Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-07-31
2001-02-27
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000, C349S134000, C349S172000, C349S184000
Reexamination Certificate
active
06195147
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. 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 view 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 miliseconds 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, 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 or ferroelectric liquid crystal 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 based on its spontaneous polarization. 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 inversion switching due to 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 counterbalance their spontaneous polarizations each other under no electric field application,. thus having no spontaneous polarization in the absence of the electric field. In more recent years, there has been reported an antiferroelectric liquid crystal showing no threshold value developed for actuating (driving) the antiferroelectric liquid crystal in an active matrix-type device.
The above-mentioned ferroelectric and antiferroelectric liquid crystal causing inversion switching based on spontaneous polarization are liquid crystal materials assuming smectic phase. 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.
In the case of a smectic liquid crystal display device using the ferroelectric liquid crystal, a thickness of an alignment control layer generally of an insulating material for effecting an alignment control, particularly a uniaxial alignment control, of the liquid crystal is made as small as possible to provide a resultant alignment control layer with a larger (electric) capacitance to minimize a reverse electric field (an electric field in reverse direction induced by a spontaneous polarization of the liquid crystal within this device), thus improving switching characteristics and a drive margin. An influence of the reverse electric field is noticeable as the spontaneous polarization becomes large, so that it is essential for the insulating alignment control layer to have a small thickness particularly in the case where a liquid crystal material having a large spontaneous polarization is employed.
Further, a chiral smectic liquid crystal device using the ferroelectric or antiferroelectric liquid crystal effects switching based on a response of the liquid crystal to an applied pulse electric field. In this instance, a magnitude of a voltage effectively applied to the liquid crystal layer is determined by a proportion (or reverse portion) of capacitances of respective layers (e.g., the liquid crystal layer and the alignment control layer) constituting the liquid crystal device.
In order to increase an effective voltage applied to the liquid crystal layer thereby to obtain better switching characteristics, a capacitance of the alignment control layer is set to be sufficiently larger than that of the liquid crystal layer. In other words, the thickness of the alignment control layer is designed to become sufficiently smaller than the liquid crystal layer thickness.
However, as the thickness of the alignment control layer is made smaller, the resultant alignment control layer is liable to fail to develop a desired alignment control performance. Consequently, it becomes difficult to realize some essential improvements in switching characteristics (reverse electric field and drive margin), response speed and an alignment characteristic in combination. Further, when an alignment control layer is formed in a uniform thickness in production process, it becomes difficult to control the uniform thickness with a decreasing film thickness.
SUMMARY OF THE INVENTION
In view of the above-mentioned circumstances, an object of the present invention is to provide a liquid crystal device, particularly a chiral smectic liquid crystal device (e.g., using a liquid crystal showing a ferroelectricity or antiferroelectricity) capable of providing a large drive margin and a high-speed switching characteristic while realizing a uniform alignment state of liquid crystal molecules.
Another object of the present invention is to provide an aligning method of a liquid crystal used in the liquid crystal device and a process for producing the device.
According to a first aspect of the present invention, there is provided a liquid crystal device: comprising a pair of substrates, and a liquid crystal disposed in an alignment state between the substrates,
wherein at least one of the substrate has a surface contacting the liquid crystal and including a first region having a larger uniaxial alignment control force and a second region having a smaller or substantially no uniaxial alignment control force, respectively acting on the liquid crystal, whereby phase transition from liquid phase to mesomorphic phase on temperature decrease, of the liquid crystal has been initiated from a portion contacting the first region and enlarged toward the second region to place the liquid crystal in the alignment state.
According to a second aspect of the present invention, there is also provided an aligning method of a liquid crystal, comprising:
providing a liquid crystal device including a pair of substrates and a liquid crystal disposed between the substrates, wherein at least one of the substrate has a surface contacting the liquid crystal and including a first region having a larger uniaxial alignment control force and a second region having a smaller or substantially no uniaxial alignment control force, respectively acting on the liquid crystal, and
Asao Yasufumi
Miura Seishi
Mori Shosei
Moriyama Takashi
Terada Masahiro
Canon Kabushiki Kaisha
Chowdhury Tarifur R.
Fitzpatrick ,Cella, Harper & Scinto
Sikes William L.
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