JP2000010074A - Liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a liquid crystal display device capable of preventing a reverse twist alignment defect of a liquid crystal from being fixed by a vertical electric field and thereby achieving a good display with a high surface pressing pressure resistance. SOLUTION: In a liquid crystal display device, the same waveform as a common voltage waveform Vcom is applied as a reset waveform Vr in a second half scanning line region T of a drain voltage waveform Dn that does not contribute to display for each scanning field. Thus, the vertical electric field applied to the liquid crystal layer 9 becomes zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and, more particularly, to an improvement in an electric drive system for enabling a good display with a high surface pressure.

[0002]

2. Description of the Related Art An active matrix type TFT liquid crystal display panel has a drain (data signal) line, a gate (scanning signal) line, an auxiliary capacitance line, a pixel electrode near each intersection of a drain line and a gate line, and a pixel electrode. Some switching thin film transistors and pixel electrodes are provided with a transparent common electrode and the like opposed to each other via a liquid crystal layer.

FIG. 4 is a plan view showing an example of such a conventional liquid crystal display panel. The liquid crystal display panel includes an active matrix panel 1 on which a thin film transistor described later is formed, and an opposing panel 2 on which a color filter is formed. The active matrix panel 1 is larger than the opposing panel 2, and terminals (not shown) are arranged on the periphery. FIG. 5 is an enlarged view of one pixel portion 1A of FIG.
FIGS. 6A and 6B are cross-sectional views taken along lines (a)-(a) and (b)-(b) of FIG. In these figures,
3 is a pixel electrode, 4 is a drain line, 5 is a gate line, 6 is a thin film transistor (TFT), 7 is a storage capacitor (Cs) line, 8 is an insulating film, 9 is a liquid crystal layer, 10 is a black matrix, and 11 is a color filter. (CF),
12 is a transparent common electrode (ITO), and 19 is a rubbing direction of the liquid crystal. In the liquid crystal display panel, the drain line 4 and the gate line 5 are provided in a matrix state,
In the vicinity of each intersection, a switching thin film transistor 6
Further, a transparent common electrode 12 facing the pixel electrode 3 via the liquid crystal layer 9 is provided. A pixel capacitance is formed by the pixel electrode 3, the common electrode 12 disposed opposite to the pixel electrode 3, and the liquid crystal layer 9 disposed therebetween.

[0004]

As described above, in the liquid crystal display panel, a thin film transistor 6, an auxiliary capacitance line 7, a drain line 4, a gate line 5 and the like are arranged around each pixel in a complicated manner. A transparent common electrode 12 is formed on the entire surface of the substrate on the color filter 11 side.

In the liquid crystal layer 9, a rubbing treatment as shown in FIG. 7 is performed in order to align the liquid crystal molecules 9a, and the liquid crystal molecules 9a are aligned as shown in FIG. In FIG. 7, 16 is the rubbing direction of the alignment film formed on the active matrix panel 1, 17 is the rubbing direction of the alignment film formed on the opposing panel 2, and FIG. 8 is the pretilt angle (α). Show.

When an electric field is applied to such a liquid crystal display panel and the screen is pressed with a finger or the like, an abnormal alignment portion (reverse twist) hidden in the wiring portion by the flow of the liquid crystal covers the pixels, and the screen of the display device is displayed. When observed, a phenomenon (disclination) in which a bright spot defect in which light leaks in pixel units remains may be observed, and a disclination line 13 is generated and displayed as shown in FIGS. 5, 6A and 6B. Is a problem. In particular, the pixel size is reduced due to the high definition, and the black matrix 10 is reduced due to the high aperture ratio.
The above problem became more prominent due to the narrower width.

SUMMARY OF THE INVENTION An object of the present invention is to improve the electric drive system of a liquid crystal display device to prevent the occurrence of disclination and to enable a good display with a high surface pressure resistance to solve the above-mentioned conventional problems. It is in.

[0008]

In order to achieve the above object, a first aspect of the present invention is to provide a drain line, a gate line, a pixel electrode near each intersection of the drain line and the gate line,
The switching element connected to the pixel electrode and the pixel electrode are a liquid crystal display device including a common electrode and the like opposed to each other with a liquid crystal layer interposed therebetween. The point is that a period for supplying a voltage having the same potential as the electrode is provided.

According to a second aspect of the present invention, a drain line, a gate line, a pixel electrode near each intersection of the drain line and the gate line, a switching element connected to the pixel electrode, and a pixel electrode are opposed via a liquid crystal layer. A liquid crystal display device including a transparent common electrode and the like, wherein a period for supplying a data voltage to each drain line and a period for supplying a voltage having the same potential as the common electrode are provided in each horizontal scanning period. .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention solves the above-mentioned problems by improving the electric drive system without changing the material and structure of each member of the liquid crystal display panel described above. FIG. 1 shows an electric drive system corresponding to the first invention, and FIG. 2 shows an electric drive system corresponding to the second invention.

First, prior to the description of the above-described driving method, the mechanism of occurrence of a bright spot defect will be described. As is clear from FIG. 8, the liquid crystal molecules 9a have a pretilt angle 14 of α = 2 or 3 degrees with respect to the substrate interface. Here, when a vertical electric field is generated between the transparent pixel electrodes 3 on the upper and lower substrates and the transparent common electrode, the liquid crystal molecules 9a rise from the side having the pretilt angle 14 and function as a liquid crystal display panel.

However, on the substrate side of the thin film transistor 6, wirings such as signal electrodes such as the auxiliary capacitance line 7, the drain line 4, and the gate line 5 are shown in addition to the pixel electrode 3, and a complicated horizontal electric field 15 is generated. ing. Of particular note is the lateral electric field between the pixel electrode 3 and the auxiliary capacitance line 7.

Here, paying attention to the directions of the liquid crystal molecules 9a and the horizontal electric field 15, on the left side of the pixel electrode 3 in FIG.
The lateral electric field 15 is the pretilt angle (α) of the liquid crystal molecules 9a.
It works in the opposite direction to 14. At the place where the horizontal electric field 15 is generated, the liquid crystal molecules 9a are aligned along the electric field, so that the alignment state is opposite to that of the liquid crystal molecules 9a by rubbing, and a reverse twist region is generated. At this time, the liquid crystal layer 9
When a pressing force is applied by a finger or the like, the above-described region enters the pixel by the flow of the liquid crystal and covers the entire pixel, and is further fixed by a vertical electric field of the wiring portion, particularly, between the pixel electrode 3 and the common electrode 12. Will be converted. Therefore, if the pixel pitch is too small or the pretilt angle 14 is too small, the reverse twist region is likely to occur, resulting in poor display.

Therefore, the present invention suppresses the fixation of the reverse twist region due to the vertical electric field, so that the vertical electric field applied to the liquid crystal layer 9 is reduced to zero during the scanning time that does not contribute to the display. An electrical driving method is adopted in which the reset signal waveform is the same as the common signal waveform, and an embodiment thereof is shown in FIGS.

FIG. 3 is an explanatory diagram of a liquid crystal display device of the present invention in which the electric drive system of the present invention shown in FIGS. The liquid crystal display panel 20 has a configuration shown in FIGS.
Is a drain voltage (data signal) generating circuit, 23 is a gate voltage (scanning signal) generating circuit, 24 is a control circuit, and the control circuit 24 is a gate signal gate1 to gate 220 having a waveform as shown in FIG. Each circuit is controlled so as to be a signal Vcom and a drain signal Dn (for black display).

When such a liquid crystal display device is driven at 60 Hz, one field (525 lines / 2) = 16.67.
msec, 1H = 63.5 μsec (the width of the gate signal is about 50
μsec), so the gate signal gate for each field
The scanning time of 1 to gate 220 is 63.5 μsec × 220
= 13.93 msec, and the surplus period T = 2.74 msec in the latter half of each field is a period that does not contribute to display. According to the present invention, the extra period T
Then, a reset voltage is supplied to each drain line 4. FIG. 1 shows a first embodiment of the driving method according to the present invention. The reset voltage Vr is equal to the drain signal D
As shown in the figure during the surplus period T of n, it has the same phase and the same potential as the common signal Vcom (the same signal is also supplied to the auxiliary capacitance line 7). As described above, when the same signal as the common signal Vcom is applied to each drain line 4, the voltage V _Ln = Dn-Vcom applied to the liquid crystal layer 9 becomes
As shown in FIG. 1, V _Ll = 0 V, and no vertical electric field is applied. Therefore, the reverse twist generated by the horizontal electric field is not fixed by the vertical electric field, and disclination is reduced. In FIG. 1, the drain signal Dn shows a case of a black display in which a voltage equal to or higher than the threshold value V _Lh for eliminating twisting is applied to the liquid crystal layer 9, and the voltage applied to the liquid crystal layer 9 is applied to the drain line 4. Even when a drain signal not applied is supplied, the period T
Are exactly the same. like this,
When the driving method of supplying the drain signal Dn to each drain line 4 was used, the number of defective pixels, which conventionally occurred about 30 pixels, was determined in a face-press test in which a load of 0.5 kg was applied to a substantially central portion of the liquid crystal display panel. Decreased to about one pixel. In addition, it has been confirmed that the number of defective pixels is less likely to occur as the drain signal reset period is longer.

Next, a first embodiment of the present invention is shown in FIG. In the first embodiment, all the gate lines are scanned, and after the supply of the data corresponding to the final gate line to each drain line is completed, each drain line is reset during an extra period T of each field. The voltage Vr was supplied. On the other hand, the driving method shown in FIG. 2 is a method in which data is supplied to each drain line 4 in the first half of the 1H period in which each gate line 5 is scanned, and a reset voltage Vr is supplied in the subsequent second half. That is, the gate signals gate1 to gate220 have 1H = 63.5.
It has a width of 1/2 of μsec, and data is supplied to each drain line 4 during this period. Then, during the latter half of 1H, a reset voltage having the same phase and the same potential as the common signal Vcom is supplied. The liquid crystal needs to be driven by an alternating current. In the case of the embodiment, the liquid crystal shows a line inversion drive in which the polarity of the data signal and the common signal is inverted every scan of each gate line 5, and the reset signal Vr has a common potential of Vcom. _In the case of _H , the corresponding potential Vr1,
If the common potential is Vcom _L is a Vr2 a potential corresponding thereto. Thus, also in the case of this embodiment, the voltage V _Ln = Dn−Vcom applied to the liquid crystal layer 9 becomes V _Ll = 0 V during the period in which the reset voltage is applied, and no vertical electric field is applied. The reverse twist generated by the horizontal electric field is not fixed by the vertical electric field, and disclination is reduced.

[0018]

As described above, according to the present invention, it is possible to prevent a reverse twist alignment defect of a liquid crystal from being fixed by preventing a vertical electric field from being generated during a scanning period that does not contribute to display. The configuration of the device itself is very simple, without any change, only by slightly changing the drain voltage waveform as the reset waveform in the region of the applied voltage waveform that does not contribute to the display. Therefore, practical effects are enormous, for example, a liquid crystal element having excellent display quality can be produced with a high yield for a higher aperture ratio and a higher definition in the future development of a liquid crystal display panel.

[Brief description of the drawings]

FIG. 1 is a timing chart showing an embodiment of the present invention.

FIG. 2 is a timing chart showing another embodiment of the present invention.

FIG. 3 is an explanatory block diagram in a case where the embodiments of FIGS. 1 and 2 are applied to a liquid crystal display device.

FIG. 4 is a plan view of a conventionally known liquid crystal display panel.

FIG. 5 is an enlarged view of one pixel section 1A of FIG. 4;

6A is an enlarged sectional view taken along line aa of FIG. 5, and FIG. 6B is an enlarged sectional view taken along line bb of FIG.

FIG. 7 is a diagram showing a rubbing direction of liquid crystal molecules.

FIG. 8 is a diagram showing pretilt angles of liquid crystal molecules.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 3 Pixel electrode 4 Drain line 5 Gate line 6 Thin film transistor 7 Auxiliary capacitance line 9 Liquid crystal layer 12 Transparent common electrode 13 Disclination line

Claims (2)

[Claims] A drain electrode, a gate electrode, a pixel electrode near each intersection of the drain line and the gate line, a switching element connected to the pixel electrode, a common electrode facing the pixel electrode via a liquid crystal layer, and the like. A liquid crystal display device comprising: a period for supplying a data voltage to each drain line in each scanning field; and a period for supplying a voltage having the same potential as a common electrode. 2. A drain line, a gate line, a pixel electrode near each intersection of the drain line and the gate line, a switching element connected to the pixel electrode, a transparent common electrode opposed to the pixel electrode via a liquid crystal layer, and the like. A liquid crystal display device comprising: a period for supplying a data voltage to each drain line and a period for supplying a voltage having the same potential as a common electrode in each horizontal scanning period.