U.S. patent application number 09/774615 was filed with the patent office on 2001-08-16 for liquid crystal display device and method of manufacturing the same.
Invention is credited to Suzuki, Seiji.
Application Number | 20010013853 09/774615 |
Document ID | / |
Family ID | 18021416 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013853 |
Kind Code |
A1 |
Suzuki, Seiji |
August 16, 2001 |
Liquid crystal display device and method of manufacturing the
same
Abstract
An liquid crystal panel is provided which is suitable for a wide
screen and for driving by the transverse electric field. The liquid
crystal display is composed of an array substrate on which TFTs are
arranged as active switching elements in a matrix form and covered
with an orientation film. On the facing surface of the opposing
substrate as a color filter, a light shielding film, color layers
of red, green, and blue are arranged, and the area excluding the
area covered by the light shielding layer is turned into a display
pixel area, and all of the surfaces of the opposing subatrate are
then covered with an orientation film. The cell gap g at the
display pixel area is formed so as to be larger than spacers in the
cell, and cell gaps of color layers overlapping the light shielding
layer are made smaller than spacers. The cell gaps of these
overlapped layers hold spaces at an compressed state with the array
substrate. That is, the step configuration is formed between the
display pixel area of red, green, and blue color layers R2, G2, and
B2 and the overlapped colored layers with the light shielding
layers composed of R1, R2, and R3. Thereby, the liquid crystal
molecules will not be subjected to the anomalous orientation and
the light leakage is avoided. At the same time, an after-image
characteristic to the IPS type a-Si TFT liquid crystal panel can be
eliminated by regulating the projection of the color layers.
Inventors: |
Suzuki, Seiji; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037-3213
US
|
Family ID: |
18021416 |
Appl. No.: |
09/774615 |
Filed: |
February 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09774615 |
Feb 1, 2001 |
|
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09190007 |
Nov 12, 1998 |
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Current U.S.
Class: |
345/92 |
Current CPC
Class: |
G02F 1/134363 20130101;
G02F 1/133514 20130101; G02F 1/13394 20130101; G02F 1/133512
20130101 |
Class at
Publication: |
345/92 |
International
Class: |
G09G 003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 1997 |
JP |
9-311782 |
Claims
What is claimed is:
1. A liquid crystal display panel comprising: an array substrate
having switching elements disposed in an matrix form and an
orientation film formed on the uppermost layer; an opposing
substrate having a light shielding layer and the color layers and
an orientation film on the uppermost layer of those films and the
color layers, in which the area excluding the area covered by said
light shielding layer is turned into the display area; and a liquid
crystal layer formed in between said array substrate and said
opposing substrate; wherein a cell gap of said display area is
formed so as to be larger than the diameter of the spacers, and the
cell gap at the color layer area overlapping the light shielding
layer is formed so as to be smaller than the diameter of the
spacer, such that said spacers in said smaller cell gap are held at
the compressed state between said array substrate.
2. A liquid crystal display panel according to claim 1, wherein
said color layer is formed higher than said display area such that
the cell gap forms a step between the display area and said color
layers.
3. A liquid crystal display panel according to claim 2, wherein
said color layer area is formed in the form of stripes.
4. A liquid crystal display panel according to claim 2, wherein the
height of said projected color layer is determined such that the
polarization anisotropy of said orientation film is within a
predetermined value.
5. A liquid crystal display panel according to claim 1, wherein
said spacers are freely movable in said cell gap of the display
area.
6. A liquid crystal display panel according to claim 5, wherein
said liquid crystal panel is constructed so as to be able to
eliminate the anomalous orientation of liquid crystal molecules and
to be able to eliminate the leakage of light by giving said liquid
crystal a restraint force (orientation restraining force) to
restraint the liquid crystal molecules into a certain
direction.
7. A liquid crystal display panel according to claim 1, wherein
said array substrate is a TFT (thin film transistor) substrate in
which TFT are arranged as switching elements so as to be operated
as an active matrix display system.
8. A liquid crystal display panel according to claim 7, wherein
said TFTs are formed on the uppermost surface of the layers formed
on said array substrate, and the cell gap formed between said TFTs
and the concaved area of color layers of the opposing substrate are
formed so as to be smaller than diameters of said spacers in the
cell.
9. A liquid crystal display panel according to claim 1, wherein
said liquid crystal display panel can be enlarged into more than a
wide image area of 14.1 inches in diagonal.
10. A liquid crystal display panel according to claim 9, wherein
said liquid crystal display panel can be driven by the transverse
electric field (IPS).
11. A method of manufacturing a liquid crystal display panel
comprising a liquid crystal layer inserted in between two
substrates, one of which is an array substrate having switching
elements arranged in a matrix form and an orientation film coated
on the upper most layer, and the other of which is a opposing
substrate as a color filter having a display pixel area coated by
color layers except an area covered by the light shielding film,
and an orientation film coated on the uppermost layer of these
layers; wherein, on the opposing substrate, the cell gap at the
display pixel area is formed so as to be larger than spacers
inserted in the cell, and the cell gap at the area of the color
layer including the light shielding layer is formed so as to be
smaller than spacers such that the cell gap is formed in a step
form, and the difference of heights between the higher display
pixel area and the lower color layer is determined such that the
polarization anisotropy of the orientation film turns into a
predetermined value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a liquid crystal display device
(LCD) and particularly relates to a wide image plane, color liquid
crystal display device having a wide angle of visibility by an
active matrix display system.
[0003] This application is based on Patent Application No. Hei
9-311782 filed in Japan, the content of which is incorporated
herein by reference.
[0004] 2. Background Art
[0005] In general, in a liquid crystal display device, a mode for
driving the liquid crystal cell by a vertical electric field is
most widely used, including a TN (twisted nematic) and an STN
(super twisted nematic) modes. However, recently, a new driving
mode by a transverse electric field (IPS) is now being intensively
researched.
[0006] When a comparison is made between the above two driving
modes in terms of an image quality of the liquid crystal cells, it
is far more difficult to obtain the good image quality with the
transverse electric field mode, due to the panel structure. In
particular, an important factor which affects on the image quality
is a spacer for maintaining the gaps of cells at a fixed space.
[0007] The spacer is a group of spherical beads for supporting a
pair of substrates facing each other at a fixed spacing. One of a
pair of substrates is a TFT (Thin Film Transistor) array substrate
(hereinafter, called "an array substrate") using TFTs as switching
elements for driving, and another one of the pair of substrates is
a color filter substrate (hereinafter, called "an opposing
substrate") on which three color layers of RGB (red, green, and
blue) are coated. When assembling a display panel, these array
substrate and the opposing substrate are adhered to form a cell,
placing spacers therebetween. As the spacer beads, elastic organic
materials such as a resin using divinylbenzene are generally used.
Although inorganic materials such as silica are sometimes used,
they are not the main material for the spacer because of a tendency
to generate foams when the pressure is reduced.
[0008] When a comparison of a leakage of the light is made between
the two types of liquid crystal panels, one driven by a vertical
electric field and the other driven by a transverse electric field,
the panel driven by the transverse electric field is more likely to
cause light leakage than the panel driven by the vertical electric
field.
[0009] One reason for the above result is based on the difference
of the normal driving modes in a display operation. That is, for
devices driven by the vertical electric field such as the TN mode
or the STN mode devices, a normally-white mode is superior for
increasing the contrast, while it is advantageous for better
contrast to use a normally-black mode for devices driven by the
transverse electric field. Thus, it is more likely for liquid
crystal display devices driven by the transverse electric field to
cause light leakage around spacers when the voltage applied to each
cell is null.
[0010] The second reason is based on the difference of the driving
directions of the liquid crystal. That is, when a device is driven
by the vertical electric field, the liquid crystal is driven in the
vertical direction perpendicular to a pair of substrates, while the
liquid crystal is twisted horizontally when driven by the
transverse electric filed. Consequently, a difference is caused in
the orientation of liquid crystal by the direction of the electric
field, especially in the direction of depth of the liquid crystal,
causes an anomalous orientation around spacers by the transverse
electric field to cause leakage of light.
[0011] The third reason is based on the presence of a chiral
crystal. In the devices driven by the vertical electric field such
as TN and STN devices, a rubbing direction of one substrate is
rotated 90 degrees or 270 degrees against the rubbing direction of
the orientation film formed on another substrate, and a chiral
material is included in the liquid crystal for facilitating the
twisted orientation at a desired direction. In contrast, in the
devices driven by the transverse electric field, the rubbing
directions of a pair of substrates are directions anti-parallel to
each other, so that the orientation of the liquid crystal is
homogeneous, and the liquid crystal does not contain the chiral
material. Consequently, since the liquid crystal has a high degree
of freedom in orientation when the device is driven by the
transverse electric field, the liquid crystal around the spacers is
thereby likely to be subjected to an anomalous orientation which
can cause leakage of light when driven by the transverse electric
field.
[0012] The liquid crystal molecules located around spacers are more
likely to be subjected to the above anomalous orientation when the
external force is applied on the cell. This is because the liquid
crystal molecules are oriented around the spherical spacers by the
external force.
[0013] Technical proposals for preventing deterioration of the
image quality by spacers are presented in, for example, Japanese
Patent Application, First Publication No. Hei 7-281195, entitled "a
liquid crystal display panel"; and in Japanese Patent Application,
First Publication No. Hei 7-281195, entitled "a liquid crystal
display device and method of manufacturing the same".
[0014] In the former Patent Application, as shown in FIG. 5,
transparent and colored CF (Color Filter) layers 52 are disposed at
an fixed intervals, black light shielding layers 53 are formed
therebetween, and spherical spacers are scattered on the surface of
the light shielding layer 53. Assume that distances from the CF
filter layer 52 and the light shielding layer 53 to the opposing
substrate 56 are LC and LB, and the diameter of spacer 54 is D, a
dimensional relationship of the liquid crystal panel is represented
as LC<D<LB.
[0015] The spacers on the light shielding layer are only held
between the pair of the substrate 51 and 56. In contrast, spacers
54 on the color filter layer 52 fall downward toward the bottom in
the liquid crystal between both substrates, when the panel is stood
in an upright position. Thereby, spacers 54 are removed from the
display pixel area 55 to prevent an anomalous orientation of the
liquid crystal and thereby avoid the deterioration of the image
quality.
[0016] An attempt of a mathematical analysis will be described. A
size of the display cell of the liquid crystal display panel is
generally within a range from 100 to 300 .mu.m, and the cell gap
between these cells are roughly 3 to 6 .mu.m.
[0017] When the panel is stood in an upright position, a spacer
located at the upper end of the screen area falls into the outer
position of the screen without abutting the substrates. The
standing angle .theta. of the panel is expressed as,
cos .theta.=cell gap/size of cells=6/100
[0018] From the above equation, a .theta. of 86.6.degree. is
obtained, corresponding to an angle when the spacer is considered
as a "point".
[0019] The falling speed of the spherical spacers in the liquid
crystal with a thickness of 100 .mu.m can be calculated by the
following Stokes' Equation, under a condition of Rep<2. 1 Vt = (
p - f ) gDp 2 / 18 = 0.4 ( m / sec )
[0020] where, .rho.p is a density of the spacer, which value is 1.1
to 1.3, when the spacer is made of organic materials such as
divinylbenzene or styren resins; .rho.f is a density of the liquid
crystal, which value is generally around 1.0 to 1.2; and .mu. is a
viscosity of the liquid crystal, which is generally around 15 to 20
mm.sup.2/sec.
[0021] When values of .rho.p=1.3, .rho.f=1.0, Dp=6 .mu.m, and
.mu.=15 mm.sup.2/sec are substituted in the above equation, the
falling speed of the spacer is obtained as 0.4 (.mu.m/sec). This
result shows that it takes 250 sec to fall a distance of 100 .mu.m.
This falling speed seems not so effective in the practical display
operation.
[0022] In turn, as shown in FIG. 6, a technique to maintain cells
at a fixed value without using spacers is proposed in Japanese
Patent Application, First Publication No. Hei 7-28119.
[0023] This proposal is related to the TN mode liquid crystal
panel, and a first projection is mounted for forming cell gaps at
the black-matrix 63 formed in the TFT 62 on the arrayed substrate
61. On the opposing substrate 65 for forming CF (Color Filters), a
second projection is formed by laminating the red layer 66, green
layers, and the blue layers. The first projection and the second
projection have a height which corresponds to a half of the cell
gap Ga. Therefore, the orientation films 70 and 71 can be
sufficiently subjected to the rubbing treatment, so that the TN
liquid crystal molecules 72 are ensured to be lined up in a regular
pattern. Thereby, it is possible to prevent the anomalous
orientation and thus the light leakage by the liquid crystal panel
in which it is not necessary to use the spacers.
[0024] In the above disclosure, if the height of the projection is
higher than 5 .mu.m or more, the rubbing treatment is then not
sufficiently executed because a part is hidden by the projection
causing irregular orientation of the liquid crystal. In order to
avoid this, the height of the projections is limited to less than
3.8 .mu.m.
[0025] In the liquid crystal panel driven by the transverse
electric field, beside the problem that it is hard to arrange the
liquid crystal molecules in a predetermined direction, there is an
important problem concerning a force of constraint for constraining
the liquid crystal molecule in a predetermined direction. If the
force of constraint in a predetermined direction (hereinafter
referred to as an orientation restraining force) is weak, a picture
image after switching from displaying another picture image will
contain the after-image of the previous image. Therefore, the
orientation restraining force has an affect on the image
quality.
[0026] As described hereinabove, the liquid crystal panel driven by
the transverse electric field has many problems that must be
solved. In contrast, the liquid crystal panel driven by the
transverse electric field has the advantageous feature that the
wide display image plane with a wide angle of visibility is
obtained.
[0027] It is therefore an object of the present invention to
provide a liquid crystal display device with a wide display image
plane and with a wide angle of visibility having a good cell image
quality by preventing a light leakage around the spacers for
maintaining a fixed cell gap and by preventing after images due to
the weak orientation restraint force.
SUMMARY OF THE INVENTION
[0028] The liquid crystal display panel of the present invention
comprises:
[0029] an array substrate having switching elements disposed in an
matrix form and an orientation film formed on the uppermost
layer;
[0030] an opposing substrate having a light shielding layer and the
color layers and an orientation film on the uppermost layer of
those films and the color layers, in which the area excluding the
area covered by said light shielding layer is turned into the
display area; and
[0031] a liquid crystal layer formed in between said array
substrate and said opposing substrate;
[0032] wherein the cell gap of said display area is formed so as to
be larger than the diameter of the spacers, and the cell gap at the
color layer area overlapping the light shielding layer is formed so
as to be smaller than the diameter of the spacer, such that said
spacers in said smaller cell gap are held at the compressed state
between said array substrate.
[0033] In this construction, said color layer is formed elevated
above said display area such that the cell gap forms a step between
the display area and said color layers.
[0034] Furthermore, said color layer area is formed in the form of
stripes and the opposing substrate is formed so as to form a step
between a display cell portion and a color filter portion, wherein
the color filter portion is formed higher than said display cell
portion.
[0035] In contrast, a method of manufacturing the liquid crystal
panel comprising the steps of:
[0036] forming an array substrate by arranging switching elements
in the matrix form and forming an orientation film on the uppermost
layer of said switching elements;
[0037] forming an opposing substrate by forming a light shielding
film and color layers and forming a display cell portion on said
color layer portion by forming the orientation film on said display
cell portion; and
[0038] forming by inserting a liquid crystal in between said array
substrate and said opposing substrate;
[0039] wherein a step is formed such that said cell gaps of said
display cell portion on the opposing substrate are larger than that
of the spacer diameter, and the cell gap of the color layers
corresponding to the light shielding layer is made smaller than the
spacer, and the height difference between said higher display
portion and said lower color portion is formed so as to define the
polarization anisotropy of said orientation film.
[0040] According to the above structure and the method of
manufacturing, the cell gap of the display cell portion is formed
higher than the spacer diameter as much as 0.3 .mu.m, the liquid
crystal molecules around the spacer are not subjected to the
anomalous orientation, so that the light leakage is prevented.
Furthermore, the after image due to the orientation restraining
force is prevented in a liquid crystal display panel of a-Si TFT
driven by an IPS (transverse electric field).
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIGS. 1(a) and 1(b) are planar views showing an array
substrate and an opposing substrate of an IPS type a-Si TFT liquid
crystal panel as an embodiment of the liquid crystal display panel
of the present invention.
[0042] FIGS. 2(a) and 2(b) are cross sectional views of FIGS. 1(a)
and 1(b) sectioned by line A-A and line B-B of FIGS. 1(a) and
1(b).
[0043] FIG. 3 is a graph showing a relationship between the
cell-gap and occupation ratio of light leaking spacers.
[0044] FIG. 4 is a graph showing the relationship between the
height of cell projections, the time of the after-image, and the
polarization anisotropy in an another embodiment of the present
invention.
[0045] FIG. 5 is a diagram of a conventional example shown in the
Japanese Patent Application, First Publication No. Hei 8-62606.
[0046] FIG. 6 is a diagram of a conventional example shown in the
Japanese Patent Application, First Publication No. Hei 8-62606.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] The liquid crystal display panel driven by the transverse
electric field (abbreviated to IPS) according to an embodiment of
the present invention will be described hereinafter referring to
attached drawings.
[0048] FIGS. 1(a) and 1(b) illustrate a pair of glass substrates
facing each other at a predetermined distance. FIG. 1(a) shows a
enlarged planar view of the array substrate 1, in which active
matrix type TFTs for switching elements are formed. FIG. 2(b) shows
an enlarged planar view of the opposing substrate 2 to the array
substrate 1, in which color filters are formed. The array substrate
1 is depicted in view of the film surface, and the opposing
substrate is depicted in view of the glass substrate side. FIGS.
2(a), 2(b) are cross-sectional views corresponding to line A-A and
line B-B of FIGS. 1(a) and 1(b).
[0049] The channel carved type amorphous silicon (a-Si) TFTs are
used for as TFT elements of the liquid crystal panel driven by the
transverse electric field, and color layers formed in the form of
stripes are used as the opposing substrate 2. This is called
hereinafter an IPS type a-Si TFT liquid crystal panel for
convenience.
[0050] A method of manufacturing the IPS type a-Si TFT liquid
crystal display panel will be described referring to FIGS. 1 and
2.
[0051] A non-alkali glass plate with a thickness of 0.7 mm is used
for the array substrate 1. IPS type TFTs are formed on this array
substrate 1. The structure of the TFT when viewed from the glass
substrate is formed in the following order.
[0052] A gate electrode 10 and the common electrode 11 are formed
at the side surface of the array substrate 1 by patterning metallic
chromium Cr. The thichness of these electrodes are commonly about
2000 .ANG., and an interlying insulating film of a silicon nitride
film is formed at a thickness of 4000 .ANG.. On the interlying
insulating film, a semiconductor film by an amorphous silicon
(a-Si) is formed at a thickness of 4000 .ANG..
[0053] After deposition of the semiconductor film, a source
electrode and a source electrode are formed thereon. The
semiconductor film is subjected to etching to form a channel 14,
and the a-Si TFT are formed.
[0054] On the array substrate formed by the above process is
completed by forming the protective insulating layer (passivation
film) 16 using silicon nitride. On the uppermost layer of the array
substrate 1, the orientation film 17 is formed at a thickness of
500 .ANG..
[0055] In turn, a non-alkali glass plate with a thickness of 0.7 mm
is used for the opposing substrate, and, on a surface of the
substrate, a light shielding film 20 is formed made of an acrylic
resin with dispersed carbon in a predetermined area corresponding
to the gate electrode 10 and the drain electrode 13 and their
surroundings of the array substrate at a thickness of 0.6
.mu.m.
[0056] After forming the light shielding film 20, color layers are
arranged so as to cover corresponding areas of the light shielding
film and the display pixel area 18. The color layers contain red
layers 21, green layers 22 and blue layers 23. The color layers are
formed by a pigment dispersed acrylic resin. The thickness of
respective color layers are defined as 1.4 .mu.m for the red layer
21, 1.3 .mu.m for the green layer 22, and 1.2 .mu.m for the blue
layer 23. An overcoat film 24 is coated on all of these color
layers. A transparent acrylic resin is used for the overcoat and
its thickness is defined as 1.0 .mu.m. In addition, an orientation
film 25 is coated on the overcoat film 24.
[0057] The orientation films 17 and 25 respectively applied for the
array substrate 1 and the opposing substrate 2 are the main
chain-type polyimide film in which a tilt generating component is
added to its main chain. The imidization is conducted at a
temperature of 230.degree. C. for 2 hours. The rubbing cloth used
for orientation of the polyimide film is a flocked fabric flocked
with a 24,000 strings/cm.sup.2 of rayon strings with a filament
diameter of 2.5 denier, a pile diameter of 120 denier, and a pile
length of 1.85 mm. The rubbing was performed by a rubbing role with
a role diameter of 150 mm, by an pile force of 0.5 mm, at a role
revolution of 1,000 rpm, and at a table speed of 10 mm/sec. The
direction of rubbing for the array substrate is set anti-parallel
to that for the opposing substrate.
[0058] Subsequently, the array substrate 1 and the opposing
substrate 2 are adhered and liquid crystal is injected in the space
between two substrates and sealed to form the liquid crystal layer
L. An all fluorine-type nematic liquid crystal containing no chiral
material is used for the formation of this liquid crystal.
Divinylbenzene type spacers 30 and 31 are installed for maintaining
the fixed cell gap.
[0059] The cell periphery of both of the array substrate 1 and the
opposing substrate 2 are sealed by curing a thermosetting sealing
material. An epoxy type sealing material is used as the sealing
material. The thermosetting condition at the sealing is 170.degree.
C. for 2 hours. A pressure of 500 g/cm.sup.2 was applied to the
panel during the sealing.
[0060] Polarizing plates 19 and 26 are disposed at respective rear
sides of both array substrate 1 and the opposing substrate 2. The
patching disposition of the polarizing plates are decided in the
direction to realize the normally-black mode.
[0061] The height of the sum of layers formed in the cell are as
follows. On the array substrate, the maximum thickness is 1.4 .mu.m
at the TFT region, and the thickness at the region of the common
electrode 11 and the drain electrode 13 is 0.8 .mu.m. Thus, the
difference of the thickness between the thickest region of TFT and
the display pixel region is designed to be 0.6 .mu.m.
[0062] On the opposing substrate 2, the difference of the heights
of the region where the light shielding film 20 overlaps with the
red layer 21, G1, (hereinafter, called "the red corner portion")
and the red display pixel region R2 is 0.6 .mu.m. Similarly, the
difference of the height between the region where the light
shielding film 20 overlaps with the green layer 22 G1 (hereinafter,
called "the green corner portion") and the height of the green
display pixel area G2 is 0.6 .mu.m, and the difference of the
height between the region where the light shielding film 20
overlaps with the blue layer 23, B1, (hereinafter called "the blue
corner region) and the blue display pixel region is 0.6 .mu.m.
[0063] Furthermore, when comparison is made of the heights between
the red corner region G1, the green corner region G1, and the blue
corner region B1, the red corner region is the highest and the
height then decreases in the order of the green corner region and
the blue corner region. Those corner layers are formed so as to
have respective height differences of 0.1 .mu.m.
[0064] In this embodiment, the diameter of the spacer is set to 5.5
.mu.m, and the cell gaps g are varied by changing the number of
spacers scattered in the cell from 5- to 300 pieces/cm.sup.2. The
evaluation is made by observing a rate of occurrence of the light
leakage of the liquid crystal around spacers (the anomalous
orientation) under a microscope when the completed panel is tapped
for 20 times for five points including a center and four corners by
a rubber made hammer at a force of 2.55 kg. The whole area of the
panel was observed with 300 spacers for each color. The measurement
of the cell gaps is executed by means of the He--Ne laser, the beam
diameter of which is 50 .mu.m. The measurement is conducted by
Senarmont method.
[0065] As shown in FIG. 3, it is understood that the rate of
occurrence of the light leakage for every color layer reduces
rapidly reaching to a minimum value when the cell gap g reaches
more than 5.8 .mu.m, that is, the cell gap is larger than the
spacer diameter by 0.3 .mu.m or more.
[0066] The reason for the above result is that, although spacers
located at the color corner layers of the opposing substrate 2,
that is, spacers located at the light shielding layer are held in a
compressed and deformed state, the diameters of spacers located at
the red layer are smaller than the cell gap g, so that they are
freely movable in the panel when a external force is applied to the
panel. Thus, liquid crystal molecules around spacers will not be
subjected to the anomalous orientation which causes the leakage of
light.
[0067] FIG. 4 shows a second embodiment of the present invention.
The cell construction and the materials of this embodiment are the
same as those of the first embodiment, except that the thickness of
the light shielding film is changed from 0.6 to 4.0 .mu.m, and that
the height of projections are changed.
[0068] The cell gap is set as a whole at 6.0 .mu.m, on the basis of
the red display cell used as a standard. The cell gap is controlled
by adjusting the number of spacers in the panel and by controlling
the pressure applied on the panel during sealing.
[0069] FIG. 4 is a graph showing the relationships between the
height of the projection, the time of the after-image, and the
polarization anisotropy. The after-image is measured by visually
measuring the remaining time of a black and white pattern after
switching to the all black pattern after the black and white
pattern with 10 mm intervals is displayed in a liquid crystal panel
for 30 seconds.
[0070] The measurement of the polarization anisotropy is performed
by the rotary phase-shifter method (refer to Japanese patent
Application, First Publication No. Hei 8-49320). The measurements
are executed by ellipsometry for a portion in a red display area R2
and for an area of a shadow remained without rubbing by the rubbing
treatment. The light source is the He--Ne laser, the incident angle
is 50 degree, and the spot size is 30 .mu.m. The measurement is
performed for 72 points by rotating the stage at every 5 degrees
for 360 degrees. The polarization anisotropy shown in FIG. 4 is a
difference between the maximum and minimum values of the phase
components in the reflected light.
[0071] It is understood that the sufficient orientation restraint
force is obtained because the after image remains less than 3
seconds, if the height of the projection is less than 3.3 .mu.m,
and the polarization anisotropy is less than 0.9.
[0072] A test is made to change the color layer projection from 0.6
to 4.0 .mu.m, and it is confirmed that the liquid crystal molecule
located at an area hidden by the projection by rubbing is oriented
in a predetermined direction for every test heights of the
projections.
[0073] Experimental work was performed by changing the kind of the
orientation film in the same condition as the second embodiment.
The kind of the orientation film used in this experiment is the
side chain type polyimide in which the tilt generating component is
added to its side chain.
[0074] The result of the experiment reveals that the height of the
projection should be less than 3.3 .mu.m and the polarization
anisotropy should be more than 1.0, for suppressing the after image
within less than 3 seconds. In this experiment also, the phenomenon
that the liquid crystal molecules can not be oriented at a hidden
area by the color layer projection was not observed for any
experimental height of the projections.
[0075] As hereinabove described, the liquid crystal panel according
to the present invention is suitable for the IPS-type (driven by
the transverse electric field) a-Si TFT driven liquid crystal, and
the cell gap of the display cell portion is formed larger than the
diameter of the spacers by 0.3 .mu.m or more, so that no anomalous
orientation occurs around the spherical spacers such that the
leakage of light is eliminated. In addition, the after-image due to
the orientation restriction force which is characteristic to the
IPS type a-Si TFT liquid crystal display panel can be eliminated by
defining the height of the projection of the color layers. These
effect allow production of a large diameter liquid crystal display
panel with a wide angle of visibility as well as a extremely high
image quality.
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