Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-03-19
2004-09-28
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000
Reexamination Certificate
active
06798473
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a half-transmission and half-reflection type color liquid crystal display device which comprises a reflection area having a reflection layer and a color filter, and a transmission area having a color filter without the reflection layer, in each pixel of Red (R), Green (G), and Blue (B) color, and a manufacturing method of the same.
2) Description of the Related Art
FIG. 9
is a cross section of a conventional color liquid crystal display device of the half-transmission and half-reflection type. As shown in
FIG. 9
, in a reflection area
100
of each pixel, a reflection layer
2
is provided on a glass substrate
1
b
as a first substrate. An overcoat layer
3
a
is formed on the glass substrate
1
b
, and red, green, or blue color filters
4
a
,
4
b
, and,
4
c
are formed on the overcoat layer
3
a
. On the other hand, the reflection layer
2
is not provided in the transmission area
101
of each pixel.
FIGS. 10A
to
10
F show process flow charts of a manufacturing process of the color liquid crystal display device shown in FIG.
9
. At first, as shown in
FIG. 10A
, a 0.1 &mgr;m-thick metal film of Al or Ag and the like that turns into the reflection layer
2
is formed on the glass substrate
1
b
by means of sputtering or vacuum evaporation. Then, a positive photo resist
9
is coated on the surface of the metal film.
As shown in
FIG. 10B
, the photo resist
9
is exposed by using a photo mask
10
that has desired patterns. Then, the development and etching are performed. As shown in
FIG. 10C
, the metal film in the transmission area
101
is removed so that the metal film remains only in the reflection area
100
, thus the reflection layer
2
is formed. As shown in
FIG. 10D
, the remaining photo resist
9
is removed.
As shown in
FIG. 10E
, the overcoat layer
3
a
with a thickness of 0.02 &mgr;m of SiO
2
or the like is formed on all over the surface of the substrate by sputtering. As shown in
FIG. 10F
, pigment dispersion type color filters
4
a
,
4
b
, and
4
c
having a thickness of around 0.7 &mgr;m are formed on the surface of the overcoat layer
3
a
. Furthermore, a transparent electrode pattern
5
b
and an alignment layer
6
b
are deposited sequentially on the color filters
4
a
,
4
b
, and
4
c
. The color liquid crystal display device having the structure shown in
FIG. 9
is obtained by injecting a liquid crystal
7
in between the substrate and a facing substrate
1
a
having the transparent electrode pattern
5
a
and the alignment layer
6
a
, after the two substrates are panel aligned.
Incidentally, in the half-transparent and half-reflection type color liquid crystal display device, it is known, in Japanese Patent Laid-Open No. 2001-281648, that the colors displayed by transmission lights are lighter in color than the colors displayed by reflection lights. This phenomenon is caused because the number of times the light passes through the color filters is different in the reflecting area
100
and in the transmission area
101
.
Namely, as shown in
FIG. 9
, in the reflection area
100
, an outside light R, which enters from the front side of the panel, reaches the reflection layer
2
, after passing through the facing substrate
1
a
, the liquid crystal
7
, and the color filters
4
a
,
4
b
, and,
4
c
, then returns through the color filters
4
a
,
4
b
, and
4
c
, the liquid crystal
7
, and the facing substrate
1
a
, after reflecting at the reflection layer
2
. This means that the light R passes through the color filters twice in the reflection area
100
.
On the other hand, in the transmission area
101
, the transmission light T, which is radiated from a backlight, for example, enters from the backside of the panel and passes through the color filters
4
a
,
4
b
, and,
4
c
, the liquid crystal
7
, and the facing substrate
1
a
. Therefore, the transmission light T passes through the color filters
4
a
,
4
b
, and,
4
c
only once. Therefore, the display by the reflection light becomes deeper than the display by the transmission light, because the reflection light passes through the color filters more often than the transmission light passes through the color filters.
The Japanese Patent Laid-Open No. 2001-281648 proposes that the thickness of the color filter in the transmission area should be about twice as thick as the thickness of the color filter in the reflection area. If this rule is followed, the chromatic variance between the reflection display and the transmission display caused by the difference of times the lights pass through the color filters is reduced. Further, the Japanese Patent Laid-Open No. 2001-281648 proposes a method of forming different color filters separately in the reflection area and in the transmission area. Each color filter has different color purity. The Japanese Patent Laid-Open No. 2001-281648 also proposes a structure comprising two layers in only the transmission area where each layer has different color purity.
According to the art disclosed in the Japanese Patent Laid-Open Publication No. 2001-281648, the thickness of the color filter in the reflection area is 0.8 &mgr;m, and the thickness of the reflection layer is 0.2 &mgr;m. Namely, the thickness of the reflection layer which is formed by conventional manufacturing methods such as sputtering or vacuum evaporation is around 0.2 &mgr;m, and the thickness of the color filter required for the color liquid crystal display device is around 0.8 &mgr;m.
Therefore, as shown in FIG. 1 of the Japanese Patent Laid-Open Publication No. 2001-281648, if the color filter is formed ranging from the reflection area to the transmission area by a single layer, the thickness of the color filter in the reflection area is 0.8 &mgr;m and the thickness of the color filter in the transmission area is 1 &mgr;m. This means that the difference between the thickness of the color filter in the reflection area and the thickness of the color filter in the transmission area is only 0.2 &mgr;m. Thus, the ratio of the thicknesses of the color filter in the transmission area and that in the reflection area is only 1:0.8=1.25, and it does not satisfy a targeted ratio of approximately 2.
Therefore, in the Japanese Patent Laid-Open Publication No. 2001-281648, in order to make the deepness of the color filter in the transmission area approximately twice as deep as the deepness of the color filter in the reflection area, not only changing the thickness of the color filters, but also forming color filters having different color purities in the reflection area and in the transmission area (in FIG. 3 of Japanese Patent Laid-Open Publication No. 2001-281648), or a two-layered structure comprising two different color filters, each having different color purity (in
FIG. 2
of Japanese Patent Laid-Open Publication No. 2001-281648), are proposed.
However, in order to differentiate the color purity of the color filter in the transmission area from the color purity of the color filter in the reflection area, it is necessary to form the color filter in either one area first, the color filter in the other area must be formed later. Also, in order to make the color filter in the transmission area the two-layered structure, it is necessary to form a first color filter only in the transmission area at first, then a second color filter layer should be formed covering both the transmission area and the reflection area. In any case, in the process of forming color filters, at least two steps are required for each color, which means six steps are required in total, resulting in a cost increase due to the increase of the production steps.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome and resolve the aforementioned problems of the prior art, and provide a half-transmission and half-reflection type color liquid crystal display device that can be manufactured by one process per color
The color liquid crystal display device according to one aspect of the present invention compr
Arai Makoto
Kaneda Yoshihiro
Chowdhury Tarifur R.
Chung David
Citizen Watch Co. Ltd.
Sughrue & Mion, PLLC
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