Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2002-05-31
2004-11-16
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370080
Reexamination Certificate
active
06818899
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiographic image pickup apparatus and, more particularly, to a radiographic image pickup apparatus used for medical diagnosis or nondestructive inspection in an industrial process.
In this specification, radiation includes electromagnetic waves such as X-rays, alpha rays, beta rays, and gamma rays, and descriptions will be made based thereon.
2. Related Background Art
X-ray photographing systems installed in hospitals, etc., are divided into analog systems in which a subject is irradiated with X-rays and a film is exposed to X-rays reaching the film after passing through the subject, and digital systems in which X-rays passing through a subject are converted into an electric signal, which is stored, for example.
As a digital system, a radiographic image pickup apparatus is known which is constituted by a phosphor for converting X-rays into visible light and a photoelectric converter for converting the visible light into an electric signal. X-rays pass through a subject and the phosphor is irradiated with the X-rays and converts the X-rays into visible light for information about internal portions of the subject's body. The photoelectric converter converts the visible light into an electrical signal and outputs this signal. In the form of the converted electrical signal, X-ray image information to be recorded, displayed, printed or used for diagnosis can be treated as digital values after being digitized by an A/D converter.
Radiographic image pickup apparatuses using an amorphous silicon semiconductor thin film for a photoelectric converter have recently been put into practical use.
FIG. 13
is a top view of an example of a photoelectric conversion substrate in which photoelectric conversion devices of a metal insulator semiconductor (MIS) type and switching devices are formed by using an amorphous silicon semiconductor thin film as materials therefor. Wirings for connecting the devices are also illustrated in FIG.
13
.
FIG. 14
is a cross-sectional view taken along the line
14
—
14
of FIG.
13
. The MIS-type photoelectric conversion device will be referred to simply as “photoelectric conversion device” in the following description for the sake of simplicity.
Photoelectric conversion devices
301
and switching devices
302
(amorphous silicon TFTs, hereinafter referred to simply as “TFT”) are formed on one substrate
303
. A lower electrode of each photoelectric conversion device and a lower electrode (gate electrode) of each TFT are formed from a common layer, i.e., a first metallic thin film layer
304
. An upper electrode of each photoelectric conversion device and upper electrodes (source electrode and drain electrode) of each TFT are also formed from a common layer, i.e., a second metallic thin film layer
305
. Gate drive wirings
306
and matrix signal wirings
307
in a photoelectric conversion circuit section are also formed from the first and second metallic thin film layers. A layer
313
is an N
+
-layer, a layer
312
is an intrinsic semiconductor layer, and a layer
311
is an insulating layer made of SiNx for example. The pixels in number corresponding to 2′2, i.e., four pixels in total are illustrated in FIG.
13
. Hatched areas in
FIG. 13
represent light receiving surfaces of the photoelectric conversion devices. Power supply lines
309
for biasing the photoelectric conversion devices are also provided. The photoelectric conversion devices and TFTs are connected to each other via contact holes
310
.
The device operation of the photoelectric conversion device singly formed will be described by way of example.
FIGS. 15A
to
15
C are energy band diagrams for explaining the device operation of the photoelectric conversion device shown in
FIGS. 13 and 14
.
FIGS. 15A
to
15
C show operations in a refresh mode and in a photoelectric conversion mode, respectively, and show states in the film thickness direction of the layers shown in
FIG. 14. A
layer M
1
is the lower electrode (G-electrode) formed of the first metallic thin film layer (e.g., film of Cr). An a-SiNx layer is an insulating layer which blocks both passage of electrons and passage of holes. It is necessary that the thickness of the a-SiNx layer be large enough to prevent a tunnel effect. Ordinarily, the thickness of the a-SiNx layer is set to 500 angstroms or more. An a-Si-layer is a photoelectric conversion semiconductor layer formed of an intrinsic semiconductor i-layer. An N
+
-layer is an N-type injection blocking layer for blocking injection of holes into the a-Si-layer. A layer M
2
is the upper electrode (D electrode) formed of the second metallic thin film layer (e.g., film of Al).
In the structure shown in
FIG. 13
, the N
+
-layer is not completely covered with the D-electrode but the D-electrode and the N
+
-layer are always equipotential since electrons can move freely therebetween. The following description should be read on this understanding.
This photoelectric conversion device has two operation modes: a refresh mode and a photoelectric conversion mode in correspondence with different ways of applying voltages to the D-electrode and a G-electrode.
In the refresh mode, for example, a negative potential is applied to the D-electrode relative to that applied to the G-electrode, and holes indicated by black round marks in the i-layer are caused by the electric field to move toward the D-electrode, as shown in FIG.
15
A. Simultaneously, electrons indicated by white round marks are injected into the i-layer. At this time, part of holes and part of electrons recombine with each other in the N
+
- and i-layers to disappear. If the device is maintained in this state for a sufficiently long time, holes in the i-layer are swept out from this layer.
To set the device in the mode shown in
FIG. 15B
from this mode, a positive potential is applied to the D-electrode relative to that applied to the G-electrode. Then electrons in the i-layer are caused to move instantaneously toward the D-electrode. However, holes are not caused to move to the i-layer since the N
+
-layer functions as an injection blocking layer. When light enters the i-layer in this state, light is absorbed to generate electron-hole pairs. These electrons are caused by the electric field to move toward the D-electrode, while the holes move through the i-layer to reach the interface between the i-layer and the a-SiNx insulating layer. Since the holes cannot move into the insulating layer, they stay in the i-layer. At this time, with the movement of electrons to the D-electrode and the movement of holes to the insulating layer interface of the i-layer, a current flows from the G-electrode to maintain the electrical neutrality in the photoelectric conversion device. This current corresponds to the electron-hole pairs generated by the light and is therefore proportional to the quantity of light entering the photoelectric conversion device. After the device has been maintained for a certain time period in the state in the photoelectric conversion mode shown in
FIG. 15B
, it enters the state in the refresh mode shown in FIG.
15
A. The holes which have stayed in the i-layer are caused to move toward the D-electrode as described above and a current flows which corresponds to this flow of the holes. This amount of holes corresponds to the entire quantity of light entering during the photoelectric conversion mode period. At this time, a current also flows which corresponds to the amount of electrons injected into the i-layer. However, this amount is approximately constant and may be subtracted from the total amount to obtain the detection result. That is, this photoelectric conversion device outputs the quantity of light entering the device in real time, and is also capable of detection of the entire quantity of light entering during a certain period.
However, in a situation where the photoelectric conversion mode period is increased for some reason or in a situation where the illumination intensity
Hannaher Constantine
Moran Timothy J.
LandOfFree
Radiographic image pickup apparatus and method of driving... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radiographic image pickup apparatus and method of driving..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radiographic image pickup apparatus and method of driving... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3278368