Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-06-11
2002-10-29
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C349S110000, C349S111000
Reexamination Certificate
active
06473067
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active matrix type liquid crystal device including active elements located at respective pixels (also called picture elements) thereby controlling the voltage applied to the liquid crystal at the respective pixels, and more particularly, to a liquid crystal device of the type in which a voltage is applied in a lateral direction (along the layer) to the liquid crystal at the respective pixels.
The present invention also relates to electronic equipment using such a liquid crystal device.
BACKGROUND TECHNOLOGY
The great majority of liquid crystal devices used in notebook personal computers or liquid crystal TV sets are operated in the twisted nematic mode. However, in the twisted nematic mode, the image displayed on a liquid crystal device looks different depending on the viewing direction. To improve the viewing direction dependence, it has been proposed to employ an in-plane switching (IPS) mode in which a voltage is applied to a liquid crystal in a lateral direction, as disclosed for example in Japanese Unexamined Patent Publication Nos. 56-091277 and 6-160878.
The principle of operation in the IPS mode will be described briefly with reference to some drawings.
FIGS. 4
a
and
4
b
are cross-sectional views illustrating the behavior of a liquid crystal in a liquid crystal panel designed to operate in the IPS mode, wherein
FIG. 4
a
is a cross-sectional view of a cell without an application of voltage and
FIG. 4
b
is a cross-sectional view of the cell under the application of a voltage greater than a threshold value. The plane views of
FIGS. 4
a
and
4
b
are given in
FIGS. 4
c
and
4
d
, respectively. In
FIG. 4
, reference numerals
401
and
409
denote a pair of polarizing plates,
402
and
408
denote a pair of substrates between which a liquid crystal is disposed,
403
denotes a color filter,
404
and
406
denote orientating films, and
405
denotes a liquid crystal molecule drawn in a schematic fashion. Furthermore, reference numeral
410
denotes a pixel electrode,
411
denotes a common electrode disposed in a pixel at a location opposite to the pixel electrode,
412
denotes an image signal line (source line), and
407
denotes an insulating layer for isolating the pixel electrode
410
and the common electrode
411
from each other. In the IPS-mode liquid crystal device, as can be seen from
FIG. 4
, the pixel electrode and the common electrode for applying a voltage across the liquid crystal are disposed on one substrate at locations apart in a lateral direction. Reference numeral
413
denotes the absorption axis of the lower polarizing plate and
414
denotes the absorption axis of the upper polarizing plate.
Although an active element such as a TFT (thin film transistor) is also disposed, it is not shown in FIG.
4
.
FIGS. 4
a
and
4
b
are a cross section taken along line X-X′ of
FIG. 5
, and
FIGS. 4
c
and
4
d
are an enlarged plane view illustrating an area surrounded by a broken line in
FIG. 5
, wherein
FIG. 5
illustrates the structure of one pixel. In the specific example shown in
FIG. 5
, two common electrodes
502
and one pixel electrode
501
are disposed in a lateral direction in one pixel, whereas there may be some other number of common electrodes
502
and pixel electrodes
501
in one pixel. Furthermore, in
FIG. 5
, reference numeral
503
denotes a scanning signal line (gate line),
504
denotes an image signal line (source line), and
505
denotes a thin film transistor(TFT).
Of the pair of substrates
402
and
408
, as shown in
FIGS. 4
a
and
4
c
, a color filter
403
is formed on the upper substrate
402
, and a line-shaped common electrode
411
and pixel electrode
410
are formed on the inner surface of the lower substrate
408
. Furthermore, orientating films
404
and
406
for orientating the liquid crystal molecules
405
are formed on the inner surfaces of the respective substrates. A liquid crystal is disposed between the pair of substrates
402
and
408
. When no voltage is applied, the liquid crystal molecules
405
are uniformly orientated at a fixed angle (within the range from 0 to 45) with respect to the longitudinal direction of the line-shaped electrodes (common electrode
411
, pixel electrode
410
). In the specific example shown in
FIG. 4
, the angle is set to 30°. On both sides of the liquid cell, there are disposed polarizing plates
401
and
409
. The upper polarizing plate
401
is disposed such that its absorption axis
414
becomes parallel to the orientation of the liquid crystal. On the other hand, the lower polarizing plate
409
is disposed such that its absorption axis
414
becomes perpendicular to the orientation of the liquid crystal. In this state, black is displayed in the pixel. The liquid crystal is made up of a material having positive dielectric anisotropy.
If an electric field
415
is applied, the liquid crystal molecules
405
are aligned so that their longitudinal axis is directed in a direction parallel to the electric field
415
, as shown in
FIGS. 4
b
and
4
d
. As a result, the orientation of the liquid crystal molecules
405
come to have a certain angle with respect to the absorption axis of the polarizing plates. The birefringence of the liquid crystal varies in accordance with the orientation angle of liquid crystal molecules which varies in response to the strength of the applied electric field. Thus, it is possible to control the transmission of light through the pair of polarizing plates thereby controlling the brightness.
In this structure, however, the pixel electrode
410
and the common electrode
411
used to apply a voltage across the liquid crystal are formed on only one substrate and there is no electrode on the other-side substrate. This can cause a problem in that the substrate tends to be electrostatically charged. The electrostatic charge disturbs the orientation of the liquid crystal and thus it becomes impossible to display a high-quality image. Once the substrate is electrostatically charged, it is difficult to remove the electrostatic charge because there is no electrode on the other-side substrate.
In view of the above, it is an object of the present invention to provide a liquid crystal device capable of displaying a high-quality image without being electrostatically charged or without being influenced by an electrostatic charge.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a liquid crystal device including a pair of substrates with a liquid crystal disposed between them, one of the substrates having, thereon, scanning signal lines and image signal lines disposed in a matrix form, active elements connected to the respective scanning signal lines and image signal lines, a pixel electrode connected to the respective active elements, and a common electrode, thereby making it possible to apply an electric field across the liquid crystal disposed between each pixel electrode and the common electrode in such a manner that the electric field is applied in a direction substantially parallel to the plane of the substrates, wherein a light-shielding metal film is formed on the other-side substrate opposite to the one of the substrate, and a fixed voltage is applied to the light-shielding metal film.
In this structure, the other-side substrate is prevented from being electrostatically charged and thus it is possible to display a high-quality image. If there were no light-shielding metal film disposed on the other-side substrate and maintained at the fixed voltage, the substrate would be electrostatically charged, and as high a voltage as a few ten thousand volts would occur between the other-side substrate and the pixel electrodes and/or the common electrode formed on the one substrate. The liquid crystal would response to that voltage. For the above reason, to achieve a high-quality image, it is important that the light-shielding metal film be formed on the other-side substrate having no electrode for driving the liquid crystal and be maintai
Oliff & Berridg,e PLC
Said Mansour M.
Seiko Epson Corporation
Shalwala Bipin
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