Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-07-06
2002-10-01
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S046000, C349S139000
Reexamination Certificate
active
06459466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to liquid-crystal display devices and methods of fabricating the same, and more particularly to a Thin Film Transistor (TFT) liquid-crystal display device and a method of fabricating the same.
2. Description of the Related Art
Recently, liquid-crystal display devices for use with information processors such as computers are widely used because of their portable size and low power consumption.
Especially to realize high quality color display, an active matrix method that controls each pixel electrode is widely applied to liquid-crystal display devices.
FIG. 1
shows a diagram of a conventional active-matrix-type liquid-crystal display device. Referring to
FIG. 1
, a liquid-crystal display device
10
includes a first TFT glass base
11
having a plurality of TFTs and transparent pixel electrodes cooperating therewith and a second glass base
12
. A liquid-crystal layer
1
between the first TFT glass base
11
and the second glass base
12
is sealed by sealing members. In the liquid-crystal display device
10
, the transparent pixel electrode may be selected turned ON through the TFT so that a orienting direction of liquid-crystal molecules is altered by the selected transparent pixel electrode. A polarization plate (not shown) is arranged in a cross Nicol state. Moreover, molecule orientation films are provided inside of the TFT glass base
11
and the glass base
12
to suppress orienting directions of liquid-crystal molecules.
FIG. 2
shows a part of the TFT glass base
11
under magnification.
Referring to
FIG. 2
, on the TFT glass base
11
, a plurality of pad electrodes
11
A supply scan signals and a plurality of scan electrodes
11
a
are extend therefrom. Also, a plurality of pad electrodes
11
B supply image signals and a plurality of signal electrodes
11
b
are extended therefrom. The extending direction of the scan electrodes
11
a
and that of signal electrodes
11
b
cross each other. TFTs
11
C are provided at every point of intersection of the scan electrodes
11
a
and signal electrodes
11
b
. Furthermore, a transparent pixel electrode
11
D is provided to each TFT
11
C. A row of TFTs
11
C is selected by a scan signal from a corresponding scan electrode
11
a
and then a particular transparent pixel electrode
11
D is operated by an image signal from a corresponding signal electrode
11
b.
FIGS. 3A
,
3
B,
3
C and
3
D show sectional views illustrating production steps of a conventional liquid-crystal display device. In these figures, every left side shows a display area including a TFT
11
C and every right side shows a terminal area including pad electrodes
11
A and
11
B.
Referring to
FIG. 3A
, in the display area, an Al—Nd or Al—Sc alloy pattern
22
A that is connected to the scan electrode
11
a
is formed as a gate electrode
22
A on a glass base
21
corresponding to the first TFT glass base
11
in FIG.
1
. Simultaneously, in the terminal area on the glass base
21
, terminal electrodes
22
B, which are made up of an Al—Nd or Al—Sc alloy pattern, corresponding to the pad electrode
11
A or
11
B are formed.
Subsequently, in the display area in
FIG. 3B
, a gate insulation film
23
A that is made up of SiN is layered over the gate electrode
22
A. Moreover, an n
−
type impurity doped amorphous silicon layer
24
A is layered over the gate insulation film
23
A. Furthermore, a channel mask film
25
A, which is made up of SiN, is formed on an area corresponding to a channel region right above the gate electrode
22
A and is etched.
In the terminal area in
FIG. 3B
, an insulation film
23
B, which is made up of the same composition (SiN) and thickness as the insulation film
23
A, is layered over the terminal electrodes
22
B and then an amorphous silicon layer
24
B, having the same thickness as the amorphous silicon layer
24
A, is layered over the insulation film
23
B.
In addition, in the display area in
FIG. 3C
, an n
+
type impurity doped amorphous silicon pattern
26
A is formed on the amorphous silicon layer
24
A and is adjoined with sides of the channel mask film
25
A. Moreover, a metal is layered on the n
+
type impurity doped amorphous silicon pattern
26
A so that a source-drain of the TFT
11
C is constituted. For example, the above metal can be constructed by Ti, Al and Ti layers.
Subsequently, in the display area in
FIG. 3D
, a mask film
27
A, which is made up of SiN, is layered so as to cover over the n
+
type impurity doped amorphous silicon and metal pattern
26
A and the channel mask film
25
A on the gate insulation film
23
A. In addition, a contact hole
28
A is provided in the mask film
27
A at one side of the amorphous silicon pattern
26
A. Furthermore, a transparent pixel electrode
29
is provided at the contact hole
28
A and contacts the amorphous silicon pattern
26
A. The transparent pixel electrode
29
corresponds to the transparent pixel electrode
11
D in FIG.
2
.
Simultaneously with steps in the display area in
FIG. 3D
, in the terminal area in
FIG. 3D
, a mask film
27
B corresponding to the mask film
27
A is layered on the insulation film
23
B. Then contact holes
28
B are formed to expose the terminal electrodes
22
B. As shown in
FIG. 4
, in a liquid-crystal display device
52
, IC devices
56
are connected to the terminal electrodes
22
B via the contact holes
28
B in the terminal area on a display panel
54
by tape automated bonding (TAB) leads (not shown).
The second glass base covers and seals the display area on the TFT glass base
21
.
Generally, to cut production cost, after a plurality of liquid-crystal displays are produced on a surface of a large glass base, the large glass base is cut into each liquid-crystal display so that a plurality of liquid-crystal display devices are completed.
FIG. 5
is a sectional view illustrating the conventional liquid-crystal display device after a cutting step. Referring to
FIG. 5
, a first glass base
40
, corresponding to the first TFT glass base
11
in
FIG. 1
, has a terminal area
47
including terminal electrodes
22
B and a display area
48
surrounded by the terminal area
47
. The first glass base
40
is sealed with a second glass base
49
, sealing members
42
and spacers (not shown) such that the first glass base
40
and the second glass base
49
face each other. The terminal area
47
is not covered with the second glass base
49
. Thus, the terminal area
47
is vulnerable to particles especially during the cutting step. In particular, when terminal electrodes
22
B in the terminal area
47
are damaged mechanically by the particles, the damage makes it impossible to connect the liquid-crystal display to external circuits so that functions as a liquid-crystal display are lost.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a Thin Film Transistor (TFT) liquid-crystal display device and method of the same in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a Thin Film Transistor (TFT) liquid-crystal display device and a method of fabricating the same that prevent particles from causing mechanical damages and improve yield of production of the same.
The above objects of the present invention are achieved by a liquid-crystal display device including: a first glass base; a second glass base facing the first glass base in a condition in which a space is defined between the first glass base and the second glass base; a liquid-crystal layer filling the space between the first glass base and the second glass base, and being sealed inside the first glass base, the second glass base and supporting members; a display area that is a surface area of the first glass base and faces the second glass base, and that includes thin-film transistors; a terminal area having terminal electrodes that connect electrically to corresponding thin-film transistors respectively; and projections provided on the terminal area such that heights of the
Greer Burns & Crain Ltd.
Ngo Julie
Sikes William L.
LandOfFree
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