Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within smectic phase
Reexamination Certificate
1992-11-12
2001-10-16
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within smectic phase
C349S034000, C349S133000
Reexamination Certificate
active
06304310
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a ferroelectric liquid crystal device applicable to, e.g., a printer head and a display, particularly a ferroelectric liquid crystal device which provides a larger apparent tilt angle and a bright display with a high contrast even by a low-voltage AC electric field.
In recent years, it has been expected to develop a large area display using a ferroelectric liquid crystal characterized by a high-speed responsiveness and a memory characteristic.
Particularly, a ferroelectric liquid crystal display of an AC stabilization scheme using a liquid crystal having a negative &Dgr;&egr; (dielectric anisotropy) is expected to realize a bright display with a high contrast.
However, in the case where a ferroelectric liquid crystal device of the above-mentioned AC stabilization scheme is used to constitute a large area display, the enlargement of an apparent tilt angle corresponding to an increase in AC voltage is rather moderate so that the following two contradictory problems arise.
(1) If the device is driven by applying a low AC voltage, the enlargement of apparent tilt angle &thgr;
a
is insufficient so that a bright display with a high contrast cannot be realized.
(2) On the other hand, as a panel having a small cell gap of 1-2 microns is used in a ferroelectric liquid crystal display, the capacitance between the upper and lower electrodes becomes much larger than that in a TN-liquid crystal panel. Further, the frequency of the AC electric field capable of achieving the AC stabilization effect is ordinarily as high as 10 kHz or higher. As a result, if an AC electric field of a high voltage is used, a large heat is evolved due to charging and discharging in the panel to result in a large temperature distribution in the panel related with a matrix circuit structure, so that only a narrow latitude is allowed for the driving voltage and driving pulse duration usable for display.
In order to solve the problem, it is desirable to provide a device capable of achieving the AC stabilization effect at an AC voltage which is sufficiently low to result in only a negligible extent of heat evolution in the panel. No method therefore, however, has been known heretofore.
SUMMARY OF THE INVENTION
In view of the problems of the prior art described above, an object of the present invention is to provide a ferroelectric liquid crystal device of the AC stabilization scheme which is capable of achieving a bright display with a high contrast at a lower AC voltage.
According to the present invention, there is provided a liquid crystal apparatus, comprising:
(a) A liquid crystal device comprising:
a pair of substrates each provided with a uniaxial alignment axis, and
a chiral smectic liquid crystal having a negative dielectric anisotropy disposed between the pair of substrates and capable of forming a higher-temperature bistable alignment state and a lower-temperature bistable alignment state in its chiral smectic C phase, the chiral smectic liquid crystal being further placed in the lower-temperature bistable alignment state formed by cooling from the higher-temperature bistable alignment state; and
(b) voltage application means including:
an AC voltage application means for applying to the chiral smectic liquid crystal and AC voltage insufficient to cause a switching from one to the other or from the other to one of the bistable alignment state, and
a switching voltage application means for applying to the chiral smectic liquid crystal a voltage of one polarity sufficient to cause a switching from one to the other of the bistable alignment state and a voltage of the other polarity sufficient to cause a switching from the other to one of the bistable alignment state.
In a preferred embodiment, the chiral smectic liquid crystal assumes smectic A phase forming a pretilt angle of liquid crystal molecules of 1.5° or larger with the substrates.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
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patent: 4793693 (1988-12-01), Shimoda et al.
patent: 4832462 (1989-05-01), Clark et al.
patent: 4867539 (1989-09-01), Goodby et al.
patent: 4900132 (1990-02-01), Bos
patent: 4932758 (1990-06-01), Hanyu et al.
patent: 4941736 (1990-07-01), Taniguchi et al.
patent: 5005953 (1991-04-01), Kawagishi
patent: 5013137 (1991-05-01), Tsuboyama et al.
patent: 8702495 (1987-04-01), None
Clark et al—“Structures And Applications of SSFLC Devices” Japan Display 86—pp. 456-458.
Inaba Yutaka
Kawagishi Hideyuki
Canon Kabushiki Kaisha
Duong Tai V.
Fitzpatrick ,Cella, Harper & Scinto
Sikes William L.
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