Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2001-01-10
2003-01-14
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370120
Reexamination Certificate
active
06507026
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a planar X-ray detector for a medical X-ray diagnostic apparatus.
In recent years, in the medical field, database are being prepared with respect to the medical data of patients in order to perform medical treatments promptly and exactly. This is because, since a patient often utilizes two or more medical institutions, a medical institution requires the data on the patient prepared in another medical institution in order to perform an exact medical treatment.
There are also demands for preparing database on image data of the radiographs, and therefore it is requested to digitize the radiograph images in accordance with the demands. In the medical X-ray diagnostic apparatus, it has been customary to photograph an image using a silver halide film. In order to digitize such an image, it is necessary to develop the photographed image, followed by reading the image with a scanner or the like, leading to requirement of much labor and time.
Recently, an image intensifier TV system of directly detecting a digital image by using a photoelectron emission film, a vacuum tube, a phosphor film, and a CCD camera of a size of about one inch has been realized. However, in the diagnosis of, for example, lungs, a large area of about 40 cm×40 cm is photographed, making it necessary to use an optical apparatus for converging light. As a result, a large volume size of the apparatus becomes a serious problem.
As a system capable of solving the problems inherent in the above two systems, proposed is a planar X-ray detector of a direct conversion type using an amorphous silicon thin film transistor (a-Si TFT). In the planar X-ray detector, an incident X-ray is directly converted into electric charges by an X-ray charge conversion film in each pixel.
FIG. 1
shows the element structure of one pixel of the conventional planar X-ray detector. A capacitor (Cst) of a laminate structure consisting of a capacitor electrode
404
, an insulating layer
103
and an auxiliary electrode
502
, and a switching TFT
402
and a protective TFT
411
, each of which is connected to the capacitor, are formed on a glass substrate
101
. A passivation film is formed on these members, having a contact hole. Formed on the passivation film is a laminate structure consisting of a pixel electrode
503
, which is connected to the auxiliary electrode
502
, a p-type contact film
601
, an X-ray charge conversion film
403
, an n-type contact film
602
, and a common electrode
603
. The pixels are arranged to form an array.
When an X-ray is incident on the planar X-ray detector, the X-ray is converted into electric charges by the X-ray charge conversion film
403
, and the electric charges are accelerated by an electric field applied between the common electrode
603
and the pixel electrode
503
and then accumulated in the capacitor. The switching TFT
402
is driven through a scanning line so as to transport the charges accumulated in the capacitor to a signal line and to an amplifier circuit
410
. The protective TFT
411
functions to release charges when excessive charges are generated.
Conventionally, a film of Se, PbI
2
or the like is mainly used as the X-ray charge conversion film
403
. On the surface of the planar X-ray detector, the X-ray charge conversion film
403
is covered with the n-type contact film
602
and the common electrode
603
. However, the X-ray charge conversion film
403
is exposed to the outside in the side surface of the planar X-ray detector. Since the material such as Se and PbI
2
gives a detrimental effect to the human body, it is undesirable for the X-ray charge conversion film
403
to be exposed to the outside. Also, in order to obtain a high-precision image, it is necessary to form the X-ray charge conversion film
403
uniformly. However, it is difficult to form a large area uniform film by using a metal or a metal compound such as Se and PbI
2
.
Japanese Patent Publication (Kokoku) No. 4-63555 discloses an X-ray sensor comprising an X-ray detecting layer formed of phosphor particles and photoconductor particles dispersed in the transparent charge transport material. The X-ray sensor is applied to an X-ray CT scanner. In the X-ray sensor, the phosphor particles irradiated with the X-ray emits fluorescent light, and the photoconductor particles irradiated with the fluorescent light generates electrons and holes, which are transported by the charge transport material. However, where the X-ray sensor is applied to a planar X-ray detector, a problem is brought about that the generated fluorescent light spreads in an isotropic manner and arrives at adjacent pixels so as to bring about crosstalk and deterioration of spatial resolution of detected image.
Japanese Patent Disclosure (Kokai) No. 3-273687 discloses a radiation absorbing material prepared by dispersing in an organic semiconductor such as metal phthalocyanine or an inorganic semiconductor of such as CdS, a metal of such as W or Pb element having an atomic number larger than that of the basal organic semiconductor or inorganic semiconductor. However, since the prior art uses a metal as the radiation absorbing material, electron-hole pairs have high probability to recombine within the metal, because there exists a large Coulombic attractive force between small distance electron-hole pair due to small velocity caused by small electric field in metal having a high conductivity, making it difficult to take out the charges to the outside, and leading to poor efficiency.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a planar X-ray detector that enables to effectively take out charges generated by an incident X-ray to the outside.
According to an aspect of the present invention, there is provided a planar X-ray detector, comprising: a pair of electrodes, and an X-ray charge conversion film disposed between the electrodes, the film containing a mixture of inorganic semiconductor particles sensitive to an X-ray and a carrier transport material.
According to another aspect of the present invention, there is provided a planar X-ray detector, comprising: an X-ray charge conversion film converting an incident X-ray into electric charges; pixel electrodes provided on the X-ray charge conversion film corresponding to respective pixels arranged in an array; switching elements connected to the respective pixel electrodes; signal lines, each of which is connected to a column of switching elements; scanning lines, each of which transmits driving signals to a raw of switching elements; and a common electrode provided on the surface of the X-ray charge conversion film opposite to the surface on which the pixel electrodes are provided, wherein the X-ray charge conversion film contains an X-ray sensitive material comprising inorganic semiconductor particles, and a carrier transport material comprising an organic semiconductor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
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patent: 4886719 (1989-12-01), Tanaka et al.
patent: 5198673 (1993-03-01), Rougeot et al.
patent: 5391882 (1995-02-01), Rhiger
patent: 5498880 (1996-03-01), Lee et al.
patent: 5874197 (1999-02-01), Felten
patent: 5886359 (1999-03-01), Bringley et al.
patent: 5925890 (1999-07-01), Van den Bogaert et al.
patent: 3-273687 (1991-12-01), None
patent: 4-063555 (1992-10-01), None
Atsuta Masaki
Ikeda Mitsushi
Kinno Akira
Sugawara Yasuhiro
Tanaka Manabu
Hannaher Constantine
Kabushiki Kaisha Toshiba
Moran Timothy J.
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