U.S. patent application number 11/902876 was filed with the patent office on 2008-04-03 for image display device and manufacturing method of the same.
This patent application is currently assigned to Hitachi Displays, Ltd.. Invention is credited to Takahiko Muneyoshi, Kiyoshi Ouchi.
Application Number | 20080079874 11/902876 |
Document ID | / |
Family ID | 39260750 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080079874 |
Kind Code |
A1 |
Muneyoshi; Takahiko ; et
al. |
April 3, 2008 |
Image display device and manufacturing method of the same
Abstract
Disorder of the initial orientation (pretilt angle) of liquid
crystal molecules and disorder of the active orientation of the
liquid crystal molecules associated with higher resolution can be
reduced to achieve high image quality display. A layer in which a
drive element is configured is bonded into an adhesive layer above
color filters for a plurality of colors provided on the inner
surface of a rear panel. The layer in which the drive element is
configured, a drive electrode (pixel electrode), a counter
electrode, and the like are buried in the adhesive layer, so that
the surface on the liquid crystal layer side is a smooth surface.
An orientation film is formed on the smooth surface, so that a
liquid crystal orientation control capability (orientation
capability) is imparted thereto. A front panel includes a
transparent substrate formed of a glass plate or a resin sheet, the
surface of which on the liquid crystal layer side is a smooth
surface. An orientation film is formed on the smooth surface, so
that a liquid crystal orientation control capability (orientation
capability) is imparted thereto.
Inventors: |
Muneyoshi; Takahiko;
(Higashiyamato, JP) ; Ouchi; Kiyoshi; (Kodaira,
JP) |
Correspondence
Address: |
Stanley P. Fisher;Reed Smith LLP
Suite 1400, 3110 Fairview Park Drive
Falls Church
VA
22042-4503
US
|
Assignee: |
Hitachi Displays, Ltd.
|
Family ID: |
39260750 |
Appl. No.: |
11/902876 |
Filed: |
September 26, 2007 |
Current U.S.
Class: |
349/106 ;
257/E21.536; 438/30 |
Current CPC
Class: |
G02F 1/1362 20130101;
G02F 1/13613 20210101; G02F 2201/48 20130101; G02F 1/136222
20210101 |
Class at
Publication: |
349/106 ; 438/30;
257/E21.536 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; H01L 21/02 20060101 H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2006 |
JP |
2006-270884 |
Claims
1. An image display device in which a rear panel and a front panel
sandwich a liquid crystal layer, the rear panel comprising: a
transparent substrate; a color filter layer for a plurality of
colors formed on the liquid crystal layer side of the transparent
substrate; an adhesive layer that buries a layer in which a drive
element is configured, the drive element formed above the color
filter layer for a plurality of colors, a drive electrode driven by
the drive element, and a counter electrode for forming an electric
field that controls the orientation of the liquid crystal molecules
in the liquid crystal layer in cooperation with the drive
electrode; and an orientation film formed on the interface between
the rear panel and the liquid crystal layer, wherein the interface
between the rear panel and the liquid crystal layer is a uniform
flat surface across a plurality of pixels formed in correspondence
to the color filters for a plurality of colors.
2. The image display device according to claim 1, wherein a stopper
layer is provided under the orientation film of the rear panel, the
stopper layer having a capability of preventing impurities from the
layer in which the drive element is configured, the adhesive layer,
or the color filters from diffusing into the liquid crystal
layer.
3. The image display device according to claim 1, wherein the drive
element is disposed in the adjacent boundary region of the color
filters for a plurality of colors, and a light blocking layer is
provided in the adjacent boundary region to block light incident
from the transparent substrate side on the drive element.
4. The image display device according to claim 3, wherein the light
blocking layer is provided between the drive element and the
adjacent boundary region of the color filters for a plurality of
colors.
5. The image display device according to claim 3, wherein the light
blocking layer is provided between the adjacent boundary region of
the color filters for a plurality of colors and the transparent
substrate.
6. The image display device according to claim 1, wherein a
polarizer plate is provided on each of the outer sides of the rear
panel and the front panel.
7. The image display device according to claim 1, wherein the
transparent substrate is a plastic substrate.
8. A method for manufacturing an image display device in which a
rear panel and a front panel sandwich a liquid crystal layer, the
step of forming the rear panel at least comprising the steps of:
the drive element formation substrate fabrication step of forming a
drive element, a drive electrode, and a counter electrode on a
stopper layer, the stopper layer provided on an element formation
substrate; the adhesion step of forming an integrated drive element
formation substrate/transparent substrate by interposing an
adhesive layer in the gap between the surface of the drive element
formation substrate, fabricated in the drive element formation
substrate fabrication step, on which the drive element, the drive
electrode, and the counter electrode are formed and the color
filter side of a transparent substrate on which color filters for a
plurality of colors are formed in advance, burying the drive
element, the drive electrode, and the counter electrode in the
adhesive layer, and bonding the drive element formation substrate;
the element formation substrate removal step of removing the
element formation substrate from the integrated drive element
formation substrate/transparent substrate; and the orientation film
formation step of forming an orientation film on the stopper layer
exposed by removing the element formation substrate so as to impart
a liquid crystal orientation control capability.
9. A method for manufacturing an image display device in which a
rear panel and a front panel sandwich a liquid crystal layer, the
step of forming the rear panel at least comprising the steps of:
the drive element formation substrate fabrication step of forming a
drive element, a drive electrode, and a counter electrode on a
stopper layer, the stopper layer provided on an element formation
substrate; the adhesion step of forming an integrated drive element
formation substrate/transparent substrate by interposing an
adhesive layer in the gap between the surface of the drive element
formation substrate, fabricated in the drive element formation
substrate fabrication step, on which the drive element, the drive
electrode, and the counter electrode are formed and the color
filter side of a transparent substrate on which color filters for a
plurality of colors are formed in advance, burying the drive
element, the drive electrode, and the counter electrode in the
adhesive layer, and bonding the drive element formation substrate;
the element formation substrate/stopper layer removal step of
removing the element formation substrate and the stopper layer from
the integrated drive element formation substrate/transparent
substrate; and the orientation film formation step of forming an
orientation film on the surface obtained by removing the element
formation substrate and the stopper layer so as to impart a liquid
crystal orientation control capability.
10. The method for manufacturing an image display device according
to claim 8, wherein the drive element formation substrate
fabrication step includes the step of forming a light blocking
layer for blocking light incident from the transparent substrate
side on the drive element, the light blocking layer disposed
between the drive element and the adjacent boundary region of the
color filters for a plurality of colors.
11. The method for manufacturing an image display device according
to claim 8, wherein the transparent substrate on which the color
filters for a plurality of colors are formed in advance is a
transparent substrate having a light blocking layer disposed on the
transparent substrate side of the adjacent boundary region of the
color filters for a plurality of colors for blocking light incident
from the transparent substrate side on the drive element.
12. The method for manufacturing an image display device according
to claim 8, wherein the transparent substrate is a plastic
substrate.
Description
[0001] The present application claims priority from Japanese
application JP2006-270884 filed on Oct. 2, 2006, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an image display device,
and is particularly suitable to a high-resolution liquid crystal
display device in which disorder of the initial orientation of
liquid crystal is reduced to improve image quality, and an image
display device using a thin substrate (flexible display), for
example, using a plastic substrate. The invention also relates to a
method for manufacturing the image display device, and particularly
to a method for manufacturing the image display device using a
transfer method.
[0003] As image display devices of televisions and information
terminals, a liquid crystal display device in which liquid crystal
material is sealed between a pair of substrates is widely used. A
liquid crystal display device of this kind typically includes a
plurality of scan signal lines and a plurality of image signal
lines, which cross the scan signal lines and are insulated
therefrom, on the principal surface (inner surface) of one of the
pair of substrates. A pixel is formed in the area surrounded by two
adjacent scan signal lines and two adjacent image signal lines. For
each pixel, a switching element for controlling on and off, a pixel
electrode and the like are formed.
[0004] In general, a thin film transistor (TFT element) is used as
the switching element. Therefore, one of the substrates on which
thin film transistors are provided is typically referred to as a
thin film transistor substrate (TFT substrate), and a panel
including the TFT substrate (one panel) is also referred to as a
rear panel. The other panel, which is paired with the rear panel,
includes color filters for a plurality of colors formed on the
principal surface of the substrate referred to as a counter
substrate in such a way that the color filters correspond to pixels
provided on the TFT substrate. The other panel is therefore also
referred to as a front panel. The counter substrate is also
referred to as a color filter substrate (CF substrate).
[0005] Examples of methods for driving a liquid crystal display
device are categorized in terms of pixel driving method as a
vertical electric field method, such as a TN method and a VA
method, and a horizontal electric field method known as an IPS
(In-plane-Switching) method. In the vertical electric field method,
the counter electrode (also referred to as a common electrode) that
faces the pixel electrode on the TFT substrate that forms the rear
panel is provided on the counter substrate that forms the front
panel. In the horizontal electric field method (hereinafter
referred to as an IPS method), the counter electrode is provided on
the TFT substrate on which the pixel electrode is formed.
[0006] On the interface between the TFT substrate, which forms the
rear panel, and the liquid crystal material, and the interface
between the counter substrate, which forms the front panel, and the
liquid crystal material, there are provided orientation films
having a function (liquid crystal orientation control function) of
controlling the direction of the liquid crystal molecules when
there is no potential difference between the pixel electrode and
the counter electrode (initial orientation) as well as controlling
the arrangement and inclination of the liquid crystal molecules
when there is a potential difference between the pixel electrode
and the counter electrode.
[0007] In particular, an IPS liquid crystal display device is known
to have a wide viewing angle because the motion of the liquid
crystal molecules is rotation in a plane parallel to the substrate
surface, so that the optical characteristics do not greatly change
with the viewing angle. However, to achieve a large viewing angle,
the initial orientation (pretilt) of the liquid crystal molecules
needs to be as parallel to the in-plane direction as possible. The
orientation film is provided on the TFT elements, wiring lines and
the like on the TFT substrate that forms the rear panel, and the
orientation film is provided on the black matrix and the color
filters on the CF substrate that forms the front panel. By forming
the orientation films as flat as possible, the pretilt angle is
reduced.
[0008] FIG. 8 is a plan view showing an example of arrangement of
wiring lines, electrodes, and drive elements for pixels in a
conventional IPS liquid crystal display device. FIG. 8 shows only
two pixels adjacent in the direction in which gate lines extend. As
shown in FIG. 8, gate lines 801 and data lines 802 are periodically
disposed on a TFT substrate (not shown) and connected to drive
elements (TFT elements) 803. The drive element 803 applies a
voltage according to an image signal from the data line 802 to a
drive electrode (pixel electrode) 804, so that an electric field
induced between the pixel electrode 804 and a counter electrode 805
causes in-plane rotation of the liquid crystal molecules and hence
off-to-on transition of the image (pixel). In FIG. 8, let L be the
pixel size in the direction in which the data lines 802 are
disposed.
[0009] FIGS. 9A and 9B are schematic cross-sectional views taken
along the direction in which the data lines for the conventional
IPS pixels described with reference to FIG. 8 are disposed. Drive
elements 911, drive electrodes 912 and counter electrodes 913 are
disposed on a rear panel 910, which is one panel, and color filters
921, 922 and 923, for example, having three separate colors (red:
R, green: G, and blue: B) and a light blocking layer (black matrix)
924 between each adjacent pair of the color filters are disposed on
a front panel 920, which is the other panel. A liquid crystal layer
930 is sandwiched between the rear panel 910 and the front panel
920.
[0010] FIG. 9A shows an exemplary case where the pixel size is L1,
and FIG. 9B shows an exemplary case where the pixel size is reduced
to L2 for higher resolution. In the rear panel 910, the sizes of
the drive element 911, the drive electrode 912, and the counter
electrode 913 cannot be easily reduced because of resolution
constraint of photolithography used in the manufacturing process.
Furthermore, reduction in film thickness of various functional
films formed on the substrate surface is limited from the viewpoint
of stable operation of the drive element and the like. Thus, the
surface roughness of the interface between the rear panel 910 and
the liquid crystal layer 930 increases with the size reduction from
L1 to L2.
[0011] Similarly, reduction in thickness of the light blocking
layer 924 and the color filters 921, 922 and 923 on the front panel
920 is limited from the viewpoint of optical characteristics. Thus,
the surface roughness increases in the vicinity where the light
blocking layer 924 is in contact with the color filters 921, 922
and 923.
[0012] Since the IPS method uses liquid crystal molecule rotation
in the plane parallel to the substrate surface to control on and
off of the pixels, it is important that the liquid crystal
molecules are oriented parallel to the substrate surface. The
so-called pretilt angle is desirably smaller than or equal to 2
degrees at the maximum, more desirably smaller than or equal to 1
degree if possible. Therefore, the interfaces where the rear panel
910 and the front panel 920 come into contact with the liquid
crystal layer 930 are required to be as flat as possible. However,
when the pixel size is reduced for higher resolution, the surface
roughness of the interface increases from the reason described
above. This causes disorder of the orientation of the liquid
crystal molecules, resulting in contrast reduction and color
shift.
[0013] JP-A-10-288796 describes a structure in which a color filter
layer is provided on a rear substrate (TFT substrate) side and a
drive element (TFT element) is formed on the color filter layer. In
this structure, an insulating film for planarization is provided on
the color filter layer including color filters and a black matrix
formed on the TFT substrate. However, JP-A-10-288796 relates to a
solution to display unevenness due to impurity ions from the color
filter layer, but does not aim to reduce disorder of the initial
orientation, which the invention is to solve. JP-A-2002-184959
relates to a transfer method similar to that used in the invention
but does not consider at all the configuration of the TFT element,
color filters and the like.
SUMMARY OF THE INVENTION
[0014] As described above, as the liquid crystal display device has
higher resolution, the footprint of elements and wiring lines in a
pixel increases in the rear panel, resulting in increased surface
roughness in the pixel. In the front panel, a reduced period of the
black matrix similarly increases the surface roughness around the
pixel. These factors reduce the orientation regulation capability
of the orientation film for preventing reduction in image quality
due to partial disorder of the arrangement of liquid crystal
molecules. That is, higher resolution reduces the pixel size, but
it is difficult to reduce the sizes of the TFT element and the
electrodes at the same rate as the pixel size reduction rate
because of photolithography constraint. The surface roughness in
the pixel therefore increases. Also in the front panel, a reduced
pixel size reduces the periods of the color filters and the black
matrix, but reduction in film thickness thereof is limited from the
viewpoint of optical characteristics. In particular, increased
surface roughness around the pixel increases disorder of the
initial orientation (pretilt angle) of the liquid crystal molecules
and disorder of the active orientation of the liquid crystal
molecules, resulting in reduction in image quality.
[0015] An object of the invention is to provide an image display
device in which disorder of the initial orientation (pretilt angle)
of the liquid crystal molecules and disorder of the active
orientation of the liquid crystal molecules associated with higher
resolution are reduced to achieve high image quality display, an
image display device with a thinner substrate, and a manufacturing
method of the same.
[0016] The image display device according to the invention is a
liquid crystal display device in which a rear panel and a front
panel sandwich a liquid crystal layer. In the invention, to achieve
the above objective, the rear panel includes a transparent
substrate; a color filter layer for a plurality of colors formed on
the liquid crystal layer side of the transparent substrate; an
adhesive layer that buries a layer in which a drive element is
configured, the drive element formed above the color filter layer
for a plurality of colors, a drive electrode driven by the drive
element, and a counter electrode for forming an electric field that
controls the orientation of the liquid crystal molecules in the
liquid crystal layer in cooperation with the drive electrode; and
an orientation film formed on the interface between the rear panel
and the liquid crystal layer. The interface between the rear panel
and the liquid crystal layer is a uniform flat surface across a
plurality of pixels formed in correspondence to the color filters
for a plurality of colors.
[0017] In the invention, a stopper layer can be provided under the
orientation film of the rear panel. The stopper layer has a
capability of preventing impurities from the layer in which the
drive element is configured, the adhesive layer, or the color
filters from diffusing into the liquid crystal layer.
[0018] In the invention, the drive element can be disposed in the
boundary region between the color filters for a plurality of colors
adjacent to each other (hereinafter referred to as "adjacent
boundary region"), and a light blocking layer can be provided in
the adjacent boundary region to block light incident from the
transparent substrate side on the drive element. The light blocking
layer can be provided between the drive element and the adjacent
boundary region of the color filters for a plurality of colors, or
between the adjacent boundary region of the color filters for a
plurality of colors and the transparent substrate. In the
invention, a polarizer plate can be provided on each of the outer
sides of the rear panel and the front panel. In the invention, the
transparent substrate can be a plastic substrate.
[0019] In a method for manufacturing the image display device
according to the invention, the step of forming the rear panel at
least includes the steps of:
[0020] forming a drive element, a drive electrode, and a counter
electrode on a stopper layer, the stopper layer provided on an
element formation substrate;
[0021] forming an integrated drive element formation
substrate/transparent substrate by interposing an adhesive layer in
the gap between the surface of the drive element formation
substrate, fabricated in the drive element formation substrate
fabrication step, on which the drive element, the drive electrode,
and the counter electrode are formed and the color filter side of a
transparent substrate on which color filters for a plurality of
colors are formed in advance, burying the drive element, the drive
electrode, and the counter electrode in the adhesive layer, and
bonding the drive element formation substrate;
[0022] removing the element formation substrate from the integrated
drive element formation substrate/transparent substrate; and
[0023] forming an orientation film on the stopper layer exposed by
removing the element formation substrate so as to impart a liquid
crystal orientation control capability.
[0024] The thickness of the stopper layer is preferably 100 nm or
smaller in consideration of the effect of the electric field on the
liquid crystal layer. The stopper layer has not only an etching
stopper function of preventing the etching from reaching the layer
in which the drive element is configured, the drive electrode, and
the counter electrode and protecting them when the element
formation substrate is etched away, but also a function of
preventing impurities from the layer in which the drive element is
configured, the adhesive layer, or the color filters from diffusing
into the liquid crystal layer.
[0025] In the manufacturing method of the invention, the stopper
layer along with the element formation substrate of the bonded
drive element formation substrate/transparent substrate may be
removed by a method for removing the element formation substrate in
a precise manner (rough removal through wet etching followed by
precise removal through dry etching, removal through mechanical
polishing, and the like).
[0026] In the manufacturing method of the invention, the drive
element formation substrate fabrication step may include the step
of forming a light blocking layer for blocking light incident from
the transparent substrate side on the drive element, the light
blocking layer disposed between the drive element and the adjacent
boundary region of the color filters for a plurality of colors.
[0027] In the manufacturing method of the invention, the
transparent substrate on which the color filters for a plurality of
colors are formed in advance may be a transparent substrate having
a light blocking layer disposed on the transparent substrate side
of the adjacent boundary region of the color filters for a
plurality of colors for blocking light incident from the
transparent substrate side on the drive element. A polarizer plate
can be provided on each of the outer sides of the rear panel and
the front panel. In the invention, the transparent substrate can be
a plastic substrate.
[0028] According to the manufacturing method of the invention, the
drive element (TFT element), the drive electrode, the counter
electrode, the color filters, the light blocking layer (black
matrix), and the like are buried in the layer having a planar
structure, so that the surface facing the liquid crystal layer (the
surface on which the orientation film is formed) becomes a
uniformly flat surface across the display area. The opposite panel
(front panel) for sealing the liquid crystal layer is formed of
only the transparent substrate whose surface facing the liquid
crystal layer has an orientation film provided thereon.
[0029] The advantages of the invention are as follows:
[0030] (1) Since the drive element (the layer in which the drive
element is configured), the drive electrode, the counter electrode,
the color filters, the light blocking layer, and the like are
buried in the planar structure, a reduced pixel size associated
with higher resolution will not increase the surface roughness. As
a result, disorder of the initial orientation (pretilt angle) of
the liquid crystal molecules and disorder of the active orientation
of the liquid crystal molecules associated with higher resolution
can be reduced to achieve high image quality display.
[0031] (2) Since the panel opposite to the rear panel (front panel)
is a transparent substrate whose inner surface has only an
orientation film formed thereon, the front panel has high flatness
independent of the pixel size.
[0032] (3) When the etching stopper layer is left, it is possible
to prevent diffusion of impurities that diffuse from the color
filter layer, the adhesive layer and the like and affect liquid
crystal driving. By setting the thickness of the etching stopper
layer to approximately 100 nm or smaller, an appropriate drive
voltage can be applied to the liquid crystal layer.
[0033] (4) Since the drive element is "transferred" onto the color
filters, a plastic substrate can be used as the transparent
substrate on which the color filters are fabricated. By using a
plastic substrate as the transparent substrate, there is provided a
thin, light-weight, breakage-resistant image display device that
can be bent to some extent (flexible display).
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a cross-sectional view of one pixel and its
vicinity for explaining a first embodiment of the image display
device according to the invention;
[0035] FIG. 2 is a cross-sectional view of one pixel and its
vicinity for explaining a second embodiment of the image display
device according to the invention;
[0036] FIGS. 3A to 3E are process diagrams for explaining an
example of a method for fabricating the rear panel in an embodiment
of the invention;
[0037] FIGS. 4A to 4E are process diagrams subsequent to FIGS. 3A
to 3E, explaining the example of the method for fabricating the
rear panel in the embodiment of the invention;
[0038] FIGS. 5A to 5D are process diagrams subsequent to FIGS. 4A
to 4E, explaining the example of the method for fabricating the
rear panel in the embodiment of the invention;
[0039] FIG. 6 is a cross-sectional view of one pixel and its
vicinity for explaining a third embodiment of the image display
device according to the invention;
[0040] FIG. 7 is a cross-sectional view of one pixel and its
vicinity for explaining a fourth embodiment of the image display
device according to the invention;
[0041] FIG. 8 is a plan view showing an example of arrangement of
wiring lines, electrodes, and drive elements for pixels in a
conventional IPS liquid crystal display device; and
[0042] FIGS. 9A and 9B are schematic cross-sectional views taken
along the direction in which data lines for the conventional IPS
pixels described with reference to FIG. 8 are disposed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] The best mode for carrying out the invention will be
described below in detail based on embodiments with reference to
the drawings.
First Embodiment
[0044] FIG. 1 is a cross-sectional view of one pixel and its
vicinity for explaining a first embodiment of the image display
device according to the invention. The image display device of the
first embodiment is a liquid crystal display device in which a rear
panel (one panel, a drive panel) 1200 and a front panel (the other
panel) 1300 sandwich a liquid crystal layer 1100. The rear panel
1200 includes a transparent substrate 1260 formed of a glass plate
or a resin sheet, the inner surface of which has color filters 1251
and 1252 for a plurality of colors disposed thereon. A layer in
which a drive element (TFT element in this embodiment) 1220 is
configured is bonded into an adhesive layer 1270 above the color
filters 1251 and 1252. The layer in which the drive element 1220 is
configured, a drive electrode (pixel electrode) 1230, a counter
electrode 1240 and the like are buried in the adhesive layer 1270,
so that the surface on the liquid crystal layer 1100 side is a
smooth surface. An orientation film 1102 is formed on the smooth
surface, so that a liquid crystal orientation control capability
(orientation capability) is imparted to the smooth surface. In the
first embodiment, a stopper layer 1210 is provided on the smooth
surface and under the orientation film 1102.
[0045] The front panel 1300 includes a transparent substrate formed
of a glass plate or a resin sheet, the surface of which on the
liquid crystal layer 1100 side is a smooth surface. An orientation
film 1103 is formed on the smooth surface, so that the liquid
crystal orientation control capability (orientation capability) is
imparted thereto.
[0046] That is, the liquid crystal layer 1100 is sandwiched between
the rear panel 1200, having the drive element (TFT element) 1220,
and the front panel 1300 via the orientation film 1102 on the rear
panel 1200 side and the orientation film 1103 on the front panel
1300 side. Polarizer plates 1402 and 1403 are disposed on the outer
sides of the rear panel 1200 and the front panel 1300,
respectively. Furthermore, the rear panel 1200 includes the stopper
layer 1210, the drive element 1220, the drive electrode (pixel
electrode) 1230, the counter electrode 1240, a protective layer
1228, a light blocking layer (black matrix) 1229, the adhesive
layer 1270, the color filters 1251, 1252, and the transparent
substrate 1260.
[0047] The drive element 1220 at least includes a light blocking
layer 1221, an insulating layer 1222, a source electrode 1223, a
drain electrode 1224, a semiconductor layer 1225, an insulating
layer 1226, and a gate electrode 1227. The drain electrode 1224 is
electrically connected to the drive electrode 123 0, so that when a
voltage is applied to the gate electrode 1227 in an appropriate
manner, the voltage from the source electrode 1223 is applied to
the drive electrode 1230 via the drain electrode 1224. Thus, an
electric field is induced between the drive electrode 1230 and the
counter electrode 1240, and switches the direction in which the
liquid crystal molecules contained in the liquid crystal layer 1100
are orientated.
[0048] In the first embodiment, a reduced pixel size associated
with higher resolution will not increase the surface roughness. As
a result, disorder of the initial orientation (pretilt angle) of
the liquid crystal molecules and disorder of the active orientation
of the liquid crystal molecules associated with higher resolution
can be reduced to achieve high image quality display.
Second Embodiment
[0049] FIG. 2 is a cross-sectional view of one pixel and its
vicinity for explaining a second embodiment of the image display
device according to the invention. Portions having the same
reference characters as those in FIG. 1 have the same functions. A
rear panel 1201 has a configuration similar to that of the rear
panel 1200 in FIG. 1 except that the stopper layer 1210 is removed.
Since the surface of the rear panel 1201 in contact with the liquid
crystal layer 1100 via the orientation film 1102 and the surface of
the front panel 1300 in contact with the liquid crystal layer 1100
via the orientation film 1103 are both substantially flat, a
reduced pixel size associated with higher resolution will not
increase the roughness of the surface of the front panel 1300 as
well as the roughness of the surface of the rear panel 1201, both
in contact with the liquid crystal layer 1100. It is thus possible
to prevent contrast reduction and color shift due to disorder of
the orientation of the liquid crystal molecules. Although FIGS. 1
and 2 show only color filters 1251 and 1252 for two colors,
full-color display requires at least three colors, R (red), G
(green) and B (blue). It is therefore noted that there is at least
a color filter for the third color outside the figures.
[0050] FIGS. 3A to 3E, FIGS. 4A to 4E, and FIGS. 5A to 5D are
process diagrams for explaining an example of a method for
fabricating the rear panels in the embodiments of the invention
using a transfer method, that is, process diagrams for explaining
an example of a method for fabricating the rear panel 1200
described in the first embodiment or the rear panel 1201 described
in the second embodiment. This process proceeds in the order of
FIG. 3A, FIG. 3B, FIG. 3C, FIG. 3D, FIG. 3E, FIG. 4A, FIG. 4B, FIG.
4C, FIG. 4D, FIG. 4E, FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D.
[0051] First, the stopper layer 1210, which becomes a layer for
stopping etching, is formed on an element formation substrate 1500
through sputtering, CVD, deposition and the like (FIG. 3B). In the
rear panel in the second embodiment, the stopper layer is removed.
The detail of the stopper layer will be described later.
[0052] A 0.12 .mu.m-thick Cr film is deposited on the entire
surface of the stopper layer 1210 through sputtering, and then the
Cr film is patterned at a predetermined position through
photolithography to form the light blocking layer 1221 (FIG.
3C).
[0053] Next, SiOx is deposited on the entire surface through CVD,
and then the SiOx is etched through photolithography to form the
insulating layer 1222 on the light blocking layer 1221 (FIG.
3C).
[0054] Then, a 0.12 .mu.m-thick ITO film is patterned at a
predetermined position through sputtering and photolithography to
form the drive electrode 1230 and the counter electrode 1240 (FIG.
3D).
[0055] Next, an Al film is patterned at a predetermined position
through deposition and photolithography to form the source
electrode 1223 and the drain electrode 1224 (FIG. 3E).
[0056] An a-Si film is patterned between the source electrode 1223
and the drain electrode 1224 through CVD and photolithography to
form the semiconductor layer 1225 (FIG. 4A).
[0057] SiOx is deposited on the entire surface through CVD, and
then an Al film is deposited on the entire surface through
deposition. Then, the SiOx and the Al film are etched through
photolithography to form the insulating layer 1226 and the gate
electrode 1227 on the semiconductor layer 1225 (FIG. 4B).
[0058] SiOx is deposited on the entire surface through CVD to
fabricate the protective layer 1228 (FIG. 4C), and then a 0.12
.mu.m-thick Cr film is deposited on the entire surface through
sputtering. Then, the Cr film is patterned at a predetermined
position through photolithography to form the light blocking layer
1229 (FIG. 4D).
[0059] Next, the adhesive layer 1270 is applied on the entire
surface (FIG. 4E). The application thickness is thick enough to
bury the drive element so as to prevent the drive element from
abutting the color filters and hence affecting the flatness of the
liquid crystal layer. The resultant structure is positioned and
bonded at a predetermined position onto the color filter formation
surface of the transparent substrate 1260 on which the color
filters 1251 and 1252 are formed in advance (FIG. 5A), followed by
hardening of the adhesive layer 1270 (FIG. 5B). Examples of the
adhesive layer 1270 may be photo-setting, thermosetting, or mixed
reaction adhesives.
[0060] Then, the back side of the transparent substrate 1260 is
covered with a protective tape or the like (not shown), and then
the element formation substrate 1500 is removed through etching
(FIG. 5C). The stopper layer 1210 stops the etching. As the etching
method, although wet etching is preferred from the viewpoint of the
etching rate, after most of the element formation substrate 1500
maybe removed through time-controlled wet etching, the remainder
may be removed by using a precisely controlled dry process method.
Alternatively, after part of the element formation substrate 1500
may be removed through mechanical polishing, the remainder may be
removed though wet etching, dry etching, or both. The rear panel
1200 is thus fabricated in the process described above.
[0061] By removing the stopper layer 1210 from the rear panel 1200
through dry etching or the like, the rear panel 1201 described in
the second embodiment can be obtained (FIG. 5D). When the stopper
layer 1210 is left as in the case of the rear panel 1200 described
in the first embodiment, it is desirable to form the stopper layer
with a thickness of 100 nm or smaller to effectively apply an
electric field to the liquid crystal layer 1100.
[0062] The surface of the drive element formation substrate 1500 is
designed to have excellent flatness. Since the state of the surface
of the drive element formation substrate 1500 is transferred to the
surface of the rear panel 1200 or the rear panel 1201 (the surface
facing the liquid crystal layer), the flatness thereof becomes
significantly excellent. Furthermore, since the front panel 1300 is
formed of only the transparent substrate basically having good
flatness, the surface of the front panel also has excellent
flatness. Therefore, a reduced pixel size will not increase the
surface roughness of the interface in contact with the liquid
crystal layer, so that it is possible to prevent disorder of the
orientation of the liquid crystal molecules associated with higher
resolution. There is therefore provided a high resolution IPS
liquid crystal display device without contrast reduction and color
shift.
[0063] Polyimide resin is applied on the rear panel 1200 or the
rear panel 1201 and baked, and then a rubbing treatment is carried
out to form the orientation film 1102. Column-like spacers (not
shown) are formed at predetermined positions on the front panel,
and then polyimide resin is applied and baked, as in the rear
panel. Then, a rubbing treatment is carried out to form the
orientation film 1103. Next, an appropriate amount of liquid
crystal material is dripped on the rear panel 1200 or the rear
panel 1201, which is bonded to the front panel 1300, followed by a
sealing treatment. Then, the polarizer plates 1402 and 1403 are
bonded. The image display device (liquid crystal display device) is
thus fabricated.
[0064] The stopper layer will now be described. When glass (major
component of which is SiO.sub.2) is used as the material of the
drive element formation substrate 1500, wet etchant to be used is a
solution containing hydrogen fluoride HF as the base component.
Therefore, the stopper layer 1210 needs to be made of an anti-HF
material or a material having a smaller etching rate than that of
glass. Table 1 shows materials that can be used and cannot be used
as the stopper layer as well as their characteristics.
TABLE-US-00001 TABLE 1 (a) Oxides (b) Fluorides (c) Others
ZrSiO.sub.4 CaF.sub.2 SiNx .alpha.-Al.sub.2O.sub.3 LiF HfO.sub.2
MgF.sub.2 TiO.sub.2 BaF.sub.2 Cubic zirconia AlF.sub.3 HfF.sub.4
Na.sub.3AlF.sub.6
[0065] When the stopper layer 1210 is left as in the case of the
rear panel 1200 of the first embodiment described in FIG. 1, (a)
oxides in Table 1, which is difficult to remove, can be used. When
the stopper layer 1210 is removed as in the case of the rear panel
1201 of the second embodiment described in FIG. 2, (b) fluorides or
(c) SiNx, which is categorized as others, can be used. However,
since fluorides generally dissolve in acid, a fluoride alone cannot
survive in the etching process where the drive element (TFT
element) 1220, the drive electrode (pixel electrode) 1230, and the
counter electrode 1240 are formed. Therefore, by first depositing a
fluoride, for example, magnesium fluoride (MgF.sub.2), on the
element formation substrate 1500 and then depositing SiO.sub.2 or
SiNx on the fluoride, both anti-hydrofluoric acid and anti-etching
process (for element formation) properties can be simultaneously
achieved. In this case, the stopper layer 1210 has a two-layer
structure of MgF.sub.2+SiO.sub.2 (or SiNx).
Third Embodiment
[0066] FIG. 6 is a cross-sectional view of one pixel and its
vicinity for explaining a third embodiment of the image display
device according to the invention. Portions having the same
reference characters as those in FIG. 1 have the same functions. In
the third embodiment, as shown in FIG. 6, the light blocking layer
1229 is disposed in the adjacent boundary region of the color
filters 1251 and 1252 on the transparent substrate 1260. According
to the third embodiment, when the pixel size is reduced, the
surface roughness increases in the vicinity where the light
blocking layer 1229 is in contact with the color filters 1251 and
1252 (adjacent boundary region), as described in FIGS. 9A and 9B.
However, by setting the layer thickness of the adhesive layer 1270
in such a way that the raised portions of the color filters 1251
and 1252 do not abut the drive element 1220 in the adhesive layer,
the flatness of the interface to the liquid crystal layer 1100 is
not affected.
Fourth Embodiment
[0067] FIG. 7 is a cross-sectional view of one pixel and its
vicinity for explaining a fourth embodiment of the image display
device according to the invention. Portions having the same
reference characters as those in FIG. 1 have the same functions. In
the fourth embodiment, a drive element 1280 has a structure in
which the vertical relationship between the semiconductor layer
1225 and the gate electrode 1227 of the drive element 1220 in the
first to third embodiments is reversed. The liquid crystal layer
1100 can be driven also in such a structure.
[0068] In particular, the transparent substrate 1260 and the front
panel (counter substrate) 1300 undergo no high-temperature process,
so that plastic substrates can be used. In this case, since a
plastic substrate is less likely broken than a glass substrate, the
thickness of the transparent substrate 1260 and the counter
substrate 1300 can be reduced. The thickness of the image display
device according to the invention can therefore be smaller than
that conventionally achievable. Furthermore, reduced thickness of
the whole display device can impart flexibility to the display
device.
[0069] Although the invention made by the inventor has been
specifically described with reference to the above embodiments, the
invention is not limited to these embodiments, but various changes
can of course be made thereto to the extent that these changes do
not depart from the spirit of the invention. In the above
embodiments, although the (one transfer) manufacturing method in
which the TFT element formed on the element formation substrate is
transferred to the transparent substrate has been described, the
TFT element formed on the element formation substrate may be
transferred to a temporary substrate and then the TFT element may
be transferred (second transfer) from the temporary substrate to
the transparent substrate.
* * * * *