X-ray detector and method of fabricating the same

Details X-ray detector and method of fabricating the same X-ray detector and method of fabricating the same

2002-08-13

2004-09-28

Wells, Nikita (Department: 2881)

Radiant energy

Invisible radiant energy responsive electric signalling

Semiconductor system

C250S370080, C250S370110, C250S370140

Reexamination Certificate

active

06797961

ABSTRACT:

This application claims the benefit of Korean Patent Application No. 2001-50167, which was filed in Korea on Aug. 21, 2001, and which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to X-ray detectors. More particularly, it relates to Thin Film Transistor (TFT) array substrates for use in X-ray detectors.
2. Description of Related Art
A widely used aid to medical diagnosis is the X-ray film. As such films produce photographic images, time consuming film-processing procedures are required to obtain the results. However, digital X-ray sensing devices (referred to hereinafter as X-ray detectors) that employ thin film transistors have been developed. Such X-ray sensing devices have the significant advantage of providing real time imaging that speeds diagnosis.
FIG. 1
is a schematic cross-sectional view illustrating the structure and operation of an X-ray detector according to a conventional art. Included are a substrate
1
, a thin film transistor
3
, a storage capacitor
2
, a pixel electrode
4
, a photoconductive film
5
, a protection film
6
, a conductive electrode
7
and a high voltage D.C. (direct current) power supply
8
.
The photoconductive film
5
produces electron-hole pairs
9
in proportion to the strength of external signals (such as incident electromagnetic waves). That is, the photoconductive film
5
acts as a converter that converts external signals, particularly X-rays, into electric signals. When an external voltage Va is applied across the conductive electrode
7
, the electron-hole pairs
9
separate such that X-ray induced electrical charges accumulate on the pixel electrode
4
. Thus, either the electrons or the holes are gathered by the pixel electrode
4
as electric charges. The electric charge species that is gathered depends on the polarity of the high voltage D.C. power supply
8
.
As shown in
FIG. 1
, the pixel electrode
4
is located beneath the photoconductive film
5
. The gathered electric charges accumulate in the storage capacitor
2
, which connects with a grounding line. Charges in the storage capacitor
2
are selectively transferred through a thin film transistor (TFT)
3
to an external image display device that produces an X-ray image.
FIG. 2
is a schematic plan view illustrating one pixel of an X-ray detector array substrate according to the conventional art, and
FIG. 3
is a cross-sectional view taken along line III—III of FIG.
2
.
As shown in
FIGS. 2 and 3
, a gate line
21
is arranged in a transverse direction on a substrate
10
. A gate electrode
22
that extends from the gate line
21
is also on the substrate
10
. A gate insulation layer
30
is formed over the substrate
10
, over the gate line
21
, and over the gate electrode
22
. An active layer
41
, comprised of amorphous silicon, is formed on the gate insulation layer
30
and over the gate electrode
22
. Ohmic contact layers
42
a
and
42
b
, which are comprised of doped amorphous silicon, are formed on the active layer
41
.
A data line
51
is on the gate insulation layer
30
. That data line is arranged perpendicular to the gate line
21
. A source electrode
52
extends from the data line
51
over the first ohmic contact layer
42
a
. A drain electrode
53
is on the second ohmic contact layer
42
b
. The drain electrode
53
is spaced apart from the source electrode
52
such that the source and drain electrodes
52
and
53
face each other across the active layer
41
. Therefore, a thin film transistor (TFT) T
1
comprised of the gate electrode
22
, the active layer
41
, the ohmic contact layers
42
a
and
42
b
, and the source and drain electrodes
52
and
53
is formed as a switching element near the crossing of the gate and data lines
21
and
51
.
Still referring to
FIGS. 2 and 3
, a common line
55
, which is comprised of the same material as the data line
51
, is arranged perpendicularly to the gate line
21
so as to cross the pixel region defined by the gate and data lines
21
and
51
. The common line
55
grounds the neighboring pixels. A first capacitor electrode
61
, made of a transparent conductive material, is formed in the pixel region and on the common line
55
. A second capacitor electrode
75
, which is also made of a transparent conductive material, is formed over the first capacitor electrode
61
. The second capacitor electrode
75
generally corresponds in size and position to the first capacitor electrode
61
. A dielectric layer
71
is interposed between the first capacitor electrode
61
and the second capacitor electrode
75
, thus forming a storage capacitor C
1
. A passivation layer
80
is formed on the second capacitor electrode
75
and over the TFT T
1
such that the passivation layer
80
protects the storage capacitor C
1
and the TFT T
1
. The passivation layer
80
includes a first contact hole
81
, which exposes a portion of the second capacitor electrode
75
, and a second contact hole
82
, which exposes a portion of the drain electrode
53
. As shown in
FIG. 3
, the second contact hole
82
penetrates both the passivation layer
80
and the dielectric layer
71
.
A pixel electrode
91
, which is made of a transparent conductive material, is formed on the passivation layer
80
in the pixel region. The pixel electrode
91
extends over the TFT T
1
. The pixel electrode contacts the second capacitor electrode
75
through the first contact hole
81
and contacts the drain electrode
53
through the second contact hole
82
. Although not shown in
FIG. 3
(but see
FIG. 6I
for similar structures), a photoconductive film that generates electric charges is on the pixel electrode
91
. The pixel electrode
91
gathers electric charges generated by the photoconductive film and applies them to the storage capacitor C
1
. Namely, the pixel electrode
91
acts as a current-collecting electrode. As previously mentioned, since the pixel electrode
91
electrically contacts the drain electrode
53
through the second contact hole
82
, the holes stored in the storage capacitor C
1
combine with the electrons that flow from the TFT T
1
.
When the X-ray image sensing device produces image signals, the electric charges stored in the storage capacitor C
1
flow to TFT T
1
by way of the pixel electrode
91
, which contacts both the first capacitor electrode
75
an one through the first contact hole
81
and the other through the second contact hole
82
, the pixel electrode
91
contact resistance is relatively large. Therefore, weak signals, which produce a small quantity of electric charges, are difficult to detect because it is difficult to distinguish between the actual signals and noise. Thus, the sensitivity of the X-ray detector is less than optimal.
Therefore, an X-ray sensing device array substrate having decreased pixel electrode contact resistance would be beneficial. Also beneficial would be an X-ray detector array having improved detection ability.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an array substrate for an X-ray detector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention is a method and an X-ray sensing device array substrate having decreased drain electrode contact resistance.
Another advantage of the present invention is a method and X-ray detector array having improved detection ability.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from that description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to accomplish at least one of the above advantages, the principles of the present invention provide for an innovate X-ray detector array substrat

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