Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-04-11
2004-03-23
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S128000
Reexamination Certificate
active
06710833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a “Multi-domain Vertical Alignment Liquid Crystal Display” (MVA-LCD) with wide viewing angle, and particularly to an MVA-LCD that can reduce the disclination lines and shorten the response time of the nematic crystal molecules.
2. Description of the Related Art
The current MVA-LCD technologies utilize an electrode such as a protrusion, a slit of a glass-coated ITO (Indium Tin Oxide), or an ITO to generate an irregular electric field within the boundary of the electrode when a voltage is applied. The irregular electric field makes the nematic LC (liquid crystal) molecules orient to different directions so as to divide a pixel into multiple domains. For the most MVA-LCD technologies, if they are classified according to the orienting directions of the nematic LC molecules when the voltage is applied, these domains are classified into four directions.
As shown in
FIG. 1
, a type of continuous zigzag protrusion structure
11
A and
11
B of the vertical-aligned LCD is disclosed according to the European Patent No. EP 0884626. The zigzag protrusions
11
A and
11
B are continuously disposed onto every pixel
12
so as to make the nematic LC molecules
13
in between the two substrates orient to four directions to generate four domains. Thus, this technique can improve the symmetry of viewing angle and eliminate the phenomenon of color shift at large viewing angle but can inevitably generate disclination lines at the tip areas of protrusions in the zigzag protrusion
11
A and
11
B. Such disclination lines not only result in the dark optical texture on the LCD, but also lower the transmittance of the LCD. Furthermore, since the electric fields at the tip areas of protrusions in the zigzag protrusion
11
A and
11
B are in an unstable state in the initial stage when the voltage is applied, the nematic LC molecules
13
in such areas are unable to orient toward a fixed direction steadily. Therefore, a negative effect is generated with respect to the response time. Consequently, the more the domains are, the better effect can be obtained to eliminate the color shift phenomenon, and the better result can also obtained to improve the symmetry of viewing angle according to the above mentioned statements. However, the more domains for the tilting of nematic LC molecules are provided, the more disclination lines are generated.
For resolving the dark optical textures due to the disclination lines and the negative effect with respect to the response time, a structure of MVA-LCD with “back-side exposure” (BSE) is proposed. However, the protrusions must be provided on both the upper and the lower substrates in the BSE type MVA-LCD. Furthermore, since the protrusion structure at the substrate with a color filter is more complicated than the regular protrusions, the protrusion structure at the substrate with a color filter must be controlled by the special manufacturing processes. Therefore, the production yield is not easy to be attained.
SUMMARY OF THE INVENTION
One of objects of the invention is to provide a MVA-LCD wherein the first and second means for controlling the tilting directions of Nematic LC molecules are provided on the pixel cells at the upper and lower substrates respectively while the first and second means are not connected to each other. Therefore, it can achieve the reduction of the disclination lines, enhance the brightness, and shorten the response time. Besides, the tilting angles of the first and second means are set in a cyclic disposition of mirror mapping wherein one upper pixel cell is corresponding to one lower pixel cell, two upper pixel cells are corresponding to two lower pixel cells, three upper pixel cells are corresponding to three lower pixel cells, and so on. Thus, the phenomenon of color shift is eliminated while the characteristics of high contrast ratio and wide viewing angle of the regular MVA-LCD are maintained at the same time.
Another object of the invention is to provide protrusions or slits of ITO being simple in structure in order to improve the production yield. Furthermore, since the structure of protrusions or the slits of ITO of the invention employs a single pixel cell as a design unit. Therefore, the invention is applicable to various sizes of products without the necessity of altering the structural design of the protrusions or the slits of ITO.
REFERENCES:
patent: 6097464 (2000-08-01), Liu
patent: 6313899 (2001-11-01), Wu et al.
patent: 6424397 (2002-07-01), Kuo
patent: 6426786 (2002-07-01), Lu et al.
patent: 6476896 (2002-11-01), Liu
patent: 6512503 (2003-01-01), Kim et al.
Akkapeddi P. R.
Chowdhury Tarifur R.
Hannstar Display Corporation
Martine & Penilla LLP
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