Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-01
2002-05-21
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S111000
Reexamination Certificate
active
06392729
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and a method for fabricating the same. More particularly, the invention relates to a liquid crystal display device and a method for fabricating the same which achieves a high aperture ratio by constructing a part of a black matrix by a color filter when the black matrix and a color filter are formed on a first substrate.
Generally, a liquid crystal display device is comprised of a first substrate and a second substrate which are disposed to face each other over a liquid crystal layer. On the first substrate, a black matrix, a color filter, a counter electrode, and the like are formed. On the second substrate, a plurality of gate signal lines and a plurality of source signal lines which are disposed so as to perpendicularly cross each other via a gate insulating layer, thin film transistors disposed at intersecting points of the plurality of gate signal lines and the plurality of source signal lines, pixel electrodes arranged in a matrix which are disposed in respective areas surrounded by the plurality of gate signal lines and the plurality of source signal lines, and the like are formed. The gate electrode of each thin film transistor is connected to the corresponding gate signal line, the source electrode is connected to the corresponding source signal line, and the drain electrode is connected to the corresponding pixel electrode.
In the liquid crystal display device, in order to increase the high brightness and good image quality of display pixels, there is an increasing demand of raising the aperture ratio of the liquid crystal display device, specifically, the aperture ratio indicative of the ratio between the pixel area and the pixel opening. Recently, for example, a liquid crystal display device having a high aperture ratio has been disclosed in U.S. Pat. No. 5,877,830 (cited document
1
).
FIGS. 5A
,
5
B, and
5
C show the configuration of the liquid crystal display device disclosed in the cited document
1
.
FIG. 5A
is a plan view.
FIG. 5B
is a cross section taken along the line VB-VB′ in FIG.
5
A.
FIG. 5C
is a cross section taken along the line VC-VC′ in FIG.
5
A.
Shown in
FIGS. 5A
,
5
B, and
5
C are a first substrate (counter substrate)
51
, a second substrate (active matrix substrate)
52
, a liquid crystal layer
53
, a black matrix (BM)
54
, a color filter
55
, a counter electrode
56
, a first alignment layer
57
, a gate signal line
58
, a storage capacitor line
58
f,
a gate insulation layer
59
, a thin film transistor (TFT)
60
, a gate electrode
60
G, a source electrode
60
S, a drain electrode
60
D, a source signal line
61
, a transparent pixel electrode
62
formed by a transparent conductive layer (ITO), a contact hole
63
, an insulating interlayer
64
, a second alignment layer
65
, a transparent conductive layer
66
, and metal conductive layers
67
a
and
67
b.
The liquid crystal display device shown in
FIGS. 5A
,
5
B, and
5
C is comprised of the first substrate
51
and the second substrate
52
arranged so as to face each other over the liquid crystal layer
53
. On the first substrate
51
, the black matrix
54
, the color filter
55
, the counter electrode
56
disposed opposite to the transparent pixel electrode
62
, and the first alignment layer
57
are sequentially formed. On the second substrate
52
, the plurality of gate signal lines
58
which are disposed in parallel and the plurality of storage capacitor lines
58
f
each of which is disposed between the neighboring gate signal lines
58
and
58
are formed. Further, the gate insulating layer
59
, the thin film transistor
60
, the insulating interlayer
64
, the transparent pixel electrode
62
, and the second alignment layer
65
are sequentially formed. The gate electrode
60
G of the thin film transistor
60
is connected to the corresponding gate signal line
58
via the metal conductive layer
67
a,
the source electrode
60
S is connected to the corresponding source signal line
61
via the metal conductive layer
67
b,
and the drain electrode
60
D is connected to the corresponding storage capacitor line
58
f
via the transparent conductive layer
66
and also connected to the corresponding transparent pixel electrode
62
via the contact hole
63
formed in the insulating interlayer
64
.
In the conventional liquid crystal display device having the configuration, the black matrix
54
formed on the first substrate
51
side covers only the peripheral part of the pixel area including the transparent pixel electrodes
62
arranged in a matrix on the second substrate
52
side and the area which is not covered with the black matrix
54
is used as an effective display area, so that a high aperture ratio is obtained.
In the conventional liquid crystal display device, the black matrix and the color filter are formed by a process as described below.
(1) First, a black matrix pattern is formed on a glass substrate by the photolithography method.
(2) For example, a pigment dispersed photosensitive resin for a green filter in which one of the three pigments constructing the color filter, for example, green pigment is dispersed is applied on the glass substrate.
(3) By using a mask for forming a green color filter, only an area in which the green color filter is to be formed on the glass substrate is irradiated with exposure light to expose the photosensitive resin layer for green filter in the area.
(4) A non-exposed area of the exposed photosensitive resin layer for green filter is removed by a developing process, thereby completing the formation of the green color filter.
(5) Then, for example, a pigment dispersed photosensitive resin for a red filter in which another one of the three pigments constructing the color filter, the red pigment, is dispersed is applied on the glass substrate on which the green color filter is formed.
(6) After that, by a process similar to the process of forming the green color filter, a red color filter is formed.
(7) A photosensitive resin for a blue filter, in which the last one of the three pigments of color filters, that is, blue pigment is dispersed is applied on the glass substrate on which the green and red color filters are formed.
(8) A blue color filter is formed by a process similar to that of forming the green color filter.
The liquid crystal display device disclosed in the cited document
1
has the following problems. Since the aperture ratio is specified by the gate signal lines
58
and the source signal lines
61
surrounding the transparent pixel electrodes
62
, it is necessary to shield the area in which a thin film transistor is formed from incident light by using a metal mask newly formed via an organic insulating layer. Since the black matrix
54
is not disposed in the display area, the reflectance for ambient light increases and the contrast is lowered. Reflection light from the metal mask in the part in which the thin film transistor
60
is formed is observed from a gap of color patterns of the color filter
55
and displayed image non-uniformity such that an image changes irregularly according to a viewing angle occurs.
In a liquid crystal display device in which metal chromium (Cr) is used as a material of the black matrix, the manufacturing cost of the black matrix itself is as high as twice or more as compared with that of an ordinary black matrix using a black resin as a material of the black matrix. Consequently, there is a problem that the manufacturing cost of the liquid crystal display device is high.
On the other hand, in the case of a general color filter, although the black matrix using a black resin is cheap, not only the resolution of a display image is inferior, but also it is difficult to stably form the black matrix having a width of 10 &mgr;m or narrower. The minimum black matrix width which can be stably formed at present is about 20 &mgr;m.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a liquid crystal display device capable of obtaining a h
Akiyama Norimasa
Hamamoto Tatsuo
Izumi Akiya
Yoshioka Masao
Antonelli Terry Stout & Kraus LLP
Chowdhury Tarifur R.
Hitachi , Ltd.
Sikes William L.
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