JP2002148344A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector having an improved productivity by using an X-ray conversion layer which directly converts X-ray to an electrical charge signal and combining with a collimator. SOLUTION: A module 6 is fabricated by providing an X-ray conversion layer 2 made of a semiconductor crystal machined in a rectangular plate form on a substrate 3, wherein the X-ray conversion layer 2 comprises a signal electrode 4 formed on its top surface, a guard electrode 5 having a ground potential formed at its edge part and a common electrode formed on its back surface. The guard electrode 5 reduces an influence of a dark current at the edge part due to a dicing process. The module 6 is positioned under the collimator part 1 polygonally on different levels, such that the guard electrode 5 at the both edge parts of the X-ray conversion layer 2 of the module 6 overlap with the guard electrodes 5 of the adjacent X-ray conversion layer 2.

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, or multi-slice X-ray CT apparatus, and more particularly to a collimator for preventing scattered radiation and directly converting an X-ray into a charge signal. The present invention relates to an array type radiation detector using an X-ray conversion layer.

[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. The radiation detector for CT is arranged continuously in a substantially arc shape on the upper side and combined with a collimator.

FIG. 4 shows a conventional collimator 20, and FIG. 5 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, and the signal line 31 from the detector section is
Is guided to the outside to protect the detector section, 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, a CdTe single crystal, a CdZnTe single crystal, or a polycrystal has been proposed as a material having good N and good photoconductive properties.

The CdTe single crystal, CdZnTe single crystal or polycrystal has been found to be useful several times to several tens times more sensitive than the conventional one, depending on the applied bias. 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 easily formed on a wafer, it is difficult to form a wafer having a uniformly large area, and the yield of productivity is extremely low. Therefore, the electrode having a small area is separated from the electrode and manufactured and used as a module. FIG.
In addition, a plurality of modules 6a around the X-ray tube focal point 7
Are continuously arranged in an arc shape, and a cross section in the channel direction of the radiation detector combined with the collimator unit 1 is shown. The X-ray conversion layer 2a provided on the substrate 3a is separated into each channel by the signal electrode 4 provided thereon.
The modules 6a are arranged in a polygonal shape with respect to the collimator unit 1, and the signal electrodes 4 are provided in accordance with the pitch of the collimator unit 1. However, in order to increase the X-ray detection efficiency as much as possible, the signal electrodes 4 It is necessary to narrow the dead zone of the above. Therefore, the space for providing the dead area at both ends is reduced. Further, when the module 6a is manufactured from a semiconductor single crystal or polycrystal, the dicing process damage occurs at the four end faces, so that a dark current becomes larger in a channel in the immediate vicinity than in an internal channel. In order to reduce the influence, it is necessary to keep the channels at both ends as far as possible from the end face. However, if the ends of the modules 6a are arranged in abutting relation, the distant portion becomes an insensitive portion, so that the width of both end channels must be reduced, and there is a possibility that the sensitivity of only the both end channels may be reduced.

In general, a semiconductor crystal is mechanically very fragile, and if the ends cut out from the module 6a are arranged in abutting relation, the crystal is chipped or broken by contact to break the element, thereby deteriorating the performance. There is a problem of causing damage. Therefore module 6 with small area
In order to avoid contact, a process of assembling with high precision is required, so that it is difficult to manufacture.

The present invention has been made in view of such circumstances, and a detector module using an X-ray conversion layer that directly converts X-rays into a charge signal is continuously arranged and assembled with a collimator. In addition, it is an object of the present invention to provide a radiation detector with improved productivity by making the dead portion between the joints of the detector modules a minimum predetermined width.

[0011]

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 unit constituted by a collimator plate for one-dimensional or two-dimensional arrangement is arranged, the X-ray conversion layer has a module structure, and a guard electrode of a ground potential is provided at both ends corresponding to a joint of the module. Provided,
The guard electrode portion is arranged in the collimator section so that the guard electrode portion overlaps with the guard electrode of an adjacent module. Further, the present invention provides such a radiation detector with X
This is used for a line CT apparatus.

The radiation detector of the present invention is configured as described above. The X-ray conversion layer is combined with a collimator as a module structure, and guard electrodes of a ground potential are provided at both ends corresponding to the joint of the module. The guard electrode portion is arranged stepwise so as to overlap the guard electrode of the adjacent module. Since the guard electrodes are provided at both ends of the module, it operates stably without affecting the noise of dark current.Since the guard electrodes are arranged stepwise so as to overlap, the space for installing the guard electrodes is reduced. The X-ray conversion layer can be widened to a predetermined width, and the X-ray conversion layer can be prevented from being broken by contact interference with an adjacent module. The productivity can be improved by arranging the modules at different levels in this way.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the radiation detector of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a cross section in the channel direction of the radiation detector of the present invention.
FIG. 2 is a diagram showing a single slice module 6 of the radiation detector of the present invention. The radiation detector includes a collimator unit 1 composed of a collimator plate for scattered radiation removal arranged in an arc with an X-ray tube focal point 7 as a center, a signal electrode 4 provided on a substrate 3, and an end A module 6 having a guard electrode 5 and a common electrode (not shown) on the lower surface, and comprising an X-ray conversion layer 2 for directly converting X-rays into a charge signal, and placing the module 6 on an arc below the collimator 1 In this configuration, a plurality of polygons are arranged at different levels in a stepwise manner.

The collimator section 1 is for removing scattered X-rays scattered by the object, and is a collimator plate converged in the direction of the X-ray tube focal point 7 so as to transmit only the X-rays transmitted through the object. It consists of. As the collimator plate, an X-ray shielding plate made of a material such as tungsten or molybdenum is used, and has the same structure as the conventional one shown in FIG. The X-ray conversion layer 2
A semiconductor material that generates a charge (electron-hole) when irradiated with radiation such as a line, for example, a CdTe single crystal or CdZ
An nTe single crystal or polycrystal is used. Although this semiconductor single crystal or polycrystal is hard and brittle, the sensitivity is several to several tens times higher than the conventional one, and the dark resistance is high,
Furthermore, the dynamic range is wide for X-ray irradiation,
It has good S / N and good photoconductive properties. X-ray conversion layer 2
Is manufactured to be slightly larger than the width of the X-ray conversion layer 2a of the conventional module 6a, and has a signal electrode 4 on an upper surface, a guard electrode 5 on an end, and a common electrode (not shown) on a lower surface. , Provided on the substrate 3 and used as the module 6. Put it on an arc corresponding to the lower part of the collimator unit 1,
The guard electrode 5 portion is arranged in a stepped polygonal shape so as to overlap with the guard electrode 5 portion of the adjacent module 6. With such a configuration, the signal electrode 4
Even if the portion is widened, there is room in the both ends of the module 6 in terms of space, so that manufacturing for providing the guard electrode 5 becomes easy. In addition, since the modules 6 are not arranged side by side, the adjacent modules 6
The X-ray conversion layer 2 of the module 6 can be prevented from being damaged. According to the pitch of the collimator plate of the collimator unit 1, several to several tens of signal electrodes 4 are provided in one module 6, the modules 6 are arranged in a polygonal shape, and the number of detectors in the channel direction is set. Is done. In the process of manufacturing the module 6 from a semiconductor single crystal or polycrystal, the guard electrode 5 is damaged at the four end faces by dicing, and the channel near the end has a larger dark current than the internal channel. Therefore, in order to suppress the influence, a guard electrode 5 is provided at the end, which is set to the ground potential, and all the dark current generated at the damaged end is caused to flow to the ground by the guard electrode 5, so that the signal electrode side It is intended to stabilize so as not to affect.

The step arrangement of the module 6 is performed by arranging the guard electrodes 5 stepwise so as to overlap with each other.
The space in which the guard electrode 5 is provided can be widened to a predetermined width, and the X-ray conversion layer 2 is not destroyed by contact interference with the adjacent module 6. The step arrangement of the module 6 includes a contact surface between the main support plate 22 and the substrate 26 of the conventional collimator 20 shown in FIG.
If the height of the contact surface between the detector mounting plate 25 and the substrate 26 is provided stepwise for each module 6, the module 6 can be disposed stepwise with respect to the collimator unit 1 as shown in FIG.

Next, a method for manufacturing the module 6 of the radiation detector will be described. The manufacturing steps include (a) a wafer preparation step, (b) a dicing cut step, (c) an electrode deposition step, (d) a substrate preparation step, (e) a bonding step of the X-ray conversion layer 2, and (f) a connection step. It is composed of

(A) In the wafer preparation step, a CdZnTe polycrystal or single crystal wafer or the like is used as the X-ray conversion layer of the semiconductor (polycrystal will be described below). CdZn
Te polycrystals are used under high temperature and high pressure conditions (high pressure Bridgman method:
Under the HPBM method, a polycrystalline rod was melted together with a control active impurity in a crucible and gradually pulled up with a seed crystal rod, or the polycrystalline rod was vertically placed in a vacuum or an inert gas. Move the fixed high-frequency coil fixedly,
The polycrystal is gradually melt-cooled to be crystallized, and the distribution of the control active impurities contained in the core wire of the polycrystal rod is made uniform. C produced in this way
The dZnTe polycrystal is mechanically cut with a wire saw or the like to prepare a disk-shaped CdZnTe polycrystal wafer. (B) In the dicing cut step, the CdZnTe polycrystalline wafer is diced and cut in a rectangular plate shape to the size of the module 6 to produce a CdZnTe plate. The dimensions in this case are processed so that the sides of the module 6 are the same as the dimensions finally finished. (C) In the electrode deposition step, a metal such as Pt or Au is pattern-vacuum deposited on the surface of the CdZnTe plate to form a signal electrode 5 and a guard electrode 5, and a common electrode is vacuum-deposited on the entire back surface. The line conversion layer 2 is manufactured. The guard electrode 5 is formed so as to surround the periphery of the CdZnTe plate. (D) In the substrate preparing step, an insulating substrate 3 provided with a pad (not shown) for connection to the outside at the end in the slice direction is prepared. (E) In the bonding step of the X-ray conversion layer 2, the common electrode side of the X-ray conversion layer 2 and the substrate 3 are bonded with a conductive adhesive or the like. (F) In the connection step, the signal electrode 4 and the guard electrode 5 are electrically connected to a pad portion (not shown) provided on the substrate 3 by a wire bonding method or the like. The pad section is connected to an amplifier (not shown) via a flexible cable (not shown).

FIG. 3 shows a radiation detector module 6b of the present invention used in multi-slice. Signal electrode 4
b is formed two-dimensionally corresponding to the collimator portion, and is electrically connected to the pad portion on the substrate (not shown) side by a solder bump method, an anisotropic conductive film (ACF), or the like. In this case as well, a guard electrode 5b is formed around the periphery, and all the dark current generated at the damaged end by dicing can be prevented by the guard electrode. As for the arrangement method of the modules 6b, the modules 6b can be similarly arranged stepwise as shown in FIG.

[0019]

According to the radiation detector of the present invention, the semiconductor crystal is machined into a rectangular plate shape, the signal electrode is formed on the upper surface, and the influence of dark current due to the dicing process on the end is stabilized. A module comprising a guard electrode to be formed and an X-ray conversion layer for directly converting an X-ray having a common electrode formed on the lower surface into a charge signal is arranged in a polygon below the collimator for removing scattered radiation, and the X-ray of the module is provided. The guard electrode portions provided at both ends of the conversion layer are arranged stepwise so as to overlap with the guard electrode portions of the adjacent modules, so that a large space can be taken for the guard electrode portion, which facilitates manufacture. The influence of the dark current at the end can be eliminated, the damage of the X-ray conversion layer of the module due to interference such as contact can be prevented, and the productivity can be improved. .

[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 single slice module of the radiation detector of the present invention.

FIG. 3 is a diagram showing a multi-slice module of the radiation detector of the present invention.

FIG. 4 is a diagram showing a collimator of a conventional radiation detector.

FIG. 5 is a diagram showing a cross section in a slice direction of a conventional radiation detector.

FIG. 6 is a diagram showing a cross section in the channel direction of a conventional radiation detector using an X-ray conversion layer.

[Description of Signs] 1 ... Collimator section 2, 2a, 2b ... X-ray conversion layer 3, 3a, 3b ... Substrate 4, 4b ... Signal electrode 5, 5b ... Guard electrode 6, 6a, 6b ... Module 7 ... X-ray tube Focus 20 ... Collimator 21 ... X-ray shielding plate 22 ... Main support plate 23 ... Support plate 24 ... Support rod 25 ... Detector mounting plate 26 ... Substrate 27 ... PDA 28 ... Scintillator 29 ... Bottom plate 30 ... Side plate 31 ... Signal line 32 ... Mounting screw

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuriko Nishimura 1-term Kuwaharacho, Nishinokyo, Nakagyo-ku, Kyoto F-term in Shimadzu Corporation (reference) 2G088 EE02 FF02 GG21 JJ04 JJ05 JJ12 JJ15 JJ32 JJ37 5F088 AA11 AB09 BB03 EA02 EA11 EA11 EA11 FA09 FA14 JA20 LA08

Claims (2)

[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 X-ray conversion layer has a module structure, guard electrodes of ground potential are provided at both ends corresponding to the joint of the module, and the collimator is stepped so that the guard electrode portion overlaps the guard electrode of an adjacent module. A radiation detector, wherein the radiation detector is arranged in a part. 2. The radiation detector according to claim 1, wherein X
A radiation detector for an X-ray CT apparatus, which is used as a detector of the X-ray CT apparatus.