Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-11-24
2002-10-08
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000, C349S040000, C349S043000, C349S054000
Reexamination Certificate
active
06462792
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a display device for displaying by applying a drive signal to a display-use pixel electrode through a switching element, more particularly relates to a matrix-type liquid crystal display device, which permits a high density display by disposing pixel electrodes in a matrix form, and also relates to a method of compensating for a defective pixel electrode in such display device.
BACKGROUND OF THE INVENTION
A conventional display device such as a liquid crystal display device, a plasma display device, etc., includes a plurality of pixel electrodes disposed in a matrix form, counter electrodes facing these pixel electrodes, and a display medium (liquid crystal, plasma, etc.,) sealed between the pixel electrodes and the counter electrodes. The described display device selectively applies a voltage to the pixel electrodes to form a display pattern on a screen. Further, by applying a voltage between the selected pixel electrode and the counter electrode, the brightness of the display medium is optically modulated by the display data to visualize the display pattern.
For the method of driving the pixel electrodes, a so-called active-matrix driving system is known wherein switching elements are connected to respective pixel electrodes disposed in a matrix form and the pixel electrodes are respectively driven by the switching elements. For the switching element, a TFT (thin-film transistor), and an MIM (metal-insulator-metal) element, etc., are generally known. On the other hand, the pixel electrodes are typically formed on the substrate in the same layer as signal lines, scanning lines (bus lines) in such a manner that they do not contact the signal lines or the scanning lines.
Additionally, the technique of forming pixel electrodes on a different layer from the bus lines by disposing the pixel electrodes on an insulting film is proposed (Japanese Laid-Open Patent Application No. 156025/1986 (Tokukaisho 61-156025). In the described arrangement, as the pixel electrodes and the bus lines are formed on different layers, an increased area of the pixel electrodes (aperture ratio) can be achieved.
The liquid crystal display device adopting the matrix-type substrate always faces a problem of a disconnection of wire due to a defect generated in the manufacturing process. In order to suppress the generation of such disconnection defect, the active-matrix type liquid crystal display device which adopts double bus lines has been proposed (SID '95 DIGEST of TECHNICAL PAPERS 4: AMLCDs 4.3; “High-Aperture and Fault-Tolerant Pixel Structure for TFT-LCDs”).
As shown in
FIG. 14
, the described active-matrix type liquid crystal display device is arranged such that two scanning lines
52
and
52
′ are formed for each pixel electrode
5
l, and the scanning lines
52
and
52
′ are short-circuited by short-circuit lines
54
formed along signal lines
53
on both sides of the pixel electrode
51
. The short-circuit lines
54
are superimposed on the pixel electrode
51
via an insulating film (not shown), and an overlapped portion functions as an auxiliary capacitance. In the described arrangement, as a TFT
55
is driven by the two scanning lines
52
and
52
′, even if a disconnection occurred in one of the scanning lines
52
and
52
′, an application of the gate voltage to the TFT
55
can be ensured through the short-circuit lines
54
.
In general, in order to prevent light from leaking through a gap formed between the pixels, a light-shielding pattern is formed on the side of the counter electrodes. In the described arrangement, however, the pixel electrode
51
and the short-circuit lines
54
are superimposed in a direction perpendicular to the substrate. Therefore, the short-circuit lines
54
form a part of the light-shielding pattern.
The arrangement where the pixel electrode and the signal line are superimposed via the insulating film will be explained.
In the arrangement shown in
FIG. 15
, peripheral portions on both sides of the pixel electrodes
51
are superimposed on the scanning lines
52
and the signal lines
53
. As shown also in
FIG. 16
, at a central portion below the pixel electrode
51
, formed is an auxiliary capacitance electrode (hereinafter referred to as Cs electrode)
56
. The Cs electrode
56
is formed on a gate-insulating film
57
used in common with the TFT
55
(see FIG.
15
). The Cs electrode
56
is in contact with a contact portion
51
a
of the pixel electrode
51
.
On a substrate
58
made of glass, formed is an auxiliary capacitance line
59
. The gate insulating film
57
is formed so as to cover the auxiliary capacitance line
59
. On both sides of the Cs electrode
56
on the gate insulating substrate
57
, lower signal lines
60
are formed, and further, signal lines
53
are formed thereon. The lower signal lines
60
and the signal lines
53
are covered with an insulating substrate
61
.
In the described arrangement, as the insulating film
61
is formed between the pixel electrode
51
and the signal lines
53
, an increased area of the pixel electrode
51
can be obtained irrespectively of the disposed positions of the signal lines
53
.
The arrangement shown in
FIG. 17
includes the Cs electrode
56
having the same structure as that of the aforementioned arrangement of
FIG. 15
, except that the Cs electrode
56
is connected to a drain electrode
62
through a connection line
63
. The arrangements shown in
FIG. 15 and
,
FIG. 17
both have the Cs-on-Common structure wherein an auxiliary line capacitance is formed by disposing the Cs electrode
56
on the common auxiliary capacitance line
59
which is used in common among all the pixels.
On the other hand, the arrangement shown in
FIG. 18
has the Cs-on-Gate structure wherein an auxiliary capacitance is formed by disposing the Cs electrode
56
on the scanning line
52
of an adjacent pixel. In this arrangement, the Cs electrode
56
is connected to a contact portion
51
b
of the pixel electrode
51
.
In the arrangement shown in
FIG. 19
, the Cs electrode
56
is connected to the drain electrode
62
through the connection line
63
.
With a demand for higher definition and higher aperture ratio, there is a tendency of reducing the width of the bus line while increasing the number of the bus-line crossing parts, which increases a disconnection of a bus-line or a leakage at a portion where the bus-lines are crossed. Furthermore, such disconnection of bus-line, or the leakage at the crossing point causes a problem that a voltage cannot be applied properly to the pixel electrode connected to the disconnected bus line. Therefore, the portion where the voltage is not applied appears as a line-shaped defect on the display screen. In the display element, such line-shaped defect is a serious problem, and a display device having such line-shaped defect is considered as an inferior good. Further, an increase in such inferior goods would lower the yield of the display device, thereby increasing a manufacturing cost.
Furthermore, when the described arrangement of adopting the double bus line is applied to the general arrangement where the pixel electrode and the bus line are formed in the same layer, as the pixel electrode is formed in the same layer as the bus line, an increased area of the pixel electrode cannot be obtained, thereby hindering an improvement of the aperture ratio. Although a small improvement in aperture ratio can be achieved by reducing an interval between the wires; this would causes the problem that a leakage between the wires is likely to occur.
In the arrangements shown in FIG.
15
through
FIG. 19
, it is permitted to arrange such that the pixel electrode
51
and the data electrodes
53
are superimposed. However, the capacitance between the pixel electrode
51
and the signal line
53
cannot be made smaller due to the insulating film
61
formed therebetween. Therefore, the problem of generating crosstalk due to the capacitance, which would lower the display quality remains unsolved.
SUMMARY
Ban Atsushi
Katayama Mikio
Shimada Takayuki
Ngo Julie
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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