Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-03-30
2004-08-24
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S130000
Reexamination Certificate
active
06781657
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a liquid crystal display device and a method of manufacturing the liquid crystal display device, and more particularly to a method of producing two tilt domains within a liquid crystal layer and a method of fabricating a liquid crystal display device using a liquid crystal layer having the two tilt domains and a liquid crystal display device using the same.
DESCRIPTION OF THE RELATED ART
Twisted nematic (TN) liquid crystal displays (LCDs) have been mainly used for notebook computers in spite of their narrow viewing angle characteristics. However, improving the viewing angle is a prerequisite for the replacement of cathode ray tube (CRT) displays by LCDs in monitor and TV markets. Therefore, recently, in order to enhance the viewing angle characteristics in the twisted nematic LCDs, various new concepts of LCDs have been suggested. For example, nematic liquid crystals using an in-plane switching (IPS) mode have been reported by R. Kiether, et al. (Proceedings of the 12th Int. Display Res. Conf., Society for Information Display and Institute of Television Engineers of Japan, Hiroshima, p. 547, 1992). A vertical alignment (VA) mode with a negative birefringent compensation film has also been proposed by K. Ohmuro, et al. (Digest of Technical Papers of 1997, Society for Information Display Int. Symposium, Society for Information Display, Boston, p. 845, 1997).
Although the IPS mode shows wide viewing angle characteristics comparable to the CRT display, the cell gap margin is narrower and the response time is rather slower than that of the TN mode. Furthermore, the IPS mode has a slight color shift in oblique viewing angles.
The VA mode with negative birefringent film shows a viewing angle range greater than 70° in polar angle for all azimuthal directions and a very fast response time of less than 25 ms. However, so as to obtain the wide viewing angles, fabrication of a dual domain or a multi-domain is further necessary. A technology of fabricating the dual domain or the multi-domain within the liquid crystal layer is described by K. Ohmuro, et al. (Society for Information Display, p. 845, 1997). Here, various technologies of forming the liquid crystal having dual domain or multi-domain structure so as to obtain such wide viewing angle were proposed. They include (1) a multiple rubbing method, (2) a multiple alignment layer method, (3) an edge fringe field method, and (4) a parallel fringe field method. The multiple rubbing method, the multiple alignment layer method and parallel fringe field method have been demonstrated on the gray scale VGA level. However, these methods require cumbersome processing. For example, each panel requires more than one rubbing for one or both substrates when the multiple rubbing method is used. Each panel requires one alignment layer patterning and etching for one or both substrates when the multiple alignment layer method is used. The indium tin oxide (ITO) layer on top of the color filter layer needs to be patterned when the parallel fringe field method is used. The process of these three methods involves coating, baking, patterning, developing and stripping of the photoresist as well as one additional rubbing and photolithography process (for the multiple rubbing method), or one additional layer coating (for the multiple alignment layer method) or ITO etching on the color filter side (for the parallel fringe field method).
Therefore, the process becomes significantly more complicated and more expensive than that of the conventional single-domain process. Moreover, the multiple rubbing method involves dissymmetry in the viewing angle.
In the liquid crystal display device of in-plane switching mode (refer to “Asia Display Proceedings of the 15th International Display Research Conference” Society for Information Display and the Institute of Television Engineers of Japan, Hamamatsu, Japan, p. 577, 1995) proposed so as to solve a narrow viewing angle of TN mode, liquid crystal molecules are first arranged in parallel with the substrates in the absence of the electric field and then twisted in the shape of the electric field. Therefore, it is known that the response time using the conventional IPS mode is not enough for displaying a fast moving image, in particular, in the gray scale operation. Therefore, it is important to improve the response time for high-performance LCDs.
Further, since liquid crystal molecules used in a liquid crystal display device using an in-plane switching mode has optical anisotropy, the picture shows a different color depending on the viewing direction. This is referred to as a color shift phenomenon. Such a color shift phenomenon decreases the display characteristic of the liquid crystal display device (refer to Euro display '96, “Complete suppression of color shift in in-plane switching mode LCDs with a multi-domain structure obtained by unidirectional rubbing method”).
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to simplify the technology for producing at least two tilt domains within a liquid crystal layer.
Another object of this invention is to provide a method of forming a liquid crystal display device, utilizing such simplified technology for producing at least two tilt domains within a liquid crystal layer.
A further object of this invention is to improve viewing angle characteristics in a liquid crystal display.
Another object of this invention is to shorten the response time in a liquid crystal display.
According to a broad aspect of the invention, so as to produce two domains within a liquid crystal layer, first, two electrodes are formed on a substrate, and a liquid crystal layer aligned vertically with respect to the substrate are then formed on the substrate where the substrate has two electrodes separated from each other by a selected distance. Finally, an electric field between the two electrodes is applied.
According to one aspect of the invention, a method for fabricating a liquid crystal display device, comprises the steps of: providing a first substrate; forming a first electrode and a second electrode on a surface of the first substrate; forming a homeotropic alignment layer on the first substrate having the two electrodes thereon; providing a second substrate; forming a homeotropic alignment layer on a surface of the second substrate; arranging the two substrates such that the homeotropic layers on the two substrates face each other and are separated by a selected distance; and forming a liquid crystal layer within a space between the two substrates.
According to another aspect of the invention, a method for fabricating a liquid crystal display device, comprises the steps of: providing a first substrate having an inner surface and an outer surface opposite the inner surface; forming a first electrode and a second electrode on the inner surface of the first substrate; forming a first homeotropic alignment layer on the inner surface of the first substrate having the two electrodes; providing a second substrate having an inner surface and an outer surface opposite the inner surface; forming a second homeotropic alignment layer on the inner surface of the second substrate; arranging the two substrates such that the two inner surfaces of the two substrates face each other separated by a selected distance; forming a liquid crystal layer within a space between the two substrates; and forming an optical compensating plate on at least one outer surface of the two substrates.
According to a further aspect of the invention, a liquid crystal display device comprises: a substrate having a surface; a first electrode formed on the surface of the substrate; a second electrode formed on the same surface of the substrate, an electric field being generated between the first electrode and the second electrode; a liquid crystal layer formed on the substrate surface and including liquid crystal molecules, the liquid crystal molecules being aligned vertically with respect to the substrate surface in an absence of the electric field between the
Kim Hyang Yul
Lee Seung Hee
Dudek James A.
Hyundai Electronics Industries Co,. Ltd.
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