JP2002090463A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector with a highly efficient X-ray conversion at a less cost by improving productivity using a semiconductor conversion layer for converting X rays directly into an electric charge signal. SOLUTION: A collimator part 44 being supported by a main support plate 5 and a support plate 6 are provided at an upper part while multi-step stages are formed on both insides in the direction of slicing of a main board 4 at a lower part and sub boards (1, 2 and 3) carrying thin X-ray conversion layers (1a, 2a and 3a) are laminated on the stage and electrically fastened thereon. A thin X-ray conversion layer 4a is provided at the central part of the main board 4 and an electric wire 43 is arranged on the surfaces over the multiple steps of the main board 4 to share an electric connection between the main board 4 and the sub boards (1, 2 and 3). Signals from the X-ray conversion layers(1a, 2a, 3a and 4a) are fetched with a switching element 10 to be transmitted outside with a flexible cable 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector used in a single-slice, dual-slice, multi-slice, or cone-beam X-ray CT apparatus. The present invention relates to an array-type radiation detector using an X-ray conversion layer that converts a signal into a signal.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, an X-ray radiated from an X-ray tube is narrowed down to a fan-shaped X-ray beam by a collimator of a radiation port, and an X-ray tube and an object facing the X-ray tube are focused on a subject. An arc-shaped collimator and detector arranged in a rotating manner are rotated, the detector captures X-ray information transmitted through the subject, and the signal is processed by a computer to obtain an X-ray tomographic image of the subject. is there. X-rays emitted from the X-ray tube can be transmitted straight through the subject or scattered by the subject. By taking in only the former information, scattered rays entering obliquely are removed, and the crosstalk occurs. To prevent this, a collimator is provided in front of the detector. In this collimator, an X-ray shielding wall is formed of a material that is difficult to transmit X-rays for each channel in front of detectors arranged one-dimensionally.

[0003] The detector is an X-ray tube comprising an X-ray detecting element comprising a scintillator element for converting X-rays into light and a photodiode for detecting the light converted by the scintillator element and outputting it as an electric signal. And about 500 to 1000 channels arranged in an arc with the center as the center. Due to the mechanical arrangement in manufacturing, a combination of a scintillator and a photodiode, which are optically bonded and combined, and 8 to 30 units are arranged on a substrate is considered as one module. It is continuously arranged in a substantially arc shape on the upper side and combined with a collimator to constitute a radiation detector for CT.

FIG. 5 shows a conventional collimator 20, and FIG. 6 shows a sectional structure of a single slice radiation detector in a slice direction. The collimator 20 includes an X-ray shielding plate 21 in the channel direction, an arc-shaped main support plate 22 provided before and after in the slice direction, a support plate 23, and a detector mounting plate 25 supporting the support plate 23. . An X-ray shielding plate 21 in the channel direction is inserted and fixed between the two main support plates 22 and the support plate 23 in the slice direction in the direction of incidence of the X-ray beam from the X-ray tube. Then, both ends of the collimator 20 are reinforced by support rods 24. The collimator 20 includes a scintillator 28 and a P
Substrate 2 on which DA (photodiode array) 27 is mounted
6 and the mounting screw 32 are combined so that the upper and lower positions are aligned. At this time, the positional accuracy of the collimator 20 and the detector unit is set accurately, and the detection sensitivity of each detector is made uniform and maximum. And the bottom plate 29, the side plate 3
0. The protection plate 33 is attached to protect the detector unit, and is integrally attached to the rotating body of the CT apparatus via the main support plate 22.

[0005] This X-ray shielding plate 2 in the channel direction
The first fixing and bonding operation has a hollow space having a shape along the entire outer shape of the collimator 20, and a jig frame having a number of vertical grooves along which the X-ray shielding plate 21 can be inserted. The X-ray shielding plate 21 cut in advance in the channel direction is inserted in the vertical direction along the groove, and
After the main support plate 22 and the support plate 23 are integrally bonded to both end surfaces of the wire shielding plate 21, the main support plate 22 and the support plate 23 are pulled out from the frame body to one of upper and lower sides. Thereafter, in the manufactured collimator 20, the detector mounting plate 25 is fixed to the support plate 23 by screws. The direction in which the X-ray shielding plate 21 is fixed in the channel direction is processed so that the directions of the grooves are respectively converged in the focal direction of the X-ray tube so that the directions of the grooves converge in the direction of the focal point of the X-ray tube. .

[0006]

A conventional radiation detector is constructed and manufactured as described above. However, in a radiation detector using a semiconductor single crystal or polycrystal which has been recently proposed, an X-ray or the like is used. A semiconductor material that generates charges (electrons-holes) when irradiated with radiation is used, has high dark resistance, has a wide dynamic range for X-ray irradiation,
For example, CdZnTe polycrystal has been proposed as a material having good N and good photoconductive properties.

It has been found that this CdZnTe polycrystal is useful 3 to 10 times more sensitively than the conventional one. Further, since each channel can be separated by an electrode, there is an advantage that a separator or the like is not necessary as in the case of forming a scintillator array, and the channel can be easily separated. However, a semiconductor single crystal or a polycrystal has a problem that a crystal interface is present on a wafer, making it difficult to produce a semiconductor single crystal or a polycrystal having a uniform area and a large thickness, resulting in a very low productivity. Therefore, if a module having a large area and a large thickness is separated into electrodes and manufactured as a module, it becomes expensive. For this reason, it is necessary to assemble small areas and to assemble them with high accuracy. Also, when X-rays are applied while a bias voltage is applied, electron-hole pairs are generated internally, but when the thickness is large, an internal electric field is formed, and the bias voltage is effectively weakened. As a result, there is a problem that the sensitivity is reduced.
Further, there is a problem that carriers traveling in the semiconductor may be trapped, leading to poor rising characteristics.

The present invention has been made in view of such circumstances, and uses a semiconductor conversion layer that directly converts X-rays into a charge signal, thereby improving productivity, reducing X-ray conversion efficiency at low cost. An object is to provide a good radiation detector.

[0009]

In order to achieve the above object, a radiation detector according to the present invention comprises an X-ray conversion layer having electrodes on upper and lower surfaces for converting X-rays directly into charge signals, In a radiation detector in which a collimator portion composed of a collimator plate for use in a one-dimensional or two-dimensional arrangement is arranged, the electric wiring of a plurality of sub-substrates configured in multiple stages and provided with the X-ray conversion layer is shared. Wiring is formed on the main substrate so that the X-ray conversion layers can be opposed or arranged in the same direction.

The radiation detector according to claim 2 is
The electric wiring of each sub-substrate provided with the X-ray conversion layer can be shared by the electric wiring of the main substrate and the anisotropic conductive film.

Furthermore, the radiation detector according to claim 3 is
A positive bias voltage is applied to the electrode on the X-ray incident surface side of the X-ray conversion layer provided on the main substrate, and the X-ray
The configuration is such that a negative bias voltage is applied to the electrode on the X-ray incident surface side of the line conversion layer.

A radiation detector according to a fourth aspect of the present invention includes an X-ray conversion layer having electrodes on the upper and lower surfaces for directly converting X-rays into a charge signal, and a collimator section for removing a scattered radiation. And a one-dimensional or two-dimensionally arranged radiation detector, using a photosensitive glass plate as a substrate, inserting and fixing the collimator plate in a groove formed by etching, and providing an X-ray conversion layer on the back surface The plurality of sub-substrates are configured in multiple stages, the wiring on the main substrate is formed so that the electric wiring of each sub-substrate can be shared, and the X-ray conversion layers are arranged to face each other or in the same direction. .

The radiation detector of the present invention is configured as described above. Thin semiconductor non-crystals and single crystals are mounted on a plurality of substrates, arranged in steps, and their electrical wirings are shared. It is configured as one radiation detector. The step arrangement of the respective substrates is arranged to be opposed or arranged in the same direction. The electrical wiring is connected by using an anisotropic conductive film. Further, a positive bias voltage is applied to the electrode on the X-ray incident surface side of the X-ray conversion layer provided on the main substrate, and a negative bias voltage is applied to the electrode on the X-ray incident surface side of the X-ray conversion layer provided on each sub-substrate. Apply voltage. With such a configuration, X
The X-ray absorption efficiency is improved by arranging the line conversion layer, and anisotropic conductive film is used to connect the electric wiring of each substrate, eliminating the need for substrate alignment at the time of mounting, releasing thermal stress at the time of connection, and repairing. It will be easier. Further, the polarity of the bias voltage is set to a positive bias on the X-ray incident side with respect to the lower main substrate having many hard X-ray components, so that the rising characteristics can be improved.

[0014] The radiation detector of the present invention comprises:
Using a photosensitive glass plate, insert and fix a collimator plate in the groove formed by etching, and configure multiple sub-substrates with an X-ray conversion layer on the back surface in multiple stages, and share the electrical wiring of each sub-substrate Wiring on the main substrate is formed so that the X-ray conversion layers can be opposed or arranged in the same direction. With this configuration, it is not necessary to separately provide a collimator section in front of the detector, and scattered radiation can be removed by providing the collimator section on each glass substrate.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the radiation detector of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a cross-sectional structure of a radiation detector of the present invention used in an X-ray CT apparatus when viewed from a channel direction.

The radiation detector is provided on a collimator 44 for removing scattered radiation, a main support plate 5 and a support plate 6 for supporting the collimator 44 from both sides, and a sub-substrate 3 for detecting incident X-rays. X-ray conversion layer 3a provided on sub-substrate 2, X-ray conversion layer 1a provided on sub-substrate 1, and X-ray conversion layer 4a provided on main substrate 4. The detector module unit 9 configured, the electric wiring 43 for sharing electric connection with each substrate, and the X-ray conversion layers (1a) ,
2a, 3a, 4a), a switching element 10 for extracting a signal, a flexible cable 8 for transmitting a signal to the outside, and a collimator unit 44 and a detector module unit 9 for mechanically aligning and fastening. And the mounting screw 7.

The present radiation detector has a thin X-ray conversion layer (1).
a, 2a, 3a, 4a) are stacked in multiple stages in the X-ray incident direction so that the X-ray absorption efficiency is equivalent to a thick X-ray conversion layer.
It is arranged and configured on a stepped stage. The electric wiring of the sub-substrate (1, 2, 3) of each layer and the electric wiring of the main substrate 4 are shared.

The main substrate 4 has, on both inner sides in the slicing direction, stages on which the sub-substrates (1, 2, 3) are stacked and electrically fixed in a multi-stage manner. A thin X-ray conversion layer 4a is provided at the center of the main substrate 4, and the electric wiring from the X-ray conversion layer 4a and the sub-substrates (1, 2, 3)
Electrical wiring 43 for sharing an electrical connection with the X-ray conversion layer (1a, 2a, 3a, 4a) is provided on the upper surface of the main substrate 4 in multiple stages. A switching element 10 and a flexible cable 8 for sending a signal to the outside are provided.

As the sub-substrates (1, 2, 3), a substrate made of a material having good X-ray transmittance is used, and a thin X-ray conversion layer (1a, 2a, 3a) is provided on the back surface. Are provided with electrical wiring. The size of the substrate is finished to a size that can be bonded and fixed to a stepped stage provided on the main substrate 4. The connection between the electric wiring of the stepped stage of the main substrate 4 and the electric wiring of the sub-substrate (1, 2, 3) is performed using an anisotropic conductive film (ACF).

The anisotropic conductive film is usually made of ACF (Anis).
This is an electrical connection material in which conductive particles such as carbon black, nickel fine particles, and ball solder are dispersed or oriented in a resin. The thickness of this anisotropic conductive film is 15 to 35 μm, and the conductive particle diameter is several μm to several tens μm.
m, a thermoplastic resin, a thermosetting resin, or a semi-thermosetting resin is selected and used for the resin in consideration of springback, thermal expansion coefficient, and reliability at the time of pressing. The anisotropic conductive film may be used in the form of a paste instead of a film.

FIG. 2 shows a bonding step using the anisotropic conductive film 19. First, (a) an anisotropic conductive film (ACF) 19 is prepared by mixing conductive particles 34 such as carbon black into an adhesive layer 35 made of a resin. (B) Next, the electrode 38 of the connection pad 41 on the substrate 39 to be connected and the substrate 37
An anisotropic conductive film (AFC) 19 is interposed between the electrode 36 and the electrode 36 of the upper connection pad 40. (C) Then, thermocompression bonding or pressure holding is performed using a heating / pressing tool 42 to maintain the insulation in the surface direction, and the electrodes 38 and 36 in the thickness direction.
Electrical connection between the two. By using this anisotropic conductive film 19, substrate alignment at the time of mounting becomes unnecessary,
Because of the crimping structure, thermal stress can be released and repair is easy.

Next, the X-ray conversion layers (1a, 2a, 3a, 4
The polarity of the voltage applied to the upper and lower electrodes in a) will be described. CdZn on the X-ray conversion layers (1a, 2a, 3a, 4a)
When using the Te polycrystal, the CdZnTe polycrystal of the main substrate 4 has a positive bias with respect to the X-ray incidence surface side, and the negative bias is applied to the other substrates mounted on the sub-substrates (1, 2, 3). Apply. This is schematically shown in FIG. Μτ product of electrons and holes of CdZnTe polycrystal (μ:
Mobility, τ: lifetime) are each 1 × 10 ⁻³ [cm ² / V].
And 6 × 10 ⁻⁶ [cm ² / V], and holes are three orders of magnitude smaller than electrons.

Therefore, it is advantageous to make electrons travel in the crystal. Incident X-rays are absorbed in the order of the sub-substrates 3, 2, and 1, but electron-hole pairs are generated near the surface, that is, on the minus bias side, so that the traveling distance of holes is short. The energy components of the X-rays passing through the sub-substrates 3, 2, 1 are mainly hard X-rays.
It is well absorbed on the back side of nTe polycrystal. Since a negative bias is applied to the back surface, the traveling distance of the holes can be short. Therefore, the probability that holes are trapped in the crystal is reduced, and the rising characteristics are improved.

Next, a specific configuration of the radiation detector will be described. The radiation detector is, for example, 1.25 m
A radiation detector for multi-slice CT capable of scanning 16 slices at m pitches. Electrodes for 16 slices are formed on each substrate (sub-substrates 1, 2, 3, and main substrate 4) so as to be separated in the slice direction (left-right direction in the drawing). As a material of the X-ray conversion layers (1a, 2a, 3a, 4a), for example, CdZnTe polycrystal is used. The detector module section 9 has 24 channels formed in the channel direction, and the plurality of detector module sections 9 are attached to the collimator section 44 via the main support plate 5 and the support plate 6.

The detector module section 9 includes, for example, four detector modules (an X-ray conversion layer 4a on the main substrate 4, an X-ray conversion layer 1a on the sub-substrate 1, and an X-ray conversion layer on the sub-substrate 2). It has a laminated structure of the layer 2a and the X-ray conversion layer 3a) on the sub-substrate 3, and each sub-substrate (1, 2, 3) is opposed to the main substrate so that the electric wiring 43 can be shared. They are arranged and electrically connected by an anisotropic conductive film (ACF) 19. Each thin X-ray conversion layer (1a, 2a, 3a,
4a) has, for example, a thickness of 0.5 mm and four X
The total thickness of the line conversion layers (1a, 2a, 3a, 4a) is 2 mm. Each sub-substrate (1, 2, 3) is provided with electric wiring, and is electrically connected to the main substrate 4 at an end portion by an anisotropic conductive film (ACF) 19.

Next, another embodiment of the radiation detector of the present invention will be described with reference to FIG. FIG. 4 shows a manufacturing process of a radiation detector in which a collimator plate is provided on each substrate except for the collimator section 44 of the radiation detector shown in FIG.

(A) A photosensitive glass plate 11 is prepared as a material for the sub-substrates (1, 2, 3) shown in FIG. Photosensitive glass is also called photosensitive chemical cutting glass, and its composition is
SiO ₂ : 81.5%, Li ₂ O: 12.0%, K
₂ O: 3.5%, Al ₂ O ₃ 3.0%, CeO ₂ : 0.
03% Ag: contains lithium oxide at 0.02%, and when this glass is irradiated with ultraviolet rays and heated, silver fine particles are first formed in the exposed portion, and then this becomes a nucleus to form microcrystals of lithium metasilicate. Precipitates. These microcrystals dissolve in hydrofluoric acid 40 to 50 times faster than the base glass. By utilizing such a large difference in solubility, only the exposed portion is selectively dissolved in hydrofluoric acid, whereby the glass can be processed with high precision.

(B) A groove 12 in which collimator plates 15b, 16b, 17b can be inserted in the channel direction is exposed on a glass substrate 15, 16, 17 having a size corresponding to the stepped lamination width of the main substrate 14 by a photomask. Then, it is processed by etching. (C) Further, the central portion is processed into a concave shape by polishing. (D) Next, the collimator plates 15b, 16b, and 17b are inserted into the grooves 12, and are adhered and fixed to the grooves 12 and the concave portions.

(E) The collimator plates 15b, 16
An electric wiring pattern for connection with the X-ray conversion layers 15a, 16a, and 17a of CdZnTe polycrystal is applied to the opposite surfaces of b and 17b by, for example, a screen printing method. At this time, the pitch between the positions of the collimator plates 15b, 16b, and 17b and the position of the dead space of the channel electrode of the electric wiring pattern is adjusted. Further, the CdZnTe polycrystalline X-ray conversion layers 15a, 15a,
The thin plates 6a and 17a are bonded and fixed to the glass substrates 15, 16, and 17 by a solder bump method, an ACF method, or the like.

The glass substrates 15, 1 thus formed
FIG. 4 (e) shows a cross section of the radiation detector composed of 6, 17 and the main substrate 14. As a result, the crosstalk of scattered radiation is further reduced and the number of those that directly shield X-rays is reduced, so that X-rays can be effectively used. Further, the collimator section 44 becomes unnecessary.

[0031]

According to the radiation detector of the present invention, a thin X-ray conversion layer is mounted on a plurality of substrates and stacked in a multi-stage manner to form an anisotropic connection for electric wiring. Since a common radiation conductive film is used and the radiation detectors are arranged facing each other or in the same direction to constitute one radiation detector, the X-ray absorption efficiency can be improved. The use of an anisotropic conductive film eliminates the need for substrate alignment at the time of mounting, releases thermal stress at the time of connection, and improves productivity. further,
Since the polarity of the bias voltage is positively biased on the X-ray incident side with respect to the lower main substrate having many hard X-ray components, the rising characteristics can be improved.

Further, since a photosensitive glass plate is used for each of the sub-substrates arranged in multiple stages and a collimator plate is inserted and fixed in the groove formed by etching, it is not necessary to separately provide a collimator portion in front of the detector. The scattered radiation can be removed by providing each of the glass substrates.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a radiation detector of the present invention.

FIG. 2 is a diagram showing a connection method of a substrate circuit of the radiation detector of the present invention.

FIG. 3 is a diagram showing a method of applying a bias voltage to each X-ray conversion layer of the radiation detector of the present invention.

FIG. 4 is a diagram showing another embodiment of the radiation detector of the present invention and a manufacturing method.

FIG. 5 is a diagram showing a collimator of a conventional radiation detector.

FIG. 6 is a diagram showing a conventional radiation detector.

[Explanation of symbols]

 1, 2, 3 ... Sub-substrate 1a ... X-ray conversion layer 2a ... X-ray conversion layer 3a ... X-ray conversion layer 4 ... Main substrate 4a ... X-ray conversion layer 5 ... Main support plate 6 ... Support plate 10 ... Switching element 14 ... Main substrate 14a ... X-ray conversion layer 15, 16, 17 ... Glass substrate 15a ... X-ray conversion layer 15b ... Collimator plate 16a ... X-ray conversion layer 16b ... Collimator plate 17a ... X-ray conversion layer 20 ... Collimator 43 ... Electrical wiring 44… Collimator section

Claims (4)

[Claims] An X-ray conversion layer having electrodes on upper and lower surfaces for directly converting X-rays into a charge signal, and a collimator section composed of a collimator plate for removing scattered radiation are arranged one-dimensionally or two-dimensionally. In the radiation detector, the wiring on the main substrate is formed so as to be able to share the electric wiring of the plurality of sub-substrates provided with the X-ray conversion layer, and the X-ray conversion layers are opposed to each other. A radiation detector, wherein the radiation detector is configured to be arranged in a direction. 2. The radiation detector according to claim 1, wherein the electric wiring of each sub-substrate provided with the X-ray conversion layer can be shared by the electric wiring of the main substrate and the anisotropic conductive film. A radiation detector, characterized in that: 3. The radiation detector according to claim 1, wherein a positive bias voltage is applied to an electrode on an X-ray incident surface side of an X-ray conversion layer provided on said main substrate, and an X-ray provided on each sub-substrate. A radiation detector characterized in that a negative bias voltage is applied to an electrode on the X-ray incident surface side of the conversion layer. 4. An X-ray conversion layer having electrodes on upper and lower surfaces for directly converting X-rays into a charge signal, and a collimator section comprising a collimator plate for removing scattered radiation are arranged one-dimensionally or two-dimensionally. In the radiation detector, a photosensitive glass plate is used as a substrate, the collimator plate is inserted and fixed in a groove formed by etching, and a plurality of sub-substrates having an X-ray conversion layer provided on a back surface thereof are configured in multiple stages. A radiation detector, wherein wirings on a main substrate are formed so that electric wirings of respective sub-substrates can be shared, and an X-ray conversion layer is arranged so as to face or in the same direction.