WO2012124309A1

WO2012124309A1 - Liquid crystal display device and electronic apparatus

Info

Publication number: WO2012124309A1
Application number: PCT/JP2012/001700
Authority: WO
Inventors: 泰高丸; 耕平田中
Original assignee: シャープ株式会社
Priority date: 2011-03-16
Filing date: 2012-03-12
Publication date: 2012-09-20

Abstract

This liquid crystal display device is provided with an alternating current drive control unit which reverses, by each period when a gate wiring line is scanned, polarity of a signal voltage to be applied to a plurality of source wiring lines. Thin film transistors include a first thin film transistor, in which a width with which a source electrode and a gate electrode overlap each other is larger than a width with which the drain electrode and the gate electrode overlap each other, and a second thin film transistor, in which a width with which the source electrode and the gate electrode overlap each other is smaller than a width with which the drain electrode and the gate electrode overlap each other. A pixel column composed of a plurality of pixels aligned along the gate wiring line includes a plurality of first pixels, each of which has a first thin film transistor formed therein, and a plurality of second pixels, each of which has a second thin film transistor formed therein.

Description

Liquid crystal display device and electronic device

The present invention relates to a liquid crystal display device and an electronic apparatus including the same.

In recent years, demand for electronic devices such as liquid crystal televisions and smartphones has increased, and liquid crystal display devices are widely used as display devices.

When a DC voltage is applied to the liquid crystal layer of the liquid crystal display device, display defects and liquid crystal deterioration occur, and therefore it is desirable that the liquid crystal display device be AC driven. Therefore, as disclosed in

Patent Documents

1 and 2, for example, a 1H line inversion driving method and a 1H dot inversion driving method are known as AC driving methods for liquid crystal display devices.

The 1H line inversion driving method is a driving method in which the polarity of all source signals is inverted every 1H period (one horizontal scanning period). In this driving method, the polarity of all signal lines becomes positive when scanning a certain scanning line, and the polarity of all signal lines is inverted and becomes negative when scanning the next scanning line. As a result, when scanning for one frame is completed, each pixel is alternately arranged with a row in which a positive signal is written in one horizontal row and a row in which a negative signal is written in one horizontal row. It becomes.

The 1H dot inversion driving method is a driving method in which the polarities of the signal lines are alternately inverted. In this driving method, when a certain scanning line is scanned, the polarity of a certain signal line becomes positive, and the polarity of the adjacent signal line becomes negative. When the next scanning line is scanned, the polarity of the signal line is inverted and becomes negative, and the polarity of the adjacent signal line becomes positive. As a result, when one frame of scanning is completed, plus and minus signals are alternately written in the vertical direction and the horizontal direction in each pixel.

Further, as disclosed in

Patent Documents

3 and 4, etc., the AC drive type liquid crystal display device displays a flicker pattern on the screen for the purpose of suppressing flicker, and generates a signal voltage and a common electrode voltage. Initial adjustment is known. For example, a display state such as pseudo halftone frame inversion driving is displayed on a flicker pattern display screen in which one polarity pixel is displayed in black (or white display) and the other polarity pixel is displayed in halftone. In this state, the voltage applied to the common electrode is adjusted so that the flicker is minimized.

On the other hand, as shown in FIG. 21, which is a plan view showing a TFT (thin film transistor) 100 used in a conventional liquid crystal display device, the TFT 100 has a U-shaped source electrode 102 having a pair of electrode limbs 101 formed in a bifurcated shape. And the drain electrode 103 disposed between the pair of electrode limbs 101, and the semiconductor layer 104 and the gate electrode 105 overlapping with the source electrode 102 and the drain electrode 103, thereby reducing the W length of the channel region 106. It is known to ensure a large amount (see

Patent Documents

5 and 6, etc.).

JP 2002-149117 A JP 2003-202542 A JP 2004-117749 A JP 2007-171358 A JP 2010-055065 A JP 2008-004771 A

Incidentally, TFTs used in liquid crystal display devices are usually formed of a-Si (amorphous silicon). When light enters the channel region of the TFT, a photocurrent is generated, and an off-leakage current is generated.

The present inventors have made an AC drive for inverting the polarity of a signal voltage applied to a source electrode in a liquid crystal display device having a TFT having a source electrode shape different from that of a drain electrode, such as the TFT having the U-shaped source electrode. As described above, it was possible to secure a large W length in the channel region as described above, but the problem was found that flicker is particularly easily visible.

The present invention has been made in view of such a point, and the object of the present invention is to significantly reduce flicker while AC driving a liquid crystal display device having a TFT whose source electrode shape is different from that of the drain electrode. It is in trying to suppress.

As a result of intensive studies on a liquid crystal display device having a TFT whose source electrode shape is different from that of the drain electrode, the inventors have reversed the polarity of the signal voltage applied to the source electrode (source wiring). It was found that the amount of off-leakage current generated in the TFT changes according to the reversal of the polarity. As a result of the change in the luminance of the pixel provided with the TFT along with the change in the off-leakage current, it has been found that flicker is easily visually recognized.

In order to achieve the above object, a liquid crystal display device according to the present invention includes a plurality of source lines, a plurality of gate lines crossing the source lines, a plurality of pixels provided in a matrix, A thin film transistor provided in each of a plurality of pixels and connected to the source wiring and the gate wiring, a pixel electrode provided in each of the plurality of pixels and connected to a drain electrode of the thin film transistor, and at least one of the gate wirings An AC drive control unit that reverses the polarity of the signal voltage applied to the plurality of source wirings for each scanning period is provided.

In addition, part of the drain electrode and part of the source electrode of the thin film transistor overlap with the gate electrode of the thin film transistor, respectively, and the overlapping width of the source electrode and the gate electrode is different from that of the drain electrode. A first thin film transistor wider than an overlap width with the gate electrode; and a second thin film transistor in which an overlap width between the source electrode and the gate electrode is narrower than an overlap width between the drain electrode and the gate electrode. A pixel column composed of the plurality of pixels arranged along the gate wiring includes a plurality of first pixels in which the first thin film transistor is formed and a plurality of second pixels in which the second thin film transistor is formed. Yes.

According to the present invention, flicker can be significantly suppressed while AC driving a liquid crystal display device having a TFT whose source electrode shape is different from that of the drain electrode.

FIG. 1 is an enlarged plan view showing a part of the TFT substrate according to the first embodiment. FIG. 2 is an enlarged plan view showing the first TFT and the second TFT. FIG. 3 is a plan view schematically showing a flicker pattern. FIG. 4 is a cross-sectional view showing a schematic configuration of the TFT. FIG. 5 is a plan view schematically showing a TFT having a first electrode and a second electrode smaller than the first electrode. FIG. 6 is a graph showing the results of Example 1. FIG. 7 is a graph showing the results of Example 2. FIG. 8 is a graph showing off-leakage currents in Examples 1 and 2. FIG. 9 is a cross-sectional view illustrating a schematic structure of a liquid crystal display device provided in the electronic apparatus according to the first embodiment. FIG. 10 is a plan view showing 1H line inversion driving of the liquid crystal display device according to the first embodiment. FIG. 11 is a plan view showing 1H line inversion driving of a liquid crystal display device as a comparative example. FIG. 12 is a graph showing a simulation result with respect to temporal change in luminance in the comparative example. FIG. 13 is a graph illustrating a simulation result of a change in luminance with time in the example. FIG. 14 is an enlarged plan view showing a part of the TFT substrate according to the second embodiment. FIG. 15 is a plan view showing 1H dot inversion driving of the liquid crystal display device according to the second embodiment. FIG. 16 is a plan view showing 1H dot inversion driving of a liquid crystal display device as a comparative example. FIG. 17 is a plan view showing an enlarged part of the TFT substrate 13 in the third embodiment. FIG. 18 is an enlarged plan view showing the first TFT and the second TFT in the third embodiment. FIG. 19 is a plan view showing 1H line inversion driving of the liquid crystal display device 1 according to the third embodiment. FIG. 20 is a plan view showing 1H line inversion driving of a liquid crystal display device as a comparative example. FIG. 21 is a plan view showing a TFT used in a conventional liquid crystal display device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

Embodiment 1 of the Invention
1 to 13 show Embodiment 1 of the present invention.

FIG. 1 is a plan view showing an enlarged part of the TFT substrate according to the first embodiment. FIG. 2 is an enlarged plan view showing the first TFT and the second TFT. FIG. 9 is a cross-sectional view illustrating a schematic structure of a liquid crystal display device provided in the electronic apparatus according to the first embodiment.

The electronic device 10 in the first embodiment is, for example, a liquid crystal television. The electronic device 10 may be a mobile device such as a smartphone or a mobile phone, or other electronic device. As shown in FIG. 9, the electronic device 10 includes a liquid crystal display device 1 as a display unit inside a housing 2.

As shown in FIG. 9, the liquid crystal display device 1 includes a liquid crystal display panel 11 and a backlight unit 12 that is a light source disposed on the back side of the liquid crystal display panel 11. That is, the liquid crystal display device 1 is configured to perform transmissive display by selectively transmitting at least light from the backlight unit 12.

As shown in FIG. 9, the liquid crystal display panel 11 includes a TFT substrate 13 that is a first substrate, and a counter substrate 14 that is a second substrate disposed to face the TFT substrate 13. A liquid crystal layer 15 is sealed between the TFT substrate 13 and the counter substrate 14 by a seal member 16.

The liquid crystal display panel 11 has a display area (not shown) and a frame-like non-display area (not shown) provided around the display area. A plurality of pixels 18 provided in a matrix are formed in the display area. Here, the pixel 18 is a minimum unit for controlling display.

The TFT substrate 13 is composed of an active matrix substrate. The TFT substrate 13 has a glass substrate (not shown) as a transparent substrate. As shown in FIG. 1, a plurality of source lines 23 extending in parallel with each other and a plurality of gate lines 22 extending so as to intersect the source lines 23 are formed on the glass substrate.

That is, the plurality of gate lines 22 and the plurality of source lines 23 are formed in a lattice shape as a whole, and the pixels 18 are formed in regions surrounded by the gate lines 22 and the source lines 23 in a rectangular shape. Each of the gate wiring 22 and the source wiring 23 is configured by a single-layer film made of one type or a multi-layer film made of a plurality of types, for example, among Al, Cu, Mo, Ti, and the like.

Each pixel 18 is provided with a TFT (thin film transistor) 20 in the vicinity of the intersection of the gate wiring 22 and the source wiring 23. The gate wiring 22 and the source wiring 23 are connected to the TFT 20. The TFT 20 in the first embodiment is a bottom gate type TFT, and a gate electrode 26 branched from the gate wiring 22 and a semiconductor layer (not shown) facing the gate electrode 26 via a gate insulating film (not shown). A source electrode 25 that is branched from the source wiring 23, and a drain electrode 29.

The gate electrode 26 and the gate wiring 22 are formed on a glass substrate and covered with the gate insulating film. The gate insulating film is composed of, for example, a single-layer film made of one of SiNx (silicon nitride) and SiO ₂ or a multi-layer film made of a plurality of kinds. On the surface of the gate insulating film, the semiconductor layer is formed in a rectangular island shape, for example. The semiconductor layer is formed of a semiconductor such as a-Si, for example.

A part of the source electrode 25 and a part of the drain electrode 29 are overlapped with the semiconductor layer and the gate electrode 26, respectively. The source electrode 25, the drain electrode 29, and the like are covered with an interlayer insulating film (not shown). The interlayer insulating film is made of, for example, SiNx.

Further, the plurality of pixels 18 are formed with pixel electrodes 30 connected to the drain electrodes 29 of the TFTs 20 provided in the pixels 18. The pixel electrode 30 is formed on the surface of the interlayer insulating film, and is composed of a transparent conductive film such as ITO (Indium Tin Oxide).

On the other hand, a common electrode (not shown) provided in common with the plurality of pixel electrodes 30 is formed on the counter substrate 14. Similar to the pixel electrode 30, the common electrode is also formed of a transparent conductive film such as ITO. Thus, the orientation of the liquid crystal layer 15 is controlled for each pixel 18 by controlling the potential difference between the common electrode having a predetermined potential and the pixel electrode 30 of each pixel 18.

<TFT configuration>
The TFT 20 in this embodiment includes a first TFT 20 a in which the source electrode 25 is larger than the drain electrode 29 and a second TFT 20 b in which the drain electrode 29 is larger than the source electrode 25.

As shown in FIGS. 1 and 2, the source electrode 25 of the first TFT 20 a includes a pair of electrode limbs 32 formed in a bifurcated shape, and a base end portion 33 formed wide on the base end side of the electrode limbs 32. have. On the other hand, the drain electrode 29 of the first TFT 20 a has a linear portion 34 extending linearly, and the tip of the linear portion 34 is disposed between the pair of electrode limbs 32.

As shown in FIG. 2, the entire electrode limb 32 of the source electrode 25 and a part of the base end portion 33 overlap the gate electrode 26. As a result, the overlapping width A of the source electrode 25 and the gate electrode 26 at the base end portion 33 is wider than the overlapping width B of the drain electrode 29 and the gate electrode 26.

On the other hand, the drain electrode 29 of the second TFT 20b has a pair of electrode limbs 36 formed in a bifurcated shape and a base end portion 37 formed wide on the base end side of the electrode limbs 36. On the other hand, the source electrode 25 of the second TFT 20 b has a linear portion 38 that extends linearly, and the tip of the linear portion 38 is disposed between the pair of electrode limbs 36.

As shown in FIG. 2, the entire electrode limb 36 of the drain electrode 29 and a part of the base end portion 37 overlap the gate electrode 26. As a result, the overlap width A between the source electrode 25 and the gate electrode 26 is narrower than the overlap width B between the drain electrode 29 and the gate electrode 26 at the base end portion 37.

<Pixel arrangement configuration>
As shown in FIG. 1, a plurality of first pixels 18 a in which first TFTs 20 a are formed and a plurality of pixels in which second TFTs 20 b are formed are arranged in a pixel column 19 including a plurality of pixels 18 arranged along the gate wiring 22. The second pixel 18b is included.

Further, in each pixel column 19, one first pixel 18 a and one second pixel 18 b are alternately arranged along the gate wiring 22. On the other hand, in the direction along the source wiring 23, a plurality of first pixels 18a or a plurality of second pixels 18b are arranged side by side.

As another arrangement example of the first pixel 18 a and the second pixel 18 b, for example, in each pixel column 19, two first pixels 18 a and two second pixels 18 b are alternately arranged along the gate wiring 22. May be arranged. That is, at least one first pixel 18 a and the same number of second pixels 18 b as the at least one first pixel 18 a are alternately arranged along the gate wiring 22 in the pixel column 19. Also good.

<AC drive control circuit>
The liquid crystal display device 1 further includes an AC drive control unit 40 that applies signal voltages having the same polarity to the plurality of source lines 23 during a period of scanning one gate line 22. The AC drive control unit 40 is configured to invert the polarity of the signal voltage applied to the plurality of source lines 23 for each period of scanning one gate line 22. That is, the driving method of the liquid crystal display device 1 is a 1H line inversion driving method in which the polarity of the signal voltage is inverted every 1H period (one horizontal scanning period).

The AC drive control unit 40 may be configured to invert the polarity of the signal voltage every time the plurality of gate wirings 22 are scanned. That is, the AC drive control unit 40 may be configured to perform nH line inversion driving. Therefore, the AC drive control unit 40 can be configured to apply signal voltages having the same polarity to the plurality of source lines 23 in each of the periods in which at least one gate line 22 is scanned.

-Production method-
Next, a method for manufacturing the liquid crystal display device 1 will be described.

The liquid crystal display device 1 is a liquid crystal display panel in which a TFT substrate 13 manufactured by forming a plurality of TFTs 20 and the like and a counter substrate 14 formed with a common electrode and the like are bonded together via a liquid crystal layer 15 and a seal member 16. 11 and the backlight unit 12 is disposed opposite to the liquid crystal display panel 11. Further, the electronic apparatus 10 is manufactured by incorporating the liquid crystal display device 1 into the housing 2 together with other functional circuits and the like.

In the method of manufacturing a liquid crystal display device, a flicker pattern is displayed on the screen for the purpose of suppressing flickering on the liquid crystal display panel 11 with the backlight unit 12 facing each other, and the signal voltage and the common electrode voltage are initially adjusted. Voltage adjusting step is included.

Here, FIG. 3 is a plan view schematically showing a flicker pattern. As shown in FIG. 3, the flicker pattern 42 is a pattern in which the pixel 18 to which a signal voltage of one polarity is applied is displayed in black (Black), and the pixel 18 in the other polarity is displayed in halftone (Gray). is there. Since the flicker pattern 42 is a display pattern in which flicker is most easily recognized on the display screen, the flicker pattern 42 is used as a display pattern when adjusting the voltage (common electrode voltage) applied to the common electrode in the counter substrate 14.

For example, as shown in FIG. 3, the flicker pattern 42 in the present embodiment is a stripe pattern in which the pixel columns 19 displayed in black and the pixel columns 19 displayed in halftone are alternately arranged one by one. . The polarity of the signal voltage in each pixel column 19 is inverted for each frame. That is, the pixel column 19 in which the polarity of each pixel 18 in the n−1 frame is “−−−−...” Becomes “+++...” In the n frame and “−−−−.・」

In the voltage adjustment step, the magnitude of the common electrode voltage is adjusted so that the flicker on the display screen is minimized while the flicker pattern 42 is displayed on the display screen of the liquid crystal display device 1.

-Effect of Embodiment 1-
Therefore, according to the first embodiment, flicker can be significantly suppressed while ensuring a large W length of each TFT 20. Hereinafter, the effects of the present invention will be described in detail.

Here, FIG. 4 is a cross-sectional view showing a schematic configuration of the TFT 20. As shown in FIG. 4, the TFT 20 includes a gate electrode 26 formed on the glass substrate 17, a gate insulating film 27 covering the gate electrode 26, and a semiconductor made of a-Si opposed to the center of the gate electrode 26. It has a layer 28, a source electrode 25 facing one end side of the gate electrode 26, and a drain electrode 29 facing the other end side of the gate electrode 26.

Part of the light of the backlight unit 12 passes through the glass substrate 17 and enters between the source electrode 25 or the drain electrode 29 and the gate electrode 26. Then, as indicated by an arrow in FIG. 4, the incident light repeatedly reflects between the source electrode 25 or the drain electrode 29 and the gate electrode 26 and enters the semiconductor layer 28. As a result, an off-leakage current is generated in the TFT 20.

FIG. 5 is a plan view schematically showing a TFT 50 having a first electrode 51 and a second electrode 52 smaller than the first electrode 51 as a source electrode or a drain electrode. In the TFT 50, a semiconductor layer 54 is formed between the first electrode 51 and the second electrode 52.

As shown in FIG. 5, for example, for the TFT 50 in which the overlap width D between the first electrode 51 and the gate electrode 53 is wider than the overlap width d between the second electrode 52 and the gate electrode 53, Since a large amount of light is incident between the first electrode 51 and the gate electrode 53 when a polar signal voltage is applied, it is considered that a large off-leakage current is generated. On the other hand, when a + polarity signal voltage is applied to the second electrode 52, the amount of light incident between the second electrode 52 and the gate electrode 53 is small, so the off-leakage current is considered to be small.

Here, an actual implementation example of the TFT 50 having the first electrode 51 formed in a U-shape and the second electrode 52 formed in an I-shape as a source electrode or a drain electrode will be described.

In the TFT 50 according to the example, the L length of the semiconductor layer 54 is 4 μm and the W length is 50 μm. The overlapping width D between the U-shaped first electrode 51 and the gate electrode 53 is 26 μm, and the overlapping width d between the I-shaped second electrode 52 and the gate electrode 53 is 6 μm. A voltage of −20 to 20 V was applied to the gate electrode. The applied voltage to the drain electrode was 4.1V, and the applied voltage to the source electrode was 0V.

In Example 1, the U-shaped first electrode 51 is used as a source electrode and the I-shaped second electrode 52 is used as a drain electrode, and light having an intensity of 1750 cd / m ² is irradiated. For the state X1 and the dark state Y1 where no light is irradiated, the change in drain current with respect to the gate voltage was measured. The measurement results are shown in the graph of FIG.

In the second embodiment, in the configuration in which the U-shaped first electrode 51 is used as the drain electrode and the I-shaped second electrode 52 is used as the source electrode, the light state X2 is irradiated with light having an intensity of 1750 cd / m ^2. The change in drain current with respect to the gate voltage was measured for the dark state Y2 where no light was irradiated. The measurement results are shown in the graph of FIG.

Regarding Example 1 and Example 2, in the dark states Y1 and Y2, as indicated by broken lines in FIGS. 6 and 7, since the light itself applied to the TFT 50 is small, the drain current value indicating the off-leakage current is relatively low. small.

Regarding Example 1, in the bright state X1, although the voltage applied to the I-shaped second electrode (drain current) 52 is larger than the U-shaped first electrode (source electrode) 51, the second electrode 52 Since the overlap width between the first electrode 51 and the gate electrode 53 is smaller than the overlap width between the first electrode 51 and the gate electrode 53, the off-leakage current is relatively small as shown by the solid line in FIG.

On the other hand, in Example 2, in the bright state X2, the applied voltage to the U-shaped first electrode (drain electrode) 51 is larger than that of the I-shaped second electrode (source electrode) 52, and the application thereof Since the overlapping width between the U-shaped first electrode 51 and the gate electrode 53 having a large voltage is larger than the overlapping width between the second electrode 52 and the gate electrode 53, as shown by the solid line in FIG. It became relatively large.

The graph of FIG. 8 shows a comparison of the off-leakage current (drain current value) in Examples 1 and 2. As shown in FIG. 8, it can be seen that the off-leakage current X2 in the bright state X2 of Example 2 is larger than the off-leakage current X1 in the bright state X1 of Example 1. On the other hand, it was confirmed that the off-leakage current Y1 in the dark state Y1 of Example 1 and the off-leakage current Y2 in the dark state Y2 of Example 2 are substantially the same and smaller than X1 and X2.

As described above, for example, as shown in FIG. 5, for the TFT 50 in which the overlap width D between the first electrode 51 and the gate electrode 53 is wider than the overlap width d between the second electrode 52 and the gate electrode 53, It can be confirmed that the off-leakage current increases when a + polarity signal voltage is applied to the second electrode 52, while the off-leakage current decreases when the + polarity signal voltage is applied to the second electrode 52.

Next, FIG. 10 is a plan view showing 1H line inversion driving of the liquid crystal display device 1 according to the first embodiment. In the liquid crystal display device 1, as shown in the upper part of FIG. 10, the signal voltage applied to the source line 23 is set to −polarity in the 1H period of scanning the pixel column 19 a for black display of a certain n−1 frame. . In the 1H period during which the next halftone display pixel row 19b is scanned, the signal voltage applied to the source line 23 is inverted to have a positive polarity. Here, the arrow of each pixel 18 in FIG. 10 indicates the direction in which the off-leakage current flows.

In the n-1 frame, in the pixel column 19b that is visually recognized as a halftone display, the off-leak current of the first pixel 18a is relatively small (S), and the off-leak current of the second pixel 18b is relatively large. (L). Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixel 18a having a relatively small off-leakage current (S) and the second pixel 18b having a relatively large off-leakage current (L).

As shown in the lower part of FIG. 10, in the pixel column 19b that is displayed in halftone in the next n frame, the off-leak current of the first pixel 18a becomes relatively large (L), and the off-leak current of the second pixel 18b. Becomes relatively small (S). Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixels 18a having a relatively large off-leakage current (L) and the second pixels 18b having a relatively small off-leakage current (S).

That is, according to this embodiment, in any frame, as a result of including the same number of (S) pixels 18 having a relatively small off-leakage current and (L) pixels 18 having a relatively large off-leakage current. Since the total leak amount of the entire display screen is the same before and after the change, flicker can be significantly suppressed. Therefore, according to the present embodiment, flicker can be significantly suppressed while ensuring a large W length of each TFT 20.

On the other hand, FIG. 11 is a plan view showing 1H line inversion driving of a liquid crystal display device as a comparative example. In this comparative example, all the pixels 118 have the same configuration, and each source electrode 125 is formed in a U shape, while each drain electrode 129 is formed in an I shape.

In this liquid crystal display device, as shown in the upper part of FIG. 11, the signal voltage applied to the source line 123 is set to -polarity in the 1H period during which the pixel column 119a for black display of a certain n-1 frame is scanned. To do. In the 1H period during which the next pixel row 119b for halftone display is scanned, the signal voltage applied to the source wiring 123 is inverted to have a positive polarity. Here, the arrow of each pixel 118 in FIG. 11 indicates the direction in which the off-leakage current flows.

In this n-1 frame, in the pixel column 119b displaying a halftone that is visually recognized, the off-leak current of each pixel 118 is relatively small (S). Accordingly, the entire screen is displayed in halftone by the (S) pixel 118 having a relatively small off-leakage current.

As shown in the lower part of FIG. 11, the off-leak current of each pixel 118 is relatively large (L) in the pixel column 119b displaying halftone in the next n frames. Therefore, the entire screen is displayed in halftone by the (L) pixel 118 having a relatively large off-leakage current.

That is, in the liquid crystal display device as the comparative example, the off-leak current of all the pixels 118 that perform halftone display is relatively small (S) before and after the frame changes, and the off-leakage of all the pixels 118 that perform halftone display. Since the state where the current is relatively large (L) is alternately switched, the flicker is easily visually recognized.

Here, FIG. 12 is a graph showing a simulation result with respect to a temporal change in luminance of the liquid crystal display device in the comparative example. FIG. 13 is a graph showing a simulation result with respect to a temporal change in luminance of the liquid crystal display device 1 in the present embodiment.

As shown in FIG. 11, when the total leak amount in the n-1 frame is different from the total leak amount in the n frame, the waveform of the luminance change has a distorted shape as shown in the graph of FIG. On the other hand, as shown in FIG. 10, when the total leak amount in the (n−1) frame is the same as the total leak amount in the n frame, the waveform in one frame period is symmetric as shown in the graph of FIG. It turns out that it will become a shape.

Since the display of the comparative example showing the distorted luminance waveform as shown in FIG. 12 is recognized by the human eye at a half frequency (that is, 10 Hz) of the drive frequency (20 Hz in this embodiment), flicker is visually recognized. It becomes easy. On the other hand, in the display of the embodiment shown in FIG. 13, since it is recognized as the same frequency as the drive frequency (that is, 20 Hz), flicker can be made difficult to be visually recognized.

<< Embodiment 2 of the Invention >>
14 to 16 show Embodiment 2 of the present invention.

FIG. 14 is a plan view showing an enlarged part of the TFT substrate 13 in the second embodiment. FIG. 15 is a plan view showing 1H dot inversion driving of the liquid crystal display device 1 according to the second embodiment. FIG. 16 is a plan view showing 1H dot inversion driving of a liquid crystal display device as a comparative example. In the following embodiments, the same portions as those in FIGS. 1 to 13 are denoted by the same reference numerals, and detailed description thereof is omitted.

In the first embodiment, an example in which the AC drive control unit 40 performs 1H line inversion drive has been described. However, the AC drive control unit 40 is not limited to this, and a plurality of AC drive control units 40 are provided for each period of scanning at least one gate wiring 22. The polarity of the signal voltage applied to the source wiring 23 may be reversed. The AC drive control unit 40 in the second embodiment is configured to perform 1H dot inversion drive.

The electronic device 10 according to the second embodiment includes a liquid crystal display device 1 as a display unit inside a housing 2 as shown in FIG. The electronic device 10 is, for example, a mobile device such as a liquid crystal television or a smartphone or other electronic devices.

The liquid crystal display panel 11 has a display area (not shown) and a frame-like non-display area (not shown) provided around the display area. A plurality of pixels 18 provided in a matrix are formed in the display area.

The TFT substrate 13 is composed of an active matrix substrate. The TFT substrate 13 has a glass substrate (not shown) as a transparent substrate. As shown in FIG. 14, a plurality of source lines 23 extending in parallel to each other and a plurality of gate lines 22 extending so as to cross the source lines 23 are formed on the glass substrate.

Each pixel 18 is provided with a TFT 20 in the vicinity of the intersection of the gate wiring 22 and the source wiring 23. The gate wiring 22 and the source wiring 23 are connected to the TFT 20. The TFT 20 in the second embodiment is a bottom gate type TFT, and a gate electrode 26 branched from the gate wiring 22 and a semiconductor layer (not shown) facing the gate electrode 26 via a gate insulating film (not shown). A source electrode 25 that is branched from the source wiring 23, and a drain electrode 29.

Further, the plurality of pixels 18 are formed with pixel electrodes 30 connected to the drain electrodes 29 of the TFTs 20 provided in the pixels 18. The pixel electrode 30 is formed on the surface of the interlayer insulating film, and is formed of a transparent conductive film such as ITO.

As shown in FIGS. 14 and 2, the source electrode 25 of the first TFT 20 a includes a pair of electrode limbs 32 formed in a bifurcated shape, and a base end portion 33 formed wide on the base end side of the electrode limbs 32. have. On the other hand, the drain electrode 29 of the first TFT 20 a has a linear portion 34 extending linearly, and the tip of the linear portion 34 is disposed between the pair of electrode limbs 32.

<Pixel arrangement configuration>
As shown in FIG. 14, a pixel column 19 including a plurality of pixels 18 arranged along the gate wiring 22 includes a plurality of first pixels 18 a in which the first TFTs 20 a are formed and a plurality of pixels in which the second TFTs 20 b are formed. The second pixel 18b is included.

Further, in each pixel column 19, two first pixels 18 a and two second pixels 18 b are alternately arranged along the gate wiring 22. On the other hand, in the direction along the source wiring 23, a plurality of first pixels 18a or a plurality of second pixels 18b are arranged side by side.

<AC drive control circuit>
The liquid crystal display device 1 further includes an AC drive control unit 40 that applies signal voltages having different polarities to the source lines 23 adjacent to each other in a period during which one gate line 22 is scanned. The AC drive control unit 40 is configured to invert the polarity of the signal voltage applied to the plurality of source lines 23 for each period of scanning one gate line 22. That is, the driving method of the liquid crystal display device 1 is a 1H dot inversion driving method in which the polarity of the signal voltage is inverted every 1H period (one horizontal scanning period).

The AC drive control unit 40 may be configured to invert the polarity of the signal voltage every time the plurality of gate wirings 22 are scanned. That is, the AC drive control unit 40 may be configured to perform nH dot inversion driving. Therefore, the AC drive control unit 40 can be configured to apply signal voltages having different polarities to the source wirings 23 adjacent to each other in each of the scanning periods of at least one gate wiring 22.

The flicker pattern in the present embodiment has, for example, a black checkered pixel 18 and a halftone display pixel 18 arranged in a zigzag pattern, and has a checkered pattern as a whole. The polarity of the signal voltage in each pixel column 19 is inverted for each frame. That is, the pixel column 19 in which the polarity of each pixel 18 in the n−1 frame is “− ++ −...” Becomes “+ − + −...” In the n frame and “− ++ −” in the n + 1 frame. + ... ".

-Effect of Embodiment 2-
Therefore, according to the second embodiment, flicker can be significantly suppressed while ensuring a large W length of each TFT 20. Hereinafter, the effects of the present invention will be described in detail.

As described in Embodiment 1 above, the present inventors reverse the polarity of the signal voltage applied to the source electrode (source wiring) in a liquid crystal display device including a TFT having a source electrode shape different from that of the drain electrode. It was found that the amount of off-leakage current generated in the TFT changes according to the reversal of the polarity. As a result of the change in the luminance of the pixel provided with the TFT along with the change in the off-leakage current, it has been found that flicker is easily visually recognized.

Here, FIG. 15 is a plan view showing 1H dot inversion driving of the liquid crystal display device 1 according to the second embodiment. As for the liquid crystal display device 1, as shown in the upper part of FIG. 15, in the 1H period in which the pixel row 19 a that performs a certain “black display, halftone display, black display, halftone display... The polarity of the signal voltage applied to the wiring 23 is “+ − + −.

In the next 1H period, the polarity of the signal voltage applied to the source wiring 23 is set to “− ++ − + · for the pixel row 19b for“ halftone display, black display, halftone display, black display.・・」 Then, a positive polarity signal voltage is applied to the pixel 18 displaying black, and a negative polarity signal voltage is applied to the pixel 18 displaying halftone. Here, the arrow of each pixel 18 in FIG. 15 indicates the direction in which the off-leakage current flows.

In the n-1 frame, the off-leakage current is relatively large (L) in the first pixel 18a displaying the halftone display that is visually recognized. On the other hand, the off-leakage current is relatively small in the second pixel 18b displaying halftone (S). Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixels 18a having a relatively large off-leakage current (L) and the second pixels 18b having a relatively small off-leakage current (S).

As shown in the lower part of FIG. 15, in the next n frames, the off-leakage current is relatively small in the first pixel 18a that is displayed as a halftone display (S). On the other hand, the off-leakage current becomes relatively large (L) in the second pixel 18b displaying halftone. Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixel 18a having a relatively small off-leakage current (S) and the second pixel 18b having a relatively large off-leakage current (L).

That is, according to the present embodiment, each frame includes the same number (S) of pixels 18 with relatively small off-leakage current (S) and pixels (L) with relatively large off-leakage current. Since the total leak amount of the entire display screen is the same before and after the change, flicker can be significantly suppressed. Therefore, according to the present embodiment, flicker can be significantly suppressed while ensuring a large W length of each TFT 20.

On the other hand, FIG. 16 is a plan view showing 1H dot inversion driving of a liquid crystal display device as a comparative example. In this comparative example, all the pixels 118 have the same configuration, and each source electrode 125 is formed in a U shape, while each drain electrode 129 is formed in an I shape.

In the liquid crystal display device, as shown in the upper part of FIG. 16, in the 1H period of scanning the pixel column 119a that performs certain “black display, halftone display, black display, halftone display... The polarity of the signal voltage applied to the source wiring 123 is “+ − + −.

In the next 1H period, the polarity of the signal voltage applied to the source wiring 123 is set to “− ++ − + · for the pixel column 119b performing“ halftone display, black display, halftone display, black display.・・」 Then, a positive polarity signal voltage is applied to the pixel 118 displaying black, and a negative polarity signal voltage is applied to the pixel 118 displaying halftone. Here, the arrow of each pixel 18 in FIG. 16 indicates the direction in which the off-leakage current flows.

In the n-1 frame, the off-leakage current is relatively large (L) in the visually recognized pixel 118 displaying halftone. Therefore, the entire screen is displayed in halftone by the (L) pixel 118 having a relatively large off-leakage current.

As shown in the lower part of FIG. 16, the off-leakage current is relatively small in the pixel 118 that is displayed in halftone in the next n frames (S). Accordingly, the entire screen is displayed in halftone by the (S) pixel 118 having a relatively small off-leakage current.

That is, in the liquid crystal display device as the comparative example, the off-leak current of all the pixels 118 that perform halftone display is relatively large (L) before and after the frame changes, and the off-leakage of all the pixels 118 that perform halftone display. Since the state where the current is relatively small (S) is alternately switched, flicker is likely to be visually recognized.

<< Embodiment 3 of the Invention >>
17 to 20 show Embodiment 3 of the present invention.

FIG. 17 is a plan view showing an enlarged part of the TFT substrate 13 in the third embodiment. FIG. 18 is an enlarged plan view showing the first TFT and the second TFT in the third embodiment.

In the first embodiment, the source electrode 25 or the drain electrode 29 of the TFT 20 is formed in a U shape, whereas in the third embodiment, the source electrode 25 and the drain electrode 29 of the TFT 20 are each formed in a rectangular shape. Is different.

The electronic device 10 according to the third embodiment includes a liquid crystal display device 1 as a display unit inside a housing 2 as shown in FIG. The electronic device 10 is, for example, a mobile device such as a liquid crystal television or a smartphone or other electronic devices.

The TFT substrate 13 is composed of an active matrix substrate. The TFT substrate 13 has a glass substrate (not shown) as a transparent substrate. As shown in FIG. 17, a plurality of source lines 23 extending in parallel to each other and a plurality of gate lines 22 extending so as to intersect the source lines 23 are formed on the glass substrate.

Each pixel 18 is provided with a TFT 20 in the vicinity of the intersection of the gate wiring 22 and the source wiring 23. The gate wiring 22 and the source wiring 23 are connected to the TFT 20. The TFT 20 in the third embodiment is a bottom gate type TFT, and a gate electrode 26 branched from the gate wiring 22 and a semiconductor layer (not shown) facing the gate electrode 26 via a gate insulating film (not shown). A source electrode 25 that is branched from the source wiring 23, and a drain electrode 29.

<Configuration of TFT>
The TFT 20 in this embodiment includes a first TFT 20 a in which the source electrode 25 is larger than the drain electrode 29 and a second TFT 20 b in which the drain electrode 29 is larger than the source electrode 25.

As shown in FIG. 17 and FIG. 18, the source electrode 25 and the drain electrode 29 of the first TFT 20a each have a rectangular portion, and are arranged so that one sides thereof face each other. The source electrode 25 of the first TFT 20 a is larger than the drain electrode 29.

As shown in FIG. 17, one end of the source electrode 25 of the first TFT 20a overlaps the gate electrode. Further, one end portion of the drain electrode 29 of the first TFT 20 a also overlaps the gate electrode 26. The overlapping width A between the source electrode 25 and the gate electrode 26 in the first TFT 20 a is wider than the overlapping width B between the drain electrode 29 and the gate electrode 26.

The source electrode 25 and the drain electrode 29 of the second TFT 20b each have a rectangular portion, and are arranged so that the sides thereof face each other. The source electrode 25 of the second TFT 20 b is smaller than the drain electrode 29.

17, also in the second TFT 20b, one end portion of the source electrode 25 overlaps the gate electrode 26, and one end portion of the drain electrode 29 overlaps the gate electrode 26. On the other hand, the overlap width A between the source electrode 25 and the gate electrode 26 in the second TFT 20 b is narrower than the overlap width B between the drain electrode 29 and the gate electrode 26.

<Pixel arrangement configuration>
As shown in FIG. 17, a plurality of first pixels 18 a in which first TFTs 20 a are formed and a plurality of pixels in which second TFTs 20 b are formed are arranged in a pixel column 19 including a plurality of pixels 18 arranged along the gate wiring 22. The second pixel 18b is included.

<AC drive control circuit>
The liquid crystal display device 1 further includes an AC drive control unit 40 that applies signal voltages having the same polarity to the plurality of source lines 23 during a period of scanning one gate line 22. The AC drive control unit 40 is configured to invert the polarity of the signal voltage applied to the plurality of source lines 23 for each period of scanning one gate line 22. That is, the driving method of the liquid crystal display device 1 is a 1H line inversion driving method in which the polarity of the signal voltage is inverted every 1H period.

-Effect of Embodiment 3-
Therefore, according to the third embodiment, even if the shape of the source electrode 25 of each TFT 20 is different from that of the drain electrode 29, flicker can be significantly suppressed. Hereinafter, the effects of the present invention will be described in detail.

FIG. 19 is a plan view showing 1H line inversion driving of the liquid crystal display device 1 according to the third embodiment. In the liquid crystal display device 1, as shown in the upper part of FIG. 19, the signal voltage applied to the source line 23 is set to + polarity in the 1H period during which the pixel column 19 a for halftone display of a certain n−1 frame is scanned. To do. In the 1H period during which the next black display pixel column 19b is scanned, the signal voltage applied to the source line 23 is inverted to have a negative polarity. Here, the arrow of each pixel 18 in FIG. 19 indicates the direction in which the off-leakage current flows.

In the n-1 frame, the off-leak current is relatively small in the pixel column 19a displaying the halftone display that is visually recognized (S), and the off-leak current is relatively large in the second pixel 18b (L). Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixel 18a having a relatively small off-leakage current (S) and the second pixel 18b having a relatively large off-leakage current (L).

As shown in the lower part of FIG. 19, in the pixel column 19a that is displayed in halftone in the next n frames, the off-leak current of the first pixel 18a becomes relatively large (L), and the off-leak current of the second pixel 18b. Becomes relatively small (S). Therefore, the same number of pixels with half-tone display on the entire screen includes the first pixels 18a having a relatively large off-leakage current (L) and the second pixels 18b having a relatively small off-leakage current (S).

That is, according to this embodiment, in any frame, as a result of including the same number of (S) pixels 18 having a relatively small off-leakage current and (L) pixels 18 having a relatively large off-leakage current. Since the total leak amount of the entire display screen is the same before and after the change, flicker can be significantly suppressed. Therefore, according to this embodiment, even if the shape of the source electrode 25 of each TFT 20 is different from that of the drain electrode 29, flicker can be significantly suppressed.

On the other hand, FIG. 20 is a plan view showing 1H line inversion driving of a liquid crystal display device as a comparative example. In this comparative example, all the pixels 118 have the same configuration, and each source electrode 125 is formed larger than the drain electrode 129.

In this liquid crystal display device, as shown in the upper part of FIG. 20, the signal voltage applied to the source line 123 is set to + polarity in the 1H period in which the pixel column 119a for halftone display of a certain n−1 frame is scanned. And In the 1H period during which the next pixel column 119b for black display is scanned, the signal voltage applied to the source wiring 123 is inverted to have a negative polarity. Here, the arrow of each pixel 118 in FIG. 20 indicates the direction in which the off-leakage current flows.

In this n-1 frame, in the pixel column 119a displaying the halftone display that is visually recognized, the off-leak current of each pixel 118 is relatively small (S). Accordingly, the entire screen is displayed in halftone by the (S) pixel 118 having a relatively small off-leakage current.

As shown in the lower part of FIG. 20, in the pixel row 119a that is displayed in halftone in the next n frames, the off-leak current of each pixel 118 is relatively large (L). Therefore, the entire screen is displayed in halftone by the (L) pixel 118 having a relatively large off-leakage current.

That is, in the liquid crystal display device as the comparative example, the off-leak current of all the pixels 118 that perform halftone display is relatively small (S) before and after the frame changes, and the off-leakage of all the pixels 118 that perform halftone display. Since the state where the current is relatively large (L) is alternately switched, the flicker is likely to be visually recognized.

The present invention is not limited to the first to third embodiments, and the present invention includes a configuration in which these first to third embodiments are appropriately combined.

As described above, the present invention is useful for a liquid crystal display device and an electronic apparatus including the same.

1 Liquid crystal display device
10 Electronic equipment
18 pixels
18a first pixel
18b second pixel
19 pixel array
20 TFT
20a 1st TFT
20b 2nd TFT
22 Gate wiring
23 Source wiring
25 Source electrode
29 Drain electrode
30 pixel electrode
32 electrode limbs
36 electrode limbs
40 AC drive controller
51 First electrode
52 Second electrode

Claims

Multiple source wires,
A plurality of gate lines crossing the source lines;
A plurality of pixels provided in a matrix;
A thin film transistor provided in each of the plurality of pixels and connected to the source wiring and the gate wiring;
A pixel electrode provided in each of the plurality of pixels and connected to a drain electrode of the thin film transistor;
An AC drive controller that inverts the polarity of the signal voltage applied to the plurality of source lines for each period of scanning at least one of the gate lines;
Part of the drain electrode and part of the source electrode of the thin film transistor overlap with the gate electrode of the thin film transistor,
The thin film transistor includes a first thin film transistor in which an overlap width between the source electrode and the gate electrode is wider than an overlap width between the drain electrode and the gate electrode, and an overlap width between the source electrode and the gate electrode is the drain. A second thin film transistor narrower than an overlapping width of the electrode and the gate electrode,
A pixel column including a plurality of the pixels arranged along the gate wiring includes a plurality of first pixels in which the first thin film transistor is formed and a plurality of second pixels in which the second thin film transistor is formed. A liquid crystal display device.
The liquid crystal display device according to claim 1,
In the pixel column, at least one of the first pixels and the same number of the second pixels as the at least one first pixel are alternately arranged along the gate wiring. Liquid crystal display device.
The liquid crystal display device according to claim 1 or 2,
The AC drive control unit is configured to apply signal voltages having the same polarity to the plurality of source lines in each of the scanning periods of the at least one gate line. .
The liquid crystal display device according to claim 3,
In the pixel column, the one first pixel and the one second pixel are alternately arranged along the gate wiring,
The AC drive control unit applies signal voltages having the same polarity to the plurality of source lines in a period for scanning the one gate line, and also performs the plurality of times for each period in which the one gate line is scanned. A liquid crystal display device configured to invert the polarity of a signal voltage applied to a source wiring.
The liquid crystal display device according to claim 1 or 2,
The AC drive control unit is configured to apply signal voltages having different polarities to the source lines adjacent to each other in each of the scanning periods of the at least one gate line. apparatus.
The liquid crystal display device according to claim 5,
In the pixel column, two first pixels and two second pixels are alternately arranged along the gate wiring,
The AC drive control unit applies signal voltages of different polarities to the source lines adjacent to each other in each period of scanning the one gate line, and for each period of scanning the one gate line. A liquid crystal display device configured to invert the polarity of a signal voltage applied to the plurality of source lines.
The liquid crystal display device according to claim 1,
The first thin film transistor includes the source electrode having a pair of electrode limbs formed in a bifurcated shape, and the drain electrode disposed between the pair of electrode limbs,
The second thin film transistor includes the drain electrode having a pair of electrode limbs formed in a bifurcated shape and the source electrode disposed between the pair of electrode limbs. apparatus.
An electronic apparatus comprising the liquid crystal display device according to any one of claims 1 to 7.