Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-06-17
2004-03-09
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C430S007000
Reexamination Certificate
active
06704076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display device, and more particularly, to a method for fabricating a CF (color filter) on a TFT (thin-film transistor) liquid crystal display device in which switching elements and color filters of a plurality of colors are formed on the same transparent substrate.
2. Description of the Related Art
In some color twisted nematic (TN) liquid crystal display devices having TFTs, color filters are provided on a counter substrate opposed to the TFT substrate where TFTs are provided. In forming the counter substrate for such liquid crystal display devices, material films of color filters of three colors containing a thermosetting resin are printed onto the transparent substrate, thereafter, the material films are hardened by being heated, thereby forming the color filters. This fabricating method is described, for example, in Japanese Unexamined Patent Publication Hei-4-369605. Then, the TFT substrate and the counter substrate are bonded together to form a liquid crystal display panel.
FIG. 1
is a cross-sectional view showing the positional relationship between the TFT substrate and the counter substrate in a conventional liquid crystal display device. In the conventional liquid crystal display device, a liquid crystal layer
230
is provided between first and second transparent substrates
201
and
223
. Hereinafter, the liquid crystal layer
230
side of the first and the second transparent substrates
201
and
223
will be referred to as the inner side, and the side opposite thereto, as the outer side.
On the inside surface of the first transparent substrate
201
, gate electrodes
203
connected to scanning lines (not shown) are formed, and a gate insulating film
204
is formed so as to cover the gate electrodes
203
. In the positions on the gate insulating film
204
corresponding to the gate electrodes
203
, semiconductor layers
205
are formed, and drain electrodes
207
and source electrodes
208
are formed so as to sandwich the semiconductor layers
205
. Further, a passivation film
209
is formed so as to cover them, and pixel electrodes
216
connected to the source electrodes
208
pixel by pixel through contact holes (not shown) formed in the passivation film
209
are formed on the passivation film
209
. On the pixel electrodes
216
, an alignment film
217
is formed.
On the inside surface of the second transparent substrate
223
, a black matrix
212
, color filters
210
of each color, a transparent common electrode
221
and an alignment film
222
are provided in succession.
In a case where the conventional liquid crystal display device in which such color filters are provided on the counter substrate is fabricated, when the TFT substrate and the counter substrate are bonded together, a position shift sometimes occurs between the region on the TFT substrate that is partitioned by the scanning lines and the data lines and in which the pixel electrodes
216
are provided, and the region on the counter substrate that is partitioned by the black matrix and in which the color filters are provided. When such a position shift occurs, colors come out in positions where no color is expected to come out in design, so that desired color development is not obtained. For this reason, it is necessary to provide between pixels a margin for compensating for the position shift, that is, a black matrix larger than the theoretical value, so that it is difficult to obtain pixels of a sufficient area. Consequently, sufficient luminance cannot be obtained. This defect becomes more conspicuous as the pitch between pixels decreases with improvement in resolution.
Therefore, recently, a liquid crystal display device in which color filters are provided on the TFT substrate has been developed, and this substrate is called a CF on a TFT substrate (Japanese Unexamined Patent Publication 2000-231123).
A method for fabricating a conventional CF on a TFT substrate will be described. FIG.
2
through
FIG. 11
are cross-sectional views showing the method for fabricating the conventional CF on a TFT substrate in order in which the fabricating steps are performed.
In the method for fabricating the conventional CF on a TFT substrate, first, scanning lines
102
and gate electrodes (not shown) are selectively formed on a transparent substrate
101
, and as shown in
FIG. 2
, a gate insulating film
104
is formed on the entire surface. Then, semiconductor layers (not shown), data lines
106
, drain electrodes (not shown) and source electrodes
108
are formed on the gate insulating film
104
, and further, a passivation film
109
is formed on the entire surface. By this step, a TFT is formed in each pixel. Further, a red negative photosensitive resin film
110
R
a
is formed on the passivation film
109
by spin coating. The viscosity of the photosensitive resin film
110
R
a
is approximately
10
(mPa.S).
Then, as shown in
FIG. 3
, the photosensitive resin film
110
R
a
is exposed by use of a photomask
111
R intercepting light for the regions other than the pixels for red and the regions of the pixels for red where contact holes for connecting the transparent pixel electrodes and the source electrodes
108
are to be formed.
Then, the photosensitive resin film
110
R
a
is developed. Since the photosensitive resin film
110
R
a
is negative, the regions of the photosensitive resin film
110
R
a
corresponding to the light-intercepted regions, that is, the regions other than the pixels for red and the regions having the pixels for red where the contact holes for connecting the transparent pixel electrodes and the source electrodes
108
are to be formed are removed by the development as shown in
FIG. 4
, so that color filters
110
R are formed.
Then, as shown in
FIG. 5
, a green negative photosensitive region film
110
G
a
is formed on the entire surface by spin coating. The viscosity of the photosensitive resin film
110
G
a
is also approximately 10 (mPa.s).
Then, as shown in
FIG. 6
, the photosensitive resin film
110
G
a
is exposed by use of a photomask
111
G intercepting light for the regions other than the pixels for green and the regions of the pixels for green where contact holes for connecting the transparent pixel electrodes and the source electrodes
108
are to be formed.
Then, as shown in
FIG. 7
, the photosensitive resin film
110
G
a
is developed. Since the photosensitive resin film
110
G
a
is negative, the regions of the photosensitive resin film
110
G
a
corresponding to the light-intercepted regions are removed by the development, so that color filters
110
G are formed.
Then, as shown in
FIG. 8
, a blue negative photosensitive region film
110
B
a
is formed on the entire surface by spin coating. The viscosity of the photosensitive resin film
110
B
a
is also approximately
10
(mPa.s).
Then, as shown in
FIG. 9
, the photosensitive resin film
110
B
a
is exposed by use of a photomask
111
B intercepting light for the regions other than the pixels for blue and the regions of the pixels for blue where contact holes for connecting the transparent pixel electrodes and the source electrodes
108
are to be formed.
Then, the photosensitive resin film
110
B
a
is developed. Since the photosensitive resin film
110
B
a
is negative, the regions of the photosensitive resin film
110
B
a
corresponding to the light-intercepted regions are removed by the development as shown in
FIG. 10
, so that color filters
110
B are formed.
Then, as shown in
FIG. 11
, a black matrix
112
is formed in the regions corresponding to the TFTs, and the scanning lines and the data lines
106
on the color filters. Further, an overcoat layer
113
is formed on the black matrix
112
, and an overcoat layer
114
having openings
114
a
in the openings of the color filters
10
R,
110
G and
10
B is formed. Then, openings
109
a
are formed in the regions of the passivation film
109
exposed in the openings
114
a.
Contact holes
115
reachin
Kikkawa Hironori
Okamoto Mamoru
Sakamoto Michiaki
Duong Tai
Hayes & Soloway P.C.
NEC LCD Technologies Ltd.
Ton Toan
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