U.S. patent application number 09/768047 was filed with the patent office on 2001-05-24 for liquid crystal display device.
Invention is credited to Hiroshi, Komatsu.
Application Number | 20010001568 09/768047 |
Document ID | / |
Family ID | 19462989 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001568 |
Kind Code |
A1 |
Hiroshi, Komatsu |
May 24, 2001 |
Liquid crystal display device
Abstract
A liquid crystal display device includes first and second
substrates, a plurality of gate bus lines and data bus lines on the
first substrate, the gate bus lines being perpendicular to the data
bus lines, a plurality of pixels defined by the gate bus lines and
the data bus lines, the pixels having a plularity of regions, at
least a pair of electrodes in each region having a common
direction, and a plurality of liquid crystal molecules between the
substrates.
Inventors: |
Hiroshi, Komatsu; (Kumi-shi,
JP) |
Correspondence
Address: |
Song K. Jung
LONG ALDRIDGE & NORMAN LLP
701 Pennsylvania Avenue N.W.
Washington
DC
20004
US
|
Family ID: |
19462989 |
Appl. No.: |
09/768047 |
Filed: |
January 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09768047 |
Jan 24, 2001 |
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08880068 |
Jun 20, 1997 |
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Current U.S.
Class: |
349/143 ;
349/123; 349/139; 349/141 |
Current CPC
Class: |
G02F 1/134363
20130101 |
Class at
Publication: |
349/143 ;
349/141; 349/139; 349/123 |
International
Class: |
G02F 001/1337; G02F
001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 1996 |
KR |
23115/1996 |
Claims
What is claimed is:
1. A liquid crystal display device, comprising: first and second
substrates; a plurality of gate bus lines and data bus lines on the
first substrate, the gate bus lines being perpendicular to the data
bus lines; a plurality of pixels defined by the gate bus lines and
the data bus lines, the pixels having a plularity of regions; at
least a pair of electrodes in each region having a common
direction; and a plurality of liquid crystal molecules between the
substrates.
2. The device according to claim 1, wherein the electrodes include
a data electrode and a common electrode.
3. The device according to claim 1, wherein an electric field
having an intensity changing gradually from the first substrate to
the second substrate is applied to the liquid crystal
molecules.
4. The device according to claim 3, wherein the liquid crystal
molecules are rotated gradually from the first substrate to the
second substrate when the electric field is applied to the
electrodes.
5. A liquid crystal display device, comprising: first and second
substrates; a plurality of gate bus lines and data bus lines on the
first substrate in a matrix form; a plurality of pixels defined by
the gate bus lines and the data bus lines, the pixels having first
and second regions; at least one common bus line at each pixel, the
common bus line being parallel to the gate bus line; at least a
pair of first and second electrodes in the first and second
regions, respectively, the first and second electrodes having first
and second electrode elongation directions (.theta..sub.EL1 and
.theta..sub.EL2) with respect to a longitudinal direction of the
common bus line; a color filter layer over the second substrate;
first and second alignment layers over the first and second
substrates, the first and second alignment layers having first and
second alignment directions (.theta..sub.R1 and .theta..sub.R2) ,
respectively; a liquid crystal layer between the first substrate
and the second substrate; a polarizer and a analyzer attached to
the first substrate and the second substrate, respectively.
6. The device according to claim 5, wherein the electrodes are
separated by a distance smaller than a thickness of the liquid
crystal layer.
7. The device according to claim 5, wherein the liquid crystal
layer has a retardation value(.DELTA.nd) of .lambda./2 (.DELTA.nd
.lambda. (where .DELTA.n is an anisotropy of a refractive index, d
is a thickness of the liquid crystal layer, and .lambda. is a
wavelength of an incident light).
8. The device according to claim 7, wherein the retardation value
is approximately 0.74.lambda..
9. The device according to claim 5, wherein the first alignment
layer has an anchoring energy lower than that of the second
alignment layer.
10. The device according to claim 9, wherein the second alignment
layer includes a polygamic acid base material.
11. The device according to claim 5, wherein the first and second
alignment layers have rubbing directions parallel to a polarized
direction of the analyzer.
12. The device accordance to claim 11, wherein the polarizer has a
polarized direction perpendicular to the polarized direction of the
analyzer.
13. The device according to claim 5, wherein the first electrode
elongation direction has an absolute value the same as that of the
second electrode elongation direction.
14. The device according to claim 5, wherein the first and second
electrode elongation directions are between 0.degree.and
90.degree.and between -90.degree.and 0.degree., respectively.
15. The device according to claim 14, wherein the first and second
electrode elongation directions are -90.degree.and 90.degree.with
respect to a longitudinal direction of the gate bus lines,
respectively.
16. The device according to claim 5, wherein the first and second
electrode elongation directions are 90.degree.and between
90.degree. and 180.degree., respectively.
17. The device according to claim 16, wherein the
.theta..sub.EL1<.thet- a..sub.R1<.theta..sub.EL2 and the
.theta..sub.R2=180.degree.-.theta..su- b.EL1.
18. The device according to claim 5, wherein the first and second
electrode elongation directions have complementary angles with
respect to the longitudinal direction of the common bus line.
19. The device according to claim 18, wherein the first and second
alignment directions have ranges of
0.degree.<.theta..sub.R1<90.deg- ree.and
-90.degree.<.theta..sub.R2<0.degree. with respect to the
common bus line, respectively.
20. The device in accordance with claim 19, wherein the first and
second alignment directions have a relationship of
.theta..sub.R1=-.theta..sub.R- 2.
21. The device according to claim 5, further comprising a first
optical compensator between the polarizer and the first
substrate.
22. The device according to claim 5, further comprising a second
optical compensator between the second substrate and the
analyzer.
23. A liquid crystal display device having a plurality of pixels
each including a plurality of regions, the device comprising: first
and second substrates; a liquid crystal molecular layer having
liquid crystal molecules between the first and second substrates; a
plurality of electrodes in each region of the pixels, an electric
field parallel to the substrates being applied to the electrodes;
and first and second alignment layers over the first and second
substrates, respectively, the first and second alignment layers
having first and second alignment directions of .theta.1 and
.theta.2 relative to an electrode elongating direction.
24. The device according to claim 23, wherein the liquid crystal
molecules in each region and a neighboring region are rotated in
directions opposite with each other when an electric field is
applied in the device.
25. The device according to claim 23, wherein the electrodes
include at least a pair of electrodes.
26. The device according to claim 25, wherein the pair of
electrodes include a data electrode and a common electrode.
27. The device according to claim 25, wherein a gap between the
pair of electrodes is smaller than a thickness of the liquid
crystal molecular layer.
28. The device according to claim 23, wherein the first alignment
direction is 0.degree.<.theta..sub.1<90.degree..
29. The device according to claim 23, wherein the second alignment
direction is -90.degree.<.theta..sub.2<0.degree..
30. The device according to claim 23, wherein the first and second
alignment directions have a relationship of
.theta..sub.1=-.theta..sub.2.
31. The device according to claim 23, wherein the liquid crystal
layer has a retardation value .DELTA.nd of .lambda./2 (
.DELTA.nd.ltoreq..lambda. (where .DELTA.n is an anisotropy of a
refractive index, d is thickness of the liquid crystal molecular
layer, and .lambda. is a wavelength of an incident light).
32. The device according to claim 31, wherein the retardation value
is about 0.74.lambda..
33. A liquid crystal display device having a plurality of pixels
each including a plurality of regions, the device comprising: first
and second substrates; a liquid crystal molecular layer having
liquid crystal molecules between the first and second substrates; a
plurality of electrodes on the first substrate in each region of
the pixels, an electric field parallel to the substrates being
applied to the electrodes, which is different from the electric
field of a neighboring region to rotate the liquid crystal
molecules in opposite directions in each neighboring region
applying to the electrodes in each region; and first and second
alignment layers over the first and second substrates, the first
and second alignment layers providing for first and second
alignment directions of .theta..sub.1 and .theta..sub.2 with
respect to a longitudinal direction of a common bus line.
34. The device according to claim 33, wherein the electrodes
includes at least a pair of electrodes.
35. The device according to claim 34, wherein the pair of
electrodes includes a data electrode and a common electrode.
36. The device according to claim 34, wherein the pair of
electrodes have a space therebetween smaller than a thickness of
the liquid crystal molecular layer.
37. The device according to claim 33, wherein the first alignment
direction has an angle of 0.degree.(.theta..sub.1 (90.degree..
38. The device according to claim 33, wherein the second alignment
direction has an angle of
-90.degree.<.theta..sub.2<90.degree..
39. The device according to claim 33, wherein an angle between the
first alignment direction and the second alignment direction is a
supplementary angle.
40. The device according to claim 33, wherein the liquid crystal
molecular layer has a retardation value (.DELTA.nd) of .lambda./2
<.DELTA.nd .ltoreq..lambda. (where .DELTA.n is an anisotropy of
a refractive index, d is a thickness of the liquid crystal layer,
and .lambda. is a wavelength of an incident light).
41. The device according to claim 39, wherein the retardation value
0.74.lambda..
Description
[0001] This application claims the benefit of Korean application
No. 1996-23115 filed on Jun. 22, 1996, which is hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal display
device, and more particularly, to an in-plane switching mode liquid
crystal display device (LCD). Although the present invention is
suitable for a wide scope of applications, it is particularly
suitable for improving the quality of picture image.
[0004] 2. Discussion of the Related Art
[0005] As a thin film transistor liquid crystal display device
(TFT-LCD) has been widely used for portable televisions or notebook
computers, an LCD having a large panel is in great demand. A
conventional TFT-LCD, however, has a problem that a contrast ratio
is changed with a direction of viewing-angle. Liquid crystal
display devices such as a twisted nematic LCD having an optical
compensator and a multi-domain LCD have been proposed to cope with
this problem. Nevertheless, such LCDs are not capable of solving
the problem in a variation of the contrast ratio and color
shifting.
[0006] An in-plane switching mode LCD to realize a wide viewing
angle has also been proposed in the JAPAN DISPLAY 92 Page 457,
Japanese Patent Unexamined Publication No. 7-36058, Japanese Patent
Unexamined Publication No. 7-225538, and ASIA DISPLAY 95 Page
707.
[0007] A conventional in-plane switching mode LCD will now be
explained with reference to FIGS. 1 to 3.
[0008] Referring first to FIGS. 1 and 2, operation of the
conventional LCD will be described as follows. Liquid crystal
molecules 8 in a liquid crystal layer 12 are aligned to have a
rubbing direction (.theta..sub.R) of
90.degree.<.theta..sub.R<180.degree.with respect to a
longitudinal elongation direction(0.degree.) of a gate bus line on
a substrate as shown in FIG. 2. A polarization axis
direction(.theta..sub.P- L2) of a analyzer 10 attached on a second
substrate 5 is parallel to the rubbing direction(.theta..sub.R). A
polarization axis direction(.theta..sub.PL1) of a polarizer 9
attached on the first substrate 1 is perpendicular to a
polarization axis direction(.theta..sub.PL2) and electrode
elongation directions(.theta..sub.EL) of a data electrode 2 and a
common electrode 3 are .theta..sub.EL290.degree. with respect to
the longitudinal elongation direction of the gate bus line. Thus,
when a voltage is not applied to a data electrode 2 and a common
electrode 3 as shown in FIG. 1A, the liquid crystal molecules 8 are
aligned with a slightly tilted direction relative to the elongation
direction(.theta..sub.EL) of the data and common electrodes along
with the rubbing direction(.theta..sub.R) in the substrate. The
elongation direction(.theta..sub.EL) of the electrodes is
perpendicular to the longitudinal direction of the gate bus line.
Conversely, when a voltage having a horizontal electric field
parallel to the longitudinal direction of the gate bus line is
applied to the liquid crystal layer 12 as shown in FIG. 1B, the
liquid crystal molecules 8 near the first substrate are rotated and
a transmittance of the liquid crystal layer 12 is changed by a
birefringence. A retardation value(.DELTA.nd) of the liquid crystal
layer 12 is about .lambda./2(for example, .DELTA.nd would be
approximately 0.21-0.36 .mu.m, where .lambda. is a wavelength of an
incident light). For example, when the liquid crystal rotation
angle is about 45 degree, the transmittance is maximum so that a
screen of the LCD becomes a black mode.
[0009] FIG. 3A is a plane view of the conventional in-plane
switching mode liquid crystal display device and FIG. 3B is a
cross-sectional view taken along the line A-A' in FIG. 3A. The
liquid crystal display device is protected by a metal frame 22
excluding a representing unit 21 of a liquid crystal panel 32. A
gate driving circuit 23, a data driving circuit 24, and a back
light housing 25 including a back light 31 are mounted on the metal
frame 22. In the representing unit 21, an exposure plate 75 (shown
in FIG. 3B) having a light diffusion plate, polarizer 63, first and
second substrates 27 and 26 constituting the liquid crystal panel
32, and an analyzer 64 are disposed on the second substrate 26.
Further, a light compensator (not shown) may be disposed between
the polarizer 63 and the first substrate 27 or between the second
substrate 26 and the analyzer 64 to improve the contrast ratio.
[0010] Generally, in the conventional TFT-LCD, the TFT is formed in
the first substrate 27 as a switching device and the color filter
is formed on the second substrate 26. However, a diode may be used
as a switching device in a diode LCD and a simple matrix LCD.
Alternatively, when the TFT is formed on the second substrate, the
color filter is formed onto the first substrate. Further, a
mono-chromiumatic LCD may also be used without the color
filter.
[0011] However, the conventional in-plane switching mode liquid
crystal display device has a problem of the color shifting with the
change of viewing angle direction. As shown in FIGS. 1C to 1D, when
a horizontal electric field is applied to the electrodes 2, 3, the
liquid crystal molecules 8 nearby the first substrate 1 are aligned
parallel to the longitudinal direction of the gate bus line,
whereas the liquid crystal molecules 8 nearby the second substrate
5 are aligned with an angle of 90.degree.-180.degree.relative to
the longitudinal direction of the gate bus line. The liquid crystal
molecules 8 are thus twisted. Therefore, color shifting is caused
in either blue or yellow in a X or Y viewing angle direction,
respectively. This color shifting mainly deteriorates the quality
of the picture image.
SUMMARY OF THE INVENTION
[0012] Accordingly, the present invention is directed to a liquid
crystal display device that substantially obviates one or more of
the problems due to limitations and disadvantages of the related
art.
[0013] An object of the present invention is to provide an in-plane
switching mode liquid crystal display device having an improved
picture image quality by preventing color shifting.
[0014] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
[0015] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described, a liquid crystal display device includes a substrate, a
gate bus line and a data bus line elongating horizontally and
vertically to form a matrix figure, a pixel which is divided into
several regions defined by the gate bus line and the data bus line,
a data electrode and a common electrode in each region of the
pixel, and alignment layer over the substrate.
[0016] In another aspect of the present invention, a liquid crystal
display device includes first and second substrates, a plurality of
gate bus lines and data bus lines on the first substrate, the gate
bus lines being perpendicular to the data bus lines, a plurality of
pixels defined by the gate bus lines and the data bus lines, the
pixels having a plurality of regions, at least a pair of electrodes
in each region having a common direction, and a plurality of liquid
crystal molecules between the substrates.
[0017] In another aspect of the present invention, a liquid crystal
display device includes first and second substrates, a plurality of
gate bus lines and data bus lines on the first substrate in a
matrix form, a plurality of pixels defined by the gate bus lines
and the data bus lines, the pixels having first and second regions,
at least one common bus line at each pixel, the common bus line
being parallel to the gate bus line, at least a pair of first and
second electrodes in the first and second regions, respectively,
the first and second electrodes having first and second electrode
elongation directions (.theta..sub.EL1 and .theta..sub.EL2) with
respect to a longitudinal direction of the common bus line, a color
filter layer over the second substrate, first and second alignment
layers over the first and second substrates, the first and second
alignment layers having first and second alignment directions
(.theta..sub.R1 and .theta..sub.R2), respectively, a liquid crystal
layer between the first substrate and the second substrate, a
polarizer and a analyzer attached to the first substrate and the
second substrate, respectively.
[0018] In another aspect of the present invention, A liquid crystal
display device having a plurality of pixels each including a
plurality of regions, the device includes first and second
substrates, a liquid crystal molecular layer having liquid crystal
molecules between the first and second substrates, a plurality of
electrodes in each region of the pixels, an electric field parallel
to the substrates applying to the electrodes, and first and second
alignment layers over the first and second substrates,
respectively, the first and second alignment layers having first
and second alignment directions of .theta.1 and .theta.2 relative
to an electrode elongating direction.
[0019] In a further aspect of the present invention, a liquid
crystal display device having a plurality of pixels each including
a plurality of regions, the device includes first and second
substrates, a liquid crystal molecular layer having liquid crystal
molecules between the first and second substrates, a plurality of
electrodes on the first substrate in each region of the pixels, an
electric field parallel to the substrates applying to the
electrodes, a different electric field from that of a neighboring
region to rotate the liquid crystal molecules in opposite
directions in each neighboring region applying to the electrodes in
each region, and first and second alignment layers over the first
and second substrates, the first and second alignment layers
providing for first and second alignment directions of .theta.1 and
.theta.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0021] FIGs. 1A to 1D are schematic views illustrating an operation
of a conventional in-plane switching mode liquid crystal display
device.
[0022] FIG. 2 illustrates an axis directional relationship in the
conventional in-plane switching mode liquid crystal display
device.
[0023] FIG. 3A illustrates the conventional in-plane switching mode
liquid crystal display device.
[0024] FIG. 3B is a cross-sectional view of the conventional
in-plane switching mode liquid crystal display device taken along
the line A-A' in FIG. 3A.
[0025] FIG. 4 is a plane view of a liquid crystal display device in
accordance with a first embodiment of the present invention.
[0026] FIG. 5 is a cross-sectional view taken along the line B-B'
of FIG. 4.
[0027] FIG. 6 illustrates an axis directional relationship of the
in-plane switching mode liquid crystal display device in accordance
with the first embodiment of the present invention.
[0028] FIGS. 7A to 7D are schematic views illustrating an operation
of the in-plane switching mode liquid crystal display device in
accordance with the first embodiment of the present invention.
[0029] FIG. 8A illustrates a gray invention region in the
conventional in-plane switching mode liquid crystal display
device.
[0030] FIG. 8B illustrates a gray inversion region of the in-plane
switching mode liquid crystal display device in accordance with the
first embodiment of the present invention.
[0031] FIG. 9 illustrates a driving voltage waveform of the
in-plane switching mode liquid crystal display device in accordance
with the first embodiment of the present invention.
[0032] FIG. 10 is a plane view of the in-plane switching mode
liquid crystal display device in accordance with a second
embodiment of the present invention.
[0033] FIG. 11 is an axis directional relationship of the in-plane
switching mode liquid crystal display device in accordance with the
second embodiment of the present invention.
[0034] FIG. 12 is a plane view of the in-plane switching mode
liquid crystal display device in accordance with a third embodiment
of the present invention.
[0035] FIG. 13 is an axis directional relationship of the in-plane
switching mode liquid crystal display device in accordance with the
third embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings.
[0037] Hereinafter, an in-plane switching mode liquid crystal
display device according to a first embodiment of the present
invention will be described with reference to FIGS. 4 to 9.
[0038] Referring to FIGS. 4 and 5, a liquid crystal panel includes
a TFT 55, a color filter layer 61, alignment layers 59, 62 over
Solo the first and second substrates 27, 26, respectively, a liquid
crystal layer 60, and a spacer 65 between the first and second
substrates 27, 26 to maintain a constant distance between the
substrates 27, 26 and a polarizer on both surfaces of the liquid
crystal panel.
[0039] In FIG. 4, the TFT 55 on the first substrate 27 is disposed
at a region where a gate bus line 41 and data bus line 42 are
crossed perpendicularly with each other. A common bus line 43
parallel to the gate bus line 41 is formed in the center of a pixel
in a matrix form. A common electrode 49 connected to the common bus
line 43 is formed in the pixel. A data electrode 48 connected to
the drain electrode 47 of the TFT 55 is formed in parallel to the
common electrode 49.
[0040] Referring to FIGS. 5 and 6, the pixel is divided into a
first region 1 and a second region II the by common bus line 43.
.theta..sub.EL1 is an electrode elongation direction in the first
region I, and .theta..sub.pL1 is a polarization direction of
polarizer 63. .theta..sub.EL2 is an electrode elongation direction
in the second region II, and .theta..sub.PL2 is a polarization
direction of analyzer 64. .theta..sub.R is a rubbing direction,
.theta..sub.LC1 and .theta..sub.LC2 are optical axis directions of
a liquid crystal molecules in the first and second region,
respectively. Electrode elongation directions of the first region I
and the second region II are symmetric to the common bus line 43.
Thus, the angles .theta..sub.EL1, .theta..sub.EL2 of the electrodes
in each region I, II relative to the common bus line 43 are the
same. A voltage is applied to the gate bus line 41 in the
longitudinal direction of the liquid crystal display device. The
rubbing direction of the is first substrate 27 is not parallel to
that of the second substrate 26. The rubbing direction is parallel
to the polarization direction(.theta..sub.PL2) of the analyzer 64.
The polarization direction(.theta..sub.PL2) of the analyzer 64 is
perpendicular to the polarization direction(.theta..sub.PL1) of the
polarizer 63.
[0041] The gate bus line 41, the common bus line 43, and the common
electrode 49 are made of an AlTa thin film (3% Ta content) having a
thickness of 0.3.mu.m deposited by a sputtering process. The AlTa
thin film surface is anodized to form the AlTa oxidation layer 52
having a thickness of 0.1 .mu.m, so that the electrode surface has
a higher insulation characteristic. Also, a short circuit due to a
thin thickness is prevented on the electrode surface. After a gate
insulating layer 57 having a thickness of 0.3 .mu.m, an amorphous
silicon(a-si) layer 44 having a thickness of 0.2 .mu.m, and
n.sup.+-Si layer are consecutively deposited on the AlTa oxidation
layer 52 by PECVD (plasma enhanced chemical vapor deposition), a
photoetching process is executed to form the TFT 55.
[0042] Then, a chromium layer having a thickness of 0.1 .mu.m is
deposited on the TFT 55 and etched by the sputtering process. A
photoetching process is further conducted to form a source
electrode 46, drain electrode 47 of the TFT 55, and the data
electrode 48. The n.sup.+-silicon layer on a channel unit of the
TFT 55 is removed by a dry-etching process using the source
electrode 46 and the drain electrode 47 as masks. Thus, a-Si layer
remains only on the channel unit. Thereafter, a passivation layer
58 having a thickness of 0.2 .mu.m is deposited on the entire
surface over the first substrate 27 by PECVD. For example,
Si.sub.xN.sub.y may be used as the passivation layer 58.
Subsequently, the passivation layer 58 is partially etched on the
end portion of the gate bus line 41 and data bus line 42 to connect
the bus lines 41, 42 with the outer driver circuit.
[0043] A storage capacitor 53 (shown in FIG. 4) is formed at an
overlapping region of the common bus line 43 and a data electrode
48. The storage capacitor 53 maintains uniform the electric charges
of the data voltage in the each pixel.
[0044] A black matrix 51 (shown in FIG. 5) and a color filter layer
61 are formed on the second substrate 26. An overcoat layer (not
shown) is formed on the black matrix 51 and the color filter layer
61 to obtain the high stability of the surface and improve the
flatness. The black matrix 51 prevents the leakage of light at the
gate bus line 41, the data bus line 42, the common bus line 43, and
the TFT 55. The black matrix 51 is formed by etching a
Cr/Cr.sub.xO.sub.y, layer having a thickness of about 0.1 .mu.m in
each region. R, G, and B layers are formed respectively on the
color filter layer of the each pixel.
[0045] In the aforementioned-structure of the LCD, the widths of
data electrode 48, the common electrode 49 and the gap between the
electrodes are 5 .mu.m each.
[0046] An alignment layers 59, 62 are formed on the first and
second substrates 27 and 20 by depositing and baking a serial
No.RN1024 of Nissan Chemical having a thickness of 0.08 .mu.m.
While the alignment layer 59 over the first substrate 27 is rubbed
in the direction of -90.degree.with respect to elongation direction
of the common bus line, the alignment layer 62 on the second
substrate is rubbed in the direction of 90.degree.. For a spacer
65, a Micropearl of SEKISUI FINE CHEMICAL having a diameter of 6.4
.mu.m is used to have a liquid crystal layer 60 having a thickness
of 6.2 .mu.m. And for liquid crystals, a positive liquid crystal
such as ZGS 5025(.DELTA.n=0.067, .DELTA..epsilon.=6.0) of CHISSO
CO. is used. At this time, the pre-tilt angle of the aligned liquid
crystal molecules is about 4.8.degree., and the retardation value
(.DELTA.nd) is about=0.41.
[0047] The optical transmission axis direction (.theta..sub.PL1) of
the polarizer 63 attached to the first substrate 27 is parallel to
the longitudinal direction of the gate bus line 41. The optical
transmission axis direction (.theta.PL.sub.2) of the analyzer 64
attached to the second substrate 26 is perpendicular to the
longitudinal direction of the gate bus line 41.
[0048] The gap between the data electrode 48 and the common
electrode 49 is thinner than a thickness of liquid crystal layer
and the retardation value (.DELTA.nd) of the liquid crystal
satisfies the following equation.
.lambda./2 <.DELTA.nd.ltoreq..lambda.
[0049] where, .DELTA.n is an anisotropy of a refractive index of
the liquid crystal, d is a thickness of the liquid crystal layer,
and .lambda. is a wavelength.
[0050] The data electrode 48 and the common electrode 49 in the
first region I and the second region II are formed to have angles
.theta..sub.EL1 and .theta..sub.EL2, respectively, with respect to
the common bus line 43. The data electrode 48 and the common
electrode 49 are symmetric with each other.
[0051] Operation of the present in-plane switching mode liquid
crystal display device will now be described with reference to
FIGS. 7A to 7D. FIGS. 7A and 7B are cross-sectional views of the
in-plane switching mode liquid crystal display device and a plane
view of off-state LCD, and FIGS. 7C and 7D are for on-state LCD,
respectively.
[0052] The elongated direction of the conventional electrodes has
an angle of 90.degree.relative to the longitudinal
direction(0.degree.) of the gate bus line. However, the electrodes
of the present invention on the first region I and the second
region II are respectively extended in the directions with angles
.theta..sub.EL1 and .theta..sub.EL2 relative to the longitudinal
direction of the gate electrode. The electrodes in the first region
I and in the second region II are thus symmetric with each other.
Here, the value of the angles satisfies the following
equations.
[0053] 0.degree.<.theta..sub.EL1 <90.degree.,
-90.degree.<.theta..sub.EL2<0.degree., and
.vertline..theta..sub.EL-
1.vertline.=.theta..sub.EL2.vertline.,
[0054]
[0055] When the voltage is not applied to the electrodes, the
optical axis of all the liquid crystal molecules in the liquid
crystal layer, set in between the first substrate 27 and the second
substrate 26 is aligned almost parallel to the substrate by the
alignment layer 59, 62, as shown FIGS. 7A and 7E. For example, the
liquid crystals between the substrates are nematic liquid crystals
without a choral dopant. A light 11 incident to the first substrate
27 is polarized linearly by the polarizer 63, transmitted to the
liquid crystal layer 60, and reaches the analyzer 64. However,
since the polarization directions of the analyzer 64 and the
polarizer 63 are perpendicular with each other, the light 11 is not
transmitted to the analyzer 64. Therefore, the LCD screen becomes a
black mode.
[0056] Conversely, when the voltage is applied to the electrodes
48, 49, a parallel electric field 13 is applied in the liquid
crystal layer 60 through a data voltage between the data electrode
48 and the common electrode 49. The parallel electric field 13 has
a maximum value (E.sub.1) on the surface of an alignment layer 59
of first substrate 27, a near threshold value (E.sub.2) on the
surface of the alignment layer 62 of the second substrate 26, and a
medium value (E.sub.M=(E.sub.1+E.sub.2)- /2) in the middle of the
liquid crystal layer. When the parallel electric field 13 is not
uniform, the intensity of the parallel electric field 13 becomes
gradually smaller from the first substrate 27 to the second
substrate 26. Such a non-uniform electric field in the liquid
crystal layer 60 can be formed by making the thickness of the
liquid crystal layer 60 larger than the gap between the electrodes.
A liquid crystal molecule 77a, which is near the surface of
alignment layer 59 in the first region I, is affected by the
non-uniform electric field. The optical axis
direction(.theta..sub.LC1) of the liquid crystal molecules is thus
changed to be perpendicular to the electrode elongation
direction(.theta..sub.EL1).
[0057] Similarly, in a liquid crystal molecule 77b near the surface
of alignment layer 59 in the second region II, the optical axis
direction(.theta..sub.LC2) is also changed to be perpendicular to
the electrode elongation direction(.theta..sub.EL2) in the second
region II. Further, since the electric field applied to the liquid
crystal molecules 78a, 78b near the surface of the alignment layer
62 in the regions I, II is the near threshold value, the molecules
78a, 78b are not affected by the electric field so that the optical
axis is not changed. Therefore, by applying the non-uniform
electric field, the liquid crystal molecules in the liquid crystal
layer between the substrates 26, 27 are gradually changed from the
first substrate 27 to the second substrate 26. As a result, the
molecules are in a twisted state.
[0058] The liquid crystal molecules 77a, 78a are twisted
counterclockwise from a direction parallel to the rubbing direction
(.theta..sub.R). The direction is perpendicular to the longitudinal
direction of the gate bus line 41 and the direction of
.theta..sub.LC1 in the first region I. The liquid crystal molecules
77b, 78b are twisted clockwise from a direction perpendicular to
the longitudinal direction of the gate bus line 41 and the
.theta..sub.LC2 in the second region II. As a result, the liquid
crystal molecules in the first region I and the second region II
are twisted in the opposite direction with each other.
[0059] When the linearly polarized light 11 through the polarizer
63 is transmitted to the liquid crystal layer 60, the polarization
direction of the light is rotated by the twisted liquid crystal
layer 60 and the optical axis direction is directed to the same
direction of the polarization direction in the analyzer 64. The
light 11 linearly polarized by the polarizer 63 and transmitted to
the liquid crystal layer 60 is thus transmitted to the analyzer so
that the LCD screen becomes a white mode.
[0060] Here, the amount of the light transmittance depends on the
twisted angle of the liquid crystal molecules. Thus, when the
twisted angle of the liquid crystal molecules become larger, the
amount of light transmittance also becomes larger. A grey level of
the liquid crystal display device can also be controlled with the
data voltage by twisting the liquid crystal molecules.
[0061] For example, when the voltage applied to the electrode is 1
V-5 V, the liquid crystal molecules in the first region I and the
second region II are arranged symmetrically with each other by the
electric field of the each region having an intermediate grey
level. Thus, the color shifting occurred in the viewing angle
directions of X, Y the first region I and the second region II is
different from each other. The viewing angle direction of X causes
the blue shift and the viewing angle direction of Y causes the
yellow shift in the first region I. On the other hand, the viewing
angle direction of X causes the yellow shift and the viewing angle
direction of Y causes the blue shift in the second region II.
Therefore, the total color shifting caused by the birefringence
ratio of the liquid crystal molecules is corrected by the color
shifting in the first and second regions I, II, so that the desired
color can be obtained in whole pixels.
[0062] In order to maximize the optical transmittance ratio of the
liquid crystal layer 60 at the maximum voltage, the retardation
value(.DELTA.nd) of the liquid crystal layer 60 must be about 0.74
.lambda.. Accordingly, the anisotropy of the refractive
index(.DELTA.n) and a thickness of the liquid crystal layer(d) has
to be limited to get the maximum optical transmittance ratio. The
general twist nematic liquid crystal layer has the anisotropy of
refractive index of about 0.06-0.09 and the thickness of 6.0-8.8
.mu.m when the wavelength of the incident light is about 0.56
.mu.m.
[0063] FIG. 8A and FIG. 8B illustrate the viewing angle
characteristics according to the conventional in-plane switching
liquid crystal display device and the first embodiment in-plane
switching liquid crystal display device, respectively. Hatched
regions are viewing angle regions with the contrast ratio of 10:1
or less. As shown in FIG. 8A, the regions have the lower contrast
ratio at four inclined viewing angle direction in the conventional
liquid crystal display device.
[0064] In the present liquid crystal display device, the regions
also have the lower contrast ratio at four inclined viewing angle
direction, as shown in FIG. 8B, but the regions are much smaller
than the regions in the conventional LCD. That is, the liquid
crystal display device of the present invention provides regions
having a contrast ratio more than 10:1 is larger than the
conventional in-plane switching LCD. Also, the viewing angle
characteristic is improved in both the vertical and horizontal
directions. This results from the color shifting according to the
viewing angle becomes smaller and the contrast ratio of the screen
is increased.
[0065] FIG. 9 is a driving voltage waveform of the liquid crystal
display device according to the first embodiment. For example, in
this embodiment, the screen size is 12.1 inch and the pixel number
of 480*640 (*R*G*B). A gate voltage V.sub.GH, ground voltage
V.sub.GL, and common voltage V.sub.CO are 20, 0, and 8 V,
respectively, and a pulse width is 31 .mu.s. The data voltage
V.sub.D is taken as a single pulse signal having a frequency of 31
.mu.s, and a maximum .+-.6 V, and minimum .+-.1 V with respect to
the common voltage V.sub.CO. The data voltage V.sub.D may be
controlled to have 5 V in the signal region. Also, by adjusting the
common voltage, the AC voltage is applied between the common
electrode 49 and the data electrode 48.
[0066] Materials for the alignment layers on the first substrate
and the second substrate do not have to be the same in the present
invention. On the first substrate, for example, the alignment layer
including a material having a lower anchoring energy and a lower
rubbing density may be coated to rotate the liquid crystal
molecules easily. On the other hand, the alignment layer such as
polygamic acids base material having a lower pre-tilt angle and
good absorption characteristics of impurity from the liquid crystal
may be coated on the second substrate to improve the viewing angle
characteristics and remove the after-image.
[0067] Also, the pixel is divided into the first region and the
second region in the first embodiment. Moreover, when the pixel is
divided into more than two regions, the first region and the second
region may be arranged to have more effective liquid crystal
display devices.
[0068] Referring to FIGS. 10 and 11, a second embodiment in the
present invention will be described as following. As shown in the
FIG. 10, the pixel is divided into a first region I and second
region II. A common bus line 153 is formed between the regions I
and II. A common electrode 148 in the second region II is connected
to a source electrode 147 of the TFT. The common electrode 148 in
the first region is elongated in the directions of
.theta.EL1=90.degree. relative to longitudinal direction of the
gate bus line 141 (i.e., 0.degree.in FIG. 11) and
90.degree.<.theta..sub.EL2<180.degree. in the second region.
A rubbing angle direction (.theta..sub.R) in the alignment layer is
relative to the longitudinal direction of the gate bus line 141.
The angle .theta..sub.R of the rubbing direction in the alignment
layer is larger than the angle .theta..sub.EL1 of the electrode
elongation direction in the first region, and smaller than the
angle .theta..sub.EL2 of the electrode elongation direction in the
second region. Thus, the relationship among the angles of
.theta..sub.EL1, .theta..sub.R, .theta..sub.EL2, is,
.theta..sub.EL1<.theta..sub.R<.theta..sub.EL2. Therefore, the
liquid crystal molecules in the first region I and the second
region II are aligned symmetrically with each other and rotated in
the opposite direction with each other having the intermediate grey
level in the applied voltage state. Therefore, the color shifting
according to the viewing angle direction is compensated as
similarly in the first embodiment.
[0069] Referring to FIGS. 12 and 13 a third embodiment will be
described. An optical axis direction of the pixel is shown in FIG.
13. While the electrode elongation direction is divided into
several regions in the pixel in the first and second embodiments,
the electrode elongation direction of all of the pixel is the same
and a rubbing direction is different from each region. Further, it
is possible to control the alignment state of the liquid crystal
molecules in each region in the third embodiment. The angles
.theta..sub.EL1, .theta..sub.EL2 of electrode elongation directions
on the first region I and the second region II are
.theta..sub.EL1=90.degree., .theta..sub.EL2=90.degree.,
respectively, relative to the longitudinal direction (shown as
0.degree.in FIG. 13) of the gate bus line 241, and the angles
.theta..sub.ER1, .theta..sub.R2 of rubbing directions in each
region are 0.degree.<.theta..sub.R1<90.degree.,
-90.degree.<.theta..sub.R2&- lt;0.degree.. Also, the
relationship between the rubbing direction(.theta..sub.R1) of the
first region I and the rubbing direction(.theta..sub.R2) of the
second region II is .theta..sub.R1=-.theta.R2. The liquid crystal
molecules on the first region I and the second region II are thus
rotated clockwise and counterclockwise, respectively.
[0070] The molecules are in the opposite direction with each other
at an intermediate grey level in the applied voltage state and
aligned symmetrically relative to the longitudinal direction of the
gate bus line 241. Thus, the color shifting according to viewing
angle direction is compensated in this embodiment.
[0071] The rubbing process is to determine the alignment direction
of the alignment layer in the each embodiments. The alignment
direction may also be determined by irradiating the ultraviolet
light into the alignment layer using the light alignment material
as an alignment layer.
[0072] The present invention provides an in-plan switching mode
liquid crystal display device that the pixel is divided into a
plurality of regions. The data electrode and the common electrode
of each region are symmetric relative to the longitudinal direction
of the gate bus line. The electrode elongation direction is in
common relative to the longitudinal direction of the gate bus line
and the rubbing directions are different from each region. The
color shifting is thus corrected by the birefringence of the liquid
crystals.
[0073] Further, since the rotation angle of the twisted liquid
crystal molecules is large, the liquid crystal layer may be formed
with a large thickness. The inexpensive driving IC may be used to
maintain the maximum transmittance ratio because of the lower
driving voltage. Also, the light through the liquid crystal layer
remains in the linearly polarized state without using the polarizer
so that the production cost is reduced for color shift correction.
Moreover, a liquid crystal display device having a high reliability
may be fabricated with the conventional twisted nematice liquid
crystal in the present invention.
[0074] It will be apparent to those skilled in the art that various
modifications and variations can be made in the liquid crystal
display device of the present invention without departing from the
spirit or scope of the invention. Thus, it is intended that the
present invention cover the modifications and variations of this
invention provided they come within the scope of the appended
claims and their equivalents.
* * * * *