Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-08-31
2003-08-19
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S487100
Reexamination Certificate
active
06608312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information reading apparatus, a method of producing the apparatus, and a radiation imaging system using the apparatus and, more particularly, to an information reading apparatus having a wavelength conversion member such as a scintillator or the like, a production method of the apparatus, and a radiation imaging system using the apparatus.
2. Related Background Art
Under the trend toward filmless roentgenography, some companies have released semiconductor instruments provided with an X-ray area sensor in recent years, and methods thereof are generally classified under two types, a direct system (a type in which X-rays are directly converted into electric signals to be read) and an indirect system (a type in which X-rays are once converted into visible light and the visible light is then converted into electric signals to be read).
FIG. 1A
is a schematic, cross-sectional view of an information reading device provided with an example of the X-ray area sensor of the indirect system.
FIG. 1B
is a schematic plan view of FIG.
1
A. In FIGS.
1
A and
1
B, numeral
401
designates a glass substrate,
402
MIS photosensor portions using amorphous silicon,
403
TFT switch portions,
404
electrode portions (areas where electrodes are provided),
411
a first protective layer made of a nitride or the like for electrically protecting the photosensor portions
402
, the TFT switch portions
403
, etc.,
412
a scintillator made of, for example, cesium iodide (CsI) as a wavelength conversion member,
413
a scintillator protecting layer made of an organic resin for protecting the scintillator
412
from external water or the like,
414
a reflective substrate with a high reflectance made of an aluminum sheet or the like, and
415
a second protective layer made of an organic substance such as polyimide (PI) or the like for protecting the photosensor portions
402
etc. from impurities in the scintillator
412
.
When X-rays are incident from the upper part of
FIG. 1A
, the X-rays permeate the reflective substrate
414
and the scintillator protecting layer
413
to be absorbed by the scintillator
412
. The scintillator
412
absorbing the X-rays emits visible light in all the directions in the bulk. At this time, since the crystals of the scintillator
412
are of the vertically grown columnar shape as illustrated in
FIG. 1A
, the light emitted in the bulk eventually travels in the longitudinal direction of the columnar shape with being reflected at grain boundaries, substantially according to the principle of light transmittance in optical fibers.
Then, most of the light is concentratedly guided to the photosensor portions
402
and TFT switch portions
403
in the lower part of FIG.
1
A. Therefore, this structure is able to achieve a high sensitivity and improvement in resolution.
A production method of the information reading device as an X-ray area sensor illustrated in
FIGS. 1A and 1B
will be described below. The X-ray area sensor illustrated in
FIGS. 1A and 1B
is a semiconductor device obtained by forming the photosensor portions
402
and TFT switch portions
403
on the glass substrate
401
, thereafter forming the first protective layer
411
thereon, and further forming the second protective layer
415
thereon. In this state the scintillator
412
is directly deposited onto the second protective layer
415
by vapor deposition while portions without necessity for the vapor deposition are preliminarily covered with a mask (not shown).
In order to make the scintillator
412
of the ideal columnar structure of cesium iodide, although the temperature during the vapor deposition is preferably not less than 200° C., but the temperatures of not less than 200° C. will deteriorate the photosensor portions
402
and the TFT switch portions
403
already formed, the scintillator
412
has to be formed at a temperature of not more than 200° C.
After the formation of the scintillator
412
through the vapor deposition, a protective film for moisture resistance is bonded thereonto to form the scintillator protecting layer
413
. An aluminum sheet as the reflective substrate
414
is then bonded thereonto, thus completing the X-ray area sensor.
When the scintillator
412
is formed in this way by directly depositing cesium iodide onto the glass substrate
401
having the photosensor portions
402
and TFT switch portions
403
formed thereon, the optically advantageous structure can be provided, but on the other hand the temperature has to be kept not more than 200° C.
This means that, where the photosensor portions
402
and TFT switch portions
403
are formed of amorphous silicon, optimization has to be implemented within the temperature range such that hydrogen atoms do not become unbound.
FIGS. 2A and 2B
are a schematic plan view and a schematic, cross-sectional view of a large information reading device, for example, provided with four area sensors, which are the semiconductor devices illustrated in
FIGS. 1A and 1B
. In the information reading device illustrated, the four area sensors are bonded onto the substrate
605
(arranged adjacent to one another) and the scintillator
412
is directly deposited onto them. The four area sensors are fixed on the substrate
605
through an adhesion layer
606
.
For this structure, a gap
650
is created between adjacent area sensors as illustrated in FIG.
2
A and the plane of the vapor deposited surfaces of the scintillator is divided near the gap; therefore, the scintillator
412
also grows in the lateral direction in the figure. The crystals of the scintillator near the gap
650
are not formed in the shape of columns perpendicular to the second protective layer
415
when compared with those in the other portions, accordingly.
FIGS. 3A and 3B
show another information reading device provided with an area sensor which has a glass substrate
401
having photosensor portions
402
and TFT switch portions
403
formed on a surface thereof, and a scintillator
412
of the optimum columnar structure provided on the surface.
In
FIGS. 3A and 3B
, numeral
511
designates a protective layer made of, for example, a nitride or the like for protecting the photosensor portions
402
, etc. from external water,
512
an adhesion layer for bonding the scintillator
412
and the protective layer
511
to each other, and
515
a seal portion made of an organic resin. Members similar to those illustrated in
FIGS. 1A and 1B
are denoted by the same reference numerals.
In the information reading device illustrated in
FIGS. 3A and 3B
, the scintillator
412
is vapor deposited on the reflective substrate
414
. The photosensor portions
402
, etc. and the protective layer
511
are formed on the glass substrate
401
to obtain a semiconductor device, and the scintillator
412
is bonded onto the protective layer
511
through the adhesion layer
512
. In the last step, the scintillator
412
and the adhesion layer
512
are sealed by a sealant
515
.
When the part of the reflective substrate
414
and the part of the glass substrate
401
are bonded to each other in this way, it becomes feasible to form the scintillator
412
on the reflective substrate
414
without care on deterioration of the photosensor portions
402
, etc. due to the temperature during the vapor deposition of the scintillator
412
, and thus to obtain the ideal columnar structure. However, since cesium iodide as the material of the scintillator
412
is brittle, it is necessary in this structure to pay close attention so as not to break the scintillator
412
when bonding the scintillator
412
and the protective layer
511
to each other.
As described above, the information reading device illustrated in
FIGS. 3A and 3B
was fabricated by bonding the scintillator and the protective layer to each other, and the scintillator was sometimes broken in part in the bonding. The reason is that cesium iodide for forming the scintillator is brittle as described above.
Further, there were desires f
Mochizuki Chiori
Morishita Masakazu
Okada Satoshi
Hannaher Constantine
Lee Shun
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