Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2000-10-25
2003-07-29
Ton, Toan (Department: 2821)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S043000, C349S139000, C438S030000
Reexamination Certificate
active
06600546
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 1999-0046346, filed on Oct. 25, 1999, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an active-matrix liquid crystal display (LCD) device and a method of fabricating the same, and more particularly, to an array substrate having thin film transistors for the active-matrix LCD device and the method of fabricating the array substrate.
An active matrix type LCD device, employing a thin film transistor (TFT) as a switching device, is typically made up of two array substrates with a liquid crystal material interposed therebetween. One substrate, which is the array substrate, has a matrix array of TFTs and pixel electrodes. The opposing substrate, which is the color filter substrate, includes a light-shielding film (also known as the black matrix), a color filter, and a common electrode.
For the array substrate, an inverted staggered type TFT is widely employed because of its simple structure and superior quality. The inverted staggered type TFT is further divided into a back-channel-etch type and an etching-stopper type, which are differentiated according to the methods of forming a channel in the TFT. Between the two, the back-channel-etch type has a simpler structure.
A typical array substrate manufacturing process requires repeated steps of depositing and patterning various layers. The patterning steps involve photolithography masks. Each photolithography step is facilitated using one mask, and the number of masks used in the fabrication process is a critical factor in determining the number of patterning steps. Namely, the production cost depends heavily on the number of masks used in the manufacturing process.
Referring to the attached drawings, a back-channel-etching type structure of an array substrate of an LCD device manufactured by a conventional method will be explained in detail.
As shown in
FIG. 1
, the LCD device
20
includes an array substrate
2
, a color filter substrate
4
opposing the array substrate
2
, a liquid crystal
10
interposed between, and a sealant
6
formed at the periphery of the gap between the two substrates
2
and
4
. The sealant
6
prevents the liquid crystal
10
from leaking out of the LCD device
20
.
The array substrate
2
includes a substrate
1
, a TFT
5
, and a pixel electrode
14
. The TFT
5
acts as a switching element for changing the orientation of the liquid crystal
10
, and the pixel electrode
14
is used as a first electrode to apply electric field to the liquid crystal
10
.
The color filter substrate
4
includes a substrate
11
, a color filter
8
, and a common electrode
12
. The color filter
8
is used for displaying colors and the common electrode
12
is used as a second electrode to apply an electric field to the liquid crystal
10
.
Referring to
FIG. 2
, a detailed description of the structure and operation of the array substrate
2
will be provided.
On the substrate
1
of the array substrate
2
, a gate line
22
is horizontally formed and a data line
24
is formed perpendicular thereto. The pixel electrode
14
is formed within the rectangular area defined by the gate and data lines
22
and
24
. Near the crossing point between the gate and data lines
22
and
24
, a portion of the gate line
22
is used as a gate electrode
26
. Also, at one end of the gate line
22
, a gate pad
18
is positioned and the gate pad contact hole
21
is formed in the gate pad
18
.
Further, again near the crossing point, the data line
24
is extended to form a source electrode
28
, and a drain electrode
30
is formed spaced apart from the source electrode
28
. Also at one end of the data line
24
, a data pad
20
is positioned and the data pad contact hole is formed in the data pad
23
.
Spaced apart from the drain electrode
30
and over a portion of the gate line
22
, an island-shaped capacitor electrode
32
is formed from the same layer as the data line
24
. An extended portion of the pixel electrode
14
overlaps the capacitor electrode
32
, and together with the extended portion forms a storage capacitor
7
to store electric charges.
A capacitor contact hole
36
is formed above the capacitor electrode
32
to electrically connect the pixel electrode
14
with the capacitor electrode
32
. Another portion of the pixel electrode
14
also overlaps a portion of the drain electrode
30
, and a drain contact hole
34
is formed at the overlapped portion to electrically connect the drain electrode
30
and the pixel electrode
14
.
As explained previously, the TFT
5
, which includes the gate, source, and drain electrodes
26
,
28
and
30
, functions as a switch for applying an electric field to the liquid crystal
10
(shown in FIG.
1
). That is to say, in operation, if a signal is applied to the gate electrode
26
of the TFT
5
, an electrical connection is established between the data line
24
and the pixel electrode
14
. When the gate electrode
26
is turned on, electric field is applied to the pixel electrode
14
according to the signal, from an external circuit (not shown), applied to the data line
24
via the data pad
20
.
Next, referring to
FIGS. 3A
to
7
A and
3
B to
7
B, a more detailed description of the structure and the fabrication method of the TFT and the storage capacitor will be provided.
FIGS. 3A
to
7
A illustrate sequential fabrication steps of a cross-section take along a line “IIIa—IIIa” of
FIG. 2
, and
FIGS. 3B
to
7
B illustrate corresponding sequential fabrication steps of a cross-section taken along a line “IIIb—IIIb” of FIG.
2
.
As shown in
FIGS. 3A and 3B
, a first metallic material is deposited on a surface of the substrate
1
and patterned with a first mask to form the gate line
22
including the gate electrode
26
and gate pad
18
(shown in FIG.
2
). For the first metallic material, a highly conductive metal such as aluminum (Al), aluminum alloy, or molybdenum (Mo) is preferred.
As shown in
FIGS. 4A and 4B
, a first insulating material is then deposited to form a gate insulating layer
50
. On the gate insulating layer
50
, a semiconductor material is deposited and doped with impurities and patterned with a second mask to form a semiconductor layer
52
and an ohmic contact layer
54
, thereby defining a first intermediate structure.
Then, as shown in
FIGS. 5A and 5B
, a second metallic material is deposited over the first intermediate structure and patterned with a third mask to form the source and drain electrodes
28
and
30
and the data line
24
. The data line
24
is connected with the source electrode
28
(FIG.
5
A). At the same time, over a portion of the gate line
22
, the second metallic material is used to form the capacitor electrode
32
with the third mask (FIG.
5
B).
Afterwards, a portion of the ohmic contact layer
54
is also etched away to form a back channel
56
(FIG.
5
A). At this point a second intermediate structure is defined, including the TFT
5
that is made up of the gate, source, and drain electrodes
26
,
28
, and
30
, the semiconductor layer
52
, the ohmic contact layer
54
, and the back channel
56
.
As shown in
FIGS. 6A and 6B
, over the second intermediate structure, a second insulating material is deposited and patterned with a fourth mask to form a passivation layer
58
. The passivation layer
58
, protecting the TFT
5
and the capacitor electrode
32
, is preferably selected from inorganic-based silicon nitride (SiN
x
), silicon oxide (SiO
2
), or organic-based benzocyclobutene (BCB) because they exhibit high light-transmissivity, a moisture-proof quality, and high durability. By patterning the second insulating layer with the fourth mask, the data pad contact, the drain contact, and the capacitor contact holes
23
,
34
and
36
are formed, thereby defining a third intermediate structure.
Then as shown in
FIGS. 7A and 7B
, on the third intermediate structure, a transparent conductive material is deposited and patterned w
Ahn Byung-chul
Kim Yong-wan
Kwon Keuk-sang
Yoo Soon-sung
Akkapeddi P. R.
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Ton Toan
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