Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-10-12
2004-08-24
Chaudharl, Chandra (Department: 2813)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S038000, C349S042000
Reexamination Certificate
active
06781659
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an active-matrix liquid crystal display device, a repair method thereof and drive method thereof, and in particular relates to an active-matrix liquid crystal display device of the transverse electric field type, a repair method thereof, and a drive method thereof.
BACKGROUND ART
Recently, together with advancements in personal computers, the trend has been for an increase in the demand for liquid crystal display devices, particularly for active-matrix liquid crystal display devices. Moreover, this trend is not limited to personal computers, and the demand for liquid crystal television (hereafter abbreviated as liquid crystal TV) is also on the rise.
One of the properties demanded of liquid crystal TVs is a broad viewing angle. A variety of different types of liquid crystal display devices have been developed in order to achieve a broad viewing angle. Among those, particular interest has been given to active-matrix liquid crystal display devices of the transverse electric field type (IPS (In-Plane Switching) mode).
Generally, in active-matrix liquid crystal display devices, a liquid crystal is injected between two glass substrates, with one of the glass substrates being provided with a plurality of signal line (data line) groups and a plurality of scanning line (gate line) groups that intersect to form a matrix. Furthermore, thin film transistors (TFTs) are disposed at each portion where the signal lines and scanning lines intersect.
In the case of active-matrix liquid crystal display devices of the transverse electric field type, pixel electrodes for controlling the arrangement of the liquid crystal at each pixel, and opposing electrodes forming a pair with the pixel electrodes, are further provided on the same substrate.
When displaying an image, the scanning lines are scanned, and the thin film transistors at the intersecting portions are turned on. When a thin film transistor is turned on, the signal potential inputted in the signed line is written onto the pixel electrode. When this happens, an electric potential difference is applied between the pixel electrode and the opposing electrode, and an electric field (transverse electric field) parallel to the substrate surface is created, and thus the liquid crystal changes from an initial alignment to a new alignment. Therefore, the amount of light that passes through the liquid crystal layer can be adjusted. That is, the polarization of light passing through the liquid crystal changes according to the applied signal voltage, and depending on that polarization, a light or dark pixel is displayed on the display screen.
In active-matrix liquid crystal display devices of the transverse electric field type, the liquid crystal molecules are always in a state parallel to the substrate, so that compared to conventional liquid crystal display panels, in which the pixel electrodes and the opposing electrodes are disposed perpendicular to the panel, the contrast does not easily change even if the panel is viewed from an oblique angle, and thus viewing angle properties can be considerably improved.
Conventional active-matrix liquid crystal display devices of the transverse electric field type are described in further detail below. FIG.
21
(
a
) is a plan view illustrating the arrangement of the electrodes, wiring, and the like in a single pixel in a liquid crystal display panel provided in a conventional active-matrix liquid crystal display device of the transverse electric field type, and FIG.
21
(
b
) is a cross-sectional view of that liquid crystal display device. Also, FIG.
22
(
a
) is a plan view illustrating the arrangement of the electrodes, wiring and the like in a single pixel in a liquid crystal display panel provided in another conventional active-matrix liquid crystal display device of the transverse electric field type, and FIG.
22
(
b
) is a cross-sectional view of that liquid crystal display device.
As shown in FIGS.
21
(
a
) and (
b
), the liquid crystal display panel has an array substrate
1001
and an opposing substrate
1002
both made of the glass substrates and disposed in opposition to one another, and a liquid crystal layer
1003
provided between the two. Formed on the surface of the array substrate
1001
is a plurality of scanning lines
1004
having a fixed spacing between one another, a plurality of signal lines
1005
that intersect with the scanning lines
1004
, pixel electrodes
1006
provided at each pixel, opposing electrodes
1007
forming a pair with the pixel electrodes
1006
, and TFTs
1008
that function as switching elements between the pixel electrodes
1006
and the signal wires
1006
. Furthermore, the opposing electrodes
1007
are disposed parallel to the scanning lines
1004
. Also, a transparent insulating layer
1009
is formed on the array substrate
1001
such that it covers the scanning lines
1004
and the opposing electrodes
1007
. The pixel electrodes
1006
are made of a plurality of pixel electrode portions
1006
a
and linking portions
1006
b
for linking the plurality of pixel electrode portions
1006
a
. The linking portions
1006
b
are provided on the scanning lines
1004
. Additionally, the opposing electrodes
1007
are made up of a plurality of opposing electrode portions
1007
a
and an opposing electrode wire
1007
b
for linking the plurality of opposing electrode portions
1007
a
. Furthermore, storage capacity portions
1015
are provided on the portions where the scanning lines
1004
and the linking portions
1006
b
overlap.
More specifically, the TFTs
1008
are provided on the array substrate
1001
and include a gate electrode
1010
, a silicon layer
1011
, which is selectively provided on the insulating layer
1009
, a source electrode
1012
, and a drain electrode
1013
.
The source electrodes
1012
are connected to the signal wires
1005
, and the drain electrodes
1013
are connected to the pixel electrodes
1006
. The pixel electrode portions
1006
a
and the opposing electrode portions
1007
a
are arranged in alternation. Thus, an electric field substantially parallel to the array substrate
1001
is generated between the pixel electrode portions
1006
a
and the opposing electrode portions
1007
a
, and the alignment of the liquid crystal molecules is controlled at each pixel.
Also, an alignment film
1014
for aligning the liquid crystal is formed on the array substrate
1001
so that it covers the scanning lines
1004
, the signal lines
1005
, the pixel electrodes
1006
, the opposing electrodes
1007
, and the TFTs
1008
.
On the other hand, the opposing substrate
1002
is made of a glass substrate, the inner surface side of which is provided with a color filter (not shown in the drawings). Furthermore, an alignment film
1014
is also formed so as to cover this color filter. The alignment films
1014
and
1014
are made of polyimide, the surface of which has been processed by rubbing. The rubbing process is performed by rubbing a surface with a roller coated with a fabric such as rayon.
Additionally, polarizers (not shown in the drawings) are provided on the outer sides of the array substrate
1001
and the opposing substrate
1002
. The two polarizers are disposed such that their respective polarizing axes are in cross nicol arrangement. Note that in the scenario described above, the linking portions
1006
b
are provided above the scanning lines
1004
in the pixel electrodes
1006
, but as shown in
FIG. 22
, it is also possible to provide the linking portions
1006
b
above the opposing electrode wiring
1007
b
in the opposing electrodes
1007
. In that configuration, storage capacity portions
1016
are provided between the linking portions
1006
b
and the opposing electrode wire
1007
b.
As described earlier, in conventional IPS mode liquid crystal display devices, the insulating layer
1009
, which is made of silicon nitride, is provided between the layer of pixel electrodes
1006
and the layer of the opposing electrodes
1007
, so that both layers are insulated from each other
Hotta Sadayoshi
Kumagawa Katsuhiko
Shiota Akinori
Takubo Yoneharu
Yamakita Hiroyuki
Chaudharl Chandra
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Pham Thanhha
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