Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-08-15
2004-05-18
Nguyen, Van Thu (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S059000, C257S350000, C257S659000
Reexamination Certificate
active
06737708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to liquid-crystal display devices, and, more particularly, to a liquid-crystal display device of an active-matrix type having a thin-film transistor and a method of producing such a liquid-crystal display device.
2. Description of the Related Art
Liquid-crystal display devices are compact and consume lower power, and, for these reasons, have been widely used in portable information processing devices, such as notebook-type personal computers. However, the use of liquid-crystal display devices is not limited to portable information processing devices. Actually, the liquid-crystal display devices have started replacing conventional CRT display devices in desktop information processing devices. Moreover, the liquid-crystal display devices are greatly expected to serve as displays for high-definition television (HDTV), and particularly for projection HDTV.
With those high-performance large-area liquid-crystal display devices, the conventional simple matrix driving system is not adequate to satisfy various conditions such as the response rate, the contrast ratio, the color purity, and so forth. Therefore, the active-matrix driving system, in which each pixel is driven by a corresponding thin-film transistor (TFT), is employed. In a liquid-crystal display device, an amorphous silicon liquid-crystal display using amorphous silicon in the active regions of TFTs has been conventionally used. However, the electron mobility of amorphous silicon is small, and cannot satisfy the conditions required in the above high-performance liquid-crystal display devices. Accordingly, it is preferable to use polysilicon TFTs in those high-performance liquid-crystal display devices.
FIG. 1
is a schematic view showing the structure of a conventional active-matrix liquid-crystal display device. As shown in
FIG. 1
, the liquid-crystal display device comprises a TFT glass substrate
1
A that carries a large number of TFTs and transparent pixel electrodes in cooperation with the TFTs, and a counter glass substrate
1
B formed on the TFT glass substrate
1
A. Between the TFT glass substrate
1
A and the counter glass substrate
1
B, a liquid-crystal layer
1
is sealed by a sealing member
1
C. In the liquid-crystal display device, the transparent pixel electrodes are selectively driven via each corresponding TFT, so that the orientations of liquid-crystal molecules can be selectively varied with each selected transparent pixel electrode in the liquid-crystal layer. Outside the glass substrates
1
A and
1
B, polarizing plates (not shown) are arranged in a crossed-Nicol state. Inside the glass substrates
1
A and
1
B, a molecular orientation film (not shown) is formed in contact with the liquid-crystal layer
1
, thereby restricting the orientations of the liquid-crystal molecules.
FIG. 2
is a sectional view of the liquid-crystal display device shown in FIG.
1
.
As shown in
FIG. 2
, a large number of pixel TFTs
11
and a peripheral circuit
1
PR for driving the pixel TFTs
11
are formed on the TFT glass substrate
1
A. Also, connection terminals and a pad electrode
1
c
are formed outside the sealing member
1
C. The peripheral circuit
1
PR is also constituted by TFTS, and an interlayer insulating film
1
AI is formed in the region enclosed by the sealing member
1
C on the TFT glass substrate
1
A in such a manner that the interlayer insulating film
1
AI covers the peripheral circuit
1
PR and the pixel TFTs
11
. On the interlayer insulating film
1
AI, a large number of pixel electrodes
14
are formed in contact with the respective pixel TFTs
11
. On the interlayer insulating film
1
AI, a molecular orientation film
1
MO is further formed in such a manner that the molecular orientation film
1
MO covers the pixel electrodes
14
and is brought into contact with the enclosed liquid-crystal layer
1
.
A large number of color filter patterns
1
CF corresponding to the pixel electrodes
14
are formed on the glass substrate
1
B, and light blocking patterns
1
BM are formed between the color filter patterns
1
CF. On the counter glass substrate
1
B, a flattening insulating film
1
BI is formed so as to cover the color filter patterns
1
CF and the light blocking patterns
1
BM. On the flattening insulating film
1
BI, a counter transparent electrode
1
ITO is uniformly formed. The counter transparent electrode
1
ITO is covered with another molecular orientation film
1
MO, which is in contact with the liquid-crystal layer
1
. The molecular orientation films
1
MO restrict the orientations of the liquid-crystal molecules in the liquid-crystal layer
1
.
Furthermore, a first polarizing film
1
PL is formed on the lower surface of the TFT glass substrate
1
A, while a second polarizing film
1
AL is formed on the upper surface of the counter glass substrate
1
B, in such a manner that the polarizing axes are perpendicular to each other.
FIG. 3
is an enlarged view of a part of the TFT glass substrate
1
A shown in FIG.
1
.
As shown in
FIG. 3
, a large number of pad electrodes
13
A that receive scanning signals, a large number of scanning electrodes
13
extending from the pad electrodes
13
A, a large number of pad electrodes
12
A that receive video signals, and a large number of signal electrodes
12
extending from the pad electrodes
12
A, are formed on the glass substrate
1
A in such a manner that the extending direction of the scanning electrodes
13
is substantially perpendicular to the extending direction of the signal electrodes
12
. At each intersection of the scanning electrodes
13
and the signal electrodes
12
, the TFT
11
is formed. Furthermore, the transparent pixel electrodes described before are formed so as to correspond to the respective TFTs
11
. Each of the TFTs
11
is selected in accordance with the scanning signal on each corresponding scanning electrode
13
, and each cooperative transparent pixel electrode
14
is driven in accordance with the video signal on each corresponding signal electrode
12
. In
FIG. 3
, the pad electrodes
12
A and
13
A are equivalent to the pad electrode
1
c
shown in FIG.
2
.
On such an insulating glass substrate, however, static electricity is often generated due to various factors during the production of the TFTs. For instance, in a case where the insulating glass substrate is attached to or removed from a processing machine, a transportation means, a jig, or a substrate holder, static electricity enters the substrate from the outside. Also, various plasma processes used for forming the TFTs on the substrate, such as the plasma CVD method, the sputtering method, or the RIE process, might result in the accumulation of static electricity inside the substrate. In these plasma processes, the conductive patterns or the diffusion regions function as antennas, and the differences in effective area among the antennas induce potential differences in the substrate. Since the substrate itself is an insulator, the induced potential differences cannot be cancelled, resulting in unrecoverable permanent damage, partially recoverable semi-permanent damage, overruns due to variations of the threshold voltage, characteristic deterioration due to a decrease of mobility, poor long-term reliability due to potential problems, or the like. As a result, the yield of the liquid-crystal display device is reduced.
To avoid the above problems, a peripheral short-circuiting ring is formed so as to surround a plurality of panel regions on a common glass substrate including the panel regions, and the TFTs within the panel regions are connected to the peripheral short-circuiting ring, thereby preventing the accumulation of electric charges on the substrate.
FIG. 4
shows an example of a common glass substrate
100
having a peripheral short-circuiting ring formed in each panel region. In
FIG. 4
, the same components as in the foregoing figures are denoted by the same reference numerals.
As shown in
FIG. 4
, a plurality of panel regions
100
A outlined by scribe r
Nagahiro Yoshio
Zhang Hong Yong
Fujitsu Display Technologies Corporation
Menz Doug
Nguyen Van Thu
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