Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-03-30
2003-02-11
Mai, Huy (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S591000
Reexamination Certificate
active
06518575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state radiation detector having a charge storing section which stores the charges of the quantity corresponding to the dose of the projected radiation as latent image charges, and being capable of recording radiation image information as a static latent image in the charge storing section.
2. Description of the Prior Art
To reduce the dose of exposure of the subject and improve the performance of diagnosis in medical radiation photographing, etc., a method has been known up to now which uses, as a photosensitive material, a solid-state radiation detector (a static recorder) with a photoconductor, such as a selenium plate, responding to radiation, such as X-rays; projects the X-rays onto the detector, and stores the charges of the quantity corresponding to the dose of the projected radiation in the charge storing section of the detector as latent image charges for recording of radiation image information as a static latent image (a charge pattern); and uses a laser beam or line light to scan the detector to read out the radiation image information from the detector.
To efficiently store latent image charges in the charge storing section, a detector which is provided with microplates (minute conductive members) or an anisotropic conductive layer has been proposed (for example, U.S. Pat. Nos. 5,166,524, 4,535,468, 3,069,551, European Patent No. 0748115A1, which corresponds to Japanese Unexamined Patent Publication No. 9(1997)-5906, and Japanese Unexamined Patent Publication No. 6(1994)-217322).
The detector as proposed in the above-mentioned U.S. Pat. No. 5,166,524 is a detector with which conductive microplates having a size approximately equal to the smallest pixel size which can be resolved are provided on the surface of the detector, and these microplates form pixels in the fixed locations on the detector. When this detector is used to record a static latent image, and read out it, the electrode of a single plate which is to contact all the microplates is disposed on the surface of the detector; a voltage is applied to this electrode for subjecting it to an electric field; X-rays are projected onto it to store the static latent image in the charge storing section for carrying out the recording; and then the single-plate electrode is removed, and a signal is taken out from the microplates.
The detector is proposed in the above-mentioned U.S. Pat. No. 4,535,468 is a detector comprising a three-layer structure which has an X-ray photoconductive layer, a trap layer, and a photoconductive layer for reading in this order, the charge storing section for storing of charges generated in the X-ray photoconductive layer being formed by the trap layer. When this detector is used to record a static latent image and read it out, a high voltage is applied across the electrodes provided on both sides of the three layer structure, and X-rays are projected to store latent image charges in the charge storing section, and then the electrodes are short-circuited to read out the latent image charges.
The detector as proposed in the above-mentioned U.S. Pat. No. 3,069,551 is a detector with which an anisotropic conductive layer is provided in the detector, and the anisotropic conductive layer forms the charge storing section, and it is almost the same as that proposed in the above-mentioned U.S. Pat. No. 4,535,468.
The detector as proposed in the above-mentioned European Patent No. 0748115A1 is a detector with which a conductive microspot layer in which a number of microspots having a size much smaller than the pixel size are disposed is provided in the detector, and latent image charges are stored in the microspots.
Further, the detector as proposed in the above-mentioned Japanese Unexamined Patent Publication No. 6(1994)-217322 is a detector with which a conductive layer, an X-ray photoconductive layer, a dielectric layer, and an electrode layer comprising a number of microplates corresponding to the pixels are stacked, and a TFT (a thin film transistor) for reading out the charges is connected to each microplate. When the static latent image is to be read out from this detector, the TFTs are scanned and driven to read out the latent image charges stored in the charge storing section to the outside of the detector.
However, with the detectors as proposed in the above-mentioned U.S. Pat. No. 5,166,524 and Japanese Unexamined Patent Publication No. 6 (1994)-217322, pixels can be formed in the fixed locations on the detector by providing microplates as stated above, but with the detector of the U.S. Pat. No. 5,166,524, a single-plate electrode must be disposed on the surface of the detector for carrying out the recording, and thereafter, this single-plate electrode must be removed for taking out a signal, which means that the recording and reading operations are cumbersome, and with the detector of Japanese Unexamined Patent Publication No. 6(1994)-217322, it is necessary to provide TFTs for charge reading in the electrode layer comprising microplates, which presents a problem that the construction of the detector is complicated, resulting in the manufacturing cost for the detector being increased.
On the other hand, the detectors of the U.S. Pat. Nos. 4,535,468, 3,069,551 and European Patent No. 0748115A1 are detectors with which the charge storing section is formed by the trap layer or the like provided in the detector, but, the trap layer or the like is not such that charges are discretely stored for each pixel, presenting problems that pixels cannot be formed in the fixed locations, and the artifact (the structure noise) having a location dependency cannot be properly compensated for.
Also with this U.S. Pat. No. 4,535,468, etc., the electrode is a stripe electrode, and line light is used as reading light, the elements of the stripe electrode being scanned along the longitudinal direction of them with the line light. This means that for the direction of arrangement of the elements, pixels can be formed in the fixed locations, but because the elements are not divided by the pixel size along the longitudinal direction of them, pixels cannot be formed in the fixed locations for the longitudinal direction, resulting in an anisotropy in sharpeness being produced.
In addition, with any of the detectors as disclosed in the above documents, it is difficult to cause the latent image charges to have the same potential for each pixel, the latent image charge around the pixel cannot sufficiently be discharged, and the information around the pixel may not easily be taken out.
The solid-state radiation detector according to the present invention is a solid-state radiation detector having a first electrode layer, a photoconductive layer for recording which exhibits a conductivity when irradiated with radiation which has been projected or light emitted by excitation on the radiation, and a second electrode layer in this order, a charge storing section for storing the charges of the quantity corresponding to the dose of the radiation or the quantity of the light as latent image charges being formed in the vicinity of the surface of the photoconductive layer for recording, and radiation image information being recorded in the charge storing section as a static latent image,
in which a conductive member for causing the latent image charges to have the same potential is discretely provided in the charge storing section for each pixel for the static latent image, and is put in the electrically non-connected state.
Here, the phrase “is provided for each pixel” means that preferably one conductive member is provided for each pixel so that the charges around the pixel can be concentrated on the pixel central portion in reading by causing the latent image charges to have the same potential, and does not involve the style in which a number of conductive members are disposed at random for one pixel, and in reading the charges around the pixel cannot be concentrated on the pixel central portion.
The phrase “is discretely provide
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