Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Patent
1998-08-19
2000-05-09
Wu, Shean C.
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
349117, 349121, 349125, 349126, 349178, 25229901, 2522996, G02F 11337, G02F 11335, C09R 1904
Patent
active
060611162
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a liquid crystal display device. Particularly, it relates to a display device which includes a vertically arranged splayed nematic liquid crystal, and birefringence function of molecules of which liquid crystal can be controlled with voltage.
BACKGROUND ART
Heretofore, as the liquid crystal display device employing electrooptical effect, there have been developed many devices using a cell such as a DSM cell employing dynamic scattering effect, guest-host cell using a coloring matter, TN cell having a twisted nematic structure, SBE (Super-Twisted Birefringence Effect) cell, and STN (Super-Twisted Nematic) cell. Among these, most generally used liquid crystal display devices are based on Schadt, Helfrich effect using a nematic liquid crystal exhibiting positive dielectric anisotropy, and the liquid crystal has a twisted nematic structure. Recently, OCB (Optically Compensated Bend) cells having a wide viewing angle have been proposed as a mode which is close to practical use (Miyashita et al., Euro-Display '93 Digest, pp 149-152).
As display devices which use a liquid crystal material having negative dielectric anisotropy, ECB (Electrically Controlled Birefringence) type liquid crystal display devices employing electrically controlled birefringence effect are generally known. The devices are to employ the change in light transmission by effectively varying birefringence due to the deformation of a nematic layer having a negative dielectric anisotropy, in an electric field. The mode in which a new orientation control is added to the ECB mode and an optical compensation plate is used is a SH (Super-Homeotropic: Yamauchi et al., SID '89 Digest, pp 378-381) mode.
In these modes, display devices which use a liquid crystal material having positive dielectric anisotropy have a narrow viewing angle and an insufficient response speed. Also, ECB type liquid crystal display devices which employ negative dielectric anisotropy have such problems that response is slow, that steepness is poor, and that threshold voltage is high.
DISCLOSURE OF THE INVENTION
Whereas STN cell have recently come to be used for the first time as information terminals of personal computers and others, and it made actualization of large display devices of a highly definite picture possible, dependency on a viewing angle and an insufficient response speed are pointed out. In the case of large cells, also there is a problem in such an aspect of manufacturing process as grinding of glass substrates for obtaining uniform cell thickness. On the other hand, active matrix type cells in which a switch is provided for every picture segment are considered as prospective ones for display devices for future color personal computers, and have been remarkably improved in response speed. However, the problem is not yet sufficiently solved that they have a large dependency on a viewing angle which is peculiar to TN cells. As the mode in which dependency on viewing angle is improved, OCB (Optically Compensated Bend) cells are also proposed. However, OCB cells have problems that since orientation of liquid crystal molecules is initially splayed, it is necessary to initially apply a high voltage for a certain period of time to stably transform the splay orientation into bend orientation, and that the OCB cells have difficulties in orientation technique.
As the mode in which a liquid crystal material having negative dielectric anisotropy is used, the ECB type liquid crystal display devices described above and devices including a SH cell which employs an optical compensation plate are known. However, the former have problems that response speed is slow, that steepness is poor, and that voltage is high, and the latter have a problem that response speed is slow whereas monochromatic display is possible and dependency on viewing angle is improved.
The present invention is to cope with the problems in conventional technology, and thus one of its objects is to provide liquid crystal display devices background of which
REFERENCES:
patent: 5621558 (1997-04-01), Shimada et al.
Murata Shizuo
Nishida Susumu
Saito Hideo
Takahashi Hiroki
Chisso Corporation
Wu Shean C.
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