Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-11
2002-01-01
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S106000
Reexamination Certificate
active
06335777
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a liquid crystal device for use in, e.g., a display apparatus for displaying images including characters and/or figures, particularly a liquid crystal device using a chiral smectic liquid crystal suitable for full-color display and a liquid crystal device having a stripe electrode structure suitable for a simple matrix driving. The present invention also relates to a process for producing the liquid crystal device and a color liquid crystal display apparatus using the liquid crystal device.
A display device of the type which controls transmission of light in combination with a polarizing device by utilizing the refractive index anisotropy of ferroelectric (or chiral smectic) liquid crystal molecules has been proposed by Clark and Lagerwall (U.S. Pat. No. 4,367,924, etc.). The ferroelectric liquid crystal has generally chiral smectic C phase (SmC*) or H phase (SmH*) of a non-helical structure in a certain temperature region and, in the SmC* or SmH* phase, shows a property of assuming either one of a first optically stable state and a second optically stable state (bright and dark states) responding to an electrical field applied thereto and maintaining such a state in the absence of an electrical field, namely bistability, and also has a quick responsiveness to the change in electrical field. Thus, it is expected to be utilized in a high speed and memory type display device and particularly to provide a large-area, high-resolution display based on its excellent function.
FIG. 1
shows a sectional view of a liquid crystal device using a ferroelectric liquid crystal based on two-valued (white and black) display.
Referring to
FIG. 1
, the liquid crystal device (panel) includes insulating substrates
1
a
and
1
b
, transparent electrodes 6a and 6b, auxiliary electrodes
7
a
and
7
b
, short-circuit prevention layers
8
a
and
8
b
, roughened surface-forming layers
9
a
and
9
b
, alignment layers
10
a
and
10
b
, an adhesive bead
11
(after adhesion), a spacer bead
12
, and a liquid crystal layer
13
. Each of the transparent electrodes
6
a
and
6
b
constitutes drive electrodes in combination with the auxiliary electrodes
7
a
and
7
b
, respectively. The drive electrodes (including the electrodes
6
a
and
7
a
and the electrodes
6
b
an
7
b
, respectively) intersect with each other at right angles to form a matrix electrode structure. At each intersection, one pixel is constituted and corresponds to a region between two broken lines in FIG.
1
.
In order to ensure a good impact (shock) resistance and keep a uniform thickness of a liquid crystal layer, an ordinary liquid crystal panel needs to use spacer beads
12
composed of an adhesive and softer material (than the spacer beads), i.e., for effecting adhesion between the upper and lower substrate members (structures) as described above.
Such spacer beads and adhesive beads have been dispersed together on one of the pair of substrate in an ordinary (liquid crystal) panel production process (substrate production process). However, in the subsequent steps, particularly in the step of applying the pair of substrates to each other, the adhesive beads are liable to be moved due to flowability and poor adhesiveness thereof at that time, thus adversely affecting performances of a resultant liquid crystal panel.
Further, the above-mentioned liquid crystal device using a ferroelectric liquid crystal has a very small cell gap (i.e., a thickness of a ferroelectric liquid crystal layer), so that the injection of the liquid crystal into the cell gap of a blank cell is not readily performed, thus resulting in a defective liquid crystal panel in a relatively high proportion. For this reason, the ferroelectric liquid crystal device is required to improve a production yield.
There has been known a liquid crystal device including the above ferroelectric liquid crystal device having a matrix electrodes structure such that a pair of substrates (electrode plates) each provided with a group of electrodes in the form of stripes are oppositely disposed so as to form a pixel at each intersection at right angles and a gap between the substrate is filled with a liquid crystal. In case where such a liquid crystal device causes a short-circuit between the electrodes and has an electrode resistance out of its specifications, it is almost difficult to repair or replace such defective electrodes. For this reason, in an actual production line, after the formation of upper and lower electrode groups, all of the electrodes are subjected to inspection (check) with respect to short-circuit and electrode (wire) resistance by placing an inspection terminal on each lead-out portion of the electrodes, thus removing defective products from the production line.
As the number of pixels per unit display area is increased for providing a higher definition display image, an electrode width for each stripe electrode becomes narrower (smaller). Accordingly, in this case, an inspection terminal is not readily placed on a lead-out portion of an objective electrode in the above-described inspection stage, thus being liable to fail to perform a correct inspection operation.
Further, in order to reduce the electrode (wire) resistance, a metal wire (metal layer) as an auxiliary electrode is generally formed on a transparent electrode within an extent not impairing a display quality. The metal wire is liable to be damaged (e.g., burned out) by an inspection terminal having a narrowed top portion corresponding to a small electrode width or is liable to cause short-circuiting with a metal piece (fragment) scraped off or removed by the terminal.
In case where the liquid crystal device as described above is incorporated into a color liquid crystal display apparatus, a color filter comprising color filter segments of at least three colors including red (R), green (G), blue (B), and optional transparent color (W: white) in the form of stripes or a mosaic color filter wherein any adjacent (parallel) two color filter elements (comprising R, G, B and optional W segments) in one direction are shifted from each other by ½ pitch of one color filter segment in the direction may generally be used. Such a color filter is generally disposed at an inner surface of one of upper and lower (a pair of) glass substrates (i.e., on a side closer to a liquid crystal layer), whereby a resultant liquid crystal device has different layer structures with respect to the upper and lower substrates different from the case of a monochromatic (white and block) liquid crystal display apparatus.
In another aspect, a chiral smectic liquid crystal (e.g., a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal) shows one orientation (alignment) state under application of an electric field of one polarity based on a certain reference potential level and shows the other orientation state under application of an electric field of the opposite polarity. Such a property is quite different from that of a twisted nematic (TN)-type liquid crystal. There has been developed a color liquid crystal display apparatus utilizing the above property of the chiral smectic liquid crystal.
The above-mentioned two orientation states of the chiral smectic liquid crystal are required to have potential energies having symmetry. However, if a pair of (upper and lower) substrates have different layer structures thereon from each other as described above, the potential energies of the two orientation states are liable to become asymmetrical. The asymmetry of the potential energies is liable to cause that of switching threshold values between orientation state and the other orientation state.
The above problem is peculiar to the chiral smectic liquid crystal and does not substantially arise in the case of the TN liquid crystal. Particularly, the asymmetry of switching threshold values is liable to narrow (decrease) a drive margin (a margin allowing a good display state) determining a latitude in selecting drive signal waveform conditions, su
Ishiwata Kazuya
Katakura Kazunori
Masaki Yuichi
Mihara Tadashi
Mori Sunao
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