Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1997-07-18
2001-02-20
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S055000, C349S052000
Reexamination Certificate
active
06191832
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix display device used as a display device for a computer display screen, a television, a light bulb of a projector or the like, and a method for correcting a defect thereof.
2. Description of the Related Art
A display device such as a liquid crystal display device or a plasma display device includes a plurality of pixel electrodes arranged in a matrix, and a plurality of counter electrodes disposed so as to oppose the respective pixel electrodes. A display medium such as liquid crystal or plasma is interposed between the pixel electrodes and the counter electrodes. In such a display device, when a driving signal is applied to the pixel electrodes, the display medium is optically modulated due to a voltage generated between the pixel electrodes and the counter electrodes. By selectively applying a driving signal to the pixel electrode taking advantage of the modulation principle, a display pattern is displayed on a screen.
One known method for driving such a display device is an active matrix driving method. An active matrix display device includes an active matrix substrate, a counter substrate disposed so as to oppose the active matrix substrate, and a display medium interposed therebetween. In the active matrix substrate, a plurality of pixel electrodes disposed in a matrix are respectively connected to switching elements so that an electric potential is selectively applied to the respective pixel electrodes via these switching elements. In general, a thin film transistor (TFT), a metal-insulator-metal (MIM) element or the like is used as the switching element.
In the conventional active matrix substrate described above, one of the bus lines, that is, a signal line, a scanning line or the like, is generally formed in the same layer as that of the pixel electrodes so as not to be in contact therewith. In recent years, an active matrix substrate having another configuration has been described (Japanese Laid-Open Patent Publication No. 61-156025). In such an active matrix substrate, an insulating film is provided so as to cover the signal lines or the scanning lines. A plurality of pixel electrodes are formed on the insulating film, and the pixel electrodes are connected to their respective switching elements. Since the pixel electrodes and the bus lines are separately formed in different layers in this configuration, it is possible to prevent an aperture ratio from being lowered by increasing the area of the pixel electrodes.
FIG. 15
is a plan view showing one pixel of the active matrix substrate having the configuration described in the above Patent Publication. In this active matrix substrate, scanning lines
52
and signal lines
53
are provided so as to cross each other. An insulating film (not shown) is formed so as to cover the scanning lines
52
and the signal lines
53
. A pixel electrode
51
is formed on the insulating film. The pixel electrode
51
is connected to a drain electrode
52
of a thin film transistor (TFT)
55
via a contact hole
51
b
formed through the insulating film. By forming the pixel electrode
51
on the insulating film covering the scanning lines
52
and the signal lines
53
(the bus lines), the pixel electrode
51
and the bus lines
52
and
53
are separately formed in different layers.
The active matrix substrate shown in
FIG. 15
has a Cs (storage capacity) on Common configuration. Specifically, a Cs line
59
common to the pixels is provided so as to be parallel to the scanning line
52
. On the Cs line
59
, a Cs electrode
56
is formed via a gate insulating film (not shown). The Cs electrode
56
is connected to the pixel electrode
51
via the contact hole
51
a
formed through the insulating film. A storage capacitor is constituted by the overlapping portion of the Cs line
59
, the gate insulating film, and the Cs electrode
56
.
In the active matrix display device using such an active matrix substrate, the disconnection of a bus line disadvantageously becomes a problem due to a defect occurring upon fabrication. In recent years, the width of the bus line has been minimized so as to prevent the aperture ratio from being lowered and thereby improving the accuracy of the display device. On the other hand, since the number of bus line intersections increases, a disconnection of a bus line and a leak at the intersection of the bus lines is more likely to occur as compared with a conventional active matrix display device. When a defect such as a disconnection of bus lines or a leak occurs, such a defect appears as a line defect on the display because a normal voltage is not applied from the bus line to the pixel electrode. The line defect is fatal for the display device; the display device which turns out to have a line defect is discarded as a defective product. As a result, the ratio of acceptable display device products is lowered thereby increasing the fabrication cost thereof.
In order to eliminate the above-mentioned problems resulting from the defects, i.e., the disconnection of the bus lines, an active matrix liquid crystal display device, in which two bus lines are provided for one pixel electrode, has been described (SID′ 95 DIGEST of TECHNICAL PAPERS 4: AMLCDs 4.3; “High-Aperture and Fault-Tolerant Pixel Structures for TFT-LCDs”).
FIG. 16
is a plan view showing an active matrix substrate of the liquid crystal display device.
In the active matrix substrate shown in
FIG. 16
, two scanning lines
52
and
52
′ are provided for each pixel electrode
51
. Each of the scanning lines
52
and
52
′ is short-circuited by short-circuit lines
54
and
54
′ which are respectively provided along signal lines
53
and
53
′. Each of the short-circuit lines
54
and
54
′ overlaps the pixel electrode
51
via an insulating film (not shown). The overlapping portion of the short-circuit lines
54
and
54
′ and the pixel electrode
51
serves as a storage capacitor.
A TFT
55
is driven by the two scanning lines
52
and
52
′ in the liquid crystal display device using such an active matrix substrate. Thus, even if a disconnection occurs in one of the two scanning lines
52
and
52
′, it is possible to apply a scan voltage to the TFT
55
via the short-circuit lines
54
and
54
′. Moreover, since the short-circuit lines
54
and
54
′ are provided so as to partially overlap the pixel electrode
51
on the active matrix substrate side, part of a light-shielding pattern formed on the counter substrate so as to prevent light from leaking from a region between the adjacent pixel electrodes
51
can be omitted.
In order to reduce the above-mentioned problems resulting from the disconnection of bus lines, the Applicant of the present invention has described an active matrix substrate as shown in
FIGS. 17 and 18
in Japanese Patent Application No. 7-251339, “Active matrix liquid crystal display device and Method for correcting pixel defect”.
FIG. 17
is a plan view showing the structure of an active matrix substrate, and
FIG. 18
is a plan view specifically showing one pixel of the active matrix substrate shown in FIG.
17
. In the illustrated active matrix substrate, a signal line
2
and a spare line
105
are alternately provided at predetermined intervals in the same layer so as to parallel to each other. The signal line
2
and the spare line
105
are connected to each other by a short-circuit line provided in the same layer. With this configuration, even if the disconnection of the signal line
2
occurs, the defective portion of the signal line
2
where the disconnection occurs is avoided through the spare line
105
. Therefore, a signal voltage can be applied to part of the signal line
2
which is positioned ahead of the disconnected portion.
This Japanese Patent Application No. 7-251339 also proposes an active matrix substrate as shown in FIG.
19
. In this active matrix substrate, a scanning line
1
and a spare line
122
are alternately provided at pred
Dudek James A.
Nguyen Dung
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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