Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-03-10
2001-10-02
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S125000, C349S135000, C349S133000
Reexamination Certificate
active
06297865
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal element (for example, a liquid crystal display element or a liquid crystal display) in which a plurality of base bodies each having a liquid crystal orientation film are opposed to each other on the liquid crystal orientation film side with a specific gap put therebetween.
A liquid crystal display (LCD) using liquid crystal as a display element, having a feature allowing a low power consumption with a thin and lightweight structure, is being applied to watches, electronic calculators, computer displays, and television receivers (TVs).
Researches and developments have been actively made to use ferroelectric liquid crystal (FLC) as the above liquid crystal for LCDS. Ferroelectric liquid crystal was first synthesized by R. B. Meyer in 1975, and a surface-stabilized ferroelectric liquid crystal enabling domain inversion by an applied electric field was invented by N. A. Clark and S. T. Lagerwall in 1980. FLC is a liquid crystal whose molecules themselves have permanent dipole moments perpendicular to major axes of the molecules, that is, it has a spontaneous polarization switchable by an applied electric field. A display using FLC has the following excellent features (1) to (3).
(1) The FLC display has a switching speed in the order of &mgr;sec, that is, it exhibits a high speed of response being as high as 1,000 times that of a twisted nematic (TN) liquid crystal display.
(2) The FLC display has a molecular arrangement basically containing no twist structure, and thereby it has less dependency on angle of visibility.
(3) The FLC display holds an image after turn-off of a power supply, that is, stores an image, and thereby it allows a simple matrix drive to be adopted for scanning lines of 1,000 lines or more capable of being matched with definition display.
The FLC display is thus expected to meet demands toward high definition, low cost, and large screen.
Such a FLC display (ferroelectric liquid crystal display element) has a structure typically shown in
FIGS. 15 and 16
. Transparent electrodes
2
a
and
2
b
made from ITO (Indium Tin Oxide) of 100 &OHgr;/□ are provided on transparent substrates
1
a
and
1
b
made of glass (Corning Code 7059, 0.7 mm thick), respectively. Each transparent electrode is patterned into a stripe pattern by etching. To be more specific, the transparent electrode
2
a
are patterned into data electrodes (column electrodes)
2
a
, and the transparent electrode
2
b
is patterned into scanning electrodes (row electrodes)
2
b
. The data electrodes
2
a
and the scanning electrodes
2
b
are disposed in such a manner as to cross each other in a matrix.
Liquid crystal orientation films
3
a
and
3
b
, represented by oblique vapor-deposition films of SiO, are formed on the transparent electrodes
2
a
and
2
b
, respectively. In formation of the oblique vapor-deposition film of SiO, a substrate is disposed obliquely downward from a SiO vapor-deposition source in a vacuum vapor-deposition system. In this case, a deposition angle between a line connecting the vapor-deposition source to the substrate and the normal line of the substrate is set at 85°. The vapor-deposition film of SiO formed on the substrate at a substrate temperature of 170° C. is then baked at 300° C. for 1 hr.
A pair of the substrates
1
a
and
1
b
with the orientation films thus prepared are assembled to be opposed to each other on the orientation film side in such a manner that the orientation-treatment direction of the film on the data electrode
2
a
side is anti-parallel to that of the film on the scanning electrode
2
b
side, and that the arrangement of the data electrodes
2
a
is perpendicular to that of the scanning electrodes
2
b
. As spacers, there are used glass beads
4
having sizes corresponding to a target gap length, for example, glass beads shinshikyu, diameter in a range of 0.8 to 3.0 &mgr;m, produced by Catalysts $ Chemicals Industries Co., Ltd.). Although in the example shown in the figures, the orientation-treatment directions of the opposed films are set to be anti-parallel to each other, they may be set to be parallel to each other.
The setting of the spacers
4
is dependent on sizes of the transparent substrates
1
a
and
1
b
. In the case where the substrate area is small, a gap between the substrates is adjusted by dispersing about 0.3 wt % of the spacers
4
in a sealing material 6 [UV hardened type adhesive (Photolec, produced by Sekisui Chemical Co., Ltd.) for bonding peripheries of the substrates. In the case where the substrate area is large, the above shinshikyu, are scattered between the substrates at an average density of 100 pieces/mm
2
, followed by adjustment of a gap between the substrates, and peripheries of the substrates constituting a cell are bonded by the sealing material
6
with a liquid crystal injection hole being ensured.
As liquid crystal to be injected between the substrates
1
a
and
1
b
, there is typically used a liquid crystal composition in which ferroelectric liquid crystal (YS-C152, produced by Chisso Corporation)
5
is homogeneously dispersed at an isotropic phase temperature using a ultrasonic homogenizer. This ferroelectric liquid crystal composition is injected under a reduced pressure at a temperature allowing the liquid crystal to exhibit a fluidity, such as an isotropic phase temperature or a chiral nematic phase temperature. The liquid crystal thus injected is gradually cooled, followed by removal of an unnecessary portion of the liquid crystal adhering on the glass substrates around the injection hole, and the cell is sealed using an epoxy based adhesive, to thus prepare a FLC display
11
.
The FLC display
11
is driven by an X-Y matrix system. In the case of using an NTSC system, 1 H (one horizontal scanning time or one selecting time) is set at 63.5 &mgr;s, and since a voltage is applied using a bipolar manner in consideration of electrically neutral condition, each selection pulse becomes 63.5/2 &mgr;s in width. A select pulse as a threshold value is applied from the row side (electrodes
2
b
), and a data pulse is applied from the column side (electrodes
2
a
).
In a ferroelectric liquid crystal element (for example, surface-stabilized ferroelectric liquid crystal element), the orientation of a molecule M is switched between states
1
and
2
shown in
FIG. 17
when an electric field E is applied thereto from the exterior. In addition, character Ps indicates a spontaneous polarization. A change in orientation of the molecule M can be converted into a change in transmittance by provision of the liquid crystal element between polarizer sheets disposed perpendicularly to each other. Such a transmittance is rapidly changed depending on the applied electric field, for example, as shown in
FIG. 18
, it is rapidly changed from 0% to 100% at a threshold voltage V
th
. A voltage width in which the transmittance is changed is generally in a range of 1 V or less.
In this way, in the related art ferroelectric liquid crystal display using the bi-stable mode, only the two states are stable, and accordingly, it is difficult to give a stable voltage width to a curve between a transmittance and an applied voltage. In other words, it is difficult or impossible to attain gradation display by voltage control.
The present applicant has studied to solve such an inconvenience and found that an analog gradation display can be achieved by giving a distribution of an effective field strength applied to liquid crystal in one pixel so as to extend a width of threshold voltages for switching between bi-stable states of the liquid crystal in the one pixel, and has already proposed a technique in Japanese Patent Laid-open No. Hei 5-262951 (hereinafter, referred to as “earlier invention”).
According to the earlier invention, to achieve the above-described subject “to extend a width of threshold voltages”, there is adopted a method of adding and dispersing ultra-fine particles of titanium oxide or the like in ferroelectric liquid crystal.
By additi
Iwamura Takashi
Kataoka Nobue
Matsui Eriko
Takanashi Hidehiko
Yasuda Akio
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
Ton Toan
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