Radiant energy – Automatic/serial detection of similar sources
Patent
1991-12-11
1993-03-23
Hannaher, Constantine
Radiant energy
Automatic/serial detection of similar sources
H01L 310272
Patent
active
051967022
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a photo-sensor for generating an electrical signal in accordance with the quantity of an incident light and a method of operating the photo-sensor and, more particularly, to a photo-sensor suitable when used as the imaging element of an imaging device or the like and a method of operating the photo-sensor. This photo-sensor includes a variety of image pickup or electrophotographic devices and a medical X-ray imaging device.
Incidentally, the "light" will be herein termed as an electromagnetic wave for generating electron-hole pairs acting as photo-carriers when it is incident upon a photoconductor.
BACKGROUND ART
A photo-sensor, i.e., a storage type photo-sensor having functions to store and read out an electric signal according to the quantity of an incident light is advantageous over a non-storage type photo-sensor in that it can produce a more intense signal to attain a higher S/N ratio because it stores an electric signal generated by an incident light during its storage time. Storage type photo-sensors and signal reading methods are known. A system for reading signals by scanning an electron beam a photoconductive type image pickup tube (the operating principle of which is disclosed in Japanese Patent Laid-Open No. 58-194231) has been disclosed in the prior art, as have a system for reading out signals through a switching element disposed at each picture element and its wiring a solid-state image sensor (as referred to pp. 123 to 134 of "Imaging Technology" published by Corona Corp.) and a system for reading out signals by irradiations with a reading light for reading out the signals (as referred to pp. 81 to 87 of SPIE, Vol. 173 (1979)).
In the prior art, on the other hand, electrophotography using a photoconductive material has a wide variety of uses including in a facsimile machine and in a copying machine. In the medical field, moreover, electrophotography called Zeroradiography is used for dental or breast inspections. In this medical field, the digitization of an image has recently advanced as far as the desire to develop a system capable of not forming an analog image using toner like the aforementioned Zeroradiography but reading out the image in the form of electric signals and digitizing the signals. The papers having proposed a system of that kind are exemplified by Japanese Patent Laid-Open No. 59-99300, U.S. Pat. No. 4,268,750 and pp. 176 to 184 of SPIE, Vol. 626 (1986).
These photo-sensors adopt various signal reading methods and the structures therefor. One example of the conventional device using no signal reading light will be described below.
With reference to FIG. 17, an X-ray imaging device will be described as an example of the photo-sensor using a storage type photoconductive layer. FIG. 17 is a diagram showing a fundamental structure for explaining the operating principle of the photo-sensor. In this photoconductive device, charges are stored by a corona discharge in the surface region of a photoconductor 1701 formed over a substrate 1702, and the photoconductor 1701 is then irradiated with an X-ray. As a result, electron-hole pairs are generated by the interaction between the X-ray and the photoconductor 1701 and are moved by the internal electric field of the photoconductor 1701 to neutralize the charges which are stored in advance in the surface of the photoconductor 1701. At this time, a charge pattern according to the intensity distribution of the incident X-ray is formed in the surface of the photoconductor 1701. Since, this charge pattern is left in the surface of the photoconductor as the residual charge, i.e., the residue of the charge neutralized by the incident X-ray, it produces an X-ray image when it is read out by an electrometer 1703. This electrometer 1703 is equipped with a plurality of probes, which can scan the vicinity of the surface of the photoconductor 1701 to detect the potential pattern. The residual charge Q is expressed by the following equation if the charge stored by the corona discharge is designa
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Hirai Tadaaki
Itoh Haruo
Okajima Ken'ichi
Takahashi Tetshuhiko
Takasaki Yukio
Hannaher Constantine
Hitachi , Ltd.
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