Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Patent
1995-10-30
1997-12-02
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
G01T 100, G01T 124, G01T 129
Patent
active
056939477
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to radiation detectors and in particular to large-area, two-dimensional, pixellated radiation detectors.
The invention has particular, though not exclusive application to such detectors used for medical imaging; for example, medical X-radiation imaging.
Pixellated radiation detectors usually comprise an array of radiation-sensitive elements layed out in two-dimensional fashion. Typically, the elements are arranged in rows and columns to form a regular array.
In one known example of such radiation detectors each element in the array comprises a reverse-biased photodiode coupled to a transistor. During signal integration, the transistor is held in a non-conducting state and an optical radiation signal derived from the incident radiation is allowed to discharge the bias applied across the photodiode. The signal is then readout by switching the transistor to its conducting state and recording the amount of charge required to restore the reverse bias across the photodiode. Such arrays are typically constructed from crystalline silicon or hydrogenated amorphous silicon (a - Si:H).
A radiation detector of this kind tends to be unsatisfactory in that the detector exhibits non-linear performance and saturation for large input signals, and leakage current in an a-Si:H sensor results in appreciable detected shot noise. Also, such radiation detectors suffer from image lag due to trapping sites in the semiconductor material.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a radiation detector comprising, first capacitive means including a two-dimensional array of discrete, charge-collection electrodes, second capacitive means including radiation conversion means, the second capacitive means being co-operable with the first capacitive means to cause charge to accumulate on said discrete, charge-collection electrodes according to the spatial distribution of intensity of radiation to which said radiation conversion means is exposed, and read-out means for outputting a signal representative of charge that accumulates on the discrete, charge collection electrodes of the first capacitive means.
The radiation detector has a dual-capacitive structure which serves to protect the read-out circuitry from exposure to relatively high electrical voltages associated with the operation of the radiation conversion means. Also, the structure of the radiation detector enables a relatively high frame rate imaging capability to be attained.
According to another aspect of the invention there is provided a radiation detector comprising, first capacitive means including a semiconductor substrate and a two-dimensional array of discrete, charge-collection electrodes formed on a first surface of the semiconductor substrate, each said charge-collection electrode forming part of a respective first capacitor,
second capacitive means comprising a second capacitor arranged in series with the first capacitors of the first capacitive means, the second capacitor comprising a layer of a radiation conversion material for converting radiation to which the layer is exposed into electrical charge and focussing means for focussing charge generated in the layer of radiation conversion material onto said discrete charge-collection electrodes, whereby charge accumulates on the charge-collection electrodes substantially according to the spatial distribution of the intensity of said radiation,
and read-out means for outputting a signal representative of charge that accumulates on the discrete, charge-collection electrodes.
DESCRIPTION OF THE DRAWINGS
Radiation detectors according to the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 illustrates diagrammatically a radiation detector according to one embodiment of the invention;
FIGS. 2(a) to 2(c) show the equivalent circuits of different implementations of the radiation converter shown in FIG. 1;
FIG. 3 shows diagramatically the read-out circuitry of th
REFERENCES:
patent: 4810881 (1989-03-01), Berger et al.
patent: 4885620 (1989-12-01), Kemmer et al.
patent: 4926052 (1990-05-01), Hatayama et al.
patent: 4945242 (1990-07-01), Berger et al.
patent: 5017989 (1991-05-01), Street et al.
patent: 5023661 (1991-06-01), Fender et al.
patent: 5043582 (1991-08-01), Cox et al.
patent: 5079426 (1992-01-01), Antonuk et al.
patent: 5132541 (1992-07-01), Conrads et al.
patent: 5153423 (1992-10-01), Conrads et al.
patent: 5164809 (1992-11-01), Street et al.
patent: 5166524 (1992-11-01), Lee et al.
patent: 5168160 (1992-12-01), Jeromin et al.
patent: 5182624 (1993-01-01), Tran et al.
patent: 5198673 (1993-03-01), Rougeot et al.
patent: 5220170 (1993-06-01), Cox et al.
patent: 5254480 (1993-10-01), Tran
patent: 5300784 (1994-04-01), Fender et al.
patent: 5313066 (1994-05-01), Lee et al.
patent: 5319206 (1994-06-01), Lee et al.
patent: 5331145 (1994-07-01), Weckler et al.
patent: 5331179 (1994-07-01), Lee et al.
patent: 5381014 (1995-01-01), Jeromin et al.
Antonuk et al., "Development of Thin-Film, Flat-Panel Arrays for Diagnostic and Radiotherapy Imaging," Conference Proceedings of SPIE Medical Imaging VI, Newport Beach, CA (Feb., 1992).
Antonuk et al., "Large Area, Flat-Panel a-Si:H Arrays for X-Ray Imaging," Physics of Medical Imaging, 1896, 18-29 (Feb., 1993).
Hannaher Constantine
The University of Surrey
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