Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-10
2003-08-05
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S156000, C349S157000, C349S153000
Reexamination Certificate
active
06603528
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal device for use in a liquid crystal optical switch, a liquid crystal optical shutter, etc., particularly to a liquid crystal device improved in display characteristics and electro-optical characteristics.
Heretofore, as a display apparatus for displaying various data or information, CRTs (cathode ray tubes) have been known and widely used for displaying motion pictures of television and video tape recorders or as monitor displays for personal computers. Based on the operation characteristic, however, the CRT is accompanied with difficulties such that the recognizability of a static image decreases due to flickering and scanning fringes caused by insufficient resolution, and the fluorescent member deteriorates due to burning. Further, it has been found that electromagnetic waves emitted from CRTs can adversely affect human bodies (e.g., health of VDT operators). Further, the CRT structurally has a large rearward space behind the display surface, so that the space economization in offices and at home may be obstructed thereby.
As a type of device solving such problems of the CRT, there has been known a liquid crystal panel (device), including a type using a twisted nematic (TN) liquid crystal as disclosed by M. Schadt and W. Helfrich, Appl. Phys. Lett., vol. 18, no. 4, pp. 127-128 (1971).
Liquid crystal devices using TN liquid crystal include a simple matrix-type liquid crystal device and an active matrix-type liquid crystal device wherein each pixel is provided with a TFT (thin film transistor).
The simple matrix-type liquid crystal device is advantageous from a viewpoint of production cost. This type of liquid crystal device is, however, accompanied with a problem that it is liable to cause crosstalk when driven in a multiplex manner using an electrode matrix of a high pixel density, and therefore the number of pixels is retracted. The problems of crosstalk and response speed can be solved by the active matrix-type liquid crystal device using TFTs, but, on the other hand, producing a larger area device of this type would be extremely difficult since inferior pixels are liable to occur. Further, even if such production is possible, the production cost would be increased enormously due to a lowering in production yield.
For providing improvements in light of the above-mentioned difficulties of the conventional types of TN liquid crystal devices, a liquid crystal device of the type which controls transmission of light in combination with a polarizing device by utilizing a refractive index anisotropy of ferroelectric (chiral smectic) liquid crystal (abbreviated as “FLC”) molecules has been proposed by Clark and Lagerwall (Japanese Laid-Open Patent Application (JP-A) 56-107216, U.S. Pat. No. 4,367,924). The ferroelectric liquid crystal (FLC) generally has chiral smectic C phase (SmC*) or H phase (SmH*) in a specific temperature range and, in the phase, shows a property of assuming either one of a first optically stable state and a second optically stable state in response to an electric field applied thereto and maintaining such a state in the absence of an electric field, namely bistability, and also have a very quick response speed because it causes inversion switching based on its spontaneous polarization. Thus, the FLC develops bistable states showing a memory characteristic and further has an excellent viewing angle characteristic. Accordingly, the FLC is considered to be suitable for constituting a high speed, high resolution and large area display device.
In the FLC panel (device), at an initial alignment stage, liquid crystal molecules placed in a first stable state and those placed in a second stable state are co-present in a domain. More specifically, in a device using a chiral smectic liquid crystal developing bistable states, an alignment control force for aligning liquid crystal molecules to be placed in a first stable state and that for aligning liquid crystal molecules to be placed in a second stable state have a substantially equal energy level. As a result, when the chiral smectic liquid crystal is disposed between a pair of substrates, each provided with an alignment film in a thickness sufficiently small to assume bistability, resultant oriented (aligned) liquid crystal molecules in a domain include a portion placed in a first stable state and a portion placed in a second stable state in combination at an initial alignment stage.
Further, similar to the FLC device, a liquid crystal device of the type wherein a refractive index anisotropy and a spontaneous polarization of liquid crystal molecules are utilized, there has been known a liquid crystal device using an anti-ferroelectric liquid crystal (abbreviated as “AFLC”). The AFLC generally has chiral smectic CA phase (SmCA*) in a specific temperature range and, in the phase, shows a property of assuming an average optically-stable state, wherein liquid crystal molecules are oriented in a direction of a normal to smectic (molecular layers under no electric field application and tilting its average molecular axis direction from the layer normal direction under application of an electric field). Further, the AFLC causes switching based on its spontaneous polarization in combination with the applied electric field, thus exhibiting a very quick response. Accordingly, the AFLC is expected to be used in a high speed liquid crystal panel.
As one of the conventional liquid crystal devices, a transmission-type liquid crystal panel (device) will be described with reference to FIG.
5
.
FIG. 5
is a schematic sectional view showing a portion closer to a boundary between a display region and a peripheral region of an embodiment of a conventional liquid crystal panel.
Referring to
FIG. 5
, a liquid crystal display panel (liquid crystal device) includes a pair of oppositely disposed glass substrates
111
and
111
which are bonded to each other via a sealing agent
112
at the periphery thereof with a gap. The gap is held by spacer beads
115
and filled with a chiral smectic liquid crystal
113
. On the surface of each of the glass substrates
111
(
111
), a laminated film
114
comprising, e.g., a transparent (ITO: indium tin oxide) electrode, an insulating film, an inorganic oxide insulating film and an aligning-treated alignment film for aligning the liquid crystal
113
sequentially disposed on the glass substrate is formed. In the peripheral region of the device, a frame-shaped masking (light-interrupting) member
116
(so called “black matrix”) comprising, e.g., a metal is disposed so as to surround the display region.
The liquid crystal display panel may generally be driven by applying a voltage of at least a certain threshold value to the liquid crystal
113
. In this case, if a cell gap between the glass substrates
111
(
111
) is not uniform over the entire picture area, an electric field applied to the liquid crystal
113
becomes nonuniform to cause image irregularity and irregularity in driving characteristics, thus resulting in inferior image qualities. Particularly, in the case of a liquid crystal display panel using the FLC or AFLC, it is necessary to provide a small cell gap of ca. 1-3 &mgr;m. Accordingly, even when a degree of nonuniformity of cell gap is slight, the resultant nonuniform cell gap significantly affects image quality.
In order to keep such a small cell gap uniform, it has been proposed to use spacer beads (spherical spacer)
115
or stripe spacers formed through flexible printing, photolithography or dry film.
The latter stripe spacers employed in a liquid crystal display panel may generally be formed in a pattern such that each stripe line extends from a liquid crystal injection port with an identical width, a gradually increasing width or a gradually decreasing width. The stripe spacers may generally be formed with a material having a prescribed viscosity so that each stripe line has an identical width and a width as large as possible.
On the other hand, the former spacer beads
115
, as shown in
FIG. 5
, may or
Hachisu Takahiro
Murata Masayoshi
Tanaka Toshimitsu
Canon Kabushiki Kaisha
Chung David
Fitzpatrick ,Cella, Harper & Scinto
Kim Robert H.
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