Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-30
2001-12-04
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000
Reexamination Certificate
active
06327015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a manufacturing method of a display device having a pixel area and a peripheral driving circuit area and, more specifically, to a manufacturing method of an active matrix type liquid crystal display device.
2. Description of the Related Art
An active matrix liquid crystal display device is conventionally known. In the active matrix liquid crystal display device, a structure is known in which a pixel area having pixels that are arranged in a matrix form and a peripheral driving circuit for driving thin-film transistors that are arranged in the pixel area are integrated on the same substrate.
FIG. 1
shows a general configuration of a panel of an active matrix liquid crystal display device in which a pixel area and a peripheral driving circuit area are integrated on a glass substrate
101
. Reference numeral
102
denotes a pixel area in which pixels are arranged in a matrix of several hundred by several hundred. The fundamental configuration of the pixel area
102
is such that source lines
104
and gate lines
105
are arranged in a matrix form, thin-film transistors
106
are arranged at each intersection of the source and gate lines, and the drains of the thin-film transistors
106
are connected to electrodes (pixel electrodes) for applying an electric filed to a liquid crystal
107
.
Reference numeral
103
denotes a peripheral driving circuit area for driving the thin-film transistors for the respective pixels. The peripheral driving circuit area
103
is also constituted of thin-film transistors. The standardized configuration of the peripheral driving circuit includes a shift register circuit and an analog buffer circuit that allows a low-impedance current flow.
In general, plural panels of the active matrix liquid display device shown in
FIG. 1
are produced at the same time by forming a plurality of
FIG. 1
configurations on a large glass substrate and then cutting the glass substrate, because this method can reduce the manufacturing cost from the case of producing the panel of
FIG. 1
one by one.
FIG. 2
shoes a general layout of active matrix liquid crystal display panels. That is, in
FIG. 2
, a single glass substrate
101
is allocated to four active matrix liquid crystal display panels
201
to
204
. The number of panels to which a single glass substrate is allocated is not limited to four, but may be set as desired
SUMMARY OF THE INVENTION
The layout as shown in
FIG. 2
can provide an advantage that the manufacturing cost of the active matrix liquid crystal display device an be reduced. However, it has been found that if panels are actually produced with the layout as shown in
FIG. 2
, failures likely occur with a particular tendency.
For example, if the single glass substrate
101
is allocated to the four panels
201
to
204
in the manner shown in
FIG. 2
, failures occur at a high probability in the panels
201
,
203
, and
204
. The reason is explained as follows. It has been found that where the active matrix liquid crystal display panel of
FIG. 1
is produced singly, more than 80% of circuit failures occur in the peripheral driving circuit area
103
. Further, observations with an optical microscope have revealed that failures are caused mainly by particles.
The fact that failures occur in the peripheral driving circuit area
103
at a high probability attributes to two concurrent factors. First, the peripheral driving circuit area
103
has a much higher degree of integration than the pixel area
102
. The second factor is as follows. In general, as exemplified in
FIG. 9
, a thin-film transistor manufacturing process includes many steps. For example, when a substrate is moved in a transition from one step to the next, minute particles fall on the substrate more likely in a region closer to the perimeter of the substrate.
Since the peripheral driving circuit area
103
has a higher degree of integration than the pixel area
102
as described above, a failure is caused by particles at a higher probability in the peripheral driving circuit area
103
. On the other hand, where semiconductor devices are formed on a single substrate, particles (dust) are distributed on the substrate in each step (in general, semiconductor devices are formed through many steps) at a higher percentage in a region closer to the perimeter of the substrate. Therefore, when a panel is produced as shown in
FIG. 1
, a failure occurs at a higher probability in the peripheral driving circuit area
103
. Once a failure occurs in the peripheral driving circuit area
103
, no signal current flows through a gate line or a source line that is connected to a location of failure, resulting in a line defect. Even if the failure does not cause a line defect, it will cause a flicker on the screen or an unclear display.
Now, where the respective cells are produced with the layout of
FIG. 2
, it is seen that the peripheral driving circuit areas
205
,
207
, and
208
, which themselves are prone to a failure due to particles, exist in regions close to the perimeter of the glass substrate
101
in which regions particles occur at a high probability. Thus, it is understood that failures occur at a high probability in the peripheral driving circuit areas
205
,
207
and
208
.
Based on the recognition of the foregoing problem, an object of the present invention is to provide a technique of suppressing failures in a case where a plurality of panels are produced from one substrate as shown in FIG.
2
.
According to one aspect of the invention, there is provided a method for manufacturing a panel that constitutes a liquid crystal display device in which a pixel area and a peripheral driving circuit area are formed in an integral manner on a substrate having a insulating surface, wherein layout is so made that a distance between the perimeter of the substrate and the peripheral driving circuit area is longer than a distance between the perimeter of the substrate and the pixel area.
In the above method, usually a glass substrate is employed as the substrate having an insulating surface. Alternatively, a quartz substrate or a resin substrate may also be used.
The pixel area has a number of pixels that are arranged in a matrix form. Each pixel has at least one switching thin-film transistor and, if necessary, a holding capacitor. The peripheral driving circuit area includes circuits for driving the thin-film transistors in the pixel area. The peripheral driving circuit may includes thin film transistors formed on the same substrate as the switching transistors.
FIG. 7
shows a specific example of the feature “layout is so made that a distance between the perimeter of the substrate and the peripheral driving circuit area is longer than a distance between the perimeter of the substrate and the pixel area.” The example of
FIG. 7
is directed to a case of producing four panels from a glass substrate
101
. In this case, distances a and b between the perimeter of the glass substrate
101
and a peripheral driving circuit area
701
are set larger than distances a′ and b′. A similar layout may be used for a case where the number of panels produced from a single substrate is larger than four. In accordance with a preferred embodiment of the invention, when the substrate
101
is 127 mm×127 mm, the distance a′ and b′ from the periphery of the substrate
101
to the pixel areas should be at least 10 mm so that the minimum quality of the thin films can be guaranteed. Also, the distance a and b from the periphery of the substrate
101
to the peripheral circuit region should be at least 1.5 times larger than the distance a′ and b′. Also, the distance c and c′ is preferably 5 mm or smaller.
According to another aspect of the invention, there is provided a method for simultaneously manufacturing four panels that constitute respective liquid crystal display devices in each of which a pixel area and a peripheral driving circuit area are formed in an integral manner on a sing
Awane Katunobu
Yamazaki Shunpei
Dudek James A.
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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