JPH1031229A - Active matrix liquid crystal display device and its drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix liquid crystal display device with a high numerical aperture and high picture quality without causing a vertical smear display fault by forming an electric field applied to a liquid crystal with a potential difference between two pixel electrodes connected to two adjacent switching transistor elements connected to the same signal electrode line. SOLUTION: A electric field to be applied to the liquid crystal is formed by the potential difference between two pixel electrodes 5, 6 connected to two adjacent switching transistor elements 11', 11" connected to the same signal electrode line 4. This voltage application is performed so that voltage signals inputted from two adjacent switching transistor elements 11', 11" connected to the same signal electrode line 4 to respective pixel electrodes are made AC voltages that positive/negative are inverted between the pixel electrodes 5, 6 adjacent in the direction of the signal electrode line using a fixed positive bias potential as a reference for off level potential of a gate voltage applied to a scan electrode line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device having a wide viewing angle and low power consumption, and a driving method thereof.

[0002]

2. Description of the Related Art A display system in which the direction of an electric field applied to a liquid crystal is substantially parallel to a substrate interface (referred to as a lateral electric field system).
Is a promising technology as an active matrix type liquid crystal display device having features such as a wide viewing angle and a low load capacity.

[0003] Such a lateral electric field system is disclosed in
In JP-A-3-21907, there is an example in which a row electrode in the next stage is also used as a reference electrode. According to this configuration, a parasitic capacitance can be reduced, an active matrix type liquid crystal display device with low load and low power consumption can be obtained, and the aperture ratio of the pixel region can be improved with a small number of arranged electrodes.

However, according to the characteristics of ordinary transistor elements, only DC driving in which the voltage applied to the liquid crystal is always unipolar (the display electrode potential is always positive with respect to the reference electrode potential) can be performed. However, when the liquid crystal is driven by a direct current, the liquid crystal is greatly deteriorated, and the service life is significantly reduced. Furthermore, there is a problem that the residual charge is accumulated and an afterimage phenomenon occurs to deteriorate the image quality.

For this reason, the basic configuration of Japanese Patent Publication No. Sho 63-21907 is to provide a reference electrode line and to perform positive and negative AC driving on the electrode connected thereto.

[0006]

The basic problem of the horizontal electric field method is that the distance between the electrodes is wider than that of the vertical electric field method in which the direction of the electric field is almost perpendicular to the substrate interface.

In order to obtain an electric field sufficient to change the alignment direction of the liquid crystal in the horizontal electric field method, the signal voltage amplitude must be increased and the distance between the electrodes must be set relatively small. For this reason, the configuration in which the signal potential is input to the pixel electrode facing the reference electrode as in Japanese Patent Publication No. 63-21907 has a problem that the ratio of the electrode wiring to the pixel is large and the aperture ratio is low.

Further, the fluctuation of the pixel electrode potential due to the jump of the display signal of another pixel in the signal line direction is directly connected to the electric field applied to the liquid crystal, and a display defect called vertical smear tends to occur. There is.

An object of the present invention is to provide an active matrix type liquid crystal display device having a high aperture ratio and high image quality which has a long service life, does not cause an afterimage phenomenon, and does not cause a vertical smear display defect.

Another object of the present invention is to provide a method for driving the above-mentioned liquid crystal display device.

[0011]

The gist of the present invention to achieve the above object is as follows.

(1) A liquid crystal is inserted between the first and second substrates, and a plurality of pixel portions are formed on the first substrate by a plurality of scanning electrode lines and signal electrode lines arranged in a matrix. An active matrix type liquid crystal display device in which the switching element provided in the pixel portion and the input signal of the electrode are used to modulate the alignment state of the liquid crystal and modulate the transmittance or reflectance of incident light by a deflecting unit. A pixel electrode is connected to the switching element, and the pixel electrode and a pixel electrode connected to another adjacent switching element connected to the same signal electrode line apply an electric field substantially parallel to a substrate surface. An active matrix, wherein the liquid crystal molecules are operated in such a manner that the major axis direction of the liquid crystal molecules is operated substantially parallel to the substrate surface by an electric field generated by the two pixel electrodes. Liquid crystal display device.

(2) The pixel electrode connected to the switching element forms a storage capacitor by overlapping a scanning electrode line adjacent to the scanning electrode line of the corresponding switching element via an insulating layer, and forms a storage capacitor. The active matrix type liquid crystal display device, wherein the active matrix type liquid crystal display device is extended to an adjacent pixel over a scanning electrode line and constitutes one pixel electrode of the adjacent pixel.

(3) The active matrix liquid crystal display device, wherein the pixel electrodes form the same pattern as pixel electrodes adjacent in the signal electrode line direction.

(4) The signal voltage applied to the pixel electrode is adjacent to the signal electrode line direction with reference to a constant positive bias potential with respect to the off-level potential of the voltage applied to the scanning electrode line. The polarity of the potential between the pixel electrodes is inverted, and the polarity of the potential is also inverted in the frame display cycle,
A method for driving an active matrix type liquid crystal display device, comprising modulating an alignment state of the liquid crystal and modulating transmittance or reflectance of incident light by a deflecting unit.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An active matrix type liquid crystal display device is driven by applying a voltage applied to liquid crystal to an active element as a switch and charging and holding a voltage to a display electrode (hereinafter, referred to as a pixel electrode). I do.

In a conventional active-matrix-type liquid crystal display device of a horizontal electric field type, a potential charged in a pixel electrode becomes an alternating waveform at a frame display frequency with respect to a reference electrode in order to drive the liquid crystal by alternating current. Thus, the video signal is charged from the drain electrode of the switching transistor element. Therefore, the electric field applied to the liquid crystal is formed by the difference between the pixel electrode potential and the reference electrode potential.

In the present invention, as shown in FIG. 1, an electric field applied to the liquid crystal is applied to two adjacent switching transistor elements (11 ', 11'') connected to the same signal electrode line (4). Is formed by a potential difference between two pixel electrodes (5, 6) connected to the pixel electrodes (5, 6).

This voltage is applied to the same signal electrode line (4).
A voltage signal input to each pixel electrode from two adjacent switching transistor elements (11 ′, 11 ″) connected to the scan electrode is fixed with respect to the off-level potential of the gate voltage applied to the scan electrode line. Of the pixel electrodes (5, 5) adjacent in the signal electrode line direction with respect to the positive bias potential of
This is realized by using an AC voltage whose polarity is inverted between 6) and 6).

In this case, when the distance between the pixel electrodes (5, 6 ″) is equal to the distance between the pixel electrode and the reference electrode in the conventional configuration, the electric field applied to the liquid crystal for the same video signal amplitude is the same as that in the conventional configuration. Therefore, the distance between the pixel electrodes can be doubled as compared with the related art. Thereby, the ratio of the electrode wiring to the pixel (a) can be reduced, and the aperture ratio can be increased.

Each of the pixel electrodes (5, 6) forms one pixel electrode of each of two pixels (a, b) adjacent in the direction of the signal electrode line (4). The pixel electrode line (6 ') that overlaps and passes over the scanning electrode line (1) in the OFF state adjacent to the scanning electrode line via the insulating film (11') is the storage capacitor (13).
Therefore, the video signal potential can be held in each pixel electrode for one frame time by utilizing this capacitance portion.

Each pixel electrode has the same shape (indicated by 6-6'-6 '') between adjacent pixels (a, b) in the signal electrode line direction. By doing so, the influence of the fluctuation of the pixel electrode potential due to the jump of the display signal of another pixel in the signal line direction becomes the same between adjacent pixel electrodes.

That is, the electric field applied to the liquid crystal is applied to two pixel electrodes (5, 6 ') connected to two adjacent switching transistor elements (11', 11 '') connected to the same signal electrode line. ') Formed by the potential difference between
The fluctuation of the pixel electrode potential due to the jump of the display signal of the other pixel in the signal line direction is canceled, and the electric field applied to the liquid crystal has no influence. Therefore, a display defect called vertical smear hardly occurs.

As described above, the signal voltage applied to each pixel electrode is based on a constant positive bias potential with respect to the off-level potential of the gate voltage applied to the scanning electrode lines (1, 2, 3). In this case, an alternating voltage is applied between the pixel electrodes (5, 6) adjacent to each other in the signal electrode line direction. The signal voltage applied to the same pixel is equal to the gate voltage applied to the scan electrode line. The liquid crystal can be AC-driven by setting an AC voltage in which the polarity is inverted every frame time based on a constant positive bias potential with respect to the OFF-level potential.

As a result, it is possible to obtain a high aperture ratio, high image quality, horizontal electric field type active matrix liquid crystal display device which has a long service life, does not cause an afterimage phenomenon, and does not cause a vertical smear display defect.

[0026]

EXAMPLES The present invention will be described more specifically with reference to examples.

Two transparent glass substrates having a thickness of 1.1 mm and having a polished surface are prepared. A thin film transistor (hereinafter, referred to as a TFT) is formed on one substrate, and a liquid crystal alignment film is further formed on an uppermost surface thereof. In this embodiment, a rubbing treatment was performed on the surface of a polyimide alignment film.
A polyimide alignment film was similarly formed on the other substrate surface, and its surface was subjected to a rubbing treatment.

The rubbing directions of the upper and lower substrates are opposed to each other, the rubbing directions are substantially parallel to each other, and the angle with the direction of the applied electric field is 85 degrees. ) Is positive, the value is 14.8 (1 kHz), and the liquid crystal panel is filled and sandwiched with a nematic liquid crystal composition having a refractive index anisotropy Δn of 0.0865 (589 nm, 20 ° C.).

The gap (d) between the substrates was 3.6 μm in a state in which liquid crystal was sealed, with spherical polymer beads dispersed and sandwiched. Thereby, Δn · d became 0.311 μm.

The above liquid crystal panel is sandwiched between two polarizing plates, the direction of the polarization transmission axis of one of the polarizing plates is set at an angle smaller by 5 ° from the rubbing direction of the alignment film, and the other polarizing plate is perpendicular to this. Placed.

Thus, when an electric field is applied to the liquid crystal layer and the gap between the electrodes for modulating the light intensity is set to 12 μm, the normally closed characteristic in which the potential difference between the electrodes is 0 V and the dark state and 5.2 V is a bright state. Obtained.

Next, FIG. 1 shows the basic structure of the TFT and various electrodes. 1A is a front view as viewed from a direction perpendicular to the substrate surface, FIG. 1B is AA ′, and FIG. 1C is BB ′.
FIG.

The TFT 11 includes an amorphous silicon 8 formed on the scanning (gate) electrode 1 via a gate insulating film 9, a signal (drain) electrode 4, and a pixel (source).
It is composed of electrodes 5. The TFT 11 has an inverted staggered structure, in which the scanning electrode line 1 is formed in the lowermost layer, and the gate insulating film 9 is formed.
, The signal electrode line 4 and the pixel electrode line 5 are formed in the upper layer by patterning the same metal layer.

In FIG. 1, reference numeral 2 denotes a scanning electrode line at the previous stage;
Is a scanning electrode line at the subsequent stage, 5 is a pixel electrode line of the preceding pixel (a), 6 is a pixel electrode line of the succeeding pixel (b), and 7 is a pixel electrode line of a further later pixel.

The pixel electrode line 5 goes over the scanning electrode line 2 in the previous stage via the gate insulating film 9 and overlaps therewith.
2 is formed to hold the signal potential from the TFT 11.

Similarly, the signal potential from the subsequent TFT 11 ′ is held in the storage capacitor 13, and the signal potential from the subsequent TFT 11 ″ is held in the storage capacitor 14. The pixel electrode line 6 at the subsequent stage is the scanning electrode line 1 in the pixel electrode line 6 '.
And the pixel (a) is configured as the pixel electrode line 6 ″ so as to face the pixel electrode line 5.

Each of the storage capacitors 12, 13, 14,...
Signal potential accumulated _{V b + V i, V b} -V i + 1, V b +
When a display signal whose sign is inverted with respect to the reference potential _Vb is input so that V _{i + 2} ,..., | V _i + V _{i +} is applied between the pixel electrode line 5 and the pixel electrode line 6 ″. Electric field E due to ₁ | potential difference
│V between the pixel electrode lines 6 and 7
_An electric field E ′ due to the potential difference of _{i + 1} + Vi _{+ 2} | is applied to control the alignment of the liquid crystal molecules in the liquid crystal layer.

Since the potential difference between the electrodes is twice as large as that of the conventional configuration by applying the positive and negative electric fields, the intensity of the electric field applied to the liquid crystal layer is the same even if the interval between the electrodes is twice as large as that of the conventional configuration.

Light incident on the liquid crystal layer between the electrodes is modulated, and increasing the distance between the electrodes leads to a higher aperture ratio.

In the above-described signal input method, the display signal of each pixel is an average of two pixel signals. However, when compared with a display device in which the pixel arrangement is alternately shifted by half the pixel pitch in the direction of the signal line. There is no big difference.

[0041] However, with the pixel pitch of the signal line direction to 1/2, the signal potential to accumulate in the storage capacitor element contiguous to the signal line _{direction, V b + V i, V} b -V i, V b + V i ₊₁ , V _b −
If a display signal is input so that V _{i + 1} , V _b + V _{i + 2} , V _b −V _{i + 2} ,..., The potential difference between the electrodes becomes | 2 · V _i |
| V _i + V _{i + 1} |, | 2 · V _{i + 1} |, | V _{i + 1} + V _{i + 2} |,
| 2 · V _{i + 2} |,..., And higher quality display can be performed.

In this case, the aperture ratio is reduced by an amount corresponding to the increase in the number of scanning electrode lines. However, in the case of a color display device, the pixel width in the scanning electrode line direction is 1/3 of the pixel width in the signal line direction. Therefore, the aperture ratio becomes higher as compared with the conventional configuration.

Further, the signal voltage applied to the same pixel electrode line is converted from an AC voltage based on a constant positive bias potential (V _b ) with respect to the off-level potential of the gate voltage applied to the scan electrode line. Then, the liquid crystal can be AC driven.

FIG. 2 shows a driving waveform of the present invention. i-1,
(a), (b),
(C) shows the T connected to the (i, i + 1) th scanning electrode line.
The signal electrode voltage to the FT is (d), (e), i, i + 1
The pixel electrode voltage (source voltage) from the TFT connected to the i-th scan electrode line is changed to (f) and (g), and the pixel electrode voltage from the TFT connected to the (i, i + 1) -th scan electrode line is used for liquid crystal. The voltage applied to the layer is shown in (h).

The scan electrode voltage V _G has a pulse width of 34.5 μs.
The repetition period is a rectangular wave of 16.6 ms, the ON voltage (high level) of the pulse is set to V _GH , and the OFF voltage (low level) is set to V _GL .

The signal electrode voltage V _D has a positive bias potential _Vb which is constant with respect to the off-level potential V _GL of the gate voltage as a center voltage V _DC , and the polarity is inverted every frame time according to the display gradation. to enter the signal voltage V _off ~V _on.
This signal voltage is input to the pixel electrode when the scan electrode voltage V _G is on-voltage (high level), but the scan electrode voltage V _G is held at the off-voltage (low level), the signal electrode a bias potential V _b If the minimum potential V _DL of the voltage V _D is set to be higher than V _GL , the gate voltage of the TFT is always negative when the gate voltage is at the off level, the TFT becomes non-conductive, and the pixel electrode voltage V The lowest potential V _{SL of S} is also held.

In the structure of the present invention, the voltage _VLC applied to the liquid crystal layer is the same as that of the TFT connected to the (i, i + 1) th scanning electrode line.
Voltage V applied to the liquid crystal layer by the pixel electrode voltage from
Since the difference between _S (i) and V _S (i + 1), the liquid crystal layer twice the voltage of the signal voltage V _off ~V _on is applied. Since this voltage is twice that of the conventional configuration, the electric field intensity applied to the liquid crystal layer is the same even if the distance between the electrodes is twice that of the conventional configuration.

It should be noted that the pixel electrode voltage V _S
As shown in (f) and (g), there is a jump of the on-voltage pulse V _GH from the preceding scanning electrode, but with the voltage V _LC applied to the liquid crystal layer, the jump of the on-voltage pulse V _GH is as follows. This is not a serious problem because the offset is offset by the on-voltage pulse _VGH of the stage.

In the configuration shown in FIG. 1A, each of the pixel electrode lines 5,
The shape of 6, 7, ... is the same as the signal line direction. Each of the pixel electrode lines 5, 6, 7,... Has another display signal from the signal electrode line 4 and the subsequent signal electrode line 10.

However, since the direction of each pixel electrode line 5, 6, 7,... Is the same as the signal line direction, the fluctuation of the pixel electrode potential due to the jump of another display signal is the same between adjacent pixel electrodes. Become. If the above-described signal input method is used, these fluctuations in the pixel electrode potential are canceled by the electric field E applied to the liquid crystal layer, and no vertical smear display failure occurs.

The basic configuration shown in FIG. 1 has the configuration shown in FIG. 3 as an electric circuit. In FIG. 3, reference numeral 1 denotes the i-th scanning electrode line, 2 denotes the (i-1) -th scanning electrode line, and 3 denotes (i +
1) scanning electrode lines at the stage 4, 4 are signal electrode lines at the j-th stage, 10
Indicates a (j + 1) -th stage signal electrode line.

The gate electrode of each TFT 11 is connected to each scanning electrode line 1, 2, 3, and the drain electrode of each TFT 11 is connected to each signal electrode line 4, 10. Each TFT1
One source electrode is connected to each display electrode line 5, 6, 7,
Each storage capacitor element 12, 13,... Is formed between each display electrode line and the preceding scanning electrode line.

An electric field is applied to the liquid crystal layer between the display electrode lines 5 and 6, between the display electrode lines 6 and 7, and the like.

The basic configuration of the present invention only needs to satisfy the electric circuit configuration shown in FIG. 3, so that a more practical configuration as shown in FIG. 4 is employed.

FIG. 4 is the same as FIG. 1 except that the shape of the display electrode lines 5, 6, 7 is different from that of FIG. 1, and the distance between the display electrode lines is configured to be about 1/2 of that in FIG. .

FIG. 5 shows an electric circuit of a part of a panel composed of a plurality of pixels. A liquid crystal display panel 1 having a controller 15, a vertical scanning circuit 16, and a video signal driving circuit 17;
8.

The pixel pitch was 110 μm in the horizontal direction (between signal electrode lines) and 330 μm in the vertical direction (between scanning electrode lines). The electrode line width was 10 μm and 9 μm for the scanning electrode line and the signal electrode line, respectively. The display electrode line width is 8 μm,
The distance between the display electrode lines and the signal electrode lines was 6 μm.

In the configuration shown in FIG. 4, the pixel is divided into two parts.
It is also possible to divide or divide into four. In particular, it is a feature of the present invention that odd division is possible.

In order to improve the contrast, an insulating black matrix was formed in a gap other than between the display electrode lines. The number of pixels is 640 × 3 × 480 by using 640 × 3 signal electrode lines and 480 scanning electrode lines.
Color filters of three colors (red), G (green), and B (blue) were formed in a vertical stripe shape on a substrate facing the substrate having the TFT element group to enable color display.

A flattening layer made of a transparent resin for flattening the surface is formed on the color filter. The input of the video signal from the video signal drive circuit 17 to the signal electrode line 4 can use a normal line inversion drive system or a dot inversion drive system.

In this embodiment, the pixel pitch in the vertical direction is three times that in the horizontal direction. However, if this ratio is reduced and higher frequency line inversion driving or dot inversion driving is performed, higher quality display can be achieved. It becomes possible.

[0062]

According to the active matrix type liquid crystal display device of the present invention, when the distance between the pixel electrodes is the same as the distance between the pixel electrode and the reference electrode in the conventional configuration, the liquid crystal is not affected by the same video signal amplitude. Since the applied electric field is twice as large as the conventional one, the distance between the pixel electrodes can be twice as large as the conventional distance between the pixel electrode and the reference electrode. Therefore, the ratio of the electrode wiring to the pixel can be reduced, so that the aperture ratio can be increased.

Further, the jump voltage from the signal electrode line to the pixel electrode is canceled by the electric field applied to the liquid crystal, so that vertical smear does not occur.

Further, the load is low and the service life is long,
It is possible to obtain a high-quality AC-driven display device that does not cause an afterimage phenomenon or vertical smear display.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a basic configuration of a pixel portion of the present invention.

FIG. 2 is an explanatory diagram showing a drive waveform according to the present invention.

FIG. 3 is an explanatory diagram showing a basic electric circuit configuration of a pixel portion of the present invention.

FIG. 4 is an explanatory diagram illustrating a configuration of a pixel unit according to an embodiment of the present invention.

FIG. 5 is an electric circuit diagram of a portion of a panel including a plurality of pixels of the present invention.

[Explanation of symbols]

1, 2, 3 ... scanning electrode lines, 4, 10 ... signal electrode lines, 5,
6, 7 ... pixel electrode line, 8 ... amorphous silicon, 9 ...
Gate insulating film, 11 TFT, 12, 13, 14 storage capacitor element, 15 controller, 16 vertical scanning circuit,
17: video signal drive circuit, 18: liquid crystal display panel.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Tetsuro Minemura 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] 1. A liquid crystal is inserted between a first substrate and a second substrate,
On the first substrate, a plurality of pixel portions are configured by a plurality of scanning electrode lines and signal electrode lines arranged in a matrix, and by a switching element provided in the pixel portion and an input signal of the electrode, In an active matrix liquid crystal display device that modulates the transmittance or reflectance of incident light by modulating the alignment state of the liquid crystal and deflecting means, a pixel electrode is connected to the switching element, and the same signal electrode as the pixel electrode is used. A pixel electrode connected to another adjacent switching element connected to the line is disposed so as to apply an electric field substantially parallel to the substrate surface. An active matrix type liquid crystal display device characterized by being configured to operate substantially parallel to a surface. 2. A pixel electrode connected to the switching element overlaps a scanning electrode line adjacent to a scanning electrode line of the corresponding switching element via an insulating layer to form a storage capacitor and form a storage capacitor. 2. The active matrix type liquid crystal display device according to claim 1, wherein the active matrix type liquid crystal display device is extended to an adjacent pixel over an electrode line and constitutes one pixel electrode of the adjacent pixel. 3. The active matrix type liquid crystal display device according to claim 1, wherein the pixel electrode has the same pattern as a pixel electrode adjacent in the signal electrode line direction. 4. The active matrix type liquid crystal display device according to claim 1, wherein the pixel is provided with a color filter. 5. A liquid crystal is inserted between the first and second substrates,
On the first substrate, a plurality of pixel portions are configured by a plurality of scanning electrode lines and signal electrode lines arranged in a matrix, a pixel electrode is connected to the switching element, the pixel electrode, A pixel electrode connected to another adjacent switching element connected to the same signal electrode line is disposed so as to apply an electric field substantially parallel to the substrate surface. The signal voltage applied to the pixel electrode is a constant positive bias potential with respect to the off-level potential of the voltage applied to the scanning electrode line. With reference to the above, the polarity of the potential between the pixel electrodes adjacent in the signal electrode line direction is inverted, and the polarity of the potential is also inverted during the frame display cycle, modulating the alignment state of the liquid crystal, and deflecting means. The driving method of an active matrix type liquid crystal display device characterized by modulating a transmittance or reflectance of the incident light Ri. 6. The driving method of an active matrix liquid crystal display device according to claim 5, wherein a potential applied between said pixel electrodes is an alternating current.