Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-07-09
2001-09-18
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S141000
Reexamination Certificate
active
06292237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active-matrix liquid-crystal display device and a substrate for use in the device and, more particularly, to a structure of storage capacitors in a substrate of an active-matrix liquid-crystal display device having a double-scanning-line feature.
2. Description of the Related Art
Since active-matrix liquid-crystal display devices typically employ a data line for each column of an arrangement of pixels, a number of data drivers is required if the number of pixels per row is large. Since the data driver is relatively costly, the use of a large number of data drivers makes the entire device expensive. Furthermore, in this type of conventional art, a small display area, namely, a small liquid-crystal display panel is difficult to manufacture. The liquid-crystal display panel having a small display area needs a miniaturized terminal section for the data lines. The liquid-crystal display panel in the conventional art having a large number of data lines places a rigorous requirement for a narrow pitch of the data line terminal section. For this reason, the manufacturing of the data line terminal section is difficult, leading to a low production yield.
FIG.
11
and
FIG. 12
show an active-matrix liquid-crystal display device, which is also filed in the Japanese Patent Office by the assignee of the present invention. The active-matrix liquid-crystal display device disclosed employs a smaller number of data lines to drive pixels compared to the other conventional devices.
FIG.
11
and
FIG. 12
show two examples of equivalent circuits of active-matrix liquid-crystal devices having half as many data lines as that in other conventional art devices. Each pixel is surrounded by a one-dot chain line. A data line Dj is shared by two pixels PX(i,j) and PX(i,j+1) (i=1, . . . , m for both pixels) in two columns with the data line Dj interposed therebetween. With this arrangement, the number of data lines is halved, and the number of data drivers is also halved.
As for each row, two adjacent pixels connected to the single data line Dj, for example, PX(i,j) and PX(i,j+1), need to be driven by separate gate lines GAi and GBi. For this reason, the number of gate lines becomes twice as many as that in the conventional art (this wiring method may be called a double-scanning-line method). The increase in the number of gate drivers does not increase the cost of the device, because the gate driver is substantially less costly than the data driver. Referring to FIG.
11
and
FIG. 12
, two adjacent pixels between two adjacent data lines are driven by different gate lines. Referring to
FIG. 11
, all dots on one side of one data line are connected to either GA gate lines or GB gate lines. Referring to
FIG. 12
, dots on one side of one data line are alternately connected to GA gate lines and GB gate lines.
Referring to
FIG. 13
, there is shown an actual structure of the above active-matrix liquid-crystal display device, in which two pixels are surrounded by two data lines and two gate lines. As shown, a thin-film transistor (hereinafter referred to as a TFT)
51
is formed on the top side of a right pixel D
5
, and on the bottom side of a left pixel D
6
. The two pixels D
5
and D
6
are arranged in a point symmetry fashion. With this arrangement, a gate line
52
widens in its portion at the TFT
51
, serving as a gate electrode for the TFT
51
. A semiconductor active layer
53
is formed on the gate electrode. Formed on the semiconductor active layer
53
are a source electrode
55
, extending from a data line
54
, and a drain electrode
56
with a spacing being maintained therebetween. The drain electrode
56
is electrically connected to a pixel electrode
58
via a contact hole
57
.
In the active-matrix liquid-crystal display device, each pixel needs a storage capacitor to hold a signal supplied thereto for one scanning period. The gate line
52
is greatly increased in width on the side of each pixel opposite to the TFT
51
, and a capacitor electrode
60
, which is electrically connected to the pixel electrode
58
via a contact hole
59
, is overlapped on a wide portion
52
a
of the gate line
52
. A storage capacitor
61
is formed of the capacitor electrode
60
, the wide portion
52
a
of the gate line
52
, and an insulating layer interposed between the capacitor electrode
60
and the wide portion
52
a
. A rectangular shape
62
represented by a one-dot chain line in
FIG. 13
shows an aperture of a black matrix formed on a counter substrate (not shown).
To achieve a desired storage capacitance in the active-matrix liquid-crystal display apparatus, the capacitor electrode
60
needs to be a sufficient area. For this reason, part of the gate line
52
is widened. The wide portion
52
a
of the gate line
52
for forming the storage capacitor
61
causes a narrow portion
52
b
in the gate line
52
at the adjacent pixel. The narrow portion
52
b
, shown in
FIG. 13
, does not overlapped with another electrode, and does not contribute to the storage capacitance. The wide portion
52
a
thus needs to compensate for the effect of the narrow portion. As seen from the area of the aperture
62
of the black matrix represented by the one-dot chain line in
FIG. 13
, the wide portion
52
a
of the gate line
52
reduces the aperture ratio of the panel.
In the gate line
52
, the narrow portion
52
b
is much narrower than the wide portion
52
a
, increasing wiring resistance.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a substrate for a double-scanning-line type active-matrix liquid-crystal display device in which each pixel has its own storage capacitor, wherein a substrate is free from problems such as a reduction in the aperture ratio and an increase in gate wiring resistance. It is also an object of the present invention to provide an active-matrix liquid-crystal display device that incorporates the substrate.
To achieve the above object, in the substrate for an active-matrix liquid crystal display device of the present invention, a plurality of data lines and a plurality of gate lines are arranged in a matrix on a substrate. Thin-film transistors having pixel electrodes connected thereto are arranged on both sides of each data line corresponding to the respective gate line. The plurality of gate lines are arranged so that the pixel electrodes on both sides of each data line are controlled by signals from corresponding paired gate lines sandwiching the pixel electrodes arranged on both sides of the data line. A storage capacitor, corresponding to each of adjacent pixel electrodes between adjacent data lines, is extended from one of the pixel electrodes to the other adjacent pixel electrode on the other gate line paired with the one controlling gate line, in order to have a desired capacitance.
The basic concept in the conventional substrate for the active-matrix liquid-crystal display device is that the storage capacitor arranged in each pixel has to be formed within the region of each pixel. A wide portion having a large area is thus required in the gate line to achieve a desired capacitance. This arrangement reduces the aperture ratio and increases the gate wiring resistance.
The feature of the present invention is that the region of the storage capacitor of one pixel extends between the adjacent data lines to the other adjacent pixel, rather than being limited to within the region of one pixel. With this arrangement, the gate line is efficiently taken advantage of for the storage capacitor, the wide portion of the gate line in the conventional art is dispensed with, and the aperture ratio is improved. Further, the gate wiring resistance is minimized because the narrow portion of the gate line is also dispensed with.
In accordance with the present invention, the storage capacitor is formed in a given pixel, in which a gate line for controlling the pixel and an opposing gate line are each provided with a wide portion and a modestly narro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Dudek James A.
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