JP2009025258A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector capable of improving the resolution. <P>SOLUTION: On a fluorescence conversion membrane 14, a light-reflecting layer 33 which is constituted by a mixture of an adhesive matter 34, which is transparent and adhesive and powder mineral matter 35 of higher refractive index than the adhesive matter 34. By the light-reflecting layer 33, the utilization efficiency of visible light converted by the fluorescence conversion membrane 14 is improved, as well, as securing moisture shutoff performance for inhibiting degradation of the fluorescence conversion membrane 14. The light-reflecting layer 33 will not infiltrate into the internal of the fluorescence conversion membrane 14 but can improve the resolution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiation detector for detecting radiation.

  As a new generation diagnostic X-ray image detector, a planar X-ray detector using an active matrix has attracted attention. By irradiating the X-ray detector with X-rays, an X-ray image or a real-time X-ray image is output as a digital signal. Since this X-ray detector is a solid-state detector, there are great expectations in terms of image quality performance and stability, and many researches and developments are underway.

  As the first application for practical use, it has been developed for the chest or general radiography for collecting still images with a relatively large dose, and has been commercialized in recent years. Commercialization is expected in the near future for applications in the circulatory and gastrointestinal fields that require higher performance and real-time video at 30 frames per second under fluoroscopic dose. For this moving image application, improvement of S / N and real-time processing technology of minute signals are important development items.

  This type of X-ray detector is roughly divided into two systems, a direct system and an indirect system. The direct method is a method in which X-rays are directly converted into a charge signal by a photoconductive film such as a-Se and led to a charge storage capacitor. On the other hand, in the indirect method, X-rays are received by a fluorescent conversion film that is a scintillator layer, and once converted into visible light, the visible light is converted into signal charges by an a-Si photodiode or CCD, and led to a charge storage capacitor. It is a method.

  Many of the X-ray detectors currently in practical use adopt the indirect method. In a conventional indirect X-ray detector, an X-ray image transmitted through a human body or the like is incident on the X-ray detector, and the image information is converted into an electrical signal. At this time, X-rays are converted into visible light by the fluorescence conversion film, and the visible light is detected for each pixel formed in a grid pattern on the photoelectric conversion substrate and is output as an electrical signal of two-dimensional image information.

  The photoelectric conversion substrate is a thin film transistor (TFT) panel manufacturing process that is similar to the manufacturing process of a liquid crystal display device. A circuit board on which signal wiring and thin film transistors are formed is created, and fluorescence from the input surface is detected on the circuit board. A photodiode element to be formed is formed in a lattice pattern for each pixel, and the photodiode element is electrically connected to a thin film transistor disposed below.

The fluorescence conversion film of the input surface is formed on the photoelectric conversion substrate manufactured by such a process. The fluorescence conversion film is made of a fluorescent material having a function of converting incident X-rays into visible light. As the fluorescent material, Gd ₂ O ₂ S: Tb (terbium-added gadolinium sulfide oxide) or CsI: Tl (thallium-added iodine) is used. Cesium) is often used.

When Gd ₂ O ₂ S: Tb is used as a fluorescent material, a film in which particulate Gd ₂ O ₂ S: Tb is dispersed in a resin is used. On the other hand, when CsI: Tl is used as a fluorescent substance, a CsI: Tl film is formed on the photoelectric conversion substrate by a vacuum deposition method. By taking appropriate manufacturing conditions at that time, A CsI: Tl film having a columnar structure in the vertical direction can be formed. The input surface having a columnar structure of CsI: Tl has higher resolution for incident X-rays than the input surface using Gd ₂ O ₂ S: Tb, and a high-performance X-ray image detector is possible.

CsI: Tl used for the input surface is hygroscopic, and it is known that the performance as the input surface deteriorates due to the presence of surrounding water. Therefore, it is necessary to isolate the input surface having a columnar structure of CsI: Tl from the surrounding environment. A method mainly used is to form a protective film that covers the entire surface of the input surface having a columnar structure of CsI: Tl and at the same time part of the photoelectric conversion substrate. By setting an appropriate material and thickness of the protective film, it is possible to prevent moisture from entering from the surroundings and to prevent deterioration of the performance of the input surface having a columnar structure due to CsI: Tl. As a material for the protective film, polyparaxylylene, which can be formed in a vacuum and has excellent step coverage, is often used. In addition, a method of forming a protective film made of a resin containing light-reflective fine particles by embedding between columns of columnar crystals (see, for example, Patent Document 1), an organic film is pasted on the input surface There is a technique to attach.
JP 2006-153707 A (page 4-5, FIG. 1-2)

  Polyparaxylylene used for protecting the CsI: Tl input surface of an X-ray image detector has excellent moisture-proof properties and step coverage, but excessive penetration into the input surface is a problem.

  In the input surface having a columnar structure of CsI: Tl, which is often used in high-performance X-ray detectors, the propagation of fluorescence through the columnar CsI: Tl with a high refractive index and between columns with a low refractive index are performed. Due to the confinement effect of the fluorescence inside the column due to the presence of the air gap, the fluorescence due to the incident X-ray reaches the photodiode element at the lower part of the input surface while maintaining the resolution, and is output to the outside as a high-resolution X-ray image. ing.

  When the input surface with this characteristic is coated with polyparaxylylene, it is formed on the input surface by vapor phase chemical vapor deposition (CVD) technology, but polyparaxylylene formed in vacuum is It is introduced by the state of the monomer gas and polymerizes and solidifies on the surface of the substance. Therefore, it easily penetrates into the fine voids inside the substance, and on the input surface having a columnar structure of CsI: Tl, a polyparaxylylene film is formed even inside the voids between the columns. As a result, the gap between the columns of the input surface having the columnar structure of CsI: Tl is narrowed, and finally, all the gaps are filled.

  For this reason, in the input surface having a columnar structure of CsI: Tl that has been coated with polyparaxylylene, the columns are reduced by reducing the gaps between the columns and impregnating the columns with polyparaxylylene having a high refractive index. The internal fluorescence confinement effect is weakened, and the resolution of the X-ray image is degraded.

  Also, in the case of a method of forming a protective film made of a resin containing light-reflecting fine particles on the input surface in a form of embedding between columns of columnar crystals, the resin has a columnar structure of CsI: Tl. The impregnation between the pillars of the surface impairs the fluorescent confinement effect inside the pillars, leading to resolution degradation of the X-ray image.

  Also, in the method of attaching an organic film on the input surface, the organic film can ensure moisture barrier properties and prevent impregnation of substances between the columns of the input surface having a columnar structure by CsI: Tl. Is possible. However, an organic film having sufficient moisture barrier properties becomes thick, and the ratio of the fluorescence generated inside the input surface to enter the organic film and diffuse in the lateral direction increases. As a result, the resolution of the X-ray image is reduced and the resolution of the X-ray image is degraded.

  The present invention has been made in view of these points, and an object thereof is to provide a radiation detector capable of improving the resolution.

  The present invention includes a photoelectric conversion substrate that converts light into an electrical signal, a fluorescent conversion film that is formed on the photoelectric conversion substrate and converts radiation into visible light, a transparent and adhesive adhesive material, and the adhesive material The light reflecting layer is formed of a mixture with an inorganic substance powder having a high refractive index and formed on the fluorescence conversion film.

  Further, the present invention includes a photoelectric conversion substrate that converts light into an electrical signal, a fluorescence conversion film that converts radiation formed on the photoelectric conversion substrate into visible light, and a transparent and adhesive material. A light reflection layer formed on the pressure-sensitive adhesive layer, comprising a mixture of at least the pressure-sensitive adhesive layer formed on the fluorescence conversion film, a transparent organic material, and a powder of an inorganic material having a higher refractive index than the organic material. And a layer.

  According to the present invention, the light reflecting layer composed of a mixture of a transparent and sticky adhesive substance and a powder of an inorganic substance having a higher refractive index than the adhesive substance is formed on the fluorescence conversion film. The reflection layer ensures moisture barrier properties and prevents deterioration of the fluorescence conversion film, improves the utilization efficiency of visible light converted by the photoelectric conversion film, and the light reflection layer penetrates into the fluorescence conversion film. Therefore, the resolution of the radiation detector can be improved.

  According to the present invention, an adhesive layer made of a transparent and adhesive adhesive substance is formed on the fluorescence conversion film, and a transparent organic substance and an inorganic material having a higher refractive index than the organic substance are formed on the adhesive layer. Since the light reflecting layer composed of the mixture with the substance powder is formed, the light reflecting layer can prevent moisture deterioration by ensuring the moisture blocking property and also prevent the visible light converted by the photoelectric converting film. Utilization efficiency can be improved, and the adhesive layer does not penetrate into the fluorescence conversion film, and the light reflection layer penetrates into the fluorescence conversion film because the adhesion layer is interposed between the fluorescence conversion film and the light reflection layer. Therefore, the resolution of the radiation detector can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 to 3 show a first embodiment.

  In FIG. 2, the perspective view of the decomposition | disassembly state of the X-ray detector 11 as a radiation detector is shown.

  The X-ray detector 11 is an indirect X-ray image detector, and includes a photoelectric conversion substrate 13 having a plurality of pixels 12 arranged in a matrix, and an input layered on the surface of the photoelectric conversion substrate 13. It is comprised by the fluorescence conversion film | membrane 14 which is a surface.

  The photoelectric conversion substrate 13 has a circuit substrate 17 in which a circuit layer 16 is formed on a glass substrate 15, and a photodiode element 18 as a photoelectric conversion element is formed on the circuit substrate 17 for each pixel.

  When X-rays 19 as radiation enter the fluorescence conversion film 14, visible light corresponding to the two-dimensional distribution of the X-rays 19 is generated in the fluorescence conversion film 14, and the generated visible light is applied to the photodiode element 18. Incident light is converted into electric charge.

  Next, FIG. 3 shows a front view schematically showing the X-ray detector 11.

  The thin film transistor (TFT) 21, the capacitor 22, and the photodiode element 18 are arranged in a lattice form as a set, and each set corresponds to the pixel 12 of the X-ray image. On the glass substrate 15, a plurality of control electrodes 23 that connect the gate electrodes of the thin film transistors 21 are arranged in the row direction, and a plurality of readout electrodes 24 that connect the drains of the thin film transistors 21 are arranged in the column direction. With such a circuit configuration, electric charges generated in each photodiode element 18 for each pixel 12 are connected to the respective capacitors 22 until the gate electrodes of the thin film transistors 21 connected thereto are turned on. When only one control electrode 23 is turned on in this state, the thin film transistors 21 in the same column connected to the control electrode 23 turned on are turned on and connected to the thin film transistors 21 through the thin film transistor 21. The charge of the capacitor 22 that has been applied flows to the readout electrode 24. As a result, image information corresponding to a specific row is output to the outside. Further, by sequentially changing the control electrode 23 to be turned on, it is possible to output the entire image information as a video signal to the outside.

  Next, FIG. 1 shows a partial sectional view of the X-ray detector 11.

A photodiode element 18 is formed on a circuit board 17 in which a circuit layer 16 is provided on a glass substrate 15, and the photodiode element 18 is covered with silicon oxide (SiO ₂ ), silicon nitride (SiNx), or the like. A protective film 27 is formed. The circuit board 17, the photodiode element 18, the protective film 27, and the like constitute the photoelectric conversion board 13. The method for manufacturing the circuit board 17 can be realized by the same technique as that of a general active liquid crystal display device, and the same material can be used.

  On the surface of the photoelectric conversion substrate 13 on which the photodiode elements 18 are formed, a fluorescence conversion film 14 that converts X-rays 19 into visible light is formed. This fluorescent conversion film 14 is a vapor phase growth method such as a vacuum deposition method, a sputtering method, or a CVD method, and a phosphor containing CsI: Tl (thallium-doped cesium iodide), which is a high-intensity fluorescent material, as a main component. A film is deposited on the conversion substrate 13 in a columnar shape. The fluorescence conversion film 14 is formed in a columnar crystal structure in which a plurality of strip-shaped columnar crystals 30 are formed in the surface direction of the photoelectric conversion substrate 13.

  On the fluorescence conversion film 14, a light reflection layer 33 is formed by laminating the fluorescence conversion film 14 so that the peripheral portion is in close contact with the photoelectric conversion substrate 13. The light reflecting layer 33 is composed of a mixture of a transparent and sticky adhesive substance 34 and a powder of an inorganic substance 35 having a higher refractive index than the adhesive substance 34. The adhesive substance 34 is composed of an adhesive gel having adhesiveness, has low fluidity, and does not penetrate between the columnar crystals 30 of the fluorescence conversion film 14. In addition, the powder of the inorganic substance 35 increases the utilization efficiency of the visible light converted by the fluorescence conversion film 14, and is made of, for example, a metal substance having excellent reflection characteristics.

  A protective film 38 that covers the light reflection layer 33 is laminated on the light reflection layer 33. The protective film 38 is made of an organic material or a metal material, and is preferably made of a metal material mainly composed of aluminum.

  In the indirect X-ray detector 11, an X-ray image transmitted through a human body or the like is incident on the X-ray detector 11, and the image information is converted into an electrical signal. At this time, X-rays are converted into visible light by the fluorescence conversion film 14, and the visible light is detected for each pixel 12 formed in a lattice shape on the photoelectric conversion substrate 13 and output as an electrical signal of two-dimensional image information. To do.

  In this X-ray detector 11, the light reflecting layer 33 formed on the fluorescence conversion film 14 can ensure moisture blocking properties and prevent deterioration of the fluorescence conversion film 14, and visible light converted by the fluorescence conversion film 14 can be prevented. Can improve the efficiency of use. In addition, the light reflecting layer 33 composed of the adhesive substance 34 does not penetrate into the fluorescence conversion film 14. As a result, the X-ray resolution of the X-ray detector 11 can be improved.

  Further, a protective film 38 can be adhered and laminated on the light reflecting layer 33. When the protective film 38 is made of a metal material containing aluminum as a main component, the moisture barrier property can be further improved.

  Next, FIG. 4 shows a second embodiment.

  On the fluorescence conversion film 14, an adhesive layer 41 is formed by laminating the periphery of the photoelectric conversion substrate 13 so that the fluorescence conversion film 14 is sealed. The adhesive layer 41 is made of an adhesive gel as a transparent and adhesive adhesive substance and does not penetrate between the columnar crystals 30 of the fluorescence conversion film 14.

  On the adhesive layer 41, a light reflecting layer 33 is formed by laminating the fluorescent conversion film 14 with its peripheral portion in close contact with the photoelectric conversion substrate 13. The light reflecting layer 33 is composed of a mixture of a transparent organic material 42 and a powder of an inorganic material 35 having a refractive index higher than that of the organic material 42.

  In this X-ray detector 11, the light reflecting layer 33 formed on the fluorescence conversion film 14 can ensure moisture blocking properties and prevent deterioration of the fluorescence conversion film 14, and visible light converted by the fluorescence conversion film 14 can be prevented. Can improve the efficiency of use. In addition, the adhesive layer 41 does not penetrate into the fluorescence conversion film 14, and the light reflection layer 33 penetrates the fluorescence conversion film 14 because the adhesion layer 41 is interposed between the fluorescence conversion film 14 and the light reflection layer 33. Can be prevented. As a result, the X-ray resolution of the X-ray detector 11 can be improved.

It is a partial sectional view of an X-ray detector showing a 1st embodiment of the present invention. It is a perspective view of the decomposition | disassembly state of a X-ray detector same as the above. It is a front view showing an X-ray detector typically. It is a partial cross section figure of the X-ray detector which shows the 2nd Embodiment of this invention.

Explanation of symbols

11 X-ray detectors as radiation detectors
13 Photoelectric conversion board
14 Fluorescence conversion film
33 Light reflection layer
34 Adhesive substances
35 Inorganic substances
38 Protective film
41 Adhesive layer

Claims (4)

A photoelectric conversion substrate that converts light into an electrical signal;
A fluorescence conversion film formed on the photoelectric conversion substrate and converting radiation into visible light;
A light-reflective layer formed on the fluorescent conversion film, which is composed of a mixture of a transparent and sticky adhesive substance and a powder of an inorganic substance having a refractive index higher than that of the adhesive substance. A radiation detector. A photoelectric conversion substrate that converts light into an electrical signal;
A fluorescence conversion film for converting radiation formed on the photoelectric conversion substrate into visible light;
Consists of a transparent and adhesive adhesive material, at least an adhesive layer formed on the fluorescence conversion film,
A radiation detector comprising: a transparent organic substance and a mixture of an inorganic substance powder having a higher refractive index than that of the organic substance, and a light reflecting layer formed on the adhesive layer. . The radiation detector according to claim 1, wherein a protective film composed of either an organic substance or a metal substance is laminated on the light reflecting layer. The radiation detector according to claim 3, wherein the protective film is made of a metal material mainly composed of aluminum.

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