid crystal displays operate when power is supplied and cease to operate when power is cut off. In this specification, the state in which power is supplied to a liquid crystal display device (power-on state) is defined as follows: The state in which the power supply is stopped (power off state) is called the off state, and the LCD A control signal for turning on the display device is called a start signal, and a control signal for turning off the display device is called a stop signal. .

[0011] The liquid crystal element provided in the liquid crystal display device is 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, 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 is applied to 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 occurs 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, and no electric field is applied to the liquid crystal, so the liquid crystal does not respond. In this specification, the liquid crystal in such a state where no electric field is applied (non-responsive state) is called the initial state (liquid crystal initial state). When a voltage is applied to the liquid crystal element, an electric field is formed, the electric field is applied to the liquid crystal, and the liquid crystal responds to display an image. responds to display an image.

[0012] On the other hand, when the same potential is applied to the pixel electrode and the common electrode, no potential difference occurs 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, and no electric field is applied to the liquid crystal, so the liquid crystal does not respond. In this specification, the liquid crystal in such a state where no electric field is applied (non-responsive state) is called the initial state (liquid crystal initial state). Therefore, no electric field is formed in the liquid crystal element, and no electric field is applied to the liquid crystal, so the liquid crystal does not respond. In this specification, the liquid crystal in such a state where no electric field is applied (non-responsive state) is called the initial state (liquid crystal initial state). In the present specification, the liquid crystal in such a state where no electric field is applied (non-responsive state) is called the initial state (liquid crystal initial state). returns to the initial state.

[0013] The liquid crystal in the liquid crystal initial state, in the display device that has become on state upon receiving the start signal, an electric field is applied and it responds to display an image, and in the display device that has become off state upon receiving the stop signal, returns to the initial state. returns to the initial state.

[0014] The liquid crystal display device disclosed in this specification has a pixel configuration that stores charge in a capacitive element and holds the voltage applied to the liquid crystal element by that charge 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 charge to leak from the capacitive element through the semiconductor element. 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. is preferably a semiconductor element with a low current value (off current value) in the off state.

[0015] If it is a semiconductor element with a low off current value, it is difficult for charge to leak from the capacitive element through the semiconductor element. Furthermore, the voltage applied to the liquid crystal element can be maintained for a long time. Therefore, it is a liquid crystal with high display image retention characteristics. It can be used as a display device.

[0016] On the other hand, in pixels that have been shut off and are in an off state, an electric field is applied and the liquid is in a responsive state. For the crystal to return to its initial state, the charge held in the capacitive element must be released through the semiconductor element. It is necessary to do so. Because an electric field continues to be applied to the liquid crystal while the charge of the capacitive element is being released, especially If the time is long, it will accelerate the degradation of the liquid crystal. Also, the liquid crystal will not respond while the charge is being released. Since the image is also preserved, especially in the case of reflective liquid crystal display devices that use ambient light as a light source, the image is This can also lead to a decrease in display quality, such as the image remaining visible even after the power is turned off (appearing as an afterimage to the human eye). To do.

[0017] Applying an unnecessary electric field to the LCD while it is in an off state where no image is displayed is, This could lead to a decrease in the image display function and reliability of the liquid crystal display device.

[0018] In the liquid crystal display device disclosed herein, before turning off the power, an electric field is applied to the liquid crystal. To prevent this, a fixed potential is input to the capacitive element to eliminate the potential difference between the electrodes of the capacitive element (capacitance (Assuming it is approximately zero), the liquid crystal is set to its initial state. In this specification, the liquid crystal in the initial state is shown in the table. The image shown is called the initial state image. The initial state image is, for example, a normally white liquid crystal display. In the case of a device, the screen will be entirely white, and in the case of a normally black LCD display, the screen will be entirely black. In the case of normally white liquid crystal displays, a monochrome screen is created by the color filter and light source. It can also be done this way.

[0019] If the power is turned off after displaying the initial state image, the LCD will not produce unnecessary electric fields while in the off state. It doesn't persist, and it can remain in a stable initial state.

[0020] Additionally, it displays an initialization image such as a completely white or completely black screen before turning off, so there is no afterimage. The display of such information on the screen could lead to the information of the image taken just before the power was turned off being leaked to others. It can be prevented.

[0021] Therefore, we provide a liquid crystal display device that maintains good image display functionality for a long time and also offers high security. It is possible.

[0022] One form of a driving method for a liquid crystal display device disclosed herein involves supplying a power potential from a power source, A screen is provided with multiple pixels, including a liquid crystal element, a liquid crystal element, and a semiconductor element, and the liquid of the liquid crystal element The crystal responds and displays an image, a stop signal is supplied by the stop means, and multiple images are displayed by the stop signal. A fixed potential is written to a basic capacitive element, causing the responding liquid crystal to become unresponsive, and the initial state image is displayed on the screen. The image is displayed, and the power supply from the power source is stopped.

[0023] One form of a liquid crystal display device driving method disclosed herein involves supplying power potential from the power supply to the driving circuit. A screen is provided with multiple pixels, including capacitive elements, liquid crystal elements, and semiconductor elements. The liquid crystal element of the liquid crystal element responds to display an image, and a stop signal is supplied by a stop means. By writing a fixed potential to multiple pixel capacitive elements, the responding liquid crystal is put into a non-responsive state, and the screen is then... The initial state image is displayed, and the supply of power potential from the power supply to the drive circuit section is stopped.

[0024] One embodiment of the driving method for a liquid crystal display device disclosed herein involves a power supply, a drive circuit unit, and a backing circuit. A power potential is supplied to the light section, and multiple pixels, including capacitive elements, liquid crystal elements, and semiconductor elements, The liquid crystal elements of the liquid crystal display an image on the provided screen, and a stop signal is sent by a stop means. The power supply is interrupted, and the power potential supply from the power supply to the backlight section is stopped, and a stop signal is triggered by multiple A fixed potential is written to the pixel's capacitive element, causing the responding liquid crystal to become unresponsive, and the screen returns to its initial state. The image is displayed, and the supply of power potential from the power supply to the drive circuit is stopped.

[0025] One embodiment of the driving method for a liquid crystal display device disclosed herein involves a power supply, a drive circuit unit, and a backing circuit. A power potential is supplied to the light section, and multiple pixels, including capacitive elements, liquid crystal elements, and semiconductor elements, The liquid crystal elements of the liquid crystal display an image on the provided screen, and a stop signal is sent by a stop means. The liquid crystal is supplied, and a stop signal is used to write a fixed potential to the capacitive elements of multiple pixels, causing the liquid crystal to respond. The device enters an unresponsive state, displaying an initial state image on the screen, and the drive circuit section and backlight section from the power supply are also activated. The power supply to the device will be cut off.

[0026] In the above configuration, the capacitive element and the liquid crystal element are electrically connected and function as a switching element. A transistor containing an oxide semiconductor layer can be used as the semiconductor element. [Effects of the Invention]

[0027] Before turning off the liquid crystal display, write a fixed potential to prevent voltage from being applied to the liquid crystal elements. It displays a pre-filled and initialized image. This prevents deterioration of the liquid crystal elements and ensures a long-lasting, high-quality image display. This allows for maintaining display functionality while also enhancing security.

[0028] Therefore, it is possible to achieve higher reliability and lower power consumption in liquid crystal display devices. Yes. [Brief explanation of the drawing]

[0029] [Figure 1] A diagram illustrating one form of liquid crystal display device. [Figure 2] A diagram illustrating one form of liquid crystal display device. [Figure 3] A diagram illustrating one form of liquid crystal display device. [Figure 4] A timing chart illustrating one method of driving a liquid crystal display device. [Figure 5] A timing chart illustrating one method of driving a liquid crystal display device. [Figure 6] A diagram illustrating one method of driving a liquid crystal display device. [Figure 7] A diagram illustrating one form of transistor applicable to liquid crystal display devices. [Figure 8] A diagram illustrating one method for fabricating transistors applicable to liquid crystal display devices. [Figure 9] A diagram and block diagram illustrating one form of liquid crystal display device. [Figure 10] A diagram showing electronic equipment. [Figure 11] A diagram illustrating one form of liquid crystal display device. [Figure 12] A photograph showing an image displayed by a liquid crystal display device. [Figure 13] A photograph showing an image displayed by a liquid crystal display device. [Modes for carrying out the invention]

[0030] The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is... Not limited to the following description, the form and details can be modified in various ways, as any person skilled in the art would know. This is easily understood. Furthermore, the present invention shall be interpreted as being limited to the contents of the embodiments described below. It's not something that can be done.

[0031] (Embodiment 1) In this embodiment, one form of a liquid crystal display device and a method for driving the liquid crystal display device is shown in Figures 1 and 2. I will use it to explain.

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

[0033] As shown in Figure 1, let's assume that image A is displayed on the screen of the liquid crystal display device. If a display image is not required due to the supply of an image signal (at the end of use), select the stop method. When the stop method 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 element, the potential difference between the electrodes of the capacitive element is eliminated. (The capacity is set to almost zero), and the liquid crystal, which was in a responsive state, is set to an initial non-responsive state. Therefore, the table The display screen shows the initial state image S that the LCD displays in its initial state. For example, in the case of a normally white LCD display, the screen will be entirely white, while a normally black LCD display will be entirely white. In the case of an LCD display, the screen will be completely black. Also, in the case of a normally white LCD display... It can also be made into a monochrome screen by using color filters or light sources.

[0034] After displaying the initial state image S, the power is shut off and the supply of power potential to the display panel is stopped. The liquid crystal display is turned off. Therefore, when the liquid crystal is off, unnecessary electric fields are applied to it. It doesn't need to continue, and it can remain in a stable initial state.

[0035] Furthermore, it displays an initialization image such as a completely white screen or a completely black screen before turning off. The display of afterimages or other images on the screen can lead to the leakage of image information from the moment the power was turned off to others. This can prevent that.

[0036] Therefore, we provide a liquid crystal display device that maintains good image display functionality for a long time and also offers high security. It is possible.

[0037] The components of the liquid crystal display device 100 in this embodiment will be explained using the block diagram in Figure 2. The crystal display device 100 includes a power supply 116, a stopping means 117, a display control circuit 113, and a display panel 1 It has 20. In the case of a transmissive liquid crystal display device or a semi-transmissive liquid crystal display device, it further has a light source and It would be good to include a backlight section.

[0038] The liquid crystal display device 100 receives an image signal (image signal data) from a connected external device. It is defined as follows: Power supply potential (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 and starting the power supply, The control signals (start pulse SP and clock signal CK) are transmitted by the display control circuit 113. It is supplied. Also, the power supply potential (high power supply potential Vdd, low power supply potential Vss, and common potential Vc The supply of om) is stopped by control by the stopping means 117, and the initial state image is displayed. Afterward, power supply 116 is turned off to stop the supply of power 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 This refers to a potential below the reference potential. Note that both the high power supply potential Vdd and the low power supply potential Vss are... It is desirable that the potential is sufficient for the transistor to operate. Note that the high power supply potential Vdd and The difference in low power supply potential Vss is sometimes called the power supply voltage.

[0040] The common potential Vcom is a reference for the potential of the image signal Data supplied to the pixel electrode. Any fixed potential will suffice; for example, the ground potential would be acceptable.

[0041] Image signal data is driven by dot inversion, source line inversion, gate line inversion, The system is configured such that the data is appropriately inverted according to the frame inversion drive and then input to the liquid crystal display device 100. That's fine. Also, if the image signal Data is an analog signal, it can be transmitted via an A / D converter, etc. The signal is then converted to a digital signal and supplied to the liquid crystal display device 100.

[0042] In this embodiment, the common electrode 128 and one electrode of the capacitive element 210 are connected to the power supply 116. A common potential Vcom, which is a fixed potential, is provided via the display control circuit 113.

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

[0044] The display panel 120 sandwiches the liquid crystal element 215 between a pair of substrates (a first substrate and a second substrate). The device has the following configuration, and the first substrate is provided with a drive circuit section 121 and a pixel section 122. The second substrate has a common connection part (also called a common contact) and a common electrode 128 (como A common connection part is provided (also called a counter electrode). The common connection part is connected to the first substrate. It electrically connects to the second substrate, and the common connection part is provided on the first substrate. It's okay to be there.

[0045] The pixel section 122 has multiple gate lines 124 (scan lines) and source lines 125 (signal lines). It is provided, and multiple pixels 123 are surrounded by gate lines 124 and source lines 125. It is arranged in a trix shape. In the display panel illustrated in this embodiment, The gate wire 124 extends from the gate wire drive circuit 121A, and the source wire 125 is a source wire drive circuit It extends from road 121B.

[0046] Furthermore, the pixel 123 has a transistor 214 as a switching element, and the transistor 214 It has a capacitive element 210 and a liquid crystal element 215 connected to it.

[0047] The liquid crystal element 215 is an element that controls the transmission or non-transmission of light by the optical modulation effect of liquid crystals. Yes. The optical modulation effect of liquid crystals is controlled by the electric field applied to the liquid crystal. The field direction varies depending on the liquid crystal material, driving method, and electrode structure, and can be selected as appropriate. For example, when using a driving method that applies an electric field in the thickness direction of the liquid crystal layer (the so-called vertical direction): Pixel electrodes are provided on the first substrate and common electrodes are provided on the second substrate, so as to sandwich the liquid crystal. The structure should be such that an electric field is applied to the liquid crystal in the direction within the substrate plane (so-called transverse electric field). When using this method, the structure should be such that the pixel electrodes and common electrodes are placed on the same plane as the liquid crystal. Furthermore, the pixel electrodes and common electrodes may have shapes with diverse aperture patterns. In terms of application, any element that controls the transmission or non-transmission of light by optical modulation is applicable. The liquid crystal material, driving method, and electrode structure are not particularly limited.

[0048] Transistor 214 is connected to one of the multiple gate lines 124 provided in the pixel section 122. A gate electrode is connected, and either the source electrode or the drain electrode is connected to a plurality of source wires 125. One of them is connected, and the other of the source electrode or drain electrode is one of the capacitive elements 210 It is connected to the electrode and one of the electrodes (pixel electrodes) of the liquid crystal element 215.

[0049] Transistor 214 is preferably a transistor with a low off-current. When transistor 214 is in the off state, the liquid crystal element connected to transistor 214 has a low off current. The charge stored in 215 and the capacitive element 210 is less likely to leak through the transistor 214. The state written before transistor 214 turns off can be retained for a long period of time. ru.

[0050] With this configuration, the capacitive element 210 maintains the voltage applied to the liquid crystal element 215. This is possible. In addition, the electrodes of the capacitive element 210 are configured to be connected to a separately provided capacitance line. That's good too.

[0051] The drive circuit section 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 located in a pixel section 1 having multiple pixels. This is a drive circuit for driving 22, and is a shift register circuit (also called a shift register). It holds.

[0052] The gate line drive circuit 121A and the source line drive circuit 121B are the same as those in the pixel unit 122. It may be formed on the same substrate, or it may be formed on a different substrate.

[0053] The drive circuit section 121 has a high power supply potential Vdd controlled by the display control circuit 113. Low power supply potential Vss, start pulse SP, clock signal CK, and image signal Data are supplied. It can be done.

[0054] Terminal 126 receives a predetermined signal (high power supply potential Vdd, low power supply) output by the display control circuit 113. Potential Vss, start pulse SP, clock signal CK, image signal Data, common potential Vc This is an input terminal that supplies power (such as OM) to the drive circuit unit 121.

[0055] The common electrode 128 provides a common potential Vcom controlled by the display control circuit 113. The wires are electrically connected at the common connection point.

[0056] A specific example of a common connection is a conductive particle in which an insulating sphere is coated with a thin metal film. By using this, an electrical connection can be made between the common electrode 128 and the common potential line. The common connection points may be configured to be provided in multiple locations within the display panel 120.

[0057] Furthermore, the liquid crystal display device may have a photometering circuit. A liquid crystal display device equipped with a photometering circuit is The brightness of the environment in which the liquid crystal display device is placed can be detected. As a result, the photometering circuit is connected. The display control circuit 113 controls the backlight and other elements according to the signal input from the photometering circuit. It is possible to control the driving method of light sources such as idlights.

[0058] In addition, color display is possible by combining color filters. Also, other optical films (polarizing films, phase difference films, anti-reflective films, etc.) They can be used in combination. In the case of transmissive liquid crystal display devices or semi-transmissive liquid crystal display devices. The light source used, such as a backlight, is selected and combined according to the application of the liquid crystal display device 100. By combining them, cold cathode fluorescent lamps and light-emitting diodes (LEDs) can be used. Using multiple LED light sources or multiple electroluminescent (EL) light sources, etc., A light source may be constructed. Three or more types of LEDs may be used as a surface light source, or white light emission may be used. LEDs may also be used. Furthermore, RGB light-emitting diodes may be placed in the backlight, If you adopt a sequential additive color mixing method (field sequential method) that displays colors by dividing the image, In some cases, a color filter may not be applied.

[0059] As described above, when the liquid crystal display is powered on and power is supplied, By using semiconductor elements with low current, power consumption can be reduced. Furthermore, Before setting the state, a fixed potential is written to the liquid crystal element to prevent voltage from being applied, and an initialization image is displayed. By doing so, the deterioration of the liquid crystal elements is prevented, maintaining good image display functionality for a long time, and security is also maintained. It can also improve performance.

[0060] Therefore, a liquid crystal display device that achieves more reliable low power consumption, and a liquid crystal display device This makes it possible to provide a driving method.

[0061] (Embodiment 2) In this embodiment, a liquid crystal can be combined with Embodiment 1 to further reduce power consumption. The method for driving the display device is shown. Parts identical to or having similar functions to those in Embodiment 1, and The process can be carried out in the same manner as in Embodiment 1, and repeated explanations will be omitted. I will omit a detailed explanation of the place.

[0062] Liquid crystal display devices display a combination of video and still images on the screen. Video consists of multiple frames. By rapidly switching between multiple corresponding different images, it is recognized as a moving image by the human eye. This refers to images that are switched more than 60 times per second (60 frames). Specifically, it means switching images 60 times per second (60 frames) or more. As a result, the human eye perceives it as a video with less flicker. On the other hand, still images are perceived as videos. Unlike partial videos, it can rapidly cut multiple images corresponding to multiple frame periods for time division. Even when switching and running, the continuous frame period, for example, frame n and (n+1) This refers to an image that does not change from frame to frame.

[0063] The liquid crystal display device according to the present invention can display moving images and still images. At that time, there are two different display modes: video display mode and still image display mode. This can be used. In this specification, the image displayed when a still image is displayed is considered a still image. Call.

[0064] The image signals of consecutive frames are different (for example, the first consecutive frame and the second consecutive frame are different). In the first frame, the first image signal of the first frame and the second image signal of the second frame are different. (ru) When displaying video, a display mode is used in which the image signal is written for each frame. , the image signals of consecutive frames are identical (for example, the first consecutive frame and the second consecutive frame In this frame, the first image signal of the first frame and the second image signal of the second frame are the same. 1) In the case of still image display, no new image signal is written, and voltage is applied to the liquid crystal element. The potential of the pixel electrodes and the common electrode is set to a floating state, and the voltage applied to the liquid crystal element is... This display mode maintains the current state and displays a still image without supplying new potential.

[0065] Liquid crystal display device in this embodiment, and the video display mode and still image display mode of the liquid crystal display device. The mode switching will be explained using Figures 3 through 6 and Figure 11.

[0066] Each component of the liquid crystal display device 200 in this embodiment will be explained using the block diagram in Figure 11. The liquid crystal display device 200 is a transmissive liquid crystal that displays images by utilizing the transmission and non-transmission of light at the pixels. An example of a display device, or a semi-transmissive liquid crystal display device, comprising an image processing circuit 110, a power supply 116, and a stop It has a stopping mechanism 117, a display panel 120, and a backlight unit 130. Reflective liquid crystal display In the case of the device, since ambient light is used as the light source, the backlight section 130 can be omitted. Cut.

[0067] The liquid crystal display device 200 receives image signals (image signal data) from connected external devices. It is defined as follows: Power supply potential (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 and starting the power supply, The control signals (start pulse SP and clock signal CK) are transmitted by the display control circuit 113. It is supplied. Also, the power supply potential (high power supply potential Vdd, low power supply potential Vss, and common potential Vc The supply of om) is stopped by control by the stopping means 117, and the initial state image is displayed. Afterward, power supply 116 is turned off to stop the supply of power potential to the display panel.

[0068] Furthermore, if the image signal Data is an analog signal, it is converted to digital via an A / D converter, etc. If the signal is converted to a barrel signal and supplied to the image processing circuit 110 of the liquid crystal display device 200, This is preferable because it makes it easier to detect differences in image signals later.

[0069] This section describes the configuration of the image processing circuit 110 and the procedure by which the image processing circuit 110 processes signals. do.

[0070] The image processing circuit 110 includes a memory circuit 111, a comparison circuit 112, a display control circuit 113, and a selection It has a selection circuit 115. The image processing circuit 110 selects the input digital image signal Data. Then it generates the display panel image signal and backlight signal. The display panel image signal is the display panel The image signal controls the 120, and the backlight signal controls the backlight unit 130. This is a signal that controls the common electrode 128. Furthermore, a signal is output to the switching element 127 to control the common electrode 128. ru.

[0071] The memory circuit 111 stores multiple frame data for image signals related to multiple frames. It has a mori. The number of frame memories that the memory circuit 111 has is not particularly limited. Any element capable of storing image signals related to multiple frames will suffice. For example, DRAM (Dynamic Random Access Memory) , memory elements such as SRAM (Static Random Access Memory) It can be constructed using [this method].

[0072] The frame memory can be configured to store the image signal for each frame period. There are no particular limitations on the number of memory slots. Also, the image signal in the frame memory is... The data is selectively read out by the comparison circuit 112 and the display control circuit 113. The frame memory 111b inside conceptually illustrates the memory area for one frame. ru.

[0073] In one of these frame memories, the liquid crystal shown in Embodiment 1 enters an initial state of non-responsiveness. It is possible to store the image signal of the initial state image (for example, a completely white screen or a completely black screen). The image signal of the initial state image, upon receiving the input of the stop signal, is controlled by the display control circuit 113. It is read and written to the screen.

[0074] The comparison circuit 112 selects image signals from consecutive frame periods stored in the memory circuit 111. The image signal is read out sequentially, and a pixel-by-pixel comparison is performed between consecutive frames of the image signal to detect the difference. This is the circuit for outputting the signal.

[0075] In this embodiment, the display control circuit 113 is determined by whether or not there is a difference in the image signal between frames. The comparison circuit 112 determines the operation of either frame between frames. If a difference is detected naturally (if there is a difference), the comparison circuit 112 determines that the image signal is for still images. It was determined that there was no signal, and the period of consecutive frames in which the difference was detected was used as the period for displaying the video. I conclude that this is the case.

[0076] On the other hand, if no difference is detected in all pixels by comparing the image signals in the comparison circuit 112 (If there is no difference), consecutive frame periods in which no difference was detected will be represented as still images. It is determined that this is the period to be shown. In other words, the comparison circuit 112 determines the image of consecutive frame periods. By detecting the presence or absence of differences in the signal, it is possible to determine whether it is an image signal for displaying a video, This determines whether the signal is an image signal for displaying a still image.

[0077] The criterion for detecting a "difference" in this comparison is that the magnitude of the difference must be at a certain level. You can also configure it so that when it exceeds a certain threshold, it is considered to have detected a difference. The difference detected by circuit 112 should be determined by the absolute value of the difference.

[0078] Furthermore, in this embodiment, the comparison circuit 112 provided inside the liquid crystal display device 200 By detecting the difference in image signals between consecutive frames, it is possible to determine whether the image is moving or still. The configuration for determining whether something is a video or a still image has been shown, but it is not possible to determine from the outside whether it is a video or a still image. This configuration may also be used to supply that signal.

[0079] The selection circuit 115 is configured to include, for example, multiple switches formed by transistors. When the comparison circuit 112 detects a difference between consecutive frames, that is, when the image is a video... The display control circuit 113 selects the video image signal from the frame memory in the memory circuit 111. Output to [this location].

[0080] Furthermore, if the comparison circuit 112 does not detect a difference between consecutive frames, the selection circuit 115 will be used. In other words, when the image is a still image, the display control circuit 113 retrieves the frame from the memory in the memory circuit 111. The image signal is not output. The image signal is not output from the frame memory to the display control circuit 113. This configuration allows for a reduction in the power consumption of the liquid crystal display device.

[0081] In this embodiment of the liquid crystal display device, the comparison circuit 112 uses the image signal for still image display. The operation performed when the signal is determined to be a still image display mode, and the comparison circuit 112 performs the operation when the image signal is determined to be a video display mode. The action taken when the signal is identified as a display signal is the video display mode.

[0082] The display control circuit 113 displays the image signal selected by the selection circuit 115 to the display panel 120, and the sequence of events. The supply of control signals (specifically, the start pulse SP and the clock signal CK) (or a signal to control the switching of stopping), power supply potential (high power supply potential Vdd, low power supply potential The system supplies a voltage Vss and a common potential Vcom to the backlight unit 130 for backlight control. The signal (specifically, the backlight control circuit 131 controls the turning the backlight on and off) This is a circuit that supplies signals for [a specific purpose].

[0083] Furthermore, the image processing circuit illustrated in this embodiment has a display mode switching function. This is also acceptable. The display mode switching function can be controlled manually or via an external device by the user of the LCD display device. By using the device to select the operating mode of the liquid crystal display, you can choose between video display mode or still image display mode. This is a function that switches the display mode.

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

[0085] For example, when operating in still image display mode, the display mode switching circuit selects circuit 1 When a mode switching signal is input to 15, the comparison circuit 112 performs a comparison over a continuous frame period. Even if the difference in the image signal is not detected, the selection circuit 115 will still receive the input image signal A mode can be executed in which numbers are output sequentially to the display control circuit 113, i.e., a video display mode. Furthermore, when operating in video display mode, the selection circuit 115 from the display mode switching circuit When a mode switching signal is input, the comparison circuit 112 analyzes the image over a continuous frame period. Even when detecting the difference in the image signal, the selection circuit 115 selects one frame of image It can execute a mode that outputs only the image signal, i.e., a still image display mode. The liquid crystal display device of this embodiment, when operating in video display mode, uses multiple time-division multiplexers. Of the images corresponding to each frame, the image corresponding to one frame will be displayed as a still image. .

[0086] Furthermore, the liquid crystal display device may have a photometering circuit. A liquid crystal display device equipped with a photometering circuit is The brightness of the environment in which the liquid crystal display device is placed can be detected. As a result, the photometering circuit is connected. The display control circuit 113, in response to the signal input from the photometering circuit, controls the backlight, etc. The method of driving the light source can be controlled.

[0087] For example, a photometric circuit could detect that the liquid crystal display was being used in a dimly lit environment. The display control circuit 113 then controls the backlight 132 to increase its light intensity and display To ensure good screen visibility, and conversely, to prevent the LCD display from being exposed to extremely bright ambient light (for example, outdoors) If it is discovered that the display is being used in direct sunlight, the display control circuit 113 will turn on the backlight 1 The intensity of light 32 is controlled to reduce the power consumed by the backlight 132.

[0088] The backlight section 130 includes a backlight control circuit 131 and a backlight 132. The backlight 132 can be selected and combined according to the application of the liquid crystal display device 200. Furthermore, cold cathode fluorescent lamps and light-emitting diodes (LEDs) can be used. Color display is also possible. In some cases, display is possible by combining color filters. Backlight 132 For example, a white light-emitting element (e.g., an LED) can be placed there. RGB LEDs are placed in position 132, and sequential additive color mixing is used to display colors through time division. When using the field sequential method, if a color filter is not used... There is also the backlight control circuit 131, which controls the backlight from the display control circuit 113. The backlight signal and power potential are supplied.

[0089] In this embodiment, the display panel 120 has a switching element 127 in addition to the pixel section 122. It has. In this embodiment, the display panel 120 has a first substrate and a second substrate, and the first The substrate is provided with a drive circuit section 121, a pixel section 122, and a switching element 127. Yes, they are.

[0090] Furthermore, the pixel 123 has a transistor 214 as a switching element, and the transistor 214 It has a capacitive element 210 and a liquid crystal element 215 connected to it (see Figure 3).

[0091] Transistor 214 is preferably a transistor with a low off-current. When transistor 214 is in the off state, the liquid crystal element connected to transistor 214 has a low off current. The charge stored in 215 and the capacitive element 210 is less likely to leak through the transistor 214. The state written before transistor 214 turns off can be retained for a long period of time. ru.

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

[0093] Examples of liquid crystals applied to liquid crystal elements include nematic liquid crystals, cholesteric liquid crystals, and smeck liquid crystals. Titic 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 crystals, side-chain polymer liquid crystals, and banana-shaped liquid crystals.

[0094] Another example of an LCD driving method is the TN (Twisted Nematic) mode. STN (Super Twisted Nematic) mode, OCB (Optica (Compensated Birefringence) mode, ECB (El (Ecologically 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 This includes features such as guest host mode.

[0095] The switching element 127 changes to a common potential according to the control signal output by the display control circuit 113. Vcom is supplied to the common electrode 128. The switching element 127 is a transistor. The gate electrode and source electrode or drain electrode of the transistor can be used. One side is connected to the display control circuit 113, and one of the source electrode or drain electrode is connected to the terminal section 1 A common potential Vcom is supplied from the display control circuit 113 via 26, and the other is shared It should be connected to the conductive electrode 128. Note that the switching element 127 is connected to the drive circuit section 121, Alternatively, it may be formed on the same substrate as the pixel portion 122, or it may be formed on a different substrate. It's okay to have it.

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

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

[0098] Source of a switching element 127 that uses a transistor, which is one form of a switching element. One of the electrodes or the drain electrode is a capacitive element 21 that is not connected to transistor 214. The other electrode of 0 and the other electrode of the liquid crystal element 215 are connected, and the switching element 127 The other end of the source electrode or drain electrode is connected to terminal 126B. Also, the switch The gate electrode of the junction element 127 is connected to terminal 126A.

[0099] Next, the signal supplied to the pixels is shown in the equivalent circuit diagram of the liquid crystal display device in Figure 3, and in Figure 4. I will explain using the timing chart shown.

[0100] Figure 4 shows the clock signal GCK supplied by the display control circuit 113 to the gate line drive circuit 121A. , and the start pulse GSP are indicated. Also, the display control circuit 113 is the source line drive circuit 12 This shows the clock signal SCK and start pulse SSP supplied to 1B. To explain the timing of the signal output, Figure 4 shows the waveform of the clock signal as a simple square wave. This is shown.

[0101] Figure 4 also shows the potential of the source line (Data line) 125, the potential of the pixel electrode, and terminal 12 The potentials of 6A, terminal 126B, and the common electrode are shown.

[0102] In Figure 4, period 1401 corresponds to the period during which the image signal for displaying the video is written. During period 1401, the image signal and common potential are supplied to each pixel of the pixel unit 122 and the common electrode. It works in this way.

[0103] Furthermore, period 1402 corresponds to the period during which a still image is displayed. During period 1402, the pixel section 1 This will stop the image signal to each of the 22 pixels and the common potential to the common electrode. (See Figure 4) During period 1402, a configuration is shown in which signals are supplied to stop the operation of the drive circuit section. However, the image signal is written periodically according to the length of the period 1402 and the refresh rate. It is preferable to have a configuration that prevents degradation of still images by incorporating this feature.

[0104] First, let's explain the timing chart for period 1401. In period 1401, Cross As the clock signal GCK, a clock signal is constantly supplied, and as the start pulse GSP, a vertical A pulse corresponding to the synchronization frequency is supplied. Also, during period 1401, the clock signal SCK is supplied. A clock signal is constantly supplied, and the start pulse SSP is set to 1 gate selection period. A corresponding pulse is supplied.

[0105] Additionally, an image signal Data is supplied to each row's pixels via the source line 125, and the gate line 12 The potential of source line 125 is supplied to the pixel electrode according to the potential of 4.

[0106] Furthermore, the display control circuit 113 connects the switching element 127 to terminal 126A of the switching element A potential is supplied to make terminal 127 conductive, and a common potential is supplied to the common electrode via terminal 126B. do.

[0107] On the other hand, period 1402 is the period during which still images are displayed. Next, the tie in period 1402 Let's explain the ming chart. In period 1402, the clock signal GCK and the start pulse G SP, clock signal SCK, and start pulse SSP all stop. Also, period 14 In step 02, the image signal Data that was being supplied to source line 125 stops. During period 1402, when both the GCK and start pulse GSP are stopped, transistor 21 4 becomes non-conductive, and the potential of the pixel electrode becomes floating.

[0108] Furthermore, the display control circuit 113 connects the switching element 127 to terminal 126A of the switching element A potential is supplied that causes 127 to become non-conductive, and the potential of the common electrode is set to a floating state.

[0109] During period 1402, the potentials of the electrodes at both ends of the liquid crystal element 215, i.e., the pixel electrodes and the common electrode, are floated. By putting it into idle mode, it is possible to display a still image without supplying any new electrical potential.

[0110] Furthermore, the clock signal supplied to the gate line drive circuit 121A and the source line drive circuit 121B By stopping the signal and start pulse, power consumption can be reduced.

[0111] In particular, transistors 214 and switching element 127 are transistors with low off-current. By using this method, the phenomenon of the voltage applied to both terminals of the liquid crystal element 215 decreasing over time is suppressed. can.

[0112] Next, the period during which the video switches to a still image (period 1403 in Figure 4), and the period from still image to video. The operation of the display control circuit during the transition period (period 1404 in Figure 4) is shown in Figure 5(A). This will be explained using (B). Figures 5(A) and (B) show the high power supply potential output by the display control circuit. Vdd, clock signal (GCK here), start pulse signal (GSP here), and This shows the potential at terminal 126A.

[0113] Figure 5(A) shows the operation of the display control circuit during the period 1403 when switching from video to still image. The control circuit stops the start pulse GSP (E1 in Figure 5(A), the first step). Next, after the start pulse signal GSP stops, the pulse output reaches the final stage of the shift register. After reaching that point, stop the multiple clock signals GCK (E2 in Figure 5(A), the second step) Next, the high power supply potential Vdd is changed to the low power supply potential Vss (E3 in Figure 5(A)). (Third step) Next, the potential of terminal 126A is set so that the switching element 127 is non-conductive. The potential is adjusted to the desired state (E4 in Figure 5(A), the fourth step).

[0114] By following the above procedure, the drive circuit unit 121 can be operated without causing a malfunction of the drive circuit unit 12 The signal supplied to 1 can be stopped. Malfunctions when switching from video to still images produce noise. Since noise is retained as a still image, the LCD display is equipped with a display control circuit that minimizes malfunctions. The display device can show still images with minimal image degradation.

[0115] Next, Figure 5(B) shows the operation of the display control circuit during the period 1404 when the image switches from a still image to a video. The display control circuit sets the potential of terminal 126A to a potential that causes the switching element 127 to conduct. (S1 in Figure 5(B), the first step). Next, the power supply voltage is set to the low power supply potential Vss. Then, the power supply potential is raised to Vdd (S2 in Figure 5(B), the second step). Next, the clock signal After first applying a high potential to the GCK signal, multiple clock signals GCK are supplied (Figure 5). S3 of B), the third step). Next, supply the start pulse signal GSP (Figure 5(B). S4 of (the fourth step).

[0116] By following the above procedure, the drive circuit unit 121 can be operated without causing any malfunction of the drive circuit unit 121. The drive signal can be resumed. By returning the potential of each wire to its appropriate position in sequence during video display, errors can be corrected. The drive circuit can be driven without any external operation.

[0117] Furthermore, Figure 6 shows the period 601 during which a video is displayed, or the period 602 during which a still image is displayed. The image signal write frequency for each frame period is schematically shown. In Figure 6, "W" represents the image signal. This indicates the writing period, and "H" indicates the period during which the image signal is held. In addition, in Figure 6, period 603 represents one frame period, but other periods That's fine.

[0118] Thus, in the configuration of the liquid crystal display device of this embodiment, the static display shown in period 602 The image signal of the picture is written in period 604, and the image signal written in period 604 is written in period 6 It is retained during other periods of 02.

[0119] The liquid crystal display device illustrated in this embodiment writes the image signal during the period when a still image is displayed. This reduces congestion frequency. As a result, it becomes possible to reduce power consumption when displaying still images. ru.

[0120] Furthermore, when displaying still images by overwriting the same image multiple times, the image transitions may not be visually apparent. When this happens, humans may experience eye strain. The liquid crystal display device of this embodiment displays images Because the frequency of signal writing is reduced, it also has the effect of reducing eye strain.

[0121] In particular, the liquid crystal display device of this embodiment uses transistors with low off-current for each pixel, and also for the common By applying this to the switching element of the electrode, the period (hours) during which the voltage can be held by the holding capacitance can be increased. The interval can be extended. As a result, the frequency of writing the image signal can be drastically reduced. This makes it possible to significantly reduce power consumption when displaying still images and reduce eye strain. It has an effect.

[0122] Furthermore, in this embodiment, when the stop means 117 is selected, the stop signal is generated. The input is received and a fixed potential is written to the capacitive elements 210 of all pixels. By writing the position, the potential difference between the electrodes of the capacitive element 210 is eliminated, and the response state is eliminated. The liquid crystal is set to an initial, unresponsive state. Therefore, the display screen will show the initial state of the liquid crystal. A status image is displayed.

[0123] After displaying the initial state image, the power supply 116 is stopped and the power potential is supplied to the display panel 120. The system is stopped, and the liquid crystal display device 200 is turned off. Therefore, the liquid crystal is not necessary when it is turned off. The necessary electric field is not constantly applied, allowing it to remain in a stable initial state.

[0124] As described above, when the liquid crystal display is powered on and power is supplied, The system appropriately selects between video display mode and still image display mode based on the image signal of the subsequent frames. To reduce power consumption and prevent voltage from being applied to the liquid crystal elements before turning off, a fixed power supply is used. By writing the position and displaying an initialization image, deterioration of the liquid crystal element is prevented, resulting in a longer period of good image display. It is possible to maintain functionality while also enhancing security.

[0125] Therefore, a liquid crystal display device that achieves more reliable low power consumption, and a liquid crystal display device This makes it possible to provide a driving method.

[0126] (Embodiment 3) This embodiment shows an example of a transistor that can be applied to the liquid crystal display device disclosed herein. The transistor structure applicable to the liquid crystal display devices disclosed herein is not particularly limited. For example, using a top gate structure or a bottom gate structure of staggered and planar type. It is possible. Also, the transistor is a single channel where one channel formation region is formed. Even in a gate structure, a double gate structure is formed with two gates, or a triple gate structure is formed with three gates. It may also be constructed in such a way. In addition, two gate insulating layers are placed above and below the channel region. A dual-gate type with a gate electrode layer is also possible. Figures 7(A) to (D) show the transistors An example of the cross-sectional structure of a transistor is shown. Note that the transistors shown in Figures 7(A) to (D) are semiconductors. This method uses oxide semiconductors. The advantages of using oxide semiconductors are, compared to The advantage is that high mobility and low off-current can be obtained through a simple and low-temperature process, but of course Hmm, other semiconductors can be used as well.

[0127] The transistor 410 shown in Figure 7(A) is a thin-film transistor with a bottom gate structure. Yes, it is also called an inverse staggered thin-film transistor.

[0128] The transistor 410 has a gate electrode layer 401 and a gate on a substrate 400 having an insulating surface. Insulating layer 402, oxide semiconductor layer 403, source electrode layer 405a, and drain electrode layer 40 It includes 5b. It also covers transistor 410 and is laminated on oxide semiconductor layer 403 as an insulating film. A layer 407 is provided. A protective insulating layer 409 is further formed on the insulating film 407. .

[0129] The transistor 420 shown in Figure 7(B) is a channel protection type (also called a channel stop type). It is a type of bottom-gate structure called an inverse staggered thin-film transistor.

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

[0131] The transistor 430 shown in Figure 7(C) is a bottom-gate thin-film transistor, and is an insulating A gate electrode layer 401, a gate insulating layer 402, and a so It includes an electrode layer 405a, a drain electrode layer 405b, and an oxide semiconductor layer 403. An insulating film 407 is provided that covers the transistor 430 and is in contact with the oxide semiconductor layer 403. A protective insulating layer 409 is further formed on the insulating film 407.

[0132] In transistor 430, the gate insulating layer 402 is connected to the substrate 400 and the gate electrode layer 40 1 is provided in contact with the gate insulating layer 402, and the source electrode layer 405a and drain electrode layer 405b is provided in contact with it. And 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 Figure 7(D) is one of the thin-film transistors with a top gate structure. Yes. Transistor 440 has an insulating layer 437 and an oxide layer on a substrate 400 having an insulating surface. Semiconductor layer 403, source electrode layer 405a, drain electrode layer 405b, gate insulating layer 4 02, comprising a gate electrode layer 401, a source electrode layer 405a, and a drain electrode layer 405b Wiring layers 436a and 436b are provided in contact with each other and are electrically connected.

[0134] In this embodiment, as described above, an oxide semiconductor layer 403 is used as the semiconductor layer. As the oxide semiconductor used in the material semiconductor layer 403, the quaternary metal oxide In-Sn- Ga-Zn-O systems, and ternary metal oxides such as In-Ga-Zn-O and In-Sn-Z nO system, In-Al-Zn-O system, Sn-Ga-Zn-O system, Al-Ga-Zn-O system Sn-Al-Zn-O system, and binary metal oxides such as In-Zn-O system, Sn-Zn- O-based, Al-Zn-O-based, Zn-Mg-O-based, Sn-Mg-O-based, In-Mg-O-based, In-O, Sn-O, and Zn-O systems can be used. The body may contain SiO2. Here, for example, an In-Ga-Zn-O based oxide semiconductor and It is an oxide containing at least In, Ga, and Zn, and there are no particular restrictions on its composition ratio. Furthermore, it may contain elements other than In, Ga, and Zn.

[0135] Furthermore, the oxide semiconductor layer 403 is represented by the chemical formula InMO3(ZnO)m (m>0). A thin film can be used. Here, M is selected from Ga, Al, Mn, and Co. ]]represents one or more metal elements. For example, as M, there are Ga, Ga and Al, Ga and Mn, or Ga and Co, etc.

[0136] Transistors 410, 420, 430, 440 using the oxide semiconductor layer 403 can reduce the current value in the off state (off-current value). 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, the frequency of the refresh operation can be reduced, resulting in an effect of suppressing power consumption.

[0137] Also, transitors 410, 420, 430, 440 using the oxide semiconductor layer 403 can obtain a relatively high field-effect mobility, enabling high-speed driving. Therefore, by using this transitor in the pixel portion of a liquid crystal display device, a high-quality image can be provided. Also, since this transitor can be fabricated separately for the drive circuit portion or the pixel portion on the same substrate, the number of parts of the liquid crystal display device can be reduced.

[0138] There is no major 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.

[0139] In transitors 410, 420, 430 having a bottom gate structure, an insulating film serving as an underlayer 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 more films selected from a silicon nitride film, a silicon oxide film, a silicon oxynitride film, or a

[0140] The materials for the gate electrode layer 401 are molybdenum, titanium, chromium, tantalum, tungsten, Metal materials such as aluminum, copper, neodymium, scandium, or compounds mainly composed of these materials It can be formed using gold material, either as a single layer or in layers.

[0141] The gate insulating layer 402 is formed by using plasma CVD or sputtering, etc. Silicon nitride layer, silicon oxide nitride layer, silicon nitride oxide layer, aluminum oxide layer, nitride Aluminum layer, aluminum oxide nitride layer, aluminum oxide nitride layer, or hafniac oxide The layer can be formed as a single layer or in multiple layers. For example, as the first gate insulating layer, A silicon nitride layer (SiNy(y)) with a thickness of 50 nm to 200 nm is created by the Razma CVD method. >0)) is formed, and a second gate insulating layer with a thickness of 5 nm or more is formed on the first gate insulating layer. By stacking silicon oxide layers (SiOx (x>0)) with a thickness of 00 nm or less, the total film thickness is 200 nm. This will serve as the gate insulating layer.

[0142] Examples of conductive films used for the source electrode layer 405a and drain electrode layer 405b include Al , elements selected from Cr, Cu, Ta, Ti, Mo, W, or elements listed above as components An alloy or an alloy film combining the above-mentioned elements can be used. In addition, Al, C A high-melting-point metal layer such as Ti, Mo, or W is placed on either the underside or the upper side of a metal layer such as u, or on both sides. A layered configuration is also acceptable. Furthermore, it prevents the formation of hillocks and whiskers in the Al film. By using Al material to which elements (such as Si, Nd, and Sc) are added, heat resistance can be improved. It becomes possible to raise the level.

[0143] Wiring layer 436a and wiring layer 43 connected to source electrode layer 405a and drain electrode layer 405b The conductive film, such as 6b, is made of the same material as the source electrode layer 405a and the drain electrode layer 405b. It can be used.

[0144] Furthermore, source electrode layer 405a, drain electrode layer 405b (wiring formed from the same layer) The conductive film (including the layer) may be formed from a conductive metal oxide. Examples of oxides include indium oxide (In2O3), tin oxide (SnO2), and zinc oxide (ZnO2). ), indium tin oxide alloy (In2O3-SnO2, abbreviated as ITO), zinc oxide alloy (In2O3-ZnO) or these metal oxide materials with silicon oxide Products containing corn can be used.

[0145] Insulating films 407, 427, and 437 are typically silicon oxide films, silicon oxide nitride films, and acid Inorganic insulating films such as aluminum oxide films or aluminum oxide nitride films can be used. ru.

[0146] The protective insulating layer 409 consists of a silicon nitride film, an aluminum nitride film, a silicon nitride oxide film, and a silicon nitride film. Inorganic insulating films, such as aluminum oxide films, can be used.

[0147] Furthermore, a planarizing insulating film is used on the protective insulating layer 409 to reduce surface irregularities caused by transistors. A planarizing insulating film may be formed. Polyimide, acrylic, benzocyclobutene Organic materials such as the above can be used. In addition to the above organic materials, low dielectric constant materials (low -k material) etc. can be used. Multiple insulating films formed from these materials can be stacked. A planar insulating film may be formed by doing so.

[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 a reverse staggered type 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 obtained by removing hydrogen, which is an n-type impurity, from the oxide semiconductor and highly purifying it so that impurities other than the main components of the oxide semiconductor are not contained as much as possible. Thus, it is an i-type (intrinsic) oxide semiconductor or an oxide semiconductor that is extremely close to the i-type (intrinsic). That is, instead of adding impurities to make it i-type, by removing impurities such as hydrogen and water as much as possible, it is characterized by being 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, carriers are extremely few (close to zero), and the carrier The ria concentration is less than 1 × 10¹⁴ / cm³, preferably less than 1 × 10¹² / cm³, and even more preferably The density is less than 1 × 10¹¹ / cm³.

[0153] Because there are extremely few carriers in the oxide semiconductor, the off-current of the transistor is reduced. This is possible. The less off-current, the better.

[0154] Specifically, the thin-film transistor having the oxide semiconductor layer described above has a channel width of 1 μm. The off-current density per unit is 10 aA / μm (1 × 10⁻¹⁷ A / μm) or less at room temperature. To make it so, and even less than 1 aA / μm (1 × 10⁻¹⁸ A / μm), and even less than 10 zA It is possible to reduce the level to less than / μm (1 × 10⁻²⁰ A / μm).

[0155] A transistor with an extremely small current value in the off state (off current value) is shown in the diagram of Embodiment 1. By using it as a transistor in the basic unit, refresh rate in the still image area The process can be carried out with a small number of image data writes.

[0156] Furthermore, the transistor 510, which has the aforementioned oxide semiconductor layer, exhibits a temperature dependence of its on-current. It is hardly observed, and the off-current remains very low.

[0157] The following describes the process of fabricating the transistor 510 on the substrate 505, using Figures 8(A) to (E). Explain.

[0158] First, a conductive film is formed on a substrate 505 having an insulating surface, and then a first photolithography is performed. The gate electrode layer 511 is formed by the process. The resist mask is made by the inkjet method. It may be formed. If the resist mask is formed by the inkjet method, a photomask is used. Therefore, manufacturing costs can be reduced.

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

[0160] An insulating film that serves as the base layer may be provided between the substrate 505 and the gate electrode layer 511. It has the function of preventing the diffusion of impurity elements from the substrate 505, and silicon nitride film, silicon oxide One or more films selected from a silicon nitride film, silicon nitride film, or silicon oxide film. It can be formed by a laminated structure.

[0161] Furthermore, the material of the gate electrode layer 511 is molybdenum, titanium, tantalum, tungsten, and Metal materials such as luminium, copper, neodymium, scandium, or alloy materials with these as the main components. It can be formed using a material, either as a single layer or in layers.

[0162] Next, a gate insulating layer 507 is formed on the gate electrode layer 511. The gate insulating layer 507 is Using plasma CVD or sputtering, etc., silicon oxide layer, silicon nitride layer, oxide Silicon nitride layer, silicon nitride oxide layer, aluminum oxide layer, aluminum nitride layer, oxide Aluminum nitride layer, aluminum nitride oxide layer, or hafnium oxide layer, either as a single layer or in a multilayer configuration. It can be formed in this way.

[0163] The oxide semiconductor of this embodiment is an acid that has had impurities removed and has been type i or substantially type i. Oxide semiconductors are used. Such highly purified oxide semiconductors are suitable for interface levels and interface charges. Because it is extremely sensitive, the interface between the oxide semiconductor layer and the gate insulating layer is important. Therefore, the gate insulating layer that comes into contact with the highly purified oxide semiconductor requires high quality.

[0164] For example, high-density plasma CVD using μ-waves (e.g., frequency 2.45 GHz) is a method for creating dense plasma CVD. This is preferable because it allows for the formation of a high-quality insulating layer with high dielectric strength. The close contact between the body and the high-quality gate insulating layer reduces the interface state and improves interface properties. Because it can be made into something.

[0165] Of course, if it can form a good insulating layer as a gate insulating layer, then sputtering or pruning can be used. Other film deposition methods, such as the razma CVD method, can be applied. Furthermore, post-deposition heat treatment can be performed. The insulating layer may be one in which the film quality of the gate insulating layer and the interface characteristics with the oxide semiconductor are modified. In any case, it is essential that the film quality as a gate insulating layer is good, as well as that of an oxide semiconductor. Any material that can reduce the density of interface states with the body and form a good interface would be acceptable.

[0166] Furthermore, the gate insulating layer 507 and the oxide semiconductor film 530 contain as much hydrogen, hydroxyl groups, and moisture as possible. To prevent contamination, sputtering is used as a pretreatment for the deposition of the oxide semiconductor film 530. In the preheating chamber of the device, the substrate 505 on which the gate electrode layer 511 is formed, or the gate insulating layer 5 The substrate 505, on which layers 07 have been formed, is preheated to remove hydrogen, moisture, etc. adsorbed on the substrate 505. It is preferable to remove impurities and exhaust them. The exhaust means provided in the preheating chamber is cryogenic. A pump is preferred. Note that this preheating process can be omitted. The heat reaches the source electrode layer 515a and drain electrode layer 515b before the insulating layer 516 is formed. The same procedure may be performed on the formed substrate 505.

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

[0168] Furthermore, before depositing the oxide semiconductor film 530 by sputtering, argon gas was introduced. Reverse sputtering is performed to generate plasma, and the powdery material adhering to the surface of the gate insulating layer 507 It is preferable to remove the substance (also called particles or dust). Reverse sputtering is a process that involves removing the particles. Without applying voltage to the get side, voltage is applied to the substrate side using an RF power supply under an argon atmosphere. This method involves forming plasma near the substrate to modify its surface. Nitrogen, helium, oxygen, etc., may be used instead.

[0169] The oxide semiconductor used in the oxide semiconductor film 530 is the quaternary metal oxide shown in Embodiment 3. And ternary metal oxides, binary metal oxides, In-O, Sn-O, Zn-O, etc. Any oxide semiconductor can be used. Furthermore, even if the oxide semiconductor contains SiO2... Good. In this embodiment, the oxide semiconductor film 530 is an In-Ga-Zn-O based oxide film. The film is deposited using sputtering with a GET. The cross-sectional view at this stage corresponds to Figure 8(A). Furthermore, the oxide semiconductor film 530 was subjected to a rare gas (typically argon) atmosphere and an oxygen atmosphere. It can be formed by sputtering under gas or in a mixed atmosphere of noble gas and oxygen. .

[0170] For example, a target for fabricating oxide semiconductor film 530 by sputtering is, As a ratio, In2O3:Ga2O3:ZnO = 1:1:1 [molar ratio] can be used. Yes, it is possible. Also, In2O3:Ga2O3:ZnO = 1:1:2 [molar ratio] Alternatively, a tar with a composition ratio of In2O3:Ga2O3:ZnO=1:1:4 [molar ratio] A GET may be used. The packing density of the oxide target is preferably 90% to 100%. The percentage is between 95% and 99.9%. By using a metal oxide target with a high packing density... Therefore, the deposited oxide semiconductor film becomes a dense film.

[0171] The sputtering gas used when depositing the oxide semiconductor film 530 is hydrogen, water, hydroxyl group or hydrogen It is preferable to use a high-purity gas from which impurities such as monoxides have been removed.

[0172] The substrate is held in a film deposition chamber under reduced pressure, and the substrate temperature is kept between 100°C and 600°C. The temperature should be between 200°C and 400°C. By depositing the film while heating the substrate, The concentration of impurities in the deposited oxide semiconductor film can be reduced. Damage caused by rinsing is reduced. And, while removing residual moisture in the deposition chamber, hydrogen and moisture are removed. The removed sputtering gas is introduced, and the oxide semiconductor is placed on the substrate 505 using the target described above. A film 530 is deposited. To remove residual moisture in the deposition chamber, an adsorption-type vacuum pump is used, for example. For example, cryopumps, ion pumps, and titanium sublimation pumps are preferred. It seems so. Also, as an exhaust method, a turbomolecular pump with a cold trap added... It may be present. The deposition chamber, which is evacuated using a cryopump, contains, for example, hydrogen atoms, water (H2 Because compounds containing O, etc. (more preferably compounds containing carbon atoms) are exhausted, The concentration of impurities in the oxide semiconductor film deposited in the said deposition chamber can be reduced.

[0173] An example of film deposition conditions is a distance of 100 mm between the substrate and the target, and a pressure of 0.6 Pa. The conditions applied are a DC power supply of 0.5kW and an oxygen atmosphere (oxygen flow rate ratio of 100%). It can be done. Furthermore, when using a pulsed DC power supply, powdery substances (particles) generated during film formation can be produced. This method is preferable because it reduces (also known as) the film thickness distribution and becomes more uniform.

[0174] Next, the oxide semiconductor film 530 is transformed into island-shaped oxide semiconductors by a second photolithography process. The material is processed into layers. Additionally, a resist mask is used to form island-shaped oxide semiconductor layers. It may also be formed by the jet method. If the resist mask is formed by the inkjet method, photomask Because no screws are used, manufacturing costs can be reduced.

[0175] Furthermore, when forming contact holes in the gate insulating layer 507, the process is carried out in an oxide semiconductor. This can be done simultaneously with the processing of film 530.

[0176] Note that the etching of the oxide semiconductor film 530 here can be done by dry etching or wet etching. Wetting is also acceptable, and both can be used. For example, wet etching of oxide semiconductor film 530 For etching, a solution of phosphoric acid, acetic acid, and nitric acid is used. This is possible. Alternatively, ITO07N (manufactured by Kanto Chemical Co., Ltd.) may be used.

[0177] Next, the oxide semiconductor layer is subjected to a first heat treatment. This first heat treatment causes the oxide semiconductor layer The conductive layer can be dehydrated or dehydrogenated. The temperature of the first heat treatment is 400°C. The temperature shall be 750°C or higher, or 400°C or higher, below the substrate's strain point. Here, the heat treatment equipment The substrate is introduced into an electric furnace, one of the furnaces, and the oxide semiconductor layer is subjected to a nitrogen atmosphere at 450°C. After a 1-hour heat treatment, water and water are removed from the oxide semiconductor layer without exposure to the atmosphere. This prevents the re-incorporation of the element and obtains the oxide semiconductor layer 531 (see Figure 8(B)).

[0178] Furthermore, the heat treatment device is not limited to electric furnaces, but also includes heat conduction or heat from heat-generating elements such as resistance heating elements. A device that heats the object to be processed by radiation may also be used. For example, GRTA(Gas R apid Thermal Anneal) equipment, LRTA (Lamp Rapid T RTA (Rapid Thermal Annealing) devices such as hermal annealing equipment al) equipment can be used. LRTA equipment uses halogen lamps, metal halide lamps. Lamps, xenon arc lamps, carbon arc lamps, high-pressure sodium lamps, high-pressure mercury lamps This is a device that heats an object to be processed by radiating light (electromagnetic waves) from a lamp or similar light source. The GRTA device is a device that performs heat treatment using high-temperature gas. Noble gases such as argon, or nitrogen, which do not react with the material being treated by heat treatment. An active gas is used.

[0179] For example, as the first heat treatment, an inert gas heated to a high temperature of 650°C to 700°C The circuit board was moved inside and heated for several minutes, then moved again and heated to a high temperature in an inert solution. GRTA (Ground-Release Analysis) can be performed by releasing gas from the source.

[0180] In the first heat treatment, nitrogen or a noble gas such as helium, neon, or argon is used. It is preferable that it does not contain water, hydrogen, etc. Alternatively, nitrogen introduced into the heat treatment device, Alternatively, the purity of noble gases such as helium, neon, and argon must be 6N (99.9999%) or higher. Preferably 7N (99.99999%) or higher (i.e., impurity concentration of 1 ppm or less, preferably) It is preferable that the concentration be 0.1 ppm or less.

[0181] Furthermore, after heating the oxide semiconductor layer in the first heat treatment, high-purity oxygen gas is added to the same furnace. A 10°C N2O gas or ultra-dry air (with a dew point of -40°C or lower, preferably -60°C or lower) is introduced. It may be added. It is preferable that the oxygen gas or N2O gas does not contain water, hydrogen, etc. Alternatively, the purity of the oxygen gas or N2O gas introduced into the heat treatment device is preferably 6N or higher. Preferably, the impurity concentration in oxygen gas or N2O gas is 7N or higher (i.e., 1 ppm or less). It is preferable to keep the concentration below 0.1 ppm. Due to the action of oxygen gas or N2O gas, Oxygen, which is simultaneously reduced by the process of removing impurities through dehydration or dehydrogenation treatment. By supplying this material, the oxide semiconductor layer is made highly pure and electrically i-type (intrinsic).

[0182] Furthermore, the first heat treatment of the oxide semiconductor layer is performed on the oxide before it is processed into an island-shaped oxide semiconductor layer. This can also be done on the semiconductor film 530. In that case, after the first heat treatment, the heating device is used The substrate is removed, and the photolithography process is performed.

[0183] Furthermore, the first heat treatment can also be performed after oxide semiconductor layer deposition, in addition to the above. After stacking the source electrode layer and the drain electrode layer on top of the layer, or the source electrode layer and the drain This can be done either after forming an insulating layer on the rain electrode layer.

[0184] Furthermore, when forming contact holes in the gate insulating layer 507, the process is carried out in an oxide semiconductor. This can be done before or after the first heat treatment is performed on the film 530.

[0185] Furthermore, by depositing the oxide semiconductor layer in two stages and performing heat treatment in two stages, the substrate Regardless of the material of the component, such as oxides, nitrides, or metals, the crystalline region (single crystal region) with a thick film thickness is a single crystal region. Even if an oxide semiconductor layer is formed having a crystalline region (i.e., a c-axis oriented region perpendicular to the film surface), Good. For example, a first oxide semiconductor film of 3 nm to 15 nm is formed, and nitrogen, oxygen, In an atmosphere of noble gas or dry air, at a temperature of 450°C to 850°C, preferably 550°C or lower. A first heat treatment is performed at a temperature of 750°C or lower, and a crystalline region (including plate-like crystals) is formed in the region including the surface. A first oxide semiconductor film having the following characteristics is formed. Then, a second oxide semiconductor film thicker than the first oxide semiconductor film is formed. Form an oxide semiconductor film of type 2, and heat at a temperature of 450°C to 850°C, preferably 600°C to 70°C. A second heat treatment is performed at a temperature below 0°C, and the first oxide semiconductor film is used as a seed for crystal growth, and upward Crystal growth is performed to crystallize the entire second oxide semiconductor film, resulting in a thick crystalline region. An oxide semiconductor layer having a region may be formed.

[0186] Next, a source electrode layer and a drain are placed on the gate insulating layer 507 and the oxide semiconductor layer 531. A conductive film is formed to form the electrode layer (including wiring formed from the same layer). Source electrode As the conductive film used for the layer and the drain electrode layer, the source electrode layer 4 shown in Embodiment 3 is used. The material used for 05a and the drain electrode layer 405b can be used.

[0187] A third photolithography step forms a resist mask on the conductive film, and selectively extracts the residue. After performing ching to form the source electrode layer 515a and the drain electrode layer 515b, a resist is applied. Remove the mask (see Figure 8(C)).

[0188] For exposure during resist mask formation in the third photolithography process, ultraviolet light and KrF light are used. It is preferable to use a laser or ArF laser. Adjacent source electrodes on the oxide semiconductor layer 531 The gap width between the lower end of the layer and the lower end of the drain electrode layer determines the transistor that is later formed. The channel length L is determined. Note that if exposure is performed with a channel length L of less than 25 nm, Extreme ultraviolet light (Ultraviolet) is a type of ultraviolet light with extremely short wavelengths ranging from a few nanometers to tens of nanometers. Using iolet, exposure during resist mask formation in the third photolithography step It is recommended to do so. Exposure with ultra-ultraviolet light has high resolution and a large depth of field. Therefore, later formation It is also possible to set the channel length L of the transistor to between 10 nm and 1000 nm. Yes, it can increase the operating speed of the circuit.

[0189] Furthermore, in order to reduce the number of photomasks and processes used in the photolithography process, The resist mask formed by a multi-tone mask, which is an exposure mask where the light has multiple intensities, is formed by the light. The etching process may be performed using a mask. A resist mask formed using a multi-gradation mask. The ske will have a shape with multiple film thicknesses, and its shape can be further deformed by etching. Because it can do this, it can be used in multiple etching processes that process different patterns. Therefore, a single multi-tone mask can accommodate at least two different patterns. This allows for the formation of a resist mask. Therefore, the number of exposure masks can be reduced. Furthermore, the corresponding photolithography process can also be reduced, thus simplifying the overall process.

[0190] Furthermore, during the etching of the conductive film, the oxide semiconductor layer 531 is etched and fragmented. It is desirable to optimize the etching conditions to avoid this. However, only the conductive film It is difficult to obtain the condition of etching without etching the oxide semiconductor layer 531 at all. Furthermore, during etching of the conductive film, only a portion of the oxide semiconductor layer 531 is etched, creating grooves. It may also become an oxide semiconductor layer having a recessed portion.

[0191] In this embodiment, a Ti film is used as the conductive film, and the oxide semiconductor layer 531 is made of In-Ga- Since a Zn-O-based oxide semiconductor was used, ammonia hydrogen peroxide (A) was used as the etchant for the conductive film. Use a mixture of humonic acid, water, and hydrogen peroxide solution.

[0192] Next, plasma treatment is performed using a gas such as N2O, N2, or Ar, and the exposed material is then... Adsorbed water and other substances attached to the surface of the oxide semiconductor layer may be removed. In this case, an insulating layer 5 becomes a protective insulating film that contacts a portion of the oxide semiconductor layer without being exposed to the atmosphere. Forms 16.

[0193] The insulating layer 516 has a thickness of at least 1 nm, and water is applied to the insulating layer 516 by sputtering or other methods. The insulating layer 516 can be formed using appropriate methods that prevent the inclusion of impurities such as hydrogen. When hydrogen is present, the hydrogen penetrates the oxide semiconductor layer, or the hydrogen affects the oxide semiconductor layer. Oxygen is extracted from the layer, and the back channel of the oxide semiconductor layer becomes less resistive (n-type). This may lead to the formation of parasitic channels. Therefore, the insulating layer 516 should be as thin as possible. To ensure that the resulting film is hydrogen-free, it is important to avoid using hydrogen in the film deposition method.

[0194] In this embodiment, a silicon oxide film with a thickness of 200 nm is used as the insulating layer 516 by sputtering. The film is deposited using this method. The substrate temperature during film deposition should be between room temperature and 300°C. The temperature is set to 100°C. For silicon oxide film deposition by sputtering, a rare gas (typically...) is used. This can be done under an argon atmosphere, an oxygen atmosphere, or a mixed atmosphere of a noble gas and oxygen. This can be done. Also, as a target, a silicon oxide target or a silicon target can be used. For example, a silicon target can be used in an oxygen-containing atmosphere. Silicon oxide can be formed by the putter method. It is formed in contact with the oxide semiconductor layer. The insulating layer 516 does not contain moisture, hydrogen ions, OH- or other impurities, and these are not present from the outside. Inorganic insulating films that block penetration are used, typically silicon oxide films and oxidative nitride films. A silicon film, aluminum oxide film, or aluminum oxide-nitride film is used.

[0195] Similar to the deposition of the oxide semiconductor film 530, residual moisture in the deposition chamber of the insulating layer 516 is removed. For this purpose, it is preferable to use an adsorption-type vacuum pump (such as a cryopump). The concentration of impurities in the insulating layer 516 deposited in the deposition chamber, which is evacuated using an op-pump, is reduced. Yes, it is possible. Furthermore, as an exhaust means for removing residual moisture in the film deposition chamber of the insulating layer 516, A turbomolecular pump with a cold trap added may also be used.

[0196] The sputtering gas used when forming the insulating layer 516 is hydrogen, water, hydroxyl groups, or hydrides. It is preferable to use a high-purity gas from which impurities have been removed.

[0197] Next, a second heat treatment (preferably 2) is performed under an inert gas atmosphere or an oxygen gas atmosphere. Perform the procedure at temperatures between 0°C and 400°C (for example, between 250°C and 350°C). For example, under a nitrogen atmosphere. A second heat treatment is performed at 250°C for 1 hour under gas pressure. After the second heat treatment, the oxide semiconductor A portion of the body layer (channel-forming region) is heated while in contact with the insulating layer 516.

[0198] Through the above steps, the oxide semiconductor film is subjected to a first heat treatment to release hydrogen. Impurities such as water, hydroxyl groups, or hydrides (also called hydrogen compounds) are removed from the oxide semiconductor layer. This constructs an oxide semiconductor that is graphically eliminated and simultaneously reduced by the impurity removal process. It can supply oxygen, which is one of the main component materials. Therefore, the oxide semiconductor layer is high Purification and electrical conversion to type i (intrinsic) are performed.

[0199] Transistor 510 is formed through the above process (see Figure 8(D)).

[0200] Furthermore, if a silicon oxide layer containing many defects is used for the insulating layer 516, after the silicon oxide layer is formed... By heat treatment, hydrogen, water, hydroxyl groups or hydrides contained in the oxide semiconductor layer are removed. The impurities are diffused into the oxide insulating layer, and the impurities contained in the oxide semiconductor layer are further reduced. It produces the effect of [this].

[0201] A protective insulating layer 506 may be formed on the insulating layer 516. For example, the RF sputtering method A silicon nitride film is formed using this method. RF sputtering is suitable for mass production, and the protective insulating layer This is a preferred method for forming a film. The protective insulating layer does not contain impurities such as moisture, and these are protected from the outside. Using an inorganic insulating film that blocks penetration, silicon nitride film, aluminum nitride film, etc. In this embodiment, the protective insulating layer 506 is formed using a silicon nitride film. (See Figure 8(E)).

[0202] In this embodiment, the protective insulating layer 506 is made of the substrate 505 formed up to the insulating layer 516. It contains high-purity nitrogen that has been heated to a temperature between 100°C and 400°C, from which hydrogen and water have been removed. A silicon nitride film is deposited using a silicon semiconductor target after introducing a sputtering gas. In this case as well, similar to the insulating layer 516, protective insulation is maintained while removing residual moisture in the processing chamber. It is preferable to form layer 506.

[0203] After the formation of the protective insulating layer 506, further heating in air at a temperature between 100°C and 200°C for at least 1 hour and 30 hours. Heat treatment may be performed for less than [number] hours. This heat treatment involves heating while maintaining a constant heating temperature. Alternatively, the temperature may be raised from room temperature to a heating temperature of 100°C to 200°C, and from the heating temperature You may repeat the process of lowering the temperature to room temperature multiple times.

[0204] Thus, a trace containing a highly purified oxide semiconductor layer fabricated using this embodiment By using an inverter, the current value in the off state (off current value) can be made lower. This allows for longer retention times of electrical signals such as image signals, and writing The interval can also be set to be longer. Therefore, the frequency of refresh operations can be reduced. Therefore, it can significantly reduce power consumption.

[0205] Furthermore, transistors containing a highly purified oxide semiconductor layer can achieve high field-effect mobility. Therefore, high-speed driving is possible. Thus, the transistor is used in the pixel section of a liquid crystal display device. By having this, it is possible to provide high-quality images. Also, with this transistor, Because the drive circuit section and the pixel section can be manufactured separately on a single substrate, liquid crystal display equipment The number of components can be reduced.

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

[0207] (Embodiment 5) The liquid crystal display devices disclosed herein are applicable to a variety of electronic devices (including gaming machines). This can be done. As for electronic devices, for example, television equipment (television, or television) (Also called a receiver), computer monitors, digital cameras, digital video cameras Cameras such as Mera, digital photo frames, mobile phones (also known as mobile phones or mobile phone devices) (u) Portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Examples include the liquid crystal display device described in the above embodiment. Examples of electronic devices that may be included are described below.

[0208] Figure 9(A) shows an e-book, consisting of a casing 9630 and a display unit 9631. It may have an operation key 9632, a solar cell 9633, and a charge / discharge control circuit 9634. The e-book shown in Figure 9(A) displays various types of information (still images, videos, text images, etc.). Functions that display, such as a calendar, date or time, on the display unit, and the display unit Functions for manipulating or editing information, and controlling processing through various software (programs). It can have functions such as [functions such as] The battery 9635 and the DC-DC converter (hereinafter abbreviated as converter) 9636 are used. The configuration is shown. The liquid crystal display device shown in any of Embodiments 1 to 4 By applying this to the display unit 9631, it is possible to maintain good image display functionality for a longer period of time and security This allows for the creation of e-books that are both highly functional and power-efficient.

[0209] By using the configuration shown in Figure 9(A), the display unit 9631 can be semi-transmissive or reflective. When using a liquid crystal display device, it is expected that it will be used in relatively bright conditions, and solar cell 9633 This is preferable because it allows for efficient power generation and charging of the battery 9635. The solar cell 9633 should be installed appropriately in the available space (front or back) of the housing 9630. Therefore, it is possible to create a configuration that allows for efficient charging of the 9635 battery, which is preferable. Furthermore, if a lithium-ion battery is used for the 9635 battery, miniaturization can be achieved. These are some of the advantages.

[0210] Furthermore, the configuration and operation of the charge / discharge control circuit 9634 shown in Figure 9(A) are shown in Figure 9(B). The lock diagram will be shown and explained. Figure 9(B) shows the solar cell 9633, battery 9635, and Converter 9636, converter 9637, switches SW1 to SW3, display unit 9631 It shows the following: battery 9635, converter 9636, converter 9637, Switches SW1 through SW3 correspond to the charge / discharge control circuit 9634.

[0211] First, let's explain an example of operation when electricity is generated by the solar cell 9633 using ambient light. The electricity generated by the solar panels is converted to a voltage suitable for charging the 9635 battery. The voltage is boosted or lowered at 9636. Then, the solar cell 9 controls the operation of the display unit 9631. When power from 633 is used, switch SW1 is turned ON, and converter 9637 The voltage will be increased or decreased to the voltage required for the display unit 9631. If you do not want the display to work, turn SW1 off and SW2 on and use battery 9635 The configuration should be such that it charges the device.

[0212] Next, we will explain an example of operation when the solar cell 9633 does not generate electricity due to ambient light. The power stored in battery 9635 is converted by turning on switch SW3. The voltage is increased or decreased by the 9637. Then, the battery operates in accordance with the operation of the display unit 9631. The power will be supplied from the Lee 9635.

[0213] Note that the solar cell 9633 was shown as an example of a charging method, but other means of charging are also available. The configuration may also include charging the Terry 9635. Alternatively, it may be done in combination with other charging methods. It can also be used as a composition.

[0214] Figure 10(A) shows a notebook-type personal computer, consisting of a main unit 3001 and a casing 300 2. It consists of a display unit 3003, a keyboard 3004, etc. Embodiment 1 By applying the liquid crystal display device shown in any of the above four to the display unit 3003, the display can be extended for a longer period of time. A notebook-type personal computer that maintains good image display capabilities, high security, and low power consumption. It can be made into a computer.

[0215] Figure 10(B) shows a personal digital assistant (PDA), and the main unit 3021 has a display unit 3023, An external interface 3025 and operation buttons 3024, etc. are provided. A stylus 3022 is included as an accessory. The liquid crystal shown in any of Embodiments 1 to 4. By applying the display device to the display unit 3023, convenience, security, and low It can be used as a low-power personal digital assistant (PDA).

[0216] Figure 10(C) shows an example of an e-book. For example, the e-book 2700 has a casing 27 It consists of two enclosures, 01 and enclosure 2703. Enclosure 2701 and enclosure 270 3 is integrated with the shaft portion 2711, and the shaft portion 2711 is used as the axis for opening and closing operations. This configuration makes it possible to operate like a paper book.

[0217] The display unit 2705 is incorporated into the housing 2701, and the display unit 2707 is incorporated into the housing 2703. It is included. Display units 2705 and 2707 are configured to display a continuation screen. Alternatively, a configuration that displays different screens is also acceptable. For example, text is displayed on the right-hand display unit (display unit 2705 in Figure 10(C)), and on the left-hand side An image can be displayed on the display unit (display unit 2707 in Figure 10(C)). Embodiment The liquid crystal display device shown in any of 1 to 4 is applied to the display unit 2705 and the display unit 2707. This allows for longer-lasting, high-quality image display, enhanced security, and low power consumption. It can be made into a powerful ebook of 2700.

[0218] Furthermore, Figure 10(C) shows an example in which the housing 2701 is equipped with an operating section, etc. For example, The enclosure 2701 is equipped with a power supply 2721, operation keys 2723, speaker 2725, etc. It is possible to turn pages using operation key 2723. Note that it is the same as the display unit of the casing. The enclosure may also be configured to include a keyboard, pointing device, etc. on its surface. On the back and sides, there are external connection terminals (earphone jack, USB terminal, etc.), a recording medium insertion slot, etc. It may also be configured to include the following. Furthermore, the e-book 2700 has the function of an electronic dictionary. It can also be structured in this way.

[0219] Furthermore, the e-book 2700 may be configured to transmit and receive information wirelessly. By wireless means, The system will be configured to allow users to purchase and download desired book data from an e-book server. It is also possible.

[0220] Figure 10(D) shows a mobile phone, which consists of two housings, housing 2800 and housing 2801. The enclosure 2801 contains a display panel 2802, a speaker 2803, and a microphone. 2804, pointing device 2806, camera lens 2807, external connection terminal It is equipped with 2808, among other things. Additionally, the 2800 housing contains a solar panel for charging portable information terminals. It is equipped with a 2810 battery cell, an external memory slot 2811, etc. The antenna is also located within the housing. It is built into the body 2801. Liquid crystal display device as shown in any of Embodiments 1 to 4. By applying this to the display panel 2802, it is possible to maintain good image display functionality for a longer period of time. This allows for a mobile phone that is both highly reliable and power-efficient.

[0221] Furthermore, the display panel 2802 is equipped with a touch panel, and the image displayed in Figure 10(D) is Multiple operation keys 2805 are shown with dotted lines. Note that the output is from solar cell 2810. A boost circuit is also implemented to increase the voltage to the voltage required for each circuit.

[0222] The display panel 2802 changes its display orientation as appropriate depending on the usage mode. Since the camera lens 2807 is located on the same plane as the 2802, video calls are possible. Speaker 2803 and microphone 2804 are not limited to voice calls, but also video calls. Recording and playback are possible. Furthermore, the casings 2800 and 2801 slide apart, as shown in the diagram. As shown in 10(D), it can be changed from an unfolded state to an overlapping state, making it suitable for carrying around. Further miniaturization is possible.

[0223] External connection terminal 2808 can be connected to various cables such as AC adapters and USB cables. It is capable of charging and data communication with personal computers, etc. By inserting a recording medium into memory slot 2811, it becomes possible to store and move larger amounts of data. ru.

[0224] Furthermore, even if it has infrared communication capabilities, television reception capabilities, etc. in addition to the above functions good.

[0225] Figure 10(E) shows a digital video camera, consisting of a main unit 3051, a display unit (A) 3057, Eyepiece 3053, operation switch 3054, display unit (B) 3055, battery 3056 It is composed of the following. Displaying the liquid crystal display device shown in any of Embodiments 1 to 4. By applying this to part (A) 3057 and display part (B) 3055, a longer-lasting and better image display is achieved. To create a digital video camera that maintains display functionality, offers high security, and consumes low power. It is possible.

[0226] Figure 10(F) shows an example of a television system. The television system 9600 is, The display unit 9603 is integrated into the housing 9601. The display unit 9603 displays video. It is possible to do so. In addition, here the stand 9605 supports the housing 9601. The configuration shown is as follows: The liquid crystal display device shown in any of Embodiments 1 to 4 is shown as a display unit 96 By applying version 03, it maintains good image display functionality for a longer period and also enhances security. Furthermore, it can be a television system that consumes low power.

[0227] The television unit 9600 is operated using the control switches on the housing 9601 and a separate remote control. This can be done using the control unit. Furthermore, the remote control unit can be accessed from the said remote control unit. The configuration may also include a display unit that shows the information to be output.

[0228] The television system 9600 will consist of a receiver, modem, and other components. It can receive more general television broadcasts, and furthermore, it can connect via a modem, either wired or wirelessly. By connecting to the communication network, one-way (sender to receiver) or two-way communication is possible. It is also possible to communicate information (between a sender and a receiver, or between receivers, etc.).

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

[0230] In this embodiment, a liquid crystal display device that displays an initialization image before being turned off is used, and as a comparative example, The results of comparing the display state of a liquid crystal display device that was turned off while still displaying the image from before it was turned off. This indicates.

[0231] Figures 12(A) and 13(A) (Figures 12(A) and 13(A) are the same photograph) This shows the screen displaying the image of the ON state before the OFF state. Note that Figures 12(A) and 13(A) are shown. The image is a black and white checkerboard pattern, and the switching element of the pixels is an oxide with a low off-current. A transistor using a monocrystalline semiconductor layer (In-Ga-Zn-O layer) was applied. The liquid crystal display device is a transmissive liquid crystal display device, and light is supplied by a backlight. In this example, the liquid crystal display is turned off, and the display panel, including the drive circuit and pixel section, is turned off. Even after the power supply to the device is cut off, the backlight remains lit so that the display status of the screen can be seen. This was done so. The liquid crystal display device in this embodiment is a normally white liquid crystal display device. In its initial state, the LCD displays white by transmitting light from the backlight.

[0232] Figure 12(B) shows that before the display device is turned off, a fixed potential is written to the capacitive element, and the liquid crystal is initialized. When the power supply potential to the display panel, including the drive circuit and pixel section, is stopped after returning to the default state, This shows the display screen immediately after the device is turned off. The display screen is the initial state of the LCD, which is a completely white screen. The image is displayed in its default state. Therefore, the liquid crystal is in a stable initial state when no electric field is applied to it in the off state. It can be seen that this is the state in which it is.

[0233] On the other hand, Figure 13(B) shows a comparative example of the grid pattern displayed in Figure 13(A). When the LCD display is turned off and the power supply to the display panel is stopped, the off state This shows the display screen immediately after the state is turned off. In Figure 13(B), the display is shown in the ON state just before turning off. A faint checkerboard pattern can be seen, indicating that an electric field continues to be applied to the LCD even after it is turned off. Exposure of an electric field to the liquid crystal for such unnecessary periods of time leads to the deterioration of the liquid crystal display. This can lead to a decrease in image display functionality and reliability.

[0234] As can be seen from the above, before turning it off, a fixed power supply is used to prevent voltage from being applied to the liquid crystal element. By writing the position and displaying an initialization image, deterioration of the liquid crystal element is prevented, resulting in a longer period of good image display. It is possible to maintain functionality while also enhancing security.

[0235] Therefore, a liquid crystal display device that achieves more reliable low power consumption, and a liquid crystal display device This makes it possible to provide a driving method. [Explanation of Symbols]

[0236] 100 LCD 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 Stopping means 120 Display Panel 121 Drive circuit section 121A Gate Line Drive Circuit 121B Source Line Drive Circuit 122 pixel section 123 pixels 124 Gate Line 125 Source Line 126 Terminal section 126A terminal 126B terminal 127 Switching elements 128 Common electrode 130 Backlight section 131 Backlight control circuit 132 Backlight 200 LCD display device 210 Capacitive elements 214 transistors 215 liquid crystal elements 400 circuit boards 401 Guard Layer 402 Gate Insulation Layer 403 Oxide semiconductor layer 405a Source electrode layer 405b Drain electrode layer 407 Insulating film 409 Protective insulating layer 410 transistors 420 transistors 427 Insulating layer 430 transistors 436a Wiring layer 436b wiring layer 437 Insulating layer 440 transistors 505 circuit board 506 Protective insulating layer 507 Gate Insulation Layer 510 transistors 511 Gridgate 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 eBooks 2701 enclosure 2703 Casing 2705 ​​Display section 2707 Display section 2711 Shaft 2721 Power supply 2723 Operation Keys 2725 Speakers 2800 cabinets 2801 enclosure 2802 Display Panel 2803 Speaker 2804 Microphone 2805 Operation Keys 2806 Pointing device 2807 Camera Lens 2808 External connection terminal 2810 solar cells 2811 External memory slot 3001 Main Unit 3002 enclosure 3003 Display section 3004 Keyboard 3021 Main Unit 3022 Stylus 3023 Display section 3024 Operation Buttons 3025 External Interface 3051 Main Unit 3053 Eyepiece 3054 Operation switch 3055 Display section (B) 3056 Battery 3057 Display section (A) 9600 Television equipment 9601 enclosure 9603 Display section 9605 Stand 9630 cabinet 9631 Display section 9632 Operation Keys 9633 Solar Cell 9634 Charge / Discharge Control Circuit 9635 Battery 9636 converter 9637 Converter

Claims

1. It has multiple pixels on which an image signal is written to a capacitor via the channel formation region of a transistor, In a liquid crystal display device, the image signal is written to the pixels less frequently in still image display mode than in video display mode. The aforementioned pixel is A first conductive layer and A first silicon nitride layer having a region above the first conductive layer, A first silicon oxide layer having a region above the first silicon nitride layer, An oxide semiconductor layer having a region above the first silicon oxide layer, A second conductive layer having a region above the oxide semiconductor layer, A third conductive layer having a region above the oxide semiconductor layer, A second silicon oxide layer having a region above the second conductive layer, a region above the third conductive layer, and a region above the oxide semiconductor layer, The present invention comprises a second silicon nitride layer having a region above the second silicon oxide layer, The first conductive layer has a region that functions as the gate electrode layer of the transistor, The first silicon nitride layer has a region in contact with the upper surface of the first conductive layer, The first silicon oxide layer has a region in contact with the upper surface of the first silicon nitride layer, The first silicon nitride layer and the first silicon oxide layer have regions that function as gate insulating layers for the transistor. The oxide semiconductor layer has a region in contact with the upper surface of the first silicon oxide layer, The oxide semiconductor layer has a region that functions as a channel formation region of the transistor, The second conductive layer has a region in contact with the upper surface of the oxide semiconductor layer, The second conductive layer has a region that functions as either the source electrode or the drain electrode of the transistor. The third conductive layer has a region in contact with the upper surface of the oxide semiconductor layer, The third conductive layer has a region that functions as the other of the source electrode or drain electrode of the transistor. The second silicon oxide layer has a region in contact with the upper surface of the second conductive layer, a region in contact with the upper surface of the third conductive layer, and a region in contact with the upper surface of the oxide semiconductor layer. The second silicon nitride layer has a region in contact with the upper surface of the second silicon oxide layer, The oxide semiconductor layer comprises 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 greater film thickness than the first oxide semiconductor layer. The second oxide semiconductor layer has crystals whose c-axis is oriented along a direction perpendicular to the surface of the second oxide semiconductor layer. A liquid crystal display device wherein the proportion of c-axis oriented crystals in the second oxide semiconductor layer is greater than the proportion of c-axis oriented crystals in the first oxide semiconductor layer.

2. In claim 1, The first oxide semiconductor layer has an oxide containing In, Ga, and Zn. The second oxide semiconductor layer comprises an oxide containing In, Ga, and Zn, in a liquid crystal display device.

3. In claim 1, The first oxide semiconductor layer has an In-Ga-Zn-O based oxide semiconductor, The liquid crystal display device has an In-Ga-Zn-O based oxide semiconductor as the second oxide semiconductor layer.

4. In claim 1, The first oxide semiconductor layer has an In-O based oxide semiconductor, The liquid crystal display device has an In-O based oxide semiconductor as the second oxide semiconductor layer.

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