Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-08-27
2004-08-10
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000
Reexamination Certificate
active
06774974
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device of the “divided alignments type”, generally termed as multi-domain alignment (particularly, multi-domain-vertical-alignment) in which, by aligning the liquid crystal molecules differently in each domain within a single pixel, the visual-angle characteristics of the respective domains compensate for each other to provide a wide viewing-angle characteristic.
BACKGROUND OF THE INVENTION
Widely known examples of liquid crystal display devices include those of the twisted nematic (TN) type and those which employ electrically-controlled birefringence (ECB). However, a problem with these conventional devices is that since the alignments of the liquid crystal molecules aligning under application of a voltage are uniform within a pixel, tonality differs depending upon the angle of view. A technique (multi-domain alignment) through which the directions of alignment of liquid crystal molecules in a single pixel are made to differ is available as a method of improving upon the visual-angle characteristic. With a liquid crystal device of this kind, the visual-angle characteristics of the multi-domains compensate for each other, as a result of which the characteristic is improved.
Multi-domain alignment methods are described in the specifications of Japanese Patent Kokai Publication JP-A-Nos. 7-318940, 8-292423, 9-80399, 9-304757 and 9-21913. These examples of the prior art place surrounding walls about a pixel and regulate the alignment of the wall surfaces to thereby realize an alignment that is symmetrical with respect to an axis perpendicular to a plate (substrate) at the center of the area surrounded by the walls. Multi-domain alignment is achieved as a result. Alternatively, protruding and recessed portions having axial symmetry with respect to the above-mentioned axis of symmetry are formed to correspond to the pixel, whereby similar multi-domain alignment is achieved. The art set forth in the specification of Japanese Patent Kokai Publication JP-A-8-292423 will be described with reference to FIG.
6
.
FIG. 6
is a sectional view showing one pixel of a conventional liquid crystal display device. As shown in
FIG. 6
, walls
23
,
24
each comprising a resist or the like are formed on a plate
1
so as to surround a pixel electrode
22
, and a recessed portion
25
consisting of a resist film is formed between the walls
23
and
24
. A counterelectrode
26
is provided on a plate
2
on the opposite side of the device. and a projecting portion
27
is formed on the counterelectrode
26
. The plates
1
,
2
are arranged to oppose each other in such a manner that the recessed and projecting portions
25
,
26
will have common axes of symmetry. If the gap between the plates
1
,
2
is filled with a mixture of at least liquid crystal and a hardening resin and the liquid crystal and hardening resin are caused to undergo phase separation, a liquid crystal area will develop in such a manner that the liquid crystal precipitates in the recess
25
or surrounds the protrusion
27
. When this occurs, the liquid crystal molecules in the vicinity of the recess
25
or in the vicinity of the protrusion
27
become oriented with axial symmetry, such as in radiating form or in the form of concentric circles, with the axis being perpendicular to the plates.
SUMMARY OF THE DISCLOSURE
In the course of investigations toward the present invention, various problems have been encountered. Particularly a number of problems arise with the example of the prior art described above.
A first problem is that distribution of spacers (spheres etc.) generally used to maintain the panel gap between the plates is inappropriate. The reason for this is that the presence of spacers in the pixel areas tends to provide nuclei resulting in poor liquid crystal alignment, thereby greatly degrading the display characteristic. In contrast, if the spacers would be provided at portions where there are no pixels in order to avoid the problem of poor alignment, this increases the number of process steps.
A second problem is the requirement of process steps for mixing the hardening resin with the liquid crystal and causing phase separation and curing after the panel is filled. As a result, process load for forming the liquid crystal alignment is great.
Accordingly, an object of the present invention is to provide a multi-domain alignment liquid crystal display device in which regulation of the alignment of liquid crystal molecules is carried out through a simple process and panel gap can be maintained in stable fashion.
According to a first aspect of the present invention, there is provided a novel active-matrix liquid crystal display device. The device comprises generally first and second transparent insulating plates arranged to oppose each other, the first plate having disposed thereon a plurality of scanning lines and a plurality of signal lines, thin-film transistors provided in the vicinity of intersections between the scanning lines and signal lines, and pixel electrodes connected to the thin-film transistors, the second plate having a black matrix provided with openings at areas that oppose the pixel electrodes, a color layer and counterelectrodes provided so as to oppose the pixel electrodes, a liquid crystal sandwiched between the opposing first and second plates being controlled by voltage impressed across the pixel electrodes and counterelectrodes. Further an orientation layer is provided on the pixel electrodes of the first plate via an insulating film, the orientation layer being formed into a curved surface and causing molecules of the liquid crystal to become oriented in a direction normal to the curved surface of the orientation layer, and columnar spacers for regulating panel gap are provided between the two opposing plates. Particularly, each pixel is provided with one spacer.
In the first aspect of present invention, each columnar spacer has an end portion on one side thereof that preferably is disposed approximately at the center of the orientation layer formed on the first plate.
In a case where the orientation layer formed on the first plate defines a cavity recessed toward the side of the first plate in a cross section taken along a normal to the plate, the diameter of the columnar spacer becomes progressively smaller in the direction toward the second plate.
In a case where the orientation layer formed on the first plate defines a protrusion directed toward the side of the second plate in a cross section taken along a normal to the plate, the diameter of the columnar spacer becomes progressively larger in the direction toward the second plate.
According to a second aspect of the present invention, there is provided an active-matrix liquid crystal display device generally comprising first and second transparent insulating plates arranged to oppose each other, the first plate having disposed thereon a plurality of scanning lines and a plurality of signal lines, thin-film transistors provided in the vicinity of intersections between the scanning lines and signal lines, and pixel electrodes connected to the thin-film transistors, the second plate having a black matrix provided with openings at areas that oppose the pixel electrodes, a color layer and counterelectrodes provided so as to oppose the pixel electrodes, a liquid crystal sandwiched between the opposing first and second plates being controlled by voltage impressed across the pixel electrodes and counterelectrodes. Further, the pixel electrodes on the first plate and an orientation layer formed on the pixel electrodes define curved surfaces, and columnar spacers for regulating panel gap are provided between the two opposing plates.
In the second aspect of the present invention, the alignment (orientation) layer is formed, e.g., by oblique vapor deposition of SiO, and molecules of the liquid crystal are oriented substantially at right angles to the plane of the plate.
Each of the columnar spacers has an end porti
Chowdhury Tarifur R.
NEC Corporation
Nguyen Hoan C.
Scully Scott Murphy & Presser
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