Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-01-21
2001-08-07
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S122000, C349S110000
Reexamination Certificate
active
06271902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color filter substrate and a color liquid crystal display device using the same, which is equipped in television sets, computers, word processors, office automation machines, and the like.
2. Description of the Related Art
FIG. 15
shows one example of a conventional color liquid crystal display device.
This color liquid crystal display device comprises a pair of substrates oppositely disposed to sandwich a liquid crystal layer
12
. One of the substrates is a color filter substrate which comprises a glass substrate
1
, and a light-shading member (a black mask)
3
, a color filter coloring layer
4
and a smoothing layer (an overcoat layer)
5
formed on the glass substrate
1
. Formed thereon are a display electrode
6
a
and an alignment film
7
a
. On the other glass substrate
2
, a display electrode
6
b
an insulating film
8
and an alignment film
7
b
are formed. Both substrates
1
and
2
are attached together through a sealing material
10
containing glass beads
9
arranged along the periphery of the substrates, and plastic beads
11
for controlling a cell gap which are arranged between the substrates to form the liquid crystal layer
12
having a liquid crystal sealed in a gap between the glass substrates
1
and
2
surrounded by the sealing material
10
. A counter portion of both display electrodes
6
a
and
6
b
which is not shaded by the light-shading member is a liquid crystal-lighting region.
The above-described color filter substrate is manufactured as shown in for example
FIGS. 16A
to
16
I which illustrate a case where a metal film is used as the black mask
3
.
First, a metal (chromium, etc.) film
3
a
is vacuum-deposited on the glass substrate
1
by sputtering or the like at a thickness of approximately 1000 angstroms, as shown in
FIG. 16A
, and a resist
13
is coated thereon, as shown in FIG.
16
B. Then, the resist
13
is exposed using a photomask
14
, as shown in
FIG. 16C
, and developed to form a resist pattern
13
a
as shown in FIG.
16
D. Thereafter, it is etched to form a black mask
3
, as shown in FIG.
16
E.
Then, a coloring layer
15
is formed, as shown in FIG.
16
F. The coloring layer
15
is formed on the whole surface of the substrate by coating a pigment-containing organic ink, or transferring a pigment-containing photo-sensitive resin. Subsequently, the coloring layer
15
is exposed using a photomask
16
, as shown in
FIG. 16G
, and developed to form a color filter coloring layer
4
(a coloring layer corresponding to an R (red) pixel in this figure) in a dot shape, as shown in FIG.
16
H. Similarly, coloring layers corresponding to G (green) and B (blue) pixels are formed in a dot shape. Additionally, a printing method may be used which comprises printing a pigment-containing organic ink on the prescribed region of the substrate for forming a color filter coloring layer.
Thereafter, an overcoat layer
5
is formed by a spin coating method or a printing method so as to improve the smoothness of the surface of the color filter substrate and to ensure its adhesive force to the display electrodes, as shown in FIG.
16
I.
A common method of improving the surface smoothness of the color filter substrate comprises mechanically polishing the surface of the color filter substrate, or ameliorating the leveling ability of the overcoat material, as disclosed in Japanese Laid-open Patent Publications Nos. 2-275903 and 3-246503. Also, it includes forming adjacent coloring layers in such a manner so as not to overlap with each other in the formation of the color filter coloring layers corresponding to each of R, G and B pixels in a dot shape, or forming a light-shading member between adjacent coloring layers as sandwich thereof both sides, for fear of the unevenness of a liquid crystal domain and a cell thickness as well as the generation of color mixture, and the like. That is, a gap (a concave portion)
24
is commonly created between the adjacent coloring layers
4
, as shown in FIG.
18
. In
FIG. 18
, a indicates a cell thickness difference, b indicates a liquid crystal-lighting display region, and c and d indicate a pixel center portion and a pixel edge portion of the liquid crystal display region, respectively.
When the above-described color filter coloring layer is formed via a process of exposing, developing, baking and the like, the UV light is refracted toward the unwanted portion in the exposure to the coloring layer
15
to form a light-leaking region e which creates an overexposure portion f, as shown in FIG.
17
A. Thus, an over-exposure portion
14
a
remains in the etching, as shown in FIG.
17
B. Then, the pixel edge portion including the over-exposure portion
14
a
is thermally deformed by baking to form a coloring layer having round edge portions
14
b
with a barrel-shaped section at the time of the completion of the baking, as shown in FIG.
17
C. When a smoothing film is formed thereon, the barrel-shaped portions are levelled to create a further difference in level.
Also, when a color filter coloring layer is formed by a printing method, the section of the coloring layer is barrel-shaped due to the surface tension of the printed coloring layer as having round edge portions similar to that shown in
FIG. 17C
, as found in for example Japanese Laid-open Patent Publication No. 4-62504. Thus, a gap (a concave portion)
24
is created between the adjacent coloring layers
4
, as shown in FIG.
18
. Moreover, in this case, the edge portions are not straight, but disoriented.
In recent years, liquid crystal display devices which permit animation operations, highly precise displays such as SVGA, XGA, etc., and large-screen displays in accordance with the development of multimedia personal computers, and large-scale liquid crystal display devices which can be adapted for CRT-substituted desk top computers have been demanded in the market. In order to meet these demands, a liquid crystal display device, especially a color liquid crystal display device using a STN(super twisted nematic)-type liquid requires such characteristics as high contrast, high brightness, high speed response, high display quality, low power consumption, and the like, for example, such characteristics as a contrast of 30:1 or more and a response speed of 200 ms or less, and the like. In order to accomplish these demands, it is necessary that the steepness of the liquid crystal (hereinafter referred to as an &agr; value) be improved for the high contrast and high brightness, that the surface of the color filter substrate be uniform for the high display quality, and that the consumed current of the back light due to the high brightness be reduced for low power consumption. Also, it is demanded that the surface smoothness of the color filter substrate as well as its sectional shape (barrel-shaped) be improved for the improvement of all of these.
However, the above-mentioned conventional color filter substrate suffers from the following problems in the improvement of the contrast. That is, as shown in
FIG. 18
, a gap (a concave portion)
24
exists between the color filter coloring layers
4
, and allows an overcoat material to flow into the gap
24
in the formation of the overcoat layer
5
to not only provide insufficient surface smoothness of the color filter substrate, but create a barrel-shaped section. Thus, a cell thickness difference a is created in a liquid crystal lighting display region b sandwiched by the display electrodes
6
a
and
6
b
. Since the cell thickness in the pixel edge portion d is increased by a compared to that of the pixel center portion c, a difference occurs in the V(voltage)−T(transmittance) curve between the pixel edge portion d and the pixel center portion c, as shown in FIG.
19
. For that reason, when the portion c is at a state of V
off
, the portion d is nearly at a state of T
on
which allows the light to pass through so that the contrast is not improved. Also, a method of improving the steepness (i.e., lowering the
Ogura Masami
Yoshimura Kazuya
Nixon & Vanderhye P.C.
Parker Kenneth
Sharp Kabushiki Kaisha
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