U.S. patent application number 10/422253 was filed with the patent office on 2003-10-30 for alignment films in a liquid crystal display device and a method of manufacturing the same.
This patent application is currently assigned to Fujitsu Display Technologies Corporation. Invention is credited to Nakanishi, Yohei, Okamoto, Kenji, Sasabayashi, Takashi, Tasaka, Yasutoshi, Yoshida, Hidefumi.
Application Number | 20030202143 10/422253 |
Document ID | / |
Family ID | 26522264 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030202143 |
Kind Code |
A1 |
Yoshida, Hidefumi ; et
al. |
October 30, 2003 |
Alignment films in a liquid crystal display device and a method of
manufacturing the same
Abstract
A liquid crystal display device including a pair of substrates
in a spaced relationship with one another. A pair of alignment
films are provided, one alignment film being formed on each
substrate such that the alignment films face one another. A liquid
crystal layer, including plural liquid crystals, is inserted
between the pair of alignment films, wherein the alignment films
impart a given pre-tilt angle to the liquid crystals. The alignment
films are composed of a material containing at least two types of
polymers having a prescribed initial alignment and different
alignment variation rates in response to ultra-violet ray
irradiation. The pre-tilt angle being adjusted, without rubbing the
alignment films, through ultraviolet exposure of the alignment
films.
Inventors: |
Yoshida, Hidefumi; (Ebina,
JP) ; Tasaka, Yasutoshi; (Kawasaki, JP) ;
Sasabayashi, Takashi; (Machida, JP) ; Nakanishi,
Yohei; (Zushi, JP) ; Okamoto, Kenji;
(Hiratsuka, JP) |
Correspondence
Address: |
Patrick G. Burns
Greer, Burns & Crain, Ltd.
Suite 2500
300 South Wacker Drive
Chicago
IL
60606
US
|
Assignee: |
Fujitsu Display Technologies
Corporation
|
Family ID: |
26522264 |
Appl. No.: |
10/422253 |
Filed: |
April 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10422253 |
Apr 24, 2003 |
|
|
|
09629287 |
Jul 31, 2000 |
|
|
|
6583835 |
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Current U.S.
Class: |
349/123 ;
349/124 |
Current CPC
Class: |
G02F 1/133761 20210101;
G02F 1/133742 20210101; G02F 1/133753 20130101; G02F 2202/022
20130101; G02F 1/133788 20130101; G02F 1/133765 20210101; G02F
1/133711 20130101 |
Class at
Publication: |
349/123 ;
349/124 |
International
Class: |
G02F 001/1337 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 1999 |
JP |
11-217878 |
May 31, 2000 |
JP |
2000-163607 |
Claims
What is claimed is:
1. A liquid crystal display device comprising: a pair of substrates
in a spaced relationship with one another; a pair of alignment
films, one said alignment film formed on each said substrate such
that said alignment films face one another; and a liquid crystal
layer, including plural liquid crystals, inserted between said pair
of alignment films; said alignment films imparting a given pre-tilt
angle to the liquid crystals, said alignment films being composed
of a material containing at least two types of polymers having a
prescribed initial alignment and different alignment variation
rates in response to ultraviolet light irradiation; wherein said
given pre-tilt angle is adjusted, without rubbing said alignment
films, by exposing said alignment films to ultraviolet light.
2. A liquid crystal display device according to claim 1, whereby at
least one of said alignment films is comprised of a material
containing mixtures of said polymers.
3. A liquid crystal display device according to claim 1, whereby
said alignment film is comprised of material containing copolymers
of said polymers.
4. A liquid crystal display device according to claim 1, whereby
one type of said two types of polymers changes an orientation of
the liquid crystal molecules from an initial orientation, and the
other type of said two types of polymers generally maintains said
initial orientation of said liquid crystal molecules.
5. A liquid crystal display device according to claim 4, whereby
said initial state of orientation is a vertical, and said one type
of said two types of polymers changes an orientation of the liquid
crystal molecules from said initial orientation to a random
horizontal orientation.
6. A liquid crystal display device according to claim 1, wherein
said alignment films are comprised of a mixture of polymer x1 which
exhibits a change of pre-tilt angle of at least 2.degree. when
irradiated with 0.5 (J/cm.sup.2) of ultra-violet rays and a polymer
x2 which exhibits a change of pre-tilt angle of generally
0.5.degree. when irradiated with at least 0.5 (J/cm.sup.2) of
ultra-violet rays.
7. A liquid crystal display device according to claim 6, wherein
said alignment films are composed of at least one of polyimide and
polyamic oxide.
8. A liquid crystal display device according to claim 7, wherein
said alignment films are comprised of a 20:80 mixture of polymer x1
and polymer x2.
9. A method of aligning an alignment film used to orient liquid
crystal molecules in a liquid crystal display device, said method
comprising the steps of: forming an alignment film a substrate,
said alignment film being composed of at least two different types
of polymers, each type of polymer exhibiting differing alignment
variation in response to ultra-violet ray irradiation; irradiating
said alignment film with ultra-violet rays at an oblique angle with
respect to a surface of said alignment film.
10. A method of forming an alignment film according to claim 9,
wherein said oblique angle is generally less than 45.degree..
11. A method of forming an alignment film according to claim 9,
wherein said alignment film is comprised of a mixture of polymer x1
which exhibits a change of pre-tilt angle of at least 2.degree.
when irradiated with 0.5 (J/cm.sup.2) of ultra-violet rays and a
polymer x2 in which the change of pre-tilt angle is 0.5.degree.
when irradiated with 0.5 (J/cm.sup.2) of ultra-violet rays.
12. A method of forming an alignment film according to claim 9,
wherein a pre-tilt angle of one type of said at least two types of
polymers changing from an initial vertical orientation to a random
horizontal orientation in response to ultra-violet irradiation, and
another type of said at least two types of polymers generally
retains said initial vertical orientation.
13. A method of forming an alignment film according to claim 9,
wherein said alignment film is composed of at least one of
polyimide and polyamic oxide.
14. A method of forming an alignment film according to claim 11,
wherein said alignment films are comprised of a 20:80 mixture of
polymer x1 and polymer x2.
15. An alignment film applied to opposing faces of a pair of
substrates in a liquid crystal display device and aligning liquid
crystal layer disposed therebetween, the alignment film comprising:
a material containing at least two types of polymers with differing
alignment variation rates in response to ultra-violet ray
irradiation, both said two types of polymers having a prescribed
initial alignment for the liquid crystal molecules in the liquid
crystal layer.
16. The alignment film according to claim 15, wherein said material
includes mixtures of the polymers.
17. The alignment film according to claim 15, wherein said material
contains a copolymer of the polymers.
18. The alignment film according to claim 15, wherein an alignment
of one of the two polymers readily changes from said initial
alignment to a second alignment in response to ultraviolet light
exposure, and the other of the two polymers is highly resistant to
changes in alignment in response to ultraviolet light exposure.
19. The alignment film according to claim 18, wherein the initial
alignment is vertical, and the second alignment is horizontal.
20. An alignment apparatus for adjusting the alignment of an
alignment film with ultraviolet light, said apparatus comprising: a
light source to irradiate scattered ultraviolet light; and an
optical mask disposed under said light source and formed with at
least one slit, wherein diffuse light, centered on said slit, is
generated by placing said optical mask above said alignment film
and irradiating scattered light from said light source through said
optical mask; wherein said diffuse light exposes said alignment
film, and produces domains in said liquid crystal that depend on
the directions of diffusion of the diffuse light.
21. The alignment apparatus according to claim 20, wherein said at
least one slit is stripe-shaped.
22. The alignment apparatus according to claim 20, wherein said
optical mask is disposed so that said slit is positioned in a
region roughly parallel to a data electrode formed in a lower part
of said alignment film.
23. The alignment apparatus according to claim 20, wherein said
optical mask is disposed so that the slit is positioned in a region
that is roughly parallel to a gate electrode formed in a lower part
of the alignment film.
24. The alignment apparatus according to claim 20, wherein said
light source is a tubular-shaped lamp.
25. The alignment apparatus according to claim 24, wherein said
optical mask and said light source are disposed so that a
lengthwise direction of said slit and a lengthwise direction of
said light source are one of parallel and orthogonal.
26. The alignment apparatus according to claim 25, further
comprising a cold mirror installed to cover a back of said light
source, said cold mirror absorbing infrared light; wherein said
alignment film is irradiated with the reflected light from said
cold mirror as scattered light in the surface along the lengthwise
direction of the light source and as parallel light in the surface
perpendicular to the lengthwise direction of said light source.
27. A method for adjusting the alignment of an alignment film in a
liquid display device and orients liquid crystal sandwiched between
a pair of alignment films, said method comprising the steps of:
placing an optical mask formed with slits above one of the
alignment films; irradiating the optical mask with scattered light
from a light source irradiating scattered ultraviolet light,
whereby diffuse light centered on said slit spreads out and exposes
the alignment film with said diffuse light, and produces domains in
said liquid crystal that depend on the directions of diffusion of
the diffuse light.
28. An alignment apparatus for exposing an alignment film with
ultraviolet light and orients liquid crystal sandwiched between a
pair of alignment films, said apparatus comprising: a light for
producing ultraviolet light; an optical mask that is disposed under
said light source, said optical mask having a slit; and an
ultraviolet light scattering mechanism formed on said slit; wherein
said optical mask is placed above said alignment film and
ultraviolet light is irradiated from said light source through said
optical mask thereby producing diffuse light, centered on said
slit, that spreads out and exposes said alignment film; further
wherein domains that depend on the directions of diffusion of the
diffuse light are produced in said liquid crystal by the
exposure.
29. A liquid crystal display device that is provided with a pair of
substrates, that are maintained in a facing relationship with a
prescribed interval defined therebetween, comprising: a pair of
alignment films, one alignment film being provided on each
substrate such that said pair of alignment films are in an opposing
relationship; a liquid crystal layer provided between the alignment
films, wherein the alignment films provide a given pretilt angle to
liquid crystals disposed therebetween; pixel electrodes formed on
one of the substrates provide an alignment control force that is
directed in the direction that cancels the orientations due to the
electric fields generated at the ends of the pixel electrodes to
the liquid crystal molecules in the region corresponding to the
ends of said pixel electrodes.
30. The liquid crystal display device according to claim 29,
wherein the liquid crystal layer has prescribed domains on the
pixel electrodes by controlling the alignment of the alignment
film.
31. A liquid crystal display device, comprising: a pair of
substrates which are maintained at a prescribed interval; an
alignment film on each substrate, such that the alignment films
faces each other; a liquid crystal layer provided between the
alignment films; a plurality of domains being produced at
prescribed boundaries in the liquid crystal; and a surface energy
of the alignment film reaches one of a maximum and a minimum at the
prescribed boundaries of the domains and one of decreases and
increases when moving away from the boundaries.
32. The liquid crystal display device according to claim 31,
wherein the alignment films imparting a given pre-tilt angle to the
liquid crystals, said alignment films being composed of a material
containing at least two types of polymers having a prescribed
initial alignment and different alignment variation rates in
response to ultra-violet ray irradiation.
33. The liquid crystal display device according to claim 32,
wherein said prescribed initial alignment is vertical, and the
alignment of said alignment films becomes constant near 90.degree.
when a given threshold of ultraviolet light exposure is
exceeded.
34. The liquid crystal display device according to claim 31,
wherein said alignment film has a property of starting to change
alignment from said prescribed initial alignment in response to
ultraviolet light exposure and resuming said prescribed initial
alignment when irradiated again by ultraviolet light.
35. An alignment method for providing a prescribed alignment to an
alignment film used to orient liquid crystals, said method
comprising: providing a light source which generates ultraviolet
light; providing a substrate having an alignment film therein,
providing an optical mask between the light source and the
substrate, the optical having at least one slit defined therein;
irradiating the optical mask with ultraviolet light such that
diffuse ultraviolet light that spreads out is transmitted through
the slit and exposes the alignment film and produces domains in
said liquid crystal that depend on the directions of diffusion of
the diffuse light.
36. The alignment method according to claim 35, wherein: each
alignment film is divided into two domains to produce mutually
different orientations in a plurality of regions, and the
orientations are controlled to tilt the liquid crystal molecules in
mutually opposite directions; further wherein the initial alignment
is one of vertical and horizontal.
37. A liquid crystal display device, comprising: a pair of
substrates which are maintained at a prescribed interval; an
alignment film on each substrate, such that the alignment films
faces each other; a liquid crystal layer provided between the
alignment films; one of said substrates having pixel electrodes
formed thereon with bus lines formed between the pixel electrodes,
said substrate having slits defined roughly parallel to the bus
lines in the vicinity of said bus lines in said pixel
electrodes.
38. An alignment apparatus for configuring an alignment of an
alignment film used to orient liquid crystals, said apparatus
comprising: a light source for irradiating ultraviolet light; an
optical mask provided under said light source and having an
ultraviolet light scattering mechanism formed thereon; wherein said
optical mask is disposed above said alignment film such that
diffuse ultraviolet light passes through said optical mask, exposes
the alignment film and produces domains in said liquid crystal that
depend on the directions of diffusion of the diffuse light.
39. The alignment apparatus according to claim 38, wherein the
scattering mechanism is formed on the surface of the optical mask
on the light source side.
40. The alignment apparatus according to claim 38, wherein said
optical mask is provided with a slit, and said scattering mechanism
is formed in the opening of the slit.
41. The alignment apparatus according to claim 38, wherein the
optical mask has stripe shaped slits formed therein for diffusing
the ultraviolet light.
42. The alignment apparatus according to claim 38, wherein when the
optical mask is disposed above an upper part of the alignment film,
a slit formed in said optical mask is positioned is roughly
parallel to a data electrode in a lower part of said alignment
film.
43. The alignment apparatus according to claim 38, wherein when the
optical mask is disposed above an upper part of the alignment film,
a slit formed in said optical mask is positioned roughly parallel
to a gate electrode formed in a lower part of said alignment
film.
44. A method for manufacturing a liquid crystal display device,
comprising: providing with a pair of substrates which are
maintained at a prescribed interval, each substrate having an
alignment film such that the alignment films face each other;
providing a liquid crystal layer between the alignment films;
provides an alignment control force that is directed in the
direction that cancels the orientations due to the electric field
generated at the ends of the pixel electrodes to the liquid crystal
molecules in the region corresponding to the ends of the pixel
electrodes formed on one of the substrates.
45. A method for manufacturing a liquid crystal display device,
comprising: providing with a pair of substrates which are
maintained at a prescribed interval, each substrate having an
alignment film such that the alignment films face each other;
providing a liquid crystal layer between the alignment films;
provides an alignment control force that is directed in the
direction that cancels the orientations due to the electric field
generated at the ends of the pixel electrodes to the liquid crystal
molecules in the region corresponding to the ends of the pixel
electrodes formed on one of the substrates.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to alignment films which
orient liquid crystals provided between the alignment films in a
liquid crystal display device, and a method for manufacturing the
alignment films.
BACKGROUND OF THE INVENTION
[0002] In recent years, liquid crystal display devices,
particularly, Thin Film Transistor (TFT) liquid crystal display
devices which have a twisted nematic (TN) display mode, have come
into wide use. For example, they are the general-purpose display
devices in personal computers.
[0003] Usually, a liquid crystal display device includes a pair of
opposing substrates that are maintained with a prescribed interval,
electrodes and alignment films formed on the facing surfaces of the
substrates, and a liquid crystal layer inserted between the
alignment films. The electrodes of one substrate are formed into a
common electrode. The electrodes of the other substrate are formed
into the pixel electrodes. The pixel electrodes are often provided
with an active matrix. In addition, electrodes are provided only on
one substrate (for example, IPS mode). A black matrix or color
filter is provided on either substrate.
[0004] In conventional liquid crystal display devices, the liquid
crystal molecules in the liquid crystal layer are oriented in the
prescribed direction by rubbing the alignment film. The alignment
film is polished by a cloth, for example rayon, which undesirably
generates dust within the clean room. Moreover, the rubbing
generates static electricity which could potentially result in the
breakdown of the TFT of the active matrix.
[0005] The inventors of the present invention have proposed in
Japanese patent application HEI 9-354940 and Japanese patent
application HEI 11-72085 a technique for orienting the liquid
crystal molecules through the use of ultra-violet rays. As
illustrated in FIG. 37, ultraviolet light is irradiated at an angle
of 45.degree., for example, with respect to the surface of the
polyimide alignment film 501, thereby orienting the liquid crystal
molecules 502.
[0006] The relationship between the pre-tilt angle and the amount
of ultra-violet ray irradiation realized by the method of Japanese
patent application 11-72085 is illustrated in FIG. 38.
[0007] From the relationship shown in the drawing, when the volume
of ultra-violet ray irradiation is low and the pre-tilt angle is
large, black points occur in locations centered around spacers used
maintain the spacing between the substrates (cell gap) of the
liquid crystal display device. Correspondingly, if the ultraviolet
light exposure is high, flow-induced orientations accompanying the
injection of liquid crystal are produced. Both are primary causes
of poor displays. In this case, an appropriate range for the
pretilt angles that obtain displays having good images is a narrow
range of no more than 1.0.degree. centered near 89.degree..
[0008] One of the problems associated with the teachings of
Japanese patent application HEI 11-72085 is strong reliance on the
proper control of the angle and intensity of the ultra-violet rays.
Optimum results require a maximum of a .+-.10% intensity deviation
in order to obtain a given pre-tilt angle. Referring to the
properties curve of FIG. 8, a deviation of .+-.0.2% commonly occurs
both in the angle of irradiation and in the intensity of the
ultra-violet rays, making it difficult to reliably obtain a
specified pre-tilt angle. Consequently, the probability of poor
display occurring increases and there is a concern that the display
will be unreliable.
[0009] Accordingly, an object of the present invention is to
provide an improved method for orientation of an orientation film
in which a desired pre-tilt angle of liquid crystal molecules can
be assured without the need for rubbing the orientation film, and
which does not suffer from the aforementioned problem relating to
proper control of the angle and intensity of the ultra-violet
rays.
[0010] Another object of the present invention is to increase the
contrast in the display surface and prevent light and dark reversal
in the display, and provide an alignment technique that exposes the
alignment film with ultraviolet light from different directions and
produces domains in the pixels. As shown in FIGS. 39A and 39(B, two
domains are created in the alignment film 611 by using an optical
mask 601 formed with a slit 602. The optical mask 601 is placed
above the alignment film 611, and parallel ultraviolet light is
irradiated at an incline from above the optical mask 601. Next,
parallel light is irradiated again at an incline having a different
angle (Unexamined Japanese Patent Publication (Kokai) No. Hei
11-133429). Thus, the alignment film 601 is irradiated multiple
times, one time for each domain. Naturally, this leads to an
increase in the number of processes.
[0011] The method disclosed in Hei 11-133429 is further problematic
as the multiple irradiations tend to cause bending of the optical
mask. As shown in FIG. 40, bending of the optical mask 601 causes
offsets in the exposure positions of the ultraviolet light on the
alignment film 611. For example, even if the ultraviolet light is
irradiated in two directions with the center of the pixel as the
boundary, the domain will have an offset center position. The size
of the glass substrate has tended to increase each year, and the
use of a 1 m.sup.2 substrate is expected. If the thickness of the
optical mask is 1 cm, bending by several dozen .mu.m at the center
of the optical mask will be apparent based on calculations. Thus,
design offsets that cannot be ignored will occur.
[0012] Consequently, if domains are created as described above, in
addition to the difficulty in controlling the angle and intensity
of the irradiated ultraviolet light, the processes will necessarily
become more complex.
[0013] In view of the problems described above, another object of
the present invention is to provide a liquid crystal display device
that has a simple structure and is provided with alignment films
that can very stably and easily obtain the appropriate pretilt
angles for the liquid crystal molecules by a simple alignment
process without rubbing.
[0014] Another object of the present invention is to provide an
alignment apparatus, an alignment method able to easily and
accurately create domains without increasing the number of
processes.
BACKGROUND OF THE INVENTION
[0015] The present invention provides an improved liquid display
device and a method for creating the same. According to a first
embodiment, the liquid crystal display device includes a pair of
substrates in a spaced relationship with one another. A pair of
alignment films are provided, one alignment film being formed on
each substrate such that the alignment films face one another. A
liquid crystal layer, including plural liquid crystals, is inserted
between the pair of alignment films, wherein the alignment films
impart a given pre-tilt angle to the liquid crystals. The alignment
films are composed of a material containing at least two types of
polymers having a prescribed initial alignment and different
alignment variation rates in response to ultra-violet ray
irradiation. The pre-tilt angle being adjusted, without rubbing the
alignment films, through ultraviolet exposure of the alignment
films.
[0016] Also disclosed is an alignment apparatus for adjusting the
alignment of an alignment film with ultraviolet light. The
alignment apparatus includes a light source to irradiate scattered
ultraviolet light, and an optical mask disposed under the light
source. The optical mask is formed with at least one slit. In
operation the optical mask is placed above the alignment film and
scattered ultraviolet light irradiates from the light source
through the optical mask. Diffuse light exposes the alignment film,
and produces domains in the liquid crystal that depend on the
directions of diffusion of the diffuse light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above-described objects of the invention will be
apparent from the following detailed description of the invention,
while referring to the attached drawings in which:
[0018] FIG. 1 is a cross-sectional view showing the overall
structure of a liquid crystal display device according to one
embodiment of the present invention;
[0019] FIG. 2 is a characteristic plot showing changes in pre-tilt
angles states for alignment films with respect to the ultraviolet
light exposure;
[0020] FIG. 3 is a characteristic plot showing the surface free
energy changes with respect to the ultraviolet light exposure for
alignment films composed of one polymer;
[0021] FIG. 4A is a characteristic plot showing the surface free
energy changes with respect to the ultraviolet light exposure for
alignment films composed of one polymer;
[0022] FIG. 4B is a characteristic plot showing the surface free
energy changes with respect to the ultraviolet light exposure for
several different alignment films;
[0023] FIG. 4C is a characteristic plot showing changes in pre-tilt
angles states for several different alignment films with respect to
the ultraviolet light exposure;
[0024] FIG. 5 is a schematic diagram of an apparatus for
irradiating an alignment film according to the present
invention;
[0025] FIG. 6 is a characteristic plot showing the ideal changes in
the pretilt angle with respect to the ultraviolet light exposure
for the alignment films in a liquid crystal display device
according to the present invention;
[0026] FIG. 7 is a cross-sectional view showing the main structures
of an apparatus for irradiating an alignment film according to
another embodiment;
[0027] FIG. 8 is a cross-sectional view showing the state of the
ultraviolet light exposure when the optical mask is bent;
[0028] FIG. 9 is a characteristic plot shows the changes in the
pretilt angle accompanying the ultraviolet light irradiating the
alignment film of the present invention;
[0029] FIGS. 10A and 10B are cross-sectional views shows the setup
of the rib-shaped parts in a substrate when there are two
domains;
[0030] FIG. 11 is a schematic diagram showing the structure of the
light source used in FIG. 7;
[0031] FIG. 12 is a diagram showing the light source of FIG. 11
scanning an optical mask;
[0032] FIGS. 13A-13C are schematic diagrams of a TFT LCD having top
and bottom domains;
[0033] FIGS. 14A-14C are schematic diagrams of a TFT LCD having
left and right domains;
[0034] FIGS. 15A-15C are schematic diagrams of a TFT LCD having
top, bottom, left, and right domains;
[0035] FIGS. 16A-16C are schematic diagrams of a TFT LCD having
top, bottom, left, and right domains;
[0036] FIGS. 17A-17C are schematic diagrams of a TFT LCD having top
and bottom domains;
[0037] FIG. 18 is a cross-sectional view showing the relationship
of the positions of the rib-shaped part and the pixel
electrode;
[0038] FIG. 19 is a characteristic plot showing the relationship
between the width of the overlap of the rib-shaped part and the
pixel electrode and the width of the poor alignment at the end of
the pixel electrode;
[0039] FIGS. 20A-C are schematic diagrams showing a modification of
the TFT LCD of FIG. 13;
[0040] FIG. 21 is a characteristic plot showing optimum values for
the width of the slit in the optical mask with a favorable
alignment state and the distance between the optical mask and the
substrate;
[0041] FIG. 22 is a cross-sectional view shows the important
structures of the alignment apparatus according to a third
embodiment;
[0042] FIG. 23 is a cross-sectional view showing a first
modification of the structure shown in FIG. 22;
[0043] FIG. 24 is a cross-sectional view showing a second
modification of the structure shown in FIG. 22;
[0044] FIGS. 25A and 25B are cross-sectional views shows the
important structures of an alignment apparatus according to a
fourth embodiment;
[0045] FIG. 26 is an oblique projection view showing the optical
mask in the alignment apparatus;
[0046] FIG. 27 is an oblique projection view showing the placement
state of the optical mask;
[0047] FIGS. 28A and 28B are top views showing the image state in
the liquid crystal display device according to the fourth
embodiment;
[0048] FIGS. 29A and 29B are top views showing the image state of
the liquid crystal display device using only alignment control for
two divisions;
[0049] FIG. 30 is an oblique projection view showing the optical
mask in the alignment apparatus according to a first
modification;
[0050] FIG. 31 is an oblique projection view showing the optical
mask in the alignment apparatus according to a second
modification;
[0051] FIGS. 32A and 32B are schematic diagrams of the light source
used in the alignment apparatus of FIGS. 25A and 25B;
[0052] FIG. 33 is a top view shows the relationship between the
scattering characteristics of the light source and the slit in the
optical mask;
[0053] FIG. 34 is a top view shows the vicinity of a pixel
electrode in the liquid crystal display device in a fifth
embodiment;
[0054] FIGS. 35A and 35B are cross-sectional views showing
orientations of the liquid crystal molecules in the pixel electrode
formed with a slit;
[0055] FIGS. 36A and 36B are schematic diagrams of another example
of a fifth embodiment;
[0056] FIG. 37 is a schematic showing the pretilt angle orientation
of liquid crystal molecules by alignment films exposed to oblique
ultraviolet light;
[0057] FIG. 38 is a characteristic plot showing changes in the
pretilt angle with respect to the ultraviolet light exposure for
alignment films composed of one polymer;
[0058] FIGS. 39A and 39B are cross-sectional views showing two
domains implemented in a conventional alignment film; and
[0059] FIG. 40 is a cross-sectional view is used to describe the
problems when the optical mask is bent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] Various specific embodiments applying the present invention
are explained in detail while referring to the drawings.
[0061] FIG. 1 is a cross-sectional view of a liquid crystal display
device according to a first embodiment. The liquid crystal display
device includes a pair of opposing transparent glass substrates 11,
12 with a liquid crystal layer 13 interposed therebetween.
[0062] A plurality of pixel electrodes 115 are formed on an
intervening insulation layer 14 provided on transparent glass
substrate 11, and a transparent alignment film 16a covers the pixel
electrodes 15. A color filter 17, a common electrode 18, and an
alignment film 16b are successively layered on the transparent
glass substrate 12. The alignment films 6a, 16b push towards each
other to hold the liquid crystal layer 13, and the glass substrates
11, 12 are fixed.
[0063] Polarizers 19,20 are provided on the outer sides of the
substrates 11, 12. The pixel electrodes 115 are formed with the
active matrix. In the illustrated example, the data bus lines 21 in
the active matrix are shown. The electrodes are provided on only
one substrate (for example, in the IPS mode).
[0064] The alignment film 16a (16b) provides a prescribed
orientation property for the liquid crystal molecules in the liquid
crystal layer 13. The prescribed orientation is realized by
irradiating ultraviolet light from an inclined direction to the
liquid crystal layer without rubbing. Specifically, the alignment
film 16a (16b) is composed of a material containing two polymers
x1, x2 having different rates of change of the pretilt angles in
response to ultraviolet light exposure. Polymer x1 responds
extremely rapidly to ultraviolet light, and its pretilt angle
rapidly decreases under a small ultraviolet light exposure. In
contrast, polymer x2 responds extremely slowly to ultraviolet light
and the pretilt angle is hardly changed at all by ultraviolet light
exposure. Using mixtures or copolymers of three or more polymers
having different rates of change of the pretilt angle may
achieved.
[0065] FIG. 38 is a graph showing the relationship between the
ultraviolet light exposure (J/cm.sup.2) and the pretilt angle
(.degree.) for a given polymer. Notably, the change in the pretilt
angle is large with respect to slight changes in the ultraviolet
light exposure, making it difficult to achieve a desired pretilt
angle. Ideally, the pretilt angle should rapidly decreases to a
desired value under a small ultraviolet light exposure, and
thereafter maintain the desired pretilt angle irregardless of
additional ultraviolet light exposure.
[0066] As shown in FIG. 2, the alignment film 16a (16b) is formed
by using polymer x1 which rapidly decreases the pretilt angle under
ultraviolet light exposure (J/cm.sup.2) and polymer x2 which does
not change the pretilt angle and has almost no dependence on the
ultraviolet light exposure. The polymer for alignment film 16a
(16b) is a vertically aligned polyimide or polyamic acid. An
example is shown below. 1
[0067] The polymer considered has the alkyl side chain (alkyl
group) R as shown in formula 1 and randomly projects to the surface
of the alignment film 16a (16b). If ultraviolet light irradiates
the surface, photodecomposition develops and breaks the straight
chain that supports the alkyl side chain R which essentially
reduces the alkyl side chain R and subsequently appears as a
decrease in the pretilt angle of the liquid crystal molecules.
Polymer x1 has a structure in which the straight that supports the
alkyl side chain R is remarkably easy to break compared to polymer
x2. Specifically, a region where photodecomposition easily occurs,
for example, a double bond region, is provided as the straight
chain supporting the alkyl side chain R of the polymer x1. If
ultraviolet light irradiates this double bond region,
photo-decomposition develops even for an extremely small exposure
and causes a substantial decrease in the pretilt angle in a short
time.
[0068] Assuming, for the purposes of illustration, a copolymer
composed of twenty percent polymer x1 and eighty percent polymer
x2. When the ultraviolet light exposure is initiated, the state of
polymer x1 within the copolymer rapidly changes until the amount of
the alkyl side chain R that manifests the pretilt angle is reduced
to essentially 0. In contrast, polymer x2 within the copolymer
maintains its initial state of vertical alignment because there is
no double bond region in the straight chain of the alkyl side chain
R. Therefore, the overall copolymer maintains a nearly constant
pre-tilt value after the specified time has elapsed in which the
amount of the alkyl side chain R is decreased to 80 percent.
[0069] The criteria for selecting polymers x1 and x2 to obtain a
suitable alignment film having the characteristics described above
will now be described.
[0070] FIG. 3 shows the relationship between the ultraviolet light
exposure time (minutes) on the alignment film surface and the
surface free energy (.gamma.s: Helmholtz free energy per unit
area). If a small amount of ultraviolet light is irradiated, the
surface energy also becomes small and the surface free energy
increases along with the ultraviolet light irradiation and finally
becomes a nearly constant value.
[0071] As shown in FIG. 4A, if the surface free energy increases
with the increase in the ultraviolet light exposure time, the
so-called injection stripe from the injection port is generated
when the liquid crystal is injected. Furthermore, when the exposure
time increases, the vertical alignment is not exhibited at the
earliest time and the alignment moves to a random horizontal
alignment.
[0072] The present inventors discovered that the surface free
energy accompanying the increase in the ultraviolet light exposure
time (amount of exposure) successively moves from region (1) to
region (4). Region (1) is the initial state exhibiting vertical
alignment, region (2) exhibits good image display with no
generation of flow-induced orientation defects or defects near the
spacers, region (3) exhibits injection strips caused by
flow-induced orientations, and region (4) exhibits horizontal
alignment.
[0073] As shown in FIG. 4B, the alignment film may be classified
according to surface free energy into three general type. Alignment
film A rapidly moves into region (4) in response to a small
ultraviolet light exposure (short time) and has random horizontal
alignments. Alignment film B moves into region (3) after a
predefined amount of ultraviolet light exposure, and at a generally
slower rate than alignment film A. Alignment film C generally
remains in region (1) regardless of the amount of ultraviolet light
exposure. Moreover, the desired state (Region (2)) is implemented
by properly combining alignment films A to C.
[0074] FIG. 4C shows the relationship between the ultraviolet light
exposure and the pretilt angle for the combinations of alignment
films A and B and alignment films A and C. If alignment films A and
B are combined, the pretilt angle continues to slowly decrease as
the ultraviolet light exposure increases and does not contribute to
an increase in the margin, and acceptable orientations are not
achieved. In contrast, if alignment films A and C are combined, a
region in which the pretilt angle hardly changes is created even if
the ultraviolet light exposure changes, and orientations having a
wide margin are achieved.
[0075] As described above, suitable polymers x1 and x2 exhibit both
extreme properties related to the manifestation of the pretilt
angle. In other words, polymer x1 will have random horizontal
alignments caused by a small ultraviolet light exposure (short time
period). In contrast, polymer x2 still maintains the initial
vertical alignment. Thus, with the surface free energy as the
criterion, alignment film A (polymer) is appropriately selected to
be polymer x1 and alignment film C to be polymer x2.
[0076] Next, the alignment method which is the main process of the
embodiment in the method for manufacturing liquid crystal display
devices is described.
[0077] Referring back to FIG. 1, after the insulation film 14 is
deposited in a layer on the surface of the transparent glass
substrate 11, the color filter 17 and the pixel electrodes 115 are
successively formed on the surface of the transparent glass
substrate 12.
[0078] Next, a vertically aligned polyimide or polyamic acid (see
formula 1) manufactured by Japan Synthetic Rubber Ltd. is used for
polymers x1 and x2 having the above properties on the surfaces of
the transparent glass substrates 11, 12. According to a preferred
embodiment, polymers x1 and x2 are mixed or copolymerized at a 2:8
ratio and form the alignment films 16a, 16b on the surfaces of the
transparent glass substrates 11, 12. However, different ratio's may
be selected depending on the desired pre-tilt angle.
[0079] FIG. 5 illustrates an alignment apparatus useful for
implementing alignment processing on the target film.
[0080] The alignment apparatus includes of a light source 31 to
irradiate non-polarized ultraviolet light, a mirror 32, and a
holder 33 for supporting the transparent glass substrate 11 (12)
forming the alignment film 16a (16b). The holder 33 supports the
transparent glass substrate 11 (12) at an incline with respect to
the optical axis of the ultraviolet light. The parallel ultraviolet
light from the light source 31 is incident at an angle of
.theta.=45.degree. with respect to the surface of the alignment
film 16a (16b) (or at a specified angle less than 45.degree.).
[0081] The light source 31 is a short-arc xenon mercury lamp,
includes a parabolic reflector 31a, and exposes nearly parallel
non-polarized ultraviolet light. The spectral distribution of the
ultraviolet light wavelengths has a peak near 250 nm. In this
spectral distribution, the wavelength components at and above 300
nm are judged to not contribute to appearance of the pretilt angle.
Ultraviolet light having a wavelength no more than 280 nm is suited
to effectively producing the pretilt angle. The P-waves and S-waves
for the polarized ultraviolet light to be irradiated can have the
state with more P-waves than S-waves or the state with only
P-waves.
[0082] The alignment apparatus having the above structure
irradiates ultraviolet light from an angle of 45.degree. at an
incline with respect to the surface of the alignment film 16a
(16b). Polymer x1 decreases the pretilt angle under several dozen
mJ/cm.sup.2 of ultraviolet light exposure. Polymer x2 produces no
change in the pretilt angle even when exposed to several J/cm.sup.2
of ultraviolet light. Therefore, the ultraviolet light exposure is
set to 1 J/cm.sup.2.
[0083] The reliable demonstration of the above properties of
polymers x1 and x2 is considered here. A suitable relationship
between the ultraviolet light exposure and the pretilt angle is at
least a 2.degree. change in the pretilt angle for ultraviolet light
exposure no more than 0.5 J/cm.sup.2 for polymer x1, and a change
of no more than 0.5.degree. in the pretilt angle for no more than 1
J/cm.sup.2 ultraviolet light exposure for polymer x2.
[0084] As shown in FIG. 6, when the ultraviolet light was actually
irradiated under these conditions, a stable pretilt angle around
89.degree. could be obtained. Fluctuations in the pretilt angle in
the ultraviolet light exposure range of 1.+-.0.3 J/cm.sup.2 were no
more than 0.1.degree.. Consequently, even if fluctuations arise in
the amount of exposure of ultraviolet light, the desired pretilt
angle is obtained. Next, the liquid crystal is injected between the
pair of transparent glass substrates 11, 12 to form the liquid
crystal layer 13, then the injection port is sealed. After
hardening, various post processes, which do form part of the
claimed invention, are performed to finish the liquid crystal
display device.
[0085] As described above, an alignment film 16a (16b) imparting a
desired pre-tilt may be easily and reliably achieved (without
rubbing).
[0086] A method and apparatus for producing domains in the
alignment films will now be explained with reference to FIG. 7
[0087] The alignment apparatus includes a light source 101 that
irradiates scattered ultraviolet light and an optical mask 102 that
is placed below the light source 101 and is formed with a slit
111.
[0088] The light source 101 is an ultraviolet lamp having the
property of scattering light. For example, a tubular low-pressure
mercury lamp is one version. Its shape is similar to an ordinary
long fluorescent lamp, but the gas component or glass material for
the heavy glass tube differs. The ultraviolet light particularly
near the wavelength of 250 nm is irradiated as scattered light.
[0089] The optical mask 102 is disposed at a constant distance from
the coating of the alignment film 103 or the printed substrate 104,
for example, separated by approximately 50 .mu.m. A slit 111 in the
optical mask 102 is formed to transmit the scattered ultraviolet
light. If the light source 101 is a mercury lamp and scans in the
direction indicated by the arrow in FIG. 7 above the optical mask
102, diffuse light that spreads out centered on the slit 111 is
produced. The diffuse light exposes the alignment film 103, and two
domains that depend on the directions of diffusion of the incline
of the diffuse light are created with the region directly under the
slit 111 as the boundary. Notably, two domains having different
inclines are created by a single ultraviolet light exposure.
[0090] Light source 101 symmetrically irradiates the diffuse
ultraviolet light from an inclined direction with respect to the
surface of the alignment film 103 about the center of symmetry
which is the region directly below the slit 111 of the optical mask
102. Therefore, two domains are automatically created in the
alignment film 103 with the center of symmetry as the boundary. In
this case, the exposure angle changes as the diffuse light moves
away from the center of symmetry to obtain a liquid crystal layer
with superior visual characteristics and a plurality of pretilt
angles. The resulting alignment film has the following properties:
(1) the directions in which the liquid crystal molecules fall in
mutually opposite directions, (2) the alignment in the central
region where the molecules fall is the vertical alignment, and (3)
the magnitude of the surface energy of the alignment film becomes
larger or smaller closer to the slit. Therefore, a liquid crystal
display device provided with this alignment film produces multiple
domains at the specified boundaries in the liquid crystal, and the
surface energy of the alignment film reaches a maximum or a minimum
at the boundaries of the domains and either decreases or increases
when moving away from the boundaries.
[0091] The expected domains are produced without being
significantly affected using the above-described structure even if
the optical mask 102 bends. By manner of illustration, FIG. 8 shows
that the center of symmetry of the irradiating light does not
change even if the optical mask 102 is bent because the original
scattered light falls incident perpendicular to the optical mask
102. However, because the region of the incoming light changes,
this margin must be estimated to design the gap between the optical
mask 2 and the substrate and the width of the slit 111.
[0092] The alignment film 103 is preferably a copolymer of the type
described previously. Specifically, a copolymer of two or more
polymers selected to provide a pretilt angle having a constant
value near 90.degree. when the ultraviolet light exposure exceeds
some level. By using alignment films having this property, the
vertical alignment is maintained directly below the slit 111 and
the pretilt angle of the liquid crystal layer has a stable
distribution from 90.degree. to the constant value in response to
the exposure angle and the amount of exposure of the scattered
light.
[0093] In addition, the preferred alignment film has the
characteristic of starting to change the pretilt angle from an
initial vertical alignment in response to ultraviolet light
exposure, and returning to the vertical alignment by exposing
ultraviolet light again.
[0094] FIG. 9 shows the changes in the pretilt angle accompanying
the ultraviolet light exposure of the alignment film. As the
ultraviolet light exposure increases, the alignment moves from
non-vertical to a vertical alignment. As described above, the
alignment rapidly changes from the initial (non-vertical) state to
a final (vertical) state in response to UV exposure, and thereafter
generally maintains the final (vertical) state regardless of
additional UV irradiation. Notably, fluctuations in UV irradiation
cause only minor changes in alignment.
[0095] In this case, because the alignment does not become the
horizontal alignment even directly below the slit 111, where a lot
of ultraviolet light is irradiated, the alignments do not become
disordered. It should be appreciated that the use of a conventional
film would result in horizontal alignment below slit 111 where a
great deal of ultraviolet light is exposed, resulting in a region
with poor alignment that emits white light results even in the
black display state. In contrast, using the alignment film of the
present invention, the alignments are continuous even in regions
such as below slit 111, and poor alignments are suppressed.
[0096] A second embodiment of the present invention will now be
explained with reference to FIGS. 10A and 10B.
[0097] As shown in FIG. 10A, the alignment of the liquid crystal
layer 112 of the second embodiment is controlled to be in the same
direction as alignment control by the electric field leaking from
the gate electrodes 113. Consequently, the alignments near the gate
electrodes 115 change continuously and disclinations do not
develop. However, when the tilt of the liquid crystal in FIG. 10A
is reversed, disclinations develop near region 114a. See, FIG. 10B.
In contrast, according to in this embodiment, the alignment is
controlled over the entire display electrode surface because
photo-alignment is used. Consequently, response is fast in this
embodiment, and disclinations do not occur.
[0098] In this display shown in FIGS. 10A and 10B, the inclination
of the side surface of rib-shaped part 116 is used to control the
alignment of the liquid crystal. If only the rib-shaped part 116 is
used, the gap with an adjacent rib-shaped part 116 must be
narrower. For example, a gap around 30 .mu.m is preferred. In this
case, however, the rib-shaped parts are often present in the
display pixels.
[0099] In this embodiment, the gaps between the rib-shaped parts
can be widened because they in combination with the
photo-alignment. During photo-alignment, the rib-shaped parts do
not necessarily have to have an active alignment control force.
Alignment by photo-alignment provides the possibility of not
determining with certainty the position in the center part shown in
FIG. 10A. For example, if the width of the slit in the optical mask
is about 20 .mu.m, the center of the domain is believed to be
difficult to reliably bring to the center of the slit. The
positions of the divisions in this domain are reliably set by
forming the rib and the rib-shaped part plays a major role in this
embodiment.
[0100] As described above, the alignment film for photo-alignment
is preferably a vertically or horizontally aligned polyimide,
polyamic acid, or crosslinked resin film (for example, polyvinyl
cinnamate). As will be appreciated by one of ordinary skill in the
art, the materials are not limited to those listed above. Moreover,
the alignment need not be limited to vertical and horizontal
alignments.
[0101] According to a preferred embodiment, the structure includes
vertically aligned polyimide. Specifically, the alignment of the
polyimide is preferably vertical in an initial state. Moreover, the
liquid crystal provided between the alignment films preferably have
negative dielectric anisotropy, particularly a fluorine liquid
crystal. In addition, the material of the rib-shaped part is a
positive photoresist.
[0102] The liquid crystal panel structure shown in FIG. 10A
includes a rib-shaped part 116 in addition to the above-described
alignment film. The rib-shaped part 16 assists in producing the two
domains. As a basic structure, this idea may also applied to
producing four domains. The liquid crystal molecules in the liquid
crystal layer 114 are set to tilt from the upper and lower gate
electrodes 113 of the pixel electrode 118 towards the center of the
pixel, or (and) the liquid crystal molecules are set to tilt from
the left and right data electrodes 115 of the pixel electrode 118
towards the center of the pixel.
[0103] A slit 111 (not illustrated in FIG. 10A, see, FIG. 11) in
the optical mask 102 on the TFT substrate 104a side is provided at
the center of the pixel and ultraviolet light is irradiated.
Similarly, ultraviolet light is irradiated at an incline on the
opposing CP side substrate 104b. The resin rib-shaped part 116 can
be provided on the TFT substrate 104a and/or the CF substrate 104b
to assist in controlling the alignment direction.
[0104] FIGS. 11A and 11B depict the light source used in the
alignment process of the present invention. FIG. 11A is a
cross-sectional view along the lengthwise direction of the lamp,
and FIG. 11B is a cross-sectional view along the widthwise
direction of the lamp.
[0105] The lamp 121 is preferably low-pressure mercury lamp
manufactured by Ushio Denki Co., Ltd.s shown in FIG. 11B, a
shielding plate 122 is disposed between the tubular ultraviolet
lamp 121 and the exposure target surface of the alignment film 103
to prevent the light from directly reaching the exposure target. A
so-called cold mirror 123 that does not reflect infrared light is
disposed at the back surface.
[0106] The lamp structure shown in FIG. 11A, irradiates ultraviolet
light perpendicular to the optical mask 102 in the widthwise
direction of the lamp 121. The slit in the optical mask 2 and the
lamp 121 are arranged orthogonal to each other. Light from the slit
111 exposes the alignment film 103 at an incline in the form of
leaks in the widthwise direction of the slit 111.
[0107] As shown in FIG. 12, the lamp 121 is caused to scan the slit
111 (while being maintained perpendicular to the slit 111) so as to
uniformly expose the entire alignment film with scattered light. As
will be appreciated by one of ordinary skill in the art, other lamp
structures may be used, without departing from the scope of the
present invention. For example, the installation direction 6f the
lamp 121 may be at 90.degree.. Moreover, it is possible to remove
the shielding plate 122 disposed directly below the lamp 121 to
allow the ultraviolet light directed toward the surface of the
alignment film 103 to be actively used while the scattered light is
directly irradiated from the lamp 121. However, by combining the
shielding plate 122 and the cold mirror 123 of this embodiment,
there is less possibility of light being irradiated in a different
direction than the direction perpendicular to the desired direction
for tilting the liquid crystal molecules, that is the elongated
direction of the slit 111. In addition, alignment is more stable
and reliable.
[0108] When light enters from the slit 111, either polarized light
or non-polarized light is acceptable, but if the alignment film
arranged in the perpendicular direction is used, non-polarized
light can be used. The light irradiation method is proximity
exposure because the light flows in and irradiates. The distance
between the optical mask 102 and the alignment film 103 is
preferably several .mu.m to 100 .mu.m. If outside of this range,
the inflow of light is inadequate, and negative effects such as not
obtaining the alignment and difficulty in specifying the boundaries
of the domains may result.
[0109] The width of the slit 111 in the optical mask 102 is
preferably several .mu.m to around 100 .mu.m. If outside of this
range, the incoming light is similarly inadequate, and negative
effects such as poor alignment and difficulty in specifying the
boundaries of the domains may result. The domains in this
embodiment are described using examples applied to a TFT LCD. FIGS.
13A, 13B and 13C show one example of a TFT LCD having two domains
on the top and bottom alignment films. It should be appreciated
that the lamp structure depicted in FIGS. 11A-12 is used to provide
UV irradiation, and reference to slit 111 is understood to refer to
the slit 111 in FIGS. 11A-12. FIG. 13A is an enlarged view near the
pixel electrode. FIG. 13B is a cross-sectional view when aligning
on the CF substrate side. FIG. 13C is a cross-sectional view when
aligning on the TFT substrate side. In FIG. 13B, the slit 111 is
provided parallel to and close to the gate electrode 113 and
irradiates ultraviolet light on the CF substrate 104b. In FIG. 13C,
the slit 111 is provided at the position that coincides with the Cs
electrode 117 and is parallel to the storage capacitive (Cs)
electrode 117 (gate electrode 113) and irradiates ultraviolet light
on the TFT substrate 104a. In both FIGS. 13A and 13B, the scattered
light is irradiated so that liquid crystal molecules tilt in the
direction from the gate electrodes 113 of the TFT substrate 104a to
the vertical center of the pixel electrode 118 of the CF substrate
104b. In addition, the rib-shaped part 116 may be provided and is
effective when installed parallel to the gate electrode 113 (CS
electrode 117) near the center of the pixel electrode 118 on the CF
substrate 104b side. Alternatively, the rib-shaped part 116 may be
installed parallel to the gate electrode 113 (Cs electrode 117) at
the position nearly coinciding with the gate electrode 113 on the
TFT substrate 104a side.
[0110] FIGS. 14A-14C showing one example of two domains on the left
and right of a TFT LCD. It should be appreciated that the lamp
structure depicted in FIGS. 1A-12 is used to provide UV
irradiation, and reference to slit 111 is understood to refer to
the slit 111 in FIGS. 1A-12. FIG. 14A is an enlarged top view of
the vicinity of a pixel electrode. FIG. 14B is a cross-sectional
view during alignment on the CF substrate side. FIG. 14C is a
cross-sectional view during alignment on the TFT substrate
side.
[0111] The slit 111 for ultraviolet light exposure on the CF
substrate 104a side is positioned parallel to the data electrode
115 and almost coincides with the position of the data electrode
115 and transmits scattered UV light. On the TFT substrate 104b
side, the slit 111 is positioned parallel to the data electrode 115
at the horizontal center of the pixel electrode 118 and transmits
scattered UV light. Therefore, the liquid crystal molecules are
oriented to tilt from the data electrodes 115 on the TFT substrate
104b to the horizontal center of the pixel electrode 118 of the CF
substrate 104a. This coincides with the alignment direction due to
the oblique leaking electric field from the data electrodes 115.
The alignment may further be stabilized by fixing the positions of
the occurrences of disclinations at the alignment boundaries using
the rib-shaped parts 116.
[0112] As best seen in FIG. 14C, the rib-shaped part 116 may be
provided to run vertically along the center of the pixel electrode
118 on the CF substrate 104a side, parallel to the data electrodes
115 at the positions that nearly coincide with the data electrodes
15 on the TFT substrate 104b side.
[0113] FIGS. 15A-16C are schematic drawings showing an example of
four domains on the left, right, top, and bottom in a TFT LCD. FIG.
15A is an enlarged top view in the vicinity of a pixel electrode
having the rib shaped element 116 formed on the TFT side, and a rib
shaped projection 155 formed on the CF substrate side. The solid
arrow 152 indicate the alignment direction of the TFT side, and
dashed arrows 153 indicate the direction of falling on the CS side.
Moreover, arrows 154 indicate the tilt direction when voltage is
applied to the liquid crystals.
[0114] FIG. 15B is a cross-sectional view during alignment along a
data electrode. FIG. 15C is a cross-sectional view during alignment
along a gate electrode. The state of the ultra violet light
irradiating the TFT substrate is generally designated 156. It
should be appreciated that the lamp structure depicted in FIGS.
11A-12 is used to provide UV irradiation, and reference to slit 111
is understood to refer to the slit 111 in FIGS. 11A-12.
[0115] If the CF substrate 104a (FIG. 15B) is placed in the
foreground of the paper, the tilt for any of the liquid crystal
molecules in FIGS. 15A-16C is in the alignment direction in which
the liquid crystal molecules fall from the four corners of the
pixel electrode 118 of the TFT substrate 104b towards the center of
the pixel electrode 118. Four domains are produced on the top,
bottom, left, and right sides of the pixel electrode 118. On
average, the liquid crystal molecules in the top right region are
aligned to fall from the northeast to the southwest. Similarly, the
tilts of the liquid crystal molecules are aligned to fall from the
southeast to the northwest in the lower right, from the southwest
to the northeast in the lower left, and from the northwest to the
southeast in the upper left.
[0116] To make the liquid crystal molecules tilt at a 45.degree.
incline, the orientation on the CF substrate 104a side and the
orientation on the TFT substrate 104b side have true directions at
90.degree. so that the liquid crystal molecules fall towards the
center in these two directions. The principle behind this alignment
direction has been disclosed, for example, in the Digest of
AM-LCD98. If the liquid crystal molecules tilt from the northeast
to the southwest, the two methods considered are (1) a method that
aligns the TFT substrate 104b side to fall towards the south and
the CF substrate 104a side to fall towards the west, and (2) a
method that aligns the TFT substrate 104b side to fall towards the
west and the CF substrate 104a side to fall towards the south.
[0117] FIGS. 15A-15C show the alignment according to method (1). On
the TFT substrate 104b side, the slit 111 in the optical mask for
ultraviolet light exposure is provided close to and parallel to the
Cs electrode 117 and irradiates scattered light (FIG. 15B). On the
CF substrate 104a side, the slit 111 in the optical mask for
ultraviolet light exposure is provided close to and parallel to the
data electrode 115 (FIG. 15A) and irradiates scattered light.
[0118] As shown in FIG. 15C, it is effective to provide a
rib-shaped part 116 on both the TFT substrate 104b and the CF
substrate 104a. On the TFT substrate 104b side, the rib-shaped
parts 116 are formed to be parallel to and close to the data
electrode 115 and the gate electrode 113, respectively. Thus, they
act to assist in creating four domains in the liquid crystal. On
the CF substrate 104a side, the rib-shaped parts 116 are formed in
a shape that extends vertically and horizontally from the center of
the pixel electrode 118. As described earlier, the rib-shaped part
acts to promote establishing the boundaries of the domain
divisions.
[0119] FIGS. 16A-16C show alignment according to method (2), in
which a rib shaped element 116 is formed on both the TFT substrate
104b and CF substrate 104a. The solid arrow 163 indicate the
alignment direction of the TFT side, and dashed arrows 162 indicate
the tilt direction of the liquid crystals on the CF side. Moreover,
arrows 164 indicate the tilt direction when voltage is applied to
the liquid crystals. On the CF substrate 104a side, the slit 111 in
the optical mask for ultraviolet light exposure is provided close
to and parallel to the gate electrode 113 and irradiates scattered
light (FIG. 16B). The state of the ultraviolet light irradiating
the CF substrate side is generally designated 165.
[0120] On the TFT substrate 104b side, the slit 111 in the optical
mask for ultraviolet light exposure is provided parallel to the
data electrode 115 near the horizontal center of the pixel
electrode 118 (FIGS. 16A and 16B). The rib-shaped parts 116 are
formed close to and parallel to the data electrode 115 and the gate
electrode 113, respectively. Notably, the rib-shaped parts 116
assist in creating four domains in the liquid crystal. On the CF
substrate 104a side, the rib-shaped parts 116 are formed in a shape
that extends vertically and horizontally from the center of the
pixel electrode 118. The state of the ultraviolet light irradiating
the CF substrate side is generally designated 165 (FIG. 16C).
[0121] The surface energy of the alignment film in the pixel of the
liquid crystal display device having domains reaches a maximum at a
domain boundary and reaches a minimum at a position separated from
the boundary. The reason is the ultraviolet light exposure differs
in a pixel. The domain boundary is directly below the slit 111, and
the surface energy reaches a maximum because most of the
ultraviolet light irradiates this part. Because only leakage light
irradiates the part separated from the boundary, the absolute
amount of ultraviolet light exposure becomes smaller and the
surface energy does not increase.
[0122] FIGS. 17A-17C shows a structure that suppresses disorder in
the alignment caused by the lateral electric fields from the data
electrodes using the rib-shaped part 116 installed on the CF
substrate side when there are two domains, an upper and a lower
domain, in a TFT LCD. The solid arrow 171 indicates the alignment
control direction, and arrow 162 indicates the tilt direction of
the liquid crystals.
[0123] FIG. 17A is an enlarged top view in the vicinity of a pixel
electrode. FIG. 17B is a cross-sectional view during alignment
along the data electrode (along line segment 17B-17B). FIG. 17C is
a cross-sectional view during alignment along the gate electrode
(along line segment 17C-17C in FIG. 17A).
[0124] As shown in FIG. 17A, on the CF substrate 104a side, the
rib-shaped parts 116 are formed horizontally in the center of the
pixel electrode 118 and parallel to the data electrodes 115 in the
parts opposite the data electrodes 115. The effect of the
rib-shaped part 116 installed parallel to this data electrode 115
is explained with reference to FIG. 17C. The liquid crystal
molecules near the data electrode 115 have a tendency to tilt
towards the center of the pixel due to the electric field from the
data electrode 115. As shown by dashed portion 174 in FIG. 17C, the
rib-shaped part 116 installed on the opposing CF substrate 104a
tilt the liquid crystal molecules in the direction away from the
pixel electrode II 8. These effects cancel each other, and the
liquid crystal molecules do not fall towards the center of the
pixel but tilt uniformly in the vertical direction.
[0125] As shown in FIG. 18, ends 116a of a rib-shaped part 116
opposite a gate electrode 115 are formed to be opposite to and
partially overlap the ends of the pixel electrodes 118 of the TFT
substrate 104b. FIG. 19 shows the relationship between the width of
this overlapping part 116a and the width of a poor alignment at the
end of a pixel electrode 118. In this case, by making the width of
the overlapping part 116a at least 1 .mu.m and more preferably 2
.mu.m, the development of poor alignments can be suppressed. When
the overlapping part 116a is actually formed, the mismatch is
maintained around 3 .mu.m and the width of the overlapping part
116a of at least 1 .mu.m is reliably obtained. If the upper limit
of the overlapping part 116a is set to 5 .mu.m in order to not harm
the function of the pixel electrode, the width is designed to be 1
.mu.m (lower limit of the required width)+3 .mu.m (mismatch) to 5
.mu.m (upper limit of the required width)+3 .mu.m (mismatch)=from
at least 4 .mu.m to no more than 8 .mu.m or from at least 5 .mu.m
to no more than 8 .mu.m. Therefore, the generation of poor
alignments can be adequately prevented.
[0126] The structure forming the rib-shaped part 116 on the CF
substrate 104a or the TFT substrate 104b has been described.
However, similar results can be obtained without the rib-shaped
parts 116 by removing slit shapes that are not part of the
electrode in the pixel electrode 118. Notably, FIG. 20A corresponds
to FIG. 13A when the slit-shaped notch 131 was formed parallel to
the Cs electrode 117 (gate electrode 113) of the pixel electrode
118 and at the position coinciding with the Cs electrode 117. FIG.
20B corresponds to FIG. 14A when the slit-shaped notch 131 was
formed in the pixel electrode 118 parallel to the data electrode
115 and at the position corresponding to the center of the pixel
electrode 118. FIG. 20C corresponds to FIG. 15A when the
slit-shaped notch 131 shaped as a cross was formed in the pixel
electrode 118.
[0127] FIG. 21 is a characteristic plot showing the test results,
about the width of the slit 111 in the optical mask with an
excellent alignment state and the optimum value of the distance
(distance A) between the optical mask and the substrate. Excellent
alignment can be obtained for a slit width from 3 .mu.m to 100
.mu.m (Region A) and a distance between the mask and the substrate
from 3 .mu.m to 100 .mu.m. Furthermore, the preferred distance
between the optical mask and the substrate is from 50 .mu.m to 100
.mu.m (Region 21B). The slit width and the distance A are nearly
equal. Excellent alignment can be obtained when the slit width is
set in the range from about the same value as distance A to about
{fraction (1/20)}th of distance A.
[0128] According to this embodiment as described above, alignment
using ultraviolet light is accurately performed in the minimum
number of processes. A vertically aligned liquid crystal display
device is implemented few disclinations in two or four domains. The
result is the ability to produce a superior bright screen when
using the TN mode. Furthermore, the response speed can provide
high-speed responsiveness that is similar to or better than in a
so-called MVA liquid crystal display device provided with many
rib-shaped parts.
[0129] FIG. 22 is a cross-sectional view of the main structures in
the alignment apparatus of another embodiment.
[0130] In this embodiment, the alignment film is a copolymer of two
polymers. Preferably, the alignment of one polymer changes from the
initial vertical alignment in response to ultraviolet light
exposure and assumes a constant value of approximately 90.degree.
when the ultraviolet light exposure exceeds some level. The other
polymer has the property of starting to change the pretilt angles
from the vertical alignment in response to ultraviolet light
exposure, and returning again to the vertical alignment when
exposed again to ultraviolet light.
[0131] Quartz glass which is transparent in the short wavelength
region (for example, 254 nm) of the ultraviolet light is preferably
used for the optical mask 201. A mask pattern of metallic chromium
is formed on one side of the optical mask 201. The mask pattern
provides a stripe-shaped slit 211 in the metallic chromium. The
stripe-shaped slits 211 are lined up at the same pitch as the pitch
of the pixels having domains. As one example, if the pixel pitch is
200 .mu.m, the width of a slit 211 is 10 m, and the width of the
metallic chromium pattern becomes 190 .mu.m from one slit 211 to
the adjacent slit 211.
[0132] The scattering mechanism 221 that scatters parallel light is
formed on the surface of the optical mask 201 on the light source
side. Scattering of the incident light is generally shown by the
dashed circle 22a. The scattering mechanism 221 may be formed, for
example, by sandblasting the surface of the optical mask 201 on the
light source side.
[0133] The alignment film 203 is irradiated with ultraviolet light
on the glass substrate 202. The optical mask 201 is placed so that
the position of the stripe-shaped slot 211 almost coincides with
the horizontal center position of the pixel and parallel to the
data electrode.
[0134] The optical mask 201 is placed in the direction parallel to
the data electrode with the position of the stripe-shaped slit 211
at the position of the data electrode of the TFT substrate 204B in
the opposing substrate 204A when ultraviolet light irradiates the
opposing substrate (CF substrate) 204A side.
[0135] After the optical mask 201 is disposed as described above,
parallel ultraviolet light is irradiated perpendicular to the
surface of the optical mask 201 on the light source side. The
irradiated ultraviolet light is scattered by the ground glass part
and is split into two directions with the center as the boundary
from the slit 211 and irradiated as illustrated.
[0136] When the TFT substrate 204B is affixed to the opposing
substrate 204A, the positions of corresponding slits become the
centers of the pitch lining up the slits. Therefore, the region
inclined in the direction perpendicular to the slit can be between
the slit on the TFT substrate 204B side and the slit on the
opposite substrate 204A side, that is within a 90 .mu.m width. The
domains in two orientations can be produced in one pixel by giving
the orientations mutually opposite directions with the position of
the slit in the center of the pixel as the boundary.
[0137] FIG. 23 is a cross-sectional view showing another example of
this embodiment. The optical mask 201 is disposed as described
above and irradiates parallel ultraviolet light perpendicular to
the surface of the optical mask 201 on the light source side.
Irradiated ultraviolet light is scattered in two directions by the
slit 211, and exposes the alignment film 203.
[0138] If the TFT substrate 204B is affixed to the opposing
substrate 204A, the positions of their mutual slits are at the
centers of the pitch lining up the slits. Thus, the region inclined
in the direction perpendicular to the slit can be between the slit
on the TFT substrate 204B side and the slit on the opposing
substrate 204A side, that is within a 90 .mu.m width Domains in two
directions can be produced in one pixel by giving the orientations
mutually opposite directions with the position of the slit in the
center of the pixel as the boundary.
[0139] FIG. 24 is a cross-sectional view showing another example of
this embodiment.
[0140] A prism 212 generally shaped like an isosceles triangular
with the width of the slit opening as its base is disposed in the
opening of the slit 211 in the optical mask 201 described
above.
[0141] Similar to the above description, the position of the
optical mask 201 is perpendicular to the surface of the optical
mask 201 on the light source side and irradiates parallel
ultraviolet light. The irradiated ultraviolet light is reflected
and refracted by the prism 212 and is split into parallel light in
two directions when the scattered light is emitted from the prism
112 as shown in the drawing and exposes the alignment film 203.
[0142] If the TFT substrate 204B is affixed to the opposing
substrate 204A, the positions of their mutual slits are at the
centers of the pitch lining up the slits. Therefore, the region
inclined in the direction perpendicular to the slit can be between
the slit on the TFT substrate 204B side and the slit on the
opposing substrate 204A side, that is within a 90 .mu.m width.
Domains in two directions can be produced in one pixel by producing
orientations having mutually opposite directions with the position
of the slit in the center of the pixel as the boundary.
[0143] Even if the ultraviolet light that exposes the surface of
the optical mask 201 on the light source side is scattered light in
this embodiment, similar to when parallel light is irradiated, the
ultraviolet light exposing the alignment film 203 can be split in
two directions to produce the desired domains. This method
disperses the ultraviolet light that exposes the alignment film 203
directly below the slit, and the ultraviolet light exposure on this
part no longer becomes excessive. In addition, domains can be
produced by one exposure on one substrate.
[0144] As described above, even if the ultraviolet light on the
optical mask 201 is parallel light, similar effects can be obtained
when scattered ultraviolet light irradiates the optical mask 201 by
scattering, or reflection or refraction by the ground glass part of
the optical mask 201 or the prism 212. This shows that an
ultraviolet light exposure device that emits parallel light as the
light source can be used.
[0145] Because the ultraviolet light can be dispersed in the part
of the alignment film 203 in the opening of the slit 211, excess
exposure light in this part can be prevented. And void areas caused
by a lower tilt in this part and flow-induced orientations can be
prevented.
[0146] Embodiment 4
[0147] Yet another embodiment will be explained with reference to
FIGS. 25A-26.
[0148] Similar to the second embodiment, the alignment film in this
embodiment is composed of two polymers. Preferably, alignment of
one polymer changes from an initial vertical alignment in response
to ultraviolet light exposure, and assumes a constant value near
90.degree. when a predetermined level of ultraviolet light exposure
is exceeded. The alignment of the other polymer starts to change
from the vertical alignment in response to ultraviolet light
exposure, but returns to the vertical alignment when exposed again
to ultraviolet light.
[0149] FIG. 25A is a cross-sectional view of the main structures in
the alignment apparatus in this embodiment. FIG. 25B is a
cross-sectional view of the main structures in the liquid crystal
display device implementing this alignment method. In FIGS. 25A and
25B, the liquid crystal molecule is generally designated 251.
[0150] Quartz glass that has the property of transmitting the short
wavelength region (for example, 254 nm) of ultraviolet light is the
material of the optical mask 301. As shown in FIG. 26, a mask
pattern made of metallic chromium is formed on one surface of the
optical mask 301. The mask pattern is provided with a stripe-shaped
alignment control slit 211 in the metallic chromium. The alignment
control slit 211 orients the liquid crystal molecules in the
desired direction, and is lined up at the same pitch as that of the
pixels having domains. As an example, if the pixel pitch is 200
.mu.m, then the width of the slit 211 is 10 .mu.m and the width of
the metallic chromium mask pattern from a slit to an adjacent slit
211 becomes 190 .mu.m.
[0151] Furthermore, an alignment correction slit 311 is provided in
the same optical mask 311. This slit must be finer than the slit
that orients the liquid crystal molecules in the desired direction
and must be disposed in a mutually perpendicular direction. The
pixel pitch is about one-third at 70 .mu.m, and the width of the
slit 311 is about 1 .mu.m.
[0152] Next, ultraviolet light irradiates the alignment film 303 on
the glass substrate 304. As shown in FIG. 27, the optical mask 301
is placed so that the position of the alignment control slit 211
almost coincides with the center position horizontally of the pixel
and is perpendicular to the data electrode 315 when ultraviolet
light irradiates the TFT substrate 304b side. The positions of the
alignment correction slits 311 are parallel to the data electrodes
315 and centered between adjacent pixel electrodes 318, that is
they are at the centers of the data electrodes 315.
[0153] The optical mask 301 only needs the alignment control slit
211 when ultraviolet light irradiates the opposite substrate 304a
side. The position of this slit 211 is the position of the gate
electrode 313 of the TFT substrate 304b in the opposite substrate
304a and is disposed in the direction perpendicular to the data
electrode 315.
[0154] After the optical mask 301 is disposed as described above,
scattered ultraviolet light is irradiated perpendicular to the
surface of the optical mask 301 on the light source side. As shown
in FIG. 25A, the irradiated ultraviolet light is split into two
directions by the slit 311.
[0155] The ultraviolet light irradiates through the slit 311, and
spreads out in a fan shape centered on the slit 311. As shown in
FIG. 25, the alignment control force that tilts the liquid crystal
molecules in some direction of the slit 311 is applied to the
alignment film 303. Thus, the directions of the force that orients
the liquid crystal molecules by the electric field at the ends of
the pixel electrode 318 and the alignment control force of the
alignment film 303 oppose each other in order to cancel the forces
that orient the liquid crystals, tilting the liquid crystal
molecules perpendicular to the direction of the desired tilts of
the liquid crystal molecules can be prevented.
[0156] The brightness changes in the image display device (device
A) that implements the alignment correction in addition to the
alignment control of two divisions by the method of this embodiment
is examined based on a comparison with the image display device
(device B) that implements only alignment control for two
divisions. In device B (FIG. 28A), the tilt of the liquid crystal
molecules by the electric fields at the ends of the pixel
electrodes 318 is generally designated 281. The desired orientation
of the liquid crystal molecules is generally designated 282.
Moreover, regions where brightness reductions occur at the ends of
the black matrix 321 are generally designated 281 in FIG. 28B.
[0157] In contrast, the tilts of the liquid crystal molecules are
eliminated at the ends of the pixel electrodes 318 in FIG. 29A
(Device A). Consequently, an excellent image is obtained without
the problem of lower brightness regions at the ends of the black
matrix 321.
[0158] If the TFT substrate 304b is affixed to the opposing
substrate 304a, the positions of their mutual slits are at the
centers of the pitch lining up the slits. The region that inclines
in the direction perpendicular to the slit can be between the slit
on the TFT substrate 304b side and the slit on the opposing
substrate 304a side, that is within a 90 .mu.m width. Domains in
two directions can be produced in one pixel by producing
orientations having mutually opposite directions with the position
of the slit in the center of the pixel electrode 318 as the
boundary.
[0159] FIG. 30 is a top view of the optical mask in another example
of this embodiment. Although similar to the above description up to
forming the slit in the optical mask, the scattering mechanism for
the incident ultraviolet light is provided on the surface on the
side opposite the alignment film 303 of the slit 211 that orients
the liquid crystal molecules in the desired direction. As a
specific example of the scattering mechanism, a groove with a
depression-shaped cross-section is provided by sandblasting only
the opening of the slit 211, forming the ground glass part 211a, or
irradiating with laser pulses.
[0160] The irradiated ultraviolet light is scattered by the ground
glass part 211a and has its irradiation width narrowed by the
alignment correction slit 211, so it does not negatively affect the
essential orientations of the liquid crystal molecules.
[0161] FIG. 31 is a top view of the optical mask in another example
of this embodiment.
[0162] Only the alignment correction slit 311 in the optical mask
301 has a prescribed height, for example, it is formed to be about
50 .mu.m. Therefore, the gap between the optical mask 301 and
alignment film 304, which are opposite each other, becomes narrower
to around 50 .mu.m only in the alignment correction slit 311 and
can narrow the width of the scattered ultraviolet light incident on
only this part. Thus, the essential orientations of the liquid
crystal molecules are not negatively affected.
[0163] FIGS. 32A and 32B are schematic diagrams of the light source
according to another used embodiment. FIG. 33 is a top view showing
the relationship between the scattering of the light source and the
slit in the optical mask.
[0164] A method for changing the direction of the tubular light
source 302 is adopted. The lengthwise direction of the light source
302 (FIG. 32B) has higher scattering than the widthwise direction
of the light source 302 (FIG. 32A). This characteristic is used in
this embodiment.
[0165] The lengthwise direction of the light source 302 for
ultraviolet light is positioned to be parallel to the direction of
the alignment correction slit 311 in the optical mask 301. Thus,
the ultraviolet light passing through the alignment correction slit
311 has a narrow scattering width and is positioned perpendicular
to the lengthwise direction of the light source 302. The
ultraviolet light that passed through the slit 211 that orients the
liquid crystal molecules in the desired orientations has a wider
scattering width. Therefore, there are no negative effects on the
essential orientations of the liquid crystal molecules.
[0166] According to this embodiment as described above, because the
directions of the alignment control force at the end of the pixel
electrode 318 and the force to orient due to the electric field
cancel each other, tilting the liquid crystal molecules in the
direction perpendicular to the desired tilt direction for the
liquid crystal molecules can be prevented. Therefore, the
occurrence of disclinations is prevented, and a decrease in the
brightness at the ends of the pixels can be suppressed.
[0167] Because new rib-shaped parts do not have to be formed, the
process that controls the alignment can be simplified by forming
the alignment correction slit 211 and the alignment control slit
311 in the optical mask 301.
[0168] A further embodiment of a liquid crystal display device
featuring a pixel electrode is described with reference to FIG.
34.
[0169] The alignment film in this embodiment is composed of two
polymers. Preferably, the pretilt angle of one polymer changes from
an initial vertical alignment in response to ultraviolet light
exposure and assumes a constant value near 90.degree. when some
level of ultraviolet light exposure is exceeded. The pretilt angle
of the other polymer starts changing from the vertical alignment in
response to ultraviolet light exposure, but resumes vertical
alignment when exposed again to ultraviolet light.
[0170] To prevent poor orientation caused by the lateral electric
field from the data electrode 415, a slit 411 is disposed near the
data electrodes 415 of the pixel electrode 418. The slit 411
extends in the direction parallel to the data electrode 415
(direction orthogonal to the gate electrode 413). An effective
width for this slit 411 falls in the range from 2 .mu.m to 5 .mu.m.
In particular, a 3 .mu.m width for the slit was confirmed as the
most effective size for suppressing poor orientation.
[0171] The provision of a fine slit 411 in the pixel electrodes 418
has the property of making the liquid crystal molecules fall in the
direction parallel to this slit 411. In this embodiment, this
action is jointly used with the photo-alignment. Essentially, if
there is liquid crystal in the gaps between the pixel electrodes,
the liquid crystal tilts in the direction away from the gap because
the electric field becomes oblique (see FIG. 35A). However, if a
fine slit, for example, a 3-.mu.m wide slit 411, is provided, the
liquid crystal molecules will tilt on both sides of a slit 411 and
the destinations disappear. Consequently, the liquid crystal
molecules are oriented to tilt towards the slit direction (see FIG.
35B). If a slit 411 is provided as shown in FIG. 34, the tilts of
the liquid crystal molecules similarly lose their destinations
because of this slit (FIG. 35B). Consequently, the liquid crystal
molecules will tilt in the direction parallel to the slit 411, and
poor orientation caused by the data electrode is suppressed.
[0172] FIG. 36 is a schematic showing another example of this
embodiment. FIG. 36A is a top view of the vicinity of a pixel
electrode. FIG. 36B is a cross-sectional view.
[0173] A plurality of slits 411 is provided over the entire pixel
electrode 418 area. Therefore, the stability of the orientation
becomes more reliable. It is important for these slits 411 to be
connected by the connector 421 in the center of the pixel electrode
418. If the relationship between the connector 421 and the slits
411 is examined, the electric field at the connector 421 is as
shown in FIG. 34B and expands in a fan shape from the connector
421. This effect tilts the liquid crystal molecules in a more
preferred direction.
[0174] According to this embodiment as described above, a liquid
crystal display device with no poor orientations and a wide viewing
angle can be implemented.
[0175] While various embodiments of the present invention have been
shown and described, it should be understood that other
modifications, substitutions and alternatives are apparent to one
of ordinary skill in the art. Such modifications, substitutions and
alternatives can be made without departing from the spirit and
scope of the invention, which should be determined from the
appended claims.
[0176] Various features of the invention are set forth in the
appended claims.
* * * * *