Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2002-02-08
2003-12-09
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S065000, C438S098000
Reexamination Certificate
active
06660555
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-53712, filed on Nov. 30, 2000, 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 image sensors. More particularly, it relates to X-ray image sensors having a TFT (Thin Film Transistor) array, and to a method for fabricating the same.
2. Discussion of the Related Art
X-ray detection has been widely used for medical diagnosis. X-ray detection typically uses an X-ray film to produce a photograph. Therefore, some predetermined developing and printing procedures are required to produce the photograph.
However, digital X-ray image sensors that employ TFTs (Thin Film Transistors) have been developed. Such X-ray image sensors have the advantage that real time diagnosis can be obtained.
FIG. 1
is a schematic, cross-sectional view illustrating the structure and operation of an X-ray image sensing device
100
. Included are a lower substrate
1
, a thin film transistor
3
, a storage capacitor
10
, a pixel electrode
12
, a photoconductive film
2
, a protection film
20
, a conductive electrode
24
and a high voltage D.C. (direct current) power supply
26
.
The photoconductive film
2
produces electron-hole pairs in proportion to the strength of external signals (such as incident electromagnetic waves or magnetic waves). That is, the photoconductive film
2
acts as a converter that converts external signals, particularly X-rays, into electric signals. Either the electrons or the holes are then gathered by the pixel electrode
12
as charges. The pixel electrode is located beneath the photoconductive film
2
. Which charge species that is gathered depends on the voltage (Ev) polarity that is applied to the conductive electrode
24
by the high voltage D.C. power supply
26
. The gathered species charges are accumulated in the storage capacitor
10
, which is formed in connection with a grounding line. Charges in the storage capacitor
10
are then selectively transferred through the TFT
3
, which is controlled externally, to an external image display device that forms an X-ray image.
In such an X-ray image sensing device, to detect and convert weak X-ray signals into electric charges it is beneficial to decrease the trap state density (for the electric charge) in the photoconductive film
2
, and to decrease charge flow in non-vertical directions. Decreasing non-vertical charge flow is usually accomplished by applying a relatively high voltage between the conductive electrode
24
and the pixel electrode
12
.
Electric charges in the photoconductive film
2
are trapped and gathered not only on the pixel electrode
12
, but also over the channel region of the TFT
3
. Even during the OFF state, the electric charges trapped and gathered on the pixel electrode
12
and on the channel region of the TFT
3
induce a potential difference between the TFT
3
and the pixel electrode. This has a similar effect as the TFT
3
being in the ON state. This adversely affects the switching of the TFT
3
and increases the OFF state leakage current. Such can result in an undesired image.
FIG. 2
is a plan view illustrating one pixel
102
of the X-ray image sensor panel
100
. Shown are the TFT
3
, a storage capacitor “S” and a pixel electrode
62
that collects charges.
The TFT
3
includes a gate electrode
31
, which is formed by an elongation of a gate line
50
, and a drain electrode
32
, which is formed by an elongation of a drain line
52
.
The storage capacitor “S” is comprised of transparent first and second capacitor electrodes
58
and
60
. A ground line
42
acts as a common electrode that is shared by adjacent pixels. Also shown are first contact holes
54
that connects the pixel electrode
62
with a source electrode
33
of the TFT
3
, and a second contact hole
56
that connects the pixel electrode
62
with the second capacitor electrode
60
.
According to the conventional art, an X-ray image sensor includes a photoelectric conversion part that produces electric charges in accordance with received electromagnetic energy; a charge storage capacitor “S” having a first capacitor electrode
58
, a dielectric layer that is deposited on the first capacitor electrode
58
, a second capacitor electrode
60
on the dielectric layer, a protection film having multiple contact hole(s)
54
and
56
on the second capacitor electrode
60
, and a pixel electrode
62
that is formed on the protection film. The pixel electrode is in contact with the second capacitor electrode
60
through the contact hole(s)
56
and collects the electric charges produced in the photoelectric conversion part. A switching TFT
3
controls the release of the electric charges stored in the storage capacitor “S”. The switching TFT includes a gate electrode
31
, a drain electrode
32
, and a source electrode
33
that contacts the pixel electrode
62
.
FIGS. 3
a
to
3
f
are sectional views, taken along the line III—III of
FIG. 2
, that illustrate a manufacturing process.
Referring to
FIG. 3
a
, a metal layer is deposited and patterned on a substrate
1
to form a taper-shaped gate electrode
31
. The substrate
1
can be a quartz substrate or a glass substrate. However, the substrate
1
is beneficially a glass panel since quartz panels are relatively expensive. The gate electrode
31
can made of a metallic material selected from a group comprised of Molybdenum (Mo), Tantalum (Ta), Tungsten (W), Niobium (Nb), and Antimony (Sb).
FIG. 3
b
illustrates the steps of depositing a first insulation film
102
and a semiconductor layer
104
. The gate insulation film
102
is formed by a deposition of an inorganic insulation film (such as a silicon nitride (SiN
x
) film or a silicon oxide(SiO
x
) film) having 4000 Å thickness. Alternatively, an organic insulation material such as BCB (benzocyclobutene) or acrylic resin can be used. After the deposition of the first insulation film
102
, a dual layer semiconductor film
104
comprised of an amorphous silicon layer
104
a
and a doped amorphous silicon film
104
b
are deposited. Although vapor deposition or ion injection can be used for the formation of the doped amorphous silicon film
104
b
, vapor deposition is usually employed.
Next, as shown
FIG. 3
c
, a second metal layer is deposited for both the source electrode
33
and the drain electrode
32
, and for the sound line
42
. That metal, beneficially Chromium (Cr) or a Cr-alloy, is then patterned to form the source electrode
33
, the drain electrode
32
and the ground line
42
. Moreover, the portion of the doped amorphous silicon film
104
b
between the source and drain electrodes
33
and
32
is eliminated by using the source and drain electrodes as masks. Then, a first capacitor electrode
58
is formed over the ground line
42
. The first capacitor electrode
58
is beneficially comprised of a transparent electrode material such as ITO (indium tin oxide). The region C in
FIG. 3
c
designates a switching transistor.
Referring to
FIG. 3
d,
a silicon nitride film having a thickness of 3000 Å forms a second insulation film
106
is deposited on the source and drain electrodes
33
and
32
, and on the first capacitor electrode
58
. The second insulating film
106
acts as protective layer for the TFT
3
and as a dielectric for a capacitor that is being formed with the first capacitor electrode
58
.
After the second insulation film
106
is deposited a second capacitor electrode
60
is formed on the second insulation film
105
and over the first capacitor electrode
58
. Beneficially, the second capacitor electrode is the same size as or a little larger than the first capacitor electrode
58
.
As shown in
FIG. 3
e
, an insulating protection film
108
is then formed. An organic substance such as BCB (benzocyclobutene) is beneficially used. BCB is a material that has a lower dielectric constant than silicon nitride, silicon oxide or acrylic resin. After formation of the protection
Brewster William M.
Chaudhuri Olik
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
LandOfFree
X-ray image sensor and method for fabricating the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray image sensor and method for fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray image sensor and method for fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117390