Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-09-25
2001-06-19
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S138000
Reexamination Certificate
active
06249330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a display device such as a liquid crystal display device which use a TFT (TFT: Thin Film Transistor) as a pixel drive element, and to a method of manufacturing such a device.
2. Description of the Prior Art
FIG. 1
is a cross-sectional view showing a bottom gate thin film transistor structure used as a switching element for a liquid crystal display panel.
A gate electrode
2
of a refractory metal is arranged on the surface of a transparent, insulating substrate
1
.
This gate electrode
2
has a taper shape wherein its width expand toward the transparent substrate
1
. A silicon oxide film
4
is formed on the transparent substrate
1
on which the gate electrode
2
is arranged via a silicon nitride film
3
.
The silicon nitride film
3
prevents infiltration of impurities contained in the transparent substrate into an active layer, described later. The silicon oxide film
4
functions together with the silicon nitride film
3
as a gate insulating film.
A polycrystalline silicon film
5
is formed on the silicon oxide film
4
so as to transverse over the gate electrode
2
.
This polycrystalline silicon film
5
is the active layer of the thin film transistor.
A stopper insulating film
6
comprising an insulating material such as silicon oxide is arranged on the polycrystalline silicon film
5
. The area of the polycrystalline silicon film
5
covered by this stopper insulating film
6
is a channel area
5
c.
Other areas of the polycrystalline silicon film
5
are a source area
5
s
and a drain area
5
d.
A silicon oxide film
7
and silicon nitride film
8
are formed on the polycrystalline silicon film
5
on which the stopper insulating film
6
is formed. This silicon oxide film
7
and silicon nitride film
8
protect the polycrystalline silicon film
5
which comprises the source area
5
s
and drain area
5
d.
A contact hole
9
is formed in a predetermined part of the silicon oxide film
7
and silicon nitride film
8
on the source area
5
s
and drain area
5
d.
An aluminum electrode
10
connected through this contact hole
9
to the source area
5
s
and drain area
5
d
is arranged on the silicon nitride film
8
. A planarizing film
11
which is insulating and is transparent to visible light is formed on the silicon nitride film
8
on which the aluminum electrode
10
is arranged. This planarizing film
11
covers imperfections due to the gate electrode
2
or stopper insulating film
6
and makes the surface smooth. A contact hole
12
is formed in the planarizing film
11
on the aluminum electrode
10
on the source area
5
s.
A transparent electrode
13
made of an ITO (Indium-Tin-Oxide) film connected to the aluminum electrode
10
via this contact hole
12
is arranged so that it extends over the planarizing film
11
. This transparent electrode
13
constructs pixel electrode of a liquid crystal display panel.
In this thin film transistor, image data supplied to the aluminum electrode
10
on the drain area is applied to the transparent electrode
13
in response to a scanning control signal applied to the gate electrode
2
.
However, the contact resistance of the ITO film was high relative to the aluminum electrode
10
, and faulty contacts often occurred. To solve this, there is a technique whereby the contact resistance is lowered by using a high melting metal such as molybdenum (Mo), for example, on the surface of the aluminum electrode
10
, but as a molybdenum sputtering step is required after the aluminum sputtering step, there was a disadvantage in that the manufacturing process became complex.
SUMMARY OF THE INVENTION
According to this invention, which was conceived in view of the aforesaid problems in the prior art, a contact hole in a planarizing film and a contact hole in an insulating film (silicon oxide and silicon nitride) are connected, and a transparent electrode is brought into direct contact with either a source area or a drain area.
By bringing the transparent electrode into direct contact with the surface of the semiconductor film, according to this invention, a thin film transistor of simplified construction can be obtained without increasing contact resistance.
Moreover, by forming the contact hole (second contact hole) in the insulating film (silicon oxide film and silicon nitride film) to be larger than the contact hole (third contact hole) in the planarizing film, the inner wall of the contact hole in the insulating film is covered by the planarizing film material.
Further, as there is no step in the inner wall of the third contact hole, this invention also has the advantage that disconnects in the transparent contact part are prevented.
REFERENCES:
patent: 5956105 (1999-09-01), Yamazaki et al.
patent: 07056190 (1995-03-01), None
Oda Nobuhiko
Yamaji Toshifumi
Cantor & Colburn LLP
Dudek James A.
Sanyo Electric Co,. Ltd.
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