Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-06-01
2003-12-16
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S039000, C349S141000, C349S143000
Reexamination Certificate
active
06665023
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, more particularly to a technology for improving a display quality of an active matrix display device. The technology employed in this invention is preferred in applying especially to the active matrix display device in which signal wires and common electrode of a display panel are formed in different layers from each other and whose display part is manufactured through divisional light-exposing.
DESCRIPTION OF THE RELATED ART
In a liquid crystal display device, images are displayed by applying an electric field to a liquid crystal material. As a method of applying the electric field, there is a static driving method by which a constant voltage signal is constantly applied to each electrode of a display panel. However, this method requires an enormous number of signal wires if a display is large in size. As a result, multiplex driving methods in which the signal voltage is applied by time-sharing are employed in this case. Among the multiplex driving methods, an active matrix method provides a high display quality since an electric charge given to the electrode can be retained until next frame.
Concerning the direction of the electric field to be applied to a liquid crystal material, the method is classified into two modes, i.e., one mode for applying the electric field perpendicular to glass substrates sandwiching the liquid crystal material, and the other mode for applying the electric field in parallel to the substrates (In-plane Switching which is often abbreviated as “IPS”). The In-Plane Switching mode is appropriate for use in a large scale monitoring since it can realize a wide field of view in terms of angle.
FIG. 5
shows an electrode structure concerning the pixel of a liquid crystal display device to which the In-Plane Switching mode is applied for driving, e.g., refer to the disclosure of Japanese Patent Kokoku Publication JP-B-63-21907/1988. This reference discloses a liquid crystal display device having a display panel equipped with a pair of substrates. One of the substrates has display electrodes (pixel electrodes) and reference electrodes (common electrodes) thereon, both electrode being formed as comb-shaped electrodes intermeshing each other. The liquid crystal display device is driven by applying an electric field having a component in parallel to the substrate surface of the panel.
Now, the structure of a conventional liquid crystal display device will be explained.
FIG. 6
is a plan view showing the whole structure of a liquid crystal display panel
501
. Referring to
FIG. 6
, display parts
504
are connected to leading wires
503
. The leading wires
503
are connected to connection terminals
502
, respectively. Divisional positions illustrated in
FIG. 6
by vertical and horizontal broken lines correspond ideally to the dividing positions between the display parts produced through divided exposure of light within an entire plane.
Namely, the display parts of a liquid crystal display device employing the IPS mode for driving the liquid crystal are prepared by patterning through the divisional light-exposing. The divisional light-exposing in this manner can take the following advantages:
1. Photomasks are of a low price; and
2. A display panel of a large size can be produced. Because the light-exposing area of one shot is limited
FIG. 5
is an enlarged fragmentary plan view showing the vicinity of the divisional positions illustrated in FIG.
6
. In a constitutional example illustrated in
FIG. 5
, the divisional position is at the center of a signal wire
111
or of a scanning wire
101
. Setting the divisional line on the center of a signal wire
111
or of a scanning wire
101
in this manner is mainly due to the following advantages:
1. good symmetry;
2. easy design of patterns; etc.
A pixel for display includes scanning wire
101
, signal wire
111
and common electrode wire
102
, which are connected to an outside driving circuit. The display pixel further includes a switching element of a TFT (Thin Film Transistor)
131
and comb-shaped pixel electrode
112
.
FIG. 7
is a cross sectional view taken along line a-a′ of FIG.
5
. Referring to
FIG. 7
, the common electrode wires
102
are formed on a glass substrate
113
of the TFT side, and the pixel electrodes
112
as well as the signal wires
111
are formed thereon through an intermediary of an interlaminar insulating film
105
. The pixel electrodes
112
and the common electrode wires
102
are arranged alternatingly in parallel. These electrodes are covered with a protective insulating film
106
, on which an orientation film
107
for orientating liquid crystal
301
is coated. Then, the top: of the orientation film
107
is treated by rubbing to complete a substrate
114
of the TFT side.
On a glass substrate
203
of a color filter (abbreviated as “CF”) side, a black matrix
201
and color layer
202
for color display are formed in this order. Further, on the color layer
202
, leveling film
207
for leveling the top of the substrate
203
, and orientation film
207
for orientating the liquid crystal
301
are provided in this order. The top of the orientation film
207
is then treated by rubbing in a direction reversed of the rubbing direction of the orientation film
107
of the TFT side.
Thus, a substrate
208
of the color filter side is completed.
Then, the liquid crystal
301
and spacer
302
(e.g., spherical particles) are encapsulated in between both of the substrates
114
and
208
. The gap therebetween is determined by a particulate diameter of the spacer
302
.
Finally, a polarizing plate
110
of the TFT side is adhered to the surface of the TFT side glass substrate
113
on which no electrode pattern is formed; and a polarizing plate
205
of the CF side., to the surface of the glass substrate
203
on which no pattern is formed. In this process, the polarizing plate
110
is arranged to make a light-transmitting direction (axis) therethrough perpendicular to the rubbing direction of the orientation film
107
. The CF side polarizing plate
205
is arranged to make a light-transmitting direction therethrough perpendicular to that of the TFT side polarizing plate
110
. A liquid crystal display panel is completed through the above steps.
In the course of forming a pattern of a layered form on the glass substrate
113
of the TFT side, light is exposed area by area to all of the spots (ideally) divided by the divisional positions shown in FIG.
5
. Hereinafter, a layer in which common electrode wires
102
and scanning wires
101
are to be formed or formed may be referred as “G layer”; a layer in which signal wires
111
and pixel electrodes
112
are to be formed or formed, to “D layer”.
Function of the conventional liquid crystal display will be explained as follows.
Referring to
FIG. 6
, signal voltages applied to connection terminals
502
are input correspondingly through leading wires
503
into scanning wires
101
, signal wires
111
and common electrode wires
102
, as illustrated in FIG.
5
.
When a signal of “ON voltage” is input through a scanning wire
101
, electric charge flows from a signal wire
111
into a pixel electrode
112
through a TFT
131
FIG. 8
shows a time chart of electric potentials applied to the scanning wire
101
, signal wire
111
or common electrode wire
102
, respectively.
When a potential difference is produced between scanning wire
101
, common electrode wire
102
and pixel electrode
112
, a lateral,electric field is applied to the liquid crystal layer in parallel to the substrates corresponding to the potential difference. As a result, liquid crystal molecules are turned to be parallel to the substrates. Then, light transmittance is changed correspondingly in the area between the neighboring parallel extending wires, e.g., between the common electrode wire
102
and the pixel electrode
112
.
FIG. 9
shows the qualitative relation of potential difference and light transmittance in between common electrode wire and pixel electrode
Watanabe Makoto
Watanabe Takahiko
Katten Muchin Zavis & Rosenman
Kim Robert H.
NEC LCD Technologies Ltd.
Qi Mike
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