U.S. patent application number 11/686675 was filed with the patent office on 2007-09-20 for liquid crystal display.
Invention is credited to Jang-Kun SONG.
Application Number | 20070216831 11/686675 |
Document ID | / |
Family ID | 19691790 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070216831 |
Kind Code |
A1 |
SONG; Jang-Kun |
September 20, 2007 |
LIQUID CRYSTAL DISPLAY
Abstract
A liquid crystal display includes a first insulating substrate,
thin transistors formed on the first insulating substrate, and
pixel electrodes connected to the thin film transistors each with
an opening pattern. A second insulating substrate faces the first
insulating substrate. A black matrix and color filters are formed
on the second insulating substrate, and a common electrode covers
the black matrix and the color filters. A protrusion pattern is
formed on the common electrode. The protrusion pattern is
pillar-shaped with top and bottom sides. The top and bottom sides
of the protrusion pattern are shaped with a circle, a rectangle, or
a rectangle with curved edges. The protrusion pattern includes a
protrusion having a relatively small thickness, and a protrusion
having a relatively large thickness. The former protrusion is used
for domain partitioning, and the latter protrusion is used as a
spacer. A vertical alignment layer is internally formed on the
substrates, and a liquid crystal is injected in-between the
substrates. Polarizing plates are externally attached to the
substrates, respectively. A bi-axial film and a .lamda./4 plate are
interposed between the respective substrates and the respective
polarizing plates. The bi-axial film and the .lamda./4 plate
transform the linear-polarizing into a circular-polarizing.
Inventors: |
SONG; Jang-Kun; (Seoul,
KR) |
Correspondence
Address: |
F. CHAU & ASSOCIATES, LLC
130 WOODBURY ROAD
WOODBURY
NY
11797
US
|
Family ID: |
19691790 |
Appl. No.: |
11/686675 |
Filed: |
March 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10713427 |
Nov 17, 2003 |
7247411 |
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11686675 |
Mar 15, 2007 |
|
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09969717 |
Oct 4, 2001 |
6678031 |
|
|
10713427 |
Nov 17, 2003 |
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Current U.S.
Class: |
349/106 ;
257/E21.002 |
Current CPC
Class: |
G02F 1/13394 20130101;
G02F 1/133707 20130101; G02F 1/133753 20130101; G02F 1/133757
20210101; G02F 1/1393 20130101; G02F 1/133742 20210101 |
Class at
Publication: |
349/106 ;
257/E21.002 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2000 |
KR |
2000-58288 |
Claims
1. A method for manufacturing a liquid crystal display (LCD),
comprising steps of: forming a black matrix layer on a substrate;
forming a color filter layer on the substrate; forming a conductive
layer on the color filter layer; forming an organic insulating
layer on the conductive layer, the organic insulating layer being
photosensitive; exposing the organic insulating film to a light
beam through a mask having an opaque area, a semitransparent area
and a transparent area on predetermined areas thereof; and
developing the organic insulating layer to form a protrusion and a
spacer taller than the protrusion, wherein the protrusion overlaps
the black matrix layer.
2. The method of claim 1, wherein the spacer is formed at a portion
of the organic insulating layer corresponding to the opaque area
and the protrusion is formed at a portion of the organic insulating
layer corresponding to the semitransparent area.
3. The method of claim 1, wherein the spacer is formed at a portion
of the organic insulating layer corresponding to the transparent
area and the protrusion is formed at a portion of the organic
insulating layer corresponding to the semitransparent area.
4. The method of claim 1, wherein the black matrix is formed
between the substrate and the color filter layer.
5. A method for manufacturing a liquid crystal display (LCD),
comprising steps of: forming a color filter layer on a substrate;
forming a conductive layer on the color filter layer; forming an
organic insulating layer on the conductive layer, the organic
insulating layer being photosensitive; exposing the organic
insulating film to a light beam through a mask having an opaque
area, a semitransparent area and a transparent area on
predetermined areas thereof; and developing the organic insulating
layer to form a protrusion having a width of 3 .mu.m to 15 .mu.m
and a spacer taller than the protrusion and having a width of 5
.mu.m to 40 .mu.m.
6. A method for manufacturing a liquid crystal display (LCD),
comprising steps of: forming a black matrix layer on a substrate
divided into a plurality of pixel regions, the black matrix
comprising a first portion formed around the pixel region and a
second portion formed within the pixel region; forming a color
filter layer on the substrate; forming a conductive layer on the
color filter layer; forming an organic insulating layer on the
conductive layer, the organic insulating layer being
photosensitive, exposing the organic insulating film to a light
beam through a mask having an opaque area, a semitransparent area
and a transparent area on predetermined areas thereof; and
developing the organic insulating layer to form a protrusion and a
spacer taller than the protrusion, wherein the spacer overlaps the
first portion of the black matrix and the protrusion overlaps the
second portion of the black matrix layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 10/713,427 filed Nov. 17, 2003, which is a continuation of U.S.
application Ser. No. 09/969,717 filed Oct. 4, 2001 (now U.S. Pat.
No. 6,678,031), the disclosures, of which are hereby incorporated
by reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a liquid crystal display
and, more particularly, to a liquid crystal display which bears
wide viewing angle.
[0004] (b) Description of the Related Art
[0005] Generally, a liquid crystal display has two substrates with
a plurality of electrodes, a liquid crystal layer sandwiched
between the two substrates, and two polarizing plates externally
attached to the substrates. Voltages are applied to the electrodes
so that the liquid crystal molecules in the liquid crystal layer
are re-oriented to thereby control the light transmission.
[0006] One of the substrates is formed with thin film transistors
for switching the voltages applied to the electrodes, and a
plurality of gate and data lines proceeding in the row and column
directions. The data lines cross over the gate lines while defining
pixel regions. A pixel electrode is formed at each pixel region.
The thin film transistors receive scanning signals from the gate
lines, and picture signals from the data lines. The thin film
transistors control the picture signals pursuant to the scanning
signals, and transmit the controlled picture signals to the pixel
electrodes. The other substrate is formed with color filters
corresponding to the pixel electrodes, and a common electrode at
its entire surface.
[0007] In a vertically aligned (VA) mode liquid crystal display,
the long axes of the liquid crystal molecules are arranged vertical
to the substrates without application of an electric field, and
under the application of voltages, inclined such that they are
disposed to be parallel to the substrates. The liquid crystal
molecules where the long axes thereof are oriented vertical to the
substrates cannot rotate the polarizing direction of the light,
whereas the liquid crystal molecules where the long axes thereof
are oriented parallel to the substrates can rotate the polarizing
direction of the light, assuming that the polarizing axes of the
polarizing plates are arranged vertical to each other. When the
liquid crystal molecules are oriented vertical to the substrates,
the light does not pass the polarizing plates so that the display
screen becomes to be in a dark state. When the liquid crystal
molecules are inclined under the application of voltages, a
predetermined amount of light passes the polarizing plates so that
the display screen becomes to be in a bright state.
[0008] In such a VA mode liquid crystal display, it has been
proposed that opening patterns or organic material-based
protrusions might be formed at the electrodes while forming
multiple pixel domains. With the formation of the multiple pixel
domains, the liquid crystal molecules are uniformly inclined in
four directions, thereby obtaining wide viewing angle.
[0009] Meanwhile, such a protrusion may be used as a spacer. The
height of the protrusion suitable for the domain partitioning may
be established to be about 1.2 .mu.m, but that suitable for the
spacer use should be established to be about 4.0 .mu.m.
Accordingly, in order to directly use the domain partitioning
protrusion as the spacer, the height of the protrusion would be
established to be about 4.0 .mu.m. However, in this case, it
becomes difficult to inject the liquid crystal material in-between
the substrates due to the barrier of the protrusion.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a liquid
crystal display with protrusion patterns which can make the desired
domain partitioning while being used for the spacer purpose.
[0011] It is another object of the present invention to provide a
liquid crystal display which bears enhanced brightness.
[0012] These and other objects may be achieved by a liquid crystal
display where protrusion patterns are formed to be used as a spacer
while making the desired domain partitioning.
[0013] According to one aspect of the present invention, the liquid
crystal display includes a first insulating substrate, and pixel
electrodes formed on the first insulating substrate each with a
plurality of opening patterns. The pixel electrode is partitioned
into a plurality of micro-regions by way of the opening patterns. A
second insulating substrate faces the first insulating substrate. A
common electrode is formed on the second insulating substrate. A
liquid crystal layer is sandwiched between the first and the second
insulating substrates. A plurality of protrusion patterns are
formed on the common electrode. The protrusion patterns are placed
at the micro-regions of the pixel electrode to regulate the
inclining directions of liquid crystal molecules in the liquid
crystal layer. The gap between the first and the second substrates
is constantly maintained by way of the protrusion patterns.
[0014] A thin film transistor is formed on the first insulating
substrate while being electrically connected to the pixel
electrode. A black matrix is interposed between the second
insulating substrate and the common electrode while being
patterned. Color filters are interposed between the second
insulating substrate and the common electrode corresponding to the
pixel electrodes.
[0015] The protrusion pattern is shaped with a pillar where the top
and the bottom sides thereof have a shape of a circle, a rectangle,
or a rectangle with curved edges. The protrusion pattern has a
height of 3.0-4.5 .mu.m.
[0016] The retardation value of the liquid crystal layer is in the
range of 0.25-0.4 .mu.m.
[0017] The light incident upon the liquid crystal layer is
circularly polarized. First and second polarizing plates are
externally attached to the first and the second substrates, and
first and second bi-axial films are interposed between the first
substrate and the first polarizing plate and between the second
substrate and the second polarizing plate, respectively.
[0018] A mono-axial film may be interposed either between the first
polarizing plate and the first bi-axial film, or between the second
polarizing plate and the second bi-axial film.
[0019] The longest axis of the first bi-axial film is perpendicular
to the longest axis of the second bi-axial film. The polarizing
axes of the first and the second polarizing plates are angled with
respect to the longest axes of the first and the second bi-axial
films by 45.degree..
[0020] First and second .lamda./4 plates are interposed between the
first substrate and the first bi-axial film and between the second
substrate and the second bi-axial film, respectively. The slow axes
of the first and the second .lamda./4 plates are perpendicular to
each other. The polarizing axes of the first and the second
polarizing plates are angled with respect to the slow axes of the
first and the second .lamda./4 plates by 45.degree..
[0021] The polarizing axis of the first polarizing plate is
parallel to the longest axis of the first bi-axial film, and the
polarizing axis of the second polarizing plate is parallel to the
longest axis of the second bi-axial film.
[0022] According to another aspect of the present invention, the
liquid crystal display includes a first insulating substrate, and
pixel electrodes formed on the first insulating substrate each with
opening patterns. A second insulating substrate faces the first
insulating substrate. A common electrode is formed on the second
insulating substrate. First and second protrusions are formed on
the common electrode. The first protrusion has a first thickness,
and the second protrusion has a second thickness larger than the
first thickness. A liquid crystal layer is sandwiched between the
first and the second substrates.
[0023] A thin film transistor is formed on the first insulating
substrate while being electrically connected to the pixel
electrode. A black matrix is interposed between the second
substrate and the common electrode while being patterned. Color
filters are interposed between the second substrate and the common
electrode corresponding to the pixel electrodes.
[0024] The first and the second protrusions may be based on a
photosensitive organic insulating film, a photoresist film, or a
silicon-containing insulating film. The first protrusion has a
width of 3-15 .mu.m.
[0025] The second protrusion is pillar-shaped with top and the
bottom sides having a shape of a polygon or a circle. The top and
the bottom sides of the second protrusion have a width of 5-40
.mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] A more complete appreciation of the invention, and many of
the attendant advantages thereof, will be readily apparent as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawings in which like reference symbols indicate the
same or the similar components, wherein:
[0027] FIG. 1 is a plan view of a liquid crystal display according
to a first preferred embodiment of the present invention where a
pixel electrode of a thin film transistor array substrate and a
protrusion pattern of a color filter substrate are illustrated;
[0028] FIG. 2A is a cross sectional view of the liquid crystal
display shown in FIG. 1;
[0029] FIG. 2B illustrates the orientation state of liquid crystal
molecules in the liquid crystal display shown in FIG. 2A under the
application of voltages;
[0030] FIG. 3 illustrates the planar orientation state of the
liquid crystal molecules shown in FIG. 2B;
[0031] FIG. 4 is a plan view of a liquid crystal display according
to a second preferred embodiment of the present invention where a
pixel electrode and a protrusion pattern of a thin film transistor
array substrate are illustrated;
[0032] FIGS. 5A to 5C sequentially illustrate the steps of
fabricating a color filter substrate for the liquid crystal display
shown in FIG. 1 or 4;
[0033] FIG. 6 illustrates occurrence of textures in a usual liquid
crystal display under the application of voltages;
[0034] FIGS. 7 to 9 are exploded views of liquid crystal displays
according to third to fifth preferred embodiment of the present
invention;
[0035] FIG. 10 illustrates occurrence of textures in the liquid
crystal display shown in FIG. 1;
[0036] FIG. 11 is a cross sectional view of a color filter
substrate for a liquid crystal display according to a sixth
preferred embodiment of the present invention;
[0037] FIG. 12A is a plan view of a pixel electrode for the liquid
crystal display shown in FIG. 11;
[0038] FIG. 12B is a plan view of a protrusion pattern formed on a
common electrode corresponding to the pixel electrode shown in FIG.
12A;
[0039] FIG. 12C illustrates the combinatorial state of the pixel
electrode shown in FIG. 12A and the protrusion pattern shown in
FIG. 12B;
[0040] FIGS. 13A to 13C sequentially illustrate the steps of
fabricating the color filter substrate shown in FIG. 11;
[0041] FIGS. 14 and 15 illustrate the processing state of the color
filter substrate shown in FIG. 11 after the coating of an organic
film together with a patterning mask;
[0042] FIG. 16 illustrates the processing state of the color filter
substrate shown in FIG. 11 after the coating of a
silicon-containing insulating film together with a patterning
mask;
[0043] FIGS. 17A to 17C sequentially illustrate the steps of
fabricating the color filter substrate shown in FIG. 11 after the
formation of a photoresist pattern;
[0044] FIG. 18A is a plan view of a pixel electrode for a liquid
crystal display according to a seventh preferred embodiment of the
present invention;
[0045] FIG. 18B is a plan view of a protrusion pattern formed on a
common electrode corresponding to the pixel electrode shown in FIG.
18A; and
[0046] FIG. 18C illustrates the combinatorial state of the pixel
electrode shown in FIG. 18A and the protrusion pattern shown in
FIG. 18B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] Preferred embodiments of this invention will be explained
with reference to the accompanying drawings.
[0048] FIG. 1 is a plan view of a liquid crystal display according
to a first preferred embodiment of the present invention where a
pixel electrode of a thin film transistor array substrate and a
protrusion pattern of a color filter substrate are illustrated.
FIG. 2A is a cross sectional view of the liquid crystal display
shown in FIG. 1. FIG. 2B illustrates the orientation state of
liquid crystal molecules in the liquid crystal display shown in
FIG. 2A under the application of voltages. FIG. 3 illustrates the
planar orientation state of the liquid crystal molecules shown in
FIG. 2B.
[0049] As shown in the drawings, a bottom substrate 1 is overlaid
with thin film transistors (not shown) and pixel electrodes 4, and
this is called the "thin film transistor array substrate." Each
pixel electrode 4 is electrically connected to the thin film
transistor while bearing opening portions 6 and 7. A top substrate
11 is overlaid with a black matrix 12, color filters 13 and a
common electrode 14, and this is called the "color filter
substrate." Polarizing plates (not shown) are externally attached
to the substrates 1 and 11 such that the polarizing axes thereof
proceed perpendicular to each other.
[0050] In the thin film transistor array substrate, the thin film
transistor switches the signals applied to the pixel electrode 4.
The thin film transistor is formed with several components (not
shown) such as a gate electrode being a part of a gate line, a
semiconductor layer formed on the gate electrode, a source
electrode formed on the semiconductor layer while being a part of a
data line, and a drain electrode facing the source electrode around
the gate electrode. The drain electrode is electrically connected
to the pixel electrode 4.
[0051] As shown in FIG. 1, the pixel electrode 4 is divided into
three regions around the opening portions 6 and 7.
[0052] When the gate signals from the outside are transmitted to
the gate lines, and the data signals from the outside are
transmitted to the data lines, channels are formed at the
semiconductor layer so that the data signals are applied to the
pixel electrodes via the drain electrodes, thereby displaying
picture images.
[0053] In the color filter substrate, the color filters 13 of red,
green and blue are positioned at the patterned portions of the
black matrix 12. The common electrode 14 is formed on the color
filters 13 with a transparent conductive material such as indium
tin oxide (ITO) and indium zinc oxide (IZO). A protrusion pattern
16 is formed on the common electrode 14 with a photosensitive
organic insulating material. In this preferred embodiment, the
protrusion pattern 16 is formed with three protrusions. Each
protrusion 16 is pillar-shaped with top and bottom sides of a
circle, a rectangle, or a rectangle bearing curved edges. The
height of the protrusion 16 is established to be 3.0-4.5 .mu.m.
When the two substrates 1 and 11 are arranged for combination, the
protrusions 16 are placed at the center of the three pixel
electrode regions one by one. The protrusion pattern 16 may be
based on a photosensitive organic insulating film, a positive or
negative photoresist film, or a silicon-containing insulating
film.
[0054] A vertical alignment layer (not shown) is formed on the thin
film transistor array substrate, and the color filter
substrate.
[0055] The two substrates 1 and 11 are arranged for combination,
and a liquid crystal 17 bearing negative dielectric anisotropy is
injected in-between the substrates 1 and 11 to thereby form a
liquid crystal layer bearing a retardation value .DELTA.nd of
0.25-0.4 .mu.m. With no application of voltage, the liquid crystal
molecules 17 are aligned to be perpendicular to the two substrates
1 and 11. When voltage is applied to the common electrode 14 and
the pixel electrodes 4, as shown in FIG. 2B, the liquid crystal
molecules 17 are aligned to be perpendicular to the fringe field f
formed between the pixel electrodes 4 and the common electrode 14.
When viewed from the direction of the IV arrow of FIG. 2B, as shown
in FIG. 3, the liquid crystal molecules 17 are aligned in four
directions around the protrusion pattern 16 so that the desired
multi-domains may be made without patterning the common electrode
14. Since the protrusion pattern 16 is cylindrical-shaped, the
injection of the liquid crystal in-between the substrates 1 and 11
can be made in a fluent manner. When the two substrates 1 and 11
are arranged for combination, the protrusion pattern 16 plays a
role of a spacer such that the cell gap can be kept in a constant
manner.
[0056] FIG. 4 is a plan view of a liquid crystal display according
to a second preferred embodiment of the present invention where a
pixel electrode of a thin film transistor array substrate and a
protrusion pattern of a color filter substrate are illustrated. In
this preferred embodiment, other components and structures of the
liquid crystal display are the same as those related to the first
preferred embodiment except that the pixel electrode 4 is shaped in
a different manner.
[0057] As shown in FIG. 4, the pixel electrode 4 is shaped with a
series of rectangles connected to each other. A protrusion 16 is
placed at the center of each rectangle. That is, the pixel
electrode 4 is divided into a plurality of micro-domains by way of
the opening pattern, and the protrusion 16 is positioned at the
center of each micro-domain.
[0058] A method of fabricating the liquid crystal display will be
now explained with reference to FIGS. 5A to 5C.
[0059] First, as shown in FIG. 5A, a black matrix 12 is formed on a
substrate 11, and color filters 13 of red, green and blue are
formed at the black matrix 12.
[0060] Thereafter, as shown in FIG. 5B, a common electrode 14 is
formed on the black matrix 12 and the color filters 13 with a
transparent conductive material such as ITO and IZO.
[0061] As shown in FIG. 5C, a protrusion pattern 16 is formed on
the common electrode 14 on the basis of a photosensitive organic
insulating film, a positive or negative photoresist film, or a
silicon-containing insulating film. In case the protrusion pattern
16 is based on a photosensitive film, the photosensitive film is
exposed to light through a mask, and developed to form the
protrusion pattern 16. In case the protrusion pattern 16 is based
on a silicon-containing insulating film, the silicon-containing
insulating film is overlaid with a photoresist pattern, and etched
through the photoresist pattern to form the protrusion pattern
16.
[0062] Meanwhile, as shown in FIG. 6, in a white state under the
application of voltage, a darkish area B is present around the
circular protrusion pattern 16 while deteriorating the brightness.
The dark area B is made because when the light linearly polarized
through the polarizing plate passes the liquid crystal layer, the
rotation of the light in the polarizing direction by way of the
liquid crystal is not made at the place where the directors of the
liquid crystal molecules 17 is parallel to or perpendicular to the
polarizing direction of the light. That is, the light linearly
polarized through the first polarizing plates directly passes the
second polarizing plate without suffering the rotation in the
polarizing direction by way of the liquid crystal 17 so that it is
intercepted by the second polarizing plate. Accordingly, a
compensation plate is preferably provided between the substrates 1
and 11 and the corresponding polarizing plates such that the light
can pass them in a state where the linear polarizing is transformed
into a circular polarizing. Since the polarizing direction is not
fixed at the circular polarizing, such a dark area B where the
directors of the liquid crystal molecules 17 are parallel to or
perpendicular to the polarizing direction is not made.
Consequently, the brightness is enhanced.
[0063] FIG. 7 is an exploded view of a liquid crystal display
according to a third preferred embodiment of the present invention.
In this preferred embodiment, other components and structures are
the same as those related to the first preferred embodiment except
that the following components are differentiated.
[0064] As shown in FIG. 7, .lamda./4 plates 21 and 22 are provided
between a first polarizing plate 41 and a top substrate 11 and
between a second polarizing plate 42 and a bottom substrate 1,
respectively. Bi-axial films 31 and 32 are provided between the
.lamda./4 plates 21 and 22 and the polarizing plates 41 and 42,
respectively. The polarizing axes of the polarizing plates 41 and
42 are perpendicular to each other, and the largest axes of the
bi-axial films 31 and 32 (the axes bearing the greatest index of
refraction) are also perpendicular to each other. The slow axes of
the .lamda./4 plates 21 and 22 are also perpendicular to each
other. The polarizing axis of the polarizing plate 41 externally
attached to the top substrate 11 is parallel to the longest axis of
the neighboring bi-axial film 31, and the polarizing axis of the
polarizing plate 42 is also parallel to the longest axis of the
neighboring bi-axial film 32. Furthermore, the polarizing axes of
the polarizing plates 41 and 42 are angled with respect to the slow
axes of the neighboring .lamda./4 plates 21 and 22 by
45.degree..
[0065] The bi-axial films 31 and 32 compensate for the difference
in the retardation value to thereby enhance the viewing angle. The
plates 21 and 22 transform the linear polarizing through the
polarizing plates 41 and 42 into the circular polarizing. That is,
when the light circular-polarized through the .lamda./4 plates 21
and 22 is incident upon the liquid crystal 17, possible occurrence
of textures with the linear polarizing is prevented while enhancing
the brightness. Furthermore, the viewing angle is compensated due
to the bi-axial films 31 and 32. As the slow axes of the .lamda./4
plates are arranged to be perpendicular to each other while making
the desired compensation effect, high contrast ratio can be
obtained irrespective of the wavelength diffusion characteristics
of the .lamda./4 plates 21 and 22. When the Rx of the bi-axial
films 31 and 32 equals 50 nm and Rz thereof equals 100 nm, the
light leakage at the side area is decreased. However, the amount of
decrease in the light leakage is not enough to be applied for use
in the liquid crystal display.
[0066] FIG. 8 is an exploded view of a liquid crystal display
according to a fourth preferred embodiment of the present
invention.
[0067] As shown in FIG. 8, bi-axial films 31 and 32 are provided
between a first polarizing plate 41 and a top substrate 11 and
between a second polarizing plate 42 and a bottom substrate 1,
respectively. The polarizing axes of the first and the second
polarizing plates 41 and 42 are perpendicular to each other, and
the longest axes of the bi-axial films 31 and 32 are also
perpendicular to each other while being angled with respect to the
neighboring polarizing plates 41 and 42 by 45.degree.,
respectively. The Rx of the bi-axial films 31 and 32 is in the
range of 100-150 nm, and the Rz thereof in the range of 80-180 nm.
In this preferred embodiment, the bi-axial film also plays the role
of a .lamda./4 plate. That is, the light linear-polarized through
the polarizing plate 42 is transformed into a circular-polarized
light by way of the bi-axial film 32. After the circular-polarized
plate passes the liquid crystal 17, it is transformed into a
linear-polarized light by way of the bi-axial film 31. In this
case, the viewing angle can be further enhanced compared to that
related to the third preferred embodiment.
[0068] FIG. 9 is an exploded view of a liquid crystal display
according to a fifth preferred embodiment of the present
invention.
[0069] As shown in FIG. 9, bi-axial films 31 and 32 are provided
between a first polarizing plate 41 and a top substrate 11 and
between a second polarizing plate 42 and a bottom substrate 1,
respectively. A mono-axial film 33 is provided between the bi-axial
film 32 and the polarizing plate 42. The polarizing axes of the
polarizing plates 41 and 42 are perpendicular to each other, and
the longest axes of the bi-axial films 31 and 32 are also
perpendicular to each other. The longest axes of the bi-axial films
31 and 32 are angled with respect to the polarizing axes of the
neighboring polarizing plates 41 and 42 by 45.degree.,
respectively. The long axis of the mono-axial film 33 is parallel
to the polarizing axis of the neighboring polarizing plate 42.
Alternatively, the mono-axial film 33 may be provided between the
bi-axial film 31 and the polarizing plate 41, and a bi-axial film
bearing a lower bi-axial degree may be used instead of the
mono-axial film 33. The Rx of the bi-axial films 31 and 32 is in
the range of 100-150 nm, and the Rz thereof in the range of 80-180
nm. The retardation value of the mono-axial film 33 is in the range
of 200 nm.+-.100 nm. In this case, the viewing angle can be further
enhanced compared to that related to the fourth preferred
embodiment.
[0070] As described above, a compensation plate is provided between
the polarizing plates 41 and 42 and the substrates 1 and 11 while
making circular polarizing, thereby widening the viewing angle. As
shown in FIG. 10, any texture is not present at the area except for
the protrusion pattern 16, and the brightness is enhanced.
[0071] Meanwhile, the protrusion pattern may be differentiated in
thickness such that the protrusions bearing a large thickness are
used as spacers, and the protrusions bearing a small thickness are
used for domain partitioning. In this case, it is preferable that
the spacer protrusions and the domain partitioning protrusions
should be formed through one photolithography process while
reducing the number of relevant processing steps.
[0072] FIG. 11 is a cross sectional view of a color filter
substrate for a liquid crystal display according to a sixth
preferred embodiment of the present invention.
[0073] As shown in FIG. 11, a black matrix 112 is formed on a
substrate 111, and color filters 113 of red, green and blue are
formed at the black matrix 112. A common electrode 114 is formed on
the color filters 113 with a transparent conductive material such
as ITO and IZO. Protrusion patterns 116 and 117 are formed on the
common electrode 114 with a photosensitive organic insulating
material. The protrusion patterns 116 and 117 are differentiated in
thickness such that the protrusion pattern 117 placed over the
black matrix 112 has a thickness larger than the protrusion pattern
116 placed over the color filters 113.
[0074] Pixel electrodes 104 are formed at the thin film transistor
array substrate each with an opening pattern. As shown in FIG. 12A,
each pixel electrode 104 is rectangular-shaped with top and bottom
sides and left and right sides, and a first opening portion 121 is
tapered from the right side of the pixel electrode 104 to the left
side at the center thereof. Both inlet edges of the first opening
portion are cut, and curved smoothly. The pixel electrode 104 is
divided into upper and lower regions around the first opening
portion 121. Second and third opening portions 122 and 123 are
formed at the upper and the lower regions of the pixel electrode
104. The second and the third opening portions 122 and 123
diagonally proceed from the top and the bottom sides of the pixel
electrode 104 toward the left center thereof such that they are
symmetrical to each other.
[0075] As shown in FIG. 12B, the protrusion pattern 116 formed on
the common electrode 114 has first to third protrusions 131 and 141
and 151 differentiated in shape. The first protrusion 131 includes
a trunk portion 132, first and second branch portions 133 and 134
proceeding from the trunk portion 132 up and downward in a slant
manner, and first and second sub-branch portions 135 and 136
proceeding from the first and second branch portions 133 and 134 up
and downward in the vertical direction. The second protrusion 141
includes a first base portion 142 proceeding parallel to the first
branch portion 133, a first horizontal limb portion 143 proceeding
from the first base portion 142 in the horizontal direction, and a
first vertical limb portion 144 proceeding from the first base
portion 142 in the vertical direction. The third protrusion 151 is
symmetrical to the second protrusion 141. That is, the third
protrusion 151 includes a second base portion 152, a second
horizontal limb portion 153, and a second vertical limb portion
154. The first to third protrusions 131, 141 and 151 are formed at
the region of the common electrode 114 corresponding to each pixel
electrode 104. The first to third protrusions 131, 141 and 151 each
have a width of 3-15 .mu.m
[0076] Meanwhile, the spacer protrusion pattern 117 bearing a
thickness larger than the domain partitioning protrusion pattern
116 is overlapped with the black matrix 112, and shaped with a
pillar where the top and the bottom sides thereof are polygon or
circle-shaped each with a width of 5-40 .mu.m.
[0077] FIG. 12C illustrates the combinatorial state of the opening
patterns of the pixel electrode 104 and the protrusion patterns
formed on the common electrode 114.
[0078] As shown in FIG. 12C, the first to third opening portions
121 to 123 of the pixel electrode 104 are overlapped with the first
to third protrusions 131, 141 and 151 formed on the common
electrode 114 to thereby divide the pixel region into a plurality
of micro-domains. The first to third opening portions 121 to 123 of
the pixel electrode 104, and the first to third protrusions 131,
141 and 151 formed on the common electrode 114 are alternately
arranged while proceeding parallel to each other except for the
first opening portion 121, the trunk portion 132 of the first
protrusion 131, and the sub-branch portions 135 and 136 of the
first protrusion 131 as well as the horizontal and vertical limb
portions 143, 144, 153 and 154 of the second and third protrusions
141 and 151 overlapped with the sides of the pixel electrode
104.
[0079] Under the application of voltage, the liquid crystal
molecules 17 are aligned in four directions while exhibiting wide
viewing angle in those directions.
[0080] In the above structure, the protrusion pattern 117 with a
relatively large thickness is used as a spacer, whereas the
protrusion pattern 116 with a relatively small thickness is used
for domain partitioning.
[0081] A method of fabricating the above-structured color filter
substrate will be now explained with reference to FIGS. 13A to
17C.
[0082] First, as shown in FIG. 13A, a black matrix 112 is formed on
an insulating substrate 111, and color filters 113 of red, green
and blue are formed at the black matrix 112.
[0083] Thereafter, as shown in FIG. 13B, a common electrode 114 is
formed on the entire surface of the substrate 111 with a
transparent conductive material such as ITO and IZO.
[0084] As shown in FIG. 13C, a photosensitive organic insulating
film 115 is coated onto the common electrode 115. A negative or
positive photoresist film, a silicon-containing insulating film may
be used instead of the photosensitive organic insulating film
115.
[0085] The photosensitive organic insulating film 115 is patterned
using a mask 100 or 110 shown in FIG. 14 or 15 to thereby form
protrusion patterns 116 and 117 differentiated in thickness, as
shown in FIG. 11. It is preferable that the mask includes a slit
pattern or a semitransparent film.
[0086] A method of forming the protrusion patterns 116 and 117
using a mask with a slit pattern or a semitransparent film will be
now explained in detail. Either a negative photosensitive organic
insulating film or a positive photosensitive organic insulating
film may be used as the target film. In the case of the negative
photosensitive organic insulating film, the light-exposed portions
are left over after the development, and the portions not exposed
to the light are entirely removed.
[0087] As shown in FIG. 14, the mask 100 includes a slit pattern to
be placed at the B area over the color filters 113, a transparent
pattern to be placed at the A area where the common electrode 114
is hollowed while contacting the black matrix 112, and an opaque
pattern to be placed at the remaining area C. When the light
exposing is made using the mask 100, the amount of light incident
upon the target film through the slit pattern is smaller than the
amount of light incident upon the target film through the
transparent pattern. Accordingly, after the light exposing and the
development are completed, as shown in FIG. 11, the protrusion
pattern 116 at the B area has a thickness smaller than the
protrusion pattern 117 at the A area, and the negative
photosensitive insulating film at the C area is removed.
[0088] In the case of the negative organic insulating film, after
the development, the upper portion thereof is wider than the lower
portion thereof while bearing a shape of a counter-taper, but
diminished during the subsequent processing steps so that the
resulting pattern exhibits a substantially vertical side.
[0089] A method of forming the protrusion patterns using a mask
with a semitransparent film will be now explained with reference to
FIG. 15. Either a negative photosensitive organic insulating film
or a positive photosensitive organic insulating film may be used as
the target film. In the case of the positive photosensitive organic
insulating film, the light-exposed portions are removed after the
development, and the portions not exposed to the light are left
over.
[0090] As shown in FIG. 15, the mask 110 includes a semitransparent
pattern to be placed at the B area over the color filters 113, an
opaque pattern to be placed at the A area where the common
electrode 114 is hollowed while contacting the black matrix 112,
and a transparent pattern to be placed at the remaining area C.
When the light exposing is made using the mask 110, the amount of
light incident upon the target film through the semitransparent
pattern is smaller than the amount of light incident upon the
target film through the transparent pattern. Accordingly, after the
light exposing and the development are completed, the positive
organic insulating film remained at the B area has a thickness
smaller than the positive organic insulating film remained at the A
area, and the positive organic insulating film at the C area is
entirely removed.
[0091] In case a negative organic insulating film is used as the
target film, it is difficult to make the portion covered by the
semitransparent film bear the desired thickness. Therefore, it is
preferable to use a positive organic insulating film as the target
film.
[0092] As described above, protrusion patterns 116 and 117
differentiated in thickness are formed using a mask 100 or 110 with
a slit pattern or a semitransparent film. The protrusion pattern
116 bearing a relatively small thickness forms fringe fields while
serving to obtain wide viewing angle. The protrusion pattern 117
bearing a relatively large thickness is used as a spacer. The
protrusion patterns 116 and 117 may be formed through one
photolithography process.
[0093] Meanwhile, a silicon-containing insulating film may be used
instead of the photosensitive organic insulating film. The
silicon-containing insulating film is first coated as the target
film, and a photoresist film is coated onto the silicon-containing
insulating film. Thereafter, the target film overlaid with the
photoresist film suffers photolithography based on a mask with a
slit pattern, or a semitransparent film. A positive photoresist
film may be used for the patterning. This process will be now
explained with reference to FIGS. 16 to 17C.
[0094] As shown in FIG. 16, a photoresist film 125 is coated onto
the silicon-containing insulating film 115. The photoresist film
125 is exposed to light through a mask 120, and developed to
thereby form photoresist patterns 126 and 127 differentiated in
thickness, as shown in FIG. 17A. The mask 120 includes a slit
pattern to be placed at the B area, an opaque pattern to be placed
at the A area, and a transparent pattern to be placed at the C
area. When the photoresist film 125 is exposed to light through the
mask 120 and developed, the photoresist film remained at the B area
has a thickness smaller than the photoresist film remained at the A
area, and the photoresist film at the C area is entirely removed. A
semitransparent pattern may be used instead of the slit pattern. In
case a negative photoresist film is used instead of the positive
photoresist film, the mask may be provided with a transparent
pattern to be placed at the A area, and an opaque pattern to be
placed at the C area.
[0095] Thereafter, as shown in FIG. 17B, the portions of the
insulating film 115 exposed through the photoresist patterns 126
and 127 are etched such that the underlying common electrode 114 is
exposed to the outside.
[0096] As shown in FIG. 17C, when the photoresist patterns 126 and
127 are etched while exposing the underlying insulating film 115,
only the photoresist pattern 127 placed at the A area is left over.
When the photoresist pattern 127 is removed, as shown in FIG. 11,
the protrusion patterns 116 and 117 differentiated in thickness are
completed.
[0097] FIGS. 18A to 18C illustrate a liquid crystal display
according to a seventh preferred embodiment of the present
invention. In this preferred embodiment, other components and
structures of the liquid crystal display are the same as those
related to the sixth preferred embodiment except for the shape of
the pixel electrode 104 and the protrusion pattern.
[0098] As shown in FIG. 18A, the pixel electrode 104 has an upper
half region and a lower half region, and a first rectangular-shaped
opening portion 161 bisects the upper half region of the pixel
electrode 104 left and right. Second and third rectangular-shaped
opening portions 162 and 163 trisect the lower half region of the
pixel electrode 104 up and down.
[0099] As shown in FIG. 18B, the common electrode 114 is overlaid
with a protrusion pattern having first to third protrusions 171,
181 and 191. The first protrusion 171 includes first and second
trunk portions 172 and 173 proceeding in the vertical direction
parallel to each other, and a branch portion 174 connected to the
first and second trunk portions 172 and 173 while proceeding in the
horizontal direction. The second and the third protrusions 181 and
191 are placed below the first and second trunk portions 172 and
173 while proceeding in the horizontal direction parallel to each
other.
[0100] FIG. 18C illustrates the combinatorial state of the opening
pattern of the pixel electrode 104 and the protrusion pattern
formed on the common electrode 114.
[0101] As shown in FIG. 18C, the first opening portion 161 of the
pixel electrode 104 and the first and second trunk portions 172 and
173 of the common electrode 114 vertically partition the upper half
region of the pixel electrode 104 into four micro-domains. The
second and third opening portions 162 and 163 of the pixel
electrode 104 and the second and third protrusions 181 and 191 of
the common electrode 114 horizontally partition the lower half
region of the pixel electrode 104 into five micro-domains.
[0102] As described above, pillar-shaped protrusion patterns are
formed on a common electrode to make the desired pixel-domain
partitioning as well as to be used as a spacer. Furthermore, a
.lamda./4 plate and a bi-axial film are provided between the top
substrate and the polarizing plate and between the bottom substrate
and the polarizing plate such that the circular-polarized light
passes the liquid crystal, thereby removing the undesirable
textures while enhancing the brightness. Furthermore, the
protrusion patterns differentiated in thickness are formed through
one photolithography process such that the protrusion pattern
bearing a relatively small thickness is used for the domain
partitioning, and the protrusion pattern bearing a relatively large
thickness is used as a spacer.
[0103] While the present invention has been described in detail
with reference to the preferred embodiments, those skilled in the
art will appreciate that various modifications and substitutions
can be made thereto without departing from the spirit and scope of
the present invention as set forth in the appended claims.
* * * * *