Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-08-03
2004-03-30
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C438S030000
Reexamination Certificate
active
06714266
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transmission type liquid crystal display device.
Conventionally, in accordance with improvement in resolution of the transmission type liquid crystal display device, there have been proposed a variety of structures for effectively shading light without impairing an opening ratio of the liquid crystal display device in order to prevent a reduction in contrast due to malfunction ascribed to a photoelectric current and leak of light from the semiconductor layer of a thin film transistor that serves as a switching element.
As a typical transmission type liquid crystal display device, there is the one shown in
FIG. 8
(Japanese Patent Laid-Open Publication No. HEI 9-43639). As shown in
FIG. 8
, this transmission type liquid crystal display device is constructed of a transparent drive substrate
101
and an opposite substrate
121
that are bonded to each other with interposition of a specified gap, and liquid crystals
120
are held in this gap.
The opposite substrate
121
is located on thie incident side of the liquid crystal display device, and an opposite electrode
122
is provided on the drive substrate
101
side. The drive substrate
101
is located on the radiating side and includes a group of pixels each constructed of a pixel electrode
115
and a switching element
103
on the drive substrate
101
and a black matrix for shading an unopened portion of individual pixels from light incident on the incident side. The black matrix is constructed of two layers of a mask light shading pattern
112
and a pad light shading pattern
113
, which are patterned to overlap each other to complemertarily shade incident light. For example, an upper layer is made of titanium (Ti), while the lower layer is made of aluminum (Al).
The drive substrate
101
is constructed of an upper layer, an intermediate layer and a lower layer. The upper layer includes the pixel electrode
115
. The lower layer includes the switching element
103
for driving each pixel electrode
115
, a gate wiring (not shown) for scanning the rows of the switching elements
103
and a signal wiring (not shown) for supplying a specified image signal to the switching elements
103
of each column.
The switching element
103
is constructed of a thin film transistor (referred to as TFT hereinafter) that has a semiconductor thin film
102
made of polycrystal silicon or the like as an active layer. A gate electrode
105
is formed on the transistor via a gate insulating film
104
. The gate electrode
105
leads to the gate wiring. The TFT that serves as the switching element
103
is provided with a source region and a drain region on both sides of the gate electrode
105
. One lead electrode
109
is connected to the source region of the semiconductor thin film
102
, and the lead electrode
109
leads to a signal wiring (not shown) The other lead electrode
110
is connected to the drain region of the semiconductor thin film
102
.
Further, the semiconductor thin film
102
is also provided with an auxiliary capacitance. This auxiliary capacitance includes the semiconductor thin film
102
that serves as one electrode and an auxiliary capacitance wiring
107
that serves as the other electrode via an insulating film
106
. The gate electrode
105
, the gate wiring and the auxiliary capacitance wiring
107
are constructed of a same layer and insulated from the lead electrodes
109
,
110
by a first interlayer insulating film
108
.
Then, bisected light shading patterns
112
,
113
exist in the intermediate layer. One light shading pattern
112
is continuously patterned along the direction of row of the pixels and at least partially shades light to the switching element
103
while being vertically held by a second interlayer insulating film
111
and a flattening film
114
so as to be insulated from the lower layer and the upper layer. The other light shading pattern
113
is discretely patterned to be interposed between the pixel electrode
115
and the lead electrode
110
, so that the light shading pattern
113
is for good electrical connection between both the electrodes as well as light shading. The lead electrode
110
is formed of a layer identical to that of the signal wiring and electrically connected to the drain region of the semiconductor thin film
102
.
In the above-mentioned transmission type liquid crystal display device, no light shading is needed if a metal or silicide is used for the gate wiring, gate electrode
105
, auxiliary capacitance wiring
107
, signal wiring and lead electrodes
109
,
110
. However, the semiconductor layer of the TFT formed of the semiconductor thin film
102
is required to be completely shaded from light due to the light transmission of the semiconductor layer. Therefore, in order to completely shade the region to be shaded from light in the lower layer by the light shading patterns
112
,
113
, the light shading patterns are required to be formed jutting out of the region (semiconductor layer of TFT) to be shaded from light taking variations in alignment and line width through the patterning process into consideration. The opening ratio is reduced by an area of the jut region, and this causes a problem that brightness of the liquid crystal display device is reduced.
Furthermore, due to the necessity of the film formation of the light shading patterns, the process is prolonged and the structure becomes complicated, disadvantageously leading to a factor of yield reduction and cost increase. Specifically, there are needed the processes of forming the interlayer insulating films, light shading patterns and contact holes.
FIG. 9
shows a sectional view of the essential part of another conventional transmission type liquid crystal display device, in which a lower layer insulating film
203
, a TFT
204
, a first interlayer insulating film
205
, a gate electrode
206
, an auxiliary capacitance wiring
207
, a signal wiring
208
, a second interlayer insulating film
209
and a pixel electrode
210
are successively formed on a transparent substrate
201
. With regard to the above transmission type liquid crystal display device, light comes from the above and goes out downward in
FIG. 9. A
reflected light R
1
from an optical system on the radiating side may be incident on the TFT
204
, and a reflected light R
2
caused by reflection of a transmitted light on the lower surface of the transparent substrate
201
may be incident on the TFT
204
. This leads to a problem that the reflected lights R
1
and R
2
are incident on the TFT to cause an optical leak current when the TFT is turned off in accordance with the dimensional reduction of pixels in company with the improvement in resolution.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a transmission type liquid crystal display device that can cope with an improvement in resolution by effectively shading light without impairing a opening ratio and by shading a rear surface reflection light, the device being able to be fabricated with a simple construction and high yield at low cost through a short process.
In order to achieve the above-mentioned object, the present invention provides a transmission type liquid crystal display device including on a transparent substrate a gate wiring; a signal wiring perpendicular to the gate wiring, an auxiliary capacitance wiring that is generally parallel to the gate wiring and perpendicular to the signal wiring, a thin film transistor having either one of a source region and a drain region connected to the signal wiring, and a pixel electrode to which the other one of the source region and the drain region of the thin film transistor is connected via a lead electrode, wherein the signal wiring, the gate wiring, the auxiliary capacitance wiring and the lead electrode are made of a light shading material, a semiconductor thin film is formed for each pixel electrode below the signal wiring, the gate wiring, the auxiliary capacitance wiring and the lead electrode via an insulating film, a regio
Higami Yoshinori
Ueda Tohru
Akkapeddi P. R.
Kim Robert H.
Sharp Kabushiki Kaisha
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