Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2001-02-26
2004-01-06
Everhart, Caridad (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S059000, C257S437000, C438S057000, C438S029000
Reexamination Certificate
active
06674106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display and an organic electroluminescent display and a display device manufacturing method. In particular, the present invention relates to a technique for improving optical characteristics of opening regions of a display device including pixels disposed in a matrix on a transparent base plate (substrate), each pixel having an opening region, in which an electro-optic element such as a liquid crystal cell and an organic electroluminescent element is formed, and a non-opening region, in which a thin film transistor for driving the electro-optic element is formed.
2. Description of the Related Art
FIG. 13
is a schematic partial sectional view showing a partial section of an example of a conventional active matrix type liquid crystal display device.
As shown in
FIG. 13
, a metal gate electrode
2
is formed on a base plate (substrate)
1
made of glass or the like. A gate insulation film
3
is formed so as to cover the gate electrode
2
. On the gate insulation film
3
, an amolphous semiconductor thin film
4
A, which operates as an active layer of a thin film transistor, is formed. On one end side of the semiconductor thin film
4
A, a drain electrode
5
D is formed with an amolphous semiconductor thin film
4
A(n+), which has a high impurity concentration and is made to have low resistance, inserted between the drain electrode
5
D and the amolphous semiconductor thin film
4
A. On the other end side of the amolphous semiconductor thin film
4
A, a source electrode
5
S is formed with another amolphous semiconductor thin film
4
A(n+), which is also made to have low resistance, inserted between the source electrode
5
S and the amolphous semiconductor thin film
4
A. A protection film
8
is formed so as to cover the drain electrode
5
D and the source electrode
5
S. On the protection film
8
, a pixel electrode
10
which comprises a transparent conductive film such as a film including indium tin oxide (ITO) as its main ingredient is formed to connect electrically with the drain electrode
5
D through a contact hole CON.
The thin film transistor which is shown in
FIG. 13
has a typical form of a bottom gate structure in which the amorphous semiconductor thin film
4
A made of amorphous silicon or the like is used as its active layer. A thin film transistor having such a structure is called as a “reverse stagger channel etch type transistor”.
FIG. 14
is a schematic partial sectional view showing a partial section of another example of a conventional display device. In
FIG. 14
, components corresponding to those of the prior art shown in
FIG. 13
are designated by reference numerals corresponding to those in
FIG. 13
for facilitating the understanding of them. Incidentally, in the following drawings, too, components corresponding to those shown in
FIG. 13
are designated by reference numerals corresponding to those in
FIG. 13
for facilitating the understanding of them.
The display device shown in
FIG. 14
has basically the same structure as that shown in FIG.
13
. However, the display device shown in
FIG. 14
differs from the one shown in
FIG. 13
in that a channel protection film
6
is formed on an amolphous semiconductor thin film
4
A that functions as an active layer. The channel protection film
6
protects a part corresponding to a channel region of the active layer, which exists right above the gate electrode
2
. The structure is called as a “reverse stagger channel protection type transistor”.
FIG. 15
is a schematic partial sectional view showing a further example of a conventional display device.
A shading film
11
is formed on a base plate
1
, and an amolphous semiconductor thin film
4
A is formed above the shading film
11
with an undercoat film
12
inserted between the amolphous semiconductor thin film
4
A and the shading film
11
. A pixel electrode
10
is connected with one end of the semiconductor thin film
4
A with an amolphous semiconductor thin film
4
A(n+), which is made to have low resistance, inserted between the semiconductor thin film
4
A and the pixel electrode
10
. A source electrode
5
S is connected with the other end of the semiconductor thin film
4
A, similarly with an amolphous semiconductor thin film
4
A(n+) inserted between the semiconductor thin film
4
A and the source electrode
5
S. The amolphous semiconductor thin film
4
A, which functions as an active layer, is covered with a channel protection film
6
and a gate insulation film
3
, and further a gate electrode
2
is formed on the gate insulation film
3
.
The structure is the reverse of the prior arts described before in vertical positions of the amolphous semiconductor thin film
4
A and the gate electrode
2
, and then is called as a “forward stagger transistor”.
FIG. 16
shows an improved type of the prior art shown in FIG.
13
.
In the structure shown in
FIG. 16
, a thin film transistor is covered with a leveling film
9
, and a pixel electrode
10
is formed on the leveling film
9
. The structure is a “high numerical aperture type transistor using a leveling film”.
A silicon nitride film or a silicon oxide film is frequently used as the gate insulation film
3
or the protection film
8
in the aforesaid prior art. Moreover, an organic resin film is frequently used as the leveling film
9
.
The structures shown in
FIGS. 13-16
are described in detail in, for example, “An Introduction to Liquid Crystal Display Engineering”, The Nikkan Kogyo Shimbun, Ltd., 1998, pp. 27-30, “The Latest Liquid Crystal Process Technique in '99”, Press Journal Inc., 1998, pp. 21-27, and “Flat Panel Display 1999”, Nikkei Business Publications, Inc., 1998, pp. 118-131.
The aforesaid display devices use an amolphous semiconductor thin film as their active layers, however the prior art shown in
FIG. 17
uses a polycrystalline semiconductor thin film such as a film including polysilicon as the main ingredient as its active layer.
A gate electrode
2
is formed on a glass base plate
1
, and a polycrystalline semiconductor thin film
4
P is formed above the gate electrode
2
with a gate insulation film
3
inserted between the polycrystalline semiconductor thin film
4
P and the gate electrode
2
. A part of the polycrystalline semiconductor thin film
4
P placed right above the gate electrode
2
is formed as a channel region, and parts on both sides of the channel region are formed as a source region S and a drain region D, where impurities are injected in a high concentration. The semiconductor thin film
4
P is covered with an interlayer insulation film
7
, and a drain electrode
5
D and a source electrode
5
S are formed on the interlayer insulation film
7
. These electrodes
5
D and
5
S are covered with a protection film
8
.
Such a structure is called as a “bottom gate type transistor” because the gate electrode
2
is disposed below the active layer.
FIG. 18
shows a structure of a thin film transistor using a polycrystalline semiconductor thin film as its active layer in the same way as the above example. In the structure of this prior art, differently from the structure shown in
FIG. 17
, a gate electrode
2
is formed above a polycrystalline semiconductor thin film
4
P with a gate insulation film
3
inserted between the gate electrode
2
and the semiconductor thin film
4
P. Such a structure is called as a “top gate type transistor”.
FIG. 19
shows a CMOS structure in which a top gate structure N-channel thin film transistor (N-channel TFT) is combined with a P-channel thin film transistor (P-channel TFT). The P-channel thin film transistor uses a polycrystalline semiconductor thin film
4
as an active layer, in which, for example, boron is injected into a source region S and a drain region D. The N-channel thin film transistor uses a polycrystalline semiconductor thin film
4
as an active layer, in which phosphorus or the like is injected into a source region S and a drain region D.
In the example,
Fujino Masahiro
Nakano Minoru
Tanaka Tsutomu
Everhart Caridad
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
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