JP2701772B2 - Liquid crystal display - Google Patents

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 a liquid crystal display device in which a viewing angle is widened by orientation division.

[0002]

2. Description of the Related Art Demand for a liquid crystal display (hereinafter referred to as "LCD") is increasing due to its compactness and low power consumption. Functionally, a large screen, high definition, and multiple gradations are being promoted. Some products already have a display size of 33 cm diagonal and a multi-tone (full color) display capability of 8 bits. When such a large screen and full color are promoted, the viewing characteristics of the LCD become more problematic, and widening the viewing angle is a major issue.

In the current LCD for OA applications, the orientation of the liquid crystal is determined, for example, in the direction of an arrow as shown in FIG. 4 (a), with the pixel electrode 21 on a thin film transistor (hereinafter referred to as TFT) substrate and the counter electrode 22 ( The alignment film (usually a polyimide film) on the CF) is subjected to a rubbing treatment (rubbing with a cloth wound around a roller) to align the liquid crystal 23 vertically asymmetrically. The liquid crystal is aligned in the rubbing direction on the TFT substrate side immediately above the TFT substrate, in the rubbing direction immediately above the color filter substrate, and is twisted between the substrates.

When no voltage is applied (or when only a low voltage is applied), the liquid crystal 23 is twisted in a lying state (parallel to the substrate), so that the plane of polarization of the incident light is rotated together with the twist of the liquid crystal due to optical rotation. Rotate. When the exit side polarizing plate is orthogonal to the incidence side, white (normally white mode) display is obtained. On the other hand, when a large voltage is applied to the liquid crystal, the liquid crystal is oriented in the rubbing direction with a slight angle (pre-tilt angle), so that the liquid crystal molecules rise in the rubbing direction. In the example of FIG. 4A, the liquid crystal molecules rise in the lower direction. When a sufficiently large voltage is applied to the liquid crystal, the liquid crystal molecules completely rise, the anisotropy of the refractive index in the signal direction of light disappears, the plane of polarization of the incident light does not rotate, and a black display is obtained in normally black. . When a voltage between black and white is applied to the liquid crystal, the liquid crystal rises according to the applied voltage. In this state, when the liquid crystal is viewed from the upper field of view and when the liquid crystal is viewed from the lower field of view, the manner in which the liquid crystal stands substantially differs, and vertical asymmetry occurs in visibility. As shown in FIG. 4A, in the upper field of view, the liquid crystal is close to a lying state, the luminance on the low gradation side increases, and the contrast decreases. On the other hand, in the lower visual field, since the liquid crystal is in a standing state, the luminance on the low gradation side drops sharply.
Occurs.

[0005] Such a decrease in contrast in the upper visual field,
In order to prevent the reversal of gradation in the lower visual field, Japanese Patent Application Laid-Open No. Sho 52-21845.
An attempt has been made for a technique for providing different orientation distributions within one pixel as disclosed in U.S. Pat. In particular, many attempts have been made to divide one pixel into two, as shown in FIG. 4B, which is effective in expanding the vertical viewing angle of the LCD, and to orient the liquid crystal 23 so that the liquid crystal stands vertically. ing. As described above, when there is a region rising downward and a region rising upward when voltage is applied, the upper and lower visual field characteristics become characteristics obtained by combining the conventional upper visual field and lower visual field characteristics, and are particularly tremendous for preventing grayscale inversion in the lower visual field. It is known to be effective.

[0006] The method of realizing the two-divided orientation is shown in FIG.
The three methods shown in (b) and (c) are (a) ID
RC91 Digest, P68, 1991, (b) S
ID92Digest, P798, 1992, JP-A-5
-210099, (c) Japan Display 9
2, P591, 1992, and JP-A-5-173137. The rubbing direction shown in FIG. 5A is a method in which the rubbing directions on the upper and lower substrates are reversed so that the orientation is reversed in each of the divided regions. In this method, the alignment of the liquid crystal becomes stable, but when rubbing is performed twice on the upper and lower substrates, that is, when the first time is performed on the entire surface, it is necessary to cover half the area in the second time, which makes the process extremely complicated. Become.

In the method shown in FIG. 5 (b), a high pretilt alignment film and a low pretilt alignment film are respectively arranged in regions divided by upper and lower substrates to improve the liquid crystal alignment in the rubbing direction on the high pretilt alignment. It is a method that rubbing can be done only once by regulating. This method reduces the number of rubbing processes that are difficult to control, and simplifies the process.However, the rising direction of the liquid crystal when voltage is applied is determined by the pretilt direction of the high pretilt alignment film. The pretilt direction is opposite to the rising direction of the liquid crystal when a voltage is applied, and the liquid crystal is in a splay alignment state as shown in FIGS. Spray orientation is shown in FIG.
Since the strain energy is larger than the normal orientation shown in (a) and (b) and attempts to return to the normal orientation due to disturbance, for example, if the lateral electric field formed between the periphery of the pixel electrode and the bus wiring around the pixel electrode is large, Display defects such as reverse tilt (regions where liquid crystal rising directions are different) and reverse twist (regions where liquid crystal twist directions are different) are likely to occur.

FIG. 5C shows an intermediate method between FIGS. 5A and 5B. In this method, a high pretilt alignment film is provided on one substrate, and rubbing is performed twice only on the high pretilt film side. This method has a smaller number of rubbings than the method (a) and is advantageous in terms of process. Also, since only one splay alignment region is provided, the rubbing direction is set such that the normal alignment side comes to a region where the influence of the lateral electric field is strong, so that the alignment stability can be easily ensured.

Generally, when such intra-pixel orientation division is performed, a transition region of the orientation occurs in which the liquid crystal lays down even when a voltage is applied at the division boundary, and a white bright line (a disclination line) occurs when displaying black. Since this causes a decrease in the contrast of the LCD, a technique for covering the alignment division region with a black matrix (hereinafter, referred to as BM) is required as disclosed in JP-A-5-281545. As shown in FIG. 6, when light is shielded by the discrete light-shielding layer (BM) 26, the boundary between the BM and the division boundary is not determined in either of the methods shown in FIGS. However, in the method shown in FIG. 5 (c), the disclination can be shielded by providing the BM on the side of the substrate to be rubbed twice, so that the width of the BM can be narrowed, and the reduction in luminance due to the BM can be prevented. Few.

The above-mentioned method of dividing the orientation of liquid crystal by changing the rubbing conditions in two regions has an increase in the process and instability of the orientation, although the degree is different. As an orientation division method for solving this problem, Japanese Patent Application Laid-Open No. 4-149410 discloses an orientation division technique using an electric field. In this method, as shown in FIG. 7A, a low pretilt alignment film is provided on both substrates, and a rubbing process is performed so as to perform splay alignment, so that the rising of the liquid crystal when voltage is applied is not dependent on the pretilt direction as much as possible. (FIG. 7B). In this state, the orientation of the liquid crystal is sensitively affected by the lateral electric field around the pixel electrode 21, and as shown in FIG.
No. 3 rises in a direction depending on the electric field around the pixel when a voltage is applied, and is dividedly oriented. However, in this state, since there is no horizontal electric field in the center of the pixel, the alignment division does not always come to the center of the pixel due to fluctuations in pretilt and imbalance in other alignment parameters.

Therefore, a technology for stabilizing the alignment division position by providing a slit on the counter electrode side at a position corresponding to the alignment division boundary is disclosed in SID93 Digest, P269, 199.
3, JP-A-6-43461. In this method, as shown in FIG. 8 (a), under normal rubbing conditions, an oblique direction orthogonal to the rubbing direction on the substrate (pixel electrode) side having a strong lateral electric field is likely to be subjected to orientation division by the lateral electric field. By forming oblique slits 27 along the opposite substrate on the opposite substrate, a horizontal electric field component is also generated in the center of the pixel as shown in FIG. 8B to stabilize the alignment division position. Further, in order to shield the above-described disclination line at the alignment division boundary, the BM is inclined in the oblique direction as shown in FIG.
Needs to be provided.

[0012]

In the above-described conventional orientation division method using a lateral electric field, it is necessary to form a BM in an oblique direction in order to shield a disclination line from light. There is a problem that the area ratio (opening ratio) through which the light passes greatly decreases, and the visibility deteriorates due to the decrease in luminance.

The present invention solves the above-mentioned problem and increases the vertical viewing angle while suppressing the visibility deterioration due to the luminance reduction.
An object is to improve the display performance of a CD.

[0014]

According to the liquid crystal display device of the present invention, a liquid crystal layer sandwiched between two polarizing plates and a transparent substrate is provided with a pixel electrode formed on a first substrate in the transparent substrate and a second electrode. In a liquid crystal display device in which the transmittance is controlled by changing the liquid crystal alignment state by applying a voltage between the counter electrodes formed on the substrate, the counter electrode on the second substrate is divided into a plurality of regions, The electrode region is eccentric with respect to the pixel electrode of the first substrate. The counter electrode may be divided in the pixel column direction or in the pixel row direction. The direction of eccentricity of the divided electrode with respect to the pixel electrode is changed for each pixel. Further, in the present invention, the liquid crystal is in a splay alignment when a low voltage is applied.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIGS. 1A and 1B are a top view and a sectional view of an LCD panel showing a first embodiment of the present invention. In this embodiment,
The opposing transparent electrode 4 on the color filter substrate 2 is divided in the column direction. Further, the opposing transparent electrode is a pixel transparent electrode 3
Are eccentric in the row direction, the direction of the eccentricity is the same for the RGB of the unit pixel, and the opposing transparent electrodes are divided so as to be eccentric in the opposite direction for the surrounding pixels.

With this configuration, a horizontal electric field in a direction corresponding to the eccentric direction of the opposing transparent electrode 4 is applied to each pixel transparent electrode 3, so that the liquid crystal rises in the horizontal electric field direction when a voltage is applied. Become. As shown by an arrow in FIG. 1A, for example, when the alignment film on the TFT substrate side is rubbed in the lower right direction, the liquid crystal is pretilted in the rubbing direction. On the other hand, since the CF substrate side is rubbed in the lower left direction, the liquid crystal sandwiched between the pixel transparent electrode and the opposing transparent electrode is splay-aligned when a low voltage is applied. For this reason, the pixel in which the opposing transparent electrode is eccentric to the right rises in the rubbing direction, but the liquid crystal in the pixel eccentric to the left rises in the opposite direction to the rubbing. The orientation of the liquid crystal is the same in each pixel, and there is no occurrence of disclination in the pixel due to the orientation division.
Therefore, a BM that shields the alignment division boundary is unnecessary,
It is possible to suppress a decrease in luminance due to the orientation division. Further, by changing the eccentric direction for each pixel, it is possible to suppress a change in color balance in the upper and lower visual fields. Note that the pretilt angle is preferably as small as possible so as not to affect the rise of the liquid crystal due to the lateral electric field.

FIGS. 2A and 2B are a top view and a sectional view of an LCD panel showing a second embodiment of the present invention. In this embodiment, the opposing electrodes are completely separated in the column direction in the first embodiment, but no slit is provided in the opposing electrodes between pixel columns or between pixels. With this configuration, the sheet resistance of the counter electrode 4 can be reduced as compared with the first embodiment, so that crosstalk and the like due to potential fluctuation of the counter electrode can be reduced.

FIGS. 3A and 3B are a top view and a sectional view of an LCD panel showing a third embodiment of the present invention. This embodiment is different from the first and second embodiments in that the opposing electrode 4 is separated in the row direction and the eccentric direction is aligned for each row. In the present embodiment, the direction of orientation changes for each row, but it is similarly possible to change the eccentricity of the counter electrode for each pixel within the same row.

The present invention includes not only the embodiments described above but also all the methods for performing the orientation division using the lateral electric field for each pixel by appropriate division of the counter electrode and eccentricity with respect to the pixel electrode.

[0020]

As described above, in the liquid crystal display device of the present invention, by dividing the counter electrode and decentering it with respect to the pixel electrode, it becomes possible to perform alignment division using a horizontal electric field for each pixel electrode. There is no need to provide a black matrix for shielding the alignment division lines required by the internal alignment division method, so that the problem of luminance reduction can be suppressed and the viewing angle of the liquid crystal display device can be widened. Therefore, by applying the present invention to a liquid crystal display device, a liquid crystal display device having a wide visual field and high image quality display performance can be realized.

[Brief description of the drawings]

FIGS. 1A and 1B are a top view and a cross-sectional view of a liquid crystal panel according to a first embodiment of the present invention.

FIGS. 2A and 2B are a top view and a sectional view of a liquid crystal panel according to a second embodiment of the present invention.

FIGS. 3A and 3B are a top view and a cross-sectional view of a liquid crystal panel according to a third embodiment of the present invention.

FIG. 4A is a plan view showing a rubbing direction during uniform alignment, a cross-sectional view showing an alignment state, and a luminance-voltage characteristic diagram,
(B) is a plan view showing a rubbing direction example at the time of divided orientation, a sectional view showing an orientation state, and a luminance-voltage characteristic diagram.

FIGS. 5A to 5C are plan views showing examples of rubbing directions.

FIG. 6 is a plan view showing a conventional example in which alignment is divided by rubbing and light is shielded.

7A is a plan view showing a conventional example in which orientation division is performed by a lateral electric field, FIG. 7B is a cross-sectional view of FIG. 7A when no voltage is applied, and FIG. It is sectional drawing of FIG.

FIG. 8A is a plan view showing a conventional example in which a slit is provided in a counter electrode and orientation division is performed by a lateral electric field;
FIG. 9B is a cross-sectional view of FIG.

9 (a) is a plan view showing a conventional example in which the light is shielded by dividing the orientation by a horizontal electric field, and FIG. 9 (b) is a cross-sectional view of FIG. 9 (a) when a voltage is applied.

10A and 10B are cross-sectional views showing a normal alignment state and a rubbing direction of a liquid crystal, and FIGS. 10C and 10D are rubbing directions and a cross-sectional view showing a splay alignment state.

[Explanation of symbols]

 1, 25 TFT substrate 2 Color filter substrate 3 Pixel transparent electrode 4 Opposing transparent electrode 5, 24 Color filter 6, 23 Liquid crystal layer 21 Pixel electrode 22 Opposing electrode 26 Discrete light shielding layer

Claims (3)

(57) [Claims] 1. A liquid sandwiched between two polarizing plates and a transparent substrate.
The crystal layer is formed on a pixel substrate formed on a first substrate in the transparent substrate.
By applying a voltage between the electrode and a counter electrode formed on the second substrate.
Liquid crystal display that controls transmittance by changing the liquid crystal alignment state
In the display device, the counter electrode on the second substrate has a plurality of
And the area of the divided counter electrode is divided into the first substrate.
Plate is eccentric to the pixel electrode and the eccentric direction is
A liquid crystal display device comprising a call was changed to every Kuseru. 2. A liquid crystal sandwiched between two polarizing plates and a transparent substrate.
A pixel electrode formed on a first substrate in the transparent substrate
And the voltage applied between the opposing electrodes formed on the second substrate
Liquid crystal display that controls transmittance by changing liquid crystal alignment state
In the apparatus, the counter electrode on the second substrate has a plurality of areas.
And the area of the divided counter electrode is divided into the first substrate
Eccentric to the pixel electrode and the eccentric direction is adjacent
A liquid crystal display device characterized by changing for each pixel . 3. A device sandwiched between the pixel electrode and a counter electrode.
The liquid crystal is splay-aligned when a low voltage is applied.
The liquid crystal display device according to claim 1 or 2, wherein: