Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-13
2003-06-03
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C257S059000, C257S347000, C349S106000, C349S110000, C349S042000
Reexamination Certificate
active
06573969
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid crystal display unit and, more particularly, to an active matrix liquid crystal display unit with spacers inserted between two substrate structures.
DESCRIPTION OF THE, RELATED ART
A typical example of the liquid crystal display is shown in FIG.
1
. The prior art liquid crystal display unit is classified in an active matrix type with inverted stagger type thin film transistors. The prior art liquid crystal display comprises substrate structures, spacers
129
and liquid crystal
130
. The spacers
129
are formed of transparent synthetic resin, and are like spherical beads. The spacers
129
are scattered over either substrate structure before the substrate structures are assembled. When the substrate structures are assembled, the spacers
129
create a gap between the two substrate structures, and the gap is filled with liquid crystal
130
.
The lower substrate structure includes a glass substrate
101
, scanning lines
102
, thin film switching transistors
110
, pixel electrodes
107
and an orientation layer
108
. The thin film switching transistor
110
includes a part of the scanning line serving as a gate electrode, a gate insulating layer
103
, a semi-conductor layer
104
, a drain electrode
105
and a source electrode
106
. The scanning lines
102
are patterned on the glass substrate
101
, and are covered with the gate insulating layer. The semiconductor layers
104
are patterned on the gate insulating layer
104
, and source/drain regions are formed in each of the semiconductor layers
104
. The source region is spaced from the drain region, and the gate electrode or the part of the scanning line
102
is opposed to a back channel
111
. The drain electrode
105
is held in contact with the drain region, and the source electrode
106
is held in contact with the source region. The pixel electrodes
107
are further patterned on the gate insulating layer
103
, and are respectively associated with the thin film switching transistors
110
. Each of the source electrodes
106
is connected to the associated pixel electrode
107
. The thin film switching transistors
110
and the pixel electrodes
107
are covered with the orientation layer
108
.
On the other hand, the upper substrate structure includes a glass substrate
121
, a black matrix
122
, a common electrode
123
and an orientation layer
128
. The black matrix
122
is patterned on the glass substrate
121
, and the common electrode
123
is patterned over the glass substrate
121
and the black matrix
122
, and the black matrix is overlapped with a part of the common electrode
123
. The common electrode
123
is covered with the orientation layer
128
, and the orientation layer
128
is spaced from the orientation layer
108
by means of the spacers
129
.
A problem is encountered in the prior art liquid crystal display unit in poor quality of images produced thereon. The poor quality images are due to the spacers
129
and obliquely incident light. In detail, the spacers
129
are scattered over one of the orientation layers
108
/
128
as described hereinbefore. It is unavoidable to position the spacers
129
over the pixel electrodes
107
. The spacers over the pixel electrodes
107
vacate the liquid crystal
130
, and permit the light to pass therethrough regardless of the orientation of liquid crystal molecules
130
. Moreover, the spacers
129
vary the orientation of the liquid crystal molecules
130
therearound, and cause the amount of transmitted light and the tint to be uncontrollable. In case where the spacers
129
were not uniformly scattered, the amount of transmitted light is varied together with the dispersion of the density of the spacers
129
. Thus, the spacers
129
are causative of the poor quality of images.
Although the black matrix
122
are formed on the glass substrate
121
, the obliquely incident light reaches the back channel
111
, and generates electron-hole pairs in the semiconductor layers
104
. The electron-hole pairs vary the transistor characteristics of the thin film switching transistor
110
, and potential difference is inappropriately applied between the associated pixel electrode
107
and the common electrode
123
. This results in the poor quality of images.
A solution is disclosed in Japanese Patent Publication of Unexamined Application (laid-open) No. 8-234212. The prior art liquid crystal display is shown in FIG.
2
. The prior art liquid crystal display also comprises substrate structures, spacers
169
and liquid crystal
170
. A difference between the two prior art liquid crystal displays is the location of the spacers
169
. The spacers
169
are not transparent. Although the spacers
129
are randomly scattered over the orientation layer
108
/
128
, the spacers
169
are located over the back channel
151
. When the substrate structures are assembled, the spacers
169
also create a gap between the two substrate structures, and the gap is filled with liquid crystal
170
.
The lower substrate structure is similar to that shown in FIG.
1
. Namely, the lower substrate structure includes a glass substrate
141
, scanning lines
142
, thin film switching transistors
150
, pixel electrodes
147
and an orientation layer
148
. The thin film switching transistor
150
includes a part of the scanning line serving as a gate electrode, a gate insulating layer
143
, a semi-conductor layer
144
, a drain electrode
145
and a source electrode
146
. The scanning lines
142
are patterned on the glass substrate
141
, and are covered with the gate insulating layer
143
. The semiconductor layers
144
are patterned on the gate insulating layer
143
, and source/drain regions are formed in each of the semiconductor layers
144
. The source region is spaced from the drain region, and the gate electrode or the part of the scanning line
142
is opposed to the back channel
151
. The drain electrode
145
is held in contact with the drain region, and the source electrode
146
is held in contact with the source region. The pixel electrodes
147
are further patterned on the gate insulating layer
143
, and are respectively associated with the thin film switching transistors
150
. Each of the source electrodes
146
is connected to the associated pixel electrode
147
. The thin film switching transistors
150
and the pixel electrodes
147
are covered with the orientation layer
148
.
The upper substrate structure includes a glass substrate
161
, a common electrode
163
and an orientation layer
168
. The common electrode
163
is patterned on the glass substrate
161
, and is covered with the orientation layer
168
. The spacers
169
are inverted between the orientation layers
148
and
168
, and the gap is filled with the liquid crystal
170
.
The spacers
129
are replaced with the spacers
169
, and are non-transparent. Even if light is obliquely incident on the prior art liquid crystal display, the non-transparent spacers
169
prevent the back channels
151
from the incident light, and keeps the transistor characteristics constant. Moreover, there is not any spacer over the pixel electrodes
147
, and the liquid crystal occupies the gap between the pixel electrodes
147
and the common electrode
163
. This results in that the turbulence is negligible in the orientation of the liquid crystal molecules. The spacers
169
are less influential on the liquid crystal molecules between the pixel electrodes
147
and the common electrode
163
. The orientation of liquid crystal molecules is simply dependent on the potential difference between the pixel electrodes
147
and the common electrode
163
, and the transmittance of the liquid crystal
170
is constant in the liquid crystal
170
under a standard bias condition. Thus, the location of the spacers
169
is effective against the poor quality of images. However, a problem is encountered in the prior art liquid crystal display unit disclosed in the Japanese Patent Publication of Unexamined Application in that malfunction takes place in the
Hidehira Masanobu
Kuroha Shoichi
Watanabe Makoto
Duong Thoi V
Hayes & Soloway P.C.
Kim Robert H.
NEC Corporation
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