Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1996-09-09
2001-07-24
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S174000
Reexamination Certificate
active
06266115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal cell and liquid crystal display device using an antiferroelectric liquid crystal. The present invention is advantageously used for a liquid crystal TV, a liquid crystal watch, various display devices, etc.
2. Description of the Related Art
Recently, a liquid crystal cell has been widely used as a display element having many features, for example, thin configuration, light weight, and low power consumption. In general, almost all display elements are formed of TN (Twisted Nematic)-type liquid crystal cells which use nematic liquid crystals. The display method using the TN-type liquid crystal cell has a very slow response speed (time). This is because the liquid crystal cell is driven based on an anisotropic characteristic of a dielectric constant of the liquid crystal. Accordingly, it has been required to improve the response speed in the TN type liquid crystal.
On the other hand, another liquid crystal cell, which uses the liquid crystal having a chiral smectic C phase (below, SmC* phase) indicating a ferroelectric characteristic (this type of liquid crystal was found by Mr. Meyer et al.), has a high response speed and a good storage characteristic which could not be achieved by the above nematic liquid crystal. Accordingly, recently, research and development have been performed to discover a ferroelectric liquid crystal cell having the above good characteristics.
However, it is very difficult to realize good molecular alignment of liquid crystal molecules and good storage characteristic, both of which are necessary for providing a good display with the above-described liquid crystal cell, because this type of liquid crystal cell is easily damaged by a shock applied from outside.
Further, recently, in the liquid crystal having the SmC* phase, an antiferroelectric phase (SmC
A
* phase), which has three stable states at the low temperature of the SmC* phase, was found by Ms. Chandani et al.
In the SMC
A
* phase, dipoles (i.e., liquid crystal molecules) are arranged in anti-parallel for an adjacent layer (i.e., as shown in
FIG. 4
dipoles are arranged in parallel in the same layer, but not arranged in parallel for the adjacent layer), and this arrangement indicates a thermodynamically stable state. Further, in the SmC
A
* phase, there is an electric field-induced phase transition between the antiferroelectric phase and the ferroelectric phase, and this electric field-induced phase transition features a double hysteresis characteristic (i.e., switching characteristic) and a threshold value for a supply voltage. As a result, research and development on the switching characteristic and threshold value have begun in order to obtain a new display method using the antiferroelectric liquid crystal cell.
Accordingly, the present invention aims to provide an improved liquid crystal cell and liquid crystal display device using an antiferroelectric liquid crystal.
SUMMARY OF THE INVENTION
The object of the present invention aims to provide an improved liquid crystal cell and a liquid crystal display device using an antiferroelectric liquid crystal which can suppress a layer rotation in the antiferroelectric liquid crystal.
In accordance with one aspect of the present invention, there is provided a liquid crystal cell including: two electrode substrates facing each other and separated by a plurality of spacers; each electrode substrate being formed by superimposing a glass substrate, a transparent electrode and an alignment film; and an antiferroelectric liquid crystal being injected between alignment films; wherein, an alignment treatment is performed to each alignment film so that an angle of layer rotation of the antiferroelectric liquid crystal is defined within a predetermined allowable range.
In a preferred embodiment, the predetermined allowable range of the angle is defined from −1° to +1°.
In another preferred embodiment, the alignment treatment for each alignment film is performed in such a way that a response time from a first ferroelectric state to an antiferroelectric state is approximately the same as a response time from a second ferroelectric state to the antiferroelectric state in the antiferroelectric liquid crystal.
In still another preferred embodiment, the alignment treatments for each alignment film has the same rubbing conditions.
In accordance with another aspect of the present invention, there is provided a liquid crystal cell including: two electrode substrates facing each other and separated by a plurality of spacers; each electrode substrate being formed by superimposing a glass substrate, a transparent electrode and an alignment film; and an antiferroelectric liquid crystal being injected between two electrode substrates; wherein, an alignment treatment is performed to each alignment film so that the difference between optical retardations of each refractive index after an alignment treatment to each alignment film is defined within a predetermined allowable range.
In a preferred embodiment, the predetermined allowable range is defined from −1 nm to +1 nm.
In accordance with still another aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal cell having two electrode substrates facing each other through a plurality of spacers and each electrode substrate being formed by superimposing a glass substrate, a transparent electrode and an alignment film, and an antiferroelectric liquid crystal being injected between two electrode substrates, being set to a first or second ferroelectric state when a positive or negative voltage is applied thereto, and being set to an antiferroelectric state when no voltage is applied thereto; and
a control apparatus connected to the liquid crystal cell for applying the positive or negative voltage thereto as a supply voltage; wherein said control apparatus controls so as to superimpose a direct current component onto the supply voltage and to apply it to the liquid crystal cell so that a response time from a first ferroelectric state to an antiferroelectric state is approximately the same as a response time from a second ferroelectric to the antiferroelectric state.
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McGraw-Hill Electronics Dictionary, 5th edition, J. Markus & N. Sclater, 1994, p.390.*
“Tristable Switching in Surface Stabilized Ferroelectric Liquid Crystal with a Large Spontaneous Polarization,” Chandani et al., JP.J.of App.Physics, vol. 27, No. 5, May 1988, pp. L729-L732.
“Ferroelectric Liquid Crystals,” Meyer, Mol. Cryst. Liq. Cryst, 1977, vol. 40, pp. 33-48.
“Smectric Layer Rotation in Antiferroelectric Liquid Crystal,” Ozaki, et al., JP.J. of App. Physics, vol. 33 (1994), pp. L-1620-L1623.
Abstract Document in 21st Crystal Forum, Fujikawa et al., Sep. 10, 1995, pp. 88-89.
“A Layer Rotation of Antiferroelectric Liquid Crystal in a Rubbing Cell,”, Fujikawa et al., (21st Liquid Crystal Forum).
“Analysis of Abnormal Alignment by Optical Methods,” Nishino et al., Abstract Document, in 17th Liquid Crystal Forum, pp. 32-33.
Fujikawa Takayuki
Ozaki Masaaki
Takeuchi Akira
Yamada Yuichiro
Yamamoto Norio
Nguyen Dung
Nippondenso Co. Ltd.
Pillsbury & Winthrop LLP
Sikes William L.
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