Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2001-12-20
2003-11-11
Bennett, G. Bradley (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370090
Reexamination Certificate
active
06646266
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a flat panel image sensor being capable of detecting an image of X-rays and other kind of radiation and visible, infrared, and other kind of light.
BACKGROUND OF THE INVENTION
Conventionally known flat panel image sensors are arranged so that while a semiconductor film, detecting X-rays and generating electric charges imparted by electron-hole pairs, is provided on an active matrix substrate, electric switches are provided in pixels arranged on the active matrix substrate in a matrix manner, and the electric switches are sequentially turned on in pixels of each column to read electric charges of pixels in each row.
For instance, the structure and principles thereof are explained in publications including L. S. Jeromin, et al., “Application of a-Si Active-Matrix Technology in a X-Ray Detector Panel” (SID 97 Digest, pp. 91-94, disclosed on May 13, 1997) and W. den Boer, et al., “Similarities between TFT Arrays for Direct-Conversion X-Ray Sensors and High-Aperture AMLCDS” (SID 98 Digest, pp. 371-374, disclosed on May 17, 1998).
Now, an arrangement of the conventional flat panel image sensor will be discussed.
FIG. 12
shows that a conventional flat panel image sensor
100
includes:
an active matrix substrate
200
which is substantially square and on which pixels
210
are arranged in a matrix manner;
a substantially square semiconductor film
300
, sharing the center with the active matrix substrate
200
, formed on the active matrix substrate
200
; and a bias electrode
400
formed on the substantially entire surface of the semiconductor film
300
.
Each pixel
210
on the active matrix substrate
200
includes, as an enlarged view of
FIG. 13
shows, electrode wires arranged in an XY matrix including a scanning wire
211
and a signal wire
212
, a thin film transistor (hereinafter, will be simply referred to as TFT)
213
, and a charge storage (hereinafter, will be simply referred to as CS)
214
formed with respect to the active matrix substrate
200
(see FIG.
12
).
The semiconductor film
300
(see
FIG. 12
) is made of a photoconductive substance that generates electric charges when X-rays and other kind of radiation are projected thereon. Photoconductivity means a characteristic that electric charges are generated when X-rays etc. are projected.
For instance, in the documents cited above, what is employed for use as the semiconductor film is amorphous selenium (hereinafter, will be simply referred to as a-Se) that has high dark resistance, exhibits satisfactory photoconductivity when exposed to X-rays, and is easy to form large films by vapor deposition.
Meanwhile, an active matrix substrate formed in a process to manufacture a liquid crystal display unit can be appropriated for use as the active matrix substrate
200
. For instance, since each pixel of the active matrix substrate used for an active matrix liquid crystal display (hereinafter, will be simply referred to as AMLCD) includes a TFT made of amorphous silicon (hereinafter, will be simply referred to as a-Si) or polysilicon (hereinafter, will be simply referred to as p-Si), XY matrix electrodes, and a CS, the active matrix substrate is easily modified as the active matrix substrate for the flat panel image sensor.
Next, a function of a conventional flat panel image sensor will be described. When X-rays and other kind of radiation are projected onto the semiconductor film
300
such as an a-Se film, electric charges are generated in the semiconductor film
300
. The charges generated in the semiconductor film
300
move toward the anodes and cathodes, if voltage is applied to the bias electrode
400
. Consequently, the electric charges are accumulated in the CS
214
formed on the active matrix substrate
200
.
The electric charges thus accumulated in the CS
214
can be taken out to the outside through the signal wire
212
, by making the TFT
213
into an on-state by means of an input signal from the scanning wire
211
.
As
FIG. 13
indicates, the electrode wire including the scanning wire
211
and the signal wire
212
, the TFT
213
, the CS
214
etc. are all provided on the active matrix substrate
200
(see
FIG. 12
) in an XY matrix manner. Thus electric charges as information of images accumulated in each CS
214
are taken out to the outside through the associated signal wire
212
by making the associated TFT
213
into an on-state by sequentially scanning an input signal with respect to the associated scanning wire
211
, so that information on a two-dimensional image of X-rays is obtainable.
Moreover, if the semiconductor film
300
of the conventional flat panel image sensor
100
exhibits photoconductivity to visible or infrared light, as well as radiation such as X-rays, the flat panel image sensor
100
can function as a two-dimensional visible or infrared image detector. For instance, since the a-Se film mentioned above exhibits a satisfactory level of photoconductivity to visible light, the film can be used as a high sensitive image sensor by utilizing avalanche effect on the application of a strong electric field.
However, the conventional flat panel image sensor
100
could discharge around the sensor due to a requirement of charging high voltage to the bias electrode
400
. Moreover, the semiconductor film
300
is susceptible to pollution.
To resolve these problems, as
FIG. 14
shows, a conventional flat panel image sensor
110
includes:
a spacer
500
which is shaped like a substantially square frame and provided on an edge of an active matrix substrate
200
;
an insulating resin
600
formed to cover both areas on the active matrix substrate
200
, one which is indicated as Y
10
on which the semiconductor chip
300
is formed, and the other which is indicated as X
10
on which the semiconductor chip
300
is not formed; and
a protective substrate
700
provided to be in parallel with the active matrix substrate
200
while keeping a certain distance from the substrate
200
by the spacer
500
.
Incidentally, the insulating resin
600
is sealed by the spacer
500
, and the protective substrate
700
and the active matrix substrate
200
are a substantially identical square.
The protective substrate
700
provided above the insulating resin
600
is situated for:
improving the strength of the flat panel image sensor
110
;
mechanically protecting an exposed surface of the insulating resin
600
; and
segregating the insulating resin
600
from outside moisture, etc.
However, in the conventional flat panel image sensor
110
, the semiconductor film
300
is arranged to have the thickness around from several hundred microns to 1 mm, to improve absorption efficiency of X-rays. Therefore, in the part Y
10
where the semiconductor film
300
is formed on the active matrix substrate
200
, the thickness of the insulating resin
600
formed on the active matrix substrate
200
differs from the thickness in the part X
10
where the semiconductor film
300
is not formed.
In other words, a thickness x
10
of the insulating resin
600
in the area X
10
is greater than a thickness y
10
of the insulating resin
600
in the area Y
10
, because the thickness equivalent to that of the semiconductor film
300
is added to the former.
Furthermore, the volume of resin materials such as a photo-setting resin, a thermosetting resin, and a two-liquid-setting resin shrinks around 5 to 10% when hardened.
For instance, assuming that the thickness of the semiconductor film
300
is 1 mm, the difference between the thicknesses x
10
and y
10
of the insulating resin
600
is 1 mm, and hence the difference in the reduction in thickness of the insulating resin
600
due to the hardening differs by around
50
to 100 &mgr;m.
In this manner, the area Y
10
on the active matrix substrate
200
where the semiconductor film
300
is formed differs from the surrounding area X
10
where the semiconductor film
300
is not formed, in the amount of the reduced thickness of the insulating resin
600
due to the hardening. Thus great internal stress is accumulated
Bennett G. Bradley
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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