Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-08-21
2003-06-24
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000
Reexamination Certificate
active
06583828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device and its manufacturing method, especially suitable for application to a liquid crystal display device including a driving-purpose thin film transistor (TFT).
2. Description of the Related Art
Recently, liquid crystal display devices are used more often as light bulbs of projectors. Along with this tendency, liquid crystal display devices must have higher optical transmittance and higher definition. Liquid crystal. display devices using conventional techniques are explained below.
As shown in
FIG. 1
, a thin-film semiconductor layer
102
made of polycrystalline Si and having a predetermined configuration is provided on a quartz glass substrate
101
in a shading region, and a gate dielectric film
103
is provided on the thin-film semiconductor layer
102
. On the gate dielectric film
103
, a gate line
104
is provided. Although not shown, a source region and a drain region are formed in the thin-film semiconductor layer
102
in self-alignment with the gate line
104
. The gate line
104
forming a gate electrode, and the source region and drain regions make up a polycrystalline Si TFT for driving pixel electrodes. On the gate dielectric film
103
in a predetermined location above the drain region, a holding capacitor line
105
is provided. The structure interposing the gate dielectric film
103
between the holding capacitor line
105
and the drain region constitute a holding capacitance element.
An inter-layer insulating film
106
is formed to cover the gate line
104
and the holding capacitor line
105
. In predetermined locations of the inter-layer insulating film
106
and the gate dielectric film
103
, contact holes
107
,
108
are made. On the inter-layer insulating film
106
, a lead-out electrode
109
is formed in connection with the drain region of the polycrystalline Si TFT through the contact hole
107
, and a signal line
110
is formed in connection with the source region of the polycrystalline Si TFT through the contact hole
108
. An inter-layer insulating film
111
is formed so as to cover the lead-out electrode
109
and signal line
110
. The inter-layer insulating film
111
has formed a contact hole
112
in a predetermined position above the lead-out electrode
109
. On the inter-layer insulating film
111
, an upper-layer shading film
113
is formed in connection with the lead-out electrode
109
through the contact hole
112
. The upper-layer shading film
113
, lead-out electrode
109
and signal line
110
stacked together shade all region excluding pixel opening regions from incident light from above. Another inter-layer insulating film
114
is formed to cover the upper-layer shading film
113
. The inter-layer insulating film
114
has formed a contact hole
115
in a predetermined position above the upper-layer shading film
113
. On the inter-layer insulating film
114
, a transparent pixel electrode
116
is provided in contact with the upper-layer shading film
113
through the contact hole
115
. The pixel electrode
116
is covered by an orientation film
117
stacked thereon.
On the orientation film
117
, a liquid crystal layer
118
is provided, which is covered by an orientation film
119
and an opposed common electrode
120
. On the opposed common electrode
120
, a transparent opposed electrode substrate
121
is provided.
In the liquid crystal display device having the above-explained configuration, a voltage applied to the transparent pixel electrode
116
connected to the thin-film semiconductor layer
102
forming TFT changes orientation of liquid crystal molecules in the liquid crystal layer
118
to control the display.
The signal line
110
, gate line
104
, holding capacitor line
105
, thin-film transistor, and so on, are located within a inter-pixel shading region provided in the TFT substrate or opposed substrate. An example of such arrangement is shown in FIG.
9
.
FIG. 9
is an example of plan-view layout of the case where the signal lines
110
of the TFT substrate and the upper-layer shading film
113
form a shading region in a complementary fashion.
As shown in
FIG. 9
, in the conventional liquid crystal device, the gate line
104
and the holding capacitor line
105
extend in parallel, and the signal lines
110
extend to intersect with these gate line
104
and holding capacitor line
105
. The lead-out electrodes
109
extend over the gate line
104
and the holding capacitor line
105
so as to bridge them in locations not overlapping the signal lines
110
. Each upper-layer shading film
113
has a geometry bridging two adjacent signal lines
110
and covering parts of the holding capacitor line
105
, the gate line
104
and lead-out electrode
109
located between these two signal lines
110
. Each contact hole
108
is formed in a location of the signal line
110
overlapping an end portion of the thin-film semiconductor layer
102
. The thin-film semiconductor layer
102
underlies the holding capacitor line
105
and the signal line layer
110
. The holding capacitor line
105
has offset portions for avoiding the contact holes
107
. Through each contact hole
107
in the offset portion, the thin-film semiconductor layer
102
and the lead-out electrode
119
are connected together. In the region where the lead-out electrode
109
and the upper-layer shading film
113
overlap, the contact hole
102
is formed to connect them. Further, in the region where the upper-layer shading film
113
and the holding capacitor line
105
overlap, the contact hole
15
is formed to connect them.
In the conventional liquid crystal device having the above-explained configuration, in order to realize a high optical transmittance and a high definition, it is necessary to reduce the inter-pixel shading regions of the liquid crystal display device.
However, according to the knowledge of the Inventor, signal lines
110
, thin-film transistors, gate lines
104
and holding capacitor lines
105
occupy their respective areas in the conventional liquid crystal display device, and this is the bar against improvement of the pixel opening ratio.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a liquid crystal display device and its manufacturing method which can reduce the inter-pixel shading area and thereby realize a high optical transmittance and a high definition.
According to the first aspect of the invention, there is provided a liquid crystal display device having a thin-film transistor formed on a substrate for driving an pixel electrode, comprising:
a holding capacitor line underlying a thin-film semiconductor layer which forms the thin-film transistor; and
a first holding capacitor dielectric film formed between the holding capacitor line and the thin-film semiconductor layer,
a first holding capacitor element being made up of the thin-film semiconductor layer and the holding capacitor line interposing the first holding capacitor dielectric film therebetween.
In the first aspect of the invention, the a first insulating film is typically interposed between the thin-film semiconductor layer and the holding capacitor line. The first insulating film has a part which is thinner than the other part thereof and forms the first holding capacitor dielectric film. Further, in the first aspect of the invention, a recess is preferably formed in the first insulating film to make the portion thinner than the other part in the first insulating film, and the recess constitutes the first holding capacitor dielectric film.
In the first aspect of the invention, the holding capacitor line is typically set in a constant electric potential.
In the first aspect of the invention, the holding capacitor line is formed in a region overlapping and flatly cover a channel region in a thin-film transistor.
In the first aspect of the invention, the first holding capacitor dielectric film may be made of a silicon oxide film, silicon nitride film, or multi-layered film of a silicon oxide
Abe Fumiaki
Sato Takusei
Wada Tomohiro
Dudek James
Kananen Ronald P.
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