U.S. patent application number 13/840275 was filed with the patent office on 2013-08-08 for liquid crystal display device.
This patent application is currently assigned to INNOLUX CORPORATION. The applicant listed for this patent is INNOLUX CORPORATION. Invention is credited to Shih-Hung FAN, Cheng-Chung PENG, Yuhren SHEN.
Application Number | 20130201430 13/840275 |
Document ID | / |
Family ID | 44369426 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130201430 |
Kind Code |
A1 |
FAN; Shih-Hung ; et
al. |
August 8, 2013 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
A new type of liquid crystal display (LCD) device with improved
high transmittance and wide-view-angle characteristics while
without gray-level inversion at an inclined viewing angle is
provided. The LCD device includes a first substrate with common
electrodes, a second substrate with at least one pixel unit, a
liquid crystal (LC) layer disposed between the first substrate and
the second substrate, a first polarizer, and a second polarizer.
The pixel unit has a pixel electrode, which is formed by at least
one dense electrode area and at least one sparse electrode area.
The LC molecules of the LC layer form a continuous-domain alignment
after being driven by a voltage.
Inventors: |
FAN; Shih-Hung; (Chu-Nan,
TW) ; SHEN; Yuhren; (Chu-Nan, TW) ; PENG;
Cheng-Chung; (Chu-Nan, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INNOLUX CORPORATION; |
Chu-Nan |
|
TW |
|
|
Assignee: |
INNOLUX CORPORATION
Chu-Nan
TW
|
Family ID: |
44369426 |
Appl. No.: |
13/840275 |
Filed: |
March 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13095323 |
Apr 27, 2011 |
|
|
|
13840275 |
|
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Current U.S.
Class: |
349/96 |
Current CPC
Class: |
G02F 2001/13712
20130101; G02F 1/1395 20130101; G02F 1/133707 20130101; G02F
1/134309 20130101 |
Class at
Publication: |
349/96 |
International
Class: |
G02F 1/1343 20060101
G02F001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2011 |
TW |
100102880 |
Claims
1. A liquid crystal display (LCD) device, at least having a display
area, comprising: a first substrate with a common electrode; a
second substrate with at least one pixel unit, wherein the pixel
unit has a pixel electrode, wherein the pixel electrode comprises a
plurality of trunk electrodes, a plurality of branch electrodes and
a plurality of sub-branch electrodes, parts of the branch
electrodes are connected to one of the trunk electrodes, and at
least two of the sub-branch electrodes are connected to one of the
branch electrodes; a liquid crystal (LC) layer, disposed between
the first substrate and the second substrate, wherein after being
driven by a voltage, the LC molecules of the LC layer form a
continuous-domain alignment; a first polarizer, disposed above the
first substrate; and a second polarizer, disposed below the second
substrate and having a polarization axis perpendicular to a
polarization axis of the first polarizer.
2. The LCD device according to claim 1, wherein the LC layer adopts
a vertically aligned n-type LC material doped with chiral dopants
or a vertically aligned. negative dielectric anisotropy LC
material.
3. The LCD device according to claim 1, wherein the electrode gap
widths between the branch electrodes are different from the
electrode gap widths of the sub-branch electrodes.
4. The LCD device according to claim 3, wherein the electrode
widths or the electrode gap widths of the branch electrodes have
equal intervals.
5. The LCD device according to claim 3, wherein the electrode width
of each branch electrodes is between 1 .mu.m and 5 .mu.m.
6. The LCD device according to claim 3, wherein the branch
electrodes are branched from the trunk electrodes at any angle, and
the sub-branch electrodes are branched form the branch electrodes
at any angle.
7. The LCD device according to claim 6, wherein the angles between
the trunk electrodes and the branch electrodes are different from
the angles between the branch electrodes and the sub-branch
electrodes.
8. The LCD device according to claim 1, wherein the sub-branch
electrodes surround an outer periphery of the trunk electrodes.
9. The LCD device according to claim 1, wherein the sub-branch
electrodes surround an outer periphery of the branch
electrodes.
10. The LCD device according to claim 1, wherein the LC layer is
doped with chiral dopants and selects optimal .DELTA.nd and d/p
parameters, so that as .alpha. is at any angle, the transmittance T
is always greater than a minimal transmittance T.sub.min, where
.DELTA.n is a birefringence of the LC material, d is a thickness of
the LC layer, p is a pitch of the chiral dopants, .alpha. is
defined to be an angle included between an alignment direction of
LC molecules in the middle LC layer and a polarization axis of one
polarizer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuing application of U.S. Ser.
No. 13/095,323, filed Apr. 27, 2011, which claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No(s). 100102880, tiled
in Taiwan, Republic of China on Jan. 26, 2011, the entire contents
of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a liquid crystal display
(LCD) device, and more particularly to an LCD device with improved
high transmittance and wide-view-angle characteristics while
without gray-level inversion at an inclined viewing angle.
[0004] 2. Description of the Related Art
[0005] An LCD device controls the light transmittance by using the
characteristic that liquid crystal (LC) molecules present different
light polarization or refraction effects under different
alignments, so as to produce images.
[0006] A twisted nematic (TN) LCD device has a good light
transmittance characteristic but has an extreme narrow viewing
angle as influenced by the structure and optical characteristic of
the LC molecules. Therefore, it is a new type of breakthrough tor
the panel display technique that a display may possess the
characteristics of wide-view-angle and high light use rate at the
same time.
[0007] To solve the transmittance and viewing angle problems, a
twisted vertical alignment model has been proposed by the inventor
of the present invention, which endows the LCD device with
advantages such as the high transmittance and the wide viewing
angle. However, the LC molecules are aligned in a vertical
alignment manner, so when the LC molecules are applied with a low
voltage and the LCD device is watched at an inclined viewing angle,
a gray-level inversion problem occurs, which causes the problem of
color shift at an inclined viewing angle and influences a normal
presentation of images of the LCD device.
[0008] This mode as an example may be obtained with reference to
FIGS. 1A to 1E FIG. 1A is a schematic view of azimuth angle and
polar angle. FIG. 1B illustrates an electrode structure of a
twisted vertical alignment mode. FIG. 1C. illustrates V-T curves of
LC at different inclined viewing angles (i.e. polar angles) when
optical axis of an upper polarizer and a lower polarizer of a LC
cell respectively set to be 0.degree. and 90.degree.. From FIGS. 1C
to 1E, it is known that a gray-level inversion occurs at an
inclined viewing angle of 55.degree. in the situation of a low gray
level voltage and an azimuth angle of 0.degree. and 90.degree..
[0009] To eliminate, the distortion of V-T curves of the inclined
viewing angle, in the prior art, two or more alignment domains are
formed in the same pixel, and the V-T curves of the inclined
viewing angle in every domain are made to be complementary so as to
eliminate the gray-level inversion characteristic. In practice,
three specific methods are provided, which are explained as
follows. In the first method, one pixel is divided into multiple
display areas, and every display area forms a different voltage by
means of capacitive coupling, thereby producing the alignment
effect of multiple display areas. In the second method, one pixel
is divided into multiple display areas and two thin film
transistors are used to make each display area form a different
voltage, thereby solving the gray-level inversion problem. in the
third method, the pixel is divided into two or more display areas
and an electronic barrier material is covered above a part of
electrode of the display area, thereby producing the alignment
effect of multiple display areas.
[0010] However, the methods for solving the gray-level inversion
problem in the prior arts have complicated LCD device processes. In
view of the above, it is the subject of the present invention to
provide a simple method with improved high transmittance and the
wide-view-angle characteristics while eliminating the gray-level
inversion at an inclined viewing angle by producing different
electrical fields in each display area, so that the LCD device can
present optimal images.
SUMMARY OF THE INVENTION
[0011] The present invention is directed to an LCD device with high
transmittance and wide-view-angle characteristics while using a
pixel electrode with at least one dense electrode area and at least
one sparse electrode area to solve gray-level inversion at an
inclined viewing angle,
[0012] To achieve the above objectives, the present invention
provides an LCD device at least having a display area, which
includes a first substrate, a second substrate, an LC layer, a
first polarizer, and a second polarizer. The first substrate has a
common electrode. The second substrate has at least one pixel unit.
The pixel unit has a pixel electrode and the pixel electrode
consists of at least one dense electrode area and at least one
sparse electrode area. The LC layer is disposed between the first
substrate and the second substrate and LC molecules form a
continuous-domain alignment after being driven by a voltage. The
first polarizer is disposed above the first substrate. The second
polarizer is disposed below the second substrate and has a
polarization axis perpendicular to a polarization axis of the first
polarizer.
[0013] In an embodiment, the pixel electrode preferably includes a
plurality of trunks. Each trunk forms a plurality of branch
electrode areas after being branched each time. The plurality of
branch electrode areas has different electrode widths and/or
electrode gap widths to form the dense electrode area and the
sparse electrode area.
[0014] In an embodiment, the LC layer is preferably doped with
chiral dopants and selects optimal .DELTA.nd and dip parameters, so
that as .alpha. is at any angle, a transmittance T is always
greater than a minimal transmittance T.sub.min, and the T.sub.min
may be 0.9 or less of a maximal transmittance, where .DELTA.n is a
birefringence of an LC material, d is a thickness of the LC layer,
p is a pitch of the chiral dopants, .alpha. is defined to be an
angle included between an alignment direction of LC molecules in
the LC layer and a polarization axis of one polarizer. Under the
maximal operating voltage, the dip parameter is preferably set
between 0.222-0.36 and .DELTA.nd parameter is preferably set
between 0.465-0.620.
[0015] To make the present invention comprehensive, the specific
contents and effects of the present invention are illustrated in
details below with reference to the exemplary embodiments in
accompanying with drawings and numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will become more fully understood from
the detailed description given herein below for illustration only,
and thus are not limitative of the present invention, and
wherein:
[0017] FIG. 1A is a schematic view of a polar angle and an azimuth
angle;
[0018] FIG. 1B is a schematic view of a twisted vertical alignment
electrode structure;
[0019] FIG. 1C shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 1B is at 0.degree. azimuth
angle;
[0020] FIG. 1D shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 1B is at 90.degree. azimuth
angle;
[0021] FIG. 1E shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 1B is at 45.degree. azimuth
angle;
[0022] FIG. 2A is a schematic view of a pixel electrode structure
in the first embodiment;
[0023] FIG. 2B is a side view of low gray level voltage molecules
in areas A and B in FIG. 2A;
[0024] FIG. 2C shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 2A is at 0.degree. azimuth
angle;
[0025] FIG. 2D shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 2A is at 90.degree. azimuth
angle;
[0026] FIG. 3A is a schematic view of a pixel electrode structure
in the second embodiment;
[0027] FIG. 3B shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 3A is at 0.degree. azimuth
angle;
[0028] FIG. 3C shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 3A is at 90.degree. azimuth
angle;
[0029] FIG. 4A is a schematic view of a pixel electrode structure
in the third embodiment;
[0030] FIG. 4B shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 4A is at 0.degree. azimuth
angle;
[0031] FIG. 4C shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 4A is at 90.degree. azimuth
angle;
[0032] FIG. 5A is a schematic view of a pixel electrode structure
in the fourth embodiment;
[0033] FIG. 5B shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 5A is at 0.degree. azimuth
angle;
[0034] FIG. 5C shows V-T curves at an inclined viewing angle when
the electrode structure in FIG. 5A is at 90.degree. azimuth angle;
and
[0035] FIGS. 6A to 6U show different of pixel electrode pattern
structure.
DETAILED DESCRIPTION OF THE INVENTION
[0036] To eliminate the problems existing in the prior arts, the
pres provides a new type of electrode architecture which is
designed for a single display area, in which one or more display
areas form a single pixel to obtain an expected function.
[0037] The present invention discloses an LCD device at least
having a display area, which includes a first substrate, a second
substrate, an LC layer, a first polarizer, and a second polarizer.
The first substrate has a common electrode. The second substrate
has at least one pixel unit. The pixel unit has a pixel electrode.
The pixel electrode consists of at least one dense electrode area
and at least one sparse electrode area. The LC layer is disposed
between the first substrate and the second substrate. After being
driven by a voltage, the LC molecules of the LC layer form a
continuous-domain alignment. The first polarizer is disposed above
the first substrate. The second polarizer is disposed below the
second substrate and has a polarization axis perpendicular to a
polarization axis of the first polarizer.
[0038] The pixel electrode includes a plurality of trunks. Each
trunk forms a plurality of branch electrode area after being
branched each time. The plurality of branch electrode areas has
different electrode widths and/or electrode gap widths, so as to
form the dense electrode area and the sparse electrode area. In
each branch electrode area, the electrode may be branched at any
angle. In an embodiment, the branch electrode areas of the dense
electrode area and the sparse electrode area may also be
respectively branched at different angles.
[0039] Furthermore, in each branch electrode area, the electrode
widths or the electrode gap widths may also have equal intervals or
non-equal intervals. The electrode width is between 1 .mu.m and 5
.mu.m.
[0040] The alignment method of the dense electrode area and the
sparse electrode area may be as follows. The dense electrode area
surrounds an outer periphery of the sparse electrode area.
Alternatively, the sparse electrode area surrounds an outer
periphery of the dense electrode area. Alternatively, the sparse
electrode area and the dense electrode area are both arranged
between the trunks.
[0041] Bumps, recesses or an electrode pattern structure that forms
a fringe field may also be disposed at a center and/or on periphery
of the pixel unit between the first substrate and the second
substrate, so as to improve the stability of molecular
alignment.
[0042] The LC layer may adopt a vertically aligned negative
dielectric anisotropy LC material doped with chiral dopants or a
vertically aligned n-type LC material. During implementation, the
LC layer is preferably doped with chiral dopants and selects
optimal .DELTA.nd and dip parameters, so that as .alpha. is at any
angle, the transmittance T is always greater than a minimal
transmittance T.sub.min and the T.sub.min may be 0.9 or less of a
maximal transmittance, where .DELTA.n is a birefringence of the LC
material, d is a thickness of the LC layer, p is a pitch of th
chiral dopants, .alpha. is defined to be an angle included between
an alignment direction of LC molecules in the middle LC layer and a
polarization axis of one polarizer. T.sub.min is, for example, 0.9
of the maximal transmittance, and under the maximal operating
voltage, the dip parameter is preferably set between 0.222-0.36 and
.DELTA.nd parameter is preferably net between 0.465-0.620.
[0043] To further explain the embodiments of the present invention,
four different implementations are illustrated as follows.
Embodiment 1
[0044] In FIG. 2A, a square LCD unit as shown in the figure is
taken as an example in this embodiment. In a display apparatus, one
or more LCD units form one pixel unit, and the LCD unit is not
limited to be square. In this embodiment, the LC layer adopts a
twisted vertical alignment mode. In the condition that T.sub.min is
0.9 of the maximal transmittance and under the maximal operating
voltage, preferably, the range of parameter dip is 0.222-0.360, the
range of parameter .DELTA.nd is 0.465-0.620, and the electrode
width is between 1-5 .mu.m. For simplicity, in this embodiment, the
simulation is carried out under the conditions that d/p=0.277 and
.DELTA.nd=0.530, and the optical axis of the upper and lower
polarizers of the liquid crystal cell are respectively set to be at
0.degree. and 90.degree..
[0045] In FIG. 2A, the electrode width of the pixel electrode
pattern is 2.5 .mu.m, in which four trunks extend to form branch
electrode areas B with a gap width of 7.5 .mu.m. Each branch
electrode area. B may extend to form a new type of branch electrode
areas A with a gap width of 2.5 .mu.m. The branch electrode areas A
are the dense electrode areas outside and the branch electrode
areas B are the sparse electrode areas inside.
[0046] After a voltage is applied, due to the function of the
surrounding fringe field, the LC molecules are inclined towards the
center of the display area and present a continuous symmetrical
alignment. The electrodes are dense and the electrical field is
large in the area A, so the LC molecules are inclined at a large
angle. The electrodes are sparse in the area Band the electrical
field in the area B is smaller than that of the area A, so the LC
molecules are inclined at a small angle (as shown in FIG. 2B). In
other words, the LC molecules in the above two areas have different
inclined angles in accordance with the changes of the voltage, and
optically form a different V-T curves.
[0047] During the implementation, the transmittance at the inclined
viewing angle of the areas A, B can be easily modulated by
modulating the electrode density and the area of the areas A and B,
thus achieving the complementary effect. As shown in FIGS. 2C and
2D, under the condition that the area of the dense electrode is set
to account for 2/9 of the total area, the transmittance curve graph
at the inclined viewing angle is simulated. It can be easily found
from the graph that the inversion at the inclined viewing angle can
be completely eliminated by the complementary of the areas A and B,
thereby further improving the characteristic of the viewing
angle.
Embodiment 2
[0048] In this embodiment, a 100 .mu.m.times.100 .mu.m square LCD
unit is taken as an example for illustration. FIG. 3A illustrates a
pixel electrode, in which the pixel electrode structure is divided
into a dense electrode area A and a sparse electrode area B. The
dense electrode area A is a periodic structure consisting of 2.5
.mu.m electrode and 2.5 .mu.m electrode gap, and the sparse
electrode area B is a periodic structure consisting of 2.5 .mu.m
electrode and 7.5 .mu.m electrode gap. The area A surrounds an
outer periphery of the area B and is connected to the area B by a
wire under the substrate.
[0049] After a voltage is applied, the electrical field of the area
A is large, so the LC molecules are inclined at a large angle. The
electrical field of the area B is small, so the LC molecules are
inclined at a small angle accordingly. At last, after the electrode
areas of the areas A and B are modulated, under the above design
conditions, when the area of the area A is smaller than 0.5 of the
total area, the V-T curve inversion at the inclined viewing angle
can be eliminated. As shown in FIGS. 3B and 3C, under the condition
that the area of the area A is 2/9 of the total area, the area A
and the area B are complementary, thus effectively eliminating the
inversion problem.
Embodiment 3
[0050] In this embodiment, a 100 .mu.m.times.100 .mu.m square LCD
unit is taken as an example for illustration. FIG. 4A illustrates a
pixel electrode, in which the pixel electrode structure has a dense
electrode area A and a sparse electrode area B formed by a trunk
branched at 45.degree.. The dense electrode area A is a periodic
structure consisting of 4 .mu.m electrode and 4 .mu.m electrode
gap, and the sparse electrode area B is a periodic structure
consisting of 4 .mu.m electrode and 12 .mu.m electrode gap. The
area A surrounds an outer periphery of the area B.
[0051] After a voltage is applied, the electrical field of the area
A is large, so the LC molecules are inclined at a large angle. The
electrical field of the area B is small, so the LC molecules are
inclined at a small angle accordingly.
[0052] At last, after the electrode areas of the areas A and B are
modulated, under the above design conditions, when the area of the
area A is smaller than 0.5 of the total area, the V-T curve
inversion at the inclined viewing angle can be eliminated. As shown
in FIGS. 4B and 4C, under the condition that the area of the area A
is 2/9 of the total area, the area A and the area B are
complementary, thus effectively eliminating the inversion
problem.
Embodiment 4
[0053] In this embodiment, a 100 .mu.m.times.100 .mu.m square LCD
unit is taken as an example for illustration. FIG. 5A illustrates a
pixel electrode, in which the pixel electrode structure has a dense
electrode area A and a sparse electrode area B on the left and the
right branched by a trunk, and the dense and sparse electrode areas
may be exchanged. The dense electrode area A is a periodic
structure consisting of 2.5 .mu.m electrode and 2.5 .mu.m electrode
gap and the sparse electrode area B is a periodic structure
consisting of 2.5 .mu.m electrode and 7.5 .mu.m electrode gap.
[0054] After a voltage is applied, the electrical field of the area
A is large, so the LC molecules are inclined at a large angle. The
electrical field of the area B is small, so the LC molecules are
inclined at a small angle accordingly.
[0055] At last, after the electrode areas of the areas A, B are
modulated, under the above design conditions, when the area of the
area A is smaller than 0.5 of the total area, the V-T curve
inversion at the inclined viewing angle can be eliminated. As shown
in FIGS. 5B and 5C, under the condition that the area of the area A
is 1/2 of the total area, the area A and the area B are
complementary, thus effectively eliminating the inversion
problem.
[0056] In addition to the above embodiments, the pattern of the
pixel electrode may also be designed to be other suitable
structures. FIGS. 6A to 6U show different pixel electrode pattern
structures. FIGS. 6A to 6K show a pixel electrode pattern structure
aligned at 45.degree. and 135.degree.. FIGS. 6L to 6U show a pixel
electrode pattern structure aligned at 0.degree. and 90.degree..
Furthermore, as shown in FIGS. 6A-6I and FIGS. 6L-6R, each branch
electrode may also be connected with more than two new branches. As
shown in FIGS. 6D, 6G, 6L and 6P, the branch connection electrode
may also be designed to have a certain angle.
[0057] As shown in FIGS. 6A and 6F, the two have the same dense
electrode period and different sparse electrode periods. In FIGS.
6J and 6S, the sparse electrode is disposed at an outer periphery
of the dense electrode. In FIG. 6K, the sparse and the dense
electrode areas have different electrode angles, In FIGS. 6H and
6Q, the widths of the sparse electrode and the dense electrode are
different. In FIGS. 6I and 6R, in the same electrode area (e.g. the
sparse electrode area herein), different periods may exist. In
FIGS. 6T and 6U, the inner and outer electrodes are endowed with
different electrode widths, thus obtaining the sparse and the dense
electrode areas.
[0058] According to the electrode pattern structures in the above
embodiments and FIGS. 6A to 6U, all the electrode and gap widths of
the sparse electrode area and the dense electrode area or the
design of the electrode shape and the area proportion are always
adjusted in accordance with different practical applications,
thereby eliminating the V-T curve inversion at the inclined viewing
angle.
[0059] In summary, the present invention can truly achieve the
expected objectives and provide an LCD device with high
transmittance and wide-view-angle characteristics while without
gray-level inversion at an inclined viewing angle. Therefore, the
present invention certainly has the industrial applicability and is
proposed and applied for a patent according to law.
[0060] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *