U.S. patent application number 13/547504 was filed with the patent office on 2013-01-17 for liquid crystal display device.
This patent application is currently assigned to Japan Display East Inc.. The applicant listed for this patent is Takato Hiratsuka, Osamu ITOU. Invention is credited to Takato Hiratsuka, Osamu ITOU.
Application Number | 20130016314 13/547504 |
Document ID | / |
Family ID | 47481338 |
Filed Date | 2013-01-17 |
United States Patent
Application |
20130016314 |
Kind Code |
A1 |
ITOU; Osamu ; et
al. |
January 17, 2013 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
A liquid crystal display device having a second substrate and a
first substrate that is placed so as to face the above-described
second substrate with pixel regions aligned in a matrix is provided
with: protrusions that are formed on pixel boarders and protrude
from the second substrate on the liquid crystal side; first
electrodes made of sidewall electrodes formed on sidewalls of
protrusions and a lower end side electrode extending from the
sidewall electrodes on the bottom side; and second electrodes made
of a first linear electrode formed within a pixel region and a
second linear electrode that is formed on the second substrate and
faces the first linear electrode.
Inventors: |
ITOU; Osamu; (Hitachi,
JP) ; Hiratsuka; Takato; (Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ITOU; Osamu
Hiratsuka; Takato |
Hitachi
Chiba |
|
JP
JP |
|
|
Assignee: |
Japan Display East Inc.
|
Family ID: |
47481338 |
Appl. No.: |
13/547504 |
Filed: |
July 12, 2012 |
Current U.S.
Class: |
349/106 ;
349/143 |
Current CPC
Class: |
G02F 1/133514 20130101;
G02F 1/133707 20130101; G02F 1/133377 20130101; G02F 2001/133357
20130101; G02F 1/13394 20130101; G02F 1/133345 20130101; G02F
1/134336 20130101 |
Class at
Publication: |
349/106 ;
349/143 |
International
Class: |
G02F 1/1343 20060101
G02F001/1343; G02F 1/1335 20060101 G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2011 |
JP |
2011-154440 |
Claims
1. A liquid crystal display device, comprising: a second substrate
having scan signal lines which run in an X direction and are
aligned in a Y direction and video signal lines which run in the Y
direction and are aligned in the X direction; and a first substrate
that is provided so as to face said second substrate with a liquid
crystal layer in between, with pixel regions between said scan
signal lines and between said video signal lines being arranged in
a matrix, characterized in that the liquid crystal display device
comprises: protrusions formed in borders between adjacent pixels
and protruding from said second substrate on the liquid crystal
side; first electrodes made of sidewall electrodes formed on
sidewalls of protrusions, and lower end side electrodes which
extend from said sidewall electrodes on bottoms of the protrusions
and run along said second substrate on the liquid crystal side,
each of said first electrodes being made of at least a pair of
sidewall electrodes formed along sides that face each other with a
pixel region in between and a lower end side electrode located
between the sidewall electrodes; and second electrodes made of
first linear electrodes which are formed within said pixel regions
on said first substrate side and run in the direction in which said
first electrodes run, and second linear electrodes which are formed
within said pixel regions on said second substrate side and run so
as to face said first linear electrodes with said liquid crystal
layer in between, and said pixel regions are made of at least first
pixel regions where said first electrodes and said second
electrodes run in a first direction and second pixel regions where
said first electrodes and said second electrodes run in a second
direction.
2. The liquid crystal display device according to claim 1,
characterized in that said first substrate comprises color filters
for a color display, a light blocking film formed at least in a
region between said color filters, and a flattening layer which is
formed in a layer above said color filters and said light blocking
film and flattens a surface on the liquid crystal side, and said
first linear electrodes are formed in a layer closer to said first
substrate than said flattening layer.
3. The liquid crystal display device according to claim 1,
characterized in that the liquid crystal display device has a first
insulating thick film formed on said second substrate on the liquid
crystal side, and said second linear electrodes are formed in a
layer closer to said first substrate than said first insulating
thick film.
4. The liquid crystal display device according to claim 1,
characterized in that said first electrodes are made of a first
conductive film in annular form around the sides of the pixels,
said second linear electrodes are made of a second conductive film
which is formed so as to cover the entire surface of the second
substrate on the liquid crystal side, is aligned in a direction of
a width of the pixels, and has two openings created so as to
sandwich the second linear electrode, and said first conductive
film and said second conductive film overlap along the sides of
each pixel, and the region that overlaps is in annular form
surrounding the pixel region.
5. A liquid crystal display device, comprising: a second substrate
having scan signal lines which run in an X direction and are
aligned in a Y direction and video signal lines which run in the Y
direction and are aligned in the X direction; and a first substrate
that is provided so as to face said second substrate with a liquid
crystal layer in between, with pixel regions between said scan
signal lines and between said video signal lines being arranged in
a matrix, characterized in that the liquid crystal display device
comprises: protrusions formed in borders between adjacent pixels
and protruding from said second substrate on the liquid crystal
side; first electrodes made of sidewall electrodes formed on
sidewalls of protrusions, and lower end side electrodes which
extend from said sidewall electrodes on bottoms of the protrusions
and run along said second substrate on the liquid crystal side,
each of said first electrodes being made of at least a pair of
sidewall electrodes formed along sides that face each other with a
pixel region in between and a lower end side electrode located
between the sidewall electrodes; and second electrodes made of
first linear electrodes which are formed within said pixel regions
on said first substrate side and run in the direction in which said
first electrodes run, and second linear electrodes which are formed
within said pixel regions on said second substrate side and run so
as to face said first linear electrodes with said liquid crystal
layer in between, and said first electrodes that reach from a lower
side portion on said second substrate side on which said sidewall
electrodes are formed to an upper side portion on said first
substrate side have a height that is greater than a thickness of
said liquid crystal layer in the pixel region sandwiched by said
first electrodes.
6. The liquid crystal display device according to claim 5,
characterized in that the liquid crystal display device has a first
insulating thick film formed on said second substrate on the liquid
crystal side and a first trench created in said first insulating
thick film so as to run along a side of a pixel region, and a side
portion of a sidewall electrode on the bottom side is integrally
connected to a lower end side electrode at the bottom of said first
trench.
7. The liquid crystal display device according to claim 6,
characterized in that said first trench penetrates through said
first insulating thick film so that a surface of a thin film layer
is exposed from beneath, and a protrusion is provided and stands on
a surface of the thin film layer that is exposed beneath through
said first trench, and said lower end side electrode is formed
along the surface of the thin film layer exposed beneath through
said first trench.
8. The liquid crystal display device according to claim 5,
characterized in that the liquid crystal display device has an
insulating film on which said protrusions are provided and stand
and a second insulating thick film formed so as to cover said
insulating film and said first electrodes, said second insulating
thick film is formed so that the film thickness in a region
sandwiched between a pair of first electrodes is greater than the
film thickness in a top portion of said protrusions, and said first
electrodes has a height that is greater than the thickness of said
liquid crystal layer in a region sandwiched between a pair of first
electrodes.
9. The liquid crystal display device according to claim 8,
characterized in that said first substrate comprises color filters
for a color display, a light blocking film formed at least in a
region between said color filters, and a flattening layer which is
formed in a layer above said color filters and said light blocking
film and flattens a surface on the liquid crystal side, the liquid
crystal display device has a second trench created in said
flattening layer so as to run along a side of a pixel region, and
the top side of a protrusion is placed in said second trench.
10. The liquid crystal display device according to claim 5,
characterized in that said first electrodes are made of a first
conductive film in annular form around the sides of the pixels,
said second linear electrodes are made of a second conductive film
which is formed so as to cover the entire surface of the second
substrate on the liquid crystal side, is aligned in a direction of
a width of the pixels, and has two openings created so as to
sandwich the second linear electrode, and said first conductive
film and said second conductive film overlap along the sides of
each pixel, and the region that overlaps is in annular form
surrounding the pixel region.
11. The liquid crystal display device according to claim 10,
characterized in that said pixel regions are made of at least first
pixel regions where said first electrodes and said second
electrodes run in a first direction and second pixel regions where
said first electrodes and said second electrodes run in a second
direction.
12. A liquid crystal display device, comprising: a second substrate
having scan signal lines which run in an X direction and are
aligned in a Y direction and video signal lines which run in the Y
direction and are aligned in the X direction; and a first substrate
that is provided so as to face said second substrate with a liquid
crystal layer in between, with pixel regions between said scan
signal lines and between said video signal lines being arranged in
a matrix, characterized in that the liquid crystal display device
comprises: protrusions formed in borders between adjacent pixels
and protruding from said second substrate on the liquid crystal
side; first electrodes made of sidewall electrodes formed on
sidewalls of protrusions, and lower end side electrodes which
extend from said sidewall electrodes on bottoms of the protrusions
and run along said second substrate on the liquid crystal side,
each of said first electrodes being made of at least a pair of
sidewall electrodes formed along sides that face each other with a
pixel region in between and a lower end side electrode located
between the sidewall electrodes; second electrodes made of first
linear electrodes which are formed within said pixel regions on
said first substrate side and run in the direction in which said
first electrodes run, and second linear electrodes which are formed
within said pixel regions on said second substrate side and run so
as to face said first linear electrodes with said liquid crystal
layer in between; and fourth electrodes formed on said first
substrate and placed so as to overlap said first electrodes as
viewed from above, and a same signal is supplied to said fourth
electrodes and said second electrodes.
13. The liquid crystal display device according to claim 12,
characterized in that said first substrate comprises color filters
for a color display, a light blocking film formed at least in a
region between said color filters, and a flattening layer which is
formed in a layer above said color filters and said light blocking
film and flattens a surface on the liquid crystal side, and said
fourth electrodes are formed in a layer closer to said first
substrate than said flattening layer.
14. The liquid crystal display device according to claim 12,
characterized in that said first substrate comprises color filters
for a color display, a light blocking film formed at least in a
region between said color filters, and a flattening layer which is
formed in a layer above said color filters and said light blocking
film and flattens a surface on the liquid crystal side, and said
fourth electrodes are formed in a layer closer to said liquid
crystal layer than said flattening layer.
15. The liquid crystal display device according to claim 14,
characterized in that said first linear electrodes are formed in a
layer closer to said first substrate than said flattening
layer.
16. The liquid crystal display device according to claim 12,
characterized in that said first linear electrodes and said fourth
electrodes are formed in a same layer.
17. The liquid crystal display device according to claim 12,
characterized in that said first linear electrodes and said fourth
electrodes are formed in different layers.
18. The liquid crystal display device according to claim 17,
characterized in that said first electrodes are made of a first
conductive film in annular form around the sides of the pixels,
said second linear electrodes are made of a second conductive film
which is formed so as to cover the entire surface of the second
substrate on the liquid crystal side, is aligned in a direction of
a width of the pixels, and has two openings created so as to
sandwich the second linear electrode, and said first conductive
film and said second conductive film overlap along the sides of
each pixel, and the region that overlaps is in annular form
surrounding the pixel region.
19. The liquid crystal display device according to claim 12,
characterized in that said pixel regions are made of at least first
pixel regions where said first electrodes and said second
electrodes run in a first direction and second pixel regions where
said first electrodes and said second electrodes run in a second
direction.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority over Japanese Patent
Application JP2011-154440 filed on Jul. 13, 2011, the contents of
which are hereby incorporated into this application by
reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to a liquid crystal display
device, and in particular, to an in-plane switching mode liquid
crystal display device where an electrical field is applied
parallel to the surface of the substrates.
[0004] (2) Description of the Related Art
[0005] In in-plane switching (IPS) mode liquid crystal display
devices, liquid crystal molecules are aligned parallel to the
surface of the panel and an electrical field (lateral electrical
field) is applied parallel to the surface of the panel so that the
liquid crystal molecules rotate by 90.degree. in the plane. In such
IPS mode liquid crystal display devices, a common electrode is
formed on the first substrate where video signal lines (drain
lines), scan signal lines (gate lines), thin film transistors and
pixel electrodes are formed, and thus, the liquid crystal layer is
operated through an electrical field in the plane of the first
substrate, which is generated by the difference in the voltages
applied to the pixel electrodes and the common electrode. In IPS
mode liquid crystal display devices having this structure, pixel
electrodes in linear form are formed so as to overlap the common
electrode in sheet form of a transparent conductive film in a layer
above the common electrode with an insulating film in between. As a
result, liquid crystal molecules incline relative to the surface of
the panel instead of being parallel thereto in the layer above the
electrodes in linear form and in the portions between adjacent
electrodes in linear form due to the electrical field generated in
the direction of the normal of the first substrate, and thus, it is
known that this causes the efficiency of the display mode to
lower.
[0006] An example of a method for increasing this efficiency of the
display mode is used in the liquid crystal display device in
JP9-258265A. This liquid crystal display device has such a
structure that protrusions are formed of an interlayer insulating
film on the first substrate where thin film transistors are formed
on the liquid crystal side, and a pixel electrode and a common
electrode (counter electrode) are formed for each pixel so as to
cover the surface of the protrusions. In particular, the structure
provides protrusions along a pair of sides of each pixel that face
each other and at the center between them with conductive films
covering the protrusions along the pair of sides as pixel
electrodes and with a conductive film covering the protrusion at
the center as being a common electrode. Furthermore, the structure
provides video signal lines in a layer beneath the pixel
electrodes, that is to say, in a layer beneath the interlayer
insulating film on which the pixel electrodes are formed.
SUMMARY OF THE INVENTION
[0007] In the mode where a lateral electrical field is applied
parallel to the plane of the first substrate through the liquid
crystal layer between the pixel electrodes and the common
electrodes that protrude into the liquid crystal layer, as in
JP9-258265A, an ideal lateral electrical field can be applied to
the liquid crystal layer. However, the alignment of liquid crystal
cannot be controlled in the places of the pixel electrodes, the
common electrodes and the vicinity thereof, and thus, it is known
that the aperture ratio is low. As a result, conventional liquid
crystal display devices have such a structure that the pixel
electrodes and the common electrodes which protrude into the liquid
crystal layer are provided so as to overlap the light blocking
film, such as a black matrix formed in the end portions of the
pixels.
[0008] In the liquid crystal display devices having this structure,
however, the pixel electrodes in the adjacent pixels are proximate
to the end portions of a pixel, and therefore, there is an
electrical field distribution in and around the pixel electrode due
to the difference in the potential between a pixel and its adjacent
pixels. This difference in the potential becomes maximum when white
is displayed through the driving for inverting the display pixel by
pixel, and in this case, there is a concern that the efficiency in
the display mode for white display may lower due to the lack of
balance in the distribution of the lateral electrical field.
Likewise, during the driving for inverting the display pixel by
pixel when a pixel displays black and its adjacent pixels display
white, the brightness for displaying black increases, that is to
say, the transmittance increases at the time when black is
displayed, and therefore, there is a concern that the contrast
ratio may lower.
[0009] In another structure for reducing the area that pixel
electrodes occupy in the area for pixels, protrusions are formed
ranging from adjacent pixels and pixel electrodes are formed on the
sidewalls of the protrusions so as to correspond to the respective
pixels. In this case, pixel electrodes for different pixels
(adjacent pixels) are formed on the sidewalls of each protrusion so
as to face each other with the protrusion in between, and
therefore, the pixel electrodes in the adjacent pixels are located
in further proximity, and thus, a resolution for the
above-described problem is urgently desired.
[0010] The present invention is provided in view of these problems,
and an object of the present invention is to provide a liquid
crystal display device where the efficiency in the display mode can
be made high even in the case where electrodes are formed so as to
stand in a liquid crystal layer.
[0011] (1) In order to solve the above-described problems, the
present invention provides a liquid crystal display device, having:
a second substrate having scan signal lines which run in an X
direction and are aligned in a Y direction and video signal lines
which run in the Y direction and are aligned in the X direction;
and a first substrate that is provided so as to face the
above-described second substrate with a liquid crystal layer in
between, with pixel regions between the above-described scan signal
lines and between the above-described video signal lines being
arranged in a matrix, wherein the liquid crystal display device
includes: protrusions formed in borders between adjacent pixels and
protruding from the above-described second substrate on the liquid
crystal side; first electrodes made of sidewall electrodes formed
on sidewalls of protrusions, and lower end side electrodes which
extend from the above-described sidewall electrodes on bottoms of
the protrusions and run along the above-described second substrate
on the liquid crystal side, each of the above-described first
electrodes being made of at least a pair of sidewall electrodes
formed along sides that face each other with a pixel region in
between and a lower end side electrode located between the sidewall
electrodes; and second electrodes made of first linear electrodes
which are formed within the above-described pixel regions on the
above-described first substrate side and run in the direction in
which the above-described first electrodes run, and second linear
electrodes which are formed within the above-described pixel
regions on the above-described second substrate side and run so as
to face the above-described first linear electrodes with the
above-described liquid crystal layer in between, and the
above-described pixel regions are made of at least first pixel
regions where the above-described first electrodes and the
above-described second electrodes run in a first direction and
second pixel regions where the above-described first electrodes and
the above-described second electrodes run in a second
direction.
[0012] (2) In order to solve the above-described problems, the
present invention provides a liquid crystal display device, having:
a second substrate having scan signal lines which run in an X
direction and are aligned in a Y direction and video signal lines
which run in the Y direction and are aligned in the X direction;
and a first substrate that is provided so as to face the
above-described second substrate with a liquid crystal layer in
between, with pixel regions between the above-described scan signal
lines and between the above-described video signal lines being
arranged in a matrix, wherein the liquid crystal display device
includes: protrusions formed in borders between adjacent pixels and
protruding from the above-described second substrate on the liquid
crystal side; first electrodes made of sidewall electrodes formed
on sidewalls of protrusions, and lower end side electrodes which
extend from the above-described sidewall electrodes on bottoms of
the protrusions and run along the above-described second substrate
on the liquid crystal side, each of the above-described first
electrodes being made of at least a pair of sidewall electrodes
formed along sides that face each other with a pixel region in
between and a lower end side electrode located between the sidewall
electrodes; and second electrodes made of first linear electrodes
which are formed within the above-described pixel regions on the
above-described first substrate side and run in the direction in
which the above-described first electrodes run, and second linear
electrodes which are formed within the above-described pixel
regions on the above-described second substrate side and run so as
to face the above-described first linear electrodes with the
above-described liquid crystal layer in between, and the
above-described first electrodes that reach from a lower side
portion on the above-described second substrate side on which the
above-described sidewall electrodes are formed to an upper side
portion on the above-described first substrate side have a height
that is greater than a thickness of the above-described liquid
crystal layer in the pixel region sandwiched by the above-described
first electrodes.
[0013] (3) In order to solve the above-described problems, the
present invention provides a liquid crystal display device, having:
a second substrate having scan signal lines which run in an X
direction and are aligned in a Y direction and video signal lines
which run in the Y direction and are aligned in the X direction;
and a first substrate that is provided so as to face the
above-described second substrate with a liquid crystal layer in
between, with pixel regions between the above-described scan signal
lines and between the above-described video signal lines being
arranged in a matrix, wherein the liquid crystal display device
includes: protrusions formed in borders between adjacent pixels and
protruding from the above-described second substrate on the liquid
crystal side; first electrodes made of sidewall electrodes formed
on sidewalls of protrusions, and lower end side electrodes which
extend from the above-described sidewall electrodes on bottoms of
the protrusions and run along the above-described second substrate
on the liquid crystal side, each of the above-described first
electrodes being made of at least a pair of sidewall electrodes
formed along sides that face each other with a pixel region in
between and a lower end side electrode located between the sidewall
electrodes; second electrodes made of first linear electrodes which
are formed within the above-described pixel regions on the
above-described first substrate side and run in the direction in
which the above-described first electrodes run, and second linear
electrodes which are formed within the above-described pixel
regions on the above-described second substrate side and run so as
to face the above-described first linear electrodes with the
above-described liquid crystal layer in between; and third
electrodes formed in a layer beneath the above-described lower end
side electrodes so as to at least partially overlap a lower end
side electrode with an insulating film in between, and the
above-described third electrodes and the above-described first
electrodes are electrically connected to each other.
[0014] (4) In order to solve the above-described problems, the
present invention provides a liquid crystal display device, having:
a second substrate having scan signal lines which run in an X
direction and are aligned in a Y direction and video signal lines
which run in the Y direction and are aligned in the X direction;
and a first substrate that is provided so as to face the
above-described second substrate with a liquid crystal layer in
between, with pixel regions between the above-described scan signal
lines and between the above-described video signal lines being
arranged in a matrix, wherein the liquid crystal display device
includes: protrusions formed in borders between adjacent pixels and
protruding from the above-described second substrate on the liquid
crystal side; first electrodes made of sidewall electrodes formed
on sidewalls of protrusions, and lower end side electrodes which
extend from the above-described sidewall electrodes on bottoms of
the protrusions and run along the above-described second substrate
on the liquid crystal side, each of the above-described first
electrodes being made of at least a pair of sidewall electrodes
formed along sides that face each other with a pixel region in
between and a lower end side electrode located between the sidewall
electrodes; second electrodes made of first linear electrodes which
are formed within the above-described pixel regions on the
above-described first substrate side and run in the direction in
which the above-described first electrodes run, and second linear
electrodes which are formed within the above-described pixel
regions on the above-described second substrate side and run so as
to face the above-described first linear electrodes with the
above-described liquid crystal layer in between; and fourth
electrodes formed on the above-described first substrate and placed
so as to overlap the above-described first electrodes as viewed
from above, and the same signal is supplied to the above-described
fourth electrodes and the above-described second electrodes.
[0015] According to the present invention, the efficiency in the
display mode can be increased even in the case where electrodes are
formed so as to stand in the liquid crystal layer.
[0016] The other effects of the present invention will be clarified
from the description of the entirety of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a diagram for illustrating the entire structure of
the liquid crystal display device according to the first embodiment
of the present invention;
[0018] FIG. 2 is a plan diagram for illustrating the structure of a
pixel in the liquid crystal display device according to the first
embodiment of the present invention;
[0019] FIG. 3 is a cross-sectional diagram along line B-B' in FIG.
2;
[0020] FIG. 4 is a diagram for illustrating the structure in detail
of electrodes in wall form in the liquid crystal display device
according to the first embodiment of the present invention;
[0021] FIG. 5 is a diagram for illustrating the distribution of an
electrical field around a pseudo-wall common electrode in the
liquid crystal display device according to the first embodiment of
the present invention;
[0022] FIG. 6 is a diagram for illustrating the distribution of an
electrical field around a conventional wall electrode;
[0023] FIG. 7 is a diagram for illustrating the distribution of an
electrical field around a conventional common electrode;
[0024] FIG. 8 is a diagram for illustrating the precision in
positioning the pseudo-wall common electrode according to the first
embodiment of the present invention;
[0025] FIG. 9 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall base in the liquid
crystal display device according to the first embodiment of the
present invention;
[0026] FIG. 10 is a graph showing the measured values in the
distribution of transmittance in one pixel in the liquid crystal
display device according to the first embodiment of the present
invention;
[0027] FIG. 11 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display panel in
the liquid crystal display device according to the second
embodiment of the present invention;
[0028] FIG. 12 is a diagram for illustrating the distribution of
equipotential surfaces in the vicinity of a wall base in the liquid
crystal display device according to the second embodiment of the
present invention;
[0029] FIG. 13 is a graph for illustrating the distribution of
equipotential surfaces in the vicinity of a wall base in the case
where the liquid crystal display device according to the first
embodiment is operated so that each pixel is inverted;
[0030] FIG. 14 is a graph showing the contrast ratio relative to
the difference between the thickness of the liquid crystal layer
and the height of the wall pixel electrodes when the liquid crystal
display device according to the second embodiment of the present
invention is operated so that each pixel is inverted;
[0031] FIG. 15 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall pixel electrode in
the case where a pixel and its adjacent pixel both display white
when the liquid crystal display device according to the first
embodiment is operated so that each pixel is inverted;
[0032] FIG. 16 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall pixel electrode in
the case where a pixel displays white and its adjacent pixel
displays black when the liquid crystal display device according to
the second embodiment is operated so that each pixel is
inverted;
[0033] FIG. 17 is a graph showing the distribution of transmittance
when the liquid crystal display device according to the second
embodiment, where a wall base WL is formed so as to have a height 2
.mu.m greater than the thickness of the liquid crystal layer LC, is
operated so that each pixel is inverted, and white is
displayed;
[0034] FIG. 18 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the third embodiment of the present invention;
[0035] FIG. 19 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the fourth embodiment of the present invention;
[0036] FIG. 20 is a diagram for illustrating the distribution of
equipotential surfaces in the vicinity of a wall base in the case
where the difference in the potential between adjacent pixels
becomes maximum when the liquid crystal display device according to
the fourth embodiment of the present invention is operated so that
each pixel is inverted;
[0037] FIG. 21 is a diagram for illustrating the distribution of
equipotential surfaces in the vicinity of a wall base in the case
where a pixel displaying white and a pixel displaying black are
adjacent to each other when the liquid crystal display device
according to the fourth embodiment of the present invention is
operated so that each pixel is inverted;
[0038] FIG. 22 is a graph showing the difference between the
thickness of the liquid crystal layer and the height of the wall
pixel electrodes and the results of measurement of the
transmittance when white is displayed and the transmittance when
black is displayed when the liquid crystal display device according
to the fourth embodiment of the present invention is operated so
that each pixel is inverted;
[0039] FIG. 23 is a graph showing the contrast ratio relative to
the difference between the thickness of the liquid crystal layer
and the height of the wall pixel electrodes when the liquid crystal
display device according to the fourth embodiment of the present
invention is operated so that each pixel is inverted;
[0040] FIG. 24 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the fifth embodiment of the present invention;
[0041] FIG. 25 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall pixel electrode
when the liquid crystal display device according to the fifth
embodiment of the present invention is operated so that each pixel
is inverted;
[0042] FIG. 26 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall pixel electrode
when the liquid crystal display device according to the fifth
embodiment of the present invention is operated so that each pixel
is inverted;
[0043] FIG. 27 is a graph showing the distance between a wall pixel
electrode and a linear pixel electrode, and the results of
measurement of the transmittance when white is displayed and the
transmittance when black is displayed when the liquid crystal
liquid crystal display device according to the fifth embodiment of
the present invention is operated so that each pixel is
inverted;
[0044] FIG. 28 is a graph showing the contrast ratio relative to
the distance between a wall pixel electrode and a linear pixel
electrode when the liquid crystal liquid crystal display device
according to the fifth embodiment of the present invention is
operated so that each pixel is inverted;
[0045] FIG. 29 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display device
according to the sixth embodiment of the present invention;
[0046] FIG. 30 is a diagram showing the distribution of
equipotential surfaces in the liquid crystal display device
according to the sixth embodiment when a pixel and its adjacent
pixel both display white;
[0047] FIG. 31 is a diagram showing the distribution of
equipotential surfaces in the liquid crystal display device
according to the sixth embodiment when a pixel displays white and
its adjacent pixel displays black;
[0048] FIG. 32 is a cross-sectional diagram for schematically
illustrating the structure of a liquid crystal display device
according to the seventh embodiment of the present invention;
[0049] FIG. 33 is a cross-sectional diagram for schematically
illustrating the structure of another liquid crystal display device
according to the seventh embodiment of the present invention;
[0050] FIG. 34 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display device
according to the eighth embodiment of the present invention;
[0051] FIG. 35 is a graph showing the transmittance of a pixel
displaying white relative to the positional misalignment between
the first common electrode and the second common electrode in a
pseudo-wall common electrode during the operation where each pixel
is inverted according to the present invention;
[0052] FIG. 36 is a graph showing the distribution of the
transmittance within a pixel in the cases where there is no
positional misalignment between the first common electrode and the
second common electrode and where there is a positional
misalignment of 3 .mu.m in the liquid crystal display device
according to the first embodiment;
[0053] FIG. 37 is a diagram showing an enlargement of a portion of
a pseudo-wall common electrode in the case where there is no
positional misalignment between the first common electrode and the
second common electrode in the liquid crystal display device
according to the eighth embodiment of the present invention;
[0054] FIG. 38 is a diagram showing an enlargement of a portion of
a pseudo-wall common electrode in the case where there is a
positional misalignment between the first common electrode and the
second common electrode in the liquid crystal display device
according to the eighth embodiment of the present invention;
[0055] FIG. 39 is a graph showing the distribution of the
transmittance within a pixel in the cases where there is no
positional misalignment between the first common electrode and the
second common electrode and where there is a positional
misalignment of 3 .mu.m in the liquid crystal display device
according to the eighth embodiment of the present invention;
[0056] FIG. 40 is a graph for illustrating the dependency of the
transmittance on the distance between the second common electrode
and the liquid crystal layer when the liquid crystal display device
according to the eighth embodiment of the present invention is
operated so that each pixel is inverted and white is displayed in
the case where there is a positional misalignment of 3 .mu.m
between the first common electrode and the second common
electrode;
[0057] FIG. 41 is a graph for illustrating the relationship between
the operating voltage and the distance between the second common
electrode and the liquid crystal layer in the liquid crystal
display device according to the eighth embodiment of the present
invention;
[0058] FIG. 42 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the ninth embodiment of the present invention;
[0059] FIG. 43 is a diagram showing an enlargement of a portion of
a pseudo-wall common electrode in the case where there is no
positional misalignment between the first common electrode and the
second common electrode in the liquid crystal display device
according to the ninth embodiment of the present invention;
[0060] FIG. 44 is a diagram showing an enlargement of a portion of
a pseudo-wall common electrode in the case where there is a
positional misalignment between the first common electrode and the
second common electrode in the liquid crystal display device
according to the ninth embodiment of the present invention;
[0061] FIG. 45 is a graph for illustrating the dependency of the
transmittance on the distance between the first common electrode
and the liquid crystal layer when the liquid crystal display device
according to the ninth embodiment of the present invention is
operated so that each pixel is inverted and white is displayed in
the case where there is a positional misalignment of 3 .mu.m
between the first common electrode and the second common
electrode;
[0062] FIG. 46 is a graph for illustrating the relationship between
the operating voltage and the distance between the first common
electrode and the liquid crystal layer in the liquid crystal
display device according to the ninth embodiment of the present
invention;
[0063] FIG. 47 is a plan diagram for schematically illustrating the
structure of the liquid crystal display device according to the
tenth embodiment of the present invention;
[0064] FIG. 48 is a cross-sectional diagram along line C-C' in FIG.
47;
[0065] FIG. 49 is a diagram for illustrating the structure of a
first transparent conductive film for forming a wall pixel
electrode in the liquid crystal display device according to the
tenth embodiment; and
[0066] FIG. 50 is a diagram for illustrating the structure of a
second transparent conductive film for forming the second common
electrode and the fourth common electrode in the liquid crystal
display device according to the tenth embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0067] In the following, embodiments of the present invention are
described in reference to the drawings. In the following
descriptions, same symbols are attached to the same components, and
the descriptions thereof are not repeated. X, Y and Z indicate the
X axis, the Y axis and the Z axis, respectively.
First Embodiment
Entire Structure
[0068] FIG. 1 is a diagram for illustrating the entire structure of
the liquid crystal display device according to the first embodiment
of the present invention. In the following, the entire structure of
the liquid crystal display device according to the first embodiment
is described in reference to FIG. 1. In the present specification,
the transmittance, excluding the effects of absorption by color
filters CF, polarizing plates POL1, POL2 and the like and the
effects of the aperture ratio, is regarded as the efficiency in the
display mode. Accordingly, the efficiency in the display mode is
100% in the case where the direction of the oscillation of linearly
polarized light emitted from the polarizing plate POL1 on the
backlight unit side is rotated by 90.degree. when it enters into
the polarizing plate POL2 on the display side.
[0069] As shown in FIG. 1, the liquid crystal display device
according to the first embodiment has a liquid crystal display
panel PNL that is formed of: a first substrate SU1 where color
filters (color layer), which face a second substrate SU2, and a
light blocking layer, which is referred to as black matrix, are
formed; the second substrate on which all pixel electrodes (first
electrodes) SE, which are pixel electrodes in wall form, and thin
film transistors TFT are formed; and a liquid crystal layer
sandwiched between the first substrate SU1 and the second substrate
SU2. The liquid crystal display device is formed by combining the
liquid crystal display panel PNL and a backlight unit (backlight
device), not shown, which works as a light source for the liquid
crystal display panel PNL. The first substrate SU1 and the second
substrate SU2 are secured to each other using a sealing material SL
applied in the periphery portion of the first substrate in annular
form, and this structure allows liquid crystal to be sealed in the
sealing material SL. In the liquid crystal display device according
to the first embodiment, the region where display pixels
(hereinafter simply referred to as pixels) are formed within the
region where liquid crystal is sealed works as a display region AR.
Accordingly, the region where no pixels are formed and which does
not relate to display does not work as a display region AR even
within the region where liquid crystal is sealed.
[0070] The first substrate SU1 has an area smaller than that of the
second substrate SU2 so that a side portion of the second substrate
SU2 on the bottom side in the figure is exposed. A driving circuit
DR formed of a semiconductor chip is mounted on this side portion
of the second substrate SU2. This driving circuit DR drives the
pixels arranged on the display region AR. In the following
description, the word "liquid crystal display device" may be used
for the liquid crystal display panel PNL. In addition, well-known
glass substrates are generally used as the bases of the first
substrate SU1 and the second substrate SU2, but transparent
insulating substrates made of a resin may be used instead.
[0071] In the liquid crystal display device according to the first
embodiment, scan signal lines (gate lines) GL are formed within the
display region AR on the surface of the second substrate SU2 on the
liquid crystal side so as to run in the X direction and be aligned
in the Y direction in FIG. 1 so that scan signals can be supplied
from the driving circuit DR. In addition, video signal lines (drain
lines) DL are formed so as to run in the Y direction and be aligned
in the X direction in FIG. 1 so that video signals (gradation
signals) can be supplied from the driving circuit. Pixels are
formed in the regions sandwiched between two adjacent drain lines
DL and between two adjacent gate lines GL, and thus, a number of
pixels are arranged in a matrix within the display region AR along
the drain lines DL and the gate lines GL.
[0072] As shown in the diagram A' showing an equivalent circuit
within a circle A in FIG. 1, each pixel has a thin film transistor
TFT that is driven so as to be turned on/off by a scan signal from
the gate line GL, a wall pixel electrode SE to which a video signal
from the drain line DL is supplied through this thin film
transistor TFT when turned on, and a first common electrode (first
linear electrode) CE1 and a second common electrode (second linear
electrode) CE2 to which a common signal having such a potential as
to be used as a reference for the potential of the video signal is
supplied through the common line CL. Though in the diagram A'
showing an equivalent circuit within a circle A in FIG. 1 the first
and second common electrodes CE1 and CE2 as well as the wall pixel
electrode SE are schematically shown in linear form, the structures
of the first and second common electrodes CE1 and CE2 as well as
the wall pixel electrode SE in the first embodiment are described
in detail below. Though the thin film transistors TFT in the first
embodiment are driven in such a manner that the drain electrode and
the source electrode are switched due to the application of the
bias, the electrodes connected to drain lines DL are referred to as
drain electrodes, and the electrodes connected to the wall pixel
electrodes SE are referred to as source electrodes for the purpose
of convenience in the present specification.
[0073] An electrical field having a component parallel to the main
surface of the second substrate SU2 is generated between the wall
pixel electrode SE and the first and second common electrodes CE1
and CE2 so that the liquid crystal molecules can be driven by this
electrical field. Such liquid crystal display devices are known as
those where a so-called wide view angle display is possible and are
referred to as IPS mode or lateral electrical field mode due to the
specificity of the application of an electrical field to the liquid
crystal. In addition, in the liquid crystal display devices having
this structure, light transmittance is minimum (black display) in
the case where no electrical field is applied to the liquid
crystal, and thus, the display is in the normally black mode where
the light transmittance increases by applying an electrical
field.
[0074] The drain lines DL and the gate lines GL respectively run
beyond the sealing material SL in an end portion so as to be
connected to the driving circuit DR for generating a drive signal,
such as a video signal or a scan signal, on the basis of an input
signal inputted through the flexible printed circuit board FPC from
an external system. Though the liquid crystal display device
according to the first embodiment has such a structure that the
driving circuit DR is formed of a semiconductor chip, which is
mounted on the second substrate SU2, either or both of the video
signal driving circuit for outputting a video signal and the scan
signal driving circuit for outputting a scan signal may be mounted
on the flexible printed circuit board FPC in a tape carrier method
or in a COF (chip on film) method so as to be connected to the
second substrate SU2 in the structure.
<Detailed Structure of a Pixel>
[0075] FIG. 2 is a plan diagram for illustrating the structure of a
pixel in the liquid crystal display device according to the first
embodiment of the present invention, FIG. 3 is a cross-sectional
diagram along line B-B' in FIG. 2, and FIG. 4 is a diagram for
illustrating the detailed structure of electrodes in wall form in
the liquid crystal display device according to the first embodiment
of the present invention. In FIG. 2, the dotted lines show the
outlines of the first common electrode CE1 and the second common
electrode CE2, and the one-dot chain lines show the outlines of the
wall bases (protrusions, wall structures) WL according to the
present invention.
[0076] As shown in FIG. 2, a pixel in the first embodiment is in a
region between drain lines (video signal lines) DL, which run in
the X direction and are aligned in the Y direction, and between
gate lines (scan signal lines) GL, which run in the Y direction and
are aligned in the X direction, and pixels are arranged in a matrix
within the display region AR in the liquid crystal display panel
PNL. Here, in the pixel in the first embodiment, the upper region
(first region) in FIG. 2 and the lower region (second region) are
inclined in different directions so that the upper region and the
lower region are symmetrical in the Y direction and connected in
the center portion of the pixel. Here, the liquid crystal molecules
are initially aligned in the direction indicated by the arrow AD in
the figure both in the upper and lower regions. In addition, though
the pixels in the first embodiment have such a structure that the
upper region is inclined counterclockwise (first direction)
relative to the Y direction and the lower region is inclined
clockwise (second direction), they may be inclined in the opposite
directions.
[0077] As described above, in the liquid crystal display panel
according to the first embodiment, each pixel is bent at the center
and the liquid crystal molecules are aligned in the direction
indicated by the arrow AD (longitudinal direction in FIG. 2). As a
result, the liquid crystal molecules rotate in the opposite
directions when a voltage is applied in the upper and lower regions
that make contact through the bent portion. That is to say, liquid
crystal molecules rotate counterclockwise in the upper region above
the bent portion and rotate clockwise in the lower region beneath
the bent portion. In a uniaxial alignment model, the liquid crystal
layer maintains the homogenous alignment and only the azimuth
thereof rotates, and in the azimuth direction, including the
alignment direction, white display tinges blue, and in the
direction perpendicular to that, white display tinges yellow.
Accordingly, in the first embodiment, regions where the direction
of rotation is opposite to each other are formed in one pixel so
that the tinging of colors depending on the direction of the view
angle is offset, and thus, the display can be made closer to
white.
[0078] In the liquid crystal display panel PNL according to the
first embodiment, a polysilicon film (polysilicon layer) PS that
becomes a semiconductor layer makes electrical contact through
contact holes CH1, which are created so as to overlap the drain
lines DL, and thus, the drain electrodes of the thin film
transistors TFT are formed. As shown in the lower left portion of
FIG. 2, this polysilicon film PS overlaps the gate line GL with a
gate insulating film, not shown, in between, and in this
overlapping region, the gate electrode GT works as the gate
electrode of the thin film transistor TFT. In addition, the other
end of the polysilicon film PS works as a drain electrode and is
electrically connected to a first transparent conductive film
(first conductive film) TCF1 through a contact hole CH2. Though the
first embodiment is a case where a polysilicon layer is used as the
semiconductor layer (semiconductor film), the structure allows for
the use of other semiconductor layers, such as an amorphous silicon
layer or a microcrystal silicon layer.
[0079] The first transparent conductive film TCF1 is formed in
annular form along the drain lines DL and the gate lines GL in such
a manner that the first transparent conductive film TCF1 is formed
in the region between the outer periphery portion, shown by the
solid line L1 in FIG. 2, and the inner periphery portion, shown by
the solid line L2. Here, the portions of the first transparent
conductive film TCF1 that run along the drain lines DL overlap the
wall bases WL on the side closer to the drain lines DL, that is to
say, on the outer periphery side. As a result, pairs of wall pixels
electrodes SE formed along the drain lines DL stand so as to
sandwich pixel regions according to the first embodiment.
[0080] In the liquid crystal display panel PNL according to the
first embodiment, second transparent conductive films (second
conductive films) TCF2 run along the gate lines GL in the X
direction and are aligned in the Y direction so as to cross the
gate lines GL and work as the common lines CL. In addition, in a
middle part of a pixel region in the X direction, a second common
electrode CE is formed so as to connect the second transparent
conductive films TCF2 formed on the upper side and the lower side
within the pixel region. Here, the second common electrode CE2 is
also formed so as to incline relative to the Y direction in the
upper part and the lower part of the pixel region and makes
electrical connection in the middle part between the upper part and
the lower part. That is to say, in the second common electrode CE2
as well, the pixel region is bent in the middle part between the
upper part and the lower part. The second common electrodes CE2
having this structure can be formed as a film by creating openings,
shown by dotted lines L3 and L4, in the transparent conductive film
that is formed so as to cover the second substrate SU2 on the
liquid crystal side, and second common electrodes CE2 in linear
form that is bent in the middle part are formed in a region
sandwiched between a pair of wall pixel electrodes SE. As described
below in detail, in the liquid crystal display panel PNL according
to the first embodiment, first common electrodes CE1 for supplying
a common signal at the same potential to a location facing a second
common electrode CE2 are formed on the first substrate SU1 on the
liquid crystal side. In addition, the first common electrodes CE1
and the second common electrodes CE2 are electrically connected in
the peripheral portion of the liquid crystal display panel PNL in
accordance with a well-known technology so that a common signal
having the same potential is supplied to the first common
electrodes CE1 and the second common electrodes CE2.
[0081] In the liquid crystal display panel PNL according to the
first embodiment, the first transparent conductive films TCF1 that
form the wall pixel electrodes SE and the second transparent
conductive films TCF2 that form the second common electrodes CE2
are provided with a third insulating film IL3 in between.
Accordingly, in the upper and lower parts of a pixel region, which
are hatched in FIG. 2, a first transparent conductive film TCF1 and
a second transparent conductive film TCF2 overlap with a third
insulating film IL3 in between, and thus, the structure according
to the first embodiment allows the regions where a first
transparent conductive film TCF1 and a second transparent
conductive film TCF2 overlap (hatched regions SC) to be used as a
capacitor.
[0082] In the first transparent conductive films TCF1 in the first
embodiment, a protrusion is formed in the middle part between the
upper part and the lower part of a pixel so as to protrude in the X
direction in FIG. 2, and this structure lowers the abnormal domain
caused by the difference in the direction of rotation of liquid
crystal molecules between the upper part and the lower part.
Likewise, in the transparent conductive films that form the second
common electrodes CE2, a protrusion is formed in the middle part
between the upper part and the lower part of a pixel so as to
protrude in the X direction in FIG. 2, and this structure reduces
the abnormal domain.
[0083] In the liquid crystal display panel PNL having the structure
according to the first embodiment, as shown in FIG. 3, the first
substrate SU1 and the second substrate SU2 are provided so as to
face each other with the liquid crystal layer LC in between. Gate
lines GL, not shown, are formed on the first substrate SU1 on the
liquid crystal side, and a first insulating film IL1 is formed on
the entire surface of the second substrate SU2 on the liquid
crystal side so as to cover the gate lines GL. This structure
allows the first insulating film IL1 to function as the gate
insulating film in regions where a thin film transistor TFT is
formed.
[0084] Drain lines DL are formed on a layer above the first
insulating film IL1, and a second insulating film IL2 is formed on
the entire surface of the second substrate SU2 so as to cover the
drain lines DL. Wall bases WL are provided and stand in a layer
above the second insulating film IL2 so as to overlap the drain
lines DL. First transparent conductive films TCF1 that form a wall
pixel electrode SE are formed on the sides and on the top of these
wall bases WL and in a layer above the second insulating film IL2
in the vicinity of the wall bases WL. In the wall pixel electrodes
WL according to the first embodiment, as described above, the wall
pixel electrode SE of an adjacent pixel is formed on a sidewall of
one wall base WL, and the wall pixel electrodes SE of adjacent
pixels are located so as to face each other with the wall base WL
in between in the direction in which the gate lines GL run.
[0085] A third insulating film IL3 is formed on the entire surface
of the second substrate SU2 in a layer above the wall bases WL and
the wall pixel electrodes SE so as to cover the wall bases WL and
the wall pixel electrodes SE, and second common electrodes CE2 are
formed in a layer above this. In addition, a second alignment film
AL2 is formed on the entire surface of the second substrate SU2 in
a layer above the third insulating film IL3 so as to cover the
second common electrodes CE2, and this structure allows the liquid
crystal molecules LCM in the liquid crystal layer LC to be aligned
in the initial alignment direction ADH, shown by the arrow in FIG.
2. In particular, the second alignment film AL2 is a well-known
optical alignment film having such properties as to align the
liquid crystal molecules LCM in the direction parallel to the
direction in which polarized ultraviolet rays oscillate when
irradiated with the polarized ultraviolet rays. In the first
embodiment, an optical alignment film is used as the second
alignment film AL2, and thus, such particular effects can be gained
that mechanical friction, such as in a rubbing method, is
unnecessary. As a result, it becomes possible to align the liquid
crystal molecules LCM on the surface of the second substrate SU2
that is uneven because the wall bases WL are provided. Here, other
well-known alignment films, such as those using a rubbing method,
can be applied.
[0086] In addition, a black matrix BM, which works as a light
blocking film, is formed on the first substrate SU1 on the liquid
crystal side so as to include locations facing the drain lines DL
with the liquid crystal layer LC in between, and color filters CF
are formed in a color layer so as to cover the black matrix BM. The
color filters CF in each pixel region are any of red (R), green (G)
or blue (B), and thus form a RGB unit pixel for a color
display.
[0087] An overcoat layer (overcoat film or flattening layer) OC is
formed in a layer above the color filters CF, and first common
electrodes CE1 are formed in a layer above the overcoat layer OC. A
first alignment film AL1 is formed in a layer above the overcoat
layer OC so as to cover the first common electrodes CE1. The first
alignment film AL1 is used in the structure where wall bases WL
that protrude greatly from the first alignment film AL1 towards the
liquid crystal layer side are not formed, and therefore may be any
type of alignment film, such as an optical alignment film or an
alignment film using a rubbing method.
[0088] Here, the first common electrodes CE1 are formed so as to
overlap the second common electrodes CE2 with the liquid crystal
layer LC in between, and at the same time have a width that is
greater than that of the second common electrodes CE2 in the
direction in which the wall pixel electrodes SE are placed
according to the first embodiment. According to the first
embodiment, this structure allows regions having the same potential
to be created in the liquid crystal layer LC within the regions
where a first common electrode CE1 and a second common electrode
CE2 overlap, and thus, pseudo-wall common electrodes (second
electrodes) where these regions are regarded as wall electrodes
(pseudo-wall electrodes) are created.
[0089] In this case, an electrical field is generated between the
wall pixel electrode SE on the side B and the pseudo-wall common
electrode in FIG. 3, which shows the pseudo-wall common electrode
at the center, so as to be parallel to the main surface of the
second substrate SU2, while an electrical field is generated
between the wall pixel electrode SE on the side B' and the
pseudo-wall common electrode so as to be parallel to the main
surface of the second substrate SU2 when an image is displayed.
These electrical fields on the sides B and B' allow the liquid
crystal molecules LCM in the respective regions to be rotated
parallel to the main surface of the second substrate SU2.
[0090] The structure according to the first embodiment allows the
wall bases WL to overlap regions that mainly include a wall pixel
electrode SE within a first transparent conductive film TCF1. That
is to say, a wall base WL is formed only in a portion where the
wall base WL makes a pair with a first common electrode CE1 or a
second common electrode CE2 so as to apply an electrical field to
the liquid crystal layer LC, and this structure allows the wall
bases WL to overlap a first transparent conductive film TCF1, and
thus does not allow the wall bases WL to extend in the vicinity of
a gate line GL. Furthermore, the structure does not allow the wall
bases WL to be formed along the sides of a pixel region on the gate
line GL side (in the Y direction). Thus, the wall structures WL are
not formed on or in the vicinity of the gate wires GL and are not
continuous because they do not cross pixels in the direction in
which the drain wires DL run. Accordingly, the wall bases WL
according to the first embodiment make it easy to form the liquid
crystal layer LC by reducing the hindrance for the movement of the
liquid crystal molecules LCM or by not preventing the injection of
liquid crystal when the liquid crystal layer LC is formed in
accordance with either a vacuum sealing method or a dropping
method. After being injected, the liquid crystal molecules LCM move
through the spaces where no wall base WL is formed so as to form
the liquid crystal layer LC. In addition, the wall bases WL
function to maintain the thickness of the liquid crystal layer LC
at constant in order to hold the liquid crystal layer LC.
[0091] As for the transparent conductive film material for forming
the transparent conductive films TCF1 and TCF2, of which the wall
pixel electrodes SE, the first common electrodes CE1 and the second
common electrodes CE2 are formed, it is possible to use ITO (indium
tin oxide) or zinc oxide-based materials, such as AZO
(aluminum-doped zinc oxide) and GZO (gallium-doped zinc oxide).
[0092] In particular, in the structure according to the first
embodiment, as shown in FIG. 4, which shows an enlargement of a
wall pixel electrode SE, the wall bases WL are rectangular in a
cross-section, and the second alignment film AL2 formed on the top
surface of a wall base WL is in proximity or makes contact with the
first alignment film AL1 formed on the first substrate SU1. Here,
the wall surfaces of the wall bases WL are perpendicular or
inclined so as to be almost perpendicular to the main surface of
the second substrate SU2, and thus, the wall bases WL may be in
forms other than rectangular in a cross-section, which may be a
trapezoid, a curve of the second order or a curve of the fourth
order.
[0093] In the pixel structure according to the first embodiment,
wall bases WL are formed so as to cross adjacent pixels, and
therefore, as shown in FIG. 4, wall pixels electrodes SE of pixels
adjacent to each other are formed on the sidewalls of a wall base
WL so as to face each other in the direction in which the drain
lines DL are aligned (in the direction B-B' in FIG. 4). That is to
say, a pair of sidewalls that respectively face pixels adjacent to
each other have wall pixel electrodes SE for their respective
adjacent pixels. The wall pixel electrodes SE in the first
embodiment are formed of a vertical portion (sidewall electrode) VP
formed on a sidewall of a wall base WL, a top portion TP formed on
the top surface of the wall base WL that extends from the end
portion of the vertical portion VP on the top side along the top
surface, and a flat portion (lower end side electrode) HP that
extends towards the pseudo-wall common electrode side from the end
portion of the wall base WL on the bottom side (on the second
substrate SU2 side) along the surface of the second insulating film
IL2 in the lower layer with a predetermined width.
[0094] Here, the top surface of a wall base WL has the top portions
TP of adjacent pixels, and therefore, the wall pixel electrodes SE
of the adjacent pixels are the closest to each other. Accordingly,
in the liquid crystal display panel PNL according to the first
embodiment, the distance between the top portions TP of the
adjacent pixels is smaller than the amount of the top portions TP
that protrudes towards the adjacent pixel (protruding width). Here,
the structure of the wall pixel electrodes SE is not limited to
this, and in another example of the structure, wall pixel
electrodes SE are formed of only a vertical portion VP and a flat
portion HP without having a top portion TP.
[0095] In addition, in the first embodiment, drain lines DL are
formed in a layer beneath the wall bases WL (on the side closer to
the second substrate SU2), that is to say, the flat portions HP are
formed from the end portion of a vertical portion VP on the side
where the drain line DL is formed in the structure of the wall
pixel electrodes SE, which has such effects that the drain lines DL
can be prevented from affecting the wall pixel electrodes SE. In
addition, at the end of a flat portion HP, that is to say, on the
side that is further from the vertical portion VP, there is an
effect of intensifying the electrical field applied to the liquid
crystal layer LC because the distance from the pseudo-wall common
electrode is shorter. Thus, in the liquid crystal display panel PNL
according to the first embodiment, the wall bases WL are formed on
the second substrate SU2 so as to protrude into the liquid crystal
layer LC towards the first substrate SU1 side with the sidewalls
(inclined surfaces) being vertical or almost vertical, and
therefore, the wall pixel electrodes SE formed on the wall bases WL
can apply an electrical field to the liquid crystal layer LC
parallel to the layer surfaces thereof. When an electrical field is
applied parallel to the layer surfaces, the alignment changes
uniformly in the liquid crystal layer, and therefore, high
transmittance can be gained and high efficiency in the display mode
can be achieved.
<Distribution of Electrical Field Around Wall Pixel Electrode
and Pseudo-Wall Common Electrode>
[0096] FIG. 5 is a diagram for illustrating the distribution of an
electrical field around a pseudo-wall common electrode in the
liquid crystal display device according to the first embodiment of
the present invention, FIG. 6 is a diagram for illustrating the
distribution of an electrical field around a conventional wall
electrode, FIG. 7 is a diagram for illustrating the distribution of
an electrical field around a conventional common electrode, and
FIG. 8 is a diagram for illustrating the precision in positioning a
pseudo-wall common electrode according to the first embodiment of
the present invention.
[0097] As shown in FIG. 5, in the liquid crystal display panel PNL
according to the first embodiment, the first common electrode CE1
formed on the first substrate SU1 and the second common electrode
CE2 formed on the second substrate SU2 are placed so as to overlap
as viewed from the display side. As a result, in the pseudo-wall
common electrode in the first embodiment, equipotential surfaces E1
and E2 respectively surround only the first common electrode CE1
and the second common electrode CE2 in the vicinity of the first
common electrode CE1 and the second common electrode CE2. Here, the
structure in the first embodiment allows the same common signal to
be supplied to the first common electrode CE1 and the second common
electrode CE2, and therefore, equipotential surfaces E3 surround
both the first common electrode CE1 and the second common electrode
CE2, that is to say, the equipotential surfaces E3 connect the
first substrate SU1 and the second substrate SU2. At this time, the
equipotential surfaces E3 are the same as the equipotential
surfaces in the case where an electrode IWE in wall form is formed
as in FIG. 6. There is a liquid crystal layer LC between the first
common electrode CE1 and the second common electrode CE2, and
therefore, the same effects can be gained for the equipotential
surfaces E3 around the pseudo-wall common electrode as in the case
where an electrode IWE in wall form is provided, and thus, the
pseudo-wall common electrode itself does not greatly lower the
transmittance. Accordingly, the structure where wall pixel
electrodes SE are provided on the wall bases WL at the ends of the
pixels and pseudo-wall common electrodes are provided at the center
of the pixels allows for high transmittance, even in the case where
the width of the pixels is relatively large, as in the liquid
crystal display panel PNL for WVGA.
[0098] As is clear from the shape of the equipotential surfaces E3
in FIG. 5, the equipotential surfaces E3 created by a pseudo-wall
common electrode are small in the width in the direction of the
width of the electrode in a region between the first common
electrode CE1 and the second common electrode CE2, that is to say,
in a region between the first substrate SU1 and the second
substrate SU2, and therefore, it is possible for the width of the
electrode that does not contribute to the driving of the liquid
crystal molecules to be small. As a result, the efficiency in
display can be improved.
[0099] In the first embodiment, the liquid crystal display panel
PNL has such a structure that the width of the first common
electrode CE1 is greater (wider) than that of the second common
electrode CE2. This is because the fact that the precision in
processing the first substrate SU1, which is the substrate having
color filters CF, is lower relative to that for the second
substrate SU2 is taken into consideration. As shown in FIG. 8, in
the case where the first common electrode CE1 and the second common
electrode CE2 face each other at an angle, for example, the first
common electrode CE1 can have a large width so that the
equipotential surfaces E3 can be provided, and thus, a pseudo-wall
common electrode can be formed. Here, the first common electrode
CE1 and the second common electrode CE2 are not limited to having
different electrode widths, and they may be formed to have the same
width. More desirably, the width of the first common electrode CE1
is the same as that of the second common electrode CE2. That is to
say, the smaller the width of the first common electrode CE1 and
the width of the second common electrode CE2 are, the narrower the
distribution of the equipotential surface E3 that surrounds the
first common electrode CE1 and the second common electrode CE2 in
FIG. 5 is, and therefore, the transmittance in the vicinity of the
pseudo-wall common electrode is higher.
[0100] In the case where only either the first common electrode CE1
or the second common electrode CE2 is provided to the pseudo-wall
common electrode having the above-described structure, the same
effects cannot be gained for the pseudo-wall common electrode. FIG.
7 is a diagram showing the equipotential surfaces in the case where
a common electrode is provided only to the second substrate SU2,
that is to say, only the second common electrode CE2 is provided.
As shown in FIG. 7, the equipotential surfaces are in concentric
form surrounding the second common electrode CE2. In this case, the
intensity of the electrical field surrounding the second common
electrode CE2 is low and the alignment of liquid crystal does not
sufficiently change, and therefore, the transmittance significantly
lowers in the vicinity thereof.
[0101] Meanwhile, in the first embodiment, wall pixel electrodes SE
for one pixel and its adjacent pixel are placed on the sidewalls of
a wall base WL that face each other, and therefore, there is an
electrical field in and around the wall base WL due to the
difference in the potential between the wall pixel electrodes SE
for the pixel and its adjacent pixel. As a result, in the case of
driving for inverting the display column by column, the difference
in the potential between the wall pixel electrodes SE formed on the
same wall base WL is maximum when the pixel displays white and its
adjacent pixel displays black. At this time, the transmittance for
white display lowers in the case where the intensity of the
electrical field within the pixels for white display becomes
uneven. In addition, the transmittance for black display increases
in the case where there is a leak in the potential in a pixel for
black display. In the structure according to the first embodiment,
as shown in FIG. 3, the height of the wall bases WL is almost equal
to the thickness of the liquid crystal layer LC, and the wall pixel
electrodes SE have a flat portion HP. This structure can reduce the
unevenness in the distribution of lateral electrical fields caused
by the fact that lines of electric force from the surface of the
vertical portion VP that forms a wall pixel electrode SE pass
through the second substrate SU2 and reach the surface of the
vertical portion VP formed on the opposite surface of the wall base
WL, and can also reduce the leakage of an electrical field to an
adjacent pixel, and thus, the transmittance for white display can
be improved and the transmittance for black display can be lowered.
That is to say, the efficiency in the display mode can be improved
and a high contrast ratio can be gained.
[0102] FIG. 9 is a diagram showing the distribution of
equipotential surfaces in the vicinity of a wall base in the liquid
crystal display device according to the first embodiment of the
present invention. In particular, the center of the wall base WL in
FIG. 9 is a pixel border, and FIG. 9 shows the distribution of
equipotential surfaces in such a state that the pixel on the right
(a pixel) displays white and the pixel on the left (its adjacent
pixel) displays black. In addition, the distribution of
equipotential surfaces shown in FIG. 9 corresponds to a case where
the difference in the potential between adjacent pixels is maximum
during the driving for inverting the display column by column.
[0103] In the case where adjacent pixels display black and white
for the driving for inverting the display column by column, the
equipotential surfaces EF1 on the white display side have a wide
distribution. Meanwhile, an equipotential surface EF2 is created
around the pixel for black display, but this is localized in the
vicinity of the wall pixel electrode SE. The fact that these
distributions of equipotential surfaces EF1 and EF2 are gained
shows that the effects of the electrical field from the wall pixel
electrode SE of the pixel for white display on the right in the
figure on the electrical field of the pixel for black display can
be reduced, and at the same time, the effects of the electrical
field from the wall pixel electrode SE of the pixel for black
display on the left in the figure on the electrical field of the
pixel for white display can be reduced.
[0104] As the liquid crystal display panel PNL according to the
first embodiment having this structure, a liquid crystal display
panel is formed using a liquid crystal material having a high
resistance which shows a nematic phase in a wide temperature range
including room temperature for the liquid crystal layer LC. In the
case where an electrical field is applied to the liquid crystal
display panel PNL according to the first embodiment parallel to the
layer plane of the liquid crystal layer LC, that is to say,
parallel to the surface of the liquid crystal display panel using
the wall pixel electrodes SE formed on the wall bases WL, the
liquid crystal layer LC is in an alignment state that is close to
the uniaxial alignment model. In this case, the retardation And of
the liquid crystal layer may be approximately 300 nm in order to
achieve both a high transmittance and achromatic color. In the
first embodiment, the index of birefringence .DELTA.n of the liquid
crystal material is 0.09, the thickness of the liquid crystal layer
is 3.3 .mu.m, and .DELTA.nd of the liquid crystal layer is 300
nm.
[0105] Here, the region where the wall bases WL are formed does not
have the liquid crystal layer LC, and therefore, the wall bases WL
themselves cause the transmittance to lower. Thus, the structure in
the first embodiment allows the wall bases WL to be located beneath
the black matrix BM in the end portions of the pixels. In the case
of the pixels for WVGA (wide video graphics array), for example,
the width of pixels (width of pixels in the X direction) is
approximately 30 .mu.m. Accordingly, in the conventional wall
electrode structure where electrodes in wall form are formed in end
portions of a pixel so that a video signal is supplied to one
electrode and a common signal is supplied to the other electrode,
the distribution of the intensity of the electrical field becomes
uneven, which lowers the transmittance, when the wall bases WL are
aligned at intervals of 30 .mu.m. In contrast, the liquid crystal
display panel PNL according to the first embodiment has such a
structure that a pseudo-wall common electrode is provided at the
center of pixels, which makes it possible to compensate the
intensity of the electrical field at the center of pixels, and
thus, the transmittance can be increased. As described above, the
pseudo-wall common electrodes are formed of a pair of common
electrodes, a first common electrode CE1 and a second common
electrode CE2.
[0106] Next, FIG. 10 is a graph showing the distribution of the
measured values of transmittance within one pixel in the liquid
crystal display device according to the first embodiment of the
present invention, and the effects of the structure of the pixels
in the first embodiment are described below in reference to FIG.
10. Here, the curve G1 in FIG. 10 is for the measured values of the
transmittance of pixels between one end and the other at the time
of white display (white display transmittance) in the case where
the width of pixels is 30 .mu.m and a pseudo-wall common electrode
is formed at a location 15 .mu.m away from an end of each pixel
when the pixels adjacent to the pixel displaying white are
displaying black. Thus, the case where a pixel is displaying white
and its adjacent pixels are displaying black corresponds to a case
where the difference in potential between adjacent pixels (a pixel
and its adjacent pixels) is maximum in the driving for inverting
the display column by column.
[0107] As is clear from the curve G1, the transmittance is low in
the region where the pseudo-wall common electrode is formed, which
is a portion 15 .mu.m away from an end of each pixel, while
approximately a constant transmittance is gained in other portions.
This shows that an electrical field (lateral electrical field)
having approximately a constant intensity is applied to the liquid
crystal layer LC within pixels, excluding the portion in the
vicinity of the pseudo-wall common electrode. Furthermore, as is
clear from the curve G1, a transmittance of 90% is gained for the
liquid crystal display device according to the first embodiment at
the time of the driving for inverting the display column by column.
In addition, the transmittance of the adjacent pixels displaying
black is 0.08%. Here, the transmittance in the present
specification is a value excluding the absorption by color filters,
polarizing plates and other members and the effects of the aperture
ratio, and thus is a value corresponding to the polarization
switching performance of the liquid crystal layer.
[0108] In contrast, in the IPS type liquid crystal display device
where the width of pixels is 30 .mu.m and pixel electrodes in
linear form are formed in a layer above the common electrode in a
plane with an insulating film in between, for example, the
transmittance for the driving for inverting the display column by
column is approximately 76%, and therefore, the transmittance can
be greatly improved in the liquid crystal display device according
to the first embodiment. That is to say, the efficiency in the
display mode can be greatly improved.
[0109] As described above, in the liquid crystal display device
according to the first embodiment, one pixel is formed of two or
more inclined pixel regions in a so-called multi-domain structure
where each pixel region is symmetrical relative to a line in the
direction in which the gate lines GL are aligned, and at the same
time, the wall pixel electrodes SE are formed of a vertical portion
VP, a flat portion HP and a top portion TP, drain lines DL are
formed in regions where a pixel is not exposed from the wall pixel
electrodes SE of its adjacent pixels as viewed from the top, and
furthermore, a pseudo-wall common electrode is formed in a region
between each pair of wall pixel electrodes SE that are formed in
the periphery portions of pixels, and this structure makes it
possible to increase the transmittance even for the pixels having
such a structure that pixels are relatively away from each other in
the direction of the width.
[0110] Though the liquid crystal display device according to the
first embodiment of the present invention provides a so-called
multi-domain structure where one pixel is formed of two regions
that are inclined in different directions (upper region and lower
region), the multi-domain structure is not limited to this. In
another example of the multi-domain structure, one pixel is formed
of three or more regions. In a particular case where one pixel is
formed of three or more regions, it is possible for all the angles
at which the regions are inclined to be different, but the
structure may allow at least two of the angles at which the regions
are inclined to be different in the arrangement.
Second Embodiment
[0111] FIG. 11 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display panel in
the liquid crystal display device according to the second
embodiment of the present invention. In the following, the liquid
crystal display device according to the second embodiment is
described in reference to FIG. 11. Here, the liquid crystal display
panel according to the second embodiment has the same structure as
in the first embodiment, except the structure of the regions
between a pair of wall pixel electrodes SE, that is to say, the
portions of the liquid crystal layer LC to which an electrical
field is applied. Accordingly, in the following, the structure of
the regions between the wall pixel electrodes SE is described in
detail. Though the description of the structure of the pixels
according to the second embodiment refers to a case of a so-called
multi-domain structure where the angles at which the wall pixel
electrodes SE are inclined are different within pixels at the
center portion, this can also be applied to a so-called single
domain structure where the pixels are formed of linear wall pixel
electrodes SE and a pseudo-wall common electrode.
[0112] As shown in FIG. 11, as in the first embodiment, the liquid
crystal display panel according to the second embodiment is formed
of a first insulating film IL1, drain lines DL, a second insulating
film IL2, wall bases WL and wall pixel electrodes SE, which are
layered in this order in layers above the second substrate SU2. In
the liquid crystal display panel according to the second
embodiment, a fourth insulating film (first insulating thick film)
IL4 is formed in each region between a pair of wall pixel
electrodes SE where liquid crystal molecules LCM are driven
(hereinafter referred to as transmission region). That is to say,
the structure allows the fourth insulating film IL4 to be formed in
the region within each pixel where the wall bases WL are not
formed.
[0113] In the second embodiment, the fourth insulating film IL4 is
formed so as to have a thickness that does not exceed the height H2
of the wall pixel electrodes SE. In the structure in the second
embodiment, through holes are created in the fourth insulating film
IL4 so as to run along the regions where the wall pixel electrodes,
including a wall base WL, are formed, and the wall bases WL and the
wall pixel electrodes SE are formed on the surface of the second
insulating film IL2 exposed from the bottom of these through holes
(exposed surface). As a result, in the liquid crystal display panel
PNL according to the second embodiment, recesses (first trenches)
are created in the second substrate SU2 on the liquid crystal side,
and the structure allows wall bases WL and wall pixel electrodes SE
to be provided and stand at the bottom of these recesses in such a
manner that the height of the wall pixel electrodes SE is greater
than the thickness of the liquid crystal layer by the depth of the
recesses, that is to say, by the thickness of the fourth insulating
film IL4. Though recesses are created in the second substrate SU2
(on the liquid crystal side) by providing through holes only in the
fourth insulating film IL4 in the second embodiment, the structure
may allow recesses to be created by providing two or more thin film
layers and creating through holes in these thin film layers.
[0114] A third insulating film IL3 is formed in a layer above the
fourth insulating film IL4 so as to cover the top surface of the
wall pixel electrodes SE and the wall bases WL. Second common
electrodes CE2, which are one transparent electrode for forming a
pseudo-wall common electrode, are formed in a layer above the third
insulating film IL3, and an alignment film AL2 is formed in a layer
above this.
[0115] The second substrate SU2 having this structure is provided
with wall bases WL formed on top of the second insulating film IL2
in such a manner that the height H2 of the wall bases WL is preset
to be greater than the thickness H1 of the liquid crystal layer LC.
After that, the vertical portion VP, the flat portion HP and the
top portion TP for forming a wall pixel electrode SE on a wall base
WL are formed through patterning, and then, a fourth insulating
film IL4 is formed on the entire surface of the second substrate
SU2, including the wall pixel electrodes SE and the second
insulating film IL2. Next, the parts of the fourth insulating film
IL4 formed in a layer above the wall bases WL and the wall pixel
electrodes SE and running along the regions where a wall pixel
electrode SE, including a wall base WL, is formed are removed so
that part of the top portions TP, the vertical portions VP and the
flat portions for forming the wall pixel electrodes SE as well as
the wall bases WL are exposed. After that, the third insulating
film IL3, the second common electrode CE2 and the second alignment
film AL2 are formed so that wall pixel electrodes SE can be formed
so as to have a height that is greater than the thickness H1 of the
liquid crystal layer LC by the thickness of the fourth insulating
film IL4. Here, a material for an organic insulating film, such as
an organic resist, can be used for the fourth insulating film IL4
so that the thickness thereof can be easily increased. In addition,
the height of the wall bases WL is sufficiently greater than the
thickness H1 of the liquid crystal layer LC.
[0116] Meanwhile, the structure of the first substrate SU1 is the
same as that of the first substrate SU1 of the above-described
liquid crystal display panel PNL according to the first embodiment.
As a result, the thickness H1 of the liquid crystal layer LC in
transmittance regions is smaller than the height H2 of the wall
pixel electrodes SE in the liquid crystal display panel PNL in the
first embodiment, even in the case where the height H1 of the
liquid crystal layer LC is the same as that of the conventional
liquid crystal display panel PNL. That is to say, the structure
allows the height H2 of the wall pixel electrodes SE to be greater
than the thickness H1 of the liquid crystal layer LC.
[0117] Next, FIG. 12 is a diagram for illustrating the distribution
of equipotential surfaces in the vicinity of a wall base in the
liquid crystal display device according to the second embodiment of
the present invention, and FIG. 13 is a graph for illustrating the
distribution of equipotential surfaces in the vicinity of a wall
base in the case where the liquid crystal display device according
to the first embodiment is driven so that the display is inverted
pixel by pixel. In the following, the structure of the pixels in
the liquid crystal display panel PNL according to the second
embodiment is described in detail in reference to FIGS. 12 and 13.
Here, the distribution of the equipotential surfaces shown in FIGS.
12 and 13 corresponds to a case where the difference of the
potential between adjacent pixels is maximum during the time of
driving for inverting the display pixel by pixel.
[0118] In the driving for inverting the display pixel by pixel, the
potentials are opposite between adjacent pixels, and therefore, the
difference in the potential is maximum between adjacent pixels in
the case where they both display white. At this time, in the liquid
crystal display panel PNL according to the second embodiment as
well, the wall pixel electrodes SE of adjacent pixels are formed in
such locations as to face each other with a wall base WL in
between. Therefore, in the case where maximum voltages having
opposite polarities are applied to adjacent pixels, that is to say,
in the case where the adjacent pixels both display white, there is
a difference in the potential that is almost two times greater than
the maximum value in the driving for inverting the display column
by column, and thus, the effects on the potentials in adjacent
pixels are greater.
[0119] FIG. 13 is a graph showing the results of measurement for
the transmittance when white is displayed and the transmittance
when black is displayed at the time of driving for inverting the
display pixel by pixel relative to the difference Hd (=H2-H1)
between the thickness H1 of the liquid crystal layer in the liquid
crystal display device according to the second embodiment and the
height H2 of the wall pixel electrodes SE in the liquid crystal
display device according to the second embodiment. In the
following, the structure of the liquid crystal display panel
according to the second embodiment is described in detail in
reference to FIGS. 12 and 13. Here, the curve G3 shows the measured
value of the transmittance of a pixel when white is displayed in
the case where the difference Hd between the height H2 of the wall
pixel electrodes SE and the thickness H1 of the liquid crystal
layer varies, and the curve G4 shows the measured value of the
transmittance of a pixel when black is displayed in the case where
the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer
varies.
[0120] As is clear from the curve G3, in the liquid crystal display
panel PNL according to the second embodiment, the height of the
wall bases WL varies, that is to say, the height H2 of the wall
pixel electrodes SE varies, and thus, it is possible to change the
display properties during the driving for inverting the display
pixel by pixel.
[0121] That is to say, the case where the difference Hd between the
height H2 of the wall pixel electrodes SE and the thickness H1 of
the liquid crystal layer is 0 .mu.m corresponds to a case where the
liquid crystal display device according to the first embodiment is
driven by inverting the display pixel by pixel, and the
transmittance when white is displayed in this case is approximately
74%. In contrast, in the case where a fourth insulating film IL4 is
formed and the height H2 of the wall pixel electrodes SE is
increased without changing the thickness H1 of the liquid crystal
layer in the transmittance region, it has become clear that the
transmittance when white is displayed increases as the difference
Hd between the height H2 of the wall pixel electrodes SE and the
thickness H1 of the liquid crystal layer increases. When Hd=0.5
.mu.m, for example, the transmittance increases to approximately
82%, while when Hd=1.0 .mu.m, it increases to 87%. In the case
where Hd is increased more, the transmittance is approximately 89%
when Hd is 2.0 .mu.m or greater, and the transmittance stays
approximately 89% even if Hd is further increased, and thus, an
increase in the transmittance is saturated when Hd=2.0 .mu.m.
[0122] Likewise, as is clear from the curve G4, in the case where
the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer is 0
.mu.m, the transmittance when black is displayed is approximately
0.43%. Meanwhile, when Hd=0.5 .mu.m, the transmittance decreases to
approximately 0.21%, while when Hd=1.0 .mu.m, it decreases to
0.14%. In the case where Hd is further greater, the transmittance
is approximately 0.08% when Hd is 2.0 .mu.m or greater, and the
transmittance stays at approximately 0.08% even if Hd is further
increased, and thus, a decrease in the transmittance is saturated
when Hd=2.0 .mu.m.
[0123] FIG. 14 is a graph showing the contrast ratio at the time of
driving for inverting the display pixel by pixel relative to the
difference Hd (=H2-H1) between the thickness H1 of the liquid
crystal layer and the height H2 of the wall pixel electrodes SE in
the liquid crystal display device according to the second
embodiment of the present invention, and in particular shows the
contrast ratio found from the efficiency in the display mode when
black is displayed (at the time of dark display) and when white is
displayed (at the time of bright display) shown in FIG. 13. As is
clear from the curve G5 in FIG. 14, in the case where the
difference Hd between the height H2 of the wall pixel electrodes SE
and the thickness H1 of the liquid crystal layer is 0 .mu.m, the
contrast ratio is approximately 170. The contrast ratio increases
as the difference Hd increases such that the contrast ratio is 390
when Hd=0.5 .mu.m, 650 when Hd=1.0 .mu.m, 870 when Hd=1.5 .mu.m,
1000 when Hd=2.0 .mu.m, 1020 when Hd=2.5 .mu.m, and 1030 when
Hd=3.0 .mu.m, respectively. Thus, in the liquid crystal display
device according to the second embodiment, the contrast ratio
increases as the difference Hd between the height H2 of the wall
pixel electrodes SE and the thickness H1 of the liquid crystal
layer increases, and then, the increase in the contrast ratio hits
the ceiling when the difference Hd between the height H2 of the
wall pixel electrodes SE and the thickness H1 of the liquid crystal
layer is close to 2 .mu.m, where the contrast ratio reaches to
1000:1.
[0124] The contrast ratio is calculated through the division of the
transmittance for bright display (transmittance when white is
displayed) by the transmittance for dark display (transmittance
when black is displayed). In the liquid crystal display device
according to the second embodiment, when the difference Hd between
the height H2 of the wall pixel electrodes SE and the thickness H1
of the liquid crystal layer is close to 2 .mu.m, the transmittance
for dark display is sufficiently low and the transmittance for
bright display is sufficiently high. Accordingly, in the structure
according to the second embodiment, the fourth insulating film IL4
and the wall pixel electrodes SE are formed so that the difference
Hd between the height H2 of the wall pixel electrodes SE and the
thickness H1 of the liquid crystal layer is 2 .mu.m or greater, and
thus, sufficient effects of the present invention can be gained in
order to gain a high contrast ratio. Therefore, in the liquid
crystal display device according to the second embodiment, it is
appropriate to form the fourth insulating film IL4 and the wall
pixel electrodes SE so that the difference Hd between the height H2
of the wall pixel electrodes SE and the thickness H1 of the liquid
crystal layer is 2 .mu.m or greater.
[0125] FIG. 17 is a graph showing the distribution of the
transmittance when the wall bases WL are formed so as to be taller
than the liquid crystal layer LC by 2 .mu.m and white is displayed
during the driving for inverting the display pixel by pixel in the
liquid crystal display device according to the second embodiment.
In particular, the curve G6 shown by a solid line shows the
distribution of the transmittance when white is displayed during
the driving for inverting the display pixel by pixel in the liquid
crystal display device according to the second embodiment. The
other curves G1 and G2 are shown for comparison, where the curve G1
shows the distribution of the transmittance when white is displayed
during the driving for inverting the display column by column in
the liquid crystal display device according to the first
embodiment, and the curve G2 shows the distribution of the
transmittance when white is displayed during the driving for
inverting the display pixel by pixel in the liquid crystal display
device according to the first embodiment.
[0126] As is clear from the curve G3, as in the liquid crystal
display device according to the first embodiment, a uniform
transmittance is gained in the portions other than the pseudo-wall
common electrode structure. At this time, the transmittance can be
as high as that in the distribution of the transmittance when white
is displayed during the driving for inverting the display column by
column in the liquid crystal display device according to the first
embodiment as shown by the curve G1. That is to say, the fourth
insulating film IL4 is formed so that the wall bases WL are taller
than the liquid crystal layer LC by 2 .mu.m in the liquid crystal
display device according to the second embodiment, and thus, the
potential can be completely blocked between adjacent pixels during
the driving for inverting the display pixel by pixel.
[0127] Meanwhile, in the case where white is displayed in pixels
adjacent to each other during the driving for inverting the display
pixel by pixel in the liquid crystal display device according to
the first embodiment, as is clear from the curve G2, the
transmittance is low in the vicinity of the pseudo-wall common
electrode, and in addition, the transmittance is not constant even
in the portions other than the pseudo-wall common electrode, and in
particular, the transmittance is low in the vicinity of the wall
pixel electrodes SE.
[0128] FIG. 15 shows the distribution of equipotential surfaces in
the vicinity of a wall pixel electrode SE at this time, where the
number of equipotential surfaces during the driving for inverting
the display pixel by pixel is greater than the number of
equipotential surfaces in a pixel when white is displayed during
the driving for inverting the display column by column shown in
FIG. 9. That is to say, though the number of equipotential surfaces
in a pixel when white is displayed is still 3 in the distribution
of equipotential surfaces shown in FIG. 15, the number of
equipotential surfaces in its adjacent pixel when black is
displayed has increased from 1 to 3. In addition, as is clear from
FIG. 15, the distribution of equipotential surfaces EF1 in a pixel
when white is displayed is biased towards the wall structure WL
side as compared to that during the driving for inverting the
display column by column shown in FIG. 9, that is to say, the
equipotential surfaces EF1 are localized in the vicinity of the
wall pixel electrode SE. This is caused by the fact that the
distance between the equipotential surfaces becomes smaller due to
the difference in the potential that is approximately two times
greater than that during the driving for inverting the display
column by column within the wall base WL, and the distribution is
biased towards the wall pixel electrode SE (wall base WL) side with
the distance between the equipotential surfaces EF1 in the
distribution shrinking in the liquid crystal layer LC. Judging from
the above, it is possible for the reduction in the transmittance in
the vicinity of the pseudo-wall common electrode as shown by the
curve G6 during the driving for inverting the display pixel by
pixel in the liquid crystal display device according to the first
embodiment to be caused by the facts that the distribution in the
intensity of the electrical field within pixels becomes uneven due
to the effects of the potential in adjacent pixels, the liquid
crystal molecules LCM in the liquid crystal layer LC cannot be
sufficiently driven, and the transmittance in different portions
within a pixel does not take the maximum value for the same
voltage. As a result, a sufficiently high transmittance cannot be
gained when white is displayed during the driving for inverting the
display pixel by pixel in the liquid crystal display device
according to the first embodiment, and thus, the transmittance when
white is displayed has decreased to 75% and the transmittance when
black is displayed with the adjacent pixels displaying white ends
up increasing to 0.43%.
[0129] In contrast, as shown in FIG. 12, the equipotential surfaces
EF1 when white is displayed are spread within the liquid crystal
layer LC to the same extent as those in a pixel when white is
displayed shown in FIG. 9 (on the right side in the figure) in the
liquid crystal display device according to the second embodiment,
and thus, it can be seen that a uniform distribution of an
electrical field is gained. In the case where black is displayed in
the pixel on the left side in the figure, and at the same time,
white is displayed in the pixel on the right side in the figure, as
shown in FIG. 16, the equipotential surfaces EF2 in the black
displaying pixel, which are equipotential surfaces within the
pixel, having the distribution of equipotential surfaces in the
vicinity of a wall base WL are spread to the vicinity of the wall
pixel electrode SE to the same extent as the above-described
distribution of the equipotential surfaces shown in FIG. 9 in the
first embodiment. In addition, the equipotential surfaces EF1 of
the white displaying pixel are also distributed, spreading into the
liquid crystal layer LC to the same extent as the equipotential
surfaces EF1 shown in FIG. 9. As a result, even in the case where a
black displaying pixel and a white displaying pixel are adjacent to
each other during the driving for inverting the display pixel by
pixel in the liquid crystal display panel PNL according to the
second embodiment, the transmittance when white is displayed can be
increased.
[0130] As described above, in the liquid crystal display device
according to the second embodiment, one pixel is formed of two or
more inclining pixel regions, wall pixel electrodes SE are placed
in peripheral portions of the pixel, a pseudo-wall common electrode
is provided within the transmittance region between the wall pixel
electrodes SE, and a fourth insulating film IL4 is formed within
the transmittance region so that the height H2 of the wall pixel
electrodes SE is greater than the thickness H1 of the liquid
crystal layer. As a result, it is possible to widen the
distribution of the equipotential surfaces in the liquid crystal
layer even in the case where wall pixel electrodes SE for adjacent
pixels are formed on one wall base WL so that a video signal can be
supplied to adjacent wall pixel electrodes SE in the driving mode
for inverting the display pixel by pixel, and thus, special effects
where the transmittance can be increased when white is displayed
and when black is displayed can be gained in addition to the
above-described effects of the liquid crystal display device
according to the first embodiment.
[0131] Thus, in the liquid crystal display device according to the
second embodiment, at least the fourth insulating film IL4 is
formed so as to have a great thickness so that the height of the
wall pixel electrodes SE is greater than the thickness of the
liquid crystal layer LC for the purpose of increasing the
transmittance during the driving for inverting the display pixel by
pixel. Furthermore, the thickness of the liquid crystal display
panel according to the second embodiment is greater than the
thickness of the liquid crystal display panel according to the
first embodiment, and thus, the thickness of the liquid crystal
layer according to the second embodiment is the same as the
thickness of the liquid crystal layer according to the first
embodiment.
Third Embodiment
[0132] FIG. 18 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the third embodiment of the present invention. The liquid
crystal display device according to the third embodiment has the
same structure as the liquid crystal display device according to
the second embodiment, except the structure of the fifth insulating
film IL5 formed between wall pixel electrodes SE that are placed in
periphery portions of the pixel so as to face each other.
Accordingly, in the following, the fifth insulating film IL5 is
described in detail.
[0133] As shown in FIG. 18, in the liquid crystal display device
according to the third embodiment, the first substrate SU1 has the
same structure as that in the first embodiment. The second
substrate SU2 has a first insulating film ILL drain lines DL, a
second insulating film IL2, wall bases WL and wall pixel electrodes
SE formed in this order on the surface on the liquid crystal side.
Here, in the liquid crystal display panel PNL according to the
third embodiment, a fifth insulating film (second insulating thick
film) IL5 is formed on the entire surface of the second substrate
SU2 so as to cover the wall bases WL and the wall pixel electrodes
SE, and a third insulating film IL3 is formed on the entire surface
of the second substrate SU2 in a layer above the fifth insulating
film IL5. Second common electrodes CE2 that form a pseudo-wall
common electrode are formed in a layer above the third insulating
film IL3, and a second alignment film AL2 is formed on the entire
surface of the second substrate SU2 so as to cover the second
common electrodes CE2.
[0134] In the liquid crystal display panel PNL according to the
third embodiment, the film thickness of the fifth insulating film
IL5 formed on the entire surface of the second substrate SU2 is
different between the transmission region and the regions excluding
this transmission region. In addition, as in the above-described
liquid crystal display panel PNL according to the second
embodiment, the film thickness of the fifth insulating film IL5 is
2.0 .mu.m in the transmission region according to the third
embodiment. Here, the film thickness of the fifth insulating film
IL5 may be 2.0 .mu.m or greater for the same reasons as in the
liquid crystal display device according to the second
embodiment.
[0135] The fifth insulating film IL5 having the above-described
structure can be formed by forming wall pixel electrodes SE after
the formation of wall bases WL, and then applying an organic
insulating film material, such as of an organic resist having a low
viscosity, to the entire surface of the second substrate SU2, which
is then hardened. That is to say, when an organic resist having a
low viscosity is used, the organic resist applied to the second
substrate SU2 using a spin coater or a slit coater flows after the
application, and thus has such a distribution in the thickness
where the thickness is small in high portions and the thickness is
great in low portions. Accordingly, in the structure where wall
pixel electrodes SE are formed on the sides of wall bases WL that
are provided and stand on the second substrate SU2 on the liquid
crystal side as that of the liquid crystal display panel PNL
according to the present invention, the film thickness of the fifth
insulating film IL5 is very great so as to be approximately equal
to the height of the wall bases WL due to the surface tense of the
organic resist when being applied in the vicinity of the places
where a wall pixel electrode SE is formed and is flat and uniform
(2 .mu.m, for example) in the transmission region, which is a
region away from the wall pixel electrodes SE. Furthermore, the
film is formed so as to be as thin as other insulating films on the
top surface of the wall bases WL. Thus, in the liquid crystal
display panel PNL according to the third embodiment, the fifth
insulating film IL5 can be formed in a desired location only
through the processes for applying and curing an organic insulating
film material having a low viscosity, and therefore, it is possible
to do without the steps required for patterning. As a result,
special effects can be gained such that the process for
manufacturing the second substrate SU2 or the liquid crystal
display device can be simplified and the cost for manufacture can
be reduced.
[0136] Here, the fifth insulating film IL5 formed on the outside of
the display region AR or the alignment film AL2 may be omitted in
the structure in order to increase the performance of the sealing
material for pasting the first substrate SU1 and the second
substrate SU2 together.
[0137] As described above, in the liquid crystal display device
according to the third embodiment, wall pixel electrodes for
adjacent pixels are respectively formed along and close to the
periphery portions within a pixel that run in the longitudinal
direction, and at the same time, a pseudo-wall common electrode is
formed within the transmission region between the pair of wall
pixel electrodes, and in addition, an organic insulating film
material having a low viscosity is applied to the entire surface of
the second substrate, including the transmission region, and is
cured so that the fifth insulating film IL5 is formed, and thus,
the height of the wall pixel electrodes SE is greater than the
thickness of the liquid crystal layer in the structure. As a
result, special effects can be gained such that the process
required for the formation of the fifth insulating film IL5, which
is an insulating film formed within the transmission region between
a pair of wall pixel electrodes, can be simplified in addition to
the above-described effects of the liquid crystal display device
according to the second embodiment.
Fourth Embodiment
[0138] FIG. 19 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the fourth embodiment of the present invention. Here, the liquid
crystal display device according to the fourth embodiment has the
same structure as the liquid crystal display device according to
the first embodiment, except the structure where an overcoat layer
OC formed on the first substrate SU1 is used as an insulating film
layer for adjusting the thickness of the liquid crystal layer in
the transmission region of each pixel as well as the height of the
wall pixel electrodes SE. Accordingly, in the following, the
structure of the first substrate SU1 is described in detail.
[0139] As shown in FIG. 19, a black matrix BM is formed on the
first substrate SU1 on the liquid crystal side according to the
fourth embodiment in such locations as to face the border portions
between adjacent pixels, and color filters CF are formed so as to
cover the black matrix BM. This structure allows the color filters
CF to correspond to either of the colors RGB, and color filters CF
of either of RGB are adjacent to each other across the regions that
overlap the black matrix BM.
[0140] In addition, an overcoat layer OC is formed in a layer above
the color filters CF. This structure according to the fourth
embodiment allows the overcoat layer OC to have recesses (second
trenches) created along regions facing the wall bases WL. That is
to say, the overcoat film OC is patterned so that the portions
facing the wall bases WL are removed from the overcoat film OC, and
thus, recesses are created in the first substrate SU1 on the liquid
crystal side as through holes in the overcoat layer OC. A first
alignment film AL1 is formed on the entire surface of the first
substrate SU1 so as to cover the overcoat layer OC and the portions
removed from the overcoat layer OC (recesses) in a layer above the
overcoat layer OC.
[0141] Meanwhile, a first insulating film IL1 is formed on the
second substrate SU2 on the liquid crystal side so as to function
as a gate insulating film formed between gate electrodes (gate
lines), not shown, formed on the surface of the second substrate
SU2 and a semiconductor layer for thin film transistors, not shown.
Second common electrodes CE2 and drain lines DL are formed in a
layer above the first insulating film ILL and in particular, the
second common electrodes CE2 and the drain lines DL are formed in
the same layer in the liquid crystal display panel PNL according to
the fourth embodiment.
[0142] In addition, wall bases WL are formed so as to cross the
drain lines DL in a layer above the drain lines DL as in the
above-described structures in the first to third embodiments.
Vertical portions VP for forming a wall pixel electrode SE are
formed on the sidewalls of each wall base WL, flat portions FP are
formed on the upper surface of the first insulating film IL1 on the
lower end side of the vertical portions VP, and top portions TP are
formed on the top surface of the wall bases WL on the upper end
side of the vertical portions VP. In the liquid crystal display
panel PNL according to the fourth embodiment, the wall bases WL are
formed so as to have a height H2 that is greater than the thickness
H1 of the liquid crystal layer LC as in the above-described liquid
crystal display panel PNL according to the second and third
embodiments. That is to say, in the liquid crystal display panel
PNL according to the fourth embodiment, the wall bases WL are
formed on top of the insulating film in a layer beneath the drain
lines DL (first insulating film IL1 according to the fourth
embodiment) as in the first embodiment, and the height H2 of the
wall bases WL is preset to be greater than the thickness H1 of the
liquid crystal layer.
[0143] A second alignment film AL2 is formed on the entire surface
of the second substrate SU2 so as to cover the wall pixel
electrodes SE and the second common electrodes CE2 in a layer above
these wall pixel electrodes SE. This second alignment film AL2
controls the initial alignment of the liquid crystal molecules LCM
in the liquid crystal layer LC.
[0144] In the liquid crystal display panel PNL according to the
fourth embodiment having this structure, when the first substrate
SU1 and the second substrate SU2 are pasted together, the top
portions TP of the wall pixel electrodes SE make contact with or
are in the proximity to the bottom portions of the recesses created
in the overcoat layer OC. As a result of the combination that makes
the top portions of the wall bases WL to be in proximity to the
portions where there is no overcoat layer OC, the wall bases WL are
taller than the thickness H1 of the liquid crystal layer by the
thickness of the overcoat layer OC. As a result, in the liquid
crystal display panel PNL according to the fourth embodiment, the
thickness of the liquid crystal layer LC within the transmission
regions of the pixels is also H1, and the liquid crystal molecules
LCM can be driven by an electrical field applied from the wall
pixel electrodes SE having a height H2 that is greater than the
thickness H1 of the liquid crystal layer.
[0145] Here, the manufacturing process for the second substrate SU2
where various wires, such as drain lines DL and gate lines GL, and
wall pixel electrodes SE are formed is more complex than that for
the first substrate SU1. In contrast, in the liquid crystal display
device according to the fourth embodiment, recesses into which wall
pixel electrodes SE are put are created in the first substrate SU1
so that the height H2 of the wall electrodes is greater than the
thickness H1 of the liquid crystal layer. Accordingly, in the
liquid crystal display device according to the fourth embodiment,
the number of steps required for the manufacture of the second
substrate SU2 can be reduced, and thus, special effects can be
gained such that the manufacturing process can be simplified.
[0146] Next, FIG. 20 is a diagram for illustrating the distribution
of equipotential surfaces in the vicinity of a wall base in the
case where the difference in the potential between adjacent pixels
becomes maximum during the driving for inverting the display pixel
by pixel in the liquid crystal display device according to the
fourth embodiment of the present invention, and FIG. 21 is a
diagram for illustrating the distribution of equipotential surfaces
in the vicinity of a wall base in the case where a pixel displaying
white and a pixel displaying black are adjacent to each other
during the driving for inverting the display pixel by pixel in the
liquid crystal display device according to the fourth embodiment of
the present invention. In the following, the display operation
using the structure of the wall pixel electrodes SE according to
the fourth embodiment is described in reference to FIGS. 20 and 21.
Here, the distribution of the equipotential surfaces shown in FIGS.
20 and 21 is the distribution of equipotential surfaces when
Hd=H2-H1=2.0 .mu.m as in the second and third embodiments.
[0147] As is clear from FIG. 20, even in the case where the
difference in the potential between adjacent pixels is maximum,
that is to say, in the case where the pixel on the right side in
FIG. 20 and its adjacent pixel on the left side both display white,
the equipotential surfaces EF1, which distribute around a pixel or
its adjacent pixel, respectively, spread widely towards the
pseudo-wall common electrodes formed at the center of the pixels
from the wall pixel electrodes SE that face each other with one
wall base WL in between. That is to say, the equipotential surfaces
EF1 spread to the vicinity of the wall pixel electrodes SE to the
same extent as the equipotential surface EF1 for the pixel
displaying white shown in FIG. 9 in the first embodiment, and
therefore, a uniform electrical field (lateral electrical field)
can be applied to the liquid crystal layer LC, and the
transmittance can be increased in the same manner as in the second
and third embodiments.
[0148] As shown in FIG. 21, in the distribution of equipotential
surfaces in the case where a pixel displays white and its adjacent
pixel displays black during the driving for inverting the display
pixel by pixel, an equipotential surface EF2 is generated so as to
surround the drain line DL and the wall pixel electrode SE in the
adjacent pixel displaying black. Here, the equipotential surface
EF2 is localized in the vicinity of the wall pixel electrode SE and
the transmittance for black lowers (improvement). Meanwhile, in the
pixel displaying white, the equipotential surface EF1 is
distributed widely towards the pseudo-wall common electrode formed
in the center portion of the pixel from the wall pixel electrode
SE, and therefore, the transmittance for white increases
(improvement).
[0149] Next, FIG. 22 is a graph showing the results of measurement
of the transmittance when white is displayed and the transmittance
when black is displayed during the driving for inverting the
display pixel by pixel relative to the difference Hd (=H2-H1)
between the thickness H1 of the liquid crystal layer and the height
H2 of the wall pixel electrodes SE in the liquid crystal display
device according to the fourth embodiment of the present invention.
In the following, the relationship between the transmittance and
the difference Hd between the thickness H1 of the liquid crystal
layer and the height H2 of the wall pixel electrodes SE in the
liquid crystal display panel according to the fourth embodiment is
described in reference to FIG. 22. Here, the curve G7 shows the
measured value of the transmittance of a pixel displaying white in
the case where the difference Hd between the height H2 of the wall
pixel electrodes SE and the thickness H1 of the liquid crystal
layer varies, and the curve G8 shows the measured value of the
transmittance of a pixel displaying black in the case where the
difference Hd between the height H2 of the wall pixel electrodes SE
and the thickness H1 of the liquid crystal layer varies.
[0150] As is clear from the curve G7, in the liquid crystal display
panel PNL according to the fourth embodiment as well, it is
possible to improve the display properties for the driving for
inverting the display pixel by pixel by changing the height of the
wall bases WL, that is to say, by changing the height H2 of the
wall pixel electrodes SE.
[0151] A case where the difference Hd between the height H2 of the
wall pixel electrodes SE and the thickness H1 of the liquid crystal
layer is 0 .mu.m corresponds to a case where the driving for
inverting the display pixel by pixel is carried out in the liquid
crystal display device according to the first embodiment, and the
transmittance when white is displayed is approximately 74%. In
contrast, in the case where recesses are provided in the portions
of the overcoat layer OC that face the wall pixel electrodes SE or
the wall bases WL, and at the same time, the height H2 of the wall
pixel electrodes SE is made greater than the thickness H1 of the
liquid crystal layer so that the height H2 of the wall pixel
electrodes SE is increased without changing the thickness H1 of the
liquid crystal layer in the transmission regions, it has become
clear that the transmittance when white is displayed increases
(improvement) as the difference Hd between the height H2 of the
wall pixel electrodes and the thickness H1 of the liquid crystal
layer increases. When Hd=0.5 .mu.m, for example, the transmittance
increases to approximately 80%, and when Hd=1.0 .mu.m, Hd=1.5
.mu.m, Hd=2.0 .mu.m, Hd=2.5 .mu.m and Hd=3.0 .mu.m, the
transmittance increases to 84%, 87%, 88%, 89% and 89%,
respectively.
[0152] Likewise, as is clear from the curve G8, in the case where
the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer is 0
.mu.m, the transmittance when black is displayed is approximately
0.43%. When Hd=0.5 .mu.m, the transmittance is decreased
(improvement) to approximately 0.23%, and when Hd=1.0 .mu.m, Hd=1.5
.mu.m, Hd=2.0 .mu.m, Hd=2.5 .mu.m and Hd=3.0 .mu.m, the
transmittance is decreased to 0.16%, 0.11%, 0.09%, 0.08% and 0.08%,
respectively.
[0153] FIG. 23 is a graph showing the contrast ratio during the
driving for inverting the display pixel by pixel relative to the
difference Hd (=H2-H1) between the thickness H1 of the liquid
crystal layer and the height H2 of the wall pixel electrodes SE in
the liquid crystal display device according to the fourth
embodiment of the present invention. Here, FIG. 23 shows the
contrast ratio found from the efficiency in the display mode when
black is displayed (at the time of dark display) and when white is
displayed (at the time of bright display) shown in FIG. 22.
[0154] As is clear from the curve G9 in FIG. 23, in the case where
the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer is 0
.mu.m, the contrast ratio is approximately 180. In contrast, when
Hd=0.5 .mu.m, the contrast ratio increases to 340, and when Hd=1.0
.mu.m, Hd=1.5 .mu.m, Hd=2.0 .mu.m, Hd=2.5 .mu.m and Hd=3.0 .mu.m,
the contrast ratio increases to 540, 800, 990, 1040 and 1050,
respectively. Thus, in the liquid crystal display device according
to the fourth embodiment as well, the contrast ratio increases as
the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer
increases, but the increase in the contrast ratio hits the ceiling
when the difference Hd between the height H2 of the wall pixel
electrodes SE and the thickness H1 of the liquid crystal layer is 2
.mu.m or greater, where the contrast ratio reaches to approximately
1000:1.
[0155] Accordingly, in the liquid crystal display device according
to the fourth embodiment as well, the overcoat layer OC and the
wall pixel electrodes SE can be formed so that the difference Hd
between the height H2 of the wall pixel electrodes SE and the
thickness H1 of the liquid crystal layer is 2 .mu.m or greater, and
as a result, the effects of the present invention can be
sufficiently gained and a high contrast ratio can be achieved.
Therefore, in the liquid crystal display device according to the
fourth embodiment, it is appropriate to form the overcoat layer OC
and the wall pixel electrodes SE so that the difference Hd between
the height H2 of the wall pixel electrodes SE and the thickness H1
of the liquid crystal layer is 2 .mu.m or greater.
[0156] Thus, in the liquid crystal display panel PNL according to
the fourth embodiment, the overcoat layer OC and the wall pixel
electrodes SE can be formed so that the height H2 of the wall pixel
electrodes SE is greater than the thickness H1 of the liquid
crystal layer by 2.0 .mu.m or greater, as in the liquid crystal
display panel PNL according to the first embodiment, and thus, the
transmittance for white and the transmittance for black can both be
increased. That is to say, it is possible for the potential in a
pixel made by the wall pixel electrode SE corresponding to its
adjacent pixel provided on the same wall base WL to be effectively
blocked in the structure according to the fourth embodiment as
well.
[0157] Though the liquid crystal display device according to the
fourth embodiment has such a structure that the recesses provided
in the first substrate SU1 make the height H2 of the wall pixel
electrodes SE greater than the thickness H1 of the liquid crystal
layer, the invention is not limited to this. Other examples of the
structure may be combinations of the first substrate SU1 according
to the fourth embodiment and the second substrate SU2 according to
the second or third embodiment. In these cases, special effects can
be gained such that the fourth insulating film IL4 or the fifth
insulating film IL5 can be formed so as to be thin, and at the same
time, recesses can be created in the overcoat layer OC so as to be
shallow.
Fifth Embodiment
[0158] FIG. 24 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the fifth embodiment of the present invention. Here, the liquid
crystal display device according to the fifth embodiment has the
same structure as the liquid crystal display device according to
the first embodiment, except that the pixel electrodes formed on
the second substrate SU2 are made of a wall pixel electrode SE1,
which is a pixel electrode in wall form, and a linear pixel
electrode SE2, which is a pixel electrode in linear form.
Accordingly, in the following, the wall pixel electrodes SE1 and
the linear pixel electrodes SE2 are described in detail.
[0159] As shown in FIG. 24, a first insulating film IL1 is formed
on the entire surface of the first substrate SU1 on the liquid
crystal side in the fifth embodiment, and drain lines DL and linear
pixel electrodes (third electrodes) SE2 are formed in proximity in
a layer above the first insulating film IL1. In particular, in the
fifth embodiment, the linear pixel electrodes (second pixel
electrodes) SE2 are provided in a layer beneath the wall pixel
electrodes (first pixel electrodes) SE1, and this structure allows
the respective linear pixel electrodes SE2 of adjacent pixels to
sandwich one drain line DL. That is to say, one drain line DL is
provided between two linear pixel electrodes SE2 in the structure.
Here, the wall pixel electrode SE1 and the linear pixel electrode
SE2 in a pixel are both electrically connected to the source
electrode of the thin film transistor in the pixel so that the
linear pixel electrode SE2 is at the same potential as the wall
pixel electrode SE1, and the structure allows them to be supplied
with the same video signal.
[0160] As in the first embodiment, a second insulating film IL2 is
formed on the entire surface of the second substrate SU2 so as to
cover the drain lines DL and the linear pixel electrodes SE2 in a
layer above the drain lines DL and the linear pixel electrodes SE2.
Here, in the liquid crystal display panel PNL according to the
fifth embodiment, it is preferable for the thickness of the second
insulating film IL2 in the fifth embodiment to be greater than the
thickness of the second insulating film IL2 in the first
embodiment.
[0161] Wall bases WL and wall pixel electrodes SE are formed in a
layer above the second insulating film IL2 and are covered by a
third insulating film IL3 formed on the entire surface of the
second substrate SU2. Second common electrodes CE2 are formed in a
layer above the third insulating film IL3, and a second alignment
film AL2 is formed on the upper surface of the second common
electrodes CE2. In addition, a second polarizing plate PL2 is
provided on the rear surface of the second substrate SU2, that is
to say, on the surface illuminated with backlight.
[0162] Meanwhile, the structure of the first substrate SU1 is the
same as in the first embodiment, and a black matrix BM, color
filters CF, an overcoat layer OC, first common electrodes CE1 and a
first alignment film AL1 are formed in this order on the first
substrate SU1 on the liquid crystal side.
[0163] Next, FIGS. 25 and 26 are diagrams showing the distribution
of equipotential surfaces in the vicinity of a wall pixel electrode
in the liquid crystal display device according to the fifth
embodiment of the present invention during the driving for
inverting the display pixel by pixel, and in reference to these,
the operation of the liquid crystal display device according to the
fifth embodiment is described. Here, FIG. 25 is a diagram showing
the distribution of equipotential surfaces in the case where a
pixel on the right side in the figure and its adjacent pixel on the
left side in the figure both display white, and FIG. 26 is a
diagram showing the distribution of equipotential surfaces in the
case where a pixel displays white and its adjacent pixel displays
black.
[0164] As is clear from FIG. 25, in the liquid crystal display
panel according to the fifth embodiment, equipotential surfaces EF1
are created so as to surround the wall pixel electrodes SE1 and the
linear pixel electrodes SE2 when a video signal is applied to the
wall pixel electrodes SE1 and the linear pixel electrodes SE2.
Here, the linear pixel electrodes SE2 are formed in a layer closer
to the substrate than the flat portions HP of the wall pixel
electrodes SE1 formed on the substrate (second substrate SU2) side.
Accordingly, pixel electrodes in wall form can be provided as pixel
electrodes (pseudo-wall pixel electrodes) that appear to be formed
of a wall pixel electrode SE1 and a linear pixel electrode SE2 and
expanded in the direction of the thickness of the liquid crystal
display panel PNL (direction Z). That is to say, as in the second
to fourth embodiments, it is possible to form pixel electrodes in
wall form that are taller than the thickness of the liquid crystal
layer so as to gain high blocking effects. As a result, the liquid
crystal molecules LCM in the liquid crystal layer LC can be driven
by an electrical field applied to a pixel corresponding to each
video signal without being affected by the video signal applied to
adjacent pixels. Even in the case where the difference in the
voltage is maximum between a pixel formed of a wall pixel electrode
SE1 and a linear pixel electrode SE2 and its adjacent pixel formed
of a wall pixel electrode SE1 and a linear pixel electrode SE2, the
equipotential surface EF1 distributes widely in the liquid crystal
layer LC both in the pixel and its adjacent pixel as in the liquid
crystal display panels PNL according to the second to fourth
embodiments.
[0165] As is clear from FIG. 26, in the case where a pixel displays
white and its adjacent pixel displays black, an equipotential
surface EF1 is created around the pixel displaying white so as to
surround the wall pixel electrode SE1 and the linear pixel
electrode SE2. In addition, a voltage of 0V is applied to the drain
line DL in FIG. 26 in the adjacent pixel displaying black, and
therefore, an equipotential surface EF2 is created so as to
surround the wall pixel electrode SE1, the linear pixel electrode
SE2 and the drain line DL. Accordingly, high blocking effects can
be gained even in the case where pixels displaying black and white
are adjacent to each other, and the liquid crystal molecules LCM in
the liquid crystal layer LC can be driven in each pixel without
being affected by a video signal applied to an adjacent pixel.
[0166] Next, FIG. 27 is a graph showing the results of measurement
of the transmittance when white is displayed and the transmittance
when black is displayed during the driving for inverting the
display pixel by pixel relative to the distance between the wall
pixel electrode and the linear pixel electrode in the liquid
crystal display device according to the fifth embodiment of the
present invention. In the following, the relationship between the
transmittance and the distance between the wall pixel electrode and
the linear pixel electrode in the liquid crystal display panel
according to the fifth embodiment is described in reference to FIG.
27. In FIG. 27, the curve G10 shows the measured value of the
transmittance of a pixel when white is displayed in the case where
the distance H3 between the wall pixel electrode SE1 and the linear
pixel electrode SE2 varies, and the curve G11 shows the measured
value of the transmittance of a pixel when black is displayed in
the case where the distance H3 between the wall pixel electrode SE1
and the linear pixel electrode SE2 varies. In the case where the
film thickness of the second insulating film IL2 is much greater
than the film thickness of the wall pixel electrode SE1 and the
linear pixel electrode SE2, the distance H3 between the wall pixel
electrode SE1 and the linear pixel electrode SE2 is approximately
the same as the film thickness of the second insulating film
IL2.
[0167] As is clear from the curve G10 in FIG. 27, in the liquid
crystal display panel PNL according to the fifth embodiment as
well, it is possible to increase the display properties during the
driving for inverting the display pixel by pixel by changing the
distance H3 between the wall pixel electrode and the linear pixel
electrode SE2, that is to say, by changing the height H4 of the
pseudo-wall pixel electrode made of the wall pixel electrode SE1
and the linear pixel electrode SE2. At this time, the thickness H1
of the liquid crystal layer is approximately the same as the height
of the wall pixel electrode SE1 in the case where the height H4
(=H2+H3) of the pseudo-wall pixel electrode is changed, and thus,
the thickness H1 of the liquid crystal layer does not change as in
the second to fourth embodiments, and therefore, the display
properties during the driving for inverting the display pixel by
pixel can be improved.
[0168] That is to say, in the case where the distance H3 between
the wall pixel electrode SE1 and the linear pixel electrode SE2,
which is the difference between the height H4 of the pseudo-pixel
electrode and the thickness H1 of the liquid crystal layer, is 0
.mu.m, the transmittance when white is displayed is approximately
80%, as in the case where the driving for inverting the display
pixel by pixel is carried out in the liquid crystal display device
according to the first embodiment. In contrast, when H3=0.5 .mu.m,
the transmittance increases to approximately 83%, and when H3=1.0
.mu.m, H3=1.5 .mu.m, H3=2.0 .mu.m, H3=2.5 .mu.m and H3=3.0 .mu.m,
the transmittance increases to 88%, 89%, 90%, 90% and 90%,
respectively.
[0169] Likewise, as is clear from the curve G11, in the case where
the distance H3 between the wall pixel electrode SE1 and the linear
pixel electrode SE2 is 0 .mu.m, the transmittance when black is
displayed is approximately 0.42%. Meanwhile, when H3=0.5 .mu.m, the
transmittance decreases (improvement) to approximately 0.22%, and
when H3=1.0 .mu.m, H3=1.5 .mu.m, H3=2.0 .mu.m, H3=2.5 .mu.m and
H3=3.0 .mu.m, the transmittance decreases to 0.14%, 0.10%, 0.09%,
0.08% and 0.08%, respectively.
[0170] FIG. 28 is a graph showing the contrast ratio during the
driving for inverting the display pixel by pixel relative to the
distance H3 between the wall pixel electrode SE1 and the linear
pixel electrode SE2 in the liquid crystal display device according
to the fifth embodiment of the present invention. Here, FIG. 28
shows the contrast ratio found from the efficiency in the display
mode when black is displayed (at the time of dark display) and when
white is displayed (at the time of bright display) shown in FIG.
27.
[0171] As is clear from the curve G12 in FIG. 28, in the case where
the distance H3 between the wall pixel electrode SE1 and the linear
pixel electrode SE2 is 0 .mu.m, the contrast ratio is approximately
190. In contrast, when H3=0.5 .mu.m, the contrast ratio increases
to 390, and when H3=1.0 .mu.m, H3=1.5 .mu.m, H3=2.0 .mu.m, H3=2.5
.mu.m and H3=3.0 .mu.m, the contrast ratio increases to 640, 830,
1030, 1100 and 1120, respectively. Thus, in the liquid crystal
display device according to the fifth embodiment as well, the
contrast ratio increases as the distance H3 between the wall pixel
electrode SE1 and the linear pixel electrode SE2 increases, but the
increase in the contrast ratio hits the ceiling when the distance
H3 between the wall pixel electrode SE1 and the linear pixel
electrode SE2 is 2 .mu.m or greater, where the contrast ratio
reaches to 1000:1.
[0172] Accordingly, in the liquid crystal display device according
to the fifth embodiment, the effects of the present invention can
be sufficiently gained when the second insulating film IL2 is
formed so that the distance H3 between the wall pixel electrode SE1
and the linear pixel electrode SE2 is 2 .mu.m or greater, and a
high contrast ratio can be gained in the liquid crystal display
device according to the fifth embodiment. Therefore, it is
appropriate for the second insulating film IL2 to be formed so that
the distance H3 between the wall pixel electrode SE1 and the linear
pixel electrode SE2 is 2 .mu.m or greater in the liquid crystal
display device according to the fifth embodiment.
[0173] Thus, in the liquid crystal display panel PNL according to
the fifth embodiment, the second insulating film IL2 can be formed
so that the height H4 of the pseudo-wall pixel electrodes formed of
a wall pixel electrode SE1 and a linear pixel electrode SE2 is
greater than the thickness H1 of the liquid crystal layer by 2.0
.mu.m or greater as in the liquid crystal display panels PNL
according to the second to fourth embodiments, and the same effects
can be gained as in the liquid crystal display device according to
the second to fourth embodiments.
[0174] Furthermore, in the liquid crystal display device according
to the fifth embodiment, it is possible to form pseudo-wall pixel
electrodes simply by forming linear pixel electrodes SE2 on the
same layer as the drain lines DL and forming the second insulating
film IL2 to have a thickness of 2.0 .mu.m, and thus, special
effects can be gained such that the height H4 of the pseudo-wall
pixel electrodes can be made greater than the thickness H1 of the
liquid crystal layer without increasing the number of steps
required for the formation of the second substrate SU2.
Sixth Embodiment
[0175] FIG. 29 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display device
according to the sixth embodiment of the present invention. Here,
the liquid crystal display device according to the sixth embodiment
has the same structure as the liquid crystal display device
according to the first embodiment, except the structure of the
third common electrodes CE3 formed on the first substrate SU1.
Accordingly, in the following, the structure of the first substrate
SU1 is described in detail.
[0176] As is clear from FIG. 29, in the liquid crystal display
device according to the sixth embodiment, a black matrix BM is
formed on the first substrate SU1 on the liquid crystal side, and
color filters CF are formed in a layer above the black matrix BM.
Here, in the liquid crystal display device according to the sixth
embodiment, third common electrodes (fourth electrodes) CE3 are
formed of a conductive thin film in a layer above the color filters
CF so as to overlap the black matrix BM in the bordering portions
between the color filters CF. Here, the third common electrodes CE3
according to the sixth embodiment are formed in such locations as
to overlap the wall pixel electrodes SE formed on the first
substrate SU1 as viewed from the top or from the bottom, that is to
say, in such locations as to face the wall pixel electrodes SE, and
the third common electrodes CE3 in adjacent pixels are connected to
each other through a common line. Here, the formation of the third
common electrodes CE3 is not limited to the regions facing the wall
pixel electrodes SE, but may run in the Y direction along the
bordering portions between adjacent pixels, like drain lines DL. In
addition, the structure allows a common signal that becomes a
reference for video signals to be supplied to the third common
electrodes CE3, which are like the below-described first common
electrodes CE1. Furthermore, the third common electrodes CE3 are
formed so as to overlap the black matrix BM, and therefore are not
limited to being made of a transparent conductive film and may be
formed of other conductive thin films that are not transparent,
such as metal thin films.
[0177] An overcoat layer OC is formed on the entire surface of the
first substrate SU1 so as to cover the third common electrodes CE3
in a layer above the third common electrodes CE3. First common
electrodes CE1 for forming pseudo-wall common electrodes are formed
in a layer above the overcoat layer OC, and a first alignment film
AL1 is formed on the entire surface of the first substrate SU1 so
as to cover the first common electrodes CE1. That is to say, the
structure allows the third common electrodes CE3 to be provided
between the overcoat layer OC and the color filters CF in such a
location as to face the wall bases WL on the first substrate
SU1.
[0178] In addition, a first insulating film IL1 is formed on the
entire surface of the second insulating film IL2 on the liquid
crystal side as in the second substrate SU2 according to the first
embodiment, and drain lines DL are formed in a layer above the
first insulating film IL1 so as to be electrically connected to the
drain electrodes of the thin film transistors, not shown. The
second insulating film IL2 is formed on the entire surface of the
second substrate SU2 so as to cover the drain lines DL in a layer
above these drain lines DL. Wall bases WL and wall pixel electrodes
SE are formed in a layer above the second insulating film IL2, and
a third insulating film IL3 is formed on the entire surface of the
second substrate SU2 so as to cover the wall bases WL and the wall
pixel electrodes SE. Second common electrodes CE2 are formed in a
layer above the third insulating film IL3, and a second alignment
film AL2 is formed so as to cover the upper surface of the second
common electrodes CE2 and the third insulating film IL3. In
addition, a second polarizing plate PL2 is provided on the rear
surface of the second substrate SU2, that is to say, on the side
illuminated with backlight.
[0179] Thus, in the liquid crystal display device according to the
sixth embodiment, third common electrodes CE3 having such a
structure as to control the potential are provided in the pixel
borders on the first substrate SU1 in such a manner that the
structure allows the potential of a pixel to be prevented from
being affected by the potential of an adjacent pixel through the
first substrate SU1, the color filters CF formed on the surface of
the first substrate SU1, and the overcoat layer OC.
[0180] FIG. 30 is a diagram showing the distribution of
equipotential surfaces when a pixel and its adjacent pixel both
display white in the liquid crystal display device according to the
sixth embodiment of the present invention, and FIG. 31 is a diagram
showing the distribution of equipotential surfaces when a pixel
displays white and its adjacent pixel displays black in the liquid
crystal display device according to the sixth embodiment of the
present invention. Here, the potential of the drain wire DL is
0V.
[0181] As shown in FIG. 30, in the case where adjacent pixels both
display white, equipotential surfaces EF1 have a distribution that
is symmetrical between the left and right in the figure relative to
the wall base WL as in the liquid crystal display device according
to the first embodiment shown in FIG. 15.
[0182] Meanwhile, when the potential is close to 0V in the vicinity
of a third common electrode CE3 as in the case where displays white
and its adjacent pixel displays black, as shown in FIG. 31, an
equipotential surface EF2 is created so as to include the wall
pixel electrode SE and the third common electrode CE3. Here, the
equipotential surface EF2 is created through the first alignment
film AL1 and the overcoat layer OC on the first substrate SU1 side
in a region including the wall pixel electrode SE and the third
common electrode CE3. Accordingly, the equipotential surface EF2
prevents the potential of the wall pixel electrode SE of the pixel
displaying white on the right side in FIG. 31 from spreading into
the color filter CF and the overcoat layer OC. As a result, it is
possible to gain special effects such that the transmittance for
black can be prevented from increasing in the case where a pixel
displays white and its adjacent pixel displays black during the
driving for inverting the display pixel by pixel, and the
transmittance when a pixel displays white and its adjacent pixel
displays black can be lowered to 0.09% (improvement) in addition to
the same effects as in the liquid crystal display device according
to the first embodiment.
[0183] As described above, in the liquid crystal display device
according to the sixth embodiment, third common electrodes CE3 are
formed along the wall bases WL on the first substrate SU1 on the
liquid crystal side so as to face the wall bases WL, and at the
same time, the structure allows the same common signal to be
supplied to the third common electrodes CE3 as to the first common
electrodes CE1. As a result, when the voltage of one of the wall
pixel electrodes SE that face each other with a wall base WL in
between is close to that of the third common electrode CE3 when
black is displayed, the equipotential surface EF2 including the
wall pixel electrodes SE and the third common electrode CE is
canceled. That is to say, in the case where the video signal
applied to at least one of the wall pixel electrodes SE that face
each other with a wall base WL in between has approximately the
same voltage as the common signal, a pseudo-wall pixel electrode is
formed of this wall pixel electrode SE and the third common
electrode CE3. Accordingly, special effects can be gained such that
the transmittance for black can be prevented from increasing when a
pixel displays white and its adjacent pixel displays black in
addition to the above-described effects of the first
embodiment.
[0184] Though the sixth embodiment is a case where third common
electrodes CE3 according to the present invention are formed in the
liquid crystal display device according to the first embodiment,
the invention is not limited to this and can be applied to the
other liquid crystal display devices according to the second to
fifth embodiments where the above-described effects can be gained
by forming third common electrodes CE3.
Seventh Embodiment
[0185] FIG. 32 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display device
according to the seventh embodiment of the present invention. In
the following, the liquid crystal display device according to the
seventh embodiment is described in reference to FIG. 32. Here, the
liquid crystal display device according to the seventh embodiment
has the same structure as the liquid crystal display device
according to the sixth embodiment, except the locations in which
the third common electrodes CE3 are formed. Accordingly, in the
following, the third common electrodes CE3 are described in
detail.
[0186] As shown in FIG. 32, a black matrix BM, color filters CF and
an overcoat layer OC are formed in this order on the first
substrate SU1 on the liquid crystal side as in the liquid crystal
display panel PNL according to the first embodiment. In the liquid
crystal display panel PNL according to the seventh embodiment,
third common electrodes CE3 are formed in the same layer as in the
first common electrodes CE1, that is to say, on the upper surface
of the overcoat layer. In addition, a first alignment film AL1 is
formed on the entire surface of the first substrate SU1 so as to
cover the first common electrodes CE1 and the third common
electrodes CE3 in a layer above the first common electrodes CE1 and
the third common electrodes CE3. In the seventh embodiment, the
third common electrodes CE3 are not limited to being made of a
transparent conductive film, like the third common electrodes CE3
in the sixth embodiment, and may be made of a conductive thin film
that is not transparent, such as metal thin films including that of
aluminum. In the liquid crystal display panel PNL according to the
seventh embodiment, only the first alignment film AL1 is formed in
a layer above the third common electrodes CE3, and therefore, it is
preferable for the third common electrodes CE3 to be made of a
conductive thin film having excellent corrosion resistance, such as
ITO.
[0187] Thus, in the liquid crystal display panel PNL according to
the seventh embodiment, the second common electrodes CE2 and the
third common electrodes CE3 are both formed between the overcoat
layer OC and the first alignment film AL1. Therefore, the wall
pixel electrodes SE and the third common electrodes CE3 are at
least located in proximity to each other with the third insulating
film IL3 and the second alignment film AL2 formed in a layer above
the wall pixel electrodes SE and the first alignment film AL1
formed on the first substrate SU1 in between, but the structure
does not allow the wall pixel electrodes SE and the third common
electrodes CE3 to be electrically connected to each other.
[0188] Accordingly, in the liquid crystal display panel PNL
according to the seventh embodiment as well, the potential of a
pixel can be prevented from being affected by the potential of its
adjacent pixel due to the intervention of the first substrate SU1,
the color filters CF formed on the surface of the first substrate
SU1, and the overcoat layer OC. Therefore, as in the liquid crystal
display panel PNL according to the sixth embodiment, special
effects can be gained such that the transmittance for black can be
prevented from increasing in the case where a pixel displays white
and its adjacent pixel displays black during the driving for
inverting the display pixel by pixel in addition to the effects in
the liquid crystal display device according to the first
embodiment.
[0189] In the case where the third common electrodes CE3 are formed
of a transparent conductive film like the first common electrodes
CE1, the third common electrodes CE3 can be simultaneously formed
in the process for forming the first common electrodes CE1, and
therefore, special effects can be gained such that the third common
electrodes CE3 can be formed without adding new steps for forming
the third common electrodes CE3.
[0190] In addition, the liquid crystal display device according to
the seventh embodiment is not limited to having the structure shown
in FIG. 32 and may have the structure shown in FIG. 33, for
example. In another example of the liquid crystal display device
according to the seventh embodiment shown in FIG. 33, a black
matrix BM is formed on the first substrate SU1 on the liquid
crystal side, and color filters CF are formed in a layer above the
black matrix BM. In the other example of the liquid crystal display
device according to the seventh embodiment, the first common
electrodes CE1 and the third common electrodes CE3 are formed in
the same layer above the color filters CF, and an overcoat layer OC
and a first alignment film AL1 are formed in this order on the
entire surface of the first substrate SU1 so as to cover both the
first common electrodes CE1 and the third common electrodes CE3 in
a layer above the first common electrodes CE1 and the third common
electrodes CE3. That is to say, the other example of the liquid
crystal display device according to the seventh embodiment has such
a structure that the second common electrodes CE2 and the third
common electrodes CE3 are both formed between the overcoat layer OC
and the first alignment film AL1, and therefore, in addition to the
above-described effects in the liquid crystal display device
according to the seventh embodiment, special effects can be gained
such that the transmittance can be prevented from being lowered,
even in the case where there is a positional misalignment, that is
to say, there is an alignment error when the first substrate SU1
and the second substrate SU2 are pasted together. Here, the effects
of having a large allowance for alignment in the other example of
the liquid crystal display device according to the seventh
embodiment can be gained for the same reasons why the
above-described first common electrodes CE1 and second common
electrodes CE2 can be misaligned.
Eighth Embodiment
[0191] FIG. 34 is a cross-sectional diagram for schematically
illustrating the structure of the liquid crystal display device
according to the eighth embodiment of the present invention. Here,
the liquid crystal display device according to the eighth
embodiment has the same structure as the liquid crystal display
device according to the second embodiment, except the locations
where the second common electrodes CE2 are formed. Accordingly, in
the following, the second common electrodes CE2 are described in
detail.
[0192] As shown in FIG. 34, in the liquid crystal display device
according to the eighth embodiment, a first insulating film ILL
drain lines DL, a second insulating film IL2 and wall bases WL are
formed in this order on the second substrate SU2 on the liquid
crystal side as in the liquid crystal display device according to
the second embodiment. Wall pixel electrodes SE are formed on the
top surface and the sidewall of a wall base WL and on the upper
surface of the second insulating film IL2 in the vicinity of the
wall base WL, and at the same time, the second common electrodes
CE2 are formed so as to run in the longitudinal direction of the
pixels in a center portion along B-B' of a pixel. A fourth
insulating film IL4 is formed in the transmittance regions of the
pixels sandwiched between a pair of wall pixel electrodes SE so as
to cover the end portions of the flat portions HP of the wall pixel
electrodes SE, the second common electrodes CE2 and the second
insulating film IL2 exposed from the surface. In addition, a third
insulating film IL3 and a second alignment film AL2 are formed in
this order on the entire surface of the second substrate SU2 so as
to cover the top surface of the wall base WL exposed from the
surface and the wall pixel electrodes SE exposed from the surface.
In the liquid crystal display device according to the eighth
embodiment as well, the fourth insulating film IL4 has a film
thickness that is greater than the other insulating films by 2.0
.mu.m or greater, and the height of the wall pixel electrodes SE is
greater than the thickness of the liquid crystal layer LC by 2.0
.mu.m or greater.
[0193] Meanwhile, a black matrix BM, color filters CF, an overcoat
layer OC, first common electrodes CE1 and a first alignment film
AL1 are layered on top of each other in this order on the first
substrate SU1 on the liquid crystal side, and the first substrate
SU1 and the second substrate SU2 are located so as to face each
other with a liquid crystal layer LC in between, and thus, the
liquid crystal display panel PNL according to the eighth embodiment
is formed. In the liquid crystal display device according to the
eighth embodiment as well, the fourth insulating film IL4 has a
film thickness of 2.0 .mu.m or greater, and therefore, the height
of the wall pixel electrodes SE can be made greater than the
thickness of the liquid crystal layer LC by the film thickness of
the fourth insulating film IL4, which is 2.0 .mu.m, and thus, the
same effects as that of the liquid crystal display device according
to the second embodiment can be gained.
[0194] Furthermore, the liquid crystal display device according to
the eighth embodiment has such a structure that the second common
electrodes CE2 are formed in a layer beneath the fourth insulating
film IL4. That is to say, the second common electrodes CE2 are
formed between the second insulating film IL2 and the fourth
insulating film IL4. Accordingly, in the liquid crystal display
device according to the eighth embodiment, special effects can be
gained such that the transmittance can be prevented from lowering
due to a positional misalignment when the first substrate SU1 and
the second substrate SU2 are pasted together, even if there is such
a positional misalignment as described below in the section of the
effects. As a result, it is possible to lower the ratio of the
occurrence of defects due to the positional misalignment when the
first substrate SU1 and the second substrate SU2 are pasted
together, and special effects can be gained such that the
productivity of the liquid crystal display device can be
increased.
[0195] Though the liquid crystal display device according to the
eighth embodiment is a case where the present invention is applied
to the liquid crystal display device according to the second
embodiment, the invention is not limited to this. For example, the
second common electrodes CE2, which are the same as in the liquid
crystal display device according to the third embodiment, can be
formed in a layer beneath the fifth insulating film IL5 so as to
provide the same positional relationship between the first common
electrodes CE1 and the second common electrodes CE2 as in the
liquid crystal display device according to the eighth embodiment.
Thus, the same effects as in the eighth embodiment can be
gained.
<Concerning Effects of Preventing Transmittance from Lowering
when there is Positional Misalignment Between First and Second
Common Electrodes>
[0196] In the case where there is a misalignment (positional
misalignment) when the first substrate SU1 and the second substrate
SU2 are combined (pasted together), there is also a misalignment in
the positional relationship between the first common electrodes CE1
and the second common electrodes CE2. In the liquid crystal display
device according to the first embodiment shown in FIG. 3, for
example, in the case where there is a positional misalignment in
such a manner where the first substrate SU1 is shifted in the
direction B relative to the second substrate SU2, the distribution
of the equipotential surfaces in the vicinity of the first common
electrodes CE1 and the second common electrodes CE2 is inclined in
the left or right direction in FIG. 8, that is to say, in the
direction in which the pseudo-wall common electrodes are aligned as
shown in FIG. 8, so as to provide an equipotential surface E3 that
surrounds both a first common electrode CE1 and a second common
electrode CE2. In this positional misalignment shown in FIG. 8, the
first common electrode CE1 is shifted in the left direction in FIG.
8 relative to the second substrate SU2, and therefore, the area
that overlaps the second common electrode CE2 in the left portion
of the first common electrode CE1 in FIG. 8 decreases. As a result,
the transmittance lowers on the left side of the pseudo-wall
electrode in FIG. 8.
[0197] FIG. 35 is a graph showing the transmittance of a pixel when
white is displayed during the driving for inverting the display
pixel by pixel relative to the amount of misalignment between the
first common electrode CE1 and the second common electrode CE2 in a
pseudo-wall common electrode in the present invention, where the
curve 13 shows the transmittance of a pixel when white is displayed
relative to the amount of misalignment between the first substrate
SU1 and the second substrate SU2 in the liquid crystal display
device according to the first embodiment.
[0198] As is clear from the curve G13, the structure of a
pseudo-wall electrode in the first embodiment has a transmittance
of 89% in the case where there is no misalignment, that is to say,
the amount of misalignment SH is 0 .mu.m. Meanwhile, when SH=0.5
.mu.m, SH=1.0 .mu.m, SH=1.5 .mu.m, SH=2.0 .mu.m, SH=2.5 .mu.m and
SH=3.0 .mu.m, the transmittance is 89%, 89%, 87%, 83%, 78% and 70%,
respectively.
[0199] Thus, the structure according to the first embodiment has a
transmittance for white display of 89% in the case where there is
no misalignment between the first substrate SU1 and the second
substrate SU2, but the transmittance for white display lowers as
the misalignment increases and lowers to 70% when the misalignment
is 3 .mu.m. Accordingly, it is preferable for the structure
according to the first embodiment to have a positional misalignment
of 1.5 .mu.m or less when the first substrate SU1 and the second
substrate SU2 are pasted together.
[0200] FIG. 36 is a graph showing the distribution of transmittance
within a pixel in the case where there is no misalignment between
the first substrate SU1 and the second substrate SU2 and in the
case where the misalignment is 3 .mu.m in the liquid crystal
display device according to the first embodiment, where the dotted
curve G16 shows a case where the amount of misalignment SH in FIG.
8 is 3.0 .mu.m, and the solid curve G17 shows a case where SH=0
.mu.m. Here, FIG. 36 shows the distribution of transmittance in a
pixel in the case where the pitch of the pixels in the width
direction is 30 .mu.m and first and second common electrodes CE1
and CE2 are located in the center portion of the pixel. In
addition, the curves G16 and G17 show the distribution of
transmittance in the case where the pixel and its adjacent pixel
both display white during the driving for inverting the display
pixel by pixel.
[0201] As is clear from the curve G17, in the case where there is
no positional misalignment between the first substrate SU1 and the
second substrate SU2, the transmittance lowers greatly in the
region close to 15 .mu.m, which is the center location of the
pseudo-wall common electrode made of a first common electrode CE1
and a second common electrode CE2. However, the transmittance is
approximately 89% in the regions expect the region where the
pseudo-wall common electrode is formed.
[0202] In the case where there is a positional misalignment of
SH=3.0 .mu.m in FIG. 8, the equipotential surface E3 is inclined
because the first common electrode CE1 is misaligned in the left
direction (direction towards the side where the distance from the
end of the pixel is smaller) relative to the second substrate SU2,
and therefore, there is an inclination in the equipotential surface
E3. As a result, the area where the first common electrode CE1 and
the second common electrode CE2 overlap decreases in the region
where the distance from the end of the pixel is smaller, and
therefore, as shown by the curve G16, the transmittance in this
region is lowered to approximately 60%.
[0203] In contrast, as shown in FIG. 37, which is a diagram showing
an enlargement of the portion of a pseudo-wall common electrode in
the liquid crystal display device according to the eighth
embodiment of the present invention, first and second alignment
films AL1 and AL2, al liquid crystal layer LC and a third
insulating film IL3 are formed between the first common electrodes
CE1 and the second common electrodes CE2 in the liquid crystal
display device according to the eighth embodiment. Accordingly, in
the distribution of equipotential surfaces created between a first
common electrode CE1 and a second common electrode CE2 in the case
where there is no positional misalignment, an equipotential surface
E1 surrounding the first common electrode CE1 is created around the
first common electrode CE1, including part of the liquid crystal
layer LC, and an equipotential surface E2 surrounding the second
common electrode CE2 is created around the second common electrode
CE2, including part of the third insulating film IL3. In addition,
an equipotential surface E3 surrounding both the first common
electrode CE1 and the second common electrode CE2 so as to form a
pseudo-wall common electrode is created so as to include part of
the first and second alignment films AL1 and AL2, the liquid
crystal layer LC and the third insulating film IL3. In the liquid
crystal display device according to the eighth embodiment, the
liquid crystal layer LC has the same thickness as the liquid
crystal display device according to the first embodiment, and
therefore, the equipotential surface E3 is formed as if it were
expanded in the direction of the thickness of the liquid crystal
display panel PNL. Furthermore, the pseudo-wall common electrode is
formed with the width of the equipotential surfaces distributed in
the liquid crystal layer LC being narrowed because the first common
electrode CE1 having a greater width is at a distance away from the
liquid crystal layer LC.
[0204] Meanwhile, in the case where there is a positional
misalignment as in FIG. 8, as shown in FIG. 38, an equipotential
surface E3 surrounding the first common electrode CE1 and the
second common electrode CE2 is inclined in the direction of the
misalignment in the distribution of equipotential surfaces created
between a first common electrode CE1 and a second common electrode
CE2. In the structure according to the eighth embodiment, as is
clear from FIG. 38, the inclination of the equipotential surface E3
is smaller because the amount of change in the equipotential
surface E3 is smaller for the same amount of misalignment due to
the increase in the distance between the first common electrode CE1
and the second common electrode CE2.
[0205] FIG. 39 is a graph showing the distribution of transmittance
within a pixel in the case where there is no misalignment between
the first substrate SU1 and the second substrate SU2 and in the
case where there is a misalignment of 3 .mu.m in the liquid crystal
display device according to the eighth embodiment of the present
invention, where the dotted curve G18 shows a case of SH=3.0 .mu.m
and the solid curve G19 shows a case of no misalignment (SH=0
.mu.m).
[0206] As is clear from FIG. 39, in the liquid crystal display
device according to the eighth embodiment, the distribution of
transmittance within a pixel is almost the same in the case where
there is no misalignment between the first substrate SU1 and the
second substrate SU2 (curve G19) and in the case where there is a
misalignment of SH=3 .mu.m (curve G18), irrelevant of whether or
not there is a misalignment. This is the effect due to the
inclination of the equipotential surface E3 being smaller as a
result of the formation of the second common electrode CE2 in a
layer beneath the third insulating film IL3 as shown in FIG.
38.
[0207] The curve G15 in FIG. 35 shows the transmittance of a pixel
when white is displayed during the driving for inverting the
display pixel by pixel relative to the positional misalignment
between the first common electrode CE1 and the second common
electrode CE2 in the liquid crystal display device according to the
eighth embodiment. As is clear from this curve G15, the
transmittance is 88% in the structure of the pseudo-wall electrode
in the eighth embodiment in the case where there is no misalignment
(SH=0 .mu.m). In addition, when SH=0.5 .mu.m, SH=1.0 .mu.m, SH=1.5
.mu.m, SH=2.0 .mu.m, SH=2.5 .mu.m and SH=3.0 .mu.m, the
transmittance is 88%, 88%, 88%, 88%, 87% and 86%, respectively.
[0208] Thus, in the structure according to the eighth embodiment,
the transmittance is 86% even when the amount of misalignment SH is
3.0 .mu.m, and the decrease in the transmittance due to the
positional misalignment between the first substrate SU1 and the
second substrate SU2 can be limited to approximately 2%, and such
special effects can be gained that approximately a constant
transmittance for white display can be gained irrelevant of the
positional misalignment between the first substrate SU1 and the
second substrate SU2.
[0209] FIG. 40 is a graph for illustrating the dependency of the
transmittance for white display on the distance between the second
common electrode CE2 and the liquid crystal layer LC during the
driving for inverting the display pixel by pixel in a case where
there is a positional misalignment of 3 .mu.m between the first
substrate SU1 and the second substrate SU2. As is clear from the
curve G20 in FIG. 40, the transmittance for white display is 70% in
the case where the second common electrode CE2 and the liquid
crystal layer LC are in proximity to each other, but it increases
as the distance K2 between the second common electrode CE2 and the
liquid crystal layer LC increases in such a manner that when K2=0.5
.mu.m, K2=1.0 .mu.m, K2=1.5 .mu.m, K2=2.0 .mu.m, K2=2.5 .mu.m and
K2=3.0 .mu.m, the transmittance is 78%, 83%, 87%, 88%, 89% and 89%,
respectively. Thus, the transmittance is 88% or greater when the
distance K2 between the second common electrode CE2 and the liquid
crystal layer LC is 2.0 .mu.m or greater, and the same
transmittance for white display as in the case where there is no
misalignment between the first substrate SU1 and the second
substrate SU2 can be gained.
[0210] FIG. 41 is a graph for illustrating the relationship between
the driving voltage and the distance between the first common
electrode and the liquid crystal layer in the liquid crystal
display device according to the eighth embodiment of the present
invention. This graphs shows a voltage (driving voltage) to be
applied between the wall pixel electrode SE and the pseudo-wall
common electrode for display (white display) with a predetermined
transmittance when the distance H5 between the second common
electrode and the liquid crystal layer (see FIG. 37) varies in the
structure according to the eighth embodiment in FIG. 34.
[0211] As is clear from the curve G21 in FIG. 41, the driving
voltage Vpc is 4.5V in the case where the distance H5 between the
second common electrode CE2 and the liquid crystal layer LC is 0
.mu.m. In addition, when H5=0.5 .mu.m, H5=1.0 .mu.m, H5=1.5 .mu.m,
H5=2.0 .mu.m, H5=2.5 .mu.m and H5=3.0 .mu.m, the driving voltage
Vpc is 4.8V, 4.9V, 5.0V, 5.0V, 5.1V and 5.1V, respectively.
[0212] Thus, in the structure according to the eighth embodiment,
the driving voltage Vpc tends to increase as the distance H5
between the second common electrode CE2 and the liquid crystal
layer LC increases. However, the increase in the driving voltage
Vpc tends to saturate, and the increase is gradual when the
distance H5 between the second common electrode CE2 and the liquid
crystal layer LC is 1.5 .mu.m or greater. That is to say, it is
clear that a high transmittance for white display can be gained
while suppressing the increase in the driving voltage Vpc by
adjusting the distance H5 between the second common electrode CE2
and the liquid crystal layer LC to 1.5 .mu.m or greater.
Accordingly, it is preferable for the liquid crystal display device
according to the eighth embodiment to be formed so as to have a
distance H5 between the second common electrode CE2 and the liquid
crystal layer LC of 1.5 .mu.m or greater. Furthermore, it is
preferable for the driving voltage Vpc to be approximately
5.0V.
[0213] As described above, the liquid crystal display device
according to the eighth embodiment has such a structure that second
common electrodes CE2, which are one common electrode of a
pseudo-wall common electrode, are formed in a layer beneath the
fourth insulating film IL4 that is provided to make the height of
the wall pixel electrodes SE greater than the thickness of the
liquid crystal layer LC, and therefore, it is possible to make the
distance between the first common electrodes CE1 and the second
common electrodes CE2 great, where the first common electrodes CE1
are the other common electrode of a pseudo-wall common electrode.
As a result, it is possible to make the inclination of the
distribution of electrical fields smaller in the pseudo-wall common
electrodes due to the positional misalignment between the first
common electrodes CE1 and the second common electrodes CE2 when the
first substrate SU1 on which the first common electrodes CE1 are
formed and the second substrate SU2 on which the second common
electrodes CE2 are formed are pasted together, and therefore,
special effects can be gained such that the transmittance can be
prevented from being lowered due to the positional misalignment
between the first common electrodes CE1 and the second common
electrodes CE2, and thus, the display quality can be improved in
addition to the effects in the liquid crystal display device
according to the second embodiment.
[0214] In the liquid crystal display device according to the eighth
embodiment, the wall pixel electrodes SE and the second common
electrodes CE2 are formed in the same layer, and thus, they are
both formed in a layer above the fourth insulating film IL4, and
therefore, special effects can be gained such that the fourth
insulating film IL4 and the second common electrodes CE2 can be
formed in the same process in the case where the wall pixel
electrodes SE are formed of a transparent conductive film, like the
second common electrodes CE2.
[0215] In the liquid crystal display device according to the eighth
embodiment, second common electrodes CE2 are formed in a layer
beneath the fourth insulating film IL4 (on the fourth insulating
film IL4 on the second substrate SU2 side), which is provided in
order to make the height of the wall pixel electrodes SE greater
than the thickness of the liquid crystal layer LC, that is to say,
in order to increase the transparency during the driving for
inverting the display pixel by pixel. This structure allows the
distance between the first common electrodes CE1 and the second
common electrodes CE2 to be greater than the thickness of the
liquid crystal layer LC. However, as shown in the first embodiment,
in the liquid crystal display devices where the height of the wall
pixel electrodes SE and the thickness of the liquid crystal layer
LC are approximately the same, the same effects of a misalignment
as described above can be gained in the case of driving for
inverting the display column by column by making the distance
between the first common electrodes CE1 and the second common
electrodes CE2 greater than the thickness of the liquid crystal
layer LC.
Ninth Embodiment
[0216] FIG. 42 is a cross-sectional diagram for illustrating the
structure of a pixel in the liquid crystal display device according
to the ninth embodiment of the present invention, which is the same
as that of the liquid crystal display device according to the
fourth embodiment, except the locations in which the first common
electrodes CE1 are formed. Accordingly, in the following, the first
common electrodes CE1 and the pseudo-wall common electrodes are
described in detail.
[0217] As shown in FIG. 42, a first insulating film ILL drain lines
DL, a second common electrode CE2 and wall bases WL are formed on
the second substrate SU2 on the liquid crystal side as in the
liquid crystal display device according to the fourth embodiment.
In addition, wall pixel electrodes SE are formed on the top surface
and a side of a wall base WL and on the upper surface of the second
insulating film IL2 in the vicinity of the wall base WL, the second
insulating film IL2 is formed so as to cover the surfaces exposed
from these, and a second alignment film AL2 is formed in a layer
above the second insulating film IL2, and thus, the second
substrate SU2 is formed.
[0218] Meanwhile, a black matrix BM is formed on the first
substrate SU1 on the liquid crystal side, and color filters CF are
formed so as to cover the black matrix BM. In the liquid crystal
display panel PNL according to the ninth embodiment, first common
electrodes CE1 are formed in a layer above the color filters CF and
an overcoat layer OC is formed so as to cover the first common
electrodes CE1. In the liquid crystal display panel PNL according
to the ninth embodiment, recesses for exposing the upper surface of
the color filters CF through the overcoat layer OC are created in
the overcoat layer OC along the regions where the wall bases WL are
formed as in the overcoat layer OC according to the fourth
embodiment. A first alignment film AL1 is formed on the entirety of
the second substrate SU2 in a layer above the overcoat layer OC so
as to cover the overcoat layer OC and the surface of the color
filters CF exposed from the overcoat layer OC.
[0219] The first substrate SU1 and the second substrate SU2 having
the above-described structure are placed so as to face each other
with a liquid crystal layer LC in between so that one end portion
of the wall pixel electrodes SE including the wall bases WL enters
into a recess created in the overcoat layer OC, and thus, the
liquid crystal display panel PNL according to the ninth embodiment
is formed. In the liquid crystal display device according to the
ninth embodiment, the overcoat layer OC is made of a relatively
thick film (preferably with a film thickness of 2.0 .mu.m or
greater), and therefore, the height of the wall pixel electrodes SE
is greater than the thickness of the liquid crystal layer LC by the
film thickness of the overcoat layer OC, and thus, the same effects
as in the liquid crystal display device according to the fourth
embodiment can be gained.
[0220] In addition, the liquid crystal display device according to
the ninth embodiment has such a structure that the first common
electrodes CE1 are formed in a layer beneath the overcoat layer OC.
That is to say, the first common electrodes CE1 are formed between
the overcoat layer OC and the color filters CF. Accordingly, in the
liquid crystal display device according to the ninth embodiment as
well, even in the case where there is a positional misalignment
between the first common electrodes CE1 and the second common
electrodes CE2 resulting from a positional misalignment when the
first substrate SU1 and the second substrate SU2 are pasted
together, such special effects can be gained that the transmittance
can be prevented from lowering due to this positional misalignment
as described in the following section of the effects. Furthermore,
it is possible to reduce the ratio of defects resulting from the
positional misalignment between the first substrate SU1 and the
second substrate SU2, and such special effects can be gained that
the productivity can be increased.
<Concerning Effects of Preventing Transmittance from Lowering at
the Time of Positional Misalignment of First and Second Common
Electrodes>
[0221] FIG. 43 is a diagram showing an enlargement of a pseudo-wall
common electrode portion in the liquid crystal display device
according to the ninth embodiment of the present invention, and
FIG. 44 is a diagram showing the distribution of equipotential
surfaces in the case where there is a positional misalignment in
the pseudo-wall common electrode in FIG. 43.
[0222] As shown in FIG. 43, first and second alignment films AL1
and AL2, a liquid crystal layer LC and an overcoat layer OC are
formed between the first common electrodes CE1 and the second
common electrodes CE2. Accordingly, in the case where there is no
positional misalignment, the equipotential surface E1 surrounding a
first common electrode CE1 is formed around the first common
electrode CE1 including part of the overcoat layer OC, and the
equipotential surface E2 surrounding a second common electrode CE2
is formed around the second common electrode CE2 including part of
the liquid crystal layer LC. In addition, the equipotential surface
E3 surrounding both the first common electrode CE1 and the second
common electrode CE2 that form a pseudo-wall common electrode
includes part of the liquid crystal layer that includes the first
and second alignment films AL1 and AL2 as well as part of the
overcoat layer OC.
[0223] Here, the liquid crystal display device according to the
ninth embodiment is formed as in the eighth embodiment so that the
thickness of the liquid crystal layer LC is the same as that of the
liquid crystal display device according to the first embodiment,
and therefore, the equipotential surface E3 is expanded in the
direction of the normal to the liquid crystal display panel PNL,
that is to say, in the direction of the thickness. Furthermore, the
first common electrodes CE1 are formed in a layer beneath the
overcoat layer OC, and therefore, the first common electrodes CE1,
which are electrodes having greater width, are formed in such
locations as to be far away from the liquid crystal layer LC in
comparison with the liquid crystal display device according to the
first embodiment, and thus, the equipotential surface E3 that is
distributed in the liquid crystal layer LC is narrower in the
width.
[0224] Meanwhile, in the case where there is the same positional
misalignment as in FIG. 8, as shown in FIG. 44, in the distribution
of the equipotential surfaces created between a first common
electrode CE1 and a second common electrode CE2, the equipotential
surface E3 surrounding the first common electrode CE1 and the
second common electrode CE2 is inclined in the direction in which
the substrates are misaligned. In the structure according to the
ninth embodiment, as is clear from FIG. 44, the inclination of the
equipotential surface E3 is small because the distance between the
first common electrode CE1 and the second common electrode CE2 is
greater, which makes the angle of inclination of the equipotential
surface E3 smaller relative to the direction of the normal to the
liquid crystal display panel PNL for the same amount of
misalignment.
[0225] The curve G14 in FIG. 35 shows the transmittance of a pixel
when white is displayed during the driving for inverting the
display pixel by pixel relative to the amount of misalignment
between the first common electrodes CE1 and the second common
electrodes CE2 in the liquid crystal display device according to
the ninth embodiment. As is clear from this curve G14, the
structure of the pseudo-wall electrode in the ninth embodiment
provides a transmittance of 87% in the case where there is no
positional misalignment (amount of misalignment SH is 0 .mu.m). In
addition, when SH=0.5 .mu.m, SH=1.0 .mu.m, SH=1.5 .mu.m, SH=2.0
.mu.m, SH=2.5 .mu.m and SH=3.0 .mu.m, the transmittance is 87%,
87%, 87%, 86%, 85% and 84%, respectively.
[0226] As described above, the structure according to the ninth
embodiment provides a transmittance of 84% when the amount of
misalignment SH is 3.0 .mu.m, and therefore, the reduction in the
transmittance due to the misalignment between the first substrate
SU1 and the second substrate SU2 can be limited to approximately
3%, and thus, special effects can be gained such that an
approximately constant transmittance for white display can be
gained irrelevant of the misalignment between the first substrate
SU1 and the second substrate SU2.
[0227] FIG. 45 is a graph for illustrating the dependency of the
transmittance for white display during the driving for inverting
the display pixel by pixel on the distance between the first common
electrode CE1 and the liquid crystal layer LC in the case where the
positional misalignment between the first substrate SU1 and the
second substrate SU2 is 3 .mu.m in the liquid crystal display
device according to the ninth embodiment.
[0228] As is clear from the curve G22 in FIG. 45, the transmittance
for white display is 70% in the case where the first common
electrode CE1 and the liquid crystal layer LC are in close
proximity to each other. However, the transmittance increases as
the distance K1 between the first common electrode CE1 and the
liquid crystal layer LC increases, and when K1=0.5 .mu.m, K1=1.0
.mu.m, K1=1.5 .mu.m, K1=2.0 .mu.m, K1=2.5 .mu.m and K1=3.0 .mu.m,
the transmittance is 77%, 81%, 84%, 86%, 87% and 88%. Thus, in the
case where the distance K1 between the first common electrode CE1
and the liquid crystal layer LC is 2.0 .mu.m or greater, the
transmittance is 86% or greater, and therefore, almost the same
transmittance for white display as in the case where there is no
misalignment between the first substrate SU1 and the second
substrate SU2 can be gained.
[0229] FIG. 46 is a graph for illustrating the relationship between
the driving voltage and the distance between the first common
electrode and the liquid crystal layer in the liquid crystal
display device according to the ninth embodiment of the present
invention, and shows a voltage (driving voltage) applied between
the wall pixel electrode SE and the pseudo-wall common electrode
for a display (white display) with a predetermined transmittance in
the case where the distance H6 between the first common electrode
and the liquid crystal layer (see FIG. 43) varies in the structure
according to the ninth embodiment in FIG. 42.
[0230] As is clear from the curve G23 in FIG. 46, the driving
voltage Vpc is 4.5V in the case where the distance H6 between the
first common electrode CE1 and the liquid crystal layer LC is 0
.mu.m. In addition, when H6=0.5 .mu.m, H6=1.0 .mu.m, H6=1.5 .mu.m,
H6=2.0 .mu.m, H6=2.5 .mu.m and H6=3.0 .mu.m, Vpc is 4.8V, 4.8V,
4.9V, 5.0V, 5.0V and 5.1V, respectively.
[0231] Thus, in the structure according to the ninth embodiment as
well, the driving voltage Vpc tends to increase as the distance H6
between the first common electrode CE1 and the liquid crystal layer
LC increases. However, the increase in the driving voltage Vpc
tends to saturate, and the increase is gradual when the distance H6
between the first common electrode CE1 and the liquid crystal layer
LC is 1.5 .mu.m or greater. That is to say, it is clear for the
liquid crystal display device according to the ninth embodiment to
be able to provide a high transmittance for white display while
limiting the increase of the driving voltage Vpc by setting the
distance H6 between the first common electrode CE1 and the liquid
crystal layer LC to 1.5 .mu.m or greater. Accordingly, it is
preferable for the liquid crystal display device according to the
ninth embodiment to be formed so that the distance H6 between the
first common electrode CE1 and the liquid crystal layer LC is 1.5
.mu.m or greater. Furthermore, it is preferable for the driving
voltage Vpc to be approximately 5.0V.
[0232] In the liquid crystal display device according to the ninth
embodiment, the first common electrodes CE1 are formed on the
overcoat layer OC on the lower layer side (on the first substrate
SU1 side) so that the distance between the first common electrodes
CE1 and the second common electrodes CE2 is greater than the
thickness of the liquid crystal layer LC (structure for driving for
inverting the display pixel by pixel). However, even in the liquid
crystal display devices where the height of the wall pixel
electrodes SE and the thickness of the liquid crystal layer LC are
approximately the same as in the first embodiment, the same effects
as those described above can be gained for the misalignment in the
case where the distance between the first common electrode CE1 and
the second common electrode CE2 is greater than the thickness of
the liquid crystal layer LC, and the driving for inverting the
display column by column is carried out.
Tenth Embodiment
[0233] FIG. 47 is a plan diagram for schematically illustrating the
structure of the liquid crystal display device according to the
tenth embodiment of the present invention, and FIG. 48 is a
cross-sectional diagram along line C-C' in FIG. 47. In addition,
FIG. 49 is a diagram for illustrating the structure of the first
transparent conductive film for forming wall pixel electrodes in
the liquid crystal display device according to the tenth
embodiment, and FIG. 50 is a diagram for illustrating the structure
of the second transparent conductive film for forming second common
electrodes and fourth common electrodes in the liquid crystal
display device according to the tenth embodiment. Here, the liquid
crystal display device according to the tenth embodiment has the
same structure as the liquid crystal display device according to
the first embodiment, expect the structures of the fourth common
electrodes CE4 and the sixth insulating film IL6. Accordingly, in
the following, the structures of the fourth common electrodes CE4
and the sixth insulating film IL6 are described in detail.
[0234] In the liquid crystal display device according to the first
embodiment, the second transparent conductive film TCF2 for forming
the second common electrodes CE2 and the first transparent
conductive film TCF1 for forming the wall pixel electrodes SE
overlap in end portions of pixels in the proximity to the gate
lines GL (hatched regions SC in FIG. 2) so that capacitors are
formed, and no electrical field is applied to the liquid crystal
layer LC in these regions SC, which are therefore non-opening
portions (non-transmittance regions). Meanwhile, in IPS mode liquid
crystal display devices, common electrodes in plate form and linear
pixel electrodes overlap so that capacitors are formed in opening
portions. Thus, the electrodes used to apply a voltage to the
liquid crystal layer can also be used as a capacitor so that the
aperture ratio and the transmittance can be increased.
[0235] In contrast, as is clear from FIG. 48, in the liquid crystal
display device according to the tenth embodiment, the second common
electrodes CE2 and the fourth common electrodes CE4 are provided
between the first insulating layer IL1 and the second insulating
layer IL2, and the wall bases WL are formed on the third insulating
layer IL3. Furthermore, wall pixel electrodes SE are formed in a
layer above them in such a manner that the flat portions HP of the
wall pixel electrodes SE overlap the fourth common electrodes CE4
with the second insulating layer IL2 in between. These portions
where the flat portion HP of a wall pixel electrode SE and a fourth
common electrode CE4 overlap are capacitors.
[0236] In the liquid crystal display device according to the tenth
embodiment in particular, the fourth common electrodes CE4 are
provided so as to be placed inside the flat portions HP of the wall
pixel electrodes SE. If they are placed outside the flat portions
HP of the wall pixel electrodes SE, an electrical field
concentrates between a wall pixel electrode SE and a fourth common
electrode CE4 that are in proximity to each other so that the
electrical field to be applied to the liquid crystal layer LC is
greatly weakened, which lowers the transmittance. In the tenth
embodiment, the fourth common electrodes CE4 are provided in side
the flat portions HP of the wall pixel electrodes SE so that the
intensity of the electrical field to be applied to the liquid
crystal layer LC can be maintained.
[0237] In FIG. 47, broken lines show the outlines of first common
electrodes CE1 and second common electrodes CE2, and one-dot chain
lines show the outlines of wall bases WL. As described above, the
second common electrodes CE2 are provided in a layer beneath the
wall pixel electrodes SE, and therefore, contact holes CE2 pass
through the second common electrodes CE2, and thus, in FIG. 47, the
contact hole CH2 is surrounded by a broken line showing the border
with a second common electrode CE2. The portions where a second
common electrode CE2 and a wall pixel electrode SE overlap function
as capacitors, and the hatched portion in FIG. 47 is a capacitor.
As is clear from the comparison of the liquid crystal display
device according to the tenth embodiment in FIG. 47 with that in
FIG. 2, the capacitors in the tenth embodiment are located closer
to the gate lines GL, and as a result, the wall bases WL run closer
to the gate lines GL so that the openings (transmission portions)
are greater. Here, the liquid crystal display device according to
the tenth embodiment in FIG. 47 and that according to the first
embodiment in FIG. 2 have capacitors with the same area, and the
liquid crystal display device according to the tenth embodiment has
greater openings (transmission portions) because parts of the
capacitors are provided in the vicinity of the drain lines DL.
[0238] As shown in FIG. 47, the liquid crystal display device
according to the tenth embodiment has pixel regions between the
drain lines DL and between the gate lines GL, like the liquid
crystal display device according to the first embodiment. In
addition, each pixel region is made of an upper region and a lower
region aligned in the longitudinal direction (Y direction) where
the upper region and the lower region are inclined in different
directions so that they are symmetrical relative to the Y
direction, and the structure allows the upper region and the lower
region to be connected in the center portion of the pixel. In the
upper region and the lower region as well, an initial alignment
process in the direction shown by the arrow AD in the figure is
carried out so that the liquid crystal molecules are initially
aligned in the same direction.
[0239] As shown in FIG. 48, the liquid crystal display device
according to the tenth embodiment also has such a structure where a
first substrate SU1 on which color filters are formed and a second
substrate SU2 on which thin film transistors are formed are
provided so as to face each other with a liquid crystal layer LC in
between. In addition, a first polarizing plate PL1 is provided on
the outer side (display side) of the first substrate SU1 and a
second polarizing plate PL2 is provided on the outer side (rear
side) of the second substrate SU2.
[0240] As in the liquid crystal display device according to the
first embodiment, a black matrix BM, color filters CF, an overcoat
layer OC, first common electrodes CE1 and a first alignment film
AL1 are formed in this order on the first substrate SU1 on the
liquid crystal side.
[0241] Meanwhile, a first insulating film ILL drain lines DL, a
second insulating film IL2 and second common electrodes CE2 are
formed in this order on the second substrate SU2 on the liquid
crystal side. In the liquid crystal display device according to the
tenth embodiment, fourth common electrodes CE4 are formed in the
same layer as the second common electrodes CE2 so as to overlap at
least the wall pixel electrodes SE. A sixth insulating film IL6 is
formed on the entire surface of the second substrate SU2 in a layer
above the fourth common electrodes CE4 and the second common
electrodes CE2 so as to cover the fourth common electrodes CE4 and
the second common electrodes CE2. The wall bases WL and the flat
portions of the wall pixel electrodes SE are formed in a layer
above the sixth insulating film IL6, and the vertical portions and
the top portions of the wall pixel electrodes SE are formed on the
sidewalls and the top surface of the wall bases WL, respectively,
and a second alignment film AL2 is formed so as to cover the
surfaces exposed from these.
[0242] In the liquid crystal display device according to the tenth
embodiment in particular, as shown in FIG. 50, a second transparent
conductive film TCF2 is formed on the entire surface of the first
substrate SU1, and openings OP2 and OP3 are created in the second
transparent conductive film TCF2 within the transmission region of
each pixel so that the region sandwiched between the two openings
OP2 and OP3 forms a second common electrode CE2. In addition, the
region sandwiched between the opening OP2 of a pixel created in the
second transparent conductive film TCF2 and the opening OP3, not
shown, of its adjacent pixel forms a fourth common electrode
CE4.
[0243] In addition, as shown in FIG. 49, the first transparent
conductive film TCF1 for forming wall pixel electrodes SE has a
portion in annular form along drain lines DL and gate lines GL
where the region (hatched region) between the outer periphery L1
and the inner periphery (periphery of the opening OP1) L2 is the
portion formed of the first transparent conductive film TCF1. In
the liquid crystal display device according to the tenth
embodiment, the portions that run in the longitudinal direction of
each pixel are wall pixel electrodes SE, like in the liquid crystal
display device according to the first embodiment.
[0244] In the liquid crystal display device according to the tenth
embodiment, the structure allows the first transparent conductive
film TCF1 and the second transparent conductive film TCF2 to
overlap with the sixth insulating film IL6 in between in the
regions within the pixels on the upper end and lower end sides,
like in the liquid crystal display device according to the first
embodiment. Furthermore, as is clear from FIG. 50, a fourth common
electrode CE4 is formed of the second transparent conductive film
TCF2 in the region sandwiched between the opening OP2 of a pixel
created in the second transparent conductive film TCF2 and the
opening OP3, not shown, of its adjacent pixel, that is to say, the
second transparent conductive film TCF2 in the region between the
pixel and its adjacent pixel, and the structure allows the fourth
common electrode CE4 to overlap a wall pixel electrode SE with the
sixth insulating film IL6 in between.
[0245] This structure of the liquid crystal display device
according to the tenth embodiment allows the hatched region SC in
FIG. 47 to surround the transmission region of the pixel along the
periphery of the pixel region so that this region SC works as a
capacitor for this pixel. That is to say, in the liquid crystal
display device according to the tenth embodiment, the structure
provides parts of a capacitor in the side regions of a pixel region
made of an upper end portion and a lower end portion in the width
direction (Y direction), and at the same time in the side regions
in the longitudinal direction (X direction) of the pixel region,
like in the liquid crystal display device according to the first
embodiment.
[0246] Here, the fourth common electrodes CE4 and the wall pixel
electrodes SE are formed so that the regions where the flat
portions for forming wall pixel electrodes SE and the fourth common
electrodes CE overlap have a large area, and thus, the capacitors
can be made large. Though in the tenth embodiment of the present
invention the fourth common electrodes are formed in the liquid
crystal display device according to the first embodiment, the
invention is not limited to this. In other examples, the fourth
common electrodes can be formed in the liquid crystal display
device according to any of the second to fourth and sixth to ninth
embodiments so that the capacitors can be made large, and the same
effects as in the tenth embodiment can be gained.
[0247] As described above, the liquid crystal display device
according to the tenth embodiment has such a structure that
capacitors are formed using wall pixel electrodes SE, that is to
say, parts of the capacitors are formed of the regions SC2 where
the wall pixel electrodes SE that run in the longitudinal direction
and the sixth insulating film IL6 overlap each other with the sixth
insulating film IL6 in between. Accordingly, in the case where
capacitors having the same capacitance as in the first embodiment
are formed, the area of parts of the capacitors provided in the end
portions of pixels in the proximity of the gate lines GL can be
made smaller, that is to say, the area of the overlapping regions
SC formed on the upper end and the lower end sides of the pixel
regions in the longitudinal direction can be reduced. As a result,
the same effects as in the first embodiment can be gained, and in
addition, the area of the transmission regions where it is possible
to drive liquid crystal molecules without lowering the capacitance
can be increased so that the aperture ratio can be increased to 69%
relative to 63% in the first embodiment, and thus, special effects
can be gained such that the transmittance can be increased by
approximately 10% as compared to the first embodiment.
[0248] Though in the second to fourth embodiments of the invention
a thin film layer having a large thickness (thick film layer) is
formed on either the first substrate SU1 or the second substrate
SU2, and at the same time, the structure allows the wall pixel
electrodes to be taller than the thickness of the liquid crystal
layer, the structure may allow the first substrate SU1 and the
second substrate SU2 to both have a thick film layer formed
thereon.
[0249] Though the invention made by the present inventors is
described in detail in reference to the embodiments, the present
invention is not limited to the above-described embodiments, and
various modifications are possible as long as the gist of the
invention is not deviated from.
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