Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-09-20
2004-02-10
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000, C349S156000, C349S157000, C349S106000, C349S110000
Reexamination Certificate
active
06690441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and, more particularly, to a multi-domain vertical alignment mode liquid crystal display (MVA-LCD).
2. Background Art
Since liquid crystal displays are thin and light, consume less electric power and do not cause flickering, they have rapidly acquired new markets, especially the laptop personal computer market. In recent years, there has been generated the demand for liquid crystal displays as the monitors of desktop personal computers, which are larger than the displays of laptop personal computers. Moreover, liquid crystal displays are now replacing the CRT displays of televisions.
The above-described large-sized liquid crystal displays particularly require luminance, contrast, etc. that are even over the entire display surfaces regardless of the angle of observation. However, twisted nematic mode liquid crystal displays (hereinafter referred to as TN-LCD's) that have been widely used heretofore have such a great problem that the viewing-angle is narrow.
To solve the above problem, a variety of improved modes such as the in-plane switching (IPS) mode and the optical compensation TN mode have recently been developed. Of these improved modes, the multi-domain vertical alignment mode (hereinafter referred to as MVA mode) is now attracting attention because it can attain (1) wide viewing angle, (2) high contrast, (3) high response speed, (4) high fidelity to color reproduction, and (5) high accuracy. In this MVA mode, displaying is controlled by inclining, by the application of a voltage, liquid crystal molecules that are vertically aligned on an alignment layer when no voltage is applied. Moreover, in order to attain high definition displaying, the direction in which liquid crystal molecules in one domain are inclined is made different from the direction in which liquid crystal molecules in a neighboring domain are inclined.
Initially proposed to attain the so-called multi-domain alignment as described above was such a technique that mask rubbing is repeated two or more times. This technique is however disadvantageous in that the yield is decreased because static electricity is generated and dust is raised in the rubbing step and that the productivity is decreased because the process is complicated. Thus, the manufacturing process employing this technique has not been fully reliable.
Under these circumstances, such a technique that projections are provided inside a liquid crystal panel to control the direction in which liquid crystal molecules are inclined, as described in Japanese Patent Publication No. 2947350, has recently come to be adopted instead of the rubbing technique. In this technique, the projections for controlling the alignment of liquid crystal molecules are provided as zigzag lines arranged in stripes. Therefore, when a voltage is applied, liquid crystal molecules are aligned evenly in four different directions with the long axes of the molecules inclined to form, in the horizontal direction, an angle of 45° with the central axis of the zigzag line. More specifically, the projections are so designed that they can divide one pixel into 4 sections whose areas are all the same and that they can control the directions of alignment of liquid crystals included in these 4 sections different from one another. Further, in this technique, the alignment-controlling projections are provided on both the color filter side and the array side so that they will be alternately arranged after cells are created.
Further, such a structure has also been devised recently that slits are formed in an ITO film as imaginary alignment-controlling projections, instead of the alignment-controlling projections to be provided on the array side.
In an MVA mode liquid crystal display provided with alignment-controlling projections, spherical spacer beads are usually used as spacers for defining the thickness of a liquid crystal layer. To fabricate such a liquid crystal display, a color filter substrate and an array substrate are adhered to each other with spacer beads having a predetermined diameter sandwiched between them. In this case, however, the alignment of liquid crystal molecules in the vicinity of the spacer beads is disrupted. As a result, double refraction takes place even when displaying is in the dark state, and leakage of light thus occurs to decrease the contrast, while the luminance at the time of light-state displaying is decreased due to disclination lines. In addition, spacer beads are, in general, sprinkled from a distant position, so that it is impossible to specify the positions of the individual spacer beads scattered on a substrate. It is therefore difficult to control the density of the spacer beads in a microscopic area. Moreover, the beads can move slightly even after cells are created. In addition, since the spacer beads that are extremely small tend to scatter in the air when they are sprinkled in a clean room, a liquid crystal display cannot be produced with satisfactorily high reliability. Unlike the conventional TN mode, the MVA mode is a double refraction mode utilizing the double refraction of liquid crystals, so that highly accurate control of the thickness of a liquid crystal layer is particularly required over the entire display area. For this reason, there have been demanded spacers that are more accurate than the conventional spacer beads.
SUMMARY OF THE INVENTION
We found that it is possible to produce, with high reliability, a multi-domain vertical alignment mode liquid crystal display that is free from lowering of luminance to be caused by disclination lines and that can display images with high contrast over the entire display area by providing, instead of spacer beads, spacers just like pillars or ribs between a driving electrode layer and a transparent electrode layer, at the position which overlaps alignment-controlling projections for controlling the direction of alignment of liquid crystals. The present invention was accomplished on the basis of this finding.
An object of the present invention is therefore to provide an MVA mode liquid crystal display that can be produced with high reliability, that is free from lowering of luminance to be caused by disclination lines and that can display images with high contrast over the entire display area; and a color filter for use in this liquid crystal display.
To fulfil the above object, the present invention provides a multi-domain vertical alignment mode liquid crystal display comprising:
a driving electrode layer in which driving electrodes corresponding to pixels are two-dimensionally arranged;
a transparent electrode layer for generating, together with the driving electrode layer, an electric field between the two electrode layers, provided in parallel with the driving electrode layer at a predetermined distance;
spacers for keeping the predetermined distance, provided just like pillars or ribs between the driving electrode layer and the transparent electrode layer;
a liquid crystal layer comprising liquid crystals having negative dielectric anisotropy, placed between the driving electrode layer and the transparent electrode layer;
vertical alignment layers for vertically aligning the liquid crystals, respectively provided on the driving electrode layer side surface and the transparent electrode layer side surface of the liquid crystal layer;
alignment-controlling projections for controlling the direction of alignment of the liquid crystals, linearly provided on the liquid crystal layer side surface of the driving electrode layer and/or that of the transparent electrode layer; and
a color layer having a colored pixel pattern of two or more colors,
wherein the spacers are provided at the position which overlaps the alignment-controlling projections; each spacer has at least one pair of side faces that are parallel to the longer direction of the alignment-controlling projection; and the horizontal area covered by the alignment-controlling projection encompasses the horizontal area
Dai Nippon Printing Co. Ltd.
Parkhurst & Wendel L.L.P.
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