Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within smectic phase
Reexamination Certificate
1999-02-25
2001-10-30
Malinowski, Walter J. (Department: 2164)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within smectic phase
Reexamination Certificate
active
06310677
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a liquid crystal device for use in light-valves for flat-panel displays, projection displays, printers, etc., and a liquid crystal display apparatus including the liquid crystal device. The present invention also relates to an aligning method of a liquid crystal in the liquid crystal device and a process for producing the liquid crystal device.
As a type of a nematic liquid crystal display device used heretofore, there has been known an active matrix-type, a liquid crystal device wherein each pixel is provided with an active element (e.g., a thin film transistor (TFT)).
As a nematic liquid crystal material used for such an active matrix-type liquid crystal device using a TFT, there has been presently widely used a twisted nematic (TN) liquid crystal as disclosed by M. Schadt and W. Helfrich, “Applied Physics Letters”, Vol. 18, No. 4 (Feb. 17, 1971), pp. 127-128.
In recent years, there has been proposed a liquid crystal device of In-Plain Switching mode utilizing an electric field applied in a longitudinal direction of the device, thus improving a viewing angle characteristic being problematic in TN-mode liquid crystal displays. Further, a liquid crystal device of a super twisted nematic (STN) mode without using the active element (TFT etc.) has also be known as a representative example of the nematic liquid crystal display device.
Accordingly, the nematic liquid crystal display device includes various display or drive modes. In any mode however, the resultant nematic liquid crystal display device has encountered a problem of a slow response speed of several ten milliseconds or above.
In order to solve the above-mentioned difficulties of the conventional types of nematic liquid crystal devices, a liquid crystal device using a liquid crystal exhibiting bistability (“SSFLC”, Surface Stabilized FLC), has been proposed by Clark and Lagerwall (Japanese Laid-Open Patent Application (JP-A) 56-107216, U.S. Pat. No. 4,367,924). As the liquid crystal exhibiting bistability, a chiral smectic liquid crystal or a ferroelectric liquid crystal (FLC) having chiral smectic C phase (SmC*) is generally used. Such a chiral smectic (ferroelectric) liquid crystal has a very quick response speed because it causes inversion switching of liquid crystal molecules by the action of an applied electric field on spontaneous polarizations of their liquid crystal molecules. In addition, the chiral smectic liquid crystal develops bistable states showing a memory characteristic and further has an excellent viewing angle characteristic. Accordingly, the chiral smectic liquid crystal is considered to be suitable for constituting a display device or a light valve of a high speed, a high resolution and a large area.
In recent years, as another liquid crystal material, an antiferroelectric liquid crystal showing tristability (tristable states) has caught attention. Similarly as in the ferroelectric liquid crystal, the antiferroelectric liquid crystal causes molecular inversion switching due to the action of an applied electric field on its spontaneous polarization, thus providing a very high-speed responsiveness. This type of the liquid crystal material has a molecular alignment (orientation) structure wherein liquid crystal molecules cancel or counterbalance their spontaneous polarizations each other under no electric field application, thus having no spontaneous polarization in the absence of the electric field.
The above-mentioned ferroelectric and antiferroelectric liquid crystal causing inversion switching based on spontaneous polarization are liquid crystal materials assuming smectic phase (chiral smectic liquid crystals). Accordingly, by using these liquid crystal materials capable of solving the problem of the conventional nematic liquid crystal materials in terms of response speed, it has been expected to realize a smectic liquid crystal display device.
As described above, the (anti-)ferroelectric liquid crystal has been expected to be suitable for use in displays exhibiting a high-speed response performance in the near future.
In the case of the above-mentioned device (cell) using an SSFLC, however, the device can basically effect only a display of two (display) levels, thus being difficult to effect a gradation display in each pixel.
In recent years, in order to allow a mode of controlling various gradation levels, there have been proposed liquid crystal devices using a specific chiral smectic liquid crystal, such as a ferroelectric liquid crystal of a short pitch-type, a polymer-stabilized ferroelectric liquid crystal or an anti-ferroelectric liquid crystal showing no threshold (voltage) value. However, these devices have not been put into practical use sufficiently.
SUMMARY OF THE INVENTION
In view of the above-mentioned circumstances, an object of the present invention is to provide a liquid crystal device using a liquid crystal having chiral smectic C phase, capable of performing a gradation level control.
Another object of the present invention is to provide a liquid crystal display apparatus including the liquid crystal device.
According to the present invention, there is provided a liquid crystal device, comprising:
a pair of oppositely disposed substrates and a liquid crystal having chiral smectic C phase disposed therebetween, each of the substrates having thereon an electrode for applying a voltage to the liquid crystal, at least one of the substrates being provided with a uniaxial alignment axis for aligning the liquid crystal,
wherein the liquid crystal is placed in an alignment state in chiral smectic C phase such that:
(a) the liquid crystal comprises smectic molecular layers forming a chevron structure,
(b) under no electric field application, the liquid crystal has an average molecular axis substantially in alignment with the uniaxial alignment axis and/or a bisector of a maximum angle formed between two extreme molecular axes established under electric field application, and
(c) under electric field application, the liquid crystal provides an effective tilt angle and a transmittance that continuously changed depending on an electric field applied thereto.
According to the present invention, there is also provided a liquid crystal display apparatus including the liquid crystal device, a drive circuit for driving the liquid crystal device and a light source.
REFERENCES:
patent: 4367924 (1983-01-01), Clark et al.
patent: 5214523 (1993-05-01), Nito et al.
patent: 5458804 (1995-10-01), Yamada et al.
patent: 5629788 (1997-05-01), Mori et al.
patent: 5728318 (1998-03-01), Yamashita et al.
patent: 5790223 (1998-08-01), Hanyu et al.
patent: 5895107 (1999-04-01), Haslam
patent: 63-143529 (1988-06-01), None
M. Schadt and W. Helfrich, “Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal”, Appl. Phys. Letters, vol. 18, No. 4, Feb. 15, 1971.
Asao Yasufumi
Mori Shosei
Moriyama Takashi
Terada Masahiro
Togano Takeshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Malinowski Walter J.
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