JP2003140194A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly align a liquid crystal with a bend deformation in a liquid crystal display device of which the response speed is accelerated by using an OCB (optically compensated bend) mode in which the liquid crystal is aligned with a bend deformation. SOLUTION: Each pixel is unexceptionally made to have a transition factor to the bend deformation in generating the bend transition with voltage application by making a shape of a pixel electrode 9 have recessing parts or projecting parts on at least one position or more. Thereby the transitions are generated in the respective pixels, the transition propagation time is shortened and the liquid crystal is certainly aligned with the bend deformation.

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 (LCD), and more particularly to an LCD using an OCB (Optical Compensated bend) mode in which a liquid crystal driving speed is high.

[0002]

2. Description of the Related Art Improving the moving image reproduction capability of LCDs and field sequential LCDs (Field Sequential LCDs;
Due to the practical application of S-LCD), L with faster response speed
CD is required. The response speed of LCD is represented by the response time of liquid crystal molecules to the electric field. If the response speed is slow, for example, when displaying a video, the previous screen remains, so
In particular, the LCD has low moving image display characteristics. An LCD using a liquid crystal having a faster response speed can display a moving image more smoothly.

Further, the FS-LCD is a system in which color display is performed by switching light of the three primary colors quickly and alternately displaying images of respective colors on one pixel. The liquid crystal used for the FS-LCD is required to have a significantly faster response speed than the liquid crystal used for the LCD of the color filter system due to its operation principle, and its practical application is awaited.

By the way, as a liquid crystal having a high response speed,
OCB-mode liquid crystals have been known for some time. The OCB mode is a name of a display mode in which a liquid crystal responds to an electric field in a bend alignment state. This uses a bend-aligned liquid crystal and an optical compensation layer. The OCB mode has a faster response speed than the liquid crystal mode used in the conventional TN or STN type LCD, so that the OCB mode is used in the L mode.
The CD is suitable for displaying moving images and FS-LCD.

It is generally known that a high voltage is applied to transfer the alignment state of the liquid crystal to the bend alignment.
However, it still takes time to transfer the entire display surface, and there is a problem that some pixels do not transfer.

In order to solve the problem, a method of changing the electric field applying method or a method of attaching a protrusion on the electrode has been considered.

FIG. 6 shows, for example, Japanese Patent Laid-Open No. 2000-3215.
It is a figure which shows the electrode of the conventional liquid crystal display device shown by 88 publication. In FIG. 6, 1 is a first electrode, 2 is a second electrode, 3 is a pixel region, 4 is a transposition factor, and 5 is a bend-transposed region.

Next, the operation will be described. FIG. 6 is a plan view showing transition from splay alignment to bend alignment in a simple matrix LCD. Liquid crystal is sealed in a cell between first and second transparent substrates made of opposing glass, and a plurality of first electrodes 1 arranged in stripes in the lateral direction are provided on the transparent first substrate. A plurality of second electrodes 2 arranged in stripes in the vertical direction are formed on the second substrate. The region where the first electrode and the second electrode overlap is a pixel region 3 in which an electric field is formed by the voltage applied to the first and second electrodes and the liquid crystal in this region is aligned.

In FIG. 6 (a), some black dots 4 shown in the cell are transposable elements that trigger bend transition. The bend transition occurs with this transposable element 4 as a starting point, and the bend transition diffuses radially around this. FIG. 6B shows this state. In the figure, the hatched region 5 is the region where the bend transition occurs, and it expands with time centering on the transposable element 4. The bend transition region 5 extends beyond the gap 1 between the adjacent pixel regions 3 and spreads across the pixel regions.
Then, as shown in FIG. 6C, the bend transition region 6
Diffuse over the entire surface of the cell. If the bend transition rate is high, the region of bend transition can be diffused over the entire surface in this way. If the bend transition is diffused over the entire surface, the response speed is evenly increased over the entire LCD.

[0010]

When an LCD using the OCB mode is to be manufactured, it is necessary to surely cause the liquid crystal in the cell of the LCD to undergo bend transition. However, there are still many unclear points regarding the physical mechanism of bend transition, and it is currently difficult to reliably bend bend over the entire cell surface.

Therefore, in the present invention, L using the OCB mode is used.
It is an object of the present invention to obtain an LCD having a high response speed by surely causing the liquid crystal to bend-transfer over the entire cell surface in a short time in a CD.

[0012]

In the liquid crystal display device according to the present invention, the electrode shape is an electrode having at least one concave portion or convex portion, and a bend transition for obtaining an OCB mode liquid crystal display device is ensured. It is designed to be performed at high speed.

Further, the electrode shape in the liquid crystal display device according to the present invention has at least one concave portion or convex portion other than the TFT junction portion, thereby promoting bend transition when a voltage is applied.

Further, since the electrode shape according to the present invention becomes a dislocation factor of bend transition and requires moderate electric field distortion, the width of the recess or projection of the electrode shape is set to 5 μm or more and 20 μm or less.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment Before explaining an example of the present invention, O using bend orientation is described.
The configuration of the CB mode liquid crystal display device will be briefly described.

FIG. 2 is a cross-sectional view of a substrate and a liquid crystal layer showing a state of alignment of liquid crystal molecules when two transparent substrates are arranged in parallel. Note that some of the liquid crystal molecules 13 in the liquid crystal layer 14 are shown focusing on the major axis direction.

FIG. 2A shows a splay alignment state when no voltage is applied. Transparent substrates 16A and 16B arranged in parallel
The liquid crystal layer 14 sandwiched in between is usually in a splay alignment state in which the long axis of the liquid crystal molecule at the center in the thickness direction is substantially parallel to the substrate surface. This is because the free energy in the splay alignment state is the smallest when no voltage is applied.

FIG. 2B shows an alignment state when a voltage is applied between electrodes (not shown) formed on the opposing surfaces of the substrates 16A and 16B. Liquid crystal molecules 13 in the liquid crystal layer 14
Rises so that its major axis is perpendicular to the substrate surface. Liquid crystal molecules near the alignment films (not shown) on the substrates 16A and 16B are aligned in the rubbing direction because they are strongly regulated by the alignment films.

FIG. 2C shows a bend alignment state. The major axis direction of the liquid crystal molecules at the center of the liquid crystal layer 14 in the thickness direction is substantially perpendicular to the substrate surface. Since the bend alignment state has a higher free energy than the splay alignment state, it is necessary to externally apply energy in order to transfer the splay alignment state to the bend alignment state.

When a certain voltage or more is applied to the electrodes of the liquid crystal display device in the splay alignment state, the liquid crystal layer transitions to the bend alignment state. Once the bend orientation is applied, by applying the voltage necessary to maintain the bend orientation,
The bend alignment state can be maintained. When the voltage applied to the liquid crystal layer 14 in the bend alignment state is increased, the rising angle of each liquid crystal molecule 13 increases while the bend alignment state is maintained, and when the applied voltage is decreased, the rising angle decreases. The change in the rising angle changes the refractive index of the liquid crystal layer 14.

The transmittance of light is controlled by utilizing the difference in refractive index between the ON state to which a high voltage is applied and the OFF state to which a low voltage is applied to display white or black. Further, gray display is possible by applying a voltage between the ON state and the OFF state. Also, by using a color filter,
Color display is also possible.

FIG. 1 is a diagram for explaining a liquid crystal display device according to a first embodiment for carrying out the present invention. 1A is a diagram showing the shape of a pixel electrode, FIG. 1B is a sectional view of a liquid crystal display device, and FIG. 1C is a plan view of an active matrix LCD.

In FIG. 1, (a) is a plan view of a first electrode which becomes a plurality of pixel electrodes 9 provided on a transparent substrate. FIG. 1B is a sectional view of the portion between the pixel electrodes.
A plurality of data lines 7 are formed on the first transparent substrate 6A,
A gate line 15 is formed on the data line 7 via an insulating film (not shown). A pixel electrode 9 is formed for each pixel on the gate line 15 via an insulating film 8 which is a flattening film, and an alignment film 10A is formed thereon. On the second transparent substrate 6B arranged so as to face the first transparent substrate 6A, a common electrode 11 is formed so as to face the plurality of pixel electrodes 9, and an alignment film 10B is formed thereon. . Liquid crystal 12 is sealed between the first and second substrates. In addition, an auxiliary capacitance electrode (not shown) is connected to the pixel electrode 9.

The alignment films 10A and 10B are rubbed in a direction substantially parallel to each other and have a pretilt angle so as to face each other. An optical compensation layer (not shown) is placed on this and visualized.

When a bend-orientation transition voltage is applied to the active matrix LCD, the transition voltage is the common electrode 11.
It is good to apply to. The common electrode 11 is the gate electrode 9,
Since the data line 7 and the gate line 15 are widely covered, if a transition voltage is applied to the common electrode 11 and various electrodes on the first substrate side are grounded, only between the pixel electrode 9 and the common electrode 11 In addition, an electric field is generated between the data line 7, the gate line 15 and the common electrode 11. At that time, when the electrode shape has a concave portion or a convex portion, electric field distortion in an oblique direction occurs. When an oblique electric field is generated, a dislocation factor of bend transition and a tilt line (disclination) that serves as a propagation path are generated, and bend transition can be reliably generated in each pixel electrode in a shorter time.

Although FIG. 1A shows an example of the shape of the pixel electrode a, it is sufficient that the electrode shape has at least one concave portion or convex portion. It may be other than that. The above points are not limited to the active matrix type LCD shown in FIG.
Also in the simple matrix type LCD as shown in FIG. 6, the same effect can be obtained if the first electrode 1 or the second electrode has a concave portion or a convex portion.

In the first embodiment, the case where the electrode shape is surrounded by a straight line has been described. However, as shown in FIG. 5, the side surrounding the pixel electrode may be a curved line. It has the same effect as 1.

Embodiment 2 FIG. 8 is a view of one pixel of one substrate viewed from above in the shape of the second embodiment of the liquid crystal display device of the present invention. As shown in FIG. The concave portion or the convex portion provided on the electrode 9 is arranged so as to avoid a position close to the TFT element 17. As a result, the bend transition can be reliably promoted when a voltage is applied. The TFT element that drives each pixel is not limited to this, and may be another type of element as long as it is an active element.

Third Embodiment FIG. 3 is a diagram for explaining the effect of the electrode shape on the bend transition occurrence according to the second embodiment for carrying out the present invention.

In FIG. 3, (a) is a plan view of a first electrode, which will be a plurality of pixel electrodes 9 provided on a transparent substrate. (B) shows the length of the convex portion of the pixel electrode as d1 (μm)
It is a figure showing the relation of d1 and a bend transition rate when it is.

The bend transition rate, which is the rate at which bend transition has occurred, is defined as the bend transition rate = pixels that have undergone bend transition 2 seconds after voltage application /
It is defined as all pixels, and shows the change of bend transition rate when the width d1 of the convex portion of the pixel electrode is changed from 0 μm (no convex portion) to 25 μm. From FIG. 3B, it can be seen that the length of the convex portion has an effect on the bend transition rate, and the best effect is obtained when the length of the convex portion is 5 to 20 μm.

Similarly, when the width of the convex portion of the pixel electrode shown in FIG. 7A is set to d2 and the change of the bend transition rate when changing from 0 μm (no convex portion) to 25 μm is examined, FIG. The result is as shown in (b). Therefore, the width of the convex portion is 5 to
When it is 20 μm, it has the best effect.

[0033]

As described above, according to the present invention, the OC
Since the electrode of the LCD having the B mode has at least one concave portion or convex portion, bend alignment can be surely obtained in a short time, and the liquid crystal of each pixel can be driven in the OCB mode. There is an effect that a high-speed LCD can be obtained.

Further, according to the present invention, since the concave portion or the convex portion is provided in addition to the TFT junction portion, the bend transition at the time of applying a voltage can be reliably promoted.

Further, according to the present invention, the width of the concave portion or the convex portion in the electrode shape is set to 5 to 20 μm,
There is an origin of bend transition for each pixel, and bend transition can be surely generated in a short time, so that a liquid crystal display device exhibiting high-speed response can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a liquid crystal display device according to a first embodiment of the present invention. FIG. 3 is a plan view showing an electrode shape, a cross-sectional view showing an active matrix LCD, and a plan view.

FIG. 2 is a cross-sectional view for explaining bend alignment and splay alignment.

FIG. 3 is a plan view showing an electrode shape and a length d of a convex portion of the electrode for explaining a liquid crystal display device according to a third embodiment of the present invention.
It is a graph which shows the relationship between 1 and a bend transition rate.

FIG. 4 is a plan view showing an example of electrode shapes of the liquid crystal display device of the present invention.

FIG. 5 is a plan view showing an example of electrode shapes of the liquid crystal display device of the present invention.

FIG. 6 is a diagram for explaining a conventional liquid crystal display device. FIG. 6 is a plan view showing diffusion of bend transition when a distance between pixels is set to be a transition distance or less in a simple matrix LCD.

FIG. 7 is a plan view showing an electrode shape for explaining a liquid crystal display device according to a third embodiment of the present invention and a width d2 of a convex portion of the electrode.
3 is a graph showing the relationship between the bend transition rate and the bend transition rate.

FIG. 8 is a plan view showing an electrode shape for explaining a liquid crystal display device according to a second embodiment of the present invention.

[Explanation of symbols]

1 first electrode, 2 second electrode, 3 pixel region, 4
Transfer factor, 5 bend transfer region, 6A / 6B transparent substrate, 7 data line, 8 insulating film, 9 pixel electrode, 10
A / 10B alignment film, 11 common electrode, 12 liquid crystal, 1
3 liquid crystal molecules, 14 liquid crystal layer, 15 gate lines, 16A
/ 16B Transparent substrate, 17 active devices.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) G09F 9/30 338 G09F 9/30 338 9/35 9/35 (72) Inventor Tetsuya Satake Chiyoda-ku, Tokyo Marunouchi 2-3-3 Sanryo Electric Co., Ltd. (72) Inventor Takahiro Nishioka Marunouchi 2-3-3 Sanyo Electric Co., Ltd. (72) Inventor Tetsuyuki Kurata 2 Marunouchi, Chiyoda-ku, Tokyo 2-chome 2-3 Sanryo Electric Co., Ltd. (72) Inventor Shingo Nagano 997 Miyoshi, Nishigoshi-cho, Kikuchi-gun, Kumamoto Prefecture Advanced Display Inc. (72) Inventor Shiro Miyake 997 Miyoshi, Nishigoshi-cho, Kikuchi-gun, Kumamoto Prefecture F-Term in Advanced Display Co., Ltd. (Reference) 2H088 HA02 HA03 HA08 JA09 JA28 MA18 2H090 KA18 LA01 MA02 MA17 MB11 MB14 2H092 GA13 GA21 JA45 NA05 PA02 QA09 QA18 5C094 AA13 BA03 BA43 CA19 EA04 EA07 FA04 JA08

Claims (3)

[Claims] 1. A first electrode provided on a transparent first substrate, a second electrode provided on a second substrate, and a first electrode formed so as to cover the first or second electrode, respectively. And a liquid crystal layer sealed between the first and second substrates and having a change from a splay alignment state to a bend alignment state by applying a voltage between the substrates. A liquid crystal display device, wherein at least one of the first electrode and the second electrode has at least one recess or protrusion in its planar structure. 2. The liquid crystal display device is a TFT liquid crystal display device, and has an electrode having at least one concave portion or convex portion in a region other than a TFT proximity portion of a pixel electrode formed on a TFT substrate. The liquid crystal display device according to claim 1. 3. The liquid crystal display device according to claim 1, wherein the width of the concave portion or the convex portion is 5 to 20 μm.