JP2007147596A - Radiation solid-state detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect a photoconducting layer without problems of an image spot and a discharge breakdown in a radiation solid-state detector having the photoconducting layer consisting primary of amorphous selenium. <P>SOLUTION: The radiation solid-state detector 10 comprises a first conductive layer 11, a photoconducting layer 12 for producing electric charges by receiving the radiation of X-rays and exhibiting conductivity, and a second conductive layer 13 consisting of a TFT, which overlie a glass substrate 14 in the order, wherein the first conductive layer 11 and the photconducting layer 12 are sealed with a polymer 20 that is formed to a film by chemical deposition and also a protective film 21 is bonded on the polymer 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radiation solid state detector provided with a photoconductive layer mainly composed of amorphous selenium, and more particularly to protection of the photoconductive layer.

  Today, in X-ray (radiation) imaging for the purpose of medical diagnosis and the like, a solid-state radiation detector (having a semiconductor as a main part) is used as an X-ray image information recording means, and the subject is transmitted through this solid-state detector Various X-ray imaging apparatuses that detect X-rays and obtain an image signal representing an X-ray image related to a subject have been proposed and put into practical use.

  Various types of solid state detectors used in this apparatus have been proposed. For example, from the aspect of the charge generation process that converts X-rays into electric charges, the signal charge obtained by detecting the fluorescence emitted from the phosphor by the photoconductive layer when irradiated with X-rays is temporarily stored in the power storage unit. Then, the stored charge is converted into an image signal (electrical signal) and output to a photo-conversion type (indirect conversion type) solid state detector, or the signal charge generated in the photoconductive layer when irradiated with X-rays. There is a direct conversion type solid state detector that collects with a charge collecting electrode, temporarily accumulates it in a power storage unit, converts the accumulated charge into an electric signal and outputs it. The solid state detector in this system has a photoconductive layer and a charge collecting electrode as main parts.

  Among the above, the direct conversion method has an advantage that the sharpness of the image is excellent because it does not go through a scintillator layer for once converting radiation into light. The present invention also relates to a direct type solid state detector having a photoconductive layer mainly composed of amorphous selenium.

  On the other hand, from the aspect of the charge reading process for reading out the accumulated charge to the outside, it is described in an optical reading method in which reading light (reading electromagnetic wave) is read by irradiating a detector, or as described in Patent Document 1. In addition, there is a TFT reading type that scans and reads out a TFT (thin film transistor) connected to the power storage unit.

The applicant of the present application has proposed an improved direct conversion type solid state detector in Patent Document 2 and the like. The improved direct conversion type solid state detector is a direct conversion type and optical readout type, and exhibits photoconductivity by receiving recording light (X-ray or fluorescence generated by X-ray irradiation). Photoconductive layer for recording, a charge transport layer that acts as an insulator for charges having the same polarity as the latent image charge, and acts as a conductor for transport charges having a polarity opposite to that of the latent image charge A photoconductive layer for reading that exhibits photoconductivity by receiving irradiation of an electromagnetic wave for reading is laminated in this order, and is formed at the interface (electric storage unit) between the photoconductive layer for recording and the charge transport layer. A signal charge (latent image charge) carrying image information is accumulated. Electrodes (first conductor layer and second conductor layer) are laminated on both sides of these three layers. Further, the solid state detector in this system has a recording photoconductive layer, a charge transport layer, and a reading photoconductive layer as main parts.
JP 2000-244824 A JP 2000-105297 A

  In the radiation solid state detector, amorphous selenium (a-Se) that is highly sensitive to radiation such as X-rays is generally used for the photoconductive layer. Se is the temperature and humidity of the outside world. When used for a long time without a protective film, there is a problem that deterioration such as a decrease in sensitivity and a decrease in image quality proceeds. Moreover, since Se has a low X-ray absorption rate, a relatively thick film is required. As a result, a high bias voltage needs to be applied in order to function as a photoconductive layer. When such a high electric field is applied, a fine defect generated in Se may lead to a large image defect. For this reason, a photoconductive layer is usually protected by attaching a protective film to the radiation solid detector with an adhesive or a pressure-sensitive adhesive.

  However, in this case, the adhesive applied to the protective film may permeate into the amorphous selenium, and the characteristics of the permeated portion may deteriorate, resulting in spots in the detected image. It is also conceivable to apply the adhesive only to the edge of the protective film so that the adhesive does not contact the amorphous selenium. In this case, a gap (air layer) is generated between the radiation solid detector and the protective film. There is a problem that electric discharge breakdown easily occurs in this portion.

  In order to avoid such a problem, it has been found that a protective film in which the protective film is installed in close contact with Se without interposing a space is effective between Se and the electrode layer installed thereabove. It came to.

  That is, the present invention provides a radiation solid state detector having a photoconductive layer mainly composed of amorphous selenium, which can protect the photoconductive layer without causing problems such as image spots and discharge breakdown. It is intended to provide.

  A solid state radiation detector according to the present invention includes an electrostatic recording unit including a photoconductive layer containing amorphous selenium as a main component, and transmits the radiation carrying image information transmitted through the subject or emitted from the subject. In a radiation solid state detector that receives image data directly by a layer and outputs image signals representing the recorded image information, the photoconductive layer is sealed with a polymer formed by chemical vapor deposition. .

  The “radiation solid state detector” in the above is a detector that detects radiation carrying image information of a subject and outputs an image signal representing a radiation image related to the subject, and converts incident radiation directly into electric charges. By storing this charge once in the power storage unit and then outputting this charge to the outside, an image signal representing a radiographic image related to the subject can be obtained.

  In the present invention, the “photoconductive layer containing amorphous selenium as a main component” means a layer having the highest weight percent component of amorphous selenium among the components of the photoconductive layer.

In the radiation solid state detector of the present invention, the polymer is preferably selected from poly-paraxylylenes. Here, poly-paraxylylene means poly-paraxylylene and poly-paraxylylene derivatives, and specific examples of preferable poly-paraxylylene include:

Etc.

  Among these, poly-monochloroparaxylylene and poly-dichloroparaxylylene have low water permeability and are more preferably used as the polymer of the present invention.

  The film thickness of the poly-paraxylylene is preferably 1 to 100 μm, and more preferably 10 to 50 μm. Moreover, it is preferable that the polymer is further sealed with a film. Here, the film thickness is preferably 5 to 50 μm.

  A solid state radiation detector according to the present invention includes an electrostatic recording unit including a photoconductive layer containing amorphous selenium as a main component, and transmits the radiation carrying image information transmitted through the subject or emitted from the subject. In a radiation solid state detector that receives image data directly by a layer and outputs an image signal representing the recorded image information, the photoconductive layer is sealed with a polymer deposited by chemical vapor deposition to detect the radiation solid state. Since it can be sealed without creating a gap with respect to the vessel, and because no adhesive is used, the adhesive does not penetrate into the photoconductive layer mainly composed of amorphous selenium, causing problems such as image spots and electric discharge destruction. It is possible to protect the photoconductive layer containing amorphous selenium as a main component without generating any.

  In addition, since the radiation solid state detector is sealed with a polymer formed by chemical vapor deposition, the adhesive is mainly composed of amorphous selenium even if a protective film is further adhered to the polymer with an adhesive. Since it does not penetrate into the photoconductive layer, it is possible to protect the photoconductive layer more firmly by sealing the polymer with a protective film.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a radiation solid state detector according to an embodiment of the present invention.

  The radiation solid state detector 10 includes a first conductive layer 11, a photoconductive layer 12 that exhibits electrical conductivity by receiving X-ray irradiation, and a second circuit including a reading circuit including a TFT and a pixel electrode. The conductive layers 13 are laminated in this order.

  The first conductive layer 11 only needs to be transparent to X-rays, and for example, a gold thin film can be used. In the present embodiment, a gold film having a thickness of 100 nm is used.

  The photoconductive layer 12 is made of amorphous selenium having high quantum efficiency and low dark current. In the present embodiment, the thickness of the photoconductive layer 12 is 200 μm.

  The second conductive layer 13 is provided with a TFT corresponding to each pixel, and the output line of each TFT is connected to a signal detection means (not shown). The control line of each TFT is connected to a TFT control means (not shown).

  When the radiation solid detector 10 is irradiated with X-rays when the electric field is formed between the first conductive layer 11 and the second conductive layer 13, the photoconductive layer Charge pairs are generated in 12, and latent image charges corresponding to the amount of the charge pairs are accumulated in the second conductive layer 13. When reading the accumulated latent image charge, the TFTs of the second conductive layer 13 are sequentially driven to output an image signal based on the latent image charge corresponding to each pixel from the output line. By detecting by the signal detecting means, the electrostatic latent image carried by the latent image charge can be read.

  In the radiation solid state detector 10 of the present embodiment, the first conductive layer 11 and the photoconductive layer 12 are sealed with a polymer 20 formed by chemical vapor deposition. As this polymer 20, various polymers can be used as long as they have low moisture permeability and do not alter amorphous selenium, and examples thereof include poly-paraxylylenes.

  The poly-paraxylylene coating is formed by chemical vapor deposition, more specifically by vapor deposition polymerization, and the first step in which vaporization of diparaxylylene as a raw material dimer occurs. Diradical paraxylylene by thermal decomposition of the dimer Is formed in three steps consisting of a second step in which the occurrence of the above occurs, a third step in which the adsorption and polymerization of the diradical paraxylylene to the base material are simultaneously performed and a film formation of a high molecular weight polyparaxylylene occurs.

In this process, the degree of vacuum is generally 0.1 to 100 Pa (10 ^{−3 to 1} Torr), the first process is performed at 100 to 200 ° C., the second process is performed at 450 to 700 ° C., and the third process is performed at room temperature. . These polyparaxylylene films obtained by the vapor deposition polymerization method can be conformally coated on the substrate, and the coating itself can be performed at room temperature. Coating can be performed without giving a history. For this reason, it is most suitable for the coating with respect to base materials, such as Se device which cannot process high temperature.

  The thickness of the polymer 20 formed by chemical vapor deposition is preferably 1 to 100 μm, and more preferably 10 to 50 μm. In the present embodiment, poly-paraxylylene is deposited as the polymer 20 with a thickness of 15 μm by a CVD method.

  As a result, the radiation solid state detector 10 can be sealed without generating a gap, and since no adhesive is used, the adhesive does not permeate the photoconductive layer 12 containing amorphous selenium as a main component. It is possible to protect the photoconductive layer 12 without causing problems such as discharge breakdown.

  Further, a protective film 21 with an adhesive is stuck on the polymer 20. The protective film 21 is a gas barrier film, and any film can be used as long as this characteristic is satisfied. Specifically, a film in which a film layer made of a polymer material and a metal thin film layer are laminated, a film in which a film layer made of a polymer material and an oxide thin film layer are laminated, and the like can be mentioned. Aluminum is preferably used as the metal thin film layer in the former, and silicon oxide and aluminum oxide are preferably used as the oxide in the latter. A more specific example of the latter is a letterpress printing GX film. Moreover, it is preferable that the thickness of the protective film 21 shall be 5-50 micrometers. In the present embodiment, a GX film made by relief printing is used as the protective film 21.

  The poly-paraxylylenes used as the polymer 20 generally have poor adhesion to other members using an adhesive, but the adhesion can be improved by performing light irradiation treatment with ultraviolet light prior to adhesion. . The necessary irradiation time is appropriately adjusted to the optimum time depending on the wavelength and wattage of the ultraviolet light source to be used, but it is preferably 1 to 50 W with a low-pressure mercury lamp, and the light irradiation is preferably performed for 1 to 30 minutes.

  In this embodiment, since sealing is performed with the polymer 20 formed by chemical vapor deposition on the radiation solid state detector 10, even if a protective film 21 is further adhered to the polymer 20 with an adhesive, Since the adhesive does not penetrate into the photoconductive layer 12 mainly composed of amorphous selenium, the photoconductive layer 12 can be protected more firmly by sealing the polymer 20 with the protective film 21 as described above. Is possible.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described TFT readout type radiation solid state detector, but a radiation solid comprising a photoconductive layer mainly composed of amorphous selenium. It can be applied to any detector.

Sectional drawing of the radiation solid state detector by one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation solid state detector 11 1st conductive layer 12 Photoconductive layer 13 2nd conductive layer 14 Glass substrate 20 Polymer 21 Protective film

Claims (6)

An electrostatic recording unit including a photoconductive layer mainly composed of amorphous selenium is provided, and the image information is received by the photoconductive layer directly receiving radiation carrying image information transmitted through the subject or emitted from the subject. In a radiation solid state detector that records and outputs an image signal representing the recorded image information,
A radiation solid-state detector, wherein the photoconductive layer is sealed with a polymer formed by chemical vapor deposition.   2. The radiation solid state detector according to claim 1, wherein the polymer is poly-paraxylylene.   The radiation solid state detector according to claim 2, wherein the poly-paraxylylene has a thickness of 1 to 100 μm.   The radiation solid state detector according to claim 2 or 3, wherein the poly-paraxylylene has a thickness of 10 to 50 µm.   6. The radiation solid state detector according to claim 1, wherein the polymer is sealed with a film.   6. The radiation solid state detector according to claim 5, wherein the film has a thickness of 5 to 50 [mu] m.

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