Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-03-22
2004-09-14
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
Reexamination Certificate
active
06791633
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and a method for manufacturing the LCD and more particularly to the LCD made up of unit pixels each having two driving elements driven by a same scanning line and two pixel electrodes to one of which a pixel voltage fed from one of two data lines is applied through one of the driving elements and to the other of which a pixel voltage fed from the other of the two data lines being opposite in polarity to the pixel voltage fed from the former of the two data lines is applied through the other of the driving elements and the method for manufacturing the above LCD.
The present application claims priority of Japanese Patent Application No.2001-085545 filed on Mar. 23, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
An LCD is widely used as a display for various information devices. The LCD is basically so configured that a liquid crystal is put in a hermetically sealed manner between a TFT (Thin Film Transistor) substrate (driving element substrate) on which a TFT is formed serving as a switching element (driving element) used to do ON/OFF switching for selection of each of unit pixels to provide a display on a screen and a facing substrate and that a plurality of unit pixels is arranged in a matrix form. Such the LCD is roughly classified, according to a difference in its display method, into a TN (Twisted Nematic)-type LCD and an IPS (In-Plane Switching)-type LCD.
In the TN-type LCD, a pixel voltage is applied to a pixel electrode formed on a TFT substrate and a common voltage is applied to a common electrode formed on a facing substrate and, by a difference between the pixel voltage and the common voltage, a longitudinal electric field is generated in a direction orthogonal to surfaces of both the TFT substrate and the facing substrate to drive a liquid crystal.
On the other hand, in the IPS-type LCD, both a pixel electrode and a common electrode are formed on a TFT substrate being one of two substrates in such a manner that both the pixel electrode and the common electrode are insulated from each other by an interlayer insulating film and, by a difference in voltages between the pixel electrode and the common electrode, a transverse electric field is generated in a direction horizontal to surfaces of both the pixel electrode and the common electrodes to drive a liquid crystal.
When the LCD is driven by the method described above, the IPS-type LCD in particular, has an advantage in that, since a longitudinal axis of its liquid crystal molecule is arranged in a horizontal direction along the surfaces of both the TFT substrate and facing substrate, a change in brightness is made small even by a change of viewing direction when the LCD is observed and it can provide a wide viewing angle. Therefore, in recent years, there is a tendency that the IPS-type LCD is preferably used.
FIG. 35
is a plan view showing configurations of a conventional IPS-type LCD.
FIG. 36
is a cross-sectional view of
FIG. 35
taken along a line L—L. In
FIGS. 35 and 36
, configurations of one unit pixel
100
only are shown. As shown in
FIGS. 35 and 36
, a liquid crystal
103
is put in a hermetically sealed manner between a TFT substrate
101
and a facing substrate
102
. The TFT substrate
101
includes a first transparent substrate
106
made of glass or a like, a first polarizer
107
formed on a rear of the first transparent substrate
106
, a scanning line (gate bus line)
108
formed on apart of a surface of the first transparent substrate
106
, common electrodes
109
formed on an other part of the surface of the first transparent substrate
106
, an interlayer insulating film
110
serving as a gate insulating film formed in a manner so as to cover the scanning line
108
and the common electrodes
109
, a semiconductor layer
113
formed on the scanning line
108
with the interlayer insulating film
110
being interposed between the semiconductor layer
113
and the scanning line
108
, a drain electrode
116
and a source electrode
117
each being connected to the semiconductor layer
113
, pixel electrodes
121
and data lines
122
formed on the interlayer insulating film
110
being integrated into the drain electrode
116
and the source electrode
117
, a passivation film
125
formed in a manner so as to cover the pixel electrodes
121
and the data lines
122
, and a first oriented film
127
formed in a manner so as to cover the pixel electrodes
121
and the data lines
122
with the passivation film
125
being interposed between the first oriented film
127
and the pixel electrodes
121
and the data lines
122
. Here, the scanning line
108
, semiconductor layer
113
, drain electrode
116
and source electrode
117
make up a TFT
129
.
On the other hand, the facing substrate
102
includes a second transparent substrate
131
made of glass or a like, a second polarizer
133
formed on a rear of the second transparent substrate
131
with a conductive layer
132
, for prevention against static electricity, being interposed between the second transparent substrate
131
and the second polarizer
133
, a black matrix layer
134
formed on a surface of the second transparent substrate
131
, a colored layer
135
serving as a color filter formed in a manner so as to cover the black matrix layer
134
, a planarized film
136
formed in a manner so as to cover the black matrix layer
134
and the colored layer
135
, and a second oriented film
137
formed on the planarized film
136
. The arrow line
139
shows an oriented direction of the liquid crystal
103
.
In order to drive the conventional LCD as described, a voltage having a different polarity by every period is cyclically applied to pixel electrodes
121
making up a unit pixel
100
, with an aim to increase a life of a liquid crystal
103
. That is, a pixel voltage Ve having a different polarity by every period as shown in
FIG. 37
is fed to the pixel electrodes
121
through the TFT
129
from the data lines
122
. In
FIG. 37
, a common voltage Vc is applied to the common electrodes
109
and the liquid crystal
103
is driven by voltage differences Vd1 and Vd2 between the pixel voltage Ve and the common voltage Vc with timing when a scanning voltage (not shown) is fed and the liquid crystal
103
holds an electric charge corresponding to each of the voltages for driving the described above.
To drive the liquid crystal
103
by cyclically feeding the pixel voltages Ve each having a different polarity by each period to the pixel electrodes
121
, three methods described below are mainly employed. A first method is called a “one-horizontal-reverse driving method” in which, to switch image data making up an image in a display, a polarity of the unit pixel
100
is reversed from a positive side to a negative side and vice versa for every one horizontal line of unit pixels
100
, as shown in
FIG. 38A. A
second method is called an“one-vertical-reverse driving method” in which, to switch the image data, the polarity of the unit pixel
100
is reversed from a positive side to a negative side and vice versa for every one vertical line of unit pixels
100
as shown in
FIG. 38B. A
third method is called a “dot-reverse driving method” in which, to switch the image data, a polarity of the unit pixel
100
is reversed from a positive side to a negative side and vice versa for every dot in such a manner that unit pixels
100
are displayed checkerwise as shown in FIG.
38
C.
FIG. 39
is a diagram showing a driving circuit employed in the conventional LCD and
FIG. 40
is an expanded diagram showing a terminal section A shown in
FIG. 39 and a
terminal section B shown in FIG.
39
. As shown in
FIG. 39
, a scanning line driving circuit
151
is connected to a scanning line
108
making up the unit pixels
100
being arranged in a matrix form and a scanning line signal is fed to each of the unit pixels
100
through the scanning line
108
, while a data line driving circuit
152
Akkapeddi Prasad R.
Foley and Lardner LLP
Kim Robert H.
NEC LCD Technologies Ltd.
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