Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-18
2003-06-03
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S191000
Reexamination Certificate
active
06573965
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a structure of a multi-domain wide-viewing angle liquid crystal display (MD-WVA-LCD), and more specifically to a structure of a multi-domain wide-viewing angle liquid crystal display with a structure of slits forming on electrodes and bumps forming above the slits.
BACKGROUND OF THE INVENTION
The market for liquid crystal display (LCD) panels is increasing rapidly, especially in their applications to notebook PCs and monitors. When LCD panels of larger size and higher resolution are used for desktop monitors, wide-viewing angles (WVA) and fast response time become very critical in meeting the monitors' requirements. In addition to contrast ratio with respect to different viewing angles, gray-scale inversion, colorimetry, and the optical response of a LCD are important features of a high quality LCD panels. However, the cost associated with designing and manufacturing a panel also needs to be considered.
Controlling liquid crystal domains is the most important technology in obtaining a wide-viewing angle for an LCD. Most of the conventional LCDs are twisted nematic (TN) LCDs having an LCD panel and crossed polarizers attached outside. The drawbacks of the conventional LCDs include narrow viewing angles (±40° horizontally and ±30° vertically), slow response (about 50 ms), and large color dispersion. Therefore, it is difficult to make high quality LCD panels. In addition, the rubbing process required in manufacturing the panels causes electric static damage ESD) and particle pollution.
Because of the demand in high quality LCD panels with wide-viewing angles, the structure of multi-domain LCDs has been developed. Each pixel is divided into several domains to compensate for the asymmetry in optics so as to increase the viewing angle of the display panel. Such LCD panels have compensation films and crossed polarizers attached outside the liquid crystal display panel. The liquid crystal mode is multi-domain vertically aligned. The multi-domain LCD panel has a wide-viewing angle and small color dispersion. In addition, it does not have electric static damage and particle pollution problems because no rubbing process is required.
FIG. 1
shows a cross-sectional view of a conventional multi-domain vertically aligned LCD with a wall-bump structure. This kind of LCD uses the combination effect of a fringe field and the wall-bump structure formed on the upper and lower substrates to form a multi-domain LCD cell of multiple independent directions. Referring to
FIG. 1
, the LCD structure
100
comprises a liquid crystal cell (LC cell), a pair of crossed polarizers
101
and
102
, compensating films
103
and
104
, and a bump structure. The liquid crystal cell comprises a pixel electrode layer
105
, a common electrode layer
106
and a pair of parallel substrates, such as a thin film transistor (TFT) substrate
108
and a color filter substrate
109
. A liquid crystal material
107
fills the space between substrates
108
and
109
. The exterior surfaces of the LC cell have respective crossed polarizers
101
and
102
disposed thereon. The compensating films
103
and
104
are applied between the crossed polarizers
101
and
102
. The bump structure comprises a plurality of bumps
111
~
117
forming on the pixel electrode layer
105
and the common electrode layer
106
respectively. This LCD has 55% light intensity of a conventional TN LCD. Also it may generate reversed disclination lines because the angle between its bump and its pixel electrode is 45°. Moreover, the horizontal gap between the upper and the lower bumps must be less than 30 &mgr;m. It requires high precision to align. Therefore, the design specification is not easy and the process window is smaller.
U.S. Pat. No. 5,309,264 also discloses a structure of a multi-domain liquid crystal molecules that uses a common electrode layer having a plurality of openings thereon to control the tilt direction of the liquid crystal molecules and to form a multi-domain LCD cell of multiple independent directions. Therefore, the display element comprises multi-domains.
FIG. 2
shows some patterns of the openings in the electrodes of this conventional multi-domain vertically aligned LCD. As shown in
FIG. 2
, the shapes of the opening patterns on the electrodes include “X” shape, “diagonal slot” shape and the “horizontal slot” shape, . . . , etc. This LCD needs higher driving voltage and the response time is longer.
The black matrix in the structure of the aforementioned multi-domain LCD needs to cover the disclination lines generated by reversely twisted and reversely tilted liquid crystal molecules. This reduces the aperture ratio by 15% to 20%.
SUMMARY OF THE INVENTION
The present invention overcomes the difficulties and the disadvantages of the structure of conventional multi-domain liquid crystal displays. The primary object of the present invention is to provide a multi-domain wide-viewing angle liquid crystal display with a structure of slits forming on electrodes and bumps forming above the slits. The structure having slits and bumps on electrodes may be formed on both upper and lower substrates or a single substrate.
According to the invention, the bump-with-slit structure formed on at least one substrate uses the bumps and the fringe field effect, or the so-called electrode slit effect, to control the tilt direction of the liquid crystal molecules and to form a multi-domain LCD cell of multiple independent directions. Therefore, the internal compensation of liquid crystal molecules decreases the color dispersion of the LCD, increases the response speed and reduces the generation of disclination lines. Also, the driving voltage for the LCD is lower and the process window is larger.
In addition, using existing ITO pattern processes makes it easy to modify the design of the bump-with-slit structure without adding extra process. For smaller bumps, the fringe field effect is the primary factor to consider in designing the structure of the invention and a higher driving voltage for the LCD is applied. On the other hand, for larger bumps, the effect of the boundary condition realignment of the bump is the primary factor and the LCD is driven by a lower driving voltage. The bump structure of the invention can be fabricated by a standard photo-lithographic process or a back side exposure (BSE) method.
In the preferred embodiments of the invention, the upper and lower substrates are parallel to each other. One of them has a color filter thereon and the other has thin film transistors thereon. The structure having slits and bumps on electrodes are formed on the electrode layer of at least one substrate. The structure of bumps and slits may have periodical configuration with various shapes on the substrates such as shapes of “horizontal slot”, “vertical slot”, “Y-inverse-Y”, “X”, “+”, “herringbone”, “T-inverse-T”, or “V-inverse-V” and the combination of these shapes.
According to the invention, the capacity storage area is designed and located under the slit of the electrode. It has periodical configuration with the same shape as the slits and the bumps. Such capacity storage area has the function of covering the disclination lines and, therefore, the aperture ratio under the black matrix area of the multi-domain wide-viewing angle LCD of the invention is increased and it is higher than that of the conventional multi-domain LCDs. Because the generation of disclination lines is reduced, the aperture ratio within the black matrix area of the multi-domain wide-viewing angle LCD of the invention is increased by 15% to 20% as compared to the conventional multi-domain LCD.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.
REFERENCES:
patent: 5309264 (1994-05-01), Lien et al.
patent: 5608556 (1997-03-01), Koma
patent: 5907380 (1999-05-01), Lien
patent: 6097
Chen Chi-Yi
Liu Hong-Da
Industrial Technology Research Institute
Schechter Andrew
Ton Toan
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