Multi-domain liquid crystal display device

Details Multi-domain liquid crystal display device Multi-domain liquid crystal display device

2001-01-12

2004-08-10

Kim, Robert H. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S039000, C349S156000, C349S191000

Reexamination Certificate

active

06774967

ABSTRACT:

This application claims the benefit of Korean Patent Application No. 2000-1403, filed on Jan. 12, 2000, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a multi-domain liquid crystal display device in which a common auxiliary electrode is formed around and in a pixel region on the same layer as a gate line, and an electric field induction window and a dielectric structure are formed in the pixel region.
2. Discussion of the Related Art
Among flat-panel displays enjoying image quality equivalent of the one offered by cathode ray tubes (CRT), liquid crystal displays (LCD) have been most widely adopted. In particular, a thin-film transistor (TFT) type LCD (TFT-LCD) has been used in personal computers, word processors, office automation equipment, and home electrical appliances including, among other items, a portable television sets. The market for suck LCDs is expected to further expand in the future. Accordingly, there is a demand for further improvement in image quality.
A description will be made by taking the TFT LCD for instance. However, the present invention is not limited to the TFT LCD but can apply to a simple matrix LCD, a plasma addressing type LCD and so forth. Generally, the present invention is applicable to LCDs which include liquid crystal sandwiched between a pair of substrates on which electrodes are respectively formed and displays images by applying voltage between the electrodes.
Currently, a mode most widely adopted for the TFT LCD is a normally-white mode that is implemented in a twisted nematic (TN) LCD. The technology of manufacturing the TN TFT LCD has advanced considerably in recent years. Contrast and color reproducibility provided by the TN TFT LCD have surpassed those offered by the CRT. However, the TN LCD has a critical drawback of a narrow viewing angle range, which limits the application of the TN LCD.
FIGS. 1A
to
1
C are diagrams for explaining the narrow viewing angle problem.
FIG. 1A
shows a state of white display to which no voltage is applied and liquid crystal molecules are aligned in the same direction with a slight inclination (about 1° to 5°). For convenience sake, the liquid crystal molecules are illustrated as in FIG.
1
A. In this state, light is seen nearly white in any azimuth. Moreover, as shown in
FIG. 1C
when voltage is applied, intermediate liquid crystal molecules, except those located near the alignment films, are aligned in a vertical direction. Incident linearly-polarized light is therefore seen black, but not twisted. At this time, the direction of light obliquely incident to a screen (panel) is twisted to some extent because it passes obliquely through the liquid crystal molecules that are aligned in the vertical direction. The light is therefore seen halftone (gray), but not perfect black.
As shown in
FIG. 1B
, when an intermediate voltage, which is lower than the voltage applied in the state shown in
FIG. 1C
, is applied, the liquid crystal molecules near the alignment films are aligned in a horizontal direction, but the liquid crystal molecules in the middle parts of cells erect themselves halfway. The birefringent property of the liquid crystal is lost to some extent. This causes transmittance to deteriorate and brings about halftone (gray) display. However, this effect occurs only to light incident perpendicularly on the liquid-crystal panel. Obliquely incident light is seen differently, that is, light is seen differently depending on whether it is seen from the left or right side of the drawing (panel). As illustrated, the liquid crystal molecules are aligned mutually parallel relative to light propagating from right below to left above. The liquid crystal hardly exerts a birefringent effect. Therefore, when the panel is seen from left, it is seen black. By contrast, the liquid crystal molecules are aligned vertically relative to light propagating from below on the right to above on the left. The liquid crystal exerts a great birefringent effect relative to incident light, and the incident light is twisted. This results in nearly white display. Thus, the most critical drawback of the TN LCD is that the display state varies depending on the viewing angle.
It is known that viewing angle performance of a liquid crystal display device (LCD) in the TN mode can be improved by setting the orientation directions of the liquid crystal molecules inside pixels to a plurality of mutually different directions. Generally, the orientation direction of the liquid crystal molecules (pre-tilt angles) that keep contact with a substrate surface in the TN mode are restricted by the direction of a rubbing treatment applied to the alignment film. The rubbing treatment is a process which rubs the surface of the alignment film in one direction by a cloth such as rayon, and the liquid crystal molecules contacting the alignment film are orientated in the rubbing direction. Therefore, viewing angle performance can be improved by making the rubbing direction different inside the pixels.
FIGS. 2A
to
2
C show a method of making the rubbing direction different inside the pixels. As shown in this drawing, an alignment film
101
is formed on a glass substrate
100
(whose electrodes, etc., are omitted from the drawing). This alignment film
101
is then bought into contact with a rotating rubbing roll
102
to execute the rubbing treatment in one direction. Next, a photo-resist is applied to the alignment film
101
and a predetermined pattern is exposed and developed by photolithography. As a result, a patterned layer
103
of the photo-resist is formed as shown in
FIGS. 2B and 2C
. Next, the alignment film
101
is brought into contact with a rubbing roll
201
that is rotating in a direction opposite the direction of the previous rotating rubbing roll
102
, so that only the open portions of the pattern are rubbed. In this way, a plurality of regions that are subjected to the rubbing treatment in different directions are formed inside the pixel, and the plural orientation directions of the liquid crystal are formed inside the pixel. Incidentally, the rubbing treatment can be done in arbitrarily different directions when the alignment film
101
is rotated relative to the rubbing roll
102
.
As described above, there are some problems related to a division of orientation directions of the liquid crystal molecules for improving the viewing angle performance in the VA LCD.
It is desirable to improve a viewing angle characteristic of a VA liquid crystal display, and to realize a VA liquid crystal display exhibiting a viewing angle characteristic that is as good as or better than that exhibited by an in-plane switching (IPS) mode LCD, while permitting the same contrast and operation speed as the conventional liquid crystal displays.
According the an embodiment of the present invention, a VA mode LCD uses a conventional vertical alignment film, and adopting a negative liquid crystal, and a domain regulating means for regulating the orientation of a liquid crystal. Liquid crystal molecules are aligned obliquely when a voltage is applied, so that the orientation will include a plurality of directions within each pixel. The domain regulating means is provided on at least one of the substrates. Further, at least one of domain regulating means has inclined surfaces (slopes). The inclined surfaces include surfaces which are almost vertical to the substrates. Rubbing need not be performed on the vertical alignment film.
In the VA LCD device, when no voltage is applied, in almost all regions of the liquid crystal other than the protrusions, liquid crystal molecules are aligned nearly vertically to the surfaces of the substrates. The liquid crystal molecules near the inclined surfaces also orientate vertically to the inclined surfaces. When a voltage is applied, the liquid crystal molecules tilt according to electric field strength. Since the electric fields are ve

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