Semi-transparent liquid crystal display device

Abstract

To provide a semi-transparent liquid crystal display device in which the characteristic shift of a transistor including a semiconductor layer containing an oxide semiconductor due to a light influence is suppressed.SOLUTION: A semi-transparent liquid crystal display device includes a display panel, a backlight, and a control unit that controls the display panel and the backlight. In a case where a still image is displayed in a plurality of subpixels with the backlight in a non-lighting state, the control unit writes each voltage corresponding to a gradation value for each subpixel constituting the still image at a first frame frequency from a source electrode of a pixel transistor of the corresponding subpixel, and in a case where a still image is displayed in the plurality of subpixels with the backlight in a lighting state, the control unit writes each voltage corresponding to a gradation value for each subpixel constituting the still image at a second frame frequency, which is higher than the first frame frequency, from the source electrode of the pixel transistor of the corresponding subpixel.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a transflective liquid crystal display device. [Background technology]

[0002] Display devices have been put to practical use, using transistors with a semiconductor layer containing an oxide semiconductor as pixel transistors that drive pixel electrodes electrically connected to the drain electrodes. Compared to transistors with a semiconductor layer containing amorphous silicon or polycrystalline silicon, transistors with a semiconductor layer containing an oxide semiconductor have a smaller amount of off-state current when the transistor is off. When used as a pixel transistor, these transistors have the advantage of being able to retain a voltage corresponding to the grayscale values ​​constituting an image input from the source electrode with a high retention rate for a long period of time. Taking advantage of this feature, a technology has also been put to practical use for reducing the frame frequency, which is the number of times per second that the voltage corresponding to the grayscale values ​​constituting an image input from the source electrode of a transistor with a semiconductor layer containing an oxide semiconductor used as a pixel transistor is refreshed, i.e., lengthening the cycle of one frame period, thereby reducing the power consumption of the display device.

[0003] For example, Patent Document 1 describes using a transistor including a semiconductor layer containing an oxide semiconductor as a pixel transistor, and setting the frame frequency to 1 Hz or less during a still image display period. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-115230 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of light-emitting elements such as OLEDs (Organic Light Emitting Diodes), QLEDs (Quantum dot Light Emitting Diodes), and micro LEDs, in which a light-emitting element is disposed as a layer above a transistor having a semiconductor layer containing an oxide semiconductor used as a pixel transistor, and a reflective electrode capable of reflecting light from the light-emitting layer provided in the light-emitting element is provided as a layer below the light-emitting layer, the transistor having a semiconductor layer containing an oxide semiconductor has a structure that is less susceptible to the effects of light, and therefore the characteristic shift of a transistor having a semiconductor layer containing an oxide semiconductor due to the effects of light does not pose a particular problem.

[0006] However, the inventors of the present disclosure have found that in a semi-transmissive liquid crystal display device including a display panel that includes a reflective region and a transmissive region and that includes, as pixel transistors, transistors having a semiconductor layer containing an oxide semiconductor, and a backlight, the transistors having a semiconductor layer containing an oxide semiconductor are significantly affected by light from the backlight, and that when voltages corresponding to gradation values ​​that constitute an image are written to the transistors having a semiconductor layer containing an oxide semiconductor at a frequency corresponding to a relatively low frame frequency during the period when the backlight is turned on, a characteristic shift of the transistor (a shift of the On voltage to the negative side) occurs due to the influence of light, causing a serious problem.

[0007] An object of one embodiment of the present disclosure is to provide a semi-transmissive liquid crystal display device in which a characteristic shift of a transistor including a semiconductor layer containing an oxide semiconductor is suppressed due to the influence of light. [Means for solving the problem]

[0008] In order to solve the above problems, the semi-transmissive liquid crystal display device of the present disclosure has: an active matrix substrate including, for each of a plurality of sub-pixels, a pixel transistor including a semiconductor layer including an oxide semiconductor, a gate electrode, a source electrode, and a drain electrode, a reflective region provided with a reflective pixel electrode electrically connected to the drain electrode, and a transmissive region provided with a transmissive pixel electrode electrically connected to the drain electrode; an opposing substrate facing the active matrix substrate; a display panel including a liquid crystal layer provided between the active matrix substrate and the counter substrate; a backlight that emits light toward the display panel; a control unit that controls the display panel and the backlight, The control unit when a still image is to be displayed on the plurality of sub-pixels in a state where the backlight is not lit, voltages corresponding to gradation values ​​of the sub-pixels constituting the still image are written from the source electrodes of the pixel transistors of the corresponding sub-pixels at a first frame frequency; When a still image is displayed on the plurality of sub-pixels while the backlight is turned on, voltages corresponding to the gradation values ​​of the sub-pixels constituting the still image are written from the source electrodes of the pixel transistors of the corresponding sub-pixels at a second frame frequency higher than the first frame frequency. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, a semi-transmissive liquid crystal display device can be provided in which a characteristic shift of a transistor including a semiconductor layer containing an oxide semiconductor, which is prevented from occurring due to the influence of light, can be prevented. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an active matrix substrate provided in a semi-transmissive liquid crystal display device of the present embodiment. [Figure 2] 1 is a cross-sectional view showing a schematic configuration of a semi-transmissive liquid crystal display device according to an embodiment of the present invention. [Figure 3] This figure explains a case where a control unit provided in a semi-transmissive liquid crystal display device of this embodiment controls the brightness of the backlight via a backlight drive circuit based on brightness data of the surrounding environment from a brightness sensor, and controls the frame frequency of the display panel via a display panel drive circuit based on display image type data from a display image type determination unit. [Figure 4] 10 is a diagram showing the degree of characteristic shift due to the influence of light in a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on the active matrix substrate of the semi-transmissive liquid crystal display device of the present embodiment. FIG. [Figure 5] 10A and 10B are diagrams showing the degree of characteristic shift of pixel transistors in each driving mode of the semi-transmissive liquid crystal display device of the present embodiment. [Figure 6] FIG. 10 is a diagram showing the degree of characteristic shift due to the influence of light in a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on an active matrix substrate of a semi-transmissive liquid crystal display device, which is a comparative example driven by a conventional method. [Figure 7] 10A and 10B are diagrams showing the degree of characteristic shift of pixel transistors in each driving mode of a transflective liquid crystal display device, which is a comparative example driven by a conventional method. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes embodiments of the present disclosure with reference to Figures 1 to 7. For the sake of convenience, components having the same functions as those described in specific embodiments will be denoted by the same reference numerals, and their description may be omitted.

[0012] [Embodiment 1] Fig. 1 is a cross-sectional view showing a schematic configuration of an active matrix substrate 1 provided in a semi-transmissive liquid crystal display device 30 of this embodiment. Fig. 2 is a cross-sectional view showing a schematic configuration of the semi-transmissive liquid crystal display device 30 of this embodiment.

[0013] 2, a semi-transmissive liquid crystal display device 30 includes a display panel 12, a backlight 20 that emits light toward the display panel 12, and a control unit 31 (shown in FIG. 3) that controls the display panel 12 and the backlight 20. The display panel 12 includes an active matrix substrate 1, a counter substrate 19 that faces the active matrix substrate 1, and a liquid crystal layer 15 provided between the active matrix substrate 1 and the counter substrate 19. Note that in this embodiment, a case will be described as an example in which the counter substrate 19 is provided with a common counter electrode (not shown) that faces the active matrix substrate 1, but the present invention is not limited to this, and the common counter electrode (not shown) may also be provided on the active matrix substrate 1 side.

[0014] 1 , the active matrix substrate 1 includes, for each of a plurality of subpixels, a semiconductor layer SM containing an oxide semiconductor, a pixel transistor TR including a gate electrode GE, a source electrode SE, and a drain electrode DE, a reflective region RA in which a reflective pixel electrode 11 electrically connected to the drain electrode DE is provided, and a transmissive region TA in which a transmissive pixel electrode 10 electrically connected to the drain electrode DE is provided. That is, each of the subpixels of the active matrix substrate 1, for example, a red subpixel, a green subpixel, and a blue subpixel, is provided with a pixel transistor TR, a reflective region RA, and a transmissive region TA. In this embodiment, a case where one pixel is formed by red, green, and blue subpixels provided on the active matrix substrate 1 will be described as an example, but this is not limiting, and one pixel may include subpixels of colors other than red, green, and blue subpixels.

[0015] The red subpixel provided on the active matrix substrate 1 overlaps, in a plan view, with a red portion of a color filter (not shown) provided on the counter substrate 19. In the transmissive region TA of the red subpixel on the active matrix substrate 1, a voltage corresponding to the gradation value of the red subpixel constituting a still image or a moving image is applied to the transmissive pixel electrode 10 in consideration of the fixed voltage value of the common counter electrode (not shown) of the counter substrate 19 so that the difference between the fixed voltage value of the common counter electrode (not shown) and the voltage value of the transparent pixel electrode 10 becomes a voltage corresponding to the gradation value of the red subpixel constituting a still image or a moving image. By adjusting the amount of light emitted from the backlight 20 that passes through the liquid crystal layer 15, it is possible to emit an amount of red light corresponding to the gradation value of the red subpixel constituting a still image or a moving image. In the reflective region RA of the red subpixel of the active matrix substrate 1, a voltage corresponding to the gradation value of the red subpixel constituting a still image or a moving image is applied to the reflective pixel electrode 11, taking into consideration the fixed voltage value of the common counter electrode (not shown), so that the difference between the fixed voltage value of the common counter electrode (not shown) of the counter substrate 19 and the voltage value of the reflective pixel electrode 11 becomes a voltage corresponding to the gradation value of the red subpixel constituting a still image or a moving image. By adjusting the amount of light that is incident from outside and reflected by the reflective pixel electrode 11 and that passes through the liquid crystal layer 15, it is possible to emit an amount of red light corresponding to the gradation value of the red subpixel constituting a still image or a moving image. The green subpixel provided on the active matrix substrate 1 overlaps, in plan view, with the green portion of a color filter (not shown) provided on the counter substrate 19, and the blue subpixel provided on the active matrix substrate 1 overlaps, in plan view, with the blue portion of a color filter (not shown) provided on the counter substrate 19. Similarly to the transmissive region TA of the red subpixel of the active matrix substrate 1 described above, the transmissive region TA of the green subpixel of the active matrix substrate 1 and the transmissive region TA of the blue subpixel of the active matrix substrate 1 can emit an amount of green light corresponding to the gradation value of the green subpixel that constitutes a still image or a moving image, and an amount of blue light corresponding to the gradation value of the blue subpixel that constitutes a still image or a moving image.The reflective region RA of the green subpixel of the active matrix substrate 1 and the reflective region RA of the blue subpixel of the active matrix substrate 1 can emit an amount of green light corresponding to the gradation value of the green subpixel constituting a still image or a moving image and an amount of blue light corresponding to the gradation value of the blue subpixel constituting a still image or a moving image, similar to the reflective region RA of the red subpixel of the active matrix substrate 1 described above. Although not shown, alignment films are provided on the surface of the common counter electrode (not shown) of the counter substrate 19 facing the liquid crystal layer 15, the surface of the transmissive pixel electrode 10 provided in the transmissive region TA facing the liquid crystal layer 15, and the surface of the reflective pixel electrode 11 provided in the reflective region RA facing the liquid crystal layer 15.

[0016] In this embodiment, a glass substrate is used as the substrate 2 provided on the active matrix substrate 1 shown in FIG. 1, but the present invention is not limited to this and a resin substrate or the like may also be used.

[0017] 1, the gate electrode GE, source electrode SE, and drain electrode DE of the pixel transistor TR provided on the substrate 2 can each be formed of a single layer or a multilayer film of a metal containing at least one of aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper. In this embodiment, the gate electrode GE is formed of a single layer film, and the source electrode SE and drain electrode DE are formed of a multilayer film of a first metal layer 4 and a second metal layer 5, but the present invention is not limited to this.

[0018] In this embodiment, the semiconductor layer SM including the oxide semiconductor of the pixel transistor TR provided on the substrate 2 shown in Fig. 1 is described as an example where it is made of an In-Ga-Zn-O based semiconductor, but is not particularly limited as long as it includes an oxide semiconductor. In this embodiment, the pixel transistor TR has a bottom gate structure as an example, but is not limited to this and the pixel transistor TR may have a top gate structure.

[0019] The first insulating film 3 provided on the substrate 2 shown in FIG. 1 so as to cover the gate electrode GE can be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these, formed by a CVD method.

[0020] The first passivation film 6 provided on the substrate 2 shown in FIG. 1 so as to cover the semiconductor layer SM, the source electrode SE, and the drain electrode DE can be composed of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these, formed by a CVD method.

[0021] 1 can be formed using, for example, a photosensitive organic material that transmits visible light. In this embodiment, the upper part of a part of the second insulating film 7 is formed in an uneven shape, but the present invention is not limited to this.

[0022] 1 is electrically connected to the drain electrode DE via a contact hole (not shown) in the first passivation film 6. The pixel electrode 8 can be formed using, for example, a transparent metal oxide (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.).

[0023] The second insulating film 7 and the second passivation film 9 provided on the pixel electrode 8 shown in FIG. 1 can be formed using, for example, a photosensitive organic material that transmits visible light.

[0024] The transparent pixel electrode 10 provided on the second passivation film 9 and in the contact hole of the second passivation film 9 shown in Fig. 1 is electrically connected to the pixel electrode 8, which is electrically connected to the drain electrode DE, via the contact hole of the second passivation film 9. The transparent pixel electrode 10 can be formed using, for example, a transparent metal oxide (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.). As shown in Fig. 1, the transparent pixel electrode 10 is provided in both the transmissive region TA and the reflective region RA of the active matrix substrate 1.

[0025] 1 is provided only in the reflective region RA of the active matrix substrate 1. The reflective pixel electrode 11 can be formed using a metal material that reflects visible light, such as Al, Mg, Li, or Ag.

[0026] The structure of the active matrix substrate 1 described above with reference to FIG. 1 is one example, and is not particularly limited as long as each of the sub-pixels includes a semiconductor layer SM containing an oxide semiconductor, a pixel transistor TR including a gate electrode GE, a source electrode SE, and a drain electrode DE, a reflective region RA in which a reflective pixel electrode 11 electrically connected to the drain electrode DE is provided, and a transmissive region TA in which a transmissive pixel electrode 10 electrically connected to the drain electrode DE is provided.

[0027] In this embodiment, the liquid crystal layer 15 shown in FIG. 2 is formed using TN type liquid crystal, but is not limited to this and may be formed using, for example, VA type liquid crystal.

[0028] 2, a glass substrate provided with a common counter electrode (not shown) facing the active matrix substrate 1 is used in this embodiment. The common counter electrode facing the active matrix substrate 1 can be formed using, for example, a transparent metal oxide (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.).

[0029] FIG. 3 is a diagram illustrating a case where a control unit 31 provided in a semi-transmissive liquid crystal display device 30 of this embodiment controls the brightness of the backlight 20 via a backlight drive circuit 33 based on brightness data BD of the surrounding environment from a brightness sensor 32, and controls the frame frequency of the display panel 12 via a display panel drive circuit 35 based on display image type data GD from a display image type determination unit 34.

[0030] The control unit 31 shown in FIG. 3 generates a backlight control signal BCD that is output to the backlight drive circuit 33 and a display panel control signal PCD that is output to the display panel drive circuit 35.

[0031] The control unit 31 generates a backlight control signal BCD based on the ambient environment brightness data BD from the brightness sensor 32. For example, the control unit 31 may generate a backlight control signal BCD that turns on the backlight 20 at a constant brightness when the ambient environment brightness data BD is less than a predetermined value, and turns off the backlight 20 when the ambient environment brightness data BD is equal to or greater than the predetermined value. The control unit 31 may also generate a backlight control signal BCD that changes the brightness of the backlight 20 in, for example, five stages according to the ambient environment brightness data BD.

[0032] Furthermore, the control unit 31 generates a display panel control signal PCD that controls the scanning signal line driving circuit and the data signal line driving circuit included in the display panel driving circuit 35, based on an externally input image signal, i.e., a gradation value for each sub-pixel that constitutes a still image or a moving image. When the semi-transmissive liquid crystal display device 30 has M rows and N columns of sub-pixels (M and N are natural numbers greater than or equal to 2), the active matrix substrate 1 includes M×N pixel transistors TR, M scanning signal lines, and N data signal lines. Each of the M scanning signal lines is electrically connected to the gate electrodes GE of the N pixel transistors TR in the same row, and each of the N data signal lines is electrically connected to the source electrodes SE of the M pixel transistors TR in the same column.

[0033] The display panel control signal PCD, which controls the scanning signal line drive circuit, generates M gate pulse signals that control M scanning signal lines, respectively. The gate pulse signals that control the M scanning signal lines become active at different times. During the active period of a particular scanning signal line, voltages corresponding to the gradation values ​​of the corresponding subpixels constituting a still or moving image are written to the N pixel transistors TR electrically connected to the scanning signal line from the source electrodes electrically connected to the N data signal lines. The period during which a particular scanning signal line becomes active is the period of one frame period, which is also the frame frequency indicating the number of refreshes per second. For example, if the frame frequency is 1 Hz, the number of refreshes per second is one, and the period of one frame period is one second. If the frame frequency is 60 Hz, the number of refreshes per second is 60, and the period of one frame period is 1 / 60 seconds.

[0034] The display panel control signal PCD that controls the data signal line drive circuit is a control signal for generating a voltage corresponding to the grayscale value of the corresponding sub-pixel based on the grayscale value of each sub-pixel that constitutes a still image or a moving image.

[0035] The display image type determination unit 34 shown in Figure 3 includes a frame memory and a comparison unit, not shown. The frame memory stores grayscale value data for each subpixel for at least two frames that are temporally adjacent to each other. The comparison unit reads out the grayscale value data for each subpixel for at least two frames (first and second frames) that are temporally adjacent to each other stored in the frame memory, compares the grayscale values ​​of the first frame with the grayscale values ​​of the second frame for each subpixel, and determines that the image is a moving image if there is a difference, or a still image if there is no difference, and outputs display image type data GD to the control unit 31.

[0036] When a still image is displayed on a plurality of sub-pixels with the backlight 20 turned off, the control unit 31 provided in the semi-transmissive liquid crystal display device 30 writes each voltage corresponding to the gradation value of each of the sub-pixels that make up the still image from the source electrode SE of the pixel transistor TR of the corresponding sub-pixel at a first frame frequency, and when a still image is displayed on a plurality of sub-pixels with the backlight 20 turned on, the control unit 31 writes each voltage corresponding to the gradation value of each of the sub-pixels that make up the still image from the source electrode SE of the pixel transistor TR of the corresponding sub-pixel at a second frame frequency that is higher than the first frame frequency.

[0037] When displaying a moving image on the plurality of sub-pixels, the control unit 31 provided in the semi-transmissive liquid crystal display device 30 writes each voltage corresponding to the gradation value of each of the sub-pixels that make up the moving image from the source electrode SE of the pixel transistor TR of the corresponding sub-pixel at a frame frequency of 60 Hz or more.

[0038] Fig. 4 is a diagram showing the degree of characteristic shift of a pixel transistor TR including a semiconductor layer SM containing an oxide semiconductor provided on the active matrix substrate 1 of the semi-transmissive liquid crystal display device 30 of this embodiment due to the influence of light. Fig. 5 is a diagram showing the degree of characteristic shift of the pixel transistor TR in each driving mode of the semi-transmissive liquid crystal display device 30 of this embodiment.

[0039] In this embodiment, a case will be described in which the frame frequency (first frame frequency) is 30 Hz when a still image is displayed on a plurality of sub-pixels with the backlight 20 off, and the frame frequency (second frame frequency) is 60 Hz when a still image is displayed on a plurality of sub-pixels with the backlight 20 on, but this is not limiting, and the first frame frequency may be 30 Hz or less and the second frame frequency may be 60 Hz or more, or the first frame frequency may be 1 Hz or less and the second frame frequency may be 30 Hz or more. Furthermore, the second frame frequency may increase in proportion to the luminance of the backlight 20.

[0040] 5, the transflective liquid crystal display device 30 has four drive modes. Specifically, the transflective liquid crystal display device 30 has a first drive mode in which moving images are displayed in a plurality of sub-pixels at high frequency driving (frame frequency 60 Hz) when the backlight 20 is off, a second drive mode in which moving images are displayed in a plurality of sub-pixels at high frequency driving (frame frequency 60 Hz) when the backlight 20 is on, a third drive mode in which still images are displayed in a plurality of sub-pixels at low frequency driving (frame frequency 30 Hz) when the backlight 20 is off, and a fourth drive mode in which still images are displayed in a plurality of sub-pixels at high frequency driving (frame frequency 60 Hz) when the backlight 20 is on. In the case of the transflective liquid crystal display device 30, when a still image is displayed in a plurality of sub-pixels, the display is performed at low frequency driving (frame frequency 30 Hz) when the backlight 20 is off, but the display is performed at high frequency driving (frame frequency 60 Hz) when the backlight 20 is on. In the first driving mode, the degree of transistor characteristic shift (shift of On voltage to the negative side) due to the influence of light in the pixel transistor TR including the semiconductor layer SM including an oxide semiconductor provided on the active matrix substrate 1 was at a level with almost no change from the initial value A, as shown in Figures 4 and 5. In addition, in each of the second driving mode, the third driving mode, and the fourth driving mode, the degree of transistor characteristic shift (shift of On voltage to the negative side) due to the influence of light in the pixel transistor TR including the semiconductor layer SM including an oxide semiconductor provided on the active matrix substrate 1 was at level B, which is a good level with only a slight change from the initial value A, as shown in Figures 4 and 5.

[0041] As described above, a semi-transmissive liquid crystal display device 30 can be realized in which the transistor characteristic shift (shift of the on voltage to the negative side) caused by the influence of light is suppressed in the pixel transistor TR having the semiconductor layer SM containing an oxide semiconductor.

[0042] Fig. 6 is a diagram showing the degree of characteristic shift due to the influence of light in a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on an active matrix substrate of a semi-transmissive liquid crystal display device as a comparative example driven by a conventional method, and Fig. 7 is a diagram showing the degree of characteristic shift in a pixel transistor in each drive mode of a semi-transmissive liquid crystal display device as a comparative example driven by a conventional method.

[0043] A comparative transflective liquid crystal display device driven by a conventional method has four drive modes, as shown in Fig. 7. Specifically, the comparative transflective liquid crystal display device driven by a conventional method has the following drive modes: a first drive mode in which moving images are displayed in a plurality of sub-pixels at high frequency (frame frequency 60 Hz) when the backlight is off; a second drive mode in which moving images are displayed in a plurality of sub-pixels at high frequency (frame frequency 60 Hz) when the backlight is on; a third drive mode in which still images are displayed in a plurality of sub-pixels at low frequency (frame frequency 30 Hz) when the backlight is off; and a fourth drive mode in which still images are displayed in a plurality of sub-pixels at low frequency (frame frequency 30 Hz) when the backlight is on. When a still image is displayed in a plurality of sub-pixels, the comparative transflective liquid crystal display device driven by a conventional method displays the image at low frequency (frame frequency 30 Hz) regardless of whether the backlight is on or off. In the first driving mode, the degree of light-induced characteristic shift (negative shift of On voltage) of a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on an active matrix substrate of a transflective liquid crystal display device as a comparative example driven by a conventional method was at a level with almost no change from the initial value A, as shown in Figures 6 and 7. In the second driving mode and the third driving mode, the degree of light-induced characteristic shift (negative shift of On voltage) of a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on an active matrix substrate of a transflective liquid crystal display device as a comparative example driven by a conventional method was at a level B, which is a good level with only a slight change from the initial value A, as shown in Figures 6 and 7. However, in the fourth driving mode, the degree of light-induced characteristic shift (negative shift of On voltage) of a pixel transistor including a semiconductor layer containing an oxide semiconductor provided on an active matrix substrate of a transflective liquid crystal display device as a comparative example driven by a conventional method was at a level C, which is a level with a large change from the initial value A, as shown in Figures 6 and 7.The C level shown in FIG. 6 affects display performance and is also a problem in terms of reliability. [Industrial Applicability]

[0044] The present disclosure can be used in transflective liquid crystal display devices. [Explanation of symbols]

[0045] 1 Active matrix substrate 2 boards 3 First insulating film 4 1st metal layer 5 Second metal layer 6 First passivation film 7 Second insulating film 7C Contact hole 8 pixel electrode 9 Second passivation film 10 Transparent pixel electrode 11 Reflective pixel electrode 12 Display panel 15 Liquid crystal layer 19 Opposing substrate 20 Backlight 30 Transflective liquid crystal display device 31 Control Unit 32 Brightness sensor 33 Backlight driver circuit 34 Display image type discrimination unit 35 Display panel drive circuit TR pixel transistor GE gate electrode SM Semiconductor layer containing oxide semiconductor SE source electrode DE drain electrode RA reflection area TA transmission area BD Surrounding environment brightness data GD Display image type data BCD backlight control signal PCD Display panel control signal

Claims

1. an active matrix substrate including, for each of a plurality of sub-pixels, a pixel transistor including a semiconductor layer including an oxide semiconductor, a gate electrode, a source electrode, and a drain electrode, a reflective region provided with a reflective pixel electrode electrically connected to the drain electrode, and a transmissive region provided with a transmissive pixel electrode electrically connected to the drain electrode; an opposing substrate facing the active matrix substrate; a display panel including a liquid crystal layer provided between the active matrix substrate and the counter substrate; a backlight that emits light toward the display panel; a control unit that controls the display panel and the backlight, The control unit when a still image is to be displayed on the plurality of sub-pixels in a state where the backlight is not lit, voltages corresponding to gradation values ​​of the sub-pixels constituting the still image are written from the source electrodes of the pixel transistors of the corresponding sub-pixels at a first frame frequency; a semi-transmissive liquid crystal display device, wherein, when a still image is displayed on the plurality of sub-pixels while the backlight is turned on, voltages corresponding to the gradation values ​​of the sub-pixels constituting the still image are written from the source electrodes of the pixel transistors of the corresponding sub-pixels at a second frame frequency higher than the first frame frequency.

2. the first frame frequency is 30 Hz or less; 2. The transflective liquid crystal display device according to claim 1, wherein the second frame frequency is 60 Hz or higher.

3. the first frame frequency is 1 Hz or less; 2. The transflective liquid crystal display device according to claim 1, wherein the second frame frequency is 30 Hz or higher.

4. The transflective liquid crystal display device according to claim 1 , wherein the second frame frequency increases in proportion to the luminance of the backlight.

5. The control unit 2. The semi-transmissive liquid crystal display device according to claim 1, wherein, when a moving image is displayed on the plurality of sub-pixels, voltages corresponding to gradation values ​​of the sub-pixels constituting the moving image are written from the source electrodes of the pixel transistors of the corresponding sub-pixels at a frame frequency of 60 Hz or more.

6. It includes a brightness sensor and a backlight drive circuit, 6. The semi-transmissive liquid crystal display device according to claim 1, wherein the control unit controls the brightness of the backlight via the backlight drive circuit based on brightness data of the surrounding environment from the brightness sensor.

7. The display device includes a display image type determination unit and a display panel drive circuit, 6. The semi-transmissive liquid crystal display device according to claim 1, wherein the control unit controls the frame frequency of the display panel via the display panel drive circuit based on the display image type data from the display image type determination unit.

Images