U.S. patent application number 09/895183 was filed with the patent office on 2001-12-27 for liquid crystal device, process for producing same and liquid crystal apparatus.
Invention is credited to Ishiwata, Kazuya, Katakura, Kazunori, Masaki, Yuichi, Mihara, Tadashi, Mori, Sunao, Saito, Tetsuro, Shimamura, Yoshinori, Tsujita, Chikako, Yokoyama, Yuko.
Application Number | 20010055084 09/895183 |
Document ID | / |
Family ID | 27471304 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055084 |
Kind Code |
A1 |
Yokoyama, Yuko ; et
al. |
December 27, 2001 |
Liquid crystal device, process for producing same and liquid
crystal apparatus
Abstract
A liquid crystal device, comprising: a pair of substrates each
provided with an electrode including one substrate having thereon a
color filter and a coating layer, and a liquid crystal layer
comprising a chiral smectic liquid crystal disposed together with
spacer beads between the pair of substrates, wherein the liquid
crystal layer has a thickness smaller than a diameter of the spacer
beads and a maximum thickness of the coating layer, the coating
layer having a pencil hardness of at most 7H. The above layer
structure between the substrates is effective in improving
resistance to external shock and providing a uniform cell gap.
Inventors: |
Yokoyama, Yuko;
(Yokohama-shi, JP) ; Masaki, Yuichi;
(Kawasaki-shi, JP) ; Ishiwata, Kazuya;
(Yokosuka-shi, JP) ; Saito, Tetsuro; (Isehara-shi,
JP) ; Shimamura, Yoshinori; (Kanagawa-ken, JP)
; Mihara, Tadashi; (Isehara-shi, JP) ; Katakura,
Kazunori; (Atsugi-shi, JP) ; Mori, Sunao;
(Yokohama-shi, JP) ; Tsujita, Chikako;
(Atsugi-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
27471304 |
Appl. No.: |
09/895183 |
Filed: |
July 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09895183 |
Jul 2, 2001 |
|
|
|
09613625 |
Jul 11, 2000 |
|
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Current U.S.
Class: |
349/133 |
Current CPC
Class: |
G09G 2300/0452 20130101;
G09G 2310/065 20130101; G02F 1/134336 20130101; G02F 1/133512
20130101; G02F 1/141 20130101; G09G 3/3629 20130101; G09G 2320/041
20130101; G02F 1/1345 20130101; G02F 1/133519 20210101; G02F
1/133514 20130101 |
Class at
Publication: |
349/133 |
International
Class: |
G02F 001/141 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 1995 |
JP |
127503/1995(PAT.) |
Apr 28, 1995 |
JP |
127504/1995(PAT.) |
Apr 28, 1995 |
JP |
127505/1995(PAT.) |
Dec 29, 1995 |
JP |
352788/1995(PAT.) |
Claims
What is claimed is:
1. A liquid crystal device, comprising: a pair of substrates each
provided with an electrode including one substrate having thereon a
color filter and a coating layer, and a liquid crystal layer
comprising a chiral smectic liquid crystal disposed together with
spacer beads between the pair of substrates, wherein the liquid
crystal layer has a thickness smaller than a diameter of the spacer
beads and a maximum thickness of the coating layer, the coating
layer having a pencil hardness of at most 7H.
2. A device according to claim 1, comprising a sealing agent
disposed between the pair of substrates at a peripheral portion
thereof, the coating layer extending to a portion corresponding to
the peripheral portion.
3. A device according to claim 1, wherein the coating layer has a
pencil hardness of 3H-7H.
4. A process for producing a liquid crystal device, comprising the
steps of: forming on a first insulating substrate a
light-interrupting layer, a color filter comprising plural color
filter segments, a coating layer, a barrier layer, a transparent
electrode, an auxiliary electrode, a short-circuit prevention
layer, a roughened surface-forming layer, and an insulating layer
in succession in this order, forming on a second insulating
substrate a transparent electrode, an auxiliary electrode, a
short-circuit prevention layer, a roughened surface-forming layer,
and an insulating layer in succession in this order, rubbing the
surface of each of the alignment layers on the first and second
substrates, dispersing adhesive beads over the alignment layer
surface formed on the first substrate or the second substrate,
disposing a sealing agent having a prescribed pattern on the
insulating layer surface formed on the second substrate or the
first substrate, dispersing spacer beads over the insulating layer
surface provided with the sealing agent, adhesively bonding the
first and second substrate to each other while fixing the first or
second substrate over which the adhesive beads are dispersed,
scribing the first and second substrates to remove an unnecessary
portion, injecting a chiral smectic liquid crystal from an
injection port into a gap between the first and second substrates,
and sealing up the injection port.
5. A process according to claim 4, wherein each of the first and
second insulating substrates comprises a glass plate immediately on
which an undercoat layer comprising SiO.sub.2 is formed in a
thickness of 200-1000 .ANG..
6. A process according to claim 4, wherein the light-interrupting
layer comprises a black stripe composed of an alloy of Mo and Ta
having a thickness of 500-1500 .ANG..
7. A process according to claim 4 wherein the color filter
comprises a resin layer having a thickness of 1.0-2.0 .mu.m and
comprising plural photosensitive resins containing at least one
pigment.
8. A process according to claim 7, wherein the photosensitive
resins comprise polyamide.
9. A process according to claim 4, wherein the coating layer
comprises an organic silane-based resin layer having a maximum
thickness of 1.5-5 .mu.m.
10. A process according to claim 4, wherein the barrier layer
comprises an SiO.sub.2 layer having a thickness of 100-1000
.ANG..
11. A process according to claim 4, wherein each of the transparent
electrodes formed on the first and second substrates comprises an
ITO layer having a thickness of 300-3000 .ANG..
12. A process according to claim 4, wherein each of the auxiliary
electrodes formed on the first and second substrates comprises a
metal lamination layer of Mo--Ta/Al/Mo--Ta having a thickness of
500-2500 .ANG..
13. A process according to claim 4, wherein each of the
short-circuit prevention layers formed on the first and second
substrates comprises a lamination layer including a Ta.sub.2O.sub.5
layer having a thickness of 500-1200 .ANG. and a Ti--Si layer
disposed thereon having a thickness of 500-1000 .ANG..
14. A process according to claim 4, wherein each of the roughened
surface-forming layers formed on the first and second substrates
comprises a Ti--Si layer having a thickness of 100-300 .ANG. and
containing SiO.sub.2 beads dispersed therein having a diameter of
300-700 .ANG..
15. A process according to claim 4, wherein each of the insulating
layer comprises a polyimide film having a thickness of 50-1000
.ANG..
16. A process according to claim 4, wherein the rubbing step is
performed by rubbing the surface of the insulating layer with a
rubbing roller about which a raised rubbing cloth comprising
aramide fiber is wound.
17. A process according to claim 4, wherein the dispersion of the
adhesive beads on one substrate is performed by dispersing a
dispersion of adhesive beads comprising a thermosetting resin
having a diameter of 2-10 .mu.m in a solvent at a density of 50-130
particles/mm.sup.2 in a region corresponding to a sealing area
within a sealing portion of the other substrate.
18. A process according to claim 17, wherein the thermosetting
resin comprises epoxy resin or acrylic resin.
19. A process according to claim 4, wherein the sealing agent
comprises a thermosetting resin.
20. A process according to claim 19, wherein the thermosetting
resin comprises epoxy resin.
21. A process according to claim 4, wherein the dispersion step of
the spacer beads is performed by dispersing the spacer beads in the
form of a dispersion in ethanol so as to provide a density of
100-700 particles/mm.sup.2.
22. A process according to claim 21, wherein the spacer beads
comprise silica beads having a diameter of 0.6-3.5 .mu.m.
23. A process according to claim 4, wherein the adhesive beads and
the spacer beads are dispersed on the first substrate and the
second substrate, respectively.
24. A process according to claim 4, wherein the resultant liquid
crystal device has a cell gap of 0.5-3 .mu.m.
25. A process according to claim 4, wherein, in the scribing step,
the first and second substrates have different scribing
positions.
26. A process according to claim 4, wherein, the sealing step of
the injection port is performed by using a room temperature curing
epoxy resin.
27. A liquid crystal device, comprising: a pair of oppositely
disposed substrates each provided with a group of transparent
electrodes in the form of stripes, and a liquid crystal disposed
between the substrates, wherein each of the transparent electrodes
partially has an auxiliary electrode in its length direction and
has both lead-out end portions in a region other than a display
region, each of the lead-out end portions including an exposed
check portion where the auxiliary electrode is patternized so as to
expose the transparent electrode.
28. A device according to claim 27, wherein the exposed check
portions has a width larger than that of the remaining portion and
are disposed alternately at every transparent electrode in their
width direction.
29. A device according to claim 27, wherein each of the exposed
check portion has both end portions where the auxiliary electrode
is connected so as to enclose the exposed check portion.
30. A device according to claim 27, wherein the device includes a
dummy electrode in a region other than a display region.
31. A device according to claim 27, wherein the pair of substrates
includes one substrate having thereon a color filter and a coating
layer, and includes a liquid crystal layer comprising a chiral
smectic liquid crystal as the liquid crystal disposed together with
spacer beads between the pair of substrates, wherein the liquid
crystal layer has a thickness smaller than a diameter of the spacer
beads and a maximum thickness of the coating layer, the coating
layer having a pencil hardness of at most 7H.
32. A device according to claim 31, comprising a sealing agent
disposed between the pair of substrates at a peripheral portion
thereof, the coating layer extending to a portion corresponding to
the peripheral portion.
33. A device according to claim 31, wherein the coating layer has a
pencil hardness of 3H-7H.
34. A color liquid crystal display apparatus, including: a liquid
crystal device, comprising: a pair of oppositely disposed first and
second substrates each provided with a group of transparent
electrodes in the form of stripes, and a liquid crystal layer
comprising a chiral smectic liquid crystal disposed together with
spacer beads between the pair of substrates, the first substrate
having thereon a color filter comprising plural color filter
segments and a coating layer, wherein the transparent electrodes on
the second substrate have a width smaller than that of the
transparent electrodes on the first substrate, scanning signal
supply means for supplying scanning signals to the transparent
electrodes on the first substrate, and data signal supply means for
supplying data signals including an interval at a prescribed
temperature or below to the transparent electrodes on the second
substrate, each of the data signals corresponding to each of color
filter segments of the color filter.
35. An apparatus according to claim 34, wherein the liquid crystal
layer has a thickness smaller than a diameter of the spacer beads
and a maximum thickness of the coating layer, and the coating layer
has a pencil hardness of at most 7H.
36. An apparatus according to claim 34, wherein the liquid crystal
device comprises a sealing agent disposed between the first and
second substrates at a peripheral portion thereof, and the coating
layer extends to a portion corresponding to the peripheral
portion.
37. An apparatus according to claim 34, wherein the coating layer
has a pencil hardness of 3H-7H.
38. A liquid crystal device, comprising: a pair of oppositely
disposed substrates each provided with a group of transparent
electrodes, and a liquid crystal disposed between the substrates,
the groups of transparent electrodes of the pair of substrates
intersect with each other to form a pixel at each intersection,
wherein one of the substrates includes a light-interrupting layer
for covering a part of the pixel located in a position
corresponding to at least one end portion of the pixel.
39. A device according to claim 38, wherein the liquid crystal
comprises a chiral smectic liquid crystal.
40. A device according to claim 38, wherein the pair of substrates
includes at least one substrate which has been subjected to
uniaxial aligning treatment from a prescribed starting position in
a uniaxial aligning direction forming an angle of 50-90.degree. C.
with respect to the light-interrupting layer, and the end portion
of the pixel has an edge line closer to the prescribed starting
position.
41. A device according to claim 39, wherein the chiral smectic
liquid crystal has a small thickness sufficient to suppress
formation of a helical structure thereof, and shows a tendency to
generate a hairpin defect and a lightning defect in pairs.
42. A device according to claim 41, wherein the lightning defect is
located a position closer to the light-interrupting layer than the
hairpin defect when the hairpin defect and the lightning defect in
pairs are generated.
43. A device according to claim 41, wherein chiral smectic liquid
crystal assumes C1 uniform alignment state.
44. A device according to claim 38, wherein the light-interrupting
layer has a width larger than that of another light-interrupting
layer located in a position corresponding to another end portion of
the pixel.
45. A device according to claim 38, wherein at least one of the
pair of substrates has a color filter comprising plural color
filter segments in the form of stripes or dots under or below a
corresponding group of transparent electrodes, each of the pixels
comprising at least one color filter segment.
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] 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.
[0002] 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.
[0003] FIG. 1 shows a sectional view of a liquid crystal device
using a ferroelectric liquid crystal based on two-valued (white and
black) display.
[0004] Referring to FIG. 1, the liquid crystal device (panel)
includes insulating substrates 1a and 1b, transparent electrodes 6a
and 6b, auxiliary electrodes 7a and 7b, short-circuit prevention
layers 8a and 8b, roughened surface-forming layers 9a and 9b,
alignment layers 10a and 10b, an adhesive bead 11 (after adhesion),
a spacer bead 12, and a liquid crystal layer 13. Each of the
transparent electrodes 6a and 6b constitutes drive electrodes in
combination with the auxiliary electrodes 7a and 7b, respectively.
The drive electrodes (including the electrodes 6a and 7a and the
electrodes 6b an 7b, 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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 1/2 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.
[0012] 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.
[0013] 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.
[0014] 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, such as a voltage level, a pulse
width and a frequency.
[0015] Accordingly, in the color liquid crystal display apparatus,
it is important to find out a parameter (or factor) largely
affecting the drive margin and to appropriately select and control
such a parameter for providing a wider drive margin.
SUMMARY OF THE INVENTION
[0016] A first object of the present invention is to provide a
liquid crystal (particularly a chiral smectic liquid crystal)
device allowing a uniform liquid crystal layer thickness and a good
shock (impact) resistance to retain good panel performance and
improved in production yield and capable of realizing a full color
display apparatus having high qualities comparable to those of a
display apparatus using a cathode ray tube (CRT).
[0017] A second object of the present invention is to provide a
liquid crystal device having a electrode structure capable of
readily ensuring inspection (check) regarding an occurrence of
short-circuit and an electrode (or wire) resistance without
damaging electrodes used.
[0018] A third object of the present invention is to provide a
color liquid crystal display apparatus capable of effecting good
display in any operation conditions while retaining a wider drive
margin.
[0019] According to the present invention, the above first object
is principally accomplished by a liquid crystal device, comprising:
a pair of substrates each provided with an electrode including one
substrate having thereon a color filter and a coating layer, and a
liquid crystal layer comprising a chiral smectic liquid crystal
disposed together with spacer beads between the pair of substrates,
wherein
[0020] the liquid crystal layer has a thickness smaller than a
diameter of the spacer beads and a maximum thickness of the coating
layer, the coating layer having a pencil hardness of at most
7H.
[0021] The above objects of the present invention are accomplished
by a process for producing a liquid crystal device, comprising the
steps of:
[0022] forming on a first insulating substrate a light-interrupting
layer, a color filter comprising plural color filter segments, a
coating layer, a barrier layer, a transparent electrode, an
auxiliary electrode, a short-circuit prevention layer, a roughened
surface-forming layer, and an insulating layer in succession in
this order,
[0023] forming on a second insulating substrate a transparent
electrode, an auxiliary electrode, a short-circuit prevention
layer, a roughened surface-forming layer, and an insulating layer
in succession in this order,
[0024] rubbing the surface of each of the insulating layers on the
first and second substrates, dispersing adhesive beads over the
alignment layer surface formed on the first substrate or the second
substrate,
[0025] disposing a sealing agent having a prescribed pattern on the
insulating layer surface formed on the second substrate or the
first substrate,
[0026] dispersing spacer beads over the alignment layer surface
provided with the sealing agent,
[0027] adhesively bonding the first and second substrate to each
other while fixing the first or second substrate over which the
adhesive beads are dispersed,
[0028] scribing the first and second substrates to remove an
unnecessary portion,
[0029] injecting a chiral smectic liquid crystal from an injection
port into a gap between the first and second substrates, and
[0030] sealing up the injection port.
[0031] According to the present invention, the above second object
is principally attained by a liquid crystal device, comprising: a
pair of oppositely disposed substrates each provided with a group
of transparent electrodes in the form of stripes, and a liquid
crystal disposed between the substrates, wherein
[0032] each of the transparent electrodes partially has an
auxiliary electrode in its length direction and has both lead-out
end portions in a region other than a display region, each of the
lead-out end portions including an exposed check portion where the
auxiliary electrode is patternized so as to expose the transparent
electrode.
[0033] In this case, the exposed check portions may preferably have
a width larger than that of the remaining portion and are disposed
alternately at every transparent electrode in their width
direction.
[0034] Further, each of the exposed check portion may preferably
have both end portions where the auxiliary electrode is connected
so as to enclose the exposed check portion.
[0035] The device may preferably include a dummy electrode in a
region other than a display region so as to form a pattern similar
to those of groups of data electrodes and scanning (common)
electrodes, whereby measurement of an electrode resistance is
performed without adversely affecting the data and scanning
electrodes.
[0036] According to the present invention, the above third object
is principally achieved by a color liquid crystal display
apparatus, including:
[0037] a liquid crystal device, comprising: a pair of oppositely
disposed first and second substrates each provided with a group of
transparent electrodes in the form of stripes, and a liquid crystal
layer comprising a chiral smectic liquid crystal disposed together
with spacer beads between the pair of substrates, the first
substrate having thereon a color filter comprising plural color
filter segments and a coating layer, wherein the transparent
electrodes on the second substrate have a width smaller than that
of the transparent electrodes on the first substrate,
[0038] scanning signal supply means for supplying scanning signals
to the transparent electrodes on the first substrate, and
[0039] data signal supply means for supplying data signals
including an interval at a prescribed temperature or below to the
transparent electrodes on the second substrate, each of the data
signals corresponding to each of color filter segments of the color
filter.
[0040] The above color liquid crystal apparatus is effective in
ensuring a wide drive margin and providing a good display state in
any environmental conditions by appropriately setting and fixing
driving conditions allowing the wide drive margin based on its
structural characteristic features.
[0041] The present invention further provides a liquid crystal
device, comprising: a pair of oppositely disposed substrates each
provided with a group of transparent electrodes, and a liquid
crystal disposed between the substrates, the groups of transparent
electrodes of the pair of substrates intersect with each other to
form a pixel at each intersection, wherein
[0042] one of the substrates includes a light-interrupting layer
for covering a part of the pixel located in a position
corresponding to at least one end portion of the pixel.
[0043] These and other objects, features and advantages of the
present invention will become more apparent upon a consideration of
the following description of the preferred embodiments of the
present invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 is a sectional view of a liquid crystal device
effecting two-valued display (black and white display).
[0045] FIG. 2 is a plan view of an embodiment of the liquid crystal
device according to the present invention.
[0046] FIGS. 3 and 4 are sectional views of the liquid crystal
device taken along A-A line and B-B line in FIG. 1,
respectively.
[0047] FIGS. 5A-5E and FIGS. 6A-6C are sectional views illustrating
production steps for a first substrate and a second substrate,
respectively, used in an embodiment of the liquid crystal device of
the invention.
[0048] FIG. 7 is a plan view of a first substrate having thereon a
color filter and alight-interrupting layer as to an embodiment of
the liquid crystal device of the invention.
[0049] FIGS. 8 and 10 are plan views showing auxiliary electrodes
on first and second substrates, respectively, as to an embodiment
of the liquid crystal device of the invention.
[0050] FIG. 9 is a plan view showing a transparent electrode formed
on a second substrate as to an embodiment of the liquid crystal
device of the invention.
[0051] FIGS. 11 and 12 are plan views of plural exposed check
portions of transparent electrodes on second and first substrate
sides, respectively, of an embodiment of the liquid crystal device
of the invention.
[0052] FIG. 13A is a plan view of a dummy electrode pattern on a
second substrate regarding an embodiment of the liquid crystal
device of the invention, and FIG. 13B is a plan view of elongated
projections on the second substrate in the vicinity of an injection
port.
[0053] FIGS. 14A and 14B are plan views illustrating embodiments of
flowing (injection) behaviors of liquid crystals as to the liquid
crystal device of the invention and an ordinary liquid crystal
device, respectively.
[0054] FIGS. 15A-15C are sectional views illustrating a step of
applying first and second substrate to each other in the process of
producing a liquid crystal device of the invention.
[0055] FIG. 16 is a plan view of a patterned sealing agent on a
substrate regarding an embodiment of the liquid crystal device of
the invention.
[0056] FIG. 17 is a block diagram of an embodiment of the color
liquid crystal display apparatus of the invention.
[0057] FIGS. 18-24 are respectively a time chart showing a set of
drive signal waveforms adopted in an embodiment of the color liquid
crystal display apparatus of the invention.
[0058] FIG. 25 shows a set of data signal waveforms.
[0059] FIG. 26 is a graph showing a relationship between different
intervals of selection period and corresponding drive margins of
the color liquid crystal display apparatus of the invention.
[0060] FIG. 27 is a plan view showing a matrix electrode structure
adopted in an embodiment of the liquid crystal device of the
invention.
[0061] FIG. 28 is a partially enlarged plan view of one pixel of an
embodiment of the liquid crystal device of the invention.
[0062] FIG. 29 is a partial sectional view of the pixel shown in
FIG. 28 taken along line A-A in FIG. 28.
[0063] FIG. 30 is a partial sectional view of another embodiment of
one pixel having a light-interrupting layer on a substrate other
than that of FIG. 29.
[0064] FIG. 31 is a display pattern on some pixels as to an
embodiment of the liquid crystal device of the invention.
[0065] FIG. 32 is a time chart showing a set of drive waveforms for
displaying the pattern shown in FIG. 31.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0066] Some preferred embodiments of the present invention will be
described with reference to the drawings.
[0067] FIG. 2 is a schematic sectional view of an embodiment of a
pixel structure of the liquid crystal device wherein a color filter
comprising color filter segments of four colors of red (R), green
(G), blue (B), transparent color (W: white) is disposed according
to the present invention. Referring to FIG. 2, a region enclosed by
broken (dotted) lines is a (one) pixel.
[0068] FIG. 3 is a schematic sectional view of the pixel structure
taken along A-A line in FIG. 2, and FIG. 4 is a schematic sectional
view of the pixel structure taken along B-B line in FIG. 2.
Referring to FIGS. 3 and 4, regions between respective two broken
lines are respectively a (one) pixel.
[0069] In FIG. 3 and/or FIG. 4, the liquid crystal device having
the pixel structure includes insulating substrates 1a and 1b, an
undercoat layer 2, a color filter 3 having a prescribed pattern
(shown in FIG. 2), a coating layer 4 having a maximum thickness (t)
for providing the color filter with an even (flat) coated surface,
a barrier layer 5, transparent electrodes 6a and 6b, auxiliary
electrodes 7a and 7b, short-circuit prevention layers 8a and 8b,
roughened surface-forming layers 9a and 9b, alignment layers 10a
and 10b, an adhesive bead 11 (after adhesion), a spacer bead 12,
and a liquid crystal layer 13 having a thickness (T), and a
light-interrupting layer 14.
[0070] In FIGS. 3 and 4, an upper substrate (having the color
filter 3) is referred herein to as a "first substrate" and a lower
substrate is referred herein to as a "second substrate" for
convenience. Incidentally, FIG. 2 is a plan view viewed from the
outside of a first substrate. Further, the liquid crystal device
may be viewed from the first substrate side or the second substrate
side but may preferably be viewed from the first substrate side
(having the color filter 3).
[0071] Hereinbelow, a preferred embodiment of the process for
producing a liquid crystal device (as shown in FIGS. 3 and 4) will
be described along production step (steps a-t) while making
reference to FIGS. 5-16.
[0072] First, production steps of structural members (elements)
formed on a first substrate are explained.
[0073] Step-a (FIG. 5A):
[0074] An insulating substrate la may generally be a transparent
substrate available as a glass for a liquid crystal device, such as
sheet (or plate 9glass or non-alkali glass. The insulating
substrate 1a may preferably have a polished (abrasion) surface on
either one side.
[0075] The insulating substrate 1a may have appropriate thickness
and size in view of picture area and production efficiency (e.g.,
in such a respect that how many display panels can be prepared by
one production operation). For example, in a production of a
large-area (14.8 inch) liquid crystal device, the insulating
substrate may preferably have a thickness of 1.1 mm.
[0076] Step-b (FIG. 5A):
[0077] On the above insulating substrate 1a, an undercoat layer 2
may preferably formed to prevent isolation (or elimination) of
alkali from a glass during and after the device production process.
The undercoat layer 2 may function as a protective layer for the
insulating substrate 1a and, e.g., comprises SiO.sub.2, MgO, SiN,
TiO.sub.2, Al.sub.2O.sub.3 and ZnO. The undercoat layer 2 may
generally have a thickness of 20-1000 .ANG..
[0078] Step-c (FIG. 5A):
[0079] The insulating substrate 1a having thereon the undercoat
layer 2 is subjected to washing (cleaning) and drying, followed by
ultraviolet-light irradiation to remove an organic substance. The
washing operation may be performed an appropriate time by using at
least one means of pure water shower, ultrasonic cleaning with pure
water, brush, etc. These means may be used singly or in combination
of two or more means.
[0080] Step-d (FIG. 5A):
[0081] On the undercoat layer 2, a light-interrupting layer 14 (as
also shown in FIG. 7) is partially formed in a pattern of stripes
(black stripes). The pattern may be other desired forms, such as
black matrix pattern. The light-interrupting layer 14 may generally
be composed of a material excellent in light-interrupting
properties, including: metals and alloys, such as Cr, Mo and alloys
of these metals; metal oxides, such as Cr.sub.2O.sub.3; and
pigment-containing organic resin, such as a resin containing a
black pigment. The light-interrupting layer 14 may generally have a
thickness of 500-1500 .ANG. in view of light-interrupting ability
of a material used. For example, the light-interrupting layer 14
composed of metal provides a sufficient light-interrupting effect
even if the layer in thin. In the present invention, a Mo--Ta alloy
layer having a thickness of at most 1000 .ANG. may preferably be
used as the light-interrupting layer 14.
[0082] The light-interrupting layer 14 may be formed on the entire
surface of the undercoat layer 2 by sputtering or coating, followed
by photolithographic (photo etching) process to be formed in a
prescribed pattern. More specifically, a resist selected in view of
adhesiveness to a material for the light-interrupting layer 14 is
applied onto the light-interrupting layer surface by, e.g., spinner
coating or printing and pre-baked at 70-120.degree. C., followed by
exposure to light (90-120 m), development, washing and drying. The
resultant substrate is then etched with an etchant (e.g., acids
selected depending on the material used), followed by washing,
peeling-off of the above resist, and further washing.
[0083] Incidentally, the light-interrupting layer 14 is formed so
as to extend to a region not related to display in the vicinity of
a sealing agent (appearing hereinafter) to somewhat leave a
non-light interrupting portion (i.e., light transmission portion)
which can be subjected to observation of an alignment state of a
liquid crystal after forming the device.
[0084] Step-e (FIG. 5B):
[0085] On the undercoat layer 2, a color filter (film) 3 comprising
color filter segments of at least three colors (preferably four
colors) of red (R), green (G), blue (B) and white (W, transparent
color) is formed in a prescribed pattern. A method of forming the
color filter 3 may include dyeing, pigment dispersion method and
electrodeposition. For example, the pigment dispersion method is
performed as follows.
[0086] A desired color resist (resin layer) comprising a
photosensitive resin (preferably polyamide) containing a prescribed
color pigment (containing no pigment for W) is applied onto the
undercoat layer 2 by using a spinner or a coater to provide a
thickness of 1.0-2.0 .mu.m, followed by leveling at a prescribed
temperature and pre-baking at about 80.degree. C. At this time,
conditions therefor, such as treatment temperature, treatment time,
and a layer thickness may appropriately be controlled depending on
resist materials. The thus treated color resist layer is exposed to
light (ultraviolet light, 200-1000 mJ). At this time, the exposure
time may appropriately be changed depending on materials for R, G,
B and W since the respective materials shows different
sensitivities. After the exposure operation, the resultant resist
layer is subjected to development wherein a developer, a developing
method, and a developing temperature may approriately be selected
depending on the resist material, followed by post-baking at
120-250.degree. C. and washing.
[0087] The respective color filter segments may be formed in a
pattern as shown in FIG. 7 such that the respective color filter
segments are separated from each other with a spacing of several
microns. The entire color filter 3 is disposed so as not to make
contact with the light-interrupting layer 14 and a sealing agent
(appearing hereinafter) is not only a display region (where display
is performed) but also a peripheral (non-display) region other than
the display region (where display is not performed). The respective
color filter segments having identical color formed in the display
region and the peripheral (non-display) region may have identical
size (dot size) or different sizes but may preferably have a dot
size in the peripheral region larger than that in the display
region.
[0088] The above color filter-forming step is performed with
respect to respective color filter segments in succession. The
order of formation may appropriately be determined depending on the
resist materials used.
[0089] Step-f (FIG. 5C):
[0090] A coating layer 4 for filling an unevenness between adjacent
color filters and providing a flat surface is formed on the color
filter (film) 3 and the light-interrupting layer 14. More
specifically, a coating liquid containing a coating material is
applied onto the surface of the color filter 3, the
light-interrupting layer 14, and a part of the undercoat layer 2 by
using a spinner, a coater or according to printing process,
followed by leveling at 60-150.degree. C. and optional post-baking
at 150-330.degree. C., as desired, to form a coating layer having a
maximum thickness (t in FIG. 3) of 1.5-5 .mu.m. The above treatment
temperature may appropriately be changed depending on the coating
material used. The coating material may be an organic substance or
an inorganic substance as long as it has a heat-resistance and a
chemical resistance sufficient to withstand the subsequent steps.
The coating material may preferably steps. The coating material may
preferably have an appropriate softness. Examples of the coating
material may preferably include polyamide, epoxy resin, and organic
silane-based resin, particularly organic silane-based resin.
[0091] The coating layer 4 has a hardness (pencil hardness as
measured by using a pencil hardness measurement apparatus according
to JIS-K5401) of at most 7H, preferably 3H to 7H. The coating layer
4 may preferably be formed so as to extend to a portion on which
sealing agent is disposed and particularly an injection port (of a
liquid crystal) is formed, thus allowing an easy injection
operation (of a liquid crystal) thereby to prevent an occurrence of
defective device due to injection failure. The coating layer may be
formed on the second substrate.
[0092] The resultant liquid crystal device produced through the
process according to the present invention is characterized by a
(soft) coating layer 4 having a hardness of at most 7H and a liquid
crystal layer 13 having a thickness (T in FIG. 3, e.g., 0.5-3
.mu.m) smaller than the maximum thickness (t) of the coating layer
(i.e., T<t), so that injection of a liquid crystal into a gap
(particularly a small cell gap as in the ferroelectric liquid
crystal device) becomes easy, thus lowering a void-occurrence rate
at that time and also even after low-temperature storage.
Consequently, a production yield is improved. The condition of
T<t is effective in enhancing a smooth injection performance.
The thickness (T) of the liquid crystal layer is also smaller than
a diameter of a spacer bead 12. In other words, the spacer bead 12
is partially embedded and fixed in opposite alignment layers 10a
and 10b, thus ensuring a uniform cell gap between the first and
second substrates. The embedding of the spacer bead 12 is readily
performed by forming a coating layer 4 having a pencil hardness of
at most 7H (preferably 4H-7H).
[0093] Step-g (FIG. 5C):
[0094] On the surface of the coating layer 4, a barrier layer 5 for
protecting the coating layer 4 and the color filter 3 in the
subsequent steps (particularly including etching process). The
barrier layer 5 may preferably comprise SiO.sub.2, MgO, SiN,
TiO.sub.2, Al.sub.2O.sub.3 and ZrO and may generally be formed in a
thickness of, e.g., 100-1000 .ANG. by printing or sputtering in
view of the material used.
[0095] Up to the above Step-g, a part of the production process of
the present invention adopted in only the first substrate is
described. Hereinbelow, Steps-h to t are adopted is not only the
first substrate but also the second substrate. Incidentally, an
insulating substrate 1b (the second substrate) may generally
comprise a material identical to that of the insulating substrate
1a (the first substrate) mentioned above.
[0096] Step-h (FIGS. 5C and 6A):
[0097] Transparent electrodes 6a and 6b each comprising a layer of
a transparent electroconductive material, such as indium tin oxide
(ITO) are formed on the barrier layer 5 (on the first substrate
side) and the insulating substrate 1b (on the second substrate
side), respectively, by sputtering, vapor-deposition, baking, etc.
The transparent electroconductive material may preferably be
In.sub.2O.sub.3 doped with 5-10% SnO.sub.2 but may appropriately be
selected from other materials in view of transmittance and
electroconductivity. The transparent electrodes 6a and 6b may
generally have a thickness of 300-3000 .ANG. but may have an
appropriate thickness in view of optical properties of a liquid
crystal and a resistance thereof. The transparent electrodes (6a,
6b) (e.g., ITO layers) are formed in prescribed patterns,
respectively, through a photolithographic (or photo etching)
process similarly as in the case of the light-interrupting layer
14. An etchant used in the above process may preferably include an
aqueous (mixture) solution of ferric chloride, hydriodic acid, and
hydrophosphorus acid (which may be used singly or in combination of
two or more species).
[0098] The pattern of the electrode 6a (on the first substrate
side) may correspond to display pixels and may preferably be
stripes each of which is disposed between the light-interrupting
layers 14 as shown in FIG. 7. On the other hand, the pattern of the
electrode 6b (on the second substrate side) may preferably
correspond to the opposite color filter pattern as shown in FIG.
9.
[0099] The pattern of the electrode 6a (on the first substrate
side) may preferably cover the entire color filter 3 disposed in
the display region and the peripheral region.
[0100] In this step, by forming electrodes (as dummy electrodes) in
the peripheral region other than the display region, it is possible
to measure an electrode resistance without adversely affecting
drive electrodes. FIG. 13A shows a group of dummy electrodes 41
separated from a group of drive electrodes 31 formed on the second
substrate. Similarly, on the first substrate, such dummy electrodes
are formed. Each of the electrodes 41 and 31 may comprise a
material identical to that of transparent electrodes (6a, 6b).
Referring to FIG. 13a, L-shaped elongated projections 42 are formed
so as to dam up the flow of solutions (or liquids) used in the
subsequent steps toward the outside the device, thus allowing a
desired layer formation. FIG. 13B shows a part of a substrate
(preferably the second substrate) in the vicinity of an injection
port formed by a sealing agent 21 wherein plural elongated
projections 43 are formed in a pattern such that respective
elongated projections 43 are disposed in parallel with each other
with an identical spacing but have different lengths gradually
decreasing toward the injection port. The elongated projections 43
are effective in allowing uniform an easy injection of a liquid
crystal.
[0101] The above elongated projections 42 and 43 may preferably
comprise a material (preferably ITO) identical to that of the
transparent electrodes 6a and 6b since these structural members 42,
43, 6a and 6b of the device can be formed at the same time to
simplify the production process of the device.
[0102] Step-i (FIGS. 5D and 6B):
[0103] On parts of the transparent electrodes 6a and 6b, auxiliary
electrodes 7a and 7b in order to reduce electrode resistances
thereof (6a, 6b) are formed, respectively. The auxiliary electrodes
(7a, 7b) may comprise metals or metal alloys, such as Cr, Al, Mo,
alloys of these metals, and Mo--Ta. In order to improve
adhesiveness to the transparent electrodes (6a, 6b) and a
photoresist used and to provide an appropriate resistance. The
respective auxiliary electrodes (7a, 7b) may each have a lamination
structure (upper lower/lower layer), such as Mo/Al, Mo/Al/Mo--Ta or
Mo--Ta/Al/Mo--Ta. In the case of using the lamination structure,
the layer structure may preferably be determined depending on
compatibility of the material used with an etchant used. In such a
respect, the lamination layer structure may more preferably be
Mo--Ta (5-10%, e.g., 200-500 .ANG. thick)/Al alloy (with, e.g., Si
or Cu) (e.g., 200-1500 .ANG. thick)/Mo--Ta (10-20%, e.g., 100-500
.ANG. thick) lamination layer having a (total) thickness of
500-2500 .ANG. formed at the same time. The above lamination layer
may be formed layer by layer while performing etching with respect
to respective layers.
[0104] The above material layer for forming the auxiliary
electrodes (7a, 7b) is formed on the entire surface of the
immediately lower layers on the first and second substrates and
subjected to a photoetching process (including the steps of resist
application-exposure-development-post baking-etching-peeling off of
resist) to form an auxiliary electrode 7a having a pattern such
that the electrode 7a has openings located over the respective
color filter segments (R, G, B, W) as shown in FIG. 8 and to form
an auxiliary electrode 7b having a pattern such that the electrode
7b is disposed on both end portions of the transparent electrode 6b
as shown in FIG. 10. The auxiliary electrodes 7a and 7b may
preferably be formed on the entire surface of the transparent
electrodes 6a and 6b in the peripheral region other than the
display region.
[0105] In a region other than the display region preferably outside
the device, respective drive electrodes (as shown by reference
numerals 31 and 32 in FIGS. 11 and 12) each have an exposed check
portion at at least one lead-out end section (preferably both
lead-out end sections) thereof.
[0106] FIG. 11 shows one lead-out end section of a group of drive
electrodes 31 (comprising the electrodes 6b and 7b on the second
substrate) each of which has an exposed check (or inspection)
portion 33 for inspection of short-circuit (a portion at which the
transparent electrode 6b is not coated with the auxiliary electrode
7b (which ordinary covers the entire transparent electrode 6b in
this portion) to expose the transparent electrode 6 surface in a
prescribed region, e.g., a region separating the auxiliary
electrode 7b portion (dotted portion in FIG. 11) from each other in
its length direction). The exposed check portion may be patternized
in various forms (e.g., in view of a check terminal form) for
checking short-circuit. At the other lead-out end section of the
drive electrodes 31, the exposed check portions are provided
similarly as in the above case.
[0107] FIG. 12 shows one lead-out end section (preferably present
in the sealing area enclosed by the sealing agent) of a group of
drive electrodes 32 (comprising the electrodes 6a and 7a on the
first substrate) each of which has an exposed check portion
similarly as in those of FIG. 11. At the other lead-out end section
of the drive electrodes 32, the similar electrode structure may be
adopted.
[0108] The respective drive electrodes 31 and 32 are very thin an
narrow layers (films), so that a terminal for short-circuit
inspection (check terminal) is correspondingly small and may
generally have a form of a fine needle, thus being liable to damage
the drive electrodes 31 and 32. Particularly, on the drive
electrode 31 having a very narrow width, the check terminal per se
is not readily placed on a desired position in some cases.
[0109] In view of the above difficulties, in the present invention,
by providing the drive electrodes with the exposed check portion
composed of, e.g., ITO transparent electrode harder than the
material (metal) of the auxiliary electrode as shown in FIGS. 11
and 12, it is possible to prevent the drive electrodes 31 an 32
from being damaged or marred. Further, as shown in FIG. 11, on the
particularly fine drive electrodes 31, somewhat wider exposed check
portions 33 are disposed alternately at every drive electrode 31 in
a direction (width direction) perpendicular to the length direction
of the electrodes 31, thus allowing the check terminal to be
readily placed thereon. In this case, any adjacent portion between
two check portions 33 in the width direction has a smaller width
than the check portion but may preferably expose the transparent
electrode thereat (i.e., the auxiliary electrode is removed) as
shown in FIG. 11. This is because, if the check terminal is placed
on a position different from an objective position (exposed check
portion) in case where the auxiliary electrode is formed in the
narrower adjacent portion, it is difficult to obviate the damage of
the drive electrodes 31, exactly auxiliary electrode adjacent to
(closer to) the objective portion. The arrangement of the exposed
check portion shown in FIG. 11 is effective in this respect. On the
other hand, on each of the drive electrodes 32 generally having a
wider width than that of the drive electrodes 31 (as is apparent
from FIGS. 11 and 12), an auxiliary electrode 6a (dotted portion in
FIG. 12) may preferably be disposed at both end portions of the
exposed check portion 33 (i.e., so as to surrounding (enclosing)
the exposed check portion 33) as shown in a lower part of FIG. 12
in order to suppress an increase in the electrode resistance. In
the present invention, the electrode structures of the drive
electrodes 31 and 32 at the lead-out end sections thereof as shown
in FIGS. 11 and 12 may appropriately be selected as an electrode
structure on the first and/or second substrates in view of widths
of electrodes used.
[0110] After forming the auxiliary electrodes 7a and 7b, the dummy
electrodes 41 and the exposed check portions 3, measurement of the
electrode resistance and inspection of an occurrence of the
short-circuit may preferably be performed by using the dummy
electrodes 41 and the exposed check portions 41, respectively.
[0111] In the present invention, the electrode structures as
mentioned above are adopted, whereby the damage of the drive
electrodes can be prevented in this step to improve not only a
device production yield through the entire production process but
also an accuracy of the inspection step per se, thus consequently
realizing a high-reliability liquid crystal device.
[0112] Step-k (FIGS. 5E and 6C):
[0113] On the entire electrode surface, short-circuit prevention
layers 8a an 8b each of which is an insulating layer for preventing
a short-circuit between the first and second (treated) substrates
are formed by sputtering, application, baking, etc. Examples of a
material therefor may include Ti--Si, SiO.sub.2, TiO.sub.2, and
Ta.sub.2O.sub.5. The short-circuit prevention layers 8a and 8b may
have a single layer structure or a lamination layer structures of
plural layers formed by using the above materials singly or in
combination of plural species. More specifically, the short-circuit
prevention layers 8a and 8b may preferably have a lamination
structure, e.g., comprising 500-1200 .ANG.-thick Ta.sub.2O.sub.5
layer (lower layer) formed by sputtering and 500-1000 .ANG.-thick
Ti--Si layer (upper layer) formed by printing with an application
solution therefor, followed by baking. The short-circuit prevention
layers 8a and 8b may preferably extend to outside a sealing portion
(described hereinafter).
[0114] Step-l (FIGS. 5E and 6C):
[0115] On the entire surface of the short-circuit prevention layers
(8a, 8b), roughened surface-forming layers 9a and 9b for preventing
movement of (chiral smectic) liquid crystal molecules during the
drive of the device are formed to provide alignment layers to be
formed thereon with roughened surfaces. This is because chiral
smectic liquid crystal molecules are liable to continually (or
intermittently) move toward the periphery of the device under
application of an applied voltage in some cases.
[0116] The roughened surface-forming layers 9a and 9b may, e.g., be
formed by dispersing SiO.sub.2 beads (diameter: 300-700 .ANG.)
within an insulating film-forming solution (Ti/Si=1/1) in an amount
of 5-30 wt. %, printing the solution with an extension plate and
baking the resultant solution to form a 100-300 .ANG.-thick layer.
Similarly as in the layers 8a and 8b, the roughed surface-forming
layers 9a and 9b may preferably extend to outside a sealing
agent.
[0117] Step-n (FIGS. 5E and 6C):
[0118] On the roughened surface-forming layers 9a and 9b, alignment
layers 10a and 10b comprising an insulating layer for controlling
the alignment direction of liquid crystal molecules are formed.
Examples of a material therefor may include organic insulating
resins (polymers), such as polyvinyl alcohol, polyimide,
polyamide-imide, polyester-imide, polyparaxylylene, polyester,
polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide,
polystyrene, cellulose resin, melamine resin, urea resin, and
acrylic resin.
[0119] Each of the (insulating) alignment layers 10a and 10b may,
e.g., be formed by applying or printing a solution of the above
material onto the surface of the roughened surface-forming layer
(9a, 9b) in a region within the sealing area (preferably in the
display region), followed by baking at 200-300.degree. C. to
provide an insulating layer having a thickness of, e.g., 50-1000
.ANG.. The insulating layer is subjected to uniaxial alignment
treatment (e.g., rubbing) by pushing a roller, about which a raised
rubbing cloth is wound, onto the alignment layer surface at a
rotation speed of 500-2000 rpm to provide alignment layers 10a and
10b. Examples of a material for the rubbing cloth may include
natural fibers, such as cotton and synthetic fibers, such as fibers
of aramide, nylon, rayon, teflon (polytetrafluoroethylene),
polypropylene, and acrylic fiber. Of these, aramid fiber may
preferably be used for the rubbing cloth.
[0120] The above rubbing treatment may be performed with respect to
a limited part of the alignment layer surface by using a mask
(frame), e.g., disposed at the periphery of the alignment layer
surface. The rubbing condition (e.g., rotation speed and moving
speed of the roller) may appropriately be selected.
[0121] After the rubbing (uniaxial aligning) treatment, the first
and second substrates having thereon the (insulating) alignment
layers 10a and 10b, respectively, are washed (or cleaned).
[0122] Step-n (FIG. 15A):
[0123] On the surface of one of the alignment layers 10a and 10b
formed over the first and second substrate (preferably the
alignment layer 10a formed over the first substrate), adhesive
beads 11 are dispersed. The adhesive beads 11 do not have
adhesiveness at normal temperature (e.g., room temperature) and at
the time of the drive of the device but assume adhesiveness under
heating, e.g., at the time of applying the first and second
substrates to each other in the subsequent step (Step-q).
[0124] Examples of a material for the adhesive beads 11 may include
thermosetting resins, such as epoxy resin and acrylic resin, not
adversely affecting a liquid crystal to be come in contact
therewith. The adhesive beads 11 may preferably have a diameter of
2-10 .mu.m and may generally be dispersed at a density of 50-130
particles/mm.sup.2 in the form of a dispersion thereof in a solvent
(e.g., isopropyl alcohol). The adhesive beads 11 are caused to
attach to the first and second substrates after the step (Step-q
appearing hereinafter) of applying the first and second substrate
each other under heating. As will be described hereinbelow, the
first and second substrates are subjected to scribing (or cutting)
to remove unnecessary portions in different positions, thus
exposing electric terminals thereof, respectively. If the adhesive
beads 11 are moved to the scribing region, an unnecessary portion
to be removed is caused to adhere to the other (opposite)
substrate. For this reason, no adhesive beads 11 may desirably be
present in the scribing region. Accordingly, the adhesive beads 11
which are liable to move at room temperature may preferably be
dispersed in a region corresponding to the sealing area within the
sealing portion.
[0125] Step-o (FIGS. 15A and 16):
[0126] On the other alignment layer formed over the other substrate
(preferably the alignment layer 10b over the second substrate) a
sealing agent 21 is patterned as shown in FIG. 16 so as to leave an
injection port 22.
[0127] Referring to FIG. 16, a dummy wall 23 in parallel with the
side wall of the sealing agent 21 is also formed by using the
sealing agent but may be formed in other positions (e.g., a
remotest position from the injection port in parallel with the
opposite wall to the wall including the injection port).
[0128] Examples of a material for the sealing agent 21 (including
one for the dummy wall 23) may include thermosetting resins, such
as thermosetting epoxy resin. The pattern of the sealing agent 21
and dummy wall 23 may be provided, e.g., by using a disperser or
through a screen printing process in view of the material used. The
pattern has prescribed thickness and width which may appropriately
be controlled in view of a cell gap, an application amount,
etc.
[0129] In case where the color filter 3 is formed in the peripheral
region other than the display region, the dummy wall 23 may be
disposed in a position corresponding to that of the color filter 3
or outside thereof. Iin view of a cell gap, the latter may
preferably be adopted in the present invention.
[0130] Step-p (FIG. 15A):
[0131] On the surface of the alignment layer (preferably the
alignment layer 10b) formed over the substrate (preferably the
second substrate having the sealing agent 21) different from the
substrate (preferably the first substrate) over which the adhesive
beads 11 are dispersed, spacer beads 12 are dispersed. The spacer
beads 12 are selected to have a diameter larger than a liquid
crystal layer thickness (T as shown in FIG. 3) and may generally
have a diameter 0.6-2.5 .mu.m. For example, when the liquid crystal
layer thickness is set to be 1 .mu.m, the spacer bead 12 may
preferably have a diameter of about 1.2-1.3 .mu.m. Examples of the
spacer beads 12 may preferably include silica beads and alumina
beads.
[0132] The spacer beads 12 may preferably be dispersed at a density
of 100-700 particles/mm.sup.2 in the form of a dispersion thereof
in a solvent (e.g., ethanol) in a region enclosed by the sealing
agent 21. The above solvent may preferably have no or poor
dissolving power to the spacer beads 12.
[0133] In the present invention, the spacer beads 12 finally having
a diameter larger than the liquid crystal layer thickness are used,
so that the spacer beads 12 are fixed in a state such that the
spacer beads 12 are partially embedded into the surfaces of the
first and second substrates (exactly between the surfaces of the
alignment layers 10a and 10b), thus suppressing movement thereto
after sealing the cell to retain a uniform liquid crystal layer
thickness.
[0134] Incidentally, with respect to the above Steps-o and p, the
formation of the pattern with the sealing agent 21 (Step-o) may
preferably be performed against a surface as smooth as possible
free from unevenness in terms of warkability and accuracy and
accordingly may desirably be performed in advance of the dispersion
of the spacer beads (Step-p). In this respect, it is important to
conduct the Step-o and the Step-p in this order.
[0135] Further, in the Step-n, the dispersion of the adhesive beads
11 may preferably be effected on the surface of a substrate on
(over) which the sealing agent 21 is patternized in order to effect
only in a region corresponding to the sealing area (enclosed by the
sealing agent 21). Accordingly it si preferred that the adhesive
beads 11 are dispersed on one substrate (e.g., the first substrate)
and the formation of the sealing agent pattern and the dispersion
of the spacer beads 12 are performed on the other substrate (e.g.,
the second substrate).
[0136] Step-q (FIGS. 15A, 15B and 15C):
[0137] The substrate (preferably the first substrate) on which the
adhesive beads 11 are dispersed (distributed) is fixed, and the
other (opposite) substrate (preferably the second substrate)
whereon the sealing agent 21 and the spacer beads 12 are disposed
is applied onto the above substrate each other so as to dispose the
above structural members (11, 12, 21) between the alignment layers
10a and 10b formed on the first and second substrates under heat
and pressure for 10-120 min., whereby the adhesive beads 11 and the
sealing agent 21 are hardened (or thermoset) to bond the first and
second substrates to each other. In a preferred embodiment, the
above adhesive bonding of the two substrates is performed while
fixing (setting) the substrate having thereon the adhesive beads 11
so as to direct the dispersion face of the adhesive beads 11 at the
uppermost (topmost) surface).
[0138] As described above, the adhesive beads 11 and the spacer
beads 12 are separately dispersed on different substrates,
respectively, and the substrate having thereon the adhesive beads
11 being liable to readily move at normal temperature is fixed,
whereby the adhesive beads 11 are not readily moved, thus
preventing localization and detachment thereof. On the other hand,
the spacer beads 12 generally has a smaller diameter than that of
the adhesive beads 11, so that the spacer beads 11 remain in the
original position even when the substrate having thereon the spacer
beads 11 is turned upside down for bonding to the fixed substrate
carrying the adhesive beads 11. As a result, the spacer beads 12 do
not readily cause localization and detachment thereof.
[0139] According to this step (Step-q), the first and second
substrates are adhesively bonded to each other while retaining
their uniform dispersion states.
[0140] Step-r:
[0141] In order to expose connection terminals of the electrodes,
the first and second substrates are subjected to scribing (cutting)
of unnecessary portions, respectively. Iin view of arrangement of
the connection terminals. The unnecessary portions of the first and
second substrates to be removed are generally different in position
from each other, so that the corresponding scribing positions
thereof are also different.
[0142] Incidentally, immediately before the scribing of the first
and second substrates, an identification means (e.g., a bar-code
label) is provided to a certain position of the substrates in the
vicinity of the injection port, thus allowing the identification of
respective blank cells prepared by scribing (cutting) the first and
second substrates.
[0143] Step-s:
[0144] A liquid crystal (preferably a chiral smectic liquid
crystal) is injected into the above-prepared blank cell (i.e., a
spacing between the first and second substrates). Examples of a
liquid crystal material are specifically described hereinafter.
[0145] The injection operation may, e.g., be generally performed as
follows.
[0146] First, a blank cell is placed in a vacuum apparatus. In a
sufficient vacuum state of the inside the apparatus (blank cell), a
liquid crystal is attached to the injection port of the cell. Then,
the reduced pressure of inside the apparatus is gradually restored
to atmospheric pressure, thus injecting the liquid crystal into the
cell at a speed which may preferably be controlled as identical as
possible.
[0147] In the present invention, a liquid crystal layer 13 formed
as described above has a thickness (T) smaller than the maximum
thickness (t) of the coating layer 4 having a pencil hardness of at
most 7H as shown in FIG. 3, whereby the liquid crystal layer 13 has
no or a little void (unfilled portion of the liquid crystal) to
minimize a defective cell due to the softness of the thicker
coating layer 4 particularly compared with a liquid crystal device
including no such a coating layer. Further, by forming the coating
layer 4 extending to the portion over which the sealing agent 21 is
disposed, the liquid crystal injection is further facilitated, thus
improving a production yield.
[0148] As shown in FIGS. 13B and 14A, the elongated projections 43
(e.g., composed of ITO) are formed in the vicinity of the injection
port, whereby the injection liquid crystal flows and extends along
the projections 43 as shown by arrows in FIG. 41A to prevent an
occurrence of an unfilled portion (void) at a position closer to
the wall (sealing agent 21) having the injection port.
[0149] FIG. 14B shows a flowing behavior of a liquid crystal in a
conventional liquid crystal cell. In this cell, the injection of
the liquid crystal is liable to become ununiform, thus leaving
voids particularly on the injection port side.
[0150] In the present invention, as shown in FIG. 14, the dummy
walls 23 are formed in parallel with the side walls of the sealing
agent 21, whereby, even if voids are left in the display region,
the voids are forced into a spacing between the dummy wall 23 and
the side wall 21 during the injection step. As a result, there is
substantially no void in the display region, thus minimizing an
occurrence of a defective cell.
[0151] Step-t:
[0152] After the completion of the liquid crystal injection, the
injection port of the liquid crystal cell is sealed up with a
sealing agent, such as room temperature curing epoxy resin,
followed by washing the cell with a weak alkaline solution to
provide a liquid crystal device (panel) according to the present
invention.
[0153] Outside the liquid crystal device (panel), a pair of
polarizers are applied to the first and second substrates 1a and
1b, respectively, and a driving integral circuit (driving IC) is
connected to the corresponding terminal of the electrodes (6a, 6b,
7a, and 7b).
[0154] The liquid crystal used in the present invention may
preferably be a chiral smectic liquid crystal composition (or
mixture) containing two or more mesomorphic compounds and at least
one optically active compound (as a chiral dopant).
[0155] Herein, the term "mesomorphic compound" means not only a
compound showing a mesomorphic (or liquid crystal) phase by itself
but also a compound not showing a mesomorphic phase as long as a
resultant liquid crystal composition containing the compound shows
a mesomorphic phase.
[0156] Examples of the above mesomorphic compounds (including the
optically active compound) may include those represented by
formulae (1)-(5) shown below. These mesomorphic compounds are mixed
in an appropriate proportion to constitute a chiral smectic liquid
crystal composition.
[0157] The mesomorphic compounds of the formulae (1) to (5) may
include those shown below: 1
[0158] wherein p and q independently denote 0, 1 or 2 satisfying
p+q=1 or 2; Y.sub.0 is hydrogen or fluorine; and R.sub.21 and
R.sub.22 independently denote a linear or branched alkyl group
having 1-18 carbon atoms capable of including at least one
methylene group which can be replaced by --O--, --S--, --CO--,
--CH.dbd.CH--, --C.ident.C--, or --CHW-- where W is halogen, CN or
CF.sub.3 provided that heteroatoms are not adjacent to each other;
2
[0159] hydrogen or fluorine; Y.sub.1 is hydrogen or fluorine;
R.sub.23 is a linear or branched alkyl group having 1-18 carbon
atoms; R.sub.24 is hydrogen, halogen, CN, or a linear or branched
alkyl group having 1-18 carbon atoms; and at least one methylene
group in the alkyl group of R.sub.23 or R.sub.24 can be replaced by
--O--, --S--, --CO--, --CH.dbd.CH--, --C.ident.C--, or
--CHW.sub.2-- where W.sub.2 is halogen, CN or CF.sub.3 provided
that heteroatoms are not adjacent to each other; 3
[0160] and R.sub.25 and R.sub.26 independently denote a linear or
branched alkyl group having 1-18 carbon atoms capable of including
at least one methylene group which can be replaced by --O--, --S--,
--CO--, --CH.dbd.CH--, --C.ident.C--, or --CHW.sub.3-- where
W.sub.3 is halogen, CN or CF.sub.3 provided that heteroatoms are
not adjacent to each other; 4
[0161] Z is O or S; and R.sub.27 and R.sub.28 independently denote
a linear or branched alkyl group having 1-18 carbon atoms capable
of including at least one methylene group which can be replaced by
--O--, --S--, --CO--, --CH.dbd.CH--, --C.ident.C--, or
--CHW.sub.3-- where W.sub.4 is halogen, CN or CF.sub.4 provided
that heteroatoms are not adjacent to each other; and 5
[0162] wherein R.sub.29 and R.sub.30 independently denote a linear
or branched alkyl group having 1-18 carbon atoms capable of
including at least one methylene group which can be replaced by
--O--, --S--, --CO--, --CH.dbd.CH--, --C.ident.C--, or
--CHW.sub.5-- where W.sub.5 is halogen, CN or CF.sub.3 provided
that heteroatoms are not adjacent to each other.
[0163] In the above formulae (1) to (5), the respective groups
R.sub.21-R.sub.30 may be an optically active or optically
inactive.
[0164] With respect to the above mesomorphic compound of the
formulae (1)-(4), examples of the mesomorphic compound of the
formula (1) may preferably include those of the formulae (1-1) to
(1-7); examples of the mesomorphic compound of the formula (2) may
preferably include those of the formulae (2-1) to (2-5); examples
of the mesomorphic compound of the formula (3) may preferably
include those of the formulae (3-1) to (3-9); and examples of the
mesomorphic compound of the formula (4) may preferably include
those of the formula (4-1) to (4-6), respectively shown below:
6
[0165] In the above formulae (1-1) to (4-6), R.sub.21 to R.sub.28
and Y.sub.1 have the same meanings as defined above.
[0166] The mesomorphic compounds of the formulae (1-1) to (4-6) may
be used singly or in combination of two or more species or used
together with other mesomorphic compounds.
[0167] Hereinbelow, a more specific embodiment of the present
invention will be explained with reference to FIGS. 1 and 3.
[0168] A color liquid crystal device (color panel) having a coating
layer 4 as shown in FIG. 3 and a monochromatic liquid crystal
device (monochromatic panel) having no coating layer 4 as shown in
FIG. 1 were prepared, respectively, in the following manner.
[0169] A blank cell 1 for the color panel (according to the
invention) and a blank cell 2 for the monochromatic panel were
prepared according to the above-described Step-a to Step-r, as
desired, specifically in the following manners, respectively.
Blank Cell 1
[0170] (First substrate)
[0171] On a sheet glass, a coating layer (siloxane; maximum
thickness (t)=3 .mu.m; pencil hardness--4H) was formed so as to
cover (coat) a color filter film pattern comprising R, G and B
color filter segments (thickness=c.a. 1.5 .mu.m). On the coating
layer, a barrier layer was formed and thereon, a c.a. 700
.ANG.-thick ITO film (transparent electrode) provided with an
auxiliary electrode and having a prescribed pattern was formed. On
the ITO film, a 2000 .ANG.-thick insulating film having a
lamination structure comprising a short-circuit prevention layer, a
roughened surface-forming layer and an alignment layer (film) was
formed to provide a first substrate.
[0172] (Second substrate)
[0173] On a sheet glass, a c.a. 700 .ANG.-thick ITO film provided
with an auxiliary electrode and having a prescribed pattern was
formed. On the ITO film, a 2000 .ANG.-thick insulating layer having
a lamination structure comprising a short-circuit prevention layer,
a roughened surface-forming layer and an alignment layer was formed
to provide a second substrate.
[0174] Adhesive beads (diameter=c.a. 5 .mu.m) were dispersed (or
distribution) over the first substrate. Separately, a sealing agent
was disposed and patternized on the second substrate and then
spacer beads (diameter=1.1 .mu.m) were dispersed over the second
substrate.
[0175] The second substrate was applied to the first substrate
(which was fixed) each to provide a cell gap of 1 .mu.m corr. to a
liquid crystal layer thickness (T), whereby a blank cell 1 was
prepared.
Blank Cell 2
[0176] A blank cell 2 was prepared in the same manner as in the
preparation of the blank cell 1 except that first and second
substrates were prepared in the same manner as in the second
substrate of the blank cell 1, respectively.
[0177] A liquid crystal mixture having a phase transition series on
temperature decrease shown below was injected into each of the
above-prepared blank cells 1 and 2 at a constant speed in
accordance with the Step-s described hereinabove, respectively.
Phase Transition Temperatures (.degree. C.)
[0178] 7
[0179] Iso.: isotropic phase,
[0180] Ch.: cholesteric phase,
[0181] SmA: smectic A phase,
[0182] SmC*: chiral smectic C phase, and
[0183] Cry.: crystal phase.
[0184] The phase transition temperature (.degree. C.) is determined
by observation through a polarizing microscope in combination with
a differential scanning calorimeter ("DSC-7" manufactured by
Parkinelmer Co.) and Metlar Hot Stage ("Thermo System FP-80/FP-82"
manufactured by Metler Co.).
[0185] The thus-prepared liquid crystal devices (color an
monochromatic panels) were subjected to evaluation of a degree of
occurrence of a void in the liquid crystal layer. More
specifically, after the injection of the liquid crystal mixture
described above, each of the color panel and the monochromatic
panel was retained at 25.degree. C. and then cooled to prescribed
temperatures (-5.degree. C., -10.degree. C., -15.degree. C.) in 1
hour, respectively, and was left standing for 100 hours at the
respective temperatures. After the standing, each of the panels was
restored to 25.degree. C. in 1 hour and then subjected to eye
observation of a void occurrence state with respect to 10 sample
panels (partially 8 sample panels), whereby the number of a
defective panel having at least one void was counted.
[0186] The results are shown in Table 1 below.
1TABLE 1 Temp. (.degree. C.) Color panel Monochromatic panel 25
0/10 0/10 -5 0/10 0/10 -10 0/10 2/10 -15 0/10 8/8 *Defective
panel/Sample used
[0187] As apparent from the above results, the liquid crystal
device (color panel) according to the present invention having the
following characteristic features (i)-(iii):
[0188] (i) Thickness (T) of the liquid crystal layer is smaller
than the diameter of spacer beads,
[0189] (ii) Thickness (T) is smaller than the maximum thickness (t)
of the coating layer, and
[0190] (iii) The coating layer has a pencil hardness of at most
7,
[0191] is effective in suppressing an occurrence of a void even
after standing for a prescribed time of lower temperatures.
[0192] As described above, according to the above liquid crystal
device of the present invention, the device has a uniform cell gap
(L.C. layer thickness) and a uniform shock (impact) resistance over
the entire panel area (particularly in the entire display region)
because of the above feature (i) and a uniform adhesive boding of
two substrates while retaining good dispersion states of adhesive
beads and spacer beads. Consequently, there is provided a liquid
crystal device capable of providing good display characteristics
and having a high durability resistant of external shock. Further,
based on the above features (ii) and (iii), the liquid crystal
device has a flexible layer structure on the glass substrate
effective in facilitating the liquid crystal injection into a
spacing (particularly a very small spacing), thus suppressing an
occurrence of a defective cell (panel). This effect is further
enhanced by forming the coating layer (providing the features (ii)
and (iii)) extending to a position over which the sealing pattern
is formed.
[0193] By providing the above features (i)-(iii), there is provided
a liquid crystal device having high performances including a
lowering in an occurrence of a void at the time of the liquid
crystal injection and after the standing at lower temperatures to
suppress an occurrence of an alignment defect of liquid crystal
molecules resulting from the void.
[0194] Hereinbelow, the color liquid crystal display apparatus
according to the present invention will be described with reference
to FIGS. 17-26.
[0195] FIG. 17 shows a block diagram of an embodiment of the color
liquid crystal display apparatus of the present invention.
[0196] Referring to FIG. 17, a color liquid crystal display
apparatus include a display portion (display panel) 101, a scanning
signal application circuit 102, two data signal application
circuits 103, a scanning signal control circuit (scanning signal
supply means) 104, a drive control circuit 105, a data signal
control circuit (data signal supply means) 106, and a graphic
controller 107.
[0197] Data sent from the graphic controller 107 are inputted into
the scanning signal control circuit 104 and the data signal control
circuit 106 via the drive control circuit 105, where the inputted
data are converted into (scanning line) address data and display
data, respectively. In accordance with the address data from the
scanning signal control circuit 104, the scanning signal
application circuit 102 generates a selection scanning signal
waveform and a non-selection scanning signal waveform to be applied
to a group of scanning (transparent) electrodes (scanning lines) of
the display portion 101. On the other hand, in accordance with the
display data from the data signal control circuit 106, the data
signal application circuits 103 disposed opposite to each other
with respect to the display portion 101 generate data signal
waveforms each of which corresponds to each of color filter
segments of red (R), green (G), blue (B) and white (W: transparent
color), respectively, to be applied to a group of data
(transparent) electrodes (data lines) of the display portion
101.
[0198] The group of scanning electrodes intersect with the group of
data electrodes at right angles to provide a large number of pixels
(1280.times.1024 pixels) at their intersections. Each of the
intersections constitutes one pixel, e.g., containing four color
filter segments (R, G, G, W).
[0199] The display portion 101 comprises the above-mentioned liquid
crystal device according to the present invention. In the liquid
crystal device, one group of transparent electrodes in the form of
stripes formed on a substrate having a color filter and a coating
layer thereon is used as the group of scanning electrodes. The
other group of transparent electrodes in the form of stripes formed
on a substrate having no color filter and no coating layer is used
as the group of data electrodes in the color liquid crystal display
apparatus of the invention. Further, the group of data electrodes
(e.g., as shown in FIG. 11) has a width narrower (smaller) than a
width of the group of scanning electrodes (e.g., as shown in FIG.
12).
[0200] A driving method of the above color liquid crystal display
apparatus will be described hereinbelow.
[0201] FIGS. 18-24 respectively show a drive signal waveform used
for the display apparatus.
[0202] In each of FIGS. 18-24, "A" represents a selection scanning
signal waveform, "B" represents a non-selection scanning signal
waveform, and "C" and "D" respectively represent a data signal
waveform. The waveforms A to D are respectively used as a voltage
waveform for displaying a light (bright) state or a dark state.
Further, "1H" represents one horizontal scan period, "BLK"
represents a clearing (erasing) pulse for clearing (resetting) a
pixel on a selected scanning electrode to provide a prescribed
display state, and "WIN" represents a writing pulse for determining
a display state of a pixel on a selected scanning electrode.
[0203] A synthetic waveform formed by combining a writing pulse
with a data signal is applied to a liquid crystal at a
corresponding pixel, whereby a display state of the corresponding
pixel is determined whether the display state resulting from the
clearing pulse continues or whether the display state resulting
from the clearing pulse is changed to the other display state.
[0204] When a high frame frequency is used, the waveforms shown in
FIGS. 21 and 22 may preferably be adopted compared with those shown
in FIGS. 23 and 24.
[0205] Further, the waveforms shown in FIGS. 18-24 may
appropriately be selected in view of flickering on a picture area
and a required drive margin.
[0206] FIG. 25 shows data signal waveforms (AA, BB and CC) applied
to a certain data electrode. Each of the waveforms (AA, BB and CC)
comprises a waveform containing only either one of signal waveforms
("light" and "dark") in succession in plural continuous horizontal
scan period.
[0207] In FIG. 25, a waveform AA is an alternating-current waveform
comprising continuously alternating pulses of a positive-polarity
pulse a and a negative-polarity pulse b each having a duration
.DELTA.T. Specifically, the waveform AA comprises a continuity of
the data signal waveform C or D shown in FIG. 21 or 22.
[0208] Waveforms BB and CC correspond to waveforms each identical
to the waveform A except that each pulse a is provided with an
interval of (1/2).DELTA.T (for BB) or that each pulse b is provided
with an interval of (1/2).DELTA.T (for CC), respectively. The
waveforms BB and CC have an identical effective value, and comprise
a continuity of the data signal waveform C shown in FIG. 23 or 24
and a continuity of the data signal waveform D shown in FIG. 23 or
24, respectively.
[0209] When the respective waveforms AA, BB and CC were applied and
observed, we have found that a degree of fluctuation of liquid
crystal molecules has varied depending on the applied waveform.
Specifically, in case where an inversion direction of liquid
crystal molecules under application of a negative polarity voltage
was one from U1 state to U2 state, it has found that liquid crystal
molecules in U1 state have considerably fluctuated by the pulse b
(negative-polarity pulse) an those in U2 state has also
considerably fluctuated by the pulse a (positive-polarity
pulse).
[0210] Such a fluctuation of liquid crystal molecules is recognized
as a change in display color thus requiring attention.
[0211] Accordingly, in order to decrease a frequency such that the
pulse b is applied to a pixel placed in U1 state, an interval (int)
of (1/2).DELTA.T is provided to the data signal waveforms C and D
as shown in FIGS. 23 and 24, whereby a direct-current pulse b other
hand that for writing in U2 state is not applied even if the data
signal waveform C or D shown in FIGS. 23 and 24 continues. In other
words, if another one pixel displaying U1 state is present on the
same data electrode, the frequency applying the direct-current
pulse b is decreased by one time per one frame. In case where all
the pixels on the same data electrode display U1 state, the
direct-current pulse b is not applied at all as shown by the data
signal waveform CC in FIG. 25. Similarly, in case where all the
pixels on the same data electrode display U2 state, the data signal
waveform BB is adopted. Consequently, the fluctuation (of liquid
crystal molecules) having limited a drive margin heretofore is
suppressed and the change in display color due to the fluctuation
is also not recognized, thus providing a wider drive margin.
[0212] We have also found that a drive margin (width) is saturated
at an interval (int) of about (1/2).DELTA.T as shown in FIG. 26
when a relationship between the interval and the drive margin has
been examined while increasing the interval by (1/2).DELTA.T. More
specifically, measurement of data shown in FIG. 26 is performed
under the following conditions:
[0213] Display apparatus: A color liquid crystal display apparatus
as shown by the block diagram of FIG. 17 including the
above-mentioned color liquid crystal panel (using Blank cell 1) as
a display portion 101.
[0214] Temperature: 10.degree. C.
[0215] Waveform: waveform of FIG. 24
[0216] Drive conditions: V.sub.1=14.3 (V), V.sub.2=-14.3 (V),
V.sub.3=5.7 (V), V.sub.4=-5.7 (V) and V.sub.5=6.4 (V).
[0217] The drive margin (width) corresponds to a width of a
duration .DELTA.T (.mu.s) capable of providing a good display state
free from crosstalk.
[0218] As is understood from FIG. 26, the interval may desirably be
as shorter as possible in order to increase a frame frequency, so
that the interval may preferably be (1/2).DELTA.T in view of the
drive margin and speed.
[0219] Further, the above measurement of drive margin may be
performed by using a smaller increment of the interval (e.g.,
(1/3).DELTA.T, (1/4).DELTA.T, etc.) but, in view of the structure
of a drive circuit, a ratio between an interval and each pulse
width may desirably be set so as to provide a simple integer. This
is because a reference clock of a drive circuit system is set so as
to have a value integer times values of a selection pulse, an
auxiliary pulse an an interval by dividing one horizontal scan
period (1H) for providing a prescribed waveform, so that, if a
ratio of pulse widths becomes too complicated, the clock becomes
very quick. As a result, it becomes necessary to provide a circuit
giving an excessively high response speed, thus resulting in
expensiveness.
[0220] In the present invention, by providing an applied pulse with
an interval of at least (1/2).DELTA.T when a selection period of
.DELTA.T is set, an application frequency (opportunity) of pulses
providing U1 and U2 states, respectively is decreased, thus
attaining a wider driving margin, a high frame frequency and a
simplified drive circuit at the same time.
[0221] The display apparatus used in the above-mentioned
measurement was driven at 10.degree. C. with the waveforms shown in
FIGS. 23 and 24 under drive conditions of: V.sub.1=14.3 (V),
V.sub.2=-14.3 (V), V.sub.3=5.7 (V), V.sub.4=-5.7 (V), (V.sub.5=6.4
(V)), and a duration .DELTA.T=80 (.mu.sec), whereby a good display
state was confirmed over the entire display area of the display
portion 101.
[0222] Further, in the case of a temperature higher than a
prescribed temperature, the drive signal waveforms as shown in
FIGS. 18-22 are used, whereby one horizontal scan period (1H) is
shortened to realize high-speed display.
[0223] As described above, according to the color liquid crystal
display apparatus according to the present invention, by providing
the substrate having thereon the color filter with wider scanning
electrodes and applying thereto a scanning signal, it is possible
to minimize an unevenness of the above substrate surface
(contacting the liquid crystal layer) thereby to allow a good drive
operation of the device. Particularly, in combination with the
driving conditions as described above, it is possible to effect a
good display with a wide drive margin in any operation condition.
Further, by appropriately selecting a drive waveform, high-speed
driving and high-quality image display free from flickering on a
picture area can also be accomplished.
[0224] Incidentally, flickering on a (display) picture (due to a
periodical change in luminance over the entire picture area) is
particularly observed when a multiplexing drive is performed.
[0225] Hereinbelow, the liquid crystal device according to the
present invention particularly having solved the problem of
flickering in multiplexing drive using a chiral smectic liquid
crystal will be specifically described.
[0226] As a driving method of the liquid crystal device described
herein, a multiplexing drive (scheme) wherein, to the
above-described matrix electrode structure constituted by a group
of scanning electrodes and a group of data electrodes, a sequential
scanning signal (waveform) is applied with respect to the scanning
electrode and a data signal (waveform) is applied with respect to
the data electrode in synchronism with the scanning signal is
generally used.
[0227] When the multiplexing drive scheme is adopted in a chiral
smectic liquid crystal device (a liquid crystal device using a
chiral smectic liquid crystal), the above-mentioned flickering
phenomenon is observed in some cases at the time of effecting a
drive (referred to s "refreshing drive" wherein a scanning signal
(waveform) is repeatedly and periodically applied to a group of
scanning electrodes.
[0228] According to the present invention, such a flickering
phenomenon can be obviated by using a color liquid crystal display
apparatus, including: a liquid crystal device, comprising: a pair
of oppositely disposed first and second substrates each provided
with a group of transparent electrodes in the form of stripes, and
a liquid crystal layer comprising a chiral smectic liquid crystal
disposed together with spacer beads between the pair of substrates,
the first substrate having thereon a color filter comprising plural
color filter segments and a coating layer, wherein the transparent
electrodes on the second substrate have a width smaller than that
of the transparent electrodes on the first substrate, scanning
signal supply means for supplying scanning signals to the
transparent electrodes on the first substrate, and data signal
supply means for supplying data signals including an interval at a
prescribed temperature or below to the transparent electrodes on
the second substrate, each of the data signals corresponding to
each of color filter segments of the color filter.
[0229] This liquid crystal device is characterized by having a
light-interrupting layer corresponding to a part of a pixel
disposed on one of the pair of substrates.
[0230] The flickering phenomenon recognized during the multiplexing
drive is considered to occur due to an irregular (abnormal)
inversion domain occurring in an end region of the pixel.
[0231] In the above liquid crystal, such an end region of the pixel
is covered by the light-interrupting layer while leaving the pixel
with a sufficient opening, thus alleviating a deterioration in
image quality due to flickering on a (display picture) area.
[0232] The above liquid crystal device using the light-interrupting
layer according to the present invention will be described in
detail with reference to FIGS. 27-32 and FIGS. 2-4.
[0233] In the following identical structure members (elements)
shown in FIGS. 27-30 are represented by identical reference
numerals, respectively.
[0234] FIG. 27 shows a schematically illustrated matrix electrode
structure of an embodiment of the above liquid crystal device of
the invention.
[0235] Referring to FIG. 27, a reference numeral 112a represents a
group of transparent electrodes (signal or data electrodes) formed
on an upper (first) substrate and a reference numeral 112b
represents a group of transparent electrodes (scanning electrodes)
formed on a lower (second) substrate. These groups of transparent
electrodes 112a and 112b intersect with each other at right angles
between the pair of oppositely disposed upper and lower substrates
to form a plurality of pixels at intersections thereof.
[0236] FIG. 28 is a schematically enlarged view of each
intersection of the electrode groups shown in FIG. 27, i.e., one
pixel wherein a light-interrupting layer 122 is provided to an end
portion (section) of an arbitrary one pixel 121 constituted by
transparent electrodes 112a and 112b at one intersection
thereof.
[0237] Referring to FIG. 28, a irregular inversion domain 123 is
completely covered with the light-interrupting layer 122 at the end
portion of the pixel 121. The upper and lower substrates are
subjected to rubbing in direction of arrows 124 and 125,
respectively, at a prescribed crossing (intersection) angle. In the
pixel 121, a hairpin defect 127 and a lightning defect in pairs 128
are present in a position of a spacer bead 126.
[0238] FIG. 29 is ia partially enlarged sectional view of the
liquid crystal device according to the present invention taken
along line A-A in FIG. 28.
[0239] Referring to FIG. 29, the liquid crystal device includes a
pair of upper and lower (first and second) substrates 131a and
131b, insulating films 133a and 133b, alignment control films 134a
and 134b, and a liquid crystal 135. Outside the substrates 131a and
131b, a pair of polarizers 137a and 137b are disposed in, e.g.,
cross nicols.
[0240] More specifically, as shown in FIG. 29, the liquid crystal
device includes a pair of parallel substrates 131a and 131b,
opposite to each other, each provided with a 300-3000 .ANG.-thick
transparent electrode (112a, 112b), and a liquid crystal 135 (e.g.,
chiral smectic liquid crystal) disposed between electrode
substrates (131a and 112a, and 131b and 112b). On a part (portion)
of the (lower) transparent electrode 112b, a light-interrupting
layer 122 is formed so as to overlap (or cover) with an irregular
inversion domain 123 occurring in the liquid crystal layer 135. On
the transparent electrodes 112a an 112b, insulating films 133a and
133b (thickness=100-3000 .ANG.) are formed, respectively, in order
to improve a controllability to the liquid crystal 135 and to
prevent short-circuiting. The insulating films 13a and 133b may
have a single layer structure or a lamination structure and may be
composed of a material identical to those for the short-circuit
prevention layers 8a and 8b and the roughened surface-forming
layers 9a and 9b as shown in FIGS. 2-6 described hereinabove.
[0241] The alignment control films 134a and 134b may generally have
a thickness of 50-1000 .ANG. and may generally comprise a polymeric
material, particularly preferably fluorine-containing polyimide
providing a high pretilt angle (an inclination angle with respect
to the alignment control film face). In addition, the alignment
control films 134a and 134b may be composed of a material identical
to those for the alignment layers 10a and 10b shown in FIGS. 2-6
described hereinabove.
[0242] At least one of the alignment control films 134a and 134b
are subjected to uniaxial aligning treatment by effecting, e.g.,
rubbing at the surface thereof in the rubbing directions 124 and
125 (as shown in FIG. 28), respectively. The crossing angle of the
rubbing directions (uniaxial aligning direction) 124 and 125 may be
at most 20 degrees, whereby a uniform alignment state (particularly
C1 uniform (alignment) state) of chiral smectic liquid crystal
molecules can be stably exhibited, thus realizing a high contrast
ratio.
[0243] The liquid crystal used in the above liquid crystal device
may contain the above-mentioned mesomorphic compounds of the
formulae (1)-(5) and the optically active compound and may
preferably be a chiral smectic liquid crystal composition (mixture)
having a chiral smectic phase (SmC*, SmH*, SmI*, SmK*, SmG*, etc.),
particularly further having cholesteric phase at a higher
temperature.
[0244] The above liquid crystal device of the invention may, e.g.,
be prepared as follows. In the following, however, the
light-interrupting layer 12 is described separately later for
convenience of explanation.
[0245] Two 1.1 mm-thick glass plates 131a and 131b were provided
with 1500 .ANG.-thick ITO transparent electrodes 112a and 112b in
the form of stripes (width 170 .mu.m, spacing 30 .mu.m) by
sputtering. On the electrode 11b, a light-interrupting layer 122
was formed (specifically described hereinafter). On the electrodes
112a and 112b, 900 .ANG.-thick Ta.sub.2O.sub.5 films for preventing
short-circuiting were formed by sputtering, and thereonto 1200
.ANG.-thick application-type insulating layers (Ti/Si=1/1, mfd. by
Tokyo Ohka K.K.) for modifying a surface state of their upper
layers were applied, followed by baking at 300.degree. C. to
constitute insulating films 133a and 133b.
[0246] A 1.5%-solution of polyamic acid ("LQ-1802", mfd. by Hitachi
Kasei Kogyo K.K.) in mixture solvent (NMP/nBC=1/1) was applied onto
the insulating films 1133a and 133b by using a spinner (2000 rpm,
20 sec.), followed by baking at 270.degree. C. for 1 hour and
further by rubbing to form 200 .ANG.-thick alignment control layers
134a and 134b.
[0247] The rubbing treatment was performed by pressing a
cylindrical rubbing roller the (peripheral) surface of which a
rubbing cloth (e.g., nylon) on the alignment control layer surface
on the glass substrate at a prescribed pressure and moving the
glass substrate in a prescribed (rubbing) direction while rotating
the rubbing roller, whereby an alignment control power was imparted
to the alignment control layer.
[0248] The alignment control power generally varies depending on an
abutting (pressing) pressure of the rubbing roller against the
alignment control film on the glass substrate and may desirably be
controlled by moving the rubbing roller in vertical direction
(changing/pressing depth) to provide an appropriate contact area
between the rubbing cloth and the alignment control film.
[0249] On one of the above-prepared substrates, spacer beads 126
(silica beads, 1.1 .mu.m-dia.) was dispersed, and on the other
substrate, a sealing agent (epoxy resin adhesive) was formed in a
prescribed pattern at the periphery part thereof by screen
printing, followed by adhesive bonding of the substrates to each
other to provide a prescribed cell gap (about 1.1 .mu.m).
[0250] In the above, the spacer beads may be alumina beads and may
have a diameter in the range of 0.1-3.5 .mu.m. Further, the cell
gap (the liquid crystal layer thickness) may appropriately be
controlled depending on liquid crystal materials used (or display
mode adopted). In the case of using a chiral smectic liquid crystal
is used, the layer thickness may preferably be set to be a very
small thickness sufficient to suppress the formation of helical
structure intrinsic to the liquid crystal in a bulk state.
[0251] Into a gap between the upper and lower substrates prepared
above, a chiral smectic liquid crystal (identical to that injected
into Blank cells 1 and 2 described above) heated to an isotropic
liquid was injected under reduced pressure by capillary action,
followed by gradual cooling to align liquid crystal molecules,
whereby a liquid crystal device characterized by having the
light-interrupting layer according to the invention was
prepared.
[0252] In the same manner, a comparative liquid crystal device was
prepared except for omitting (not forming) the light-interrupting
layer 122.
[0253] When the comparative liquid crystal device was driven by
applying a drive waveform (Vope=20 V, Vseq=5.7 V) including a
scanning signal (S.sub.1, S.sub.2, S.sub.3) and a data signal I in
combination shown in FIG. 32 for displaying a display image
(alternating "white" and "black") shown in FIG. 31 to scanning
electrodes repeatedly and periodically in synchronism with the data
signal I applied to the corresponding data electrode (i.e.,
effecting refreshing drive), flickering on a picture area was
confirmed.
[0254] As a result of further investigation, we have found that an
irregular inversion domain (as shown by 123 in FIG. 29) is present
in an end position (portion) of each pixel and charges its size by
the above refreshing drive. We have also ascertained that such an
irregular inversion domain 123 extends (originates) from region in
the liquid crystal layer 135 corresponding to an edge line (ridge)
of the upper transparent electrode 112a closer to the lightning
defect 128 than the hairpin defect 127 as shown in FIGS. 28 and 29
when these defects (128, 127) are caused to occur. In other words,
taking a positional relationship among the rubbing directions (124,
125), the lightning defect 128 and the hairpin defect 127 within
respect to alignment of the chiral smectic liquid crystal as shown
in FIG. 28 into account, it has been found that the above edge line
is present at a lower edge portion of each pixel as shown in FIG.
28, which is also located in a position closer to a rubbing start
position (lower side in FIG. 28) and is defined by the upper
transparent electrode 112a disposed perpendicular to the average
rubbing direction (a direction of the center line between the
arrows 124 and 125 shown in FIG. 27). The above lightning and
hairpin defect (128, 127) is capable of arbitrarily occurring in a
domain e.g., in a C1 uniform alignment state of the liquid crystal
to provide another alignment state (e.g., C2 alignment state) under
the influence of presence of a contaminant or local strain within
the cell.
[0255] In view of the above, according to the present invention, by
providing the light-interrupting layer 122 in a region (an end
portion of the pixel) corresponding to the irregular inversion
domain 123 so as to visually hide the irregular inversion domain
123, the flickering due to the domain 123 is minimized or
suppressed. Specifically, the light-interrupting layer 122 is
formed on the lower transparent electrode 112b in a position
corresponding to an end portion of each pixel having the side line
located, e.g., on the left-hand side of the rubbing direction in
FIG. 29 on the drawing in order to light-interrupt the irregular
inversion domain 123 having an edge forming an angle of 50-90
degrees with the rubbing direction 124.
[0256] The light-interrupting layer may be patterned in an
appropriate form, e.g., stripes (preferably black stripes as
mentioned hereinabove) in view of the structure to a cell used
(e.g., a color liquid crystal device). In a liquid crystal device,
other than that shown in FIGS. 28 and 29, having a
light-interrupting layer patternized in black matrix (i.e., plural
end portions of each pixel is covered by the light-interrupting
layer), it is possible to form the widest light-interrupting layer
(having the longest distance to a light-transmission region of the
adjacent pixel) at an end portion at which the irregular inversion
domain occurs.
[0257] Examples of a material for the light-interrupting layer 122
may be identical to those for the auxiliary electrodes 7a and 7b
shown in FIGS. 2-6 described hereinbefore. A particularly preferred
material therefor is low-resistance metal (e.g., molybdenum). The
light-interrupting layer 122 may be formed in a single or
lamination layer (total thickness of about 1500 .ANG.) by, e.g.,
sputtering.
[0258] FIG. 30 shows a schematic sectional view of the liquid
crystal device identical to that of FIG. 29 except that the
light-interrupting layer 122 is formed on the upper transparent
electrode 112a.
[0259] In this liquid crystal device (shown in FIG. 30), the
light-interrupting effect of the light-interrupting layer 122 is
somewhat lowered compared with that of the device shown in FIG. 29
since the light-interrupting layer 122 is formed on the transparent
electrode 112a having the edge line corresponding to the
origination position of the irregular inversion domain 123 thereby
to extend the irregular inversion domain 123. In this case,
however, the light-interrupting layer 122 is effective in lowering
an electrode resistance since the layer 122 is formed on the
transparent electrode 112a in its length (longitudinal) direction.
Further, the transparent electrode 112b may be formed in various
patterns (e.g., as shown in FIG. 9) having an edge line
substantially perpendicular to the average rubbing direction. In
case where the lower transparent electrode 112b has the edge line
similar to that of the upper transparent electrode 112a in the form
of stripes as shown in FIG. 29, the arrangement of the
light-interrupting layer 122 as shown in FIG. 30 is effective in
hiding the irregular inversion domain 123 originated from the edge
line of the lower transparent electrode 122b.
[0260] The problem of an occurrence of the irregular inversion
domain originated from the edge line perpendicular to the average
rubbing direction is common to the monochromatic liquid crystal
devices as shown in FIGS. 27-30 and the color liquid crystal device
as described hereinabove.
[0261] With reference to FIGS. 2-4, the irregular inversion domain
and the light-interrupting layer for hiding the irregular inversion
domain will be explained in the case of using the color liquid
crystal device.
[0262] In case where the color liquid crystal device shown in FIGS.
2 and 3 has an average rubbing direction from the left side to the
right side on the drawing, the irregular inversion domain occurs in
the liquid crystal layer 13 originated from the left-hand edge line
of each stripe electrode 6b (which lines also provide the alignment
layer 10a surface with an unevenness (not shown)) and extends
toward the right side in the average rubbing direction. In this
case, the auxiliary electrode 7a corresponding the above edge line
of the electrode 6b on the first substrate side and the auxiliary
electrode 7b covering the above edge line of the electrode 6b on
the second substrate also function as the light-interrupting layer
in combination, thus hiding the irregular inversion domain from an
observer.
[0263] On the other hand, in case where the color liquid crystal
device shown in FIGS. 2 and 4 has an average rubbing direction from
the left side to the right side on the drawing (FIG. 4), the
irregular inversion domain occurs in the liquid crystal layer B
originated from the left-hand edge lines of each stripe electrodes
6a and 6b (which lines also provide the surfaces of the alignment
films 10a and 10b with an unevenness (not shown), respectively) and
extends rightward on the drawing (FIG. 4). In this case, the
auxiliary electrode 7a and the light-interrupting layer 14 each
corresponding to the edge lines of the electrodes 6a and 6b
together function as a light-interrupting layer for preventing the
irregular inversion domain from being recognized by an
observer.
[0264] As described above, according to the present invention, by
providing a light-interrupting layer in a portion corresponding to
an end portion of each pixel including an edge line closer to a
rubbing initiation (starting) position and perpendicular to an
average rubbing direction the irregular inversion domain leading to
flickering on a display picture area is effectively
light-interrupted to minimize the flickering, thus improving a
display quality.
* * * * *