Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-11-30
2003-08-19
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S040000, C349S041000, C349S051000, C349S192000, C345S093000
Reexamination Certificate
active
06608655
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and particularly relates to a liquid crystal display device which provides a display by a matrix driving system.
BACKGROUND OF THE INVENTION
In recent years, a liquid crystal display device has been widely used for providing a display of a personal computer, a word processor, a terminal display device for office automation, and a television and others thanks to its low power consumption, thin structure, and light weight. Accordingly, a display with a larger capacity and higher picture quality has been demanded.
A conventional liquid crystal display device has performed a simple-matrix driving in accordance with a voltage averaging method of the STN (Super Twisted Nematic) system. However, since a sufficient contrast ratio cannot be obtained due to the increase of scanning lines, this method is not suitable for a display with a large capacity. Therefore, an active-matrix driving has been developed to provide a switching element on each of the pixels constituting a display screen.
As the aforementioned switching element, a thin-film transistor and a two-terminal nonlinear element are used, and the liquid crystal display device with the two-terminal nonlinear element has been highly evaluated because of the simple construction and low manufacturing cost. A device having a structure of metal-insulator-metal (hereinafter, referred to as MIM) has been put into practical use. For example, a conventional MIM element is produced as follows:
Firstly, as shown in
FIGS. 19 and 20
, on a glass substrate
51
, a tantalum thin-film, which is formed to be a signal wire
52
and a lower electrode
53
, is laminated with a thickness of 3000 Å in accordance with a sputtering method, etc., and is patterned into a predetermined form so as to obtain the signal wire
52
and the lower electrode
53
by a photolithography method. Thereafter, in accordance with an anodic oxidation method, an anodic oxidation is performed on the surface of the lower electrode
53
so that an insulating film
54
is formed with a thickness of 600 Å.
And then, in this state, titanium formed to be an upper electrode
55
is laminated on the entire area of the substrate with a thickness of 4000 Å by the sputtering method, etc., and is patterned into a predetermined form by the photolithography method so as to be formed as the upper electrode
55
.
Further, a transparent electrode film which is made of ITO and others is laminated on the substrate, and the substrate is subjected to patterning so as to form a pixel electrode
56
.
FIG. 21
illustrates an arrangement pattern of pixels composed of MIM elements and pixel electrodes
56
, said MIM elements and pixel electrodes
56
being formed in accordance with the aforementioned process.
As described in
FIG. 21
, in the liquid crystal display device which uses the matrix driving system, a parasitic capacity appears in each pixel due to the effects of neighboring pixels and wires. Further, in addition to the case of the aforementioned liquid crystal display device which uses a two-terminal element such as an MIM element and others, the parasitic capacity appears to some extent even in the case of a liquid crystal display device using other active elements or in the case of a liquid crystal display device using the simple-matrix driving system. Especially, in the case of the liquid crystal display device which uses the two-terminal elements, the effect of the parasitic capacity becomes the greatest.
That is, in the case of the liquid crystal display device using the two-terminal element as a switching element, when an element capacity varies in accordance with a change in element dimensions and others of the two-terminal element, a threshold voltage V
th
varies accordingly; therefore, a lighting condition differs between pixels. Consequently, with regard to all pixels, it is significant to obtain uniform capacity ratios of a pixel capacity and the element capacity. The pixel capacity is a capacity of the pixel electrode
56
, and the element capacity is a capacity of the MIM element. Here, the parasitic capacity greatly influences the capacity ratio.
The specific explanation will be given in accordance with FIG.
21
. Based upon one pixel (sample pixel) among a plurality of pixels which are arranged in a matrix form, signal wires
52
a
and
52
b
, which are respectively disposed on the left and right of the sample pixel, add respectively parasitic capacities C
1
and C
2
to a pixel electrode
56
a
of the sample pixel. Further, a pixel electrode
56
b
of a pixel which exists above the sample pixel adds a parasitic capacity C
3
, and a pixel electrode
56
c
of a pixel which exists below the sample pixel adds a parasitic capacity C
4
.
The parasitic capacities C
1
through C
4
are added to the pixel capacity of the pixel electrode
56
a
, thereby having an effect on the capacity ratio of the pixel capacity and the element capacity. Namely, with regard to the respective pixels, even if element dimensions of the two-terminal element are arranged so as to be uniform in order to keep the element capacity at a certain amount, the capacity ratio of the pixel capacity and the element capacity varies in accordance with a change in the parasitic capacity.
However, in the conventional arrangement, as shown in
FIG. 22
, pixel electrodes
56
d
, which exist on the right end, do not have the signal wire
52
on its right; therefore, the parasitic capacity C
2
is not added. Further, pixel electrodes
56
e
, which exist on the upper end or the lower end, do not have the pixel electrodes
56
above or below; thus, the parasitic capacity C
3
or C
4
is not added. Moreover, in the case of pixel electrodes
56
f
, which exist on the upper right corner or the lower right corner, parasitic capacities C
2
and C
3
are not added, or parasitic capacities C
2
and C
4
are not added.
Hence, with regard to the liquid crystal display device which uses the aforementioned MIM element, each of the parasitic capacities which are applied to the pixel electrodes
56
d
,
56
e
or
56
f
is smaller than the parasitic capacity which is applied to the pixel
56
a
, illustrated in FIG.
21
. Consequently, since a lighting condition differs between pixels, it becomes impossible to provide an even lighting display.
Namely, as illustrated in
FIG. 22
, with regard to pixels which exist on the upper end, lower end, and on the right end (pixels indicated by slanting lines in FIG.
22
), the threshold voltage V
th
becomes lower, resulting in an uneven display. Therefore, for example, in the case of a gradation display, this arrangement causes adverse effects.
SUMMARY OF THE INVENTION
With regard to a liquid crystal display device with the matrix driving system, the objective of the present invention is to provide a liquid crystal display device which is capable of reducing the influence caused by a difference in parasitic capacity so as to provide an even display.
In order to achieve the aforementioned objective, the liquid crystal display device of the present invention, in which a plurality of pixels forming a display screen are arranged in a matrix form and all pixels forming each pixel line are connected with a signal wire for each of the pixel lines, is provided with a first dummy wire which is formed on the outside of the final pixel line with no neighboring signal wire other than a signal wire being connected with the final pixel line, and which applies to the pixel electrodes of the final pixel line the same amount of parasitic capacity as a between-line parasitic capacity which is applied from a neighboring signal wire, wherein the first dummy wire is electrically connected with the neighboring signal wire.
With the aforementioned liquid crystal display device, the first dummy wire applies to the pixel electrodes of the final pixel line the same amount of parasitic capacity as the between-line parasitic capacity which is applied from the neighboring signal wire. Therefore, with regard to pixel
Fujikawa Yohsuke
Matoba Masakazu
Chowdhury Tarifur R.
Sharp Kabushiki Kaisha
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