Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-06-17
2002-12-31
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S370090, C257S437000
Reexamination Certificate
active
06501062
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading device and a radiation image pick-up apparatus, and specifically to an image reading device comprising a sensor substrate having at least a plurality of photosensors for executing photoelectric conversion of the light entered in the sensor substrate and to a radiation image pick-up apparatus utilizing such image reading device. More specifically, it relates to an image reading device formed with a large-area process to enable a large area image reading, and a radiation image pick-up apparatus utilizing such image reading device.
2. Related Background Art
For reading information such as an image for example in an image reader, there are conventionally known a reading device employing a reduction optical system and a CCD sensor, and a reading device employing a television camera.
Also, based on the recent development of a semiconductor material for photoelectric conversion by utilizing a non-single-crystalline semiconductor represented by hydrogenated amorphous silicon, there is recently proposed an image reading device having a plurality of photosensors formed on a large-sized substrate by using this material which can read an image with a large area.
Besides, the non-single-crystalline semiconductor can be utilized not only as the photoelectric conversion semiconductor material of the photosensor but also as the semiconductor material of the thin film transistor. Therefore, signal processing portions can also be formed on the large-sized substrate together with the photosensors. Furthermore, the photoelectric conversion semiconductor layer of the photosensor and the semiconductor layer of the thin film transistor can be composed of the same layer.
Furthermore, in case of forming a capacitance element such as a capacitor on the same substrate, a semiconductor layer may be interposed between the opposed electrodes if they are mutually insulated. Based on this fact, it is possible to make common the order of deposition for the films constituting the photosensor, the films constituting the thin film transistor and the films constituting the capacitance element, and the films constituting each element can therefore be made common.
It was therefore rendered possible to produce the image reading device with a large area at a low cost.
As another application of such large-area image reading device, there is also conceived a device for converting a radiation image into a visible image by a fluorescent plate which emits visible light by absorbing a radiation such as X-ray, and reading such visible image. A compact X-ray image pick-up apparatus of high performance is being realized by incorporating such image reading device thereto.
In Japanese Patent Application Laid-Open No. 9-298287 the present inventor has proposed one of the above-mentioned image reading devices.
FIG. 13A
is a plan view of one pixel of the image reading device proposed by the present inventor, and
FIG. 13B
is a cross-sectional view taken along the line
13
B—
13
B in FIG.
13
A. Also,
FIG. 14
is an equivalent circuit diagram of one pixel of this image reading device.
One pixel is composed of a MIS photosensor S
11
, and a driving thin film transistor T
11
serving as the driving portion of the photosensor. These drawings show a signal wiring SIG, a gate line gn of the driving thin film transistor T
11
, the upper electrode S and lower electrode G of the MIS sensor, and capacitances Cgs and Cgd respectively formed by overlapping the gate electrode with the source electrode and by overlapping the gate electrode with the drain electrode. Charges generated in the MIS photosensor S
11
by light are accumulated in the capacitances Cgs and Cgd through the thin film transistor T
11
, and are then read by a reading circuit not shown in the drawings. Though the above is limited to one bit, but in the fact the capacitances Cgs and Cgd are the sum of capacitances connected to other transistors, respectively. Thus the accumulation capacitances utilize Cgs and Cgd.
FIGS. 15A and 15B
are energy band illustrations Qf the photosensor showing the operations in a refreshing mode and a photoelectric conversion mode, respectively, wherein numerals
1
to
5
indicate each layer in the thickness direction thereof. In
FIG. 15A
showing the refreshing mode, the electrode S is given a negative potential with respect to the electrode G, whereby holes represented by black circles (&Circlesolid;) in a hydrogenated amorphous silicon layer
3
are guided to the electrode S by the electric field. At the same time, electrons represented by open circles (∘) are injected into the hydrogenated amorphous silicon layer
3
. In this time, a part of the holes and a part of the electrons recombine and vanish in an N
+
hydrogenated amorphous silicon layer
2
and the hydrogenated amorphous silicon layer
3
. If this state continues for a sufficiently long time, the holes in the hydrogenated amorphous silicon layer
3
are removed from the hydrogenated amorphous silicon layer
3
. When next state becomes a state of the photoelectric conversion mode shown in
FIG. 15B
, the electrode S is given a positive potential with respect to the electrode G, whereby the electrons in the hydrogenated amorphous silicon layer
3
are instantaneously guided to the electrode S. However, the holes are not guided to the hydrogenated amorphous silicon layer
3
because the N
+
hydrogenated amorphous silicon layer
2
functions as an injection inhibiting layer. When light enters the hydrogenated amorphous silicon layer
3
in this state, the light is absorbed and electron-hole pairs are generated. The electrons are guided to the electrode by the electric field, while the holes move in the hydrogenated amorphous silicon layer
3
and reach the interface of a hydrogenated amorphous silicon nitride layer
4
but are stopped at the interface and remain in the hydrogenated amorphous silicon layer
3
. As the electrons move to the electrode S while the holes move in the hydrogenated amorphous silicon layer
3
to the interface with the hydrogenated amorphous silicon nitride layer
4
, a current flows from the electrode G in order to maintain the electrical neutrality in the device. This current corresponding. to the electron-hole pairs generated by the light is proportional to the incident light.
FIG. 16
shows the entire circuit of the image reading device. Photosensors and thin film transistors for driving the photosensors can be formed on the same substrate by the same process. In the circuit diagram there are shown photosensors S
11
to S
33
, thin film transistors T
11
to T
33
for driving the photosensors, a reading power source Vs and a refreshing power source Vg connected, respectively through switches SWs and SWg, to the lower electrode G of all the photosensors S
11
to S
33
. The switch SWs is connected through an inverter to a refreshing control circuit RF while the switch SWg is connected directly to the refreshing control circuit RF. The switch SWg is turned on during the refreshing period while the switch SWs is turned on during other periods. The output signal is supplied by a signal wiring SIG to a detecting integrated circuit IC.
In the circuit shown in
FIG. 16
, nine pixels are divided into three blocks, and the outputs of three pixels in each block are transferred simultaneously and signals are successively converted into outputs by the detecting integrated circuit. For the purpose of simplicity, there is illustrated a two-dimensional image input portion of nine pixels but there are in practice provided a larger number of pixels in a high density. As an example, in case an image reading device of 40×40 cm is formed with pixels of a size of 150×150 &mgr;m, there are provided approximately 1.8 million pixels.
FIG. 17
schematically shows an X-ray image reading device formed by combining the above-described image reading device with a fluorescent plate, and an X-ray image pick-up apparatus utilizing such image reading. devic
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le Que T.
Luu Thanh X.
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