Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-02-18
2003-07-29
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370090
Reexamination Certificate
active
06600160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric converter and a radiation reader, more particularly to a photoelectric converter capable of performing the read operation at higher sensitivity and higher speed and a radiation reader capable of reading the information for radiation represented by (&agr;-rays, &bgr;-rays, &ggr;-rays or x-rays at a high sensitivity.
2. Related Background Art
In the case of a photoelectric converter and a radiation reader for reading the information based on radiation by wavelength-converting the radiation into the sensitivity region of the photoelectric converter with a wavelength converter such as a photoluminescent body (for example, scintillator), electric charges based on the input information photoelectric-converted by a photoelectric-converting section is transferred to a capacitance to amplify a signal voltage.
However, to amplify a signal voltage by transferring electric charges from the capacitance of a photoelectric-conversion element itself to an external capacitance like the case of reading signal charges with a conventional circuit, a relatively-large S/N ratio can be obtained but a parasitic capacitance may be formed on a signal line when arranging a plurality of sensors. For example, when arranging 2,000×2,000 area sensors equivalent to an X-ray film at a size of 200×200 &mgr;m per cell and manufacturing an area sensor with a size of 40×40 cm, a capacitance is formed because the gate and source of a transistor for transferring electric charges are overlapped each other. Because the above overlap corresponds to the number of pixels, one signal line has an overlap C
gs
capacitance of 0.05 pF×2,000 area sensors=100 pF even if one area sensor has a capacitance of approx. 0.05 pF. Because a sensor capacitance C
s
is equal to approx. 1 pF, when assuming a signal voltage generated in a sensor as V
1
, the output voltage V
0
of the signal line is obtained from the following expression.
V
0
=(
C
s
/(
C
s
+C
gs
×1000))×
V
1
Thus, the output voltage lowers to 1/100.
That is, to constitute an area sensor having a large area, an output voltage is greatly lowered.
Moreover, to read a dynamic image under the above condition, a sensitivity and a high-speed operation capable of reading 30 images per sec. or more are requested. Particularly, in the case of a nondestructive inspection including X-ray diagnosis, higher sensitivity allowing the number of signal charges to increase up to 100 to 400 times is requested because there is a request for minimizing the dose of X-rays to be irradiated.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problems and its object is to provide a photoelectric converter capable of preventing an output voltage from lowering due to increase of a parasitic capacitance and resultantly having higher sensitivity and more-advanced performance and a radiation reader having the photoelectric converter.
It is another object of the present invention to provide a photoelectric converter having a large opening ratio, that is, a large rate of the light-receiving-section region in an area necessary for one pixel and resultantly capable of achieving a high sensitivity and an advanced performance and a radiation reader having the photoelectric converter.
It is still another object of the present invention to provide a photoelectric converter capable of reading a dynamic image.
It is still another object of the present invention to provide a radiation reader capable of further reducing the dose of radiation such as X-rays.
It is still another object of the present invention to provide a photoelectric converter having a semiconductor layer comprising in one pixel: a photoelectric conversion element, a reading field-effect transistor having a gate for receiving signal charges generated in the photoelectric conversion element and a source and a drain for reading a signal corresponding to the signal charges accumulated in the gate, selection-switch means set between the reading field-effect transistor and a power supply, and reset means for resetting the gate; wherein
the photoelectric conversion element, the reading field-effect transistor, the selection-switch means, and the reset means are formed on a common insulating support body.
It is still another object of the present invention to provide a radiation reader comprising a photoelectric converter having a semiconductor layer comprising in one pixel: a photoelectric conversion element, a reading field-effect transistor having a gate for receiving signal charges generated in the photoelectric conversion element and a source and a drain for reading a signal corresponding to the signal charges accumulated in the gate, selection-switch means set between the reading field-effect transistor and a power supply, and reset means for resetting the gate; wherein the photoelectric conversion element, the reading field-effect transistor, the selection-switch means, and the reset means are formed on a common insulating support body; and a photoluminescent body set on the photoelectric conversion element to absorb radiation and emit light in a wavelength band which can be detected by the photoelectric conversion element.
It is still another object of the present invention to provide a radiation reader having the following in one pixel: a radiation reading element which includes an electric-charge discharging layer for absorbing radiation and discharging electric charges and in which at least the electric-charge discharging layer is constituted so as to be held by two conductive layers, a reading field-effect transistor having a gate for receiving signal charges generated in the radiation reading element and a source and a drain for reading a signal corresponding to the signal charges accumulated in the gate, selection-switch means set between the reading field-effect transistor and a power supply, and reset means for resetting the gate.
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Kobayashi Isao
Morishita Masakazu
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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