Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-16
2002-02-05
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S172000, C349S037000
Reexamination Certificate
active
06344889
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display using a liquid crystal material having spontaneous polarization and a method of manufacturing the same.
A liquid crystal display has characteristic features such as low consumption power, light weight, and small height and is therefore extensively used as the monitor display of a personal computer, a car navigation system, or the like. However, when compared to a CRT this liquid crystal display has disadvantages such as a low response speed and a narrow viewing angle. As the size and resolution of a liquid crystal display increase, demands for a high response speed and a wide viewing angle are increasing.
A liquid crystal display using a liquid crystal having spontaneous polarization has attracted attention as a display mode capable of high-speed response. Normally, spontaneous polarization is exploited as an intrinsic characteristic or induced by application of an electric field. Examples of a liquid crystal material like this are a ferroelectric liquid crystal (including an SS-FLC (Surface Stabilized Ferroelectric Liquid Crystal), a surface stabilized monostable ferroelectric liquid crystal, a DHF (Deformed Helix Ferroelectric liquid crystal), a twisted FLC (Ferroelectric Liquid Crystal), an APD (Alternating Polarization Domain), and a polymer stabilized ferroelectric liquid crystal), an anti-ferroelectric liquid crystal (including a thresholdless anti-ferroelectric liquid crystal), and a liquid crystal having an electro-clinic effect.
The operation principle of the aforementioned display mode is to transmit/intercept light by using the property that the optical axis of a liquid crystal, which is sandwiched between two polarizing plates whose transmission axes are shifted 90° and which can be regarded as a uniaxial crystal, rotate in the plane parallel to the substrate to which the polarizing plate is attached. In this display mode, inconvenience such as a color change occurs when the liquid crystal display is viewed obliquely. This is so because the apparent liquid crystal refractive index when a liquid crystal display is observed in a direction parallel to the optical axis of a liquid crystal differs from that when the display is viewed in a direction perpendicular to the optical axis.
To solve this inconvenience, Jpn. Pat. Appln. KOKAI Publication No. 9-120065 has proposed a method which increases the viewing angle by forming two regions where alignment directions are perpendicular to each other.
In a liquid crystal display described in Jpn. Pat. Appln. KOKAI Publication No. 9-120065, the area of two regions where alignment directions are perpendicular to each other is as small as about the pixel size which is generally a few tens of &mgr;m to several hundred &mgr;m. Mask rubbing is used to make the alignment directions of these regions different from each other. Mask rubbing is performed by steps of 1) coating a rubbed alignment film with a photoresist, 2) pre-baking, 3) mask exposure, 4) development, 5), post-baking 6) rubbing, 7) photoresist removal, and 8) alignment film cleaning. Mask rubbing thus having complicated steps increases the manufacturing cost, and this lowers the yield.
Jpn. Pat. Appln. KOKAI Publication No. 9-120065 has also proposed a method of forming the two regions only by making the alignment directions of upper and lower substrates perpendicular to each other. Although the steps of this method are simple, the method is inapplicable to a liquid crystal having a nematic phase or an isotropic phase on the high-temperature side of a chiral smectic C phase. This is because a liquid crystal having this phase sequence has no smectic A phase and hence is set in a twisted state when the alignment directions of upper and lower substrates are perpendicular to each other, so it is impossible to form two regions having different smectic layer directions.
A method of forming two regions having different smectic layer directions by using a liquid crystal having a nematic phase or an isotropic phase on the high-temperature side of a chiral smectic C phase is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-221718. In this method, a liquid crystal is filled into a liquid crystal cell having an alignment film under heating and phase-transited by cooling from a nematic phase or an isotropic phase into a chiral smectic C phase, thereby forming the two regions.
When the method described in this Jpn. Pat. Appln. KOKAI Publication No. 10-221718 is used, it is possible to form two regions having different smectic layer directions by using a liquid crystal having a nematic phase or an isotropic phase on the high-temperature side of a chiral smectic C phase. However, this method has the problem that although the two regions can be formed, locations where these two regions are formed cannot be controlled. In some cases, a desired viewing angle or desired gray scale display cannot be obtained.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display having a wide viewing angle and a liquid crystal display manufacturing method capable of obtaining a liquid crystal display having a wide viewing angle with simple steps.
To achieve the above object, a liquid crystal display according to the first aspect of the present invention comprises a first substrate, a second substrate opposing the first substrate, a liquid crystal material sandwiched between the first and the second substrate and having spontaneous polarization which has one of a nematic phase and an isotropic phase on a high-temperature side of a chiral smectic C phase, a first region of a portion of the liquid crystal material, and a second region of the liquid crystal material adjacent to the first region, wherein the liquid crystal material is aligned such that the direction of a smectic layer in the liquid crystal material in the first region is different from that in the liquid crystal material in the second region.
Also, a liquid crystal display according to the second aspect of the present invention comprises a first substrate, a second substrate opposing the first substrate, a plurality of pixel electrodes formed on a surface of the first substrate which opposes the second substrate, a pair of comb common electrodes formed on that surface of the second substrate, which opposes the first substrate, and having a plurality of interdigitated teeth, and a liquid crystal material sandwiched between the first and the second substrate and having spontaneous polarization which has one of a nematic phase and an isotropic phase on a high-temperature side of a chiral smectic C phase, wherein a direction of a smectic layer in the liquid crystal material in a first region sandwiched between one of the comb common electrodes and the pixel electrode is different from a direction of a smectic layer in the liquid crystal material in a second region sandwiched between the other of the comb common electrodes and the pixel electrode.
The liquid crystal displays according to the first and second aspects described above are preferably constituted as follows.
An angle the smectic layer in the first region makes with that in the second region is 115 to 155°
The first substrate has a plurality of pixel regions, the first and the second region are present in each of the plurality of pixel regions, and volumes of the liquid crystal material in the first and the second region are substantially equal.
Letting p be a chiral pitch of the liquid crystal material and d be a distance between the first and the second substrate, d<p.
A tilt angle of the liquid crystal material is substantially 22.5°.
The liquid crystal display according to the first aspect is desirably practiced such that the first substrate has a plurality of pixel regions, each of the plurality of pixel regions is divided into two regions correspondingly to the first and the second region, and a direction of a dividing line for dividing each of the plurality of pixel regions into the two regions is substantially parallel to an ali
Fukushima Rieko
Hasegawa Rei
Takatoh Kohki
Yamaguchi Hajime
Yamaguchi Takeshi
Finnegan Henderson Farbow Garrett & Dunner, L.L.P.
Ton Toan
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