Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1997-06-26
2002-06-25
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S050000
Reexamination Certificate
active
06411348
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active matrix substrate having formed thereon a matrix of non-linear elements serving as switching elements, such as thin film transistors, and to a producing method of the same.
BACKGROUND OF THE INVENTION
In a general liquid crystal display element, a display pattern is formed on the screen by selectively driving a matrix of pixel electrodes. In other words, in the above liquid crystal display element, when a voltage is applied across a selected pixel electrode and an opposing electrode, a liquid crystal interposed between these two electrodes as a display medium is optically modulated, and such an optical modulation is recognized as a display pattern.
The active matrix driving method is known as a driving method of the above pixel electrodes. In this method, a matrix of independent pixel electrodes are connected to their respective switching elements, so that each pixel electrode is driven by the ON/OFF action of the switching element. An example of the switching element is a non-linear element, such as a thin film transistor (hereinafter, referred to as TFT), an MIM (metal insulator metal) element, a MOS (metal oxide semiconductor) transistor element, and a diode.
As shown in
FIG. 15
as an example, an active matrix substrate using TFTs as the switching elements is arranged in such a manner that a plurality of parallel scanning lines
104
are provided to intersect at right angles with a plurality of parallel signal lines
105
.
A pixel electrode
102
is provided to each rectangular area enclosed by the scanning lines
104
and signal lines
105
. Also, a TFT
101
functioning as the switching element is provided in the vicinity of each intersection of the scanning lines
104
and signal lines
105
.
Each TFT
101
comprises a gate electrode
101
g
connected to the scanning line
104
electrically, a source electrode
101
s
connected to the signal line
105
electrically, and a drain electrode
101
d
connected to the pixel electrode
102
electrically.
The switching element like the TFT
101
is produced by repeating the film forming and etching steps of a conductor layer, a semiconductor layer, and an insulating layer. Thus, a static electricity is often generated during the producing process or transportation process from one apparatus to another, the switching elements formed on the substrate are susceptible to the static-induced damage.
To solve the above problem, various methods have been proposed to protect the switching elements and the like from the static electricity generated during the producing process.
For example, a method disclosed in Japanese Laid-open Patent Application No. 106788/1988 (Tokukaisho No. 63-106788) is illustrated in
FIG. 16
, in which a conductor short-ring
108
is provided to interconnect all the input terminals electrically. To be more specific, scanning line input terminals
106
connected to the scanning lines
104
in an active matrix portion
103
and signal line input terminals
107
connected to the signal lines
105
in the active matrix portion
103
are interconnected electrically through the conductor short-ring
108
. According to this arrangement, a static electricity inputted into any of the scanning line input terminals
106
and signal line input terminals
107
can be dispersed to all the other input terminals
106
and
107
through the conductor short-ring
108
.
In other words, when a static electricity is inputted one of the scanning line input terminals
106
and signal line input terminals
107
, the input static electricity is dispersed to all the other input terminals
106
and
107
through the conductor short-ring
108
interconnecting these input terminals
106
and
107
electrically. Thus, if a static electricity is inputted into one of the scanning line input terminals
106
, the switching elements
101
and pixel electrodes
102
connected to the corresponding scanning line
104
are not affected by the input static electricity.
However, if the input terminals are interconnected through the conductor short-ring
108
as shown in
FIG. 16
, the conductor short-ring
108
must be removed before a driver is mounted to each input terminal. Therefore, there is no static electricity preventing means in the steps after the driver is mounted, and the switching elements and the like formed on the substrate may be damaged by the static electricity.
To solve the above problem, the above reference discloses an other method of preventing the switching elements and the like from the static electricity generated during the producing process, which is illustrated in FIG.
17
. More specifically, the scanning lines
104
and signal lines
105
between the active matrix portion
103
and the scanning line input terminals
106
/signal line input terminals
107
are interconnected electrically through a semiconductor short-ring
109
of high resistance made of a semiconductor having a high resistance. According to this arrangement, a static electricity inputted into any of the scanning line input terminals
106
and signal line input terminals
107
can be dispersed to all the other input terminals
106
and
107
.
In other words, when a static electricity is inputted into any of the scanning line input terminals
106
and signal line input terminals
107
, the input static electricity is dispersed to all the other input terminals
106
and
107
by means of the semiconductor short-ring
109
of high resistance through the scanning lines
104
and signal lines
105
.
When all the lines are interconnected through the semiconductor short-ring
109
of high resistance in the above manner, it is not necessary to remove the semiconductor short-ring
109
of high resistance before the driver is mounted to each input terminal. Consequently, the static-induced damage to the switching elements is prevented in the steps not only before but also after the driver is mounted.
However, when the active matrix substrate uses the above semiconductor short-ring
109
of high resistance, it becomes quite difficult to stabilize a resistance value of the semiconductor layer during the producing process, and a problem occurs if the resistance value of the semiconductor short-ring
109
of high resistance is not set to an adequate value. That is, when the resistance value of the semiconductor short-ring
109
of high resistance is too small, there occurs a serious defect, namely, leakage between the input terminals. On the other hand, when the resistance value of the semiconductor short-ring
109
of high resistance is too large, the semiconductor short-ring
109
of high resistance can not function as a short-ring.
Further, in the method of using the semiconductor layer as the short-ring, if a channel etch type TFT is used as the switching element of the active matrix portion
103
, the semiconductor layer which will be made into the short-ring must be masked by a photoresist when the semiconductor layer is produced concurrently with the TFT.
Therefore, this method can not adopt a short-cut process, in which the gap in the TFT is etched using the source and drain electrodes as the mask. In other words, since the photoresist is not used in the above short-cut process, the photoresist is not left on the semiconductor layer in the portion which will be made into the short-ring. Consequently, the semiconductor layer which is supposed to be made into the short-ring is also etched away when the channel portion (gap) of the TFT is etched.
Therefore, as previously mentioned, to protect the unwanted etching of the semiconductor layer, an additional step is necessary to form a photoresist on the semiconductor layer which will be made into the short-ring before the gap of the TFT is etched. This not only increases the number of the steps in the producing process of the active matrix substrate, but also extends the producing time as well as increasing the manufacturing costs.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an active matrix substrate which can
Katayama Mikio
Kawai Katsuhiro
Okamoto Masaya
Shimada Takayuki
Yamakawa Shinya
Duong Tai V.
Nixon & Vanderhye P.C.
Sikes William L.
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