Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-07-12
2002-11-05
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000, C345S100000, C349S042000, C349S043000, C349S045000, C349S047000
Reexamination Certificate
active
06476788
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image display device and a method of making the same, and particularly to an image display device suitable for increasing the number of pixels and a method of making the same.
A prior art image display device will be explained hereunder with reference to
FIGS. 6 and 7
.
FIG. 7
illustrates a structure of a prior art poly-Si TFT (thin film transistor) liquid crystal display device. There are a pixel area
120
, a signal line shift register
121
, a signal line selection switch
122
, a gate line shift register
124
and a gate line drive buffer
125
formed on a substrate
109
.
A plurality of pixels each comprising a poly-Si TFT
128
, a pixel electrode
50
connected thereto and a pixel capacitance
129
formed by the pixel electrode
50
are arranged in a matrix in the pixel area
120
, and a gate and a drain of each poly-Si TFT
128
are connected to a gate line
127
and a signal line
126
, respectively. For simplicity, only one pixel is shown in FIG.
7
.
One end of the gate line
127
is connected to the gate line drive buffer
125
which in turn is scanned by the gate line shift register
124
. One end of the signal line
126
is connected to the signal line selection switch
122
which in turn is scanned by the signal line shift register
121
. The signal line selection switch
122
is supplied with signals via an analog signal input line
123
.
The following explains the operation of the prior art liquid crystal device. The gate line shift register
124
selects the gate lines
127
sequentially via the gate line drive buffer
125
. Poly-Si TFTs
128
in pixels in a row corresponding to a selected one of the gate lines
127
are turned on. During this ON period, the signal line shift register
121
scans the signal line selection switch
122
sequentially. The signal line selection switch
122
connects the signal lines
126
to the analog signal input line
123
sequentially when the signal line selection switch
122
is scanned, and consequently display signals inputted to the analog signal input line
123
are written into the respective pixel capacitances
129
sequentially via the signal lines
126
and the poly-Si TFTs
128
.
FIG. 6
illustrates a cross-sectional view of a poly-Si TFT
128
disposed in each pixel and also a cross-sectional view of one of poly-Si TFTs constituting the gate line shift register
124
or the signal line shift register
121
disposed around the pixel area
120
on the substrate
109
on which the poly-Si TFTs
128
are formed.
Here, for the sake of simplicity, I shall assume an n-channel TFT. The poly-Si TFT
128
disposed in each pixel comprises a gate
101
, a channel region
150
formed of a poly-Si thin film, an n
+
source region
102
, an n
−
source region
103
, an n
+
drain region
105
, and an n
−
drain region
104
. The poly-Si TFT constituting the gate line shift register
124
or the signal line shift register
121
comprises a gate
106
, a channel region
151
formed of a poly-Si thin film, an n
−
source region
107
and an n
+
drain region
108
. Both the above-explained two poly-Si TFTs are identical in structure and fabrication process except for dimensions. The only exception is such that the poly-Si TFT
128
is provided with the n
−
source region
103
and the n
−
drain region
104
to reduce leakage current through the poly-Si TFT
128
serving as a pixel switch when it is off. In
FIG. 6
, reference numeral
109
denotes a quartz glass substrate,
110
is a gate insulating film, and
111
is a protective film.
The prior art as explained above is disclosed in detail in SID (Society for Information Display International Symposium) 94 Digest of Technical Papers, pp.87-90 (1994), for example.
As the number of pixels in the display device is increased, the operating speeds of peripheral circuits such as the gate line shift register
124
and the signal line shift register
121
, are required to increase further.
But, with the prior art technique, there is a problem in that it is difficult to optimize the designs of the peripheral circuits and the pixel area independently of each other. If the gate insulating film is made thinner for the purpose of speed-up of the peripheral circuits, for example, the poly-Si TFT
128
in the pixel area becomes incapable of withstanding a high voltage required for driving the liquid crystal.
SUMMARY OF THE INVENTION
To solve the above problems, an image display device according to an embodiment of the present invention comprises a plurality of pixels arranged in a matrix, the plurality of pixels each being provided with a pixel switching means, a pixel electrode coupled with the pixel switching means for applying an electric field to a material producing an electro-optical effect; a common electrode for cooperating with the pixel electrode in driving the material producing an electro-optical effect; a plurality of gate lines each extending in parallel with each other and connected to a corresponding row of the pixel switching means for selecting the corresponding row of the pixel switching means in a predetermined order; a gate line driver circuit for driving the plurality of gate lines; a plurality of signal lines extending in such a manner as to intersect the plurality of gate lines for supplying display signal voltages to the pixel electrodes via selected ones of the pixel switching means; and a display signal voltage applying circuit for applying the display signal voltages to respective ones of the plurality of signal lines, wherein the pixel switching means each is comprised of a poly-Si TFT of a first type structure, the display signal voltage applying circuit contains a plurality of poly-Si TFTs of a second type structure, a gate of each of the poly-Si TFTs of the first type structure is disposed to oppose a first side of a first poly-Si thin film for forming a channel of the poly-Si TFT of the first type structure with a first gate insulating film interposed therebetween and is connected to a corresponding one of the plurality of gate lines, a gate of each of the plurality of poly-Si TFTs of the second type structure is disposed to oppose a first side of a second poly-Si thin film for forming a channel of each of the plurality of poly-Si TFTs of the second type structure with a second gate insulating film interposed therebetween, sources and drains of the poly-Si TFTs of the first and second type structures are disposed approximately in a same plane on a same substrate of the image display device, and the first side of the first poly-Si thin film and the first side of the second poly-Si thin film are on opposite sides of the same plane from each other.
To solve the above problems, an image display device according to another embodiment of the present invention comprises a plurality of pixels arranged in a matrix, the plurality of pixels each being provided with a pixel switching means, a pixel electrode coupled with the pixel switching means for applying an electric field to a material producing an electro-optical effect; a common electrode for cooperating with the pixel electrode in driving the material producing an electro-optical effect; a plurality of gate lines each extending in parallel with each other and connected to a corresponding row of the pixel switching means for selecting the corresponding row of the pixel switching means in a predetermined order; a gate line driver circuit for driving the plurality of gate lines; a plurality of signal lines extending in such a manner as to intersect the plurality of gate lines for supplying display signal voltages to the pixel electrodes via selected ones of the pixel switching means; and a display signal voltage applying circuit for applying the display signal voltages to respective ones of the plurality of signal lines, wherein the pixel switching means each is comprised of a poly-Si TFT of a first type structure, the display signal voltage applying circuit contains a plurality of poly-Si TFTs of a second ty
Dinh Duc Q
Hitachi , Ltd.
Kenyon & Kenyon
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