Liquid crystal display device

Abstract

To provide a liquid crystal display device which can display an image in both modes of a reflective mode with external light used as an illumination light source and a transmissive mode using a backlight.SOLUTION: In one pixel, a region (reflection region) where light made incident through a liquid crystal layer is reflected to perform display and a region (transmission region) where light from a backlight is transmitted to perform display are disposed. Therein, image display can be performed in both modes of a reflective mode with external light used as an illumination light source and a transmissive mode with the backlight used as an illumination light source. In addition, two transistors connected to respective different pixel electrode layers are disposed in one pixel and two transistors are separately operated, so that display in the reflection region and display in the transmission region can be independently controlled.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor device having a circuit formed of transistors and a manufacturing method thereof. The present invention relates to electronic equipment incorporating an electro-optical device, typically a liquid crystal display panel, as a component. [Background technology]

[0002] In order to obtain high-quality images in a liquid crystal display device, pixel electrodes are arranged in a matrix. An active matrix transistor is used as a switching element connected to each pixel electrode. Liquid crystal display devices are attracting attention.

[0003] A metal oxide is used as a channel forming region for a switching element connected to each pixel electrode. An active matrix type liquid crystal display device using such a transistor is already known (particularly See Patent Document 1 and Patent Document 2).

[0004] Active matrix liquid crystal displays are broadly divided into two types: transmissive and reflective. The type is known.

[0005] A transmissive liquid crystal display uses a backlight such as a cold cathode fluorescent lamp to optically modulate the liquid crystal. By utilizing this effect, light from the backlight passes through the liquid crystal and is output to the outside of the liquid crystal display device. Select the output state and the non-output state, display light and dark, and combine them. By adjusting the brightness of the display, an image is displayed.

[0006] Transmissive LCD devices use a backlight, so they may not be suitable for use in environments with strong external light, such as outdoors. The display is difficult to read.

[0007] In addition, a reflective liquid crystal display device utilizes the optical modulation effect of liquid crystal to reflect external light, i.e., incident light, onto a screen. The state where the light is reflected by the element electrode and output to the outside of the device, and the state where the incident light is not output to the outside of the device. By selecting the two, light and dark are displayed, and then combining them, an image is displayed. It is something.

[0008] Reflective LCDs, unlike transmissive LCDs, do not use a backlight. Therefore, it has the advantage of consuming little power, and is in high demand as a portable information terminal. I'm waiting.

[0009] Reflective LCD devices use external light, so they are not suitable for displaying images in environments with strong external light, such as outdoors. On the other hand, in a dimly lit environment, i.e. in an environment with low external light, it is difficult to recognize the display. It is difficult to do so. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2007-123861 A [Patent Document 2] JP 2007-96055 A Summary of the Invention [Problem to be solved by the invention]

[0011] To provide a liquid crystal display device which allows image display to be recognized even in a dimly lit environment around the liquid crystal display device. This is one of the challenges.

[0012] In addition, it has both a reflective mode that uses external light as the illumination source and a transmissive mode that uses a backlight. It is an object of the present invention to provide a liquid crystal display device capable of displaying images at high resolution. [Means for solving the problem]

[0013] In one pixel, the area that reflects the light that enters through the liquid crystal layer to display something (reflective area) and a region (transmissive region) through which light from the backlight passes for display. The images are taken in both the reflective mode using external light and the transmissive mode using backlight. In addition, one pixel has two transistors connected to separate pixel electrode layers. A transistor is provided, and the connected transistors are operated separately. The display areas of the pixel electrode layers can be controlled independently.

[0014] When there is external light and the brightness is sufficient, the liquid crystal display device is in a reflective mode. Furthermore, power consumption can be reduced by displaying still images.

[0015] In addition, when the external light is weak or completely absent, the backlight is turned on in the transmissive mode to display an image. Enables display.

[0016] In addition, a sensor is provided to detect the brightness of the surroundings of the liquid crystal display device, and the data obtained by the sensor is Depending on the data, it can be set to reflective mode, transmissive mode, or the backlight can be turned on and off and the light intensity can be adjusted. It is preferable to do so.

[0017] As a backlight source, it consumes less power than a cold cathode fluorescent lamp and can adjust the intensity of the light. It is preferable to use multiple light emitting diodes (LEDs) that can be adjusted. By using D, the intensity of light can be adjusted partially, the contrast is large, and the visibility of the color is improved. It is possible to provide high quality image display.

[0018] One embodiment of the present invention disclosed in this specification is a display panel, a backlight unit, and an image processing circuit. The display panel has a light-transmitting property and is connected to the first scanning lines and the first signal lines. A first system of pixel electrodes that control the alignment state of the liquid crystal are connected to the first system of pixel electrodes. a first sub-pixel having a transistor for reflecting visible light; A second system of pixel electrodes that are connected to the scanning lines and the second system of signal lines and control the alignment state of the liquid crystal. and a transistor connected to a pixel electrode of the second system. A first driving circuit for controlling a pixel unit including a plurality of pixels including the pair of the first driving circuit and the plurality of pixels in time The backlight unit includes a plurality of light-emitting elements and a second light-emitting device for controlling the plurality of light-emitting elements in time. The image processing circuit has a memory circuit for storing an image signal and a drive circuit for storing the image signal. A comparison circuit is provided for comparing the image signals and calculating a difference, and the comparison circuit detects the difference. The consecutive frame periods are determined to be a moving image period, and the image processing circuit outputs the first system of the display panel. A first signal including a moving image is output to the signal line of the integrated circuit, and the image processing circuit outputs a first image to the backlight unit. A video mode that outputs a second signal that is synchronized with the signal, and a video mode where the comparator detects no difference. The frame period following the still image is determined to be a still image period, and the image processing circuit outputs a still image during the still image period. The image processing circuit converts the image data into a black and white still image and transmits the black and white still image to the second signal line of the display panel. and outputting a first signal including the first pixel signal to the backlight unit, the image processing circuit stopping the output of the signal to the backlight unit. This is a liquid crystal display device that has a still image mode.

[0019] Another embodiment of the present invention disclosed in this specification is a display panel, a backlight unit, and an image processing a first scanning line and a second scanning line; A first system of pixel electrodes is connected to the signal lines of the first system of pixels, and controls the alignment state of the liquid crystal. a first system sub-pixel including a transistor connected to the pixel electrode; and a second system sub-pixel including a first pixel that reflects visible light. A second pixel is connected to the second scanning line and the second signal line to control the alignment state of the liquid crystal. a second pixel electrode including a first pixel electrode and a transistor connected to a second pixel electrode; A plurality of pixels including pairs of sub-pixels of a system, and a first control circuit for controlling a pixel unit including the plurality of pixels in a time-dependent manner. The backlight unit includes a plurality of light-emitting elements and a driving circuit for driving the plurality of light-emitting elements in a time-dependent manner. the image processing circuit has a memory circuit for storing an image signal; A comparison circuit is provided for comparing the image signals stored in the memory circuit and calculating a difference, The consecutive frame periods where the difference is detected are judged to be moving image periods, and the image processing circuitry A first signal including a moving image is output to the first signal line of the panel, and the image processing circuit detects the backlight. A video mode in which a second signal synchronized with the first signal is output to the video input section, and a comparison circuit detects the difference between the first and second signals. The continuous frame period in which no image is detected is determined to be a still image period, and the image processing circuit The still image of the period is converted into a black and white still image, and the image processing circuit outputs the second signal line of the display panel. The image processing circuit outputs a first signal including a black and white still image to the backlight unit. The camera has a still image mode that stops the power supply, and the still image mode is activated according to the brightness of the external light detected by the photometry circuit. It is a liquid crystal display device that adjusts the brightness when switching between video and still images using a backlight. do.

[0020] Another embodiment of the present invention disclosed in this specification is a display panel, a backlight unit, and an image processing a display panel having a light-transmitting property and a first scanning line and a first signal line; The first system of pixel electrodes is connected to the first system of pixel electrodes, which control the alignment state of the liquid crystal. a first-system sub-pixel including a transistor including an oxide semiconductor layer connected to the first sub-pixel; It reflects visible light, is connected to the second scanning line and the second signal line, and controls the alignment state of the liquid crystal. A transistor including a second pixel electrode for controlling the second pixel electrode and an oxide semiconductor layer connected to the second pixel electrode. a plurality of pixels including a pair of sub-pixels of a second system having a transistor; A first driver circuit for controlling a pixel portion including a plurality of light emitting diodes is provided. a second drive circuit that controls the light emitting elements of the backlight unit in a time-dependent manner; The image processing circuit compares the image signal stored in the memory circuit with the image signal stored in the memory circuit. A comparison circuit is provided for calculating a difference between the adjacent frames. The image processing circuit judges that the period is a moving image period and outputs a moving image to the first signal line of the display panel. The image processing circuit outputs a first signal including a first pixel, and the image processing circuit outputs a second pixel to the backlight unit in synchronization with the first signal. The video mode outputs a signal and the comparison circuit detects consecutive frame periods during which no difference is detected. It is determined that it is a still image period, and the image processing circuit converts the still image data during the still image period into a black and white still image. The image processing circuit converts the first signal including a black and white still image into a second signal line of the display panel. The image processing circuit outputs a signal to the backlight unit, and the still image display mode is selected. The liquid crystal display device has the above structure.

[0021] The above configuration solves at least one of the above problems.

[0022] In addition, a plurality of structures are provided in one pixel, a reflective electrode is provided on the side surface of the structure, and It is also one aspect of the present invention to use a pixel electrode having a transparent electrode therein.

[0023] In addition, a liquid crystal display device disclosed in the present specification and further comprising a solar cell, The panel can be opened and closed freely, and the power from the solar cell is used for the display panel, backlight, and can provide electronic equipment that supplies the image processing circuitry.

[0024] In this specification, the term "semiconductor" refers to any device that can function by utilizing semiconductor properties. Electro-optical devices, semiconductor circuits, and electronic equipment are all considered to be semiconductor devices. can. Effect of the Invention

[0025] It is possible to provide a liquid crystal display device capable of displaying images in accordance with various environments with different external light brightnesses. It is also possible to achieve low power consumption when displaying still images. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a block diagram illustrating one embodiment of a liquid crystal display device. [Diagram 2] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Diagram 3] 1A to 1C illustrate one mode of a driving method of a liquid crystal display device. [Figure 4] 1A to 1C illustrate one mode of a driving method of a liquid crystal display device. [Diagram 5] 1A to 1C illustrate one mode of a driving method of a liquid crystal display device. [Figure 6] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 7] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 8] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 9] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 10]1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 11] 1A to 1C illustrate one mode of a transistor that can be used in a liquid crystal display device. [Figure 12] 1A to 1C illustrate one mode of a manufacturing method of a transistor that can be used in a liquid crystal display device. [Figure 13] 1A to 1C are diagrams illustrating one embodiment of an electronic device. [Figure 14] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 15] 1A and 1B illustrate one embodiment of a liquid crystal display device. [Figure 16] 1A and 1B illustrate one embodiment of a liquid crystal display device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following description, and those skilled in the art will recognize that the present invention may be modified in various ways in form and detail. The present invention is not limited to the description of the following embodiments. It is not something that can be done.

[0028] (Embodiment 1) In this embodiment, a liquid crystal display device having a still image mode and a moving image mode will be described with reference to FIG. In this specification, the image signal input to the display device is a still image. The operation that is performed after determining that the camera is still is called still image mode, and the operation that is performed after determining that the camera is a video is called video mode. It shall be so.

[0029] The liquid crystal display device 100 of this embodiment includes an A / D conversion circuit 102, an image processing circuit 110, a display The display device includes a display panel 120 and a backlight unit 130 (see FIG. 1).

[0030] The image processing circuit 110 includes a memory circuit 111, a comparison circuit 112, a selection circuit 115, a display control circuit 113, and a field sequential signal generating circuit 114.

[0031] The display panel 120 includes a driver circuit 121 and a pixel portion 122. The pixel 123 has a first pixel connected to a first scanning line and a first signal line. A pair of sub-pixels 123a and a pair of sub-pixels 123b connected to a scanning line and a signal line of a second system are connected to the pair of sub-pixels 123a and a pair of sub-pixels 123b connected to a scanning line and a signal line of a second system. The second system includes the sub-pixels 123a and 123b. are arranged in pairs in a matrix in the pixel section 122 as pixels 123.

[0032] The sub-pixel 123a includes a first transistor and a pixel connected to the first transistor. The pixel electrode and the counter electrode facing the pixel electrode are sandwiched between the pixel electrode and the counter electrode. A liquid crystal element is formed by supporting the pixel electrode, and the pixel electrode has a light transmitting property. In this case, an electrode that is transparent and transmits visible light is called a transmissive electrode or a transparent electrode. .

[0033] The sub-pixel 123b includes a second transistor and a pixel connected to the second transistor. The pixel electrode and the counter electrode facing the pixel electrode are sandwiched between the pixel electrode and the counter electrode. A liquid crystal element is formed by supporting the pixel electrodes, and the pixel electrodes reflect light incident thereon through the liquid crystal layer.

[0034] An example of a liquid crystal element is a device that controls the transmission or non-transmission of light by the optical modulation action of liquid crystal. The element can be constructed by a pair of electrodes and a liquid crystal layer. The optical modulation of the liquid crystal is controlled by the electric field (i.e., the vertical electric field) applied to the liquid crystal. Specifically, examples of liquid crystal elements include nematic liquid crystal, cholesteric liquid crystal, Smectic liquid crystal, discotic liquid crystal, thermotropic liquid crystal, lyotropic liquid crystal, Low molecular weight liquid crystal, polymer liquid crystal, polymer dispersed liquid crystal (PDLC), ferroelectric liquid crystal, antiferroelectric liquid crystal, Examples of liquid crystals include main chain type liquid crystals, side chain type polymer liquid crystals, and banana type liquid crystals. The operating method is TN (Twisted Nematic) mode, STN (Super Twisted Nematic mode, OCB (Optically Compe nsated birefringence mode, ECB (Electricall y Controlled Birefringence mode, FLC (Ferro electric Liquid Crystal) mode, AFLC (AntiFer polymeric Liquid Crystal (PDLC) mode, er Dispersed Liquid Crystal) mode, PNLC (Pol ymer Network Liquid Crystal) mode, guest host mode Examples include .

[0035] The backlight unit 130 includes a backlight control circuit 131 and a backlight 132. The backlight 132 has light emitting elements 133 arranged therein.

[0036] In this embodiment, the backlight 132 has a plurality of light emitting elements 133 that emit light of different colors. A combination of different luminous colors is, for example, red (R), green (G), and blue (B). Three types of light-emitting elements can be used. By using the three primary colors R, G, and B, It can display color images.

[0037] In addition, colors can be expressed by simultaneously illuminating multiple R, G, and B light-emitting elements (for example, (Yellow (Y) is represented by R and G, Cyan (C) is represented by G and B, Magenta (M) is represented by B and R, etc.) Another light-emitting element emitting R, G, and B may be disposed in addition to the R, G, and B light-emitting elements.

[0038] In addition, in order to enrich the color reproduction characteristics of the display device, light emitting elements that emit light other than the three primary colors are used. The colors that can be expressed using R, G, and B light-emitting elements are shown in the chromaticity diagram. The colors are limited to those shown inside the triangle drawn by the three points corresponding to the luminous colors of the By adding additional light-emitting elements arranged outside the triangle, the color reproduction characteristics of the display device can be improved. It can be done.

[0039] For example, from the center of the chromaticity diagram, radians outward toward the point on the chromaticity diagram that corresponds to blue light-emitting element B. Deep Blue (DB) is a color represented by a coordinate point located at the center of the chromaticity diagram. At a certain coordinate point on the chromaticity diagram that corresponds to the red light-emitting element R, The light emitting element emitting a deeper red (Deep Red: DR) than that shown in FIG. Can be used in addition to the 32 R, G, and B.

[0040] Next, a signal flow in the display device exemplified in this embodiment will be described.

[0041] An analog image signal 140 is input from an image signal source 101 to a liquid crystal display device 100. The analog image signal includes image signals, e.g., red (R), green (G), and blue (B) signals. Contains the signal.

[0042] The A / D conversion circuit 102 converts the analog image signal into a digital image signal 141 (digital image signal The image signal is converted to a digital signal and output to the image processing circuit 110. By converting the image signals in advance, it is possible to easily detect the difference in the image signals later. It is appropriate.

[0043] The image processing circuit 110 converts the input digital image signal Data into an LC image signal 142 and a The LC image signal 142 controls the display panel 120. The backlight signal 143 is a signal for controlling the backlight unit 130. .

[0044] The memory circuit 111 provided in the image processing circuit 110 stores image signals relating to a plurality of frames. The number of frame memories in the memory circuit 111 is is not particularly limited, and is an element capable of storing image signals relating to a plurality of frames. The frame memory may be, for example, a dynamic random access memory (DRAM). ccess Memory), SRAM (Static Random Access The memory may be configured using a memory element such as a memory.

[0045] The frame memory may be configured to store an image signal for each frame period. The number of frame memories is not particularly limited. It is selectively read out by a comparison circuit 112 and a display control circuit 113 .

[0046] The comparison circuit 112 selects image signals of successive frame periods stored in the memory circuit 111. The image signals of consecutive frames are compared pixel by pixel to detect the difference. This is a circuit for outputting the signal.

[0047] Depending on whether or not a difference is detected, the operation of the display control circuit 113 and the selection circuit 115 is determined. By comparing the image signals in the comparator circuit 112, a difference is detected in any pixel. When the difference is detected, the consecutive frame period in which the difference is detected is determined to be a video period. On the other hand, when the comparison circuit 112 compares the image signals, no difference is detected in any of the pixels. A continuous frame period in which the difference is not detected when the difference is detected is determined to be a still image period. That is, the comparison circuit 112 compares the image signals of successive frame periods with By detecting the difference, it is possible to determine whether the signal is an image signal for displaying a moving image or a still image. The purpose of the present invention is to determine whether the image signal is for

[0048] In addition, when the difference obtained by the comparison exceeds a certain level, it is considered that a difference has been detected. The comparison circuit 112 may be set to determine whether the difference is large or small. The detection of the difference may be determined based on the absolute value of the difference.

[0049] In this embodiment, the comparison circuit 112 compares image signals in successive frame periods. We have shown a configuration in which the difference between the two images is detected to determine whether the image is a video or a still image. By supplying a signal to switch between still images or videos from the The display may be configured to display a moving image or a still image depending on the display mode.

[0050] Video is created by switching between multiple frames of images at high speed, which is time-divided into multiple frames. Specifically, for example, an image that moves 60 times per second (60 frames) By switching between images at least one frame, the human eye perceives it as a video with less flicker. On the other hand, still images are different from video images in that they are divided into multiple frames. Although it is operated by switching at high speed, in consecutive frame periods, for example, the nth frame, This refers to an image signal that does not change from the (n+1)th frame onwards.

[0051] The selection circuit 115 includes a plurality of switches, for example, switches formed of transistors. When a difference is detected by the difference calculation in the comparison circuit 112, that is, when consecutive When the image displayed between frames is a moving image, the image signal is stored in the memory circuit 111. This is a circuit for selecting an image signal from the frame memory and outputting it to the display control circuit 113. do.

[0052] When the comparison circuit 112 does not detect a difference between the image signals by calculation, the selection circuit 115 That is, when the image displayed between successive frames is a still image, the image signal is displayed. This is a circuit that does not output to the control circuit 113. In the case of a still image, the selection circuit 115 selects By configuring the display control circuit 113 not to output from the frame memory, power consumption is reduced. It can be reduced.

[0053] In the display device of this embodiment, the comparison circuit 112 judges the image to be a still image and performs a moving image. An operation performed when the comparator circuit 112 judges the image to be a moving image is called a still image mode, and an operation performed when the comparator circuit 112 judges the image to be a moving image is called a moving image mode.

[0054] The image processing circuit exemplified in this embodiment may have a mode switching function. The mode switching function is performed by the user of the display device either manually or by using an external device. A function for switching between a moving image mode and a still image mode by selecting an operation mode of the display device. It is Noh.

[0055] Therefore, the display device exemplified in this embodiment may have a mode switching circuit. The mode switching circuit is connected to the selection circuit 115. The user of the display device can switch the operation mode of the display device manually or using an external device. It is an input means for obtaining information.

[0056] The selection circuit 115 controls the display of the image signal in response to the signal input from the mode switching circuit. It can also be output to the circuit 113.

[0057] For example, when the device is operating in still image mode, the user may switch the operating mode and When a mode switching signal is input from the switching circuit to the selection circuit 115, the comparison circuit 112 Even if the selection circuit does not detect a difference between image signals in successive frame periods, 115 is a mode in which input image signals are sequentially output to the display control circuit 113, i.e., a moving image Also, when the camera is in video mode, the user can switch the operation mode. Instead, when a mode switching signal is input from the mode switching circuit to the selection circuit 115, In the case where the comparator circuit 112 detects the difference between the image signals in successive frame periods, However, the selection circuit 115 is in a mode of outputting only the image signal of the selected one frame. That is, the display device of the present embodiment can execute a still image mode. When operating in mode, one frame of an image that is divided into multiple frames is a still image. is displayed as:

[0058] The display control circuit 113 is a display control circuit for controlling a display selected by the selection circuit 115 in response to the detection of the difference by the comparison circuit 112. The circuit optimizes the image signal received by the display panel 120 and the backlight unit 130. do.

[0059] For example, even if the digital image signal 141 is made up of R, G, and B signals, The image signal is optimized according to the light emission characteristics of the R, G, and B light emitting elements of the CRT 132. It is preferable to use light emitting elements other than R, G, and B in the backlight 132. When provided, the display control circuit 113 converts the signal for driving the light emitting element from the original image signal. and optimizes the color reproduction characteristics of the display device.

[0060] For example, a digital image signal Data(1) consisting of R, G, and B is converted into R, G, B, DR A digital image signal Da suitable for the backlight 132 having five color light emitting elements of When converting the original digital image signal Data(1 ) to generate a digital image signal Data(2) expressed using light-emitting elements DR and DB. At the same time, the original digital image signal Data(1) is generated using the light emitting elements DR and DB. The digital image signal Data(2) is subtracted from the digital image signal Data( 3) is generated. Then, a digital image signal D ata(2) and a digital image signal Data( 3) A backlight 132 having light emitting elements of five colors R, G, B, DR, and DB. The digital image signal Data(4) is generated based on the optimized image quality.

[0061] The display device exemplified in this embodiment includes a first system of sub-pixels connected to a first system of signal lines. The second system of sub-pixels 123a and the second system of sub-pixels 123b are connected to the second system of signal lines. Then, the display control circuit 113 determines the signal line to which the image signal is output.

[0062] Specifically, when the comparison circuit 112 judges that the image is a moving image, the display control circuit 113 outputs an image signal to the sub-pixels 123a of the first system, and if the comparator circuit 112 determines that the image is a still image, The image signal is output to the sub-pixels 123b of the second system.

[0063] The field sequential signal generating circuit 114 outputs the image signal generated by the display control circuit 113. Based on the signal, the driving circuit 121 of the display panel 120 and the backlight of the backlight unit 130 are This is a circuit for controlling the output control circuit 131.

[0064] The field sequential signal generating circuit 114 also includes a display panel 120 and a backlight. A start pulse SP for synchronizing the start unit 130 and a control signal such as a clock signal CK are supplied. It is also a circuit for controlling switching on and off.

[0065] Next, the field sequential signal generating circuit 114 outputs a driving circuit 1 21, and a method for controlling the backlight control circuit 131 of the backlight unit 130 The operation of the field sequential signal generating circuit 114 is as follows. The operation differs depending on whether the image is judged to be a still image or not. The backlight 132 includes R, G, and B light-emitting elements (specifically The lighting fixture shall have an LED.

[0066] First, the field sequential signal generation circuit when the comparison circuit 112 judges that the image is a moving image The operation of the field sequential signal generating circuit 114 will be described. The image signal containing the image is processed in video mode. The signal generating circuit 114 converts the image signals optimized by the display control circuit 113 into The image is compressed by 1 / (3n) times. Note that n is the number of subframes that one frame is divided into. The value of n is the same as that used when the time axis is compressed by 1 / (3n) times. A field sequential color image signal corresponding to R, G, and B (for example, R1, G1 , B1, R2, G2, B2) are supplied to the driving circuit 121.

[0067] The field sequential signal generating circuit 114 also generates a backlight signal 143. The backlight signal 143 is supplied to the R The signals are used to light up the R, G, and B light-emitting elements. This signal is paired with the sequential color image signal.

[0068] The display panel 120 and the backlight unit 130 are also configured to generate a field sequential signal. It operates in synchronization with the sync signal generated by circuit 114 to display moving images.

[0069] On the other hand, if the comparator circuit 112 judges the image signal to be a still image, the field sequential signal The signal generating circuit 114 does not generate a field sequential color image signal, but generates a single frame The still image data is supplied to a drive circuit 121 of a display panel 120 .

[0070] Then, the field sequential signal generating circuit 114 outputs a signal to the driving circuit 121 and the back The supply of image signals and each control signal to the light control circuit 131 is stopped.

[0071] The display device exemplified in the embodiment may have a photometry circuit. The display device can detect the brightness of the environment in which the display device is placed. The display control circuit 113 connected to the circuit controls the display panel in response to a signal input from the photometry circuit. The driving method of the panel 120 can be changed.

[0072] For example, the photometry circuit may be used when the display device exemplified in this embodiment is used in a dim environment. When this is detected, the display control circuit 113 performs a Even if the pixel is a pixel, the image signal is output to the sub-pixels 123a of the first system, and the backlight 132 is turned on. Since the sub-pixels 123a of the first system have light-transmitting pixel electrodes, they are illuminated by the backlight. It is possible to provide still images with high visibility.

[0073] In addition, for example, the photometry circuit may detect the brightness of the display device exemplified in this embodiment under extremely bright external light ( When it is detected that the display is being used outdoors (for example, under direct sunlight), the display control circuit 113 Even if the comparator circuit 112 judges that the image signal is a moving image, the image signal is not output to the sub-pixel 123 of the second system. The second system sub-pixel 123b is a pixel that reflects light incident through the liquid crystal layer. The electrodes provide still and video images with high visibility even under extremely bright outdoor light. Can be provided.

[0074] During the period when a still image is displayed according to the configuration of this embodiment, image signals are frequently written. This can reduce the number of operations such as the above. It also displays still images without using the backlight. Therefore, the power consumption is extremely small.

[0075] In addition, the display device exemplified in this embodiment can display a still image while reducing power consumption. In addition, it is possible to display full-color images and videos without using color filters. Yes, it is possible. Because the color filter does not absorb the light from the backlight, the light utilization efficiency is high. Power consumption is also reduced when displaying full-color images and moving images.

[0076] In addition, when viewing an image obtained by writing image signals multiple times, the image is switched multiple times. Therefore, the human eye will perceive the image as fatigue. As described in the present embodiment, the number of times that the image signal is written is reduced. This also has the effect of reducing eye fatigue.

[0077] Note that this embodiment mode can be appropriately combined with other embodiment modes described in this specification. .

[0078] (Embodiment 2) In this embodiment mode, a method for driving a liquid crystal display device will be described with reference to a pixel connection diagram, a timing chart, and the like. First, FIG. 2 shows a schematic diagram of a display panel of a liquid crystal display device. FIG. 2 shows a pixel portion 151, a first scanning line 152 (also called a gate line), a first signal line 153 (also called data line), second scanning line 154, second signal line 155, pixel 156 , a common electrode 169 (also called a common electrode), a capacitance line 170, and a first scanning line driver circuit 157 , a first signal line driver circuit 158, a second scanning line driver circuit 159, and a second signal line driver circuit 1 It has 60.

[0079] The pixel 156 is roughly divided into a transmissive electrode section 161 and a reflective electrode section 162. The pixel transistor 163, the liquid crystal element 164, and the capacitor element 165. The gate of the transistor 163 is connected to the first scanning line 152, and the third transistor is either the source or the drain. One terminal is connected to the first signal line 153, and the second terminal which is the other of the source and the drain is One electrode of the liquid crystal element 164 and a first electrode of the capacitor element 165 are connected to each other. The other electrode of the capacitor 164 is connected to a common electrode 169. The electrode is connected to a capacitance line 170 .

[0080] The reflective electrode section 162 includes a pixel transistor 166, a liquid crystal element 167, and a capacitance element 168. The pixel transistor 166 has a gate connected to the second scan line 154 and a source or The first terminal, which is one of the drains, is connected to the second signal line 155, and the The other second terminal is connected to one electrode of the liquid crystal element 167 and a first electrode of the capacitor element 168. The other electrode of the liquid crystal element 167 is connected to a common electrode 169. A second electrode of the capacitance element 168 is connected to a capacitance line 170 .

[0081] In FIG. 2, the first scanning line 152 and the second scanning line 154 are connected to a first scanning line driving circuit. The first signal line 157 and the second scanning line driver circuit 159 are driven separately. 53 and the second signal line 155 are connected to a first signal line driver circuit 158 ​​and a second signal line driver circuit 160 supplies separate image signals (hereinafter referred to as first data and second data) The liquid crystal element 164 of the transmissive electrode portion 161 and the liquid crystal element 16 of the reflective electrode portion 162 are In 7, gradation control is performed based on different image signals.

[0082] The pixel transistor 163 and the pixel transistor 166 each have a thin oxide semiconductor layer. It is preferable that the pixel electrode is configured by a thin film transistor (hereinafter also referred to as TFT).

[0083] A thin film transistor has at least three terminals including a gate, a drain, and a source. A channel region is provided between the drain region and the source region. A current can be passed through the drain region, the channel region, and the source region. The source and drain depend on the transistor structure and operating conditions, so it is unclear which is the source and which is the drain. Therefore, it is difficult to determine whether the device is a source or a drain. In the claims or drawings, the regions functioning as the source and drain are In some cases, the term "source" or "drain" is not used. In such cases, for example, They may be referred to as the first terminal and the second terminal, respectively. Alternatively, they may be referred to as a source region and a drain region.

[0084] The first scanning line driver circuit 157, the first signal line driver circuit 158, and the second scanning line driver circuit The second signal line driver circuit 160 and the pixel portion 151 are provided on the same substrate. However, it is not necessary to provide the pixel section 151 on the same substrate. A first scanning line driver circuit 157, a first signal line driver circuit 158, a second scanning By providing the scan line driver circuit 159 and the second signal line driver circuit 160, the number of connection terminals with the outside can be reduced. This can reduce the size of the liquid crystal display device.

[0085] The pixels 156 are arranged (arranged) in a matrix. The term "arranged in a straight line" means that the pixels are arranged in a straight line in the vertical or horizontal direction. This includes cases where the characters are arranged in a square pattern or on a jagged line.

[0086] In addition, when it is explicitly stated that A and B are connected, it means that A and B are electrically connected. A and B are connected functionally, A and B are directly connected, This includes cases where

[0087] Next, the operation of the display panel will be explained together with the operation of the backlight with reference to FIG. As explained in the above embodiment, the operation of the display panel can be broadly divided into the display of moving images and the The period is roughly divided into a display period 301 and a still image display period 302 .

[0088] In addition, the cycle (or frame frequency) of one frame period in the moving image display period 301 is It is preferable to have a frame rate of 1 / 60 seconds or less (60Hz or more). This prevents the viewer from noticing flickering in the image. In the image display period 302, the cycle of one frame period is extremely long, for example, one minute or more (0. 017Hz or less), compared to switching the same image multiple times. It is also possible that eye strain can be reduced.

[0089] The pixel transistor 163 and the pixel transistor 166 are formed of an oxide semiconductor. When using the above, the off-current can be reduced. The retention time of the electric signal can be extended, and the writing interval can be set to be longer. The cycle of one frame period can be lengthened, and the refresh operation during the still image display period 302 can be shortened. This reduces the frequency of operations, thereby further reducing power consumption.

[0090] In the moving image display period 301 shown in FIG. 3(A), as described in the above embodiment, A driving circuit control signal for displaying a moving image by a first scanning line driving A signal is supplied to a first signal line driver circuit 157 and a first signal line driver circuit 158 ​​(hereinafter referred to as a first driver circuit). A driving circuit control signal for displaying black in each pixel is sent to the second scanning line driving circuit 159 and The signal is supplied to a second signal line driver circuit 160 (hereinafter referred to as a second driver circuit) and In the moving image display period 301 shown in FIG. A backlight signal 143 for color display by the blinking sequential drive is generated. The backlight is then turned on, and the display panel starts to display color. It is possible to display the image.

[0091] In the still image display period 302 shown in FIG. 3A, as described in the above embodiment, the reflected light The black and white gradation (indicated as BK / W in the figure) is expressed by the transparency or non-transparency of A drive circuit control signal for writing an image signal of a picture is supplied to the second drive circuit, The second driving circuit is operated during a period other than when the image signal is written. By deactivating the control signal, it is possible to reduce power consumption. In the still image display period 302, the display is visually recognized by utilizing reflected light from outside. The backlight control signal disables the backlight, and the display panel switches between black and white. It is possible to display still images in a variety of tones.

[0092] Next, in regard to the moving image display period 301 in FIG. 3(A), a still image display period 302 is shown in FIG. 3(B). The details of this will be explained using a timing chart in FIG. 3(C). The timing charts shown in FIG. 3(C) and FIG. 3(D) are exaggerated for the purpose of explanation. Please note that unless otherwise specified, the signals do not operate synchronously.

[0093] First, FIG. 3B will be described. In FIG. 3B, during a moving image display period 301, The clock signal supplied to the first scanning line driving circuit 157 and the second scanning line driving circuit 159 in the Signal GCK (GCK1,2 in the figure), and start pulse GSP (GSP1,2 in the figure), The clock signal S supplied to the first signal line driving circuit 158 ​​and the second signal line driving circuit 160 CK (SCK1,2 in the figure), start pulse SSP (SSP1,2 in the figure), The first data, the second data, and the backlight illumination state are shown. The backlight is an example of a plurality of light-emitting elements, and is configured to sequentially light up three colors of RGB. The backlight uses LEDs, which consumes less power. It is possible to increase the power output and extend the service life.

[0094] During the moving image display period 301, the clock signals GCK1 and GCK2 are constantly supplied. The start pulses GSP1 and GSP2 are pulses that correspond to the vertical sync frequency. The clock signals SCK1 and SCK2 are always supplied. SSP1 and SSP2 are pulses corresponding to one gate selection period. In order to display video in a field sequential manner, the image signal is first sent to the camera for displaying R (red). Then, the R backlight is turned on, and then the G (green) display is turned on. Then, write to each pixel, turn on the G backlight, and then display B (blue). The image signal is varied by repeatedly writing to each pixel and then turning on the backlight of B. By doing so, the viewer can visually recognize the color display in the video. In the example of 01, the second data is an image signal for displaying the gradation of BK (black), and pixel 1 The second data is written to the reflective electrode portion 162 of the pixel 56. By converting the image signal into an image signal, the reflective electrode portion 162 is irradiated with external light. This causes light leakage. This can improve the problem of visibility of the moving image of the transparent electrode portion 161, that is, the visibility is reduced. Cut.

[0095] Next, FIG. 3C will be described. In FIG. 3C, for the still image display period 302, The still image writing period 303 and the still image holding period 304 will be described separately.

[0096] In the still image writing period 303, the clock supplied to the second scanning line driving circuit 159 is The signal GCK2 is a clock signal for writing one screen. The second scanning line driving circuit 1 The start pulse GSP2 supplied to 59 is a pulse for writing one screen. The clock signal SCK2 supplied to the signal line driver circuit 160 is a clock for writing one screen. A start pulse SSP2 is supplied to the second signal line driving circuit 160. This is a pulse for writing one screen. In the still image writing period 303, reflected light is used. A still image is displayed by the image signal BK / W for displaying black and white gradation. The backlight for display is turned off.

[0097] In the still image holding period 304, a first driving circuit and a second driving circuit are driven by Clock signals GCK1,2, start pulses GSP1,2, clock signals SCK1,2, The supply of start pulses SSP1 and SSP2 is stopped. In the case of the stationary type, the power consumption can be reduced, and the power consumption can be reduced. In the image holding period 304, the image signal written to the pixel in the still image writing period 303 is turned off. The current is maintained by pixel transistors with extremely small currents, so a still image displayed in color can be displayed for one minute. The still image can be held for the above period. Also, the still image holding period 304 is held in the capacitor. Before the image signal changes due to the passage of a certain period, a new still image writing period 303 is started. Then, write the same image signal as the previous period (refresh operation) and write a still image again. This may be set as the retention period 304 .

[0098] The liquid crystal display device described in this embodiment aims to reduce power consumption when displaying a still image. It is possible.

[0099] This embodiment can be implemented in appropriate combination with the configuration described in the first embodiment. be.

[0100] (Embodiment 3) In this embodiment, a configuration different from the driving method of the liquid crystal display device described in the second embodiment is used. The above embodiment will be described with reference to a timing chart. The timing chart shows the backlight driving method during the moving image display period 301 described in 2. Show and explain the example.

[0101] The difference between the timing chart in FIG. 4(A) and FIG. 3(B) is that after the image signal is written, In addition, a backlight off period (BL in FIG. 4(A)) is provided after the backlight is turned on. The point is to provide a period during which the backlight is turned off before writing the next image signal. This can reduce color flicker and improve visibility.

[0102] A configuration different from that of FIG. 4(A) is shown in FIG. 4(B). The difference between this and Fig. 4(A) is that instead of the backlight off period BL, the backlight is lit during the B (blue) light emission period. The advantage of this is that a blue light emission period is provided before the next image signal is written. As with the case where the lights are turned off during a period of time, it is possible to reduce color flickering and improve visibility. Cut.

[0103] In the second embodiment, RGB light-emitting elements are used as an example of the light-emitting elements used in the backlight. Although the example using the three colors has been described, other configurations may be used. As shown in FIG. 1, the backlight may be controlled using five color light emitting elements 311. .

[0104] The light emitting element 311 shown in FIG. 5A includes, as an example, a first red light emitting element R1, a second red light emitting element R2, and a Regarding the light emitting element R2, the green light emitting element G, the first blue light emitting element B1, and the second blue light emitting element B2, Next, in FIG. 5(B), the above-mentioned embodiment is shown in the same manner as in FIG. 4(A) and (B). When the backlight is turned on as shown in FIG. 5(A) during the moving image display period 301 described in the second embodiment, The control will now be described.

[0105] In FIG. 5B, the first red image signal is written as the backlight illumination, following the writing of the R image signal. The first color light emitting element R1 and the first blue light emitting element B1 are turned on. Also, the G image signal is written. The backlight is turned on only when the green light emitting element G and the second blue light emitting element B2 are turned on. In addition, the first blue signal is used as the backlight light following the writing of the B image signal. The first blue light emitting element B1 and the second blue light emitting element B2 are turned on. Next, the R image signal is written. Following this, the second red light emitting element R2 and the second blue light emitting element R3 are turned on to light up the backlight. The backlight is turned on after the G image signal is written. The green light emitting element G and the first blue light emitting element B1 are turned on. Following this, the second blue light emitting element B2 and the first blue light emitting element B3 are turned on to turn on the backlight. Turn on child B1.

[0106] By using the configuration of FIG. 5B, the blue light emission period occurs during the period when the RGB color elements are switched. Since the first red light emitting element can be provided, the same effect as that of FIG. Element R1 and second red light emitting element R2, first blue light emitting element B1 and second blue light emitting element B2 It is also possible to use light-emitting elements made of materials with different color coordinates, The range of color expression can be expanded.

[0107] The liquid crystal display device described in this embodiment aims to reduce power consumption when displaying a still image. It is possible.

[0108] This embodiment can be implemented in appropriate combination with the configuration described in the first embodiment. be.

[0109] (Embodiment 4) 6 shows the configuration of the liquid crystal display module 190. The liquid crystal display module 190 has a backlight. a display unit 130, a display panel 120 in which liquid crystal elements are arranged in a matrix, and a display panel 1 The backlight unit 130 has a polarizing plate 125a and a polarizing plate 125b sandwiching the polarizing plate 20. Light elements, such as three primary color LEDs (133R, 133G, and 133B) arranged in a matrix A diffusion plate 134 is disposed between the display panel 120 and the light emitting element. It can be used as the light emitting part 130. In addition, the FPC (flexible printed circuit board) which is the external input terminal can be used as the light emitting part 130. The printed circuit 126 is electrically connected to a terminal portion provided on the display panel 120. There are.

[0110] In FIG. 6, three colors of light 135 are shown by arrows (R, G, and B). The pulsed lights of different colors are sequentially emitted from the light source unit 130 in synchronization with the backlight unit 130. The liquid crystal display module 190 modulates the light emitted by the liquid crystal elements of the display panel 120 that operate in conjunction with the liquid crystal display module 190. The light emitted sequentially reaches the observer, who perceives the light as an image.

[0111] In addition, in FIG. 6, external light 139 passes through the liquid crystal element on the display panel 120 and is reflected by the lower electrode. The intensity of the light passing through the liquid crystal element is controlled by the image signal. Since the image is modulated by the reflected light of the outside light 139, the observer can also capture the image. .

[0112] FIG. 7(A) is a plan view of the display area, and FIG. 7(B) is an equivalent circuit, showing one pixel. FIG. 8 is a cross-sectional view taken along lines V1-V2, W1-W2, and X1-X2 in FIG. 7(A). FIG.

[0113] In FIG. 7, a plurality of source wiring layers (source electrode layers or drain electrode layers 555b, 565 b) are arranged parallel to each other (extending in the vertical direction in the figure) and spaced apart from each other. The gate wiring layers (including the gate electrode layer 551) are arranged in a direction substantially perpendicular to the source wiring layers. The capacitance wiring layers are arranged so as to extend in the direction (left and right direction in the figure) and are spaced apart from each other. The gate wiring layers are arranged adjacent to each other, and are approximately parallel to the gate wiring layers. The source wiring layer 14 extends in the row direction, that is, in a direction substantially perpendicular to the source wiring layer (the left-right direction in the figure).

[0114] The liquid crystal display device of FIG. 7 and FIG. 8 is a semi-transmissive liquid crystal display device, and the pixel region is a reflective region 49 The reflective area 498 is made up of a reflective electrode as a pixel electrode layer. A transparent electrode layer 576 is formed as a pixel electrode layer in the transmissive region 499. As shown in FIG. 7 and FIG. 8, the transparent electrode layer 576 and the reflective electrode layer 577 are formed by an insulating film 571. When the two layers are stacked so that their ends overlap with one another through a gap, the display area can be efficiently set in the pixel area. In FIG. 8, a transparent electrode layer 576 and an insulating film 57 are formed on the interlayer film 413. 1, the reflective electrode layer 57 and the reflective electrode layer 57 are stacked in this order. 7, an insulating film 571, and a transparent electrode layer 576 may be laminated in this order.

[0115] As shown in FIG. 7B, a reflective electrode layer 577 and a source electrode layer or The transistor 560 electrically connected to the drain electrode layer 565b, the transparent electrode layer 576 and and a transistor 550 electrically connected to the source or drain electrode layer 555b. The transistor 560 is a transistor for the reflection region that controls the on / off of the reflection region. The transistor 550 is a transistor for the transparent region that controls the on / off of the transparent region. It is.

[0116] Insulating films 407 and 409 and an interlayer film 413 are provided over the transistors 550 and 560. In the respective openings (contact holes) formed in the insulating films 407 and 409 and the interlayer film 413, In the transistor 550, a transparent electrode layer 576 and a reflective electrode layer 560 are provided. 77 and electrically connected to each other.

[0117] As shown in FIG. 8, a common electrode layer (also called a counter electrode layer) 448 is formed on the second substrate 442. The transparent electrode layer 576 and the reflective electrode layer 577 on the first substrate 441 and the liquid crystal layer 444 are In the liquid crystal display device of FIG. 7 and FIG. 8, the transparent electrode layer 576 and An alignment film 460a is provided between the reflective electrode layer 577 and the liquid crystal layer 444, and a common electrode layer 448 An alignment film 460b is provided between the alignment film 460a and the liquid crystal layer 444. is an insulating layer that has the function of controlling the alignment of liquid crystals. Depending on the liquid crystal material, it may not be necessary to provide it. good.

[0118] Transistors 550 and 560 are examples of inverted staggered transistors with bottom gate structures. The transistor 550 includes a gate electrode layer 551, a gate insulating layer 402, a semiconductor layer 553, A source or drain electrode layer 555a and a source or drain electrode layer 555 b, the transistor 560 includes a gate electrode layer 551, a gate insulating layer 402, a semiconductor layer 563, a source electrode layer or a drain electrode layer 565a, and a source electrode layer or a drain electrode Also, the transistors 550 and 560 each have a capacitance. 8, in the reflective region 498, a capacitor layer formed in the same process as the gate electrode layer 551 is a gate insulating layer 402; and a source or drain electrode layer 555a. A conductive layer 579 formed in the same process as 555b, 565a, and 565b is laminated to form a capacitance. In addition, a metal such as aluminum (Al) or silver (Ag) is provided to cover the capacitance wiring layer 558. A reflective electrode layer 577 formed from any reflective conductive film and a wiring layer 580 formed in the same process are formed. It is preferable to do so.

[0119] In the semi-transmissive liquid crystal display device of this embodiment, the transistor 550 is turned on and off to control the This allows a moving image to be displayed in color in the transparent area 499, and the transistor 560 is turned on and off. By controlling the reflection area 498, a monochrome (black and white) still image is displayed. By separately operating transistors 550 and 560, the reflective region 49 The display of the transparent area 499 and the display of the transparent area 8 can be controlled independently.

[0120] In the transmission region 499, incident light from a backlight provided on the first substrate 441 side is incident on the first substrate 441. By using RGB light-emitting diodes (LEDs) for the backlight, In addition, in this embodiment, a light emitting diode (LED) A time-division additive color mixing method (field sequential method) that uses will be adopted.

[0121] On the other hand, in the reflective region 498, external light incident from the second substrate 442 side is reflected by the reflective electrode layer 5 The display is achieved by reflection by 77.

[0122] An example of forming unevenness on a reflective electrode layer 577 in a liquid crystal display device is shown in FIG. 9 and FIG. In FIG. 9, the surface of the interlayer film 413 is made uneven in the reflective region 498 to form a reflective electrode layer. This is an example of forming a concave-convex shape on the surface of the interlayer film 413. The concave-convex shape on the surface of the interlayer film 413 is formed by selectively etching. For example, the photosensitive organic resin may be processed by photolithography. By carrying out the above steps, an interlayer film 413 having a concave and convex shape can be formed. In the reflective region 498, a convex structure is provided on the interlayer film 413, and the reflective electrode layer 577 is FIG. 10 shows an example of forming a concave-convex shape. For example, the insulating layer 480 may be made of silicon oxide or silicon nitride. Inorganic insulating layer such as silicon, organic resin such as polyimide resin, acrylic resin, etc. as insulating layer 482 First, a silicon oxide film is formed on the interlayer 413 by a sputtering method. A polyimide resin film is formed on the silicon oxide film by a coating method. The polyimide resin film is etched using the polyimide film as an etching stopper. The silicon oxide film is etched using the polyimide resin layer as a mask, As shown in FIG. 10, a convex structure is formed by stacking an insulating layer 480 and an insulating layer 482. It is possible.

[0123] As shown in FIG. 9 and FIG. 10, when the surface of the reflective electrode layer 577 is uneven, the incident external light is reflected. This diffuses the light and improves the visibility of the display. do.

[0124] This embodiment mode can be freely combined with any of the first to third embodiment modes.

[0125] (Embodiment 5) In this embodiment, an example of a transistor that can be applied to the liquid crystal display device disclosed in this specification will be described. The structure of a transistor that can be applied to the liquid crystal display device disclosed in this specification is not particularly limited. For example, a staggered type or planar type having a top gate structure or a bottom gate structure is used. In addition, the transistor can be a single gate transistor in which one channel forming region is formed. In the case of a gate structure, a double gate structure with two gates or a triple gate structure with three gates Alternatively, two gate insulating layers may be disposed above and below the channel region. A dual gate type having a gate electrode layer may be used. An example of a cross-sectional structure of a transistor is shown in FIG. The transistor uses an oxide semiconductor as a semiconductor. The advantage of this is that high mobility and low off-current can be obtained through a relatively simple and low-temperature process. Of course, other semiconductors may be used.

[0126] The transistor 410 shown in FIG. 11A is a thin film transistor having a bottom gate structure. This is also called an inverted staggered thin film transistor.

[0127] The transistor 410 includes a gate electrode layer 401, a gate The insulating layer 402, the oxide semiconductor layer 403, the source electrode layer 405a, and the drain electrode layer 40 In addition, an insulating film that covers the transistor 410 and is stacked on the oxide semiconductor layer 403 On the insulating film 407, an insulating film 409 is further formed.

[0128] The transistor 420 shown in FIG. 11B is a channel protection type (also called a channel stop type). This is one of the bottom-gate structures known as inverted staggered thin-film transistors.

[0129] The transistor 420 includes a gate electrode layer 401, a gate The insulating layer 402, the oxide semiconductor layer 403, and the oxide semiconductor layer 403 are provided so as to cover a channel formation region thereof. The insulating layer 427 functioning as a channel protective layer, the source electrode layer 405a, and the drain electrode In addition, an insulating film 409 is formed to cover the transistor 420.

[0130] The transistor 430 shown in FIG. 11C is a bottom-gate thin film transistor. On a substrate 400 having a surface, a gate electrode layer 401, a gate insulating layer 402, a source electrode layer 403, and a gate insulating layer 404 are formed. The transistor includes a drain electrode layer 405a, a drain electrode layer 405b, and an oxide semiconductor layer 403. An insulating film 407 is provided to cover the gate 430 and to be in contact with the oxide semiconductor layer 403. An insulating film 409 is further formed on the film 407 .

[0131] In the transistor 430, the gate insulating layer 402 is connected to the substrate 400 and the gate electrode layer 400. 1, a source electrode layer 405a and a drain electrode layer 405b are provided on the gate insulating layer 402. The gate insulating layer 402 and the source electrode layer 405b are provided in contact with each other. In FIG. 5a, an oxide semiconductor layer 403 is provided over a drain electrode layer 405b.

[0132] The transistor 440 shown in FIG. 11D is a thin film transistor having a top gate structure. The transistor 440 is formed on a substrate 400 having an insulating surface, an insulating layer 437, an oxide a gate insulating layer; 402, a gate electrode layer 401, a source electrode layer 405a, and a drain electrode layer 405b. The wiring layers 436a and 436b are provided adjacent to each other and are electrically connected to each other.

[0133] In this embodiment, as described above, the oxide semiconductor layer 403 is used as the semiconductor layer. The oxide semiconductor used for the oxide semiconductor layer 403 is an In-Sn oxide, which is an oxide of a quaternary metal. -Ga-Zn-O system, In-Ga-Zn-O system which is an oxide of a ternary metal, In-Sn -Zn-O 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 In-Zn-O system, Sn- Zn-O system, Al-Zn-O system, Zn-Mg-O system, Sn-Mg-O system, In-Mg-O system In-O, Sn-O, Zn-O, etc. can be used. The oxide semiconductor may contain SiO2. For example, the In-Ga-Zn-O oxide semiconductor The conductor is an oxide containing at least In, Ga, and Zn, and there is no particular restriction on the composition ratio. Also, elements other than In, Ga, and Zn may be included.

[0134] 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 one selected from Ga, Al, Mn, and Co. Or it represents multiple metal elements. For example, M can be Ga, Ga and Al, Ga and Mn, or or Ga and Co.

[0135] The transistors 410, 420, 430, and 440 including the oxide semiconductor layer 403 are in an off state. Therefore, the current value (off-state current value) in the OFF state can be reduced. The retention time of the electric signal can be extended, and the writing interval can be set to be longer. This reduces the frequency of refresh operations, thereby reducing power consumption. do.

[0136] The transistors 410, 420, 430, and 440 each including the oxide semiconductor layer 403 are Since a relatively high field effect mobility can be obtained, high speed operation is possible. By using this transistor in the pixel part of the device, color separation can be suppressed, resulting in high-quality images. In addition, the transistor can be provided on the same substrate as a driver circuit section or a pixel circuit section. Since it can be manufactured separately for each element, the number of parts in a liquid crystal display device can be reduced. can.

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

[0138] In the bottom-gate transistors 410, 420, and 430, an insulating film serving as a base film The base film may be provided between the substrate and the gate electrode layer. It has a function of preventing the formation of oxides, and is a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, or a silicon oxide nitride film. The insulating film may be formed by laminating one or more films selected from silicon carbide films.

[0139] The material of the gate electrode layer 401 is molybdenum, titanium, chromium, tantalum, tungsten, Metallic materials such as aluminum, copper, neodymium, and scandium, or alloys containing these as the main components It can be formed of a gold material in a single layer or in a multilayer structure.

[0140] The gate insulating layer 402 is formed by depositing silicon oxide using a plasma CVD method, a sputtering method, or the like. silicon layer, silicon nitride layer, silicon oxynitride layer, silicon nitride oxide layer, aluminum oxide layer , an aluminum nitride layer, an aluminum oxynitride layer, an aluminum nitride oxide layer, or an aluminum oxide layer. The aluminum layer can be formed as a single layer or a stacked layer. For example, the first gate insulating layer and Then, a silicon nitride layer (SiN y (y>0)) was formed on the first gate insulating layer as a second gate insulating layer with a thickness of 5 nm. A silicon oxide layer (SiOx (x>0)) of 300 nm or less is laminated to a total thickness of 20 The gate insulating layer is set to 0 nm.

[0141] The conductive film used for the source electrode layer 405a and the drain electrode layer 405b is, for example, Al , Cr, Cu, Ta, Ti, Mo, W, or elements containing the above elements. The alloy film may be a film of a combination of the above elements. A high melting point metal layer such as Ti, Mo, W, etc. on either or both the upper and lower sides of a metal layer such as Cu In addition, in order to prevent the occurrence of hillocks and whiskers in the Al film, By using Al material with added elements (Si, Nd, Sc, etc.) that prevent heat buildup, heat resistance is improved. It is possible to improve it.

[0142] The wiring layer 436a and the wiring layer 436b are connected to the source electrode layer 405a and the drain electrode layer 405b, respectively. The conductive film such as 6b is also made of the same material as the source electrode layer 405a and the drain electrode layer 405b. It can be used.

[0143] In addition, the source electrode layer 405a, the drain electrode layer 405b (wiring formed in the same layer as this The conductive film (including the layer) may be formed of a conductive metal oxide. The oxides are indium oxide (In2O3), tin oxide (SnO2), zinc oxide (ZnO ), indium oxide tin oxide alloy (In2O3-SnO2, abbreviated as ITO), indium oxide Indium zinc oxide alloy (In2O3-ZnO) or these metal oxide materials with silicon oxide Containing kon can be used.

[0144] The insulating film 407 and the insulating layers 427 and 437 are typically made of a silicon oxide film or a silicon oxynitride film. An inorganic insulating film such as an aluminum oxide film or an aluminum oxynitride film is used. can be done.

[0145] The insulating film 409 may be a silicon nitride film, an aluminum nitride film, a silicon oxynitride film, or a silicon oxynitride film. An inorganic insulating film such as an aluminum film can be used.

[0146] In addition, a planarizing insulating film is formed on the insulating film 409 in order to reduce surface irregularities caused by the transistor. The planarizing insulating film may be made of polyimide, acrylic, benzocyclobutene, etc. In addition to the above organic materials, low-k materials can be used. In addition, a plurality of insulating films made of these materials can be laminated. A planarization insulating film may be formed by this.

[0147] In this manner, in this embodiment, by using a transistor including an oxide semiconductor layer, It is possible to provide a more highly functional liquid crystal display device.

[0148] (Embodiment 6) In this embodiment, an example of a transistor including an oxide semiconductor layer and a manufacturing method thereof will be described with reference to FIGS. The following will be described in detail. This can be done in the same manner as in the above embodiment, and the repeated explanation will be omitted. A detailed description will be omitted.

[0149] 12A to 12E show examples of cross-sectional structures of transistors. The transistor 510 shown in FIG. 12E is the same as the transistor 410 shown in FIG. This is an inverted staggered thin film transistor with a similar bottom gate structure.

[0150] The oxide semiconductor used in the semiconductor layer of this embodiment is an oxide semiconductor that is formed by absorbing hydrogen, which is an n-type impurity, into the oxide semiconductor. The oxide semiconductor is then highly purified to remove impurities other than the main component thereof as much as possible. As a result, an i-type (intrinsic) oxide semiconductor or an oxide semiconductor that is as close to i-type (intrinsic) as possible is obtained. In other words, instead of adding impurities to make it i-type, impurities such as hydrogen and water are By removing as much as possible, it is possible to obtain a highly purified i-type (intrinsic semiconductor) or something close to it. Therefore, the oxide semiconductor layer of the transistor 510 is highly purified and and an oxide semiconductor layer that has been made electrically i-type (intrinsic).

[0151] In addition, there are very few carriers (close to zero) in highly purified oxide semiconductors. The rear concentration is less than 1×1014 / cm3, preferably less than 1×1012 / cm3, more preferably Preferably, it is less than 1×10 11 / cm 3 .

[0152] Since there are very few carriers in the oxide semiconductor, the off-state current of the transistor 510 can be reduced. The smaller the off-current, the more preferable it is.

[0153] Specifically, the thin film transistor having the above-mentioned oxide semiconductor layer has a channel width of 1 μm. The off-state current density per unit area is 10aA / μm (1×10-17A / μm) or less at room temperature. Furthermore, it is necessary to keep the current at 1aA / μm (1×10-18A / μm) or less, and even to keep it at 10zA / μm (1×10-20A / μm) or less.

[0154] A transistor having an extremely small current value in an off state (off current value) is used as the image display device according to the first embodiment. By using it as a transistor in the elemental part, the refresh operation in the still image area This can reduce the number of times the work needs to be written.

[0155] In addition, the on-state current of the transistor 510 including the above-described oxide semiconductor layer has little temperature dependence. Almost no change is observed and the off-current remains very small.

[0156] Hereinafter, a transistor 510 is formed on a substrate 505 using FIG. 12(A) to FIG. 12(E). The process for doing so will be described.

[0157] First, a conductive film is formed on a substrate 505 having an insulating surface, and then a first photolithography process is performed. A gate electrode layer 511 is formed by a process. If the resist mask is formed by the inkjet method, a photomask is not used. This reduces manufacturing costs.

[0158] The substrate 505 having an insulating surface is the same as the substrate 400 shown in the fifth embodiment. In this embodiment mode, a glass substrate is used as the substrate 505.

[0159] An insulating film serving as a base film may be provided between the substrate 505 and the gate electrode layer 511. The silicon nitride film, the silicon oxide film, and the like have a function of preventing the diffusion of impurity elements from the substrate 505. The insulating layer is made of one or more films selected from a silicon oxide film, a silicon nitride film, and a silicon oxynitride film. The insulating film can be formed by a laminate structure.

[0160] The material of the gate electrode layer 511 is molybdenum, titanium, tantalum, tungsten, or aluminium. Aluminum, copper, neodymium, scandium, and other metal materials, or alloys containing these as the main components The insulating film can be formed in a single layer or a laminated layer using a material.

[0161] Next, a gate insulating layer 507 is formed on the gate electrode layer 511. The gate insulating layer 507 is A silicon oxide layer, a silicon nitride layer, etc. are formed by using a plasma CVD method, a sputtering method, etc. , silicon oxynitride layer, silicon nitride oxide layer, aluminum oxide layer, aluminum nitride layer A single layer of aluminum oxide nitride, aluminum oxide nitride, or hafnium oxide is formed. can be formed by laminating.

[0162] The oxide semiconductor of this embodiment is an oxide semiconductor that is made i-type or substantially i-type by removing impurities. Such highly purified oxide semiconductors have low resistance to interface states and interface charges. Since the oxide semiconductor layer is extremely sensitive to the temperature, the interface between the oxide semiconductor layer and the gate insulating layer is important. Therefore, the gate insulating layer in contact with the highly purified oxide semiconductor is required to have high quality.

[0163] For example, high-density plasma CVD using microwaves (e.g., 2.45 GHz frequency) produces dense This is preferable because it allows the formation of a high-quality insulating layer with high dielectric strength. The close contact between the gate insulating layer and the high-quality gate insulating layer reduces the interface state and improves the interface characteristics. This is because it can be said that

[0164] Of course, if a good insulating layer can be formed as a gate insulating layer, sputtering is also possible. Other deposition methods such as the plasma CVD method and the like can be applied. Even if the insulating layer is one in which the film quality of the gate insulating layer and the interface characteristics with the oxide semiconductor are modified by In any case, the film quality as a gate insulating layer is good, and the oxidation Any material may be used as long as it can reduce the interface state density with the solid semiconductor and form a good interface.

[0165] In addition, the gate insulating layer 507 and the oxide semiconductor film 530 contain hydrogen, a hydroxyl group, and moisture as much as possible. In order to prevent the oxide semiconductor film 530 from being broken down, sputtering was performed as a pretreatment for the formation of the oxide semiconductor film 530. In the preheating chamber of the heating apparatus, the substrate 505 on which the gate electrode layer 511 is formed or the gate insulating layer 5 The substrate 505 on which the above-mentioned steps 107 are formed is preheated to remove hydrogen, moisture, etc. adsorbed on the substrate 505. It is preferable to desorb impurities and evacuate them. A pump is preferable. This preheating process can be omitted. Before the insulating layer 516 is formed, the source electrode layer 515a and the drain electrode layer 515b are heated. The same may be done with the formed substrate 505 .

[0166] Next, a film having a thickness of 2 nm to 200 nm, preferably 5 nm or more, is formed on the gate insulating layer 507. An oxide semiconductor film 530 having a thickness of 30 nm or less is formed (see FIG. 12A).

[0167] Note that before the oxide semiconductor film 530 is formed by a sputtering method, argon gas is introduced. The reverse sputtering is performed by introducing the metal into the gate insulating layer 507 to generate plasma. It is preferable to remove the powdery substances (also called particles or dust) that are stuck to the surface. In the experiment, no voltage was applied to the target side, and a voltage was applied to the substrate side using an RF power supply in an argon atmosphere. This method applies a voltage to generate plasma near the substrate to modify the surface. Instead of the atmosphere, nitrogen, helium, oxygen, etc. may be used.

[0168] The oxide semiconductor used for the oxide semiconductor film 530 is the oxide semiconductor of the quaternary metal described in Embodiment 5. oxides of ternary metals, oxides of binary metals, In-O, Sn-O, Zn- O-based oxide semiconductors can be used. In this embodiment, the oxide semiconductor film 530 is an In—Ga—Zn—O-based oxide. The film is formed by sputtering using a nitride target. The cross section at this stage is shown in Fig. 12. The oxide semiconductor film 530 is heated in a rare gas (typically, argon) atmosphere. The material is deposited by sputtering in a mixed atmosphere of rare gas and oxygen, or in a gas atmosphere of oxygen. It can be formed.

[0169] Examples of targets for forming the oxide semiconductor film 530 by a sputtering method include The composition ratio is In2O3:Ga2O3:ZnO=1:1:1 [molar ratio]. In addition, In2O3:Ga2O3:ZnO=1:1:2 [mol number ratio], or In2O3:Ga2O3:ZnO=1:1:4 [molar ratio] The filling rate of the oxide semiconductor film forming target is 90% or more and 10% or more. The filling rate is 0% or less, preferably 95% to 99.9%. By using the target, the formed oxide semiconductor film becomes a dense film.

[0170] The oxide semiconductor film 530 is formed using a sputtering gas of hydrogen, water, a hydroxyl group, or a hydrogen atom. It is preferable to use a high-purity gas from which impurities such as oxides have been removed.

[0171] The substrate is held in a film-forming chamber maintained in a reduced pressure state, and the substrate temperature is preferably set to 100° C. or more and 600° C. or less. The temperature is preferably 200° C. or higher and 400° C. or lower. In addition, the concentration of impurities in the oxide semiconductor film can be reduced. Damage caused by etching is reduced. The removed sputtering gas is introduced, and an oxide semiconductor is deposited on the substrate 505 using the target. In order to remove the residual moisture in the deposition chamber, a suction type vacuum pump, e.g. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means is preferably a turbo pump with a cold trap. The deposition chamber evacuated using a cryopump may be filled with, for example, hydrogen atoms, water (H2O), Compounds containing hydrogen atoms (and more preferably compounds containing carbon atoms) are exhausted. Therefore, the impurity concentration in the oxide semiconductor film formed in the deposition chamber can be reduced.

[0172] As an example of the film formation conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa. The conditions were: DC power supply 0.5kW, oxygen (oxygen flow rate 100%) atmosphere. In addition, when a pulsed DC power supply is used, the powdery substances (particles, etc.) generated during film formation are reduced. This is preferable because it can reduce the amount of adhesion (also referred to as the "friction") and make the film thickness distribution uniform.

[0173] Next, the oxide semiconductor film 530 is subjected to a second photolithography process to form an island-shaped oxide semiconductor In addition, a resist mask for forming an island-shaped oxide semiconductor layer is applied to the ink. If the resist mask is formed by the inkjet method, the photomask Since no disks are used, manufacturing costs can be reduced.

[0174] In addition, when a contact hole is formed in the gate insulating layer 507, the process is performed using an oxide semiconductor. This can be done simultaneously with the processing of the membrane 530 .

[0175] Note that the etching of the oxide semiconductor film 530 here may be dry etching or wet etching. For example, the oxide semiconductor film 530 may be subjected to wet etching. The etching solution used for etching is a mixture of phosphoric acid, acetic acid, and nitric acid. Alternatively, ITO07N (manufactured by Kanto Chemical Co., Ltd.) may be used.

[0176] Next, the oxide semiconductor layer is subjected to a first heat treatment. The conductor layer can be dehydrated or dehydrogenated. The temperature of the first heat treatment is 400° C. The temperature is set to 750°C or higher, or 400°C or higher but lower than the distortion point of the substrate. The substrate was placed in an electric furnace, which is one of the equipment used for the deposition of oxide semiconductor layers, and the temperature was raised to 450°C in a nitrogen atmosphere. After the heat treatment for 1 hour, the oxide semiconductor layer was cooled to room temperature and then cooled to room temperature. Thus, an oxide semiconductor layer 531 is obtained (see FIG. 12B).

[0177] The heat treatment device is not limited to an electric furnace, and may be a heat treatment device using heat conduction or heat from a heating element such as a resistance heating element. The apparatus may be equipped with a device for heating the object to be treated by radiation. For example, a GRTA (Gas Rapid Thermal Anneal) equipment, LRTA (Lamp Rapid Thermal Annealing equipment such as RTA (Rapid Thermal Annealing) The LRTA device can be used with halogen lamps, metal halide lamps, etc. lamp, xenon arc lamp, carbon arc lamp, high pressure sodium lamp, high pressure A device that heats the workpiece by radiating light (electromagnetic waves) emitted from a lamp such as a mercury lamp. The GRTA device is a device that uses high-temperature gas to perform heat treatment. The gas used is a rare gas such as argon or nitrogen, which does not react with the workpiece during heat treatment. A suitable inert gas is used.

[0178] For example, the first heat treatment is performed by heating an inert gas to a high temperature of 650° C. or more and 700° C. or less. The substrate is then moved into the inert gas chamber and heated for a few minutes. GRTA may be performed to release the gas.

[0179] In the first heat treatment, nitrogen or a rare gas such as helium, neon, or argon is used. It is preferable that the nitrogen introduced into the heat treatment device does not contain water, hydrogen, etc. Or the purity of rare gases such as helium, neon, and argon must be 6N (99.9999%) or higher. Preferably, the concentration of impurities is 7N (99.99999%) or more (i.e., the impurity concentration is 1 ppm or less, It is preferable to keep the concentration of the ion exchange resin at 0.1 ppm or less.

[0180] After the oxide semiconductor layer is heated by the first heat treatment, high-purity oxygen gas, high-purity Introduce 100% N2O gas or ultra-dry air (dew point below -40℃, preferably below -60℃). 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 more. or 7N or more (i.e., impurity concentration in oxygen gas or N2O gas is 1 ppm or less, preferably It is preferable to set the concentration to 0.1 ppm or less. At the same time, the amount of impurities was reduced by the dehydration or dehydrogenation process. By supplying oxygen, the oxide semiconductor layer is highly purified and electrically made i-type (intrinsic). do.

[0181] In addition, the first heat treatment of the oxide semiconductor layer is performed on the oxide semiconductor layer before it is processed into the island-shaped oxide semiconductor layer. The semiconductor film 530 may be subjected to the first heat treatment. In that case, the semiconductor film 530 may be heated by the heating device after the first heat treatment. The substrate is taken out and a photolithography process is performed.

[0182] In addition to the above, the first heat treatment may be performed after the oxide semiconductor layer is formed. After laminating a source electrode layer and a drain electrode layer on the insulating layer, or This may be performed either after forming an insulating layer on the drain electrode layer or after forming an insulating layer on the drain electrode layer.

[0183] In addition, when a contact hole is formed in the gate insulating layer 507, the process is performed using an oxide semiconductor. This may be done before or after film 530 is subjected to the first heat treatment.

[0184] In addition, the oxide semiconductor layer is formed in two separate steps and heat-treated in two separate steps. Regardless of the material of the component, such as oxide, nitride, or metal, the film thickness is thick and the crystal region (single crystal region) is thick. In other words, even if an oxide semiconductor layer having a crystal region in which the c-axis is oriented perpendicular to the film surface is formed, For example, a first oxide semiconductor film having a thickness of 3 nm to 15 nm is formed, and nitrogen, oxygen, In a rare gas or dry air atmosphere, the temperature is 450°C to 850°C, preferably 550°C or lower. The first heat treatment is performed at 750°C or less to form a crystalline region (including plate-like crystals) in the region including the surface. Then, a second oxide semiconductor film having a thickness larger than that of the first oxide semiconductor film is formed. The oxide semiconductor film of 2 is formed at 450° C. or higher and 850° C. or lower, preferably 600° C. or higher and 70° C. or lower. A second heat treatment is performed at a temperature of 0° C. or lower. The first oxide semiconductor film is used as a seed for crystal growth. The second oxide semiconductor film is entirely crystallized by crystal growth, resulting in a thick crystalline region. Alternatively, an oxide semiconductor layer having a SiO 2 region may be formed.

[0185] Next, a source electrode layer and a drain electrode layer are formed on the gate insulating layer 507 and the oxide semiconductor layer 531. A conductive film is formed to become the source electrode layer (including wiring formed in the same layer). As the conductive film used for the source electrode layer and the drain electrode layer, The materials used for the drain electrode layer 405a and the drain electrode layer 405b can be used.

[0186] A resist mask is formed on the conductive film by a third photolithography process, and selective etching is performed. After forming the source electrode layer 515a and the drain electrode layer 515b by etching, a resist The mask is removed (see FIG. 12(C)).

[0187] In the third photolithography process, ultraviolet light or KrF laser is used for exposure when forming the resist mask. The source electrodes adjacent to each other on the oxide semiconductor layer 531 are preferably irradiated with a laser beam or an ArF laser beam. The width of the gap between the bottom end of the drain electrode layer and the bottom end of the drain electrode layer determines the width of the gap between the bottom end of the drain electrode layer and the bottom end of the drain electrode layer. The channel length L is determined. Note that, when performing exposure with a channel length L of less than 25 nm, Extreme ultraviolet rays have extremely short wavelengths, ranging from a few nm to a few tens of nm. iolet) was used to control the exposure during resist mask formation in the third photolithography process. Extreme ultraviolet light exposure has high resolution and a large depth of focus. It is also possible to set the channel length L of the transistor to 10 nm or more and 1000 nm or less. This enables faster circuit operation and, because the off-current is extremely small, it also consumes less power. It is also possible to streamline the process.

[0188] In order to reduce the number of photomasks and steps used in the photolithography process, The resist pattern is formed by a multi-tone mask, which is an exposure mask that allows the light to be projected at multiple intensities. The etching process may be performed using a resist mask formed using a multi-tone mask. The mask has a shape with multiple film thicknesses, and the shape can be further deformed by etching. This allows for multiple etching processes to be performed to create different patterns. Therefore, one multi-tone mask can handle at least two different patterns. Therefore, the number of exposure masks can be reduced. Since the corresponding photolithography process can also be eliminated, the process can be simplified.

[0189] Note that when the conductive film is etched, the oxide semiconductor layer 531 is etched and divided. It is desirable to optimize the etching conditions so that no defects are found. It is possible to obtain a condition in which the oxide semiconductor layer 531 is etched without being etched at all. Therefore, the oxide semiconductor layer 531 is only partially etched during etching of the conductive film. The oxide semiconductor layer may have a groove (a recess).

[0190] In this embodiment, a Ti film is used as the conductive film, and an In-Ga- Since a Zn-O-based oxide semiconductor was used, ammonia hydrogen peroxide (AH) was used as an etchant for the conductive film. A mixture of ammonia, water, and hydrogen peroxide is used.

[0191] Then, a plasma treatment is performed using a gas such as N2O, N2, or Ar to remove the exposed Water or the like adsorbed on the surface of the oxide semiconductor layer may be removed by the plasma treatment. In this case, the insulating layer 5, which is a protective insulating film that is in contact with a part of the oxide semiconductor layer without being exposed to the air, is formed. Form 16.

[0192] The insulating layer 516 has a thickness of at least 1 nm. The insulating layer 6 can be formed by using a method that does not allow impurities such as water and hydrogen to be mixed in. When hydrogen is contained in the insulating film 516, the hydrogen penetrates into the oxide semiconductor layer or the hydrogen is absorbed in the oxide semiconductor layer. The oxygen in the oxide semiconductor layer is extracted, and the back channel of the oxide semiconductor layer becomes low-resistance (n-type). Therefore, the insulating layer 516 should be as thin as possible. It is important that the deposition process does not use hydrogen, resulting in a hydrogen-free film.

[0193] In this embodiment, a silicon oxide film having a thickness of 200 nm is formed as the insulating layer 516 by sputtering. The substrate temperature during film formation should be between room temperature and 300°C. In the embodiment, the temperature is set to 100° C. The silicon oxide film is formed by sputtering using a rare gas. (typically argon) atmosphere, oxygen atmosphere, or a mixture of rare gas and oxygen atmosphere. The target may be a silicon oxide target or a silicon target. For example, a silicon target can be used to produce a fluorine-containing oxide film. Silicon oxide can be formed by sputtering in an atmosphere. The insulating layer 516 formed in contact with the layer does not contain impurities such as moisture, hydrogen ions, and OH-. The inorganic insulating film is used to block these substances from entering from the outside. Silicon film, silicon oxynitride film, aluminum oxide film, aluminum oxynitride film, etc. etc. can be used.

[0194] In the same manner as in the formation of the oxide semiconductor film 530, moisture remaining in the deposition chamber for 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 contained in the insulating layer 516 formed in a deposition chamber evacuated using an opamp was reduced. In addition, the following exhaust means can be used to remove residual moisture in the deposition chamber for the insulating layer 516: A turbo pump plus a cold trap may also be used.

[0195] The insulating layer 516 is formed using a sputtering gas such as hydrogen, water, a hydroxyl group, or a hydride. It is preferable to use a high-purity gas from which impurities have been removed.

[0196] Next, a second heat treatment (preferably a second heat treatment) is performed under an inert gas atmosphere or an oxygen gas atmosphere. For example, the heating is performed in a nitrogen atmosphere. The second heat treatment is performed at 250° C. for 1 hour under atmospheric pressure. A portion of the layer (channel formation region) is heated while in contact with the insulating layer 516 .

[0197] Through the above steps, the oxide semiconductor film is subjected to the first heat treatment to remove hydrogen, Impurities such as moisture, a hydroxyl group, or hydride (also called a hydrogen compound) are intentionally removed from the oxide semiconductor layer. supplying oxygen that is simultaneously reduced by the impurity removal process. As a result, the oxide semiconductor layer is highly purified and becomes electrically i-type (intrinsic).

[0198] Through the above steps, a transistor 510 is formed (see FIG. 12D).

[0199] In addition, when a silicon oxide layer containing many defects is used as the oxide insulating layer, The heat treatment reduces hydrogen, moisture, a hydroxyl group, hydride, or the like contained in the oxide semiconductor layer. Impurities are diffused into the oxide insulating layer, and the impurities contained in the oxide semiconductor layer are further reduced. This has the effect of

[0200] A protective insulating layer 506 may be further formed on the insulating layer 516. For example, RF sputtering The silicon nitride film is formed by RF sputtering, which is suitable for mass production. This is a preferable method for forming the protective insulating layer. The protective insulating layer 506 does not contain impurities such as moisture. In order to prevent these substances from entering the device from the outside, inorganic insulating films are used. In this embodiment, the protective insulating layer 506 can be formed using an aluminum oxide film or the like. It is formed using a silicon nitride film (see FIG. 12(E)).

[0201] In this embodiment, the substrate 505 on which the insulating layer 516 is formed is used as the protective insulating layer 506. It contains high-purity nitrogen that has been heated to a temperature between 100℃ and 400℃ and has had hydrogen and moisture removed. Sputtering gas is introduced and a silicon nitride film is formed using a silicon semiconductor target. In this case, similarly to the insulating layer 516, the protective insulating layer is formed while removing the residual moisture in the processing chamber. A border layer 506 is preferably deposited.

[0202] After the protective insulating layer 506 is formed, the protective insulating layer 506 is heated in the air at 100° C. to 200° C. for 1 hour or more. Heat treatment may be performed for 30 hours or less. This heat treatment is performed by maintaining a constant heating temperature. It may be heated, or the temperature may be increased from room temperature to a heating temperature of 100°C or more and 200°C or less. The temperature may be lowered from 30° C. to room temperature several times.

[0203] In this manner, the transistor including the highly purified oxide semiconductor layer manufactured according to this embodiment By using a transistor, the current value in the off state (off current value) can be reduced. Therefore, the retention time of electrical signals such as image data can be extended. Therefore, the write interval can be set longer, and the frequency of refresh operations can be reduced. This makes it possible to reduce power consumption.

[0204] In addition, a transistor including a highly purified oxide semiconductor layer can have high field-effect mobility. Therefore, when this transistor is used in a pixel portion of a liquid crystal display device, high speed operation is possible. By using the same transistor, a high quality image can be provided. Since the driver circuit section and pixel section can be separately manufactured on the same substrate, The number of items can be reduced.

[0205] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0206] (Embodiment 7) In this embodiment, the amount of reflected light and the amount of transmitted light per pixel of a semi-transmissive liquid crystal display device are improved. The pixel configuration will be described with reference to FIGS. 14, 15, and 16. FIG.

[0207] FIG. 14 is a diagram for explaining the planar configuration of a pixel according to the present embodiment. The cross-sectional structures of the S1-S2 portion, the T1-T2 portion, and the U1-U2 portion shown by the dashed lines in FIG. The pixel described in this embodiment has a transparent substrate 800 as a pixel electrode. An electrode 823 and a reflective electrode 825 are laminated with an insulating layer 824 sandwiched therebetween.

[0208] The transparent electrode 823 is formed by insulating films 827, 828, and a contact hole provided on the organic resin film 822. It is connected to the drain electrode 857 of the transistor 851 through a contact hole 855. The drain electrode 857 overlaps with the capacitance wiring 853 via the gate insulating layer, and forms a storage capacitance 871 (see Figure 15(A)).

[0209] The gate electrode 858 of the transistor 851 is connected to the wiring 852. The electrode 856 is connected to the wiring 854. The transistor 851 is The transistors described can be used (see FIG. 14).

[0210] The reflective electrode 825 is formed by a contact provided on the insulating film 827, the insulating film 828, and the organic resin film 822. It is connected to the drain electrode 867 of the transistor 861 through a contact hole 865. The drain electrode 867 is connected to the capacitance wiring 86 via the gate insulating layer (see FIG. 15(E)). 3 to form a storage capacitor 872.

[0211] The gate electrode 868 of the transistor 861 is connected to the wiring 862, and the source electrode 8 66 is connected to a wiring 864. The transistor 861 is the same as that described in the other embodiments. A transistor having such a configuration can be used (see FIG. 14).

[0212] By reflecting external light by the reflective electrode 825, the pixel electrode is made to function as a pixel electrode of a reflective liquid crystal display device. The reflective electrode 825 has a plurality of openings 826. The reflective electrode 825 does not exist in the opening 826, and the structure 820 and the transparent electrode 823 protrude from the opening 826. The light from the backlight is transmitted through the opening 826 (see FIG. 15(B)). In this way, the pixel electrode can function as a pixel electrode of a transmissive liquid crystal display device.

[0213] In the semi-transmissive liquid crystal display device shown in this embodiment, the reflective electrode 825 and the transparent electrode 823 are insulated from each other. The transparent electrode 823 is electrically isolated by a layer 824. The potential applied to the reflecting electrode 825 is controlled by the transistor 861. The potentials of the reflective electrode 825 and the transparent electrode 823 can be controlled independently. Therefore, when the semi-transmissive liquid crystal display device is operated as a transmissive liquid crystal display device, the reflective electrode 825 The liquid crystal display can be made to show black.

[0214] FIG. 16 is a cross-sectional view showing an example different from that shown in FIG. 15(B). In one embodiment of the present invention, the structure 820 and the transparent electrode 823 are not protruding. In FIG. 15B, the backlight exit port 841 and the opening 826 are approximately the same size. 16, the size of the backlight exit port 841 and the size of the opening 826 are The sizes are different, and the distances from the backlight entrance 842 are also different. In comparison, the cross-sectional shape of FIG. 15(B) can transmit a larger amount of light, and is therefore more preferable. do.

[0215] In the opening 826, a structure 820 is formed so as to overlap the opening 826. 14, showing the configuration of the pixel electrode and the structure 820. FIG. 15(C) is an enlarged view of portion 880, and FIG. 15(D) is an enlarged view of portion 881. FIG.

[0216] Reflected light 832 indicates external light reflected by the reflective electrode 825. The organic resin film 822 is The upper surface has a curved surface with projections and recesses. The curved surface with projections and recesses is reflected in the reflecting electrode 825. This increases the reflective area and reduces the glare of things other than the displayed image. The visibility of the displayed image can be improved. The angle θR between the two opposing inclined surfaces from the most bent point of 5 is 90° or more. The angle is preferably set to 100° or more and 120° or less (see FIG. 15(D)).

[0217] The structure 820 has a backlight emission port 841 on the opening 826 side, and the backlight ( The backlight entrance port 842 is provided on the side of the structure 820 (not shown). , which is located above the surface of the reflective electrode 825 and protrudes from the upper end of the reflective electrode. That is, the distance H between the upper end of the structure 820 and the upper end of the reflective electrode is 0.1 μm or more and 3 μm or less. The area of ​​the backlight exit port 841 is preferably 0.3 μm or more and 2 μm or less. The area of ​​the backlight entrance 842 is made larger than that of the structure 820. The surfaces (surfaces other than the backlight exit port 841 and the backlight entrance port 842) are provided with a reflective layer. The structure 820 is made of silicon oxide, silicon nitride, silicon oxynitride, etc. The reflective layer 821 can be made of a material having a light-transmitting property, such as aluminum. Materials with high light reflectance, such as aluminum (Al) or silver (Ag), can be used.

[0218] Transmitted light 831 emitted from the backlight passes through the backlight incident light port 842 and enters the structure. A part of the incident transmitted light 831 passes directly through the backlight exit port 84 1, but a part of it is reflected by the reflective layer 821 toward the backlight exit port 841. The light is reflected and partly reflected back towards the backlight entrance port 842 .

[0219] At this time, light passes through the backlight exit port 841 and the backlight entrance port 842 of the structure 820. When the cross-sectional shape of the structure 820 is viewed, the opposing side surfaces on the left and right are inclined. The angle θT between the side surfaces is less than 90°, preferably between 10° and 60°. The transmitted light 831 incident from the backlight incident light port 842 is efficiently emitted to the backlight. It can be guided to the light port 841 (see FIG. 15(C)).

[0220] For example, in one pixel, the area of ​​the pixel electrode is 100% and it functions as a reflective electrode. The electrode area that functions as a transparent electrode (the area of ​​the opening 826) is called ST. In this case, in a conventional semi-transmissive liquid crystal display device, the area of ​​the electrode functioning as a reflective electrode is The total area of ​​SR and the electrode area ST that functions as a transparent electrode is 100% of the pixel electrode area. In the semi-transmissive liquid crystal display device having the pixel configuration shown in this embodiment, Since the electrode area ST functioning as the opening corresponds to the area of ​​the backlight entrance 842, The area ST of the portion 826 can be increased. Since ST corresponds to the area of ​​the backlight entrance 842, the brightness of the backlight is increased. This allows the amount of transmitted light to be increased without causing the electrode to function as a reflective electrode. The total area of ​​the area SR and the electrode area ST functioning as a transparent electrode must be 100% or more. In other words, the apparent area of ​​the pixel electrode can be made 100% or more.

[0221] By using this embodiment, a transflective LCD with brighter and better display quality can be obtained without increasing power consumption. A liquid crystal display device can be obtained.

[0222] (Embodiment 8) In this embodiment, an electronic device including the liquid crystal display device described in the above embodiment is An example will be described.

[0223] FIG. 13A shows an electronic book (also called an E-book), which includes a housing 9630 and a display portion 963. 1, an operation key 9632, a solar cell 9633, and a charge / discharge control circuit 9634 may be included. The electronic book shown in FIG. 13(A) contains various information (still images, videos, text images, etc.). Function to display calendar, date or time on the display, function to display on the display The ability to manipulate or edit information stored in a computer, and to control processing using various software (programs) In FIG. 13A, the charge and discharge control circuit 9634 As an example, the battery 9635 and the DCDC converter (hereafter referred to as the converter 9636) The configuration shown in FIG.

[0224] By using the structure shown in FIG. 13A, a semi-transmissive liquid crystal display device can be used as the display portion 9631. When using the device, it is expected that it will be used in relatively bright conditions, and the solar cell 9633 will generate power. This is preferable because it can efficiently charge the battery 9635. The battery 9633 efficiently charges the battery 9635 on the front and back of the housing 9630. The battery 9635 is preferably a lithium-ion battery. The use of an ON battery has advantages such as miniaturization.

[0225] The configuration and operation of the charge / discharge control circuit 9634 shown in FIG. A block diagram is shown and explained in FIG. 13(B). 5, converter 9636, converter 9637, switches SW1 to SW3, display unit 96 31 shows Battery 9635, Converter 9636, Converter 963 7. Switches SW1 to SW3 correspond to the charge / discharge control circuit 9634.

[0226] First, an example of operation in which power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is converted to a voltage for charging the Battery 9635. The voltage is increased or decreased by the photovoltaic cell 9636. When power from the 633 is used, switch SW1 is turned on and the converter 9637 The voltage is increased or decreased to a voltage required for the display unit 9631. When not displaying the battery, turn SW1 off and SW2 on to power the battery. The charging may be performed in the above-mentioned manner.

[0227] Next, an example of operation when external light does not generate power by the solar cell 9633 will be described. The power stored in the Battery 9635 is converted by turning on the switch SW3. The voltage is increased or decreased by the power supply 9637. Power will be drawn from Lee 9635.

[0228] Although the solar cell 9633 is shown as an example of a charging means, the battery may be charged by other means. It may be configured to charge the Terry 9635. It may also be configured to charge the Terry 9635 in combination with other charging means. This may also be configured.

[0229] This embodiment mode can be implemented in appropriate combination with the configurations described in other embodiments. It is. [Explanation of symbols]

[0230] 100 LCD display device 101 Image signal supply source 102 A / D conversion circuit 110 Image processing circuit 111 Memory circuit 112 Comparison circuit 113 Display control circuit 114 Field sequential signal generation circuit 115 Selection circuit 120 Display Panel 121 Drive circuit 122 Pixel section 123 Pixel section 123a Subpixel 123b subpixel 125a polarizing plate 125b Polarizing plate 126 FPC 130 Backlight section 131 Backlight control circuit 132 Backlight 133 Light emitting element 133R LED 133G LED 133B LED 134 Diffuser 135 light 139 Outdoor Light 140 Analog Image Signal 141 Digital Image Signal 142 LC image signal 143 Backlight Signal 151 Pixel section 152 1st scan line 153 First signal line 154 Second Scan Line 155 Second signal line 156 pixels 157 First scanning line driving circuit 158 First signal line driver circuit 159 Second scanning line driving circuit 160 Second signal line driver circuit 161 Transparent electrode section 162 Reflective electrode section 163 Pixel Transistor 164 Liquid crystal element 165 Capacitive element 166 pixel transistor 167 Liquid crystal element 168 Capacitive element 169 Common electrode 170 Capacitive Line 190 Liquid crystal display module 301 Video display period 302 Still image display period 303 Still image writing period 304 Still Image Retention Period 311 Light emitting element 400 Substrates 401 Gate electrode layer 402 Gate insulating layer 403 Oxide semiconductor layer 405a Source electrode layer 405b Drain electrode layer 407 Insulating Film 409 Insulating film 410 Transistor 413 Interlayer Film 420 Transistor 427 Insulating Layer 430 Transistor 436a Wiring layer 436b wiring layer 437 Insulating Layer 440 Transistor 441 Substrate 442 Substrate 444 Liquid crystal layer 448 Common electrode layer 460a Alignment film 460b Alignment film 480 Insulating layer 482 Insulating Layer 498 Reflection area 499 Transparent area 505 Board 506 Protective insulation layer 507 Gate Insulation Layer 510 Transistor 511 Gate electrode layer 515a Source electrode layer 515b Drain electrode layer 516 Insulating Layer 530 Oxide Semiconductor Film 531 Oxide Semiconductor Layer 550 Transistor 551 Gate electrode layer 553 Semiconductor Layer 555a Source electrode layer or drain electrode layer 555b Source electrode layer or drain electrode layer 558 Capacitive wiring layer 560 Transistor 563 Semiconductor Layer 565a Source electrode layer or drain electrode layer 565b Source electrode layer or drain electrode layer 571 Insulating Film 576 Transparent electrode layer 577 Reflective electrode layer 579 Conductive Layer 580 wiring layer 800 boards 820 Structure 821 Reflective layer 822 Organic resin film 823 Transparent electrode 824 Insulating layer 825 Reflective electrode 826 Opening 827 Insulating film 828 Insulating film 831 Transmitted light 832 Reflected light 841 Backlight exit port 842 Backlight entrance port 851 Transistor 852 Wiring 853 Capacitance wiring 854 Wiring 855 Contact Hole 856 Source Electrode 857 Drain electrode 858 Gate electrode 861 Transistor 862 Wiring 863 Capacitance wiring 864 Wiring 865 Contact Hole 866 Source Electrode 867 Drain electrode 868 Gate electrode 871 Holding capacity 872 holding capacity 880 parts 881 parts 9630 Case 9631 Display section 9632 Operation key 9633 Solar Cells 9634 Charge / discharge control circuit 9635 Battery 9636 Converter 9637 Converter

Claims

1. A display panel is provided. the display panel includes a first pixel electrode, a second pixel electrode, and a structure; the first pixel electrode has a function of transmitting light; The second pixel electrode is a liquid crystal display device having a function of reflecting light, the first pixel electrode and the second pixel electrode have an overlapping region with an insulating layer interposed therebetween; the first pixel electrode has a region located on the structure; the insulating layer has a region located above the first pixel electrode, the second pixel electrode has a region located on the insulating layer; the second pixel electrode has a plurality of openings; one of the plurality of openings has an area overlapping the structure, In one of the plurality of openings, the structure has a region that protrudes higher than an upper surface of the second pixel electrode.

2. A display panel is provided. the display panel includes a first pixel electrode, a second pixel electrode, a structure, and a transistor; the first pixel electrode has a function of transmitting light; The second pixel electrode is a liquid crystal display device having a function of reflecting light, the first pixel electrode and the second pixel electrode have an overlapping region with an insulating layer interposed therebetween; the first pixel electrode has a region located on the structure; the insulating layer has a region located above the first pixel electrode, the second pixel electrode has a region located on the insulating layer; the second pixel electrode has a plurality of openings; one of the plurality of openings has an area overlapping the structure, In one of the plurality of openings, the structure has a region protruding from an upper surface of the second pixel electrode, the second pixel electrode is electrically connected to one of the source and the drain of the transistor; the transistor has an oxide semiconductor layer in a channel formation region, The liquid crystal display device, wherein the oxide semiconductor layer is In--O.

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