Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2002-04-02
2004-05-11
Tran, Minh-Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S073000, C349S049000, C349S050000
Reexamination Certificate
active
06734460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an active matrix substrate partially constituting a liquid crystal display device, and a method of fabricating the same.
2. Description of the Related Art
FIG. 1
is a cross-sectional view of a conventional active matrix substrate
100
partially constituting a liquid crystal display device.
The active matrix substrate
100
is comprised of a glass substrate
101
, a thin chromium (Cr) film
102
formed as a gate electrode partially on the glass substrate
101
, a silicon nitride film
103
formed as an electrically insulating film, covering the thin chromium film
102
and the glass substrate
101
therewith, an active layer
104
formed on the silicon nitride film
103
, n+ doped amorphous silicon film
105
formed partially on the active layer
104
, a thin chromium (Cr) film
106
formed as a barrier film on the n+ doped amorphous silicon film
105
, and an indium tin oxide (ITO) film
107
which will make a pixel electrode and which makes contact with the thin chromium film
106
and covers the silicon nitride film
103
therewith.
The active matrix substrate
100
is fabricated as follows.
First, the thin chromium film
102
which will define a gate electrode is formed on the glass substrate
101
by sputtering. Then, the thin chromium film
102
is patterned into a gate electrode.
Then, the silicon nitride film
103
, the active layer
104
and the n+ amorphous silicon film
105
are successively formed on the glass substrate
101
by plasma-enhance chemical vapor deposition (PECVD) at 300 degrees centigrade.
Then, a data wiring layer comprised of the active layer
104
and then n+ doped amorphous silicon film
105
is patterned into an island by photolithography and dry etching.
Then, the thin chromium film
106
is formed on the n+ doped amorphous silicon film
105
by sputtering. The thin chromium film
106
acts as a barrier layer between the data wiring layer and the ITO film
107
.
Then, the thin chromium film
106
and the n+ doped amorphous silicon film
105
are patterned.
Then, the ITO film
107
which will define a pixel electrode is formed by sputtering, and then, is patterned.
Thus, the active matrix substrate
100
including a thin film transistor having an amorphous silicon film, as a switching device, is fabricated through the above-mentioned steps.
Since glass has a high specific gravity, the active matrix substrate
100
including the glass substrate
101
is relatively heavy.
In particular, since glass is readily broken, the glass substrate
101
has to be formed to have a great thickness, resulting that the active matrix substrate
100
is unavoidably heavy.
These days, a liquid crystal display device is required to be light and thin, and hence, an active matrix substrate which is a part of a liquid crystal display device has to be fabricated lighter and thinner.
However, for the reasons mentioned above, there is limitation in fabricating a liquid crystal display device including a glass substrate, lighter and thinner.
Consequently, in order to fabricate a liquid crystal display device lighter and thinner, many attempts have been made to use a resin substrate in place of a glass substrate, because a resin substrate is lighter than a glass substrate and can be fabricated thinner than a glass substrate.
For instance, Japanese Unexamined Patent Publication No. 11-103064 (A) has suggested an active matrix substrate including a thin film transistor (TFT) as a switching device which thin film transistor is comprised of a thin polysilicon film formed on a resin substrate.
A thin film transistor includes a gate insulating film as an indispensable part. A gate insulating film is formed generally by plasma-enhanced chemical vapor deposition (PECVD) or sputtering.
A resin substrate generally has about 200 degrees centigrade as a maximum resistance to heat. The inventors had conducted various experiments, and found out that a gate insulating film formed by PECVD or sputtering at 200 degrees centigrade or lower, which is a maximum resistance of a resin substrate to heat, would have a low density and cause much current leakage, resulting in that the gate insulating film was not practicable. Accordingly, even if steps other than a step of forming a gate insulating film were carried out at 200 degrees centigrade or lower, it would be impossible to form a high-quality gate insulating film.
In the above-mentioned experiments, the inventors had also found out that a gate insulating film formed by PECVD or sputtering at 300 degrees centigrade or higher had a high density and had caused only small current leakage, and hence, the gate insulating film was sufficiently practicable.
However, 300 degrees centigrade is over a maximum resistance of a resin substrate to heat. Hence, if PECVD or sputtering were carried out at 300 degrees centigrade or higher for forming a gate insulating film, a resin substrate would be thermally destroyed.
Japanese Unexamined Patent Publication No. 10-173194 (A) has suggested a method of fabricating a semiconductor device, including the steps of forming a first inorganic insulating thin film on a resin substrate or resin film without exposing a surface on which the first inorganic insulating thin film is to be formed, to plasma, forming a second inorganic insulating thin film on the first inorganic insulating thin film with the surface being exposed to plasma, and forming a thin semiconductor film on either the first inorganic insulating thin film or the second inorganic insulating thin film.
Japanese Unexamined Patent Publication No. 11-174424 (A) has suggested a substrate to be used for a liquid crystal display panel which substrate is composed of copolymer polycarbonate resin containing 3,3,5-trimethyl-1,1-di(4-phenol) cyclohexyridene, bisphenol, and bisphenol constituents wherein the bisphenol is contained in the range of 30 to 99 mol %.
Japanese Unexamined Patent Publication No. 7-74374 (A) has suggested a thin film diode including a first electrode layer formed on a substrate, a semiconductor layer formed on the first electrode layer, a buffer layer formed on the semiconductor layer, and a second electrode layer formed on the buffer layer, wherein the semiconductor layer and the buffer layer have almost the same pattern as each other.
The above-mentioned problem remains unsolved even in the above-mentioned Publications.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem in the prior active matrix substrates, it is an object of the present invention to provide an active matrix substrate which includes a resin substrate and is capable of avoiding thermal destruction of a resin substrate.
In view of the shortcomings in the above-mentioned conventional active matrix substrates, the inventors paid attention to a diode which is not necessary to include a gate insulating film. That is, the inventors selected a diode as a switching device to be used for an active matrix substrate, in place of a thin film transistor.
In one aspect of the present invention, there is provided an active matrix substrate including (a) a substrate composed of resin, and (b) a polysilicon thin film diode formed on the substrate.
The active matrix substrate in accordance with the present invention is not necessary to include a gate insulating film having low quality and low reliability, unlike a conventional active matrix substrate including a thin film transistor, ensuring enhancement in performances and reliability.
In addition, it is possible to use a resin substrate having a smaller thickness than a glass substrate in the active matrix substrate in accordance with the present invention. Hence, in comparison with an active matrix substrate including a glass substrate, it would be possible to reduce a height of an active matrix substrate, and hence, a height of a liquid crystal display device including the active matrix substrate in accordance with the present invention.
It is preferable that the polysilicon thin film diode is formed as a lateral di
Okumura Hiroshi
Sukegawa Osamu
Hayes & Soloway P.C.
NEC LCD Technologies Ltd.
Tran Minh-Loan
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