U.S. patent application number 09/804141 was filed with the patent office on 2001-09-13 for vertical alignment mode liquid crystal display device and method for manufacturing the same.
Invention is credited to Mizushima, Shigeaki, Watanabe, Noriko.
Application Number | 20010020993 09/804141 |
Document ID | / |
Family ID | 26589163 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010020993 |
Kind Code |
A1 |
Watanabe, Noriko ; et
al. |
September 13, 2001 |
Vertical alignment mode liquid crystal display device and method
for manufacturing the same
Abstract
At least one of alignment films in the liquid crystal display
device has a first alignment regulation region provided within each
of a plurality of picture-element regions for aligning liquid
crystal molecules of a liquid crystal layer approximately
vertically, and a second alignment regulation region provided
outside the plurality of picture-element regions for aligning the
liquid crystal molecules of the liquid crystal layer in a single
azimuth direction. When a voltage is applied to the first alignment
regulation region having vertically aligned liquid crystal
molecules, these vertically aligned liquid crystal molecules are
tilted in the same direction as that of the liquid crystal
molecules regulated by the alignment film of the second alignment
regulation region. Thus, even in a turned-on state of the vertical
alignment liquid crystal display device, uniform alignment is
obtained across the entire display plane, so that high-quality
display is realized.
Inventors: |
Watanabe, Noriko; (Nara-shi,
JP) ; Mizushima, Shigeaki; (Ikoma-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
1100 North Glebe Rd., 8th Floor
Arlington
VA
22201-4714
US
|
Family ID: |
26589163 |
Appl. No.: |
09/804141 |
Filed: |
March 13, 2001 |
Current U.S.
Class: |
349/130 ;
349/129 |
Current CPC
Class: |
G02F 1/133753 20130101;
G02F 1/133761 20210101; G02F 1/133738 20210101; G02F 1/1393
20130101; G02F 1/133742 20210101 |
Class at
Publication: |
349/130 ;
349/129 |
International
Class: |
G02F 001/137 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2000 |
JP |
2000-098056 |
Jan 29, 2001 |
JP |
2001-019729 |
Claims
What is claimed is:
1. A liquid crystal display device, comprising: a pair of
substrates; a liquid crystal layer provided between the pair of
substrates; an electrode for applying a voltage to the liquid
crystal layer; and a pair of alignment films formed on respective
surfaces of the pair of substrates which face the liquid crystal
layer, the liquid crystal display device having a plurality of
picture-element regions for providing display, wherein at least one
of the pair of alignment films has a first alignment regulation
region provided within each of the plurality of picture-element
regions for aligning liquid crystal molecules of the liquid crystal
layer approximately vertically, and a second alignment regulation
region provided outside the plurality of picture-element regions
for aligning the liquid crystal molecules of the liquid crystal
layer in a single azimuth direction.
2. The liquid crystal display device according to claim 1, wherein
the liquid crystal molecules in the first alignment regulation
region has a tilt angle in a range of 88.degree. to 90.degree. with
respect to a surface of the at least one alignment film, and the
liquid crystal molecules in the second alignment regulation region
has a tilt angle in a range of 0.degree. to 87.degree. with respect
to the surface of the at least one alignment film.
3. The liquid crystal display device according to claim 1, wherein
the at least one alignment film further has the second alignment
regulation region within each of the plurality of picture-element
regions.
4. The liquid crystal display device according to claim 1, wherein
the second alignment regulation region is arranged such that a
distance from any point within the first alignment regulation
region to the second alignment regulation region is 50 .mu.m or
less.
5. The liquid crystal display device according to claim 1, wherein
the second alignment regulation region is arranged such that a
distance to an adjacent second alignment regulation region with a
corresponding first alignment regulation region interposed
therebetween is 100 .mu.m or less.
6. The liquid crystal display device according to claim 1, wherein
the at least one alignment film has a plurality of second alignment
regulation regions, and each of the plurality of second alignment
regulation regions defines the same single azimuth direction.
7. The liquid crystal display device according to claim 1, wherein
both of the pair of alignment films have the first and second
alignment regulation regions, and the second alignment regulation
region of one of the alignment films is arranged so as to face the
second alignment regulation region of the other alignment film with
the liquid crystal layer interposed therebetween.
8. A method for manufacturing a liquid crystal display device
including a pair of substrates, a liquid crystal layer provided
between the pair of substrates, an electrode for applying a voltage
to the liquid crystal layer, and a pair of alignment films formed
on respective surfaces of the pair of substrates which face the
liquid crystal layer, the liquid crystal display device having a
plurality of picture-element regions for providing display, wherein
at least one of the pair of alignment films has a first alignment
regulation region provided within each of the plurality of
picture-element regions for aligning liquid crystal molecules of
the liquid crystal layer approximately vertically, and a second
alignment regulation region provided outside the plurality of
picture-element regions for aligning the liquid crystal molecules
of the liquid crystal layer in a single azimuth direction, wherein
the first and second alignment regulation regions are formed by a
process comprising the steps of: forming a vertical alignment film
at the surface of the substrate; selectively radiating actinic rays
to the vertical alignment film so as to apply to the vertical
alignment film a function to align the liquid crystal molecules in
an azimuth direction; and rubbing the vertical alignment film.
9. The method according to claim 8, wherein the actinic rays are
ultraviolet rays.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a liquid crystal display
device (LCD) having excellent display quality and a method for
manufacturing the same. More particularly, the present invention
relates to a vertical alignment mode LCD having high display
quality and a convenient, useful method for manufacturing the
same.
[0002] Currently, the LCDs are used as display devices for various
information processors including personal computers and navigation
systems. The current mainstream is TN (Twisted Nematic) mode LCDs,
one of the horizontal alignment modes.
[0003] In the liquid crystal layer of the TN mode LCDs, liquid
crystal molecules having positive dielectric anisotropy are
provided between a pair of substrates so as to be aligned
approximately horizontally with respect to the substrate surface.
The alignment direction of the liquid crystal molecules at one of
the substrates is twisted by 90.degree. from that of the liquid
crystal molecules at the other substrate. The TN mode LCDs provide
display in so-called normally white mode. More specifically, the TN
mode LCDs provide white display in a turned-off state, and black
display in a turned-on state. However, satisfactory black display
is less likely to be obtained with the TN mode LCDs. The reason for
this is as follows: in the TN mode LCDs, even in a turned-on state
(i.e., when a voltage is applied), the liquid crystal molecules
located close to the substrate are not oriented in parallel with an
electric field (vertically to the substrate) and maintain their
horizontal alignment. Thus, light with its polarization plane
rotated by the birefringence of such horizontally aligned liquid
crystal molecules passes through the liquid crystal panel.
[0004] In recent years, practical applications of vertical
alignment mode LCDs have been studied. The vertical alignment mode
LCDs are the LCDs in which liquid crystal molecules having negative
dielectric anisotropy are aligned vertically to the substrate
surface. The vertical alignment mode LCDs are advantageous over the
TN mode LCDs in that high-quality black display is more easily
obtained and thus high contrast ratio display is more easily
realized. In the vertical alignment mode, almost all liquid crystal
molecules are aligned approximately vertically to the substrate
surface in a turned-off state. Therefore, the liquid crystal layer
does not rotate the polarization plane of light, whereby nearly
perfect black display can be realized.
[0005] However, the vertical alignment mode LCDs have the following
problem.
[0006] In the vertical alignment mode, the liquid crystal molecules
are aligned approximately vertically to the alignment film surface.
Therefore, it is difficult to apply the alignment regulation force
in an azimuth direction to the liquid crystal molecules. As a
result, high-quality white display is less likely to be obtained
when the liquid crystal molecules are oriented horizontally
(vertically to an electric field) by applying a voltage to the
liquid crystal layer. This problem will now be described with
reference to FIGS. 11 and 12.
[0007] FIG. 11 is a plan view of a conventional vertical alignment
LCD 400. FIG. 12 is a cross-sectional view of the LCD 400 in a
turned-on state (i.e., when a voltage is applied). FIG. 12
corresponds to a cross-sectional view taken along line 12A-12A' of
FIG. 11.
[0008] The LCD 400 has a liquid crystal layer 30 between a TFT
(Thin Film Transistor) substrate 10 and a color filter substrate
20. The liquid crystal layer 30 has liquid crystal molecules 32
having negative dielectric anisotropy. The TFT substrate 10 has a
glass substrate 11, gate lines 12 formed thereon, source lines 14,
and picture-element electrodes 18 each connected to a corresponding
source line 14 through a corresponding TFT 16. The color filter
substrate 20 has a glass substrate 21, a color filter layer 27
formed thereon, and a counter electrode 28. Each of the TFT
substrate 10 and the color filter substrate 20 has a vertical
alignment film 42 at its surface facing the liquid crystal layer
30. Note that the hatched regions of the color filter layer 27
represent a black matrix.
[0009] When the LCD 400 is in the driven state, an electric field
(arrow E) is generated between the picture-element electrode 18 and
the gate line 12, as shown in FIG. 12. As a result, the liquid
crystal molecules 32 located near the gate lines 12 are tilted in
the directions shown by arrows A and B according to the intensity
of the electric fields. Similarly, in the cross section taken along
line 12B-12B' of FIG. 11, the liquid crystal molecules 32 located
near the source lines 14 are tilted in response to the electric
field generated between the source line 14 and the picture-element
electrode 18.
[0010] Thus, the liquid crystal molecules 32 located near the gate
lines 12 and source lines 14 tend to be tilted in different
directions, respectively. In other words, if the liquid crystal
molecules 32 are not subjected to alignment regulation in the
azimuth direction (the direction defined within the display plane
or within the plane of the liquid crystal layer), the liquid
crystal molecules 32 located in the corresponding portions tend to
be tilted in response to the electric fields, so that four regions
are produced where the liquid crystal molecules 32 are oriented in
different azimuth directions, respectively. However, these four
regions are unstable and also the effect of the electric field in
each picture-element region is not necessarily uniform. Therefore,
these four regions cannot be formed stably at a desired area ratio
in each picture-element region. Such variation in the area ratio of
the four regions degrades the display quality. This is visually
recognized as unevenness of the display when the LCD is viewed
obliquely.
[0011] An example of the most common, convenient method for
controlling the alignment direction of the liquid crystal molecules
(hereinafter, the alignment direction refers to the azimuth
alignment direction unless otherwise specified) is a rubbing method
in which the alignment film is rubbed to provide a slight tilt
angle in the vertical alignment (the tilt angle as used herein is
an angle from the normal of the alignment film surface, and
indicates displacement from the vertical alignment). In order to
obtain the alignment regulation force exceeding the effect of the
electric field, a tilt angle of about 3.degree. or more is
generally required. However, the vertical alignment film subjected
to the rubbing method does not have enough alignment regulation
force. Therefore, a stable tilt angle is less likely to be obtained
by the rubbing method. In other words, a slight difference in
rubbing conditions results in variation in tilt angle of the liquid
crystal molecules within the display plane, and this variation in
tilt angle is visually recognized as stripe-shaped alignment
defects.
[0012] Other methods for obtaining the alignment regulation force
include a method utilizing an electric field (Japanese Laid-Open
Publication Nos. 6-301036 and 7-230097), a method utilizing the
effect of uneven shape of the surface facing the liquid crystal
layer (IDW '97, p. 159, "A Vertically Aligned LCD Proving
Super-High Image Quality"), and the like. However, none of these
methods are desirable due to insufficient alignment regulation
force, an increased number of manufacturing processes, or the
like.
[0013] Moreover, Japanese Laid-Open Publication No. 7-64092
discloses a method for preventing generation of a disclination line
at the boundary between two or more differently aligned regions
within a single picture-element region of the normally white mode
TN display. More specifically, a vertically aligned region is
formed at the boundary between the differently aligned regions in
order to prevent generation of the disclination line. In this
method, however, alignment of the picture-element region is
partially changed at the vertically aligned region, and the
alignment film in the vertically aligned region does not have force
to regulate the alignment direction of the liquid crystal molecules
and thus does not stabilize the alignment of the liquid crystal
molecules in a single direction.
SUMMARY OF THE INVENTION
[0014] The present invention is made in view of the aforementioned
problems, and it is an object of the present invention to provide a
vertical alignment mode liquid crystal display device having high
display quality without producing unevenness of the display and
alignment defects, and a convenient, useful method for
manufacturing the same.
[0015] The aforementioned object is achieved by the following
liquid crystal display device and method for manufacturing the
same. According to the present invention, a liquid crystal display
device includes a pair of substrates, a liquid crystal layer
provided between the pair of substrates, an electrode for applying
a voltage to the liquid crystal layer, and a pair of alignment
films formed on respective surfaces of the pair of substrates which
face the liquid crystal layer, and has a plurality of
picture-element regions for providing display. At least one of the
pair of alignment films has a first alignment regulation region
provided within each of the plurality of picture-element regions
for aligning liquid crystal molecules of the liquid crystal layer
approximately vertically, and a second alignment regulation region
provided outside the plurality of picture-element regions for
aligning the liquid crystal molecules of the liquid crystal layer
in a single azimuth direction. Thus, the aforementioned object is
achieved.
[0016] The liquid crystal molecules in the first alignment
regulation region may have a tilt angle in a range of 88.degree. to
90.degree. with respect to a surface of the at least one alignment
film, and the liquid crystal molecules in the second alignment
regulation region may have a tilt angle in a range of 0.degree. to
87.degree. with respect to the surface of the at least one
alignment film.
[0017] The at least one alignment film may further have the second
alignment regulation region within each of the plurality of
picture-element regions.
[0018] Preferably, the second alignment regulation region is
arranged such that a distance from any point within the first
alignment regulation region to the second alignment regulation
region is 50 .mu.m or less.
[0019] Preferably, the second alignment regulation region is
arranged such that a distance to an adjacent second alignment
regulation region with a corresponding first alignment regulation
region interposed therebetween is 100 .mu.m or less.
[0020] The at least one alignment film may have a plurality of
second alignment regulation regions, and each of the plurality of
second alignment regulation regions may define the same single
azimuth direction.
[0021] Preferably, both of the pair of alignment films have the
first and second alignment regulation regions, and the second
alignment regulation region of one of the alignment films is
arranged so as to face the second alignment regulation region of
the other alignment film with the liquid crystal layer interposed
therebetween.
[0022] According to the present invention, in a method for
manufacturing a liquid crystal display device including a pair of
substrates, a liquid crystal layer provided between the pair of
substrates, an electrode for applying a voltage to the liquid
crystal layer, and a pair of alignment films formed on respective
surfaces of the pair of substrates which face the liquid crystal
layer, the liquid crystal display device having a plurality of
picture-element regions for providing display, wherein at least one
of the pair of alignment films has a first alignment regulation
region provided within each of the plurality of picture-element
regions for aligning liquid crystal molecules of the liquid crystal
layer approximately vertically, and a second alignment regulation
region provided outside the plurality of picture-element regions
for aligning the liquid crystal molecules of the liquid crystal
layer in a single azimuth direction, wherein the first and second
alignment regulation regions are formed by a process including the
steps of forming a vertical alignment film at the surface of the
substrate, selectively radiating actinic rays to the vertical
alignment film so as to apply to the vertical alignment film a
function to align the liquid crystal molecules in an azimuth
direction, and rubbing the vertical alignment film. Thus, the
aforementioned object is achieved. Preferably, the actinic rays are
ultraviolet rays.
[0023] Hereinafter, functions of the present invention will be
described.
[0024] At least one of alignment films in the liquid crystal
display device of the present invention has a first alignment
regulation region provided within each picture-element region for
aligning the liquid crystal molecules approximately vertically, and
a second alignment regulation region provided outside the
picture-element regions (hereinafter, also referred to as "in a
region other than the picture-element regions") for aligning the
liquid crystal molecules in a single azimuth direction. The liquid
crystal molecules having their alignment direction regulated by the
alignment film of the second alignment regulation region regulate
the alignment direction of the liquid crystal molecules located
near the second alignment regulation region due to the unique
continuous property of the liquid crystal (property like continuous
matter). Accordingly, when a voltage is applied to the first
alignment regulation region having vertically aligned liquid
crystal molecules, these vertically aligned liquid crystal
molecules are tilted in the same direction as that of the liquid
crystal molecules regulated by the alignment film of the second
alignment regulation region. Thus, even in the turned-on state of
the vertical alignment liquid crystal display device, uniform
alignment is obtained across the entire display plane, so that
high-quality display is realized.
[0025] A tilt angle of the liquid crystal molecules with respect to
the alignment film surface in the second alignment regulation
region is smaller than that in the first alignment regulation
region. More specifically, the alignment regulation force is
applied to the liquid crystal molecules such that the tilt angle in
the first alignment regulation region falls within the range of
88.degree. to 90.degree. and the tilt angle in the second alignment
regulation region falls within the range of 0.degree. to
87.degree.. If the tilt angle in the first alignment regulation
region is less than 88.degree., variation in tilt angle is
increased, which may possibly cause non-uniform display, resulting
in degraded display quality. On the other hand, if the tilt angle
in the second alignment regulation region is larger than
87.degree., the force to regulate alignment in a single direction
is reduced, which may possibly make sufficient alignment regulation
impossible.
[0026] The second alignment regulation region may be provided not
only outside the picture-element regions but also within each of
the plurality of picture-element regions. It is preferable to
provide the second alignment regulation region also within each
picture-element region, because this enables the alignment
regulation force applied from the second alignment regulation
region to the liquid crystal molecules in the liquid crystal layer
to be efficiently transmitted to the vertically aligned liquid
crystal molecules in the first alignment regulation region.
[0027] In the case where the second alignment regulation region is
arranged such that the distance from any point within the first
alignment regulation region to the second alignment regulation
region is 50 .mu.m or less, the alignment regulation force of the
alignment film in the second alignment regulation region well
reaches the liquid crystal molecules within the first alignment
regulation region, thereby allowing driving with sufficiently rapid
response. In order to obtain stable alignment and sufficiently
rapid response, it is preferable that the plurality of second
alignment regulation regions define the same alignment direction.
By forming the second alignment regulation region in both of the
pair of alignment films such that the respective second alignment
regulation regions face each other with the liquid crystal layer
interposed therebetween, the alignment regulation force of the
alignment film in the second alignment regulation region can be
applied to the liquid crystal molecules with improved efficiency.
Note that the distance from any point within the first alignment
regulation region to the second alignment regulation region means
the shortest distance from that point within the first alignment
regulation region to the boundary between the first and second
alignment regulation regions.
[0028] The second alignment regulation region of the alignment film
may be formed by exposing the surface of the vertical alignment
film to a chemical solution such as alkali or acid, or by
selectively (partially) radiating actinic rays (hereinafter, also
referred to as energy radiation) such as light, electron beams, ion
beams, or X rays to the vertical alignment film. In particular, in
the case where the second alignment regulation region is formed by
partially radiating light to the alignment film, light, laser light
or the like need only be radiated through a mask onto the vertical
alignment film having the first alignment regulation region.
Therefore, increase in the number of processes can be
minimized.
[0029] Ultraviolet (UV) rays are efficient actinic rays for forming
the second alignment regulation region. According to the
manufacturing method of the present invention, a uniform tilt angle
is applied to the alignment film by a method other than the rubbing
method, that is, by radiating actinic rays such as UV rays. As a
result, the liquid crystal molecules can be stably aligned in the
azimuth direction. Moreover, in the case where these methods are
combined with the rubbing method, the rubbing method is conducted
so as to apply a tilt angle of 88.degree. to 90.degree. to the
vertical alignment film of the first alignment region. Thus, the
azimuth direction defined by the second alignment regulation region
can be made uniform across the whole display plane without causing
any undesirable display as well as alignment defects in the first
alignment regulation regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a plan view schematically showing picture-element
regions of an LCD according to a first embodiment of the present
invention.
[0031] FIG. 2 is a cross-sectional view schematically showing the
picture-element region of the LCD according to the first embodiment
of the present invention.
[0032] FIG. 3 is a schematic diagram showing the step of applying
to a vertical alignment film the alignment regulation force in the
azimuth direction according to a method for manufacturing the LCD
according to the present invention.
[0033] FIG. 4 is a plan view schematically showing the case where a
second alignment regulation region R2 of the first embodiment has a
wave shape.
[0034] FIG. 5 is a plan view schematically showing the case where
the second alignment regulation region R2 of the first embodiment
has a saw-tooth shape.
[0035] FIG. 6 is a plan view schematically showing the case where
the second alignment regulation region R2 of the first embodiment
has a star shape.
[0036] FIG. 7 is a plan view schematically showing picture-element
regions of an LCD according to a second embodiment of the present
invention.
[0037] FIG. 8 is a cross-sectional view schematically showing the
picture-element region of the LCD according to the second
embodiment of the present invention.
[0038] FIG. 9 is a plan view schematically showing picture-element
regions of an LCD according to a third embodiment of the present
invention.
[0039] FIG. 10 is a cross-sectional view schematically showing the
picture-element region of the LCD according to the third embodiment
of the present invention.
[0040] FIG. 11 is a plan view schematically showing picture-element
regions of a conventional vertical alignment LCD.
[0041] FIG. 12 is a cross-sectional view schematically showing the
picture-element region of the LCD of FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Hereinafter, a liquid crystal display device and a method
for manufacturing the same according to embodiments of the present
invention will be described. The present invention is not limited
to the following embodiments.
[0043] (Embodiment 1)
[0044] FIG. 1 schematically shows a planar structure of
picture-element regions of a vertical alignment mode LCD 100
according to the first embodiment. FIG. 2 schematically shows a
cross-sectional structure of the picture-element region of the LCD
100. FIG. 2 corresponds to a cross-sectional view taken along line
2A-2A' of FIG. 1. Both figures show the state when a voltage is not
applied.
[0045] The LCD 100 has a liquid crystal layer 30 between a TFT
substrate 10 and a color filter substrate 20. The liquid crystal
layer 30 has liquid crystal molecules 32 having negative dielectric
anisotropy. The TFT substrate 10 has a glass substrate 11, gate
lines 12 formed thereon, source lines 14, and picture-element
regions 18 each connected to a corresponding source line 14 through
a corresponding TFT 16. The color filter substrate 20 has a glass
substrate 21, a color filter layer 27 formed thereon, and a counter
electrode 28. Each of the TFT substrate 10 and the color filter
substrate 20 has an alignment film 19, 20 at its surface facing the
liquid crystal layer 30. Note that the hatched regions of the color
filter layer 27 represent a black matrix.
[0046] Each of the alignment films 19 and 29 of the LCD 100 has a
first alignment regulation region R1 provided within each
picture-element region for aligning the liquid crystal molecules
32a of the liquid crystal layer 30 approximately vertically, and a
second alignment regulation region R2 provided outside the
picture-element regions for aligning the liquid crystal molecules
32b in a single azimuth direction (arrow HD). In this example, both
alignment films 19 and 29 have the second alignment regulation
region R2 such that the respective second alignment regulation
regions R2 of the alignment films 19 and 29 face each other.
However, the present invention is not limited to this, and at least
one of the alignment films 19 and 29 need only have the second
alignment regulation region R2. In the present embodiment, the
first and second alignment regulation regions R1 and R2 are
arranged such that the boundary B1, B2, B3, B4 between the first
and second alignment regulation regions R1 and R2 matches the
boundary between the picture-element region and the region other
than the picture-element region.
[0047] In the LCD 100, the second alignment regulation region R2 is
also provided in a part of each picture-element region, in addition
to the outside of the picture-element regions. In FIG. 1, the
boundary between the first and second alignment regulation regions
R1 and R2 provided within the picture-element region is denoted by
B5 and B6. It is preferable to provide the second alignment
regulation region R2 also within each picture-element region,
because this enables the alignment regulation force applied from
the second alignment regulation region R2 to the liquid crystal
molecules 32b to be efficiently transmitted to the vertically
aligned liquid crystal molecules 32a in the first alignment
regulation region R1. However, the present invention is not limited
to this.
[0048] For example, in the case where the picture-element region is
small in size, the alignment direction of the liquid crystal
molecules 32 within the picture-element region can be regulated
stably enough only with the second alignment regulation region R2
provided outside the picture-element regions. In order to obtain
sufficiently stable alignment as well as sufficiently rapid
response, it is preferable to arrange the first and second
alignment regulation regions R1 and R2 such that the distance
between adjacent second alignment regulation regions R2 with a
corresponding first alignment regulation region R1 therebetween is
100 .mu.m or less.
[0049] More specifically, referring to FIG. 1, it is preferable to
arrange the first and second alignment regulation regions R1 and R2
such that all of the following distances W1, W2 and W3 is 100 .mu.m
or less: the distance W1 between the boundary B1 at the gate line
12 and the boundary B3 facing the boundary B1 with the first
alignment regulation region R1 therebetween; the distance W2
between the boundary B2 at the source line 14 and the boundary B5
facing the boundary B2 with the first alignment regulation region
R1 therebetween; and the distance W3 between the boundary B4 at the
source line 14 and the boundary B6 facing the boundary B4 with the
first alignment regulation region R1 therebetween. In the case
where the distance W1 between the boundaries B1 and B3 as well as
the distance W4 between the boundaries B2 and B4 are both 100 .mu.m
or less, the alignment direction of the liquid crystal molecules 32
within the picture-element region can be regulated stably enough
only with the second alignment regulation region R2 provided
outside the picture-element regions.
[0050] Note that, in the specification, a region of the LCD
corresponding to a "picture element" (a minimum display unit) is
referred to as a "picture-element region". In color LCDs, R (Red),
B (Blue) and G (Green) picture elements correspond to a single
"pixel". In active-matrix LCDs, a picture-element electrode and a
counter electrode facing the picture-element electrode define a
picture-element region. The present invention is not limited to the
active-matrix LCDs as exemplified in the embodiments. For example,
the present invention may be applied to simple-matrix LCDs. The
simple-matrix LCD has stripe-shaped column electrodes and row
electrodes crossing perpendicular thereto, and each intersection
region of the row and column electrodes defines a picture-element
region. In the strict sense, in the LCDs having a black matrix, a
region corresponding to an opening of the black matrix out of the
region to which a voltage is applied depending on the display state
corresponds to a picture-element region.
[0051] The alignment films 19 and 29 are typically formed from a
vertical alignment film material. The alignment film of the first
alignment regulation regions R1 is a vertical alignment film formed
by a normal method. This vertical alignment film aligns the liquid
crystal molecules 32a at a tilt angle of approximately 90.degree.
with respect to the surface of the film.
[0052] The alignment film of the second alignment regulation
regions R2 is also formed from a vertical alignment film material.
However, the surface of this alignment film is subjected to a
process described below as well as a rubbing process so as to align
the liquid crystal molecules 32b at a given tilt angle in a given
azimuth direction (arrow HD). More specifically, the liquid crystal
molecules 32b are tilted at a tilt angle of 0.degree. to 87.degree.
with respect to the surface of the alignment film 19 (29) so as to
be aligned in a single direction. It is preferable that the
plurality of second alignment regulation regions R2 define the same
alignment direction, and that this alignment direction is typically
the same across the whole display plane (liquid crystal layer).
[0053] Hereinafter, a method for manufacturing the LCD 100 is
described with reference to FIG. 3. Among the constituent elements
of the LCD 100, the elements other than the alignment films 19 and
29 having the second alignment regulation regions R2 are the same
as those of the known LCDs. Therefore, description of the
manufacturing method thereof is omitted.
[0054] As shown in FIG. 3, a substrate 10' (20') (which will later
serve as the TFT substrate 10 and the color filter substrate 20,
respectively) having a picture-element electrode 18 (counter
electrode 28) formed on the glass substrate 11 (21) is prepared. It
should be understood that other elements such as TFTs 16 or color
filter layer 27 are formed on the glass substrate 11 (21).
[0055] A film 19' (29') of a vertical alignment film material is
formed substantially over the whole surface of the substrate 10'
(20). For example, polyimide resin, one of the organic polymer
materials, is used as the vertical alignment film material. This
vertical alignment film 19' (29') has a property to align the
liquid crystal molecules vertically.
[0056] UV rays are radiated through a mask 40 onto the vertical
alignment film 19' (29') formed at the surface of the substrate 10'
(20'). The mask 40 has a light-transmitting portion 40a for
transmitting the UV rays therethrough, and a light-shielding
portion 40b for blocking them. The light-transmitting portion 40a
is provided so as to correspond to the second alignment regulation
regions R2 shown in FIG. 1. Accordingly, the UV rays are radiated
through the mask 40 onto the regions of the vertical alignment film
19' (29') that will later serve as the second alignment regulation
regions R2. The regions irradiated with the UV rays have the
alignment regulation force to align the liquid crystal molecules at
a tilt angle of 0.degree. to 87.degree. with respect to the surface
of the substrates. The tilt angle depends on the UV radiation
amount. The tilt angle of 0.degree. to 87.degree. can be obtained
by the UV radiation of 0.1 J/cm.sup.2 to 30 J/cm.sup.2. Thus, a
tilt angle is applied to the vertical alignment film by the method
other than the rubbing method, that is, by radiation of actinic
rays such as UV rays. As a result, the liquid crystal molecules can
be stably aligned in the azimuth direction. Moreover, the tilt
direction (azimuth direction to which the liquid crystal molecules
are tilted) is defined by rubbing the surface of the vertical
alignment film 19' (29').
[0057] In the present embodiment, the UV rays are radiated onto the
whole region other than the picture-element regions as well as onto
a part of each picture-element region in order to form the second
alignment regulation regions R2 shown in FIG. 1. This UV radiation
step may be conducted at any time after formation of the vertical
alignment film 19' (29'). More specifically, this step may be
conducted right after application of the vertical alignment
material or after pre-baking thereof. Alternatively, this step may
be conducted after baking or rubbing thereof.
[0058] For example, a mask similar to a commonly used photomask may
be used as the mask 40. Instead of the UV rays, other energy
radiation such as visible light, infrared light and X rays may be
used. Laser light having a prescribed wavelength for the alignment
film material may alternatively be used. UV rays having a
wavelength of 400 nm or less are preferable as actinic rays readily
providing high energy for changing the alignment regulation force
of the vertical alignment film. The light having such a wavelength
can be readily obtained with a high-pressure mercury lamp, a
low-pressure mercury lamp, a mercury-xenon lamp, or the like.
[0059] The TFT substrate 10 and the color filter substrate 20 thus
obtained are laminated together such that their respective second
alignment regulation regions face each other. A liquid crystal
material is then introduced therein, whereby the LCD 100 is
obtained.
[0060] The effect of alignment regulation by the second alignment
regulation regions R2 provided in the alignment films 19 and 29 was
observed up to about 50 .mu.m (within the display plane) from the
boundaries B1 to B6 between the first and second alignment
regulation regions R1 and R2. In the present embodiment, the width
of the picture-element region (corresponding to the distance W4 of
FIG. 1) is about 90 .mu.m. Therefore, provision of the second
alignment regulation regions R2 in the regions other than the
picture-element regions is enough to obtain sufficient alignment
regulation force. However, stronger alignment regulation force was
able to be obtained by providing the second alignment regulation
region R2 also within the picture-element regions.
[0061] The arrangement of the second alignment regulation regions
R2 in the regions other than the picture-element regions and within
the picture-element regions may be different from that shown in the
present embodiment. The number of second alignment regulation
regions R2 as well as the shape thereof is selected appropriately
according to the size of the picture-element regions, strength of
the alignment regulation force, and the like. Depending on the size
of the picture-element regions, the second alignment regulation
region R2 may not be formed within the picture-element regions. The
alignment regulation force is increased as the distance between
adjacent second alignment regulation regions R2 with a
corresponding first alignment regulation region R1 therebetween is
reduced. Therefore, in the case where the stronger alignment
regulation force is required, the number of second alignment
regulation regions R2 need only be increased.
[0062] Note that, in FIG. 1, the second alignment regulation region
R2 has a line-shaped stripe. However, the second alignment
regulation region R2 may have a wave shape (see FIG. 4), mountain
shape, or saw-tooth shape (see FIG. 5). The second alignment
regulation region R2 may have such a shape that connects figures of
the same shape together, or may have such a shape that connects
figures of different shapes together. Alternatively, the second
alignment regulation region R2 may have a circular or elliptical
shape, polygonal shape such as triangle or quadrangle, or a shape
having two-dimensional irregularities such as star shape (see FIG.
6). The same effects can be obtained even with such shapes.
[0063] In the region other than the picture-element regions, the
area of the second alignment regulation region R2 is selected
arbitrarily. Within the picture-element region, the area of the
second alignment regulation region R2 is selected so that the total
area of the second alignment regulation region R2 within each
picture-element region is smaller than a half of the area of the
picture-element region. As the area of the second alignment
regulation region R2 is increased, their effect on the
transmittance and display quality of the LCD is increased.
Therefore, it is preferable that the area of the second alignment
regulation region R2 within each picture-element region is as small
as possible. There is no limitation in the regions other than the
picture-element regions.
[0064] The second alignment regulation region R2 is required to
have a width of at least 10 .mu.m. For example, referring to FIG.
1, each of the following widths W5, W6 and W7 must be at least 10
.mu.m: the width W5 of the second alignment regulation region R2
including the region of the gate line 12; the width W6 of the
second alignment regulation region R2 including the region of the
source line 14; and the width W7 of the second alignment regulation
region R2 provided within the first alignment regulation region R1.
If the width of the second alignment regulation region R2 is less
than 10 .mu.m, the alignment regulation force is reduced, making it
difficult to strongly regulate the alignment direction of the first
alignment regulation region R1. Accordingly, the larger width of
the second alignment regulation region R2 is more preferable.
However, as the width of the alignment regulation region R2 is
increased, the amount of light leakage in black display is also
increased. Therefore, an appropriate value must be selected.
[0065] In the present embodiment, the boundary between the first
and second alignment regulation regions R1 and R2 matches the
boundary between the picture-element region and the region other
than the picture-element region. However, the boundary between the
first and second alignment regulation regions R1 and R2 may be
displaced either toward the picture-element region or the region
other than the picture-element region by 10 .mu.m or less.
[0066] In the present embodiment, a mask similar to the photomask
is used as the mask 40. However, gathered light may be directed
onto a prescribed region without using the mask 40. In the present
embodiment, UV rays are radiated to the surface of the vertical
alignment film 19 (29') in order to form the second alignment
regulation regions R2. However, actinic rays (energy radiation)
such as electron beams, ion beams, X rays may alternatively be
radiated thereto.
[0067] In the present embodiment, the second alignment regulation
regions R2 are formed on both substrates 10 and 20 of the LCD such
that the respective second alignment regulation regions R2 face
each other with the liquid crystal layer 30 interposed
therebetween. However, the second alignment regulation regions R2
may be formed on only one of the substrates (10 or 20) so as to
face the first alignment regulation regions R1. Alternatively, the
second alignment regulation regions R2 may be divided between both
substrates. More specifically, a part of the second alignment
regulation regions R2 may be formed on one substrate, and the
remainder may be formed on the other substrate. Stronger alignment
regulation force is obtained when the second alignment regulation
regions R2 are formed on both substrates. However, sufficient
alignment regulation force is obtained even when the second
alignment regulation regions R2 are formed only on one
substrate.
[0068] (Embodiment 2)
[0069] FIG. 7 schematically shows a planar structure of
picture-element regions of a vertical alignment mode LCD 200
according to the second embodiment. FIG. 8 schematically shows a
cross-sectional structure of the picture-element region of the LCD
200. FIG. 8 corresponds to a cross-sectional view taken along line
8A-8A' of FIG. 7. Both figures show the state when a voltage is not
applied. Note that, regarding the LCD 200, description of the
structure substantially the same as that of the LCD 100 of the
first embodiment is omitted.
[0070] The LCD 200 is different from the LCD 100 in arrangement of
the second alignment regulation regions R2. In the LCD 200 as well,
the second alignment regulation regions R2 are provided on both of
the TFT substrate 10 and the color filer substrate 20 such that the
respective second alignment regulation regions R2 face each other
with the liquid crystal layer 30 interposed therebetween. Like the
first embodiment, however, the present invention is not limited to
this.
[0071] Each of the alignment films 19 and 29 of the LCD 200 has an
island-shaped quadrangular second alignment regulation region R2
within each picture-element region. The second alignment regulation
region R2 is not formed in a region where the tilt direction of the
liquid crystal molecules 32 due to the alignment regulation force
of the second alignment regulation region R2 is the same as that of
the liquid crystal molecules 32 due to the electric field generated
between the picture-element electrode 18 and the gate line 12
(i.e., in the vicinity of the lower side of each picture-element
region in FIG. 7). In other words, the alignment regulation force
of the electric field can be used in this region.
[0072] Note that, in FIG. 7, the second alignment regulation region
R2 formed within each picture-element region has a quadrangular
shape. However, the second alignment regulation region R2 may be a
stripe of line shape, wave shape, mountain shape, or saw-tooth
shape. The second alignment regulation region R2 may have such a
shape that connects figures of the same shape together, or may have
such a shape that connects figures of different shapes together.
Alternatively, the second alignment regulation region R2 may have a
circular or elliptical shape, polygonal shape such as triangle or
hexagon, or a shape having two-dimensional irregularities such as
star shape. The same effects can be obtained even with such
shapes.
[0073] Note that, as described in the first embodiment, in the
region other than the picture-element regions, the area of the
second alignment regulation region R2 is selected arbitrarily.
Within the picture-element region, the area of the second alignment
regulation region R2 is selected so that the total area of the
second alignment regulation region R2 within each picture-element
region is smaller than a half of the area of the picture-element
region. As the area of the second alignment regulation region R2 is
increased, their effect on the transmittance and display quality of
the LCD is increased. Therefore, it is preferable that the area of
the second alignment regulation region R2 within each
picture-element region is as small as possible. There is no
limitation in the regions other than the picture-element
regions.
[0074] As in the first embodiment, the second alignment regulation
region R2 is required to have a width of at least 10 .mu.m. For
example, in FIG. 7, the second alignment regulation region R2
provided within the picture-element region is required to have a
width of at least 10 .mu.m. The larger width of the second
alignment regulation region R2 is more preferable. However, as the
width of the second alignment regulation region R2 is increased,
the amount of light leakage in black display is also increased.
Therefore, an appropriate value must be selected.
[0075] The second alignment regulation region R2 can be formed by
the same method as that described in the first embodiment. In the
second embodiment as well, UV radiation is conducted in the range
of 0.1 J/cm.sup.2 to 30 J/cm.sup.2 so that the tilt angle of the
liquid crystal molecules 32b with respect to the surface of the
alignment film 19, 29 falls within the range of 0.degree. to
87.degree. (within the range of 3.degree. to 90.degree. from the
normal direction). The tilt angle of the liquid crystal molecules
32a in the first alignment regulation region R1 is also
approximately 90.degree. as in the first embodiment.
[0076] The effect of alignment regulation by the second alignment
regulation regions R2 provided in the alignment films 19 and 29 was
observed up to about 50 .mu.m (within the display plane) from the
boundary between the first and second alignment regulation regions
R1 and R2. In the present embodiment, stronger alignment regulation
force was able to be obtained by providing the second alignment
regulation region R2 also within the picture-element regions.
[0077] In the present embodiment, the boundary between the first
and second alignment regulation regions R1 and R2 partially matches
the boundary between the picture-element region and the region
other than the picture-element region. However, the boundary
between the first and second alignment regulation regions R1 and R2
may be displaced either toward the picture-element region or the
region other than the picture-element region by 10 .mu.m or less.
Note that, as described in the first embodiment, the arrangement of
the second alignment regulation region R2 is not limited to the
above examples, and various modifications are possible.
[0078] (Embodiment 3)
[0079] FIG. 9 schematically shows a planar structure of
picture-element regions of a vertical alignment mode LCD 300
according to the third embodiment. FIG. 10 schematically shows a
cross-sectional structure of the picture-element region of the LCD
300. FIG. 10 corresponds to a cross-sectional view taken along line
10A-10A' of FIG. 9. Both figures show the state when a voltage is
not applied. Note that, regarding the LCD 300, description of the
structure substantially the same as that of the LCD 100 of the
first embodiment is omitted.
[0080] The LCD 300 is different from the LCD 100 in arrangement of
the second alignment regulation regions R2. In the LCD 300 as well,
the second alignment regulation regions R2 are provided on both of
the TFT substrate 10 and the color filer substrate 20 such that the
respective second alignment regulation regions R2 face each other
with the liquid crystal layer 30 interposed therebetween. Like the
first embodiment, however, the present invention is not limited to
this.
[0081] As in the first embodiment, each of the alignment films 19
and 29 of the LCD 300 has a first alignment regulation region R1
provided within each picture-element region for aligning the liquid
crystal molecules 32a of the liquid crystal layer 30 approximately
vertically, and a second alignment regulation region R2 provided
outside the picture-element regions for aligning the liquid crystal
molecules 32b in a single azimuth direction (arrow HD). In this
embodiment, like the first embodiment, the first and second
alignment regulation regions R1 and R2 are arranged such that the
boundary B1, B2, B3, B4 between the first and second alignment
regulation regions R1 and R2 matches the boundary between the
picture-element region and the region other than the
picture-element region.
[0082] Each of the alignment films 19 and 29 of the LCD 300 has a
line-shaped second alignment regulation region R2 approximately in
the center of each picture-element region. This line-shaped
alignment regulation region R2 is a region connecting the boundary
B2 and the opposing boundary B4. In FIG. 9, the boundary between
the first and second alignment regulation regions R1 and R2
provided within the picture-element region is denoted by B7 and B8.
As in the first embodiment, the second alignment regulation region
R2 is required to have a width of at least 10 .mu.m.
[0083] In the present embodiment, the line-shaped second alignment
regulation region R2 connecting the boundary B2 and the opposing
boundary B4 is provided approximately in the center of each
picture-element region. Therefore, excellent alignment regulation
force was able to be obtained. In other words, even when the
distance W1 between the boundaries B1 and B3 is about 200 .mu.m,
both the distance W8 between the boundary B1 and the opposing
boundary B7 and the distance W9 between the boundary B3 and the
opposing boundary B8 are 100 .mu.m or less. Therefore, the distance
from any point within the first alignment regulation region R1
surrounded by the second alignment regulation region R2 to the
second alignment regulation region R2 is 50 .mu.m or less (within
the display plane). Thus, the alignment regulation force of the
second alignment regulation region R2 well reaches the liquid
crystal molecules within the first alignment regulation region R1,
whereby sufficiently rapid response can be obtained.
[0084] Note that, like the first embodiment, the shape of the
second alignment regulation region R2 formed within the
picture-element region is not limited to the line shape shown in
FIG. 9, but may have another shape. Moreover, regarding the area,
width and arrangement of the second alignment regulation region R2
as well as the method for forming it are the same as those
described in the first embodiment, and various modifications are
also possible.
[0085] According to the present invention, at least one of the
alignment films of the vertical alignment mode LCD has an alignment
regulation region provided within each picture element region for
aligning the liquid crystal molecules approximately vertically, and
an alignment regulation region provided outside the picture-element
regions for aligning the liquid crystal molecules in a single
azimuth direction. As a result, a vertical alignment mode LCD
having uniform, high display quality can be obtained.
[0086] Moreover, according to the present invention, the alignment
regulation region for regulating alignment of the liquid crystal
molecules in the azimuth direction can be formed by merely
selectively applying a relatively simple process to the vertical
alignment film. Therefore, increase in the number of manufacturing
processes is minimized, so that the vertical alignment mode LCD can
be manufactured with improved efficiency over the conventional
examples.
[0087] While the present invention has been described in a
preferred embodiment, it will be apparent to those skilled in the
art that the disclosed invention may be modified in numerous ways
and may assume many embodiments other than that specifically set
out and described above. Accordingly, it is intended by the
appended claims to cover all modifications of the invention that
fall within the true spirit and scope of the invention.
* * * * *