Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-02-18
2004-12-14
Niebling, John F. (Department: 2812)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S306000, C349S039000, C349S041000
Reexamination Certificate
active
06831318
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of thin film transistor array driver circuits used to drive active matrix liquid crystal display devices and their manufacturing methods. More particularly, the present invention relates to thin film transistor arrays for driving liquid crystal display devices that include a charge capacitor.
BACKGROUND OF THE INVENTION
Display devices using liquid crystal achieve low power consumption and reduced weight, which represent considerable improvements on conventional CRT displays. In particular, active matrix liquid crystal display devices using thin film transistors (TFTs), acting as a switching device for each pixel, are extensively used in displays for notebook PCs and car navigation systems due to their advantages of sharp images with less crosstalk. The use of these active matrix liquid crystal display devices is rapidly extending to large display monitors.
A conventional circuit containing a TFT array for driving this type of liquid crystal display devices is described next with reference to drawings.
FIG. 3
is a schematic diagram of an example of a conventional TFT array in a liquid crystal display device.
FIG. 4
is a sectional view taken along the broken line
4
—
4
in FIG.
3
. In this example, as shown in
FIGS. 3 and 4
, scanning lines
2
and video signal lines
5
are disposed in a matrix on a glass substrate
1
. A pixel electrode
7
, TFT
13
, and storage capacitor
14
are disposed in a region surrounded by the scanning lines and video signal lines. The TFT
13
is mainly made of an amorphous silicon semiconductor layer
4
. The TFT drain electrode
11
and the pixel electrode
7
are connected through a contact pattern
8
. The video signal line
5
also acts as the source electrode of the TFT
13
. The storage capacitor
14
is formed between an upper electrode
10
and the scanning line
2
so as to sandwich the first insulating film
3
which becomes a gate insulator. A second insulating layer
6
is formed as a passivation insulating layer for protecting the TFT
13
.
Operation of the liquid crystal display device using the TFT array as configured above is described next.
First, when voltage is applied to the scanning line
2
, which is the TFT gate electrode, a channel is established in the amorphous silicon semiconductor layer
4
of the TFT
13
. Then, video signals from the video signal line
5
are fed to the drain electrode
11
through the TFT channel, and reach the pixel electrode
7
to change the orientation of the liquid crystal (not illustrated) held between the pixel electrode
7
and counter electrode (not illustrated) to the intended degree by a magnetic field established between the pixel electrode
7
and the counter electrode facing the pixel electrode
7
. This adjusts the light transmittance to produce the required images.
In general, a storage capacitor is provided to the pixel electrode for maintaining the pixel electrode potential until the scanning signals are applied for the next frame. With the increased size of monitor displays, formation of a uniform electric capacitance in this storage capacitor is becoming a key factor in reducing defects such as uneven luminance and improving image quality of uniformity.
TFT arrays as described above are generally manufactured by means of the next key steps. Midway steps in the manufacturing process are described next with reference to
FIGS. 6A
to
6
D.
FIGS. 6A
to
6
D are sectional views taken along the broken line
6
—
6
in
FIG. 3
, with the left part illustrating the storage capacitor
14
and the right part illustrating the TFT
13
.
A first metal layer is formed on the glass substrate
1
, and the metal is selectively etched to form the pattern of the scanning lines
2
. Then, the gate insulator
3
, which is the first insulating layer, is formed. The semiconductor layer is next formed, and the pattern of the TFT channel
4
is etched (FIG.
6
A). Next, a second metal layer is formed, and this is selectively etched to simultaneously form patterns of the video signal line
5
, drain electrode
11
, and upper electrode
10
on the storage capacitor (FIG.
6
B). The second insulating layer
6
, which is the TFT passivation layer, is next formed and this layer is selectively etched to create openings
8
and
12
respectively on the drain electrode
11
and the upper electrode
10
of the storage capacitor (FIG.
6
C). Finally, a transparent conductive layer is formed, and this is selectively etched to form the pattern of the pixel electrode
7
.
With this conventional configuration, however, the exposed gate insulator
3
is often over-etched during the step of etching the channel
4
of the TFT
13
, as is clear from FIG.
6
A. As a result, the thickness of the remaining gate insulator
3
becomes non-uniform, also causing non-uniform thickness in a dielectric layer of the storage capacitor
14
. This results in variations in capacitance of the storage capacitor
14
among pixels, leading to image defects such as uneven luminance.
SUMMARY OF THE INVENTION
The present invention aims to offer a thin film transistor array and its manufacturing method for achieving a uniform electric capacitance for the storage capacitors and reducing defects such as uneven luminance so as to improve image uniformity. It is therefore an object of this invention to provide a driving circuit which may be used, inter alia, for driving a display device comprising:
a thin film transistor
a pixel electrode electrically connected to said thin film transistor
a scanning line connected to the thin film transistor;
an insulating layer over said scanning line;
a semiconductor layer over a portion of the insulating layer and the scanning line and
a storage capacitor comprising an upper capacitor electrode formed over the semiconductor layer electrically connected to said pixel electrode.
Another object of this invention is a circuit for driving a display device comprising an array of a plurality of display elements each of the display elements comprising a pixel electrode, the circuit also comprising an array of scanning lines and an array of signal lines the signal lines arrayed substantially perpendicular to the scanning lines and electrically insulated therefrom, and a plurality of individual drivers, one driver for each display element, each of the individual drivers comprising:
a thin film transistor connected to a scanning line and a pixel electrode;
a storage capacitor electrically connected to the pixel electrode comprising an upper capacitor electrode, a dielectric layer and a lower electrode wherein the dielectric layer comprises an insulating layer over the lower electrode and a semiconductor layer over the insulating layer and under the upper electrode.
Still an object of this invention is a display device comprising an array of liquid crystal display elements each comprising a pixel electrode the display device further comprising an electronic circuit for driving the display device, the electronic circuit comprising an array of scanning lines and an array of signal lines the signal lines arrayed substantially perpendicular to the scanning lines and electrically insulated therefrom, and a plurality of individual drivers, one driver for each display element, each of said individual drivers comprising:
a thin film transistor connected to one of said scanning lines and said pixel electrode;
a storage capacitor also electrically connected to said pixel electrode, comprising an upper capacitor electrode, a lower electrode and a dielectric layer therebetween, wherein said dielectric layer comprises a first insulating layer over said lower electrode and a semiconductor layer over said first insulating layer and under said upper electrode.
Further, still in accordance with this invention, there is contemplated a method for manufacturing the thin film transistor array of the present invention that comprises the steps of forming a scanning line pattern on the insulated substrate; depositing the first insulating layer; forming a semiconductor isla
Uno Mitsuhiro
Yonekura Hiroaki
Isaac Stanetta
Matsushita Electric - Industrial Co., Ltd.
Niebling John F.
RatnerPrestia
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