Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-10
2002-08-06
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000
Reexamination Certificate
active
06429916
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device including color filters and switching elements such as TFTs (Thin-Film Transistors) which are formed on a common substrate, and a manufacturing method of the liquid crystal display device.
Description of the Prior Art
FIG. 1
is a schematic plan view showing a channel-etched type TFT which is formed on an active matrix substrate of a conventional liquid crystal display device, in which the layout of a pixel is a shown.
FIG. 2
is a cross sectional view of the TFT of FIG.
1
.
FIGS. 3A and 3B
are cross sectional views of pads of the TFT of
FIGS. 1 and 2
, in which
FIG. 3A
shows a gate pad section and
FIG. 3B
shows a data pad section.
Referring to
FIG. 2
, a gate electrode
2
a
is formed on a transparent insulator substrate
1
, and a gate insulator layer
3
is deposited so as to cover the transparent insulator substrate
1
and the gate electrode
2
a
. On the gate insulator layer
3
, a semiconductor layer
4
is formed so as to overlay on the gate electrode
2
a
. A source electrode
6
a
and a drain electrode
7
, which are formed on different sides of the semiconductor layer
4
, are respectively connected to the semiconductor layer
4
via an ohmic contact layer
5
. Part of the deposited ohmic contact layer
5
between the source electrode
6
a
and the drain electrode
7
is removed by etching, and thus the ohmic contact layer
5
remains only between the source electrode
6
a
and the semiconductor layer
4
and between the drain electrode
7
and the semiconductor layer
4
.
On the above structure, a passivation layer
8
is formed. On the passivation layer
8
, a transparent conductive layer for becoming a pixel electrode
9
is deposited so as to be connected to the drain electrode
7
via a contact hole
11
through the passivation layer
8
. A scanning signal is supplied to the gate electrode
2
a
via a gate line
2
b
, and a video signal is supplied to the source electrode
6
a
via a source line
6
b
, and thereby electric charges are written in the pixel electrode
9
.
In the following, a manufacturing method of the active matrix substrate which has been shown in
FIGS. 1 through 3B
will be described referring to
FIGS. 4A through 4E
. Incidentally, only the part shown in
FIG. 2
is shown in
FIGS. 4A through 4E
(and thus the gate pad section and the data pad section of
FIGS. 3A and 3B
are not shown). The following explanation will be given mainly with regard to one pixel.
First, as shown in
FIG. 4A
, a conductive layer of Al, Mo, Cr, etc. is deposited on the transparent insulator substrate
1
(formed of glass, for example) by sputtering to the thickness of 100~400 nm, and thereafter the first patterning step is executed so as to form the gate line
2
b
(unshown in
FIG. 4A
, shown in FIG.
1
), the gate electrode
2
a
and a gate pad
2
c
(unshown in
FIG. 4A
, shown in
FIG. 3A
) (which is connected to an external display signal processor board) are formed by photo-lithography.
Subsequently, as shown in
FIG. 4B
, the gate insulator layer
3
(formed of silicon nitride), the semiconductor layer
4
(formed of amorphous silicon) and the ohmic contact layer
5
(formed of n
+
amorphous silicon) are successively deposited by means of plasma CVD (Chemical Vapor Deposition) to the thicknesses of approximately 400 nm, 300 nm and 50 nm respectively, and thereafter the second patterning step is executed so as to pattern and form the semiconductor layer
4
and the ohmic contact layer
5
at once.
Subsequently, as shown in
FIG. 4C
, a layer of Mo, Cr, etc. is sputtered to the thickness of 100~200 nm so as to cover the gate insulator layer
3
and the ohmic contact layer
5
, and thereafter the third patterning step is executed so as to pattern and form the source electrode
6
a
, the source line
6
b
, the drain electrode
7
and a data pad
7
a
(unshown in
FIG. 4C
, shown in
FIG. 3B
) (which is connected to the external display signal processor board) are formed by photo-lithography. Thereafter, unnecessary part of the ohmic contact layer
5
on the channel of the TFT is removed.
Subsequently, as shown in
FIG. 4D
, the passivation layer
8
(formed of an inorganic material such as silicon nitride) is deposited on the back channel of the TFT, the source electrode
6
a
, the source line
6
b
, the drain electrode
7
and the data pad
7
a
(unshown in
FIG. 4D
, shown in
FIG. 3B
) by means of plasma CVD to the thickness of approximately 100~200 nm, and thereafter the fourth patterning step is executed so as to form the contact hole
11
(for the connection of the drain electrode
7
and the pixel if electrode
9
) and remove unnecessary part of the passivation layer
8
on the data pad
7
a
(unshown in
FIG. 4D
, shown in
FIG. 3B
) and remove unnecessary parts of the gate insulator layer
3
and the passivation layer
8
on the gate pad
2
c
(unshown in
FIG. 4D
, shown in FIG.
3
A).
Finally, as shown in
FIG. 4E
, the transparent conductive layer for becoming the pixel electrode
9
is deposited by sputtering so as to be connected to the drain electrode
7
via the contact hole
11
through the passivation layer
8
, and thereafter the fifth patterning step is executed so as to pattern and form the pixel electrode
9
.
As explained above, the active matrix substrate which has been shown in FIG.
4
A through
FIG. 4E
can be manufactured by only five patterning steps, therefore, the manufacturing process can be shortened considerably. A liquid crystal display device is manufactured by coupling the substrate and another substrate (which is provided with color filters and electrodes thereon) together so as to sandwich liquid crystal.
However, in the above active matrix substrate, light leaks out between the gate line
2
b
and the pixel electrode
9
and between the source line
6
b
and the pixel electrode
9
as can be seen in the plan view of FIG.
1
. Therefore, the light leakage has to be shielded by providing a black matrix (or black matrixes) to the color filter substrate (that is, the aforementioned “another substrate”). In consideration of the precision of the placement of the color filter substrate on the active matrix substrate, the light shielding area of the black matrixes has to be made considerably large, thereby the opening area ratio of the liquid crystal display device is necessitated to be small, and thereby the usage efficiency of the back light of the liquid crystal display device has to be lowered.
In order to enlarge the opening area ratio of the liquid crystal display device, a structure (CF on TFT structure) and a manufacturing method of a liquid crystal display device, in which the color filters are formed directly on the active matrix substrate, have been proposed in, for example, the first embodiment of Japanese Patent Application Laid-Open No.HEI10-39292. If we add some necessary conditions etc. which have not been mentioned in the document, the actual manufacturing method of the CF on TFT structure according to the document becomes as follows.
FIGS. 5A through 5H
are cross sectional views showing the manufacturing method of the CF on TFT structure according to the above document. The TFT shown
FIG. 5A
is called a “channel protection TFT”. Incidentally, the following explanation will be given mainly with regard to one pixel.
First, as shown in
FIG. 5A
, a gate electrode
2
a
is formed on a transparent insulator substrate
1
, and a gate insulator layer
3
is deposited so as to cover the transparent insulator substrate
1
and the gate electrode
2
a
. On the gate insulator layer
3
, a semiconductor layer
4
is formed so as to overlay on the gate electrode
2
a
, and a source electrode
6
a
and a drain electrode
7
are formed to be connected to the semiconductor layer
4
. After completing such a channel protection TFT
10
b
, a passivation layer
8
is deposited so as to cover the above structure.
Subsequently, as shown in
FIG. 5B
, a pigments-dispersed photoresist for becoming the black matrix
15
is c
Ihara Hirofumi
Kikkawa Hironori
Maruyama Muneo
Nakata Shinichi
Okamoto Mamoru
Katten Muchin Zavis & Rosenman
Parker Kenneth
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