JP5388275B2 - Radiation solid state detector - Google Patents

Description

  The present invention relates to a radiation solid state detector provided with a photoconductive layer that directly generates an electric charge when irradiated with electromagnetic waves, and more particularly to improvement of durability.

  Conventionally, in the medical field and the like, various radiation solid state detectors that record radiation images related to a subject by receiving radiation transmitted through the subject and output an electrical signal corresponding to the recorded radiation image have been proposed and put into practical use. ing.

As a radiation solid-state detector system, a direct conversion system that directly converts radiation into electric charge and accumulates the charge, and radiation is once converted into light by a scintillator such as CsI: Tl or GOS (Gd ₂ O ₂ S: Tb). There is an indirect conversion method in which the light is converted into charges by the photoconductive layer and stored. The reading method is roughly divided into an optical reading method using reading light and an electric reading method using a TFT (thin film transistor), a CCD (charge coupled device), a CMOS (complementary metal oxide semiconductor) sensor, and the like.

  As an optical solid-state detector of the optical reading system, for example, the charge generated in the photoconductive layer for recording due to the irradiation of radiation is accumulated and the charge having the opposite polarity to the accumulated charge is charged to the linear electrode. It is known to read the accumulated charge by combining each charge of the charge pair generated in the reading photoconductive layer with the accumulated charge and the charged charge.

  As an electrical reading type radiation solid state detector, for example, charges generated by irradiation of radiation are collected by a pixel electrode for each pixel, stored in a storage capacitor connected to the pixel electrode, and the stored charge is stored in an electrical device such as a TFT. It is known to read by turning on and off the target switch one line at a time.

In the direct conversion radiation solid-state detector, various materials such as CdTe and HgI ₂ are used for the photoconductive layer, but most commonly, it is highly sensitive to radiation such as X-rays. Amorphous selenium (a-Se) is used. a-Se is easily affected by the temperature and humidity of the outside world, and 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 a-Se has a low X-ray absorptivity, a relatively thick film thickness 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 a-Se may lead to a large image defect. For this reason, as described in Patent Document 1, a photoconductive layer is usually protected by attaching a protective film to a radiation solid detector with an adhesive or a pressure-sensitive adhesive.

JP 2008-251999 A JP 2003-315466 A

  Here, the structure of the radiation solid detector as described above will be described with reference to FIG. FIG. 4 is a cross-sectional view of a conventional radiation solid state detector.

  The conventional radiation solid state detector 100 includes a flat plate-like first electrode layer 111 (bias electrode), a photoconductive layer 112 that generates electric charge directly upon receiving X-ray irradiation, and has a reading function. A second electrode layer 113 composed of a circuit and a pixel electrode is laminated on a glass substrate 114, and the first electrode layer 111 and the photoconductive layer 112 are sealed with a polymer 120 formed by chemical vapor deposition, and A protective film 121 is attached from above. Further, between the first electrode layer 111 and the photoconductive layer 112, injection of unnecessary charges from the first electrode layer 111 to the photoconductive layer 112 is prevented, and an image detected by the detector is not detected. A charge injection blocking layer 115 is provided to prevent a deterioration in image quality.

  In this radiation solid state detector 110, a radio field image is recorded by applying a high electric field between the first electrode layer 111 and the second electrode layer 113. In this case, a flat plate-like first electrode layer is used. At the end edge portion 111 (A arrow portion in FIG. 4), the electric field concentrates to form a stronger electric field than the central portion. If the charge injection blocking layer 115 is disposed between the first electrode layer 111 and the photoconductive layer 112 as described above, excessive charge is accumulated near the edge of the first electrode layer 111. Therefore, there is a problem that a-Se (photoconductive layer 112) under the charge injection blocking layer 115 is crystallized by inducing charge injection from the second electrode layer 113 as a counter electrode.

  In order to solve such a problem, the charge injection blocking layer 115 is disposed on the inner side so as not to reach the edge of the first electrode layer 111, so that the excess in the vicinity of the edge of the first electrode layer 111 is obtained. Accumulation of charge can be suppressed. However, since the edge of the charge injection blocking layer 115 must be outside the image detection area of the detector in order to eliminate the generation of artifacts and the like, the detection area is made to be, for example, a radiation solid state detector for mammography. In the case where it is desired to secure the edge of the detector as much as possible, there is a problem that the charge injection blocking layer 115 cannot be sufficiently inward from the edge of the first electrode layer 111.

  Therefore, when the degradation of the photoconductive layer at the edge of the bias electrode is to be suppressed by a method other than the above, as described in Patent Document 2, in the photoconductive layer adjacent to the edge of the bias electrode, In order to prevent generation of charge pairs that cause deterioration of the conductive layer, the radiation solid state detector is provided with a collimator that shields X-rays that are irradiated outside the effective detection region (the edge of the bias electrode) of the radiation solid state detector. However, in this case, since there is a distance between the collimator and the radiation solid state detector, the X-rays scattered around cannot be prevented from entering and the edge of the bias electrode cannot be prevented. Therefore, there is a problem that X-rays cannot be shielded with high accuracy and deterioration of the photoconductive layer cannot be sufficiently suppressed.

  In view of the above circumstances, the present invention provides a solid-state radiation detector that includes a photoconductive layer that directly generates an electric charge when irradiated with electromagnetic waves, and that detects radiation solid state that suppresses deterioration of the photoconductive layer at the edge of the bias electrode. The purpose is to provide a vessel.

  The radiation solid-state detector of the present invention includes a first electrode layer, a photoconductive layer that generates charges when irradiated with electromagnetic waves, and a second electrode layer that includes a plurality of divided electrodes. A radiation solid-state detector comprising a protective film provided so as to protect at least the first electrode layer and the photoconductive layer, wherein the edge of the first electrode layer is laminated on the substrate in order from the layer. An electromagnetic wave shielding member that shields electromagnetic waves is provided directly on the protective film above at least a part of the portion.

  Here, the “protective film” means a film that is in close contact with the surface of the radiation solid detector and covers at least the first electrode layer and the photoconductive layer, and is not limited in its function. .

  The “electromagnetic wave shielding member” means a member that inhibits transmission of electromagnetic waves by absorbing and / or reflecting electromagnetic waves.

  This electromagnetic wave shielding member preferably has insulating properties.

  Furthermore, “the electromagnetic wave shielding member is provided directly on the protective film” means that the electromagnetic wave shielding member is provided on the protective film without interposing a space, and the protective film and the electromagnetic wave shielding member. In addition, those including inclusions such as a thin film different from the protective film are also included.

  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.

  According to the radiation solid-state detector of the present invention, the first electrode layer, the photoconductive layer that generates an electric charge when irradiated with electromagnetic waves, and the second electrode layer that includes a plurality of divided electrodes are provided as the second electrode layer. An edge of the first electrode layer of a radiation solid detector comprising a protective film so as to protect at least the first electrode layer and the photoconductive layer. An electromagnetic wave shielding member that shields electromagnetic waves is provided directly on the protective film above at least a part of the part, and causes deterioration of the photoconductive layer in the photoconductive layer adjacent to the edge of the first electrode layer. Since the charge pair is not generated, it is possible to suppress the deterioration of the photoconductive layer at the edge portion of the first electrode layer.

The top view of the radiation solid detector by one embodiment of the present invention II-II line sectional view in FIG. The graph which shows the change of the intensity | strength of an output signal when recording operation is performed in multiple times about the said radiation solid state detector Cross section of conventional radiation solid state detector

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a top view of a radiation solid state detector according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG.

  The radiation solid state detector 10 includes a first electrode layer 11, a photoconductive layer 12 that generates electric charge directly by being irradiated with X-rays, and exhibits conductivity, a reading circuit including a TFT, and a second electrode including a pixel electrode. The electrode layer 13 is laminated on the glass substrate 14, and the first electrode layer 11 and the photoconductive layer 12 are sealed with a polymer 20 formed by chemical vapor deposition, and a protective film 21 is further applied thereon. ing. Also, between the first electrode layer 11 and the photoconductive layer 12, injection of unnecessary charges from the first electrode layer 11 to the photoconductive layer 12 is prevented, and the image detected by the detector A charge injection blocking layer 15 is provided to prevent the image quality from deteriorating.

  In addition, as shown in FIGS. 1 and 2, an electromagnetic wave shielding member 22 that shields electromagnetic waves is provided on the protective film 21 above the edge portion (A arrow portion in FIG. 2) of the first electrode layer 11. Yes.

  The first electrode 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 a-Se having high quantum efficiency and low dark current. In the present embodiment, the thickness of the photoconductive layer 12 is 200 μm.

  The second electrode 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).

  The charge injection blocking layer 15 can use antimony sulfide or the like. As shown in FIG. 2, the edge of the charge injection blocking layer 15 is arranged on the inner side so as not to reach the edge of the first electrode layer 11, thereby the vicinity of the edge of the first electrode layer 11. It is possible to suppress the accumulation of excessive charges in the.

  As the polymer 20 that seals the first electrode layer 11 and the photoconductive layer 12, various types can be used as long as they have low moisture permeability and do not alter a-Se. For example, poly-paraxylylenes can be used. Can be mentioned.

  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 penetrate into the photoconductive layer 12 containing a-Se as a main component. It is possible to protect the photoconductive layer 12 without causing problems such as spots or discharge breakdown.

  Further, a protective film 21 with an adhesive is stuck on the polymer 20. The protective film 21 needs to have a dielectric breakdown strength that exceeds the potential applied to the radiation solid detector 10, and further needs to be a member that does not interfere with radiation transmission due to the function of the radiation solid detector 10. . In addition, in order to ensure insulation over a long period of time, it is necessary to ensure adhesion durability to the device. As a material satisfying such a function, there is a PET film, or an aluminum laminated film in which a resin film such as PET or nylon is formed on an aluminum surface. However, it is desirable to use a PET film because grounding treatment for the film is unnecessary.

  The voltage applied to the radiation solid state detector 10 is used in the range of about 2 kV to 10 kV depending on the thickness of the photoconductive layer. However, the protective film 21 is used to ensure insulation with a margin even in a high humidity environment. The dielectric breakdown strength of is desirably 10 kV or more. In order to obtain the dielectric breakdown strength of 10 kV or more with a margin, the PET film thickness is desirably 50 μm or more. An acrylic pressure-sensitive adhesive or an epoxy-based adhesive can be applied to the PET film, but it is desirable to use a pressure-sensitive adhesive that does not require a curing time.

The electromagnetic shielding member 22 has a different optimum material depending on the irradiation wavelength of the electromagnetic wave to be irradiated for recording. A tungsten compound, a tantalum or a tantalum compound, a barium compound, a cesium compound, a gadolinium compound, or the like can be used, and BiF ₃ , Bi ₂ O ₃ , PbO, BaSO ₄ , CsBr, CsI, and Gd ₂ O ₃ are preferable.

  It is preferable that the X-ray absorbing material is mixed with a volatile solvent containing urethane resin or the like and applied to the upper portion of the protective film 21 along the edge portion of the upper first electrode layer 11. Of course, the protective film 21 may be pasted on the polymer 20 after the X-ray absorbing material is applied on the protective film 21 in advance.

  When visible light or infrared light is used as the electromagnetic wave irradiated for recording, a black light-shielding material is preferable, for example, a black adhesive PET film.

  Degradation evaluation of the radiation solid detector 10 formed as described above is performed, and this evaluation will be described below. Since this evaluation is accelerated, the irradiation wavelength is not X-rays (28 keV), but 530 nm green light whose intensity is adjusted so as to generate charges equivalent to the generated charge amount at the time of X-ray 1R irradiation. Was irradiated on the entire surface of the radiation solid state detector 10. Moreover, the insulating black shielding tape which absorbs green light in connection with this was installed on the protective film 21. FIG. For this deterioration evaluation, the change in signal intensity of the electrode (outside the effective detection region in FIG. 2) located at the end of the radiation solid detector 10 was used. It has been found that there is a correlation between the deterioration of the signal intensity and the deterioration of a-Se (photoconductive layer 12).

  The evaluation results are shown in FIG. FIG. 3 is a graph showing changes in the intensity of the output signal when the recording operation is performed a plurality of times. In this graph, the horizontal axis represents the number of operations (10,000 times), and the vertical axis represents the signal intensity (normalized to an initial value of 1).

  As shown in this graph, when the black shielding tape is provided, the signal value is secured about 60% of the initial value even if the recording operation is performed 300,000 times, whereas the black shielding tape is not provided. In this case, the signal value sharply decreases up to about 100,000 times, and no signal is output after 200,000 times. Thus, it has been found that the provision of the electromagnetic wave shielding member has a significant effect on the deterioration of a-Se.

  The radiation solid detector 10 formed as described above irradiates the photoconductive layer 12 with X-rays when an electric field is formed between the first electrode layer 11 and the second electrode layer 13. Then, charge pairs are generated in the photoconductive layer 12 and latent image charges corresponding to the amount of the charge pairs are accumulated in the second electrode layer 13. When reading the accumulated latent image charge, the TFTs of the second electrode 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.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described electric solid-state radiation solid-state detector, and a photoconductive layer that directly generates a charge when irradiated with electromagnetic waves is provided. The present invention can be applied to any radiation solid state detector provided.

DESCRIPTION OF SYMBOLS 10 Radiation solid state detector 11 1st electrode layer 12 Photoconductive layer 13 2nd electrode layer 14 Glass substrate 15 Charge injection block layer 20 Polymer 21 Protective film 22 Electromagnetic wave shielding member

Claims (3)

A first electrode layer;
A photoconductive layer that generates electric charges when irradiated with electromagnetic waves;
A second electrode layer that is two-dimensionally arranged and includes a plurality of divided electrodes that form a pixel detection region, and is laminated on the substrate in order from the second electrode layer;
A radiation solid state detector provided with a protective film so as to protect at least the first electrode layer and the photoconductive layer,
A charge injection blocking layer for blocking charge injection from the first electrode layer to the photoconductive layer between the first electrode layer and the photoconductive layer;
The charge injection blocking layer is disposed so as to cover the inner side of the first electrode layer and the end of the pixel detection region;
An electromagnetic wave shielding member that shields the electromagnetic wave is provided directly on the protective film above at least a part of the edge of the first electrode layer and only outside the pixel detection region. A radiation solid state detector. The electromagnetic wave shielding member, the radiation solid-state detector according to claim 1, wherein a has an insulating property. The electromagnetic wave shielding member, bismuth or bismuth compound, lead or lead compounds, tungsten or tungsten compounds, tantalum or tantalum compound, a barium compound, a cesium compound, or claim 1, characterized in that it comprises at least one of gadolinium compound The radiation solid state detector according to 2 .

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