JP2007214191A - Radiation detector and radiographic examination equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector capable of controlling deterioration of the detection characteristics of a semiconductor crystal object, even in the case of a wiring board having a thermal expansion coefficient different substantially from that of the semiconductor crystal object, and to provide radiographic examination equipment using the detector. <P>SOLUTION: In the radiation detector, a semiconductor detector 20 comprises: a wiring board 21 having a thermal expansion coefficient of 8.0×10<SP>-6</SP>[1/°C] or more, for example, a board consisting of a glass epoxy board or a flexible printed wiring board; and a semiconductor detection element 22 and the like arranged on the wiring board 21. The semiconductor detection element 22 is extended to an almost plated-shape semiconductor crystal object 23 and to the whole Y-axis direction of the semiconductor crystal object 23 in its undersurface. Eight element electrodes 24<SB>1</SB>-24<SB>8</SB>consisting of Au, for example, by a predetermined width are arranged in the direction of the X-axis. The element electrodes 24<SB>1</SB>-24<SB>8</SB>and pad electrodes 26<SB>1</SB>-26<SB>8</SB>arranged in the wiring board 21 are secured by bumps 28 composed of conductive adhesives of shearing modulus smaller than Young's modulus of the semiconductor crystal object 23. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radiation detector and a radiation inspection apparatus, and more particularly to a radiation detector and a radiation inspection apparatus that detect gamma rays emitted from a radioisotope in a subject.

  In recent years, tomographic apparatuses have been widely used to obtain information inside a living body (subject). Examples of the tomography apparatus include an X-ray computed tomography (X-ray CT) apparatus, a magnetic resonance imaging apparatus, a SPECT (single photon emission CT) apparatus, and a positron tomography (PET) apparatus. An X-ray CT apparatus irradiates a cross section of a living body with a narrow X-ray beam from multiple directions, detects transmitted X-rays, and calculates the spatial distribution of the degree of X-ray absorption in the cross section by a computer. Calculated and imaged. In this way, morphological abnormalities inside the living body, such as bleeding spots, can be grasped.

  In addition, since the PET apparatus can obtain precise information on the function information in the subject, development has been actively promoted in recent years. In a diagnostic method using a PET apparatus, first, a test drug labeled with a positron nuclide is introduced into a subject by injection or inhalation. The test drug introduced into the subject is accumulated in a specific part having a function corresponding to the test drug. For example, when a saccharide test drug is used, it is selectively accumulated at sites with high metabolism such as cancer cells. At this time, positrons are emitted from the positron nuclide of the test agent, and when the emitted positrons and surrounding electrons are combined and annihilated, two gamma rays (so-called annihilation gamma rays) are emitted in a direction of about 180 degrees from each other. The Therefore, the two gamma rays are simultaneously detected by a radiation detector arranged around the subject, and the image of the radioisotope in the subject is acquired by regenerating an image with a computer or the like. As described above, since the function information in the body of the subject can be obtained with the PET apparatus, the pathology of various intractable diseases can be elucidated.

In the PET apparatus, it has been proposed to use a semiconductor detection element to detect gamma rays (see, for example, Patent Document 1). As shown in FIG. 1, the semiconductor crystal element 100 has a structure in which electrodes 103 and 105 are provided on a semiconductor crystal body 104 such as CdTe. The semiconductor detection element 100 detects gamma rays as electrical signals by utilizing the property that gamma rays incident on the semiconductor crystal body 104 generate electron-hole pairs. Since the semiconductor detection element 100 has a simple structure, the semiconductor detection element 100 can be easily reduced in size and can detect the incident position of gamma rays with high accuracy. As a result, the position of the positron nuclide of the subject that is the source of gamma rays can be acquired with high accuracy, and the spatial resolution of the PET apparatus can be improved.
Japanese Patent Laid-Open No. 4-196180

  By the way, a semiconductor crystal body, particularly a CdTe crystal body, is fragile and easily broken, and defects are easily generated in the crystal by applying external stress. When a defect occurs in the CdTe crystal, electrons and holes generated by the incidence of gamma rays in the CdTe crystal are difficult to reach the electrodes, and the gamma ray detection characteristics deteriorate.

In particular, stress is easily applied to the CdTe crystal when or after the CdTe crystal is bonded to the wiring board. In particular, stress is applied to the CdTe crystal due to the difference in thermal expansion coefficient between the wiring substrate and the CdTe crystal due to cooling after joining the CdTe crystal and the wiring substrate by heating. The thermal expansion coefficient (linear expansion coefficient) of the CdTe crystal is 4.9 × 10 ⁻⁶ [1 / ° C.]. When an alumina substrate (coefficient of thermal expansion: 6.9 × 10 ⁻⁶ [1 / ° C.]) or a glass substrate (7.7 × 10 ⁻⁶ [1 / ° C.]) is used as the wiring substrate, the CdTe crystal The difference in thermal expansion coefficient is small, and the detection characteristics hardly deteriorate.

However, when a glass epoxy substrate (thermal expansion coefficient 30 × 10 ⁻⁶ [1 / ° C.]) is used as the wiring board, the difference in thermal expansion coefficient from the CdTe crystal is large and the detection characteristics are deteriorated. As shown in FIG. 1, when the glass epoxy substrate 101 and the CdTe crystal body 104 are joined by the conductive adhesive 102, when the glass epoxy substrate 101 contracts during cooling, the compressive stress is transferred to the CdTe via the conductive adhesive 102. Applied to the crystal 104. Since the conductive adhesive 102 is provided on the entire bonding surface between the glass epoxy substrate 101 and the CdTe crystal 104, the shrinkage of the glass epoxy substrate 101 is directly transmitted to the CdTe crystal 104 and compressed to the entire CdTe crystal 104. Stress is applied. As a result, there is a problem that the detection characteristics of the CdTe crystal 104 are deteriorated and cannot be practically used.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a radiation detector capable of suppressing deterioration of detection characteristics of a semiconductor crystal even on a wiring substrate having a large difference in thermal expansion coefficient from that of the semiconductor crystal. And a radiation inspection apparatus using the same.

According to one aspect of the present invention, there is provided a radiation detector including a wiring board and a semiconductor detection element that generates electron-hole pairs upon incidence of radiation on the wiring board, the semiconductor detection element having a substantially plate shape. And a first electrode composed of a plurality of element electrodes arranged perpendicularly to the thickness direction of the semiconductor crystal body and spaced apart from each other on the first main surface on the wiring board side at substantially equal intervals And a second electrode portion made of a metal film substantially covering the second main surface on the second main surface on the opposite side, and the wiring board has the first electrode on the surface thereof And a thermal expansion coefficient of 8.0 × 10 ⁻⁶ [1 / ° C.] or more, and the semiconductor detection element includes each of the element electrodes and the pad electrode. Each of them is made of a conductive adhesive having elasticity that is smaller than the Young's modulus of the semiconductor crystal. That is secured by a bump like bonding portion becomes, the radiation detector in which the bump-like adhesive portion is characterized by comprising disposed in a part of the region where the device electrode and the pad electrode facing each other are provided.

  According to the present invention, a substrate having a larger thermal expansion coefficient than the conventional one is used for the wiring substrate. A bump-like adhesive portion made of a conductive adhesive is used between the semiconductor detection element and the wiring board. The bump-like adhesive part is made of a material whose misalignment elasticity is less than the Young's modulus of the semiconductor crystal in the solidified state. Therefore, it absorbs the stress caused by the difference in thermal expansion coefficient between the wiring board and the semiconductor crystal, and thus the semiconductor. The stress applied to the crystal body is suppressed. Therefore, even if a wiring substrate having a large difference in thermal expansion coefficient from that of the semiconductor crystal is used, deterioration of the detection characteristics of the semiconductor crystal can be suppressed. Furthermore, since a wiring board with a low manufacturing cost can be used, the manufacturing cost can be reduced as compared with an alumina substrate or a glass substrate.

  The thermal expansion coefficient is represented by (ΔL / L) / ΔT [1 / ° C.] using a change in length ΔL in the temperature change ΔT, where L is the length of the object, and is a so-called linear expansion coefficient. is there. In the present specification and claims, the thermal expansion coefficient is indicated by a linear expansion coefficient.

  In addition, the first main surface of the semiconductor crystal body may be configured such that a groove portion for suppressing stress caused by thermal expansion of the wiring board is formed between adjacent element electrodes. By providing a groove portion between adjacent element electrodes on the first electrode portion side of the semiconductor crystal body, stress caused by a difference in thermal expansion coefficient between the wiring substrate and the semiconductor crystal body is concentrated on the region where the groove portion is formed. As a result, the application of stress to the region of the semiconductor crystal that is in contact with the device electrode can be avoided, and deterioration of detection characteristics can be further suppressed.

  According to another aspect of the present invention, any one of the above radiation detectors that detects radiation generated from a subject containing a radioisotope, and detection including an incident time and an incident position of radiation acquired from the radiation detector Information processing means for acquiring distribution information of the radioisotope in the subject based on the information is provided.

  According to the present invention, it is possible to reduce the manufacturing cost of the radiation inspection apparatus while maintaining the performance by suppressing the deterioration of the detection characteristics in the radiation detector and providing an inexpensive radiation detector.

  ADVANTAGE OF THE INVENTION According to this invention, the radiation detector which can suppress deterioration of the detection characteristic of a semiconductor crystal body, and a radiation inspection apparatus using the same can be provided even if it is a wiring board with a large thermal expansion coefficient difference with a semiconductor crystal body.

  Embodiments will be described below with reference to the drawings.

(First embodiment)
FIG. 2 is a block diagram showing the configuration of the PET apparatus according to the first embodiment of the present invention. Referring to FIG. 2, the PET apparatus 10 is disposed around the subject S, detects a gamma ray, and processes detection data from the detector 11. An information processing unit 12 that regenerates image data at the position of the positron nuclide RI, a display unit 13 that displays image data, a control unit 14 that controls movement of the subject S and the detector 11, and the information processing The input / output unit 15 includes a terminal that sends instructions to the unit 12 and the control unit 14, a printer that outputs image data, and the like.

  The detector 11 includes a semiconductor detection unit 20 and a detection circuit 16. The semiconductor detector 20 is arranged so that the incident surfaces of the gamma rays γa and γb face the subject S. Note that a test drug labeled with a positron nuclide RI is introduced into the subject S in advance.

When the positron from the positron nuclide RI disappears, two gamma rays γ _a and γ _b generated simultaneously are detected. Since the two gamma rays γ _a and γ _b are emitted at an angle of about 180 degrees, they enter the semiconductor detection unit 20 of the detector 11 facing each other with the subject S interposed therebetween. Each of the two semiconductor detector 20 the gamma ray gamma _a, is gamma _b the incident gamma gamma _a, and sends an electric signal (detection signal) the detection circuit 16 caused by the incidence of the gamma _b.

The detection circuit 16 determines the time (incident time) and the incident position where the gamma rays γ _a and γ _b are incident on the detection element from the detection signal, and sends the information (detection data) to the information processing unit 12. The detection circuit 16 includes, for example, an analog ASIC for calculating an incident time from a detection signal that is an analog signal, a digital ASIC that transmits the incident time and the incident position to the information processing unit as digital data, and the like.

  The information processing unit 12 performs coincidence detection and image data regeneration using an image regeneration algorithm based on the detection data. In the coincidence detection, when there are two or more pieces of detection data whose incident times substantially coincide with each other, it is determined that these pieces of detection data are valid and used as coincidence information. In the coincidence detection, detection data whose gamma ray incident times do not match is determined to be invalid and discarded. Then, based on the coincidence information, the detection element number included in the coincidence information, the position information of the detection element corresponding to the coincidence information, and the like, based on a predetermined image regeneration algorithm (for example, expectation maximization (Expectation Maximization method)) Regenerate the image data. The display unit 13 displays the image data regenerated in response to a request from the input / output unit 15.

  With the above configuration and operation, the PET apparatus 10 detects gamma rays from the positron nuclide RI selectively located in the body of the subject S, and regenerates image data of the distribution state of the positron nuclide RI.

The detectors 11 _{1 to} 11 ₈ are arranged around the subject S over 360 degrees. Each of the detectors 11 _{1 to} 11 ₈ is provided with a semiconductor detector 20 on the subject S side. Here, the body axis direction of the subject S is defined as the Z-axis direction (Z and −Z directions). The detector 11 may be movable relative to the subject S in the Z-axis direction. Although eight detectors 11 ₁ to 11 ₈ in FIG. 2 is shown the number of these are only examples, the number of detectors 11 ₁ to 11 ₈ is appropriately selected.

  FIG. 3 is an exploded perspective view showing the configuration of the semiconductor detection unit of the first embodiment, and FIG. 4 is a schematic plan view of the semiconductor detection unit of the first embodiment. FIG. 3 is a diagram of the semiconductor detection unit viewed from the substantially incident side of the gamma rays. For convenience of explanation, components arranged on the wiring board are shown separated upward. FIG. 4 is a perspective view of the semiconductor detection element 22.

Referring to FIGS. 3 and 4, the semiconductor detection unit 20 includes a wiring board 21, a semiconductor detection element 22 disposed on the wiring board 21, and a pad electrode 26 ₁ electrically connected to the semiconductor detection element 22. ˜26 ₈ (indicated by reference numeral 26 unless otherwise specified), the wiring pattern 30 formed on the wiring substrate 21, and the detection signal of the semiconductor detection element 22 are sent to the detection circuit (detection circuit 16 shown in FIG. 3). Connector 29a and the like.

  The semiconductor detection element 22 includes a substantially flat semiconductor crystal 23, a first electrode portion 24 formed on the lower surface of the semiconductor crystal 23, and a second electrode portion 25 formed on the upper surface.

The material of the semiconductor crystal 23 is, for example, cadmium telluride (CdTe), Cd _1-x Zn _x Te (CZT), thallium bromide (TlBr), silicon or the like sensitive to gamma rays having an energy of 511 keV. Can be mentioned. Moreover, the dopant for controlling electroconductivity etc. may be contained in these materials. CdTe is preferable in that the photoelectric absorption probability per unit length is about 100 times that of silicon. Silicon is preferable because it has a higher mechanical strength than CdTe, and thus crystal defects are less likely to occur during processing. The semiconductor crystal body 23 is obtained by forming a semiconductor crystal using a Bridgeman method, which is a semiconductor crystal growth method, or a moving heating method, and cutting it into a flat plate shape with a predetermined crystal orientation. When the semiconductor crystal 23 is made of CdTe, In is diffused in the interface between the semiconductor crystal 23 and the first electrode portion 24. As a result, a Schottky junction is formed between the semiconductor crystal body 23 and the first electrode portion 24.

  The second electrode portion 25 is made of a conductive film that substantially covers the upper surface of the semiconductor crystal body 23. A negative bias voltage Vb is applied to the second electrode portion 25 to serve as a cathode. When the semiconductor crystal 23 is made of CdTe, Pt is used for the second electrode portion 25. The bias voltage Vb is a DC voltage and is set to, for example, −60V to −1000V. The bias voltage is formed on the second electrode portion 25 from the outside of the wiring substrate 21 through the connector 29b, the wiring pattern 30a, the pad 31, and the wire 32.

The first electrode portion 24 extends to the entire lower surface of the semiconductor crystal body 23 in the Y-axis direction, and is formed with eight element electrodes 24 _{1 to} 24 ₈ (particularly refused) formed with a predetermined width in the X-axis direction. Unless otherwise indicated, reference numeral 24 is also provided. Each of the element electrodes 24 is separated from and electrically insulated from the element electrodes 24 adjacent in the X-axis direction. The element electrode 24 is made of, for example, an Au film, and has a width (length in the X-axis direction) of 0.5 mm, an interval in the X-axis direction of 0.1 mm, and a depth (length in the Y-axis direction) of 5 mm. The Each of the element electrodes 24 is grounded via a resistor and functions as an anode. Although the number of element electrodes 24 is eight here, the number is not particularly limited as long as it is two or more.

  Next, the operation of the semiconductor detection element 22 will be described. In the semiconductor detection element 22, when gamma rays are incident on the semiconductor crystal body 23, electron-hole pairs are generated in the semiconductor crystal body 23. Since an electric field is applied to the semiconductor crystal body 23 from the device electrode 24 toward the second electrode portion 25, holes are attracted to the second electrode portion 25 and electrons are attracted to the device electrode 24. At this time, electrons are attracted to the nearest element electrode 24, and a detection signal indicating that gamma rays are incident on a detection circuit connected to each element electrode 24 is formed.

As the wiring board 21, a board having a thermal expansion coefficient of 8.0 × 10 ⁻⁶ [1 / ° C.] or more is used. Examples of such a substrate include a printed board containing a resin such as a glass epoxy board or a flexible printed board. A printed circuit board containing a resin is easier and cheaper to design and manufacture than conventionally used alumina and glass substrates. As the PET apparatus increases in size, more detectors are required and a corresponding number of wiring boards 21 are required. Therefore, the cost reduction of the wiring board 21 greatly contributes to the cost reduction of the PET apparatus 10. However, the thermal expansion coefficient of the wiring board 21 should be set to 20 × 10 ⁻⁶ [1 / ° C.] or less. If the thermal expansion coefficient of the wiring board 21 exceeds 20 × 10 ⁻⁶ [1 / ° C.], it will be difficult to sufficiently absorb the stress described in detail later by the bumps 28.

The glass epoxy board is obtained by impregnating a glass cloth with a modified epoxy board and thermosetting, for example, a so-called FR-4 or FR-5 grade printed wiring board. The thermal expansion coefficient of the glass epoxy substrate is 10 × 10 ^{−6 to} 16 × 10 ⁻⁶ [1 / ° C.] in the in-plane direction (in-plane direction of the XY plane in FIG. 3).

Further, the flexible printed circuit board is obtained by forming a wiring pattern on a film of polyester resin or polyimide resin with copper foil or copper plating. The thermal expansion coefficient of the flexible printed circuit board is 12 × 10 ^{−6 to} 20 × 10 ⁻⁶ [1 / ° C.] in the in-plane direction. Note that the glass epoxy substrate and the flexible printed circuit board may be either a single layer substrate or a multilayer laminated substrate.

In the semiconductor detection element 22, the first electrode portion 24 and the pad electrodes 26 _{1 to} 26 ₈ provided on the wiring substrate 21 are fixed to each other by a bump 28 made of a conductive adhesive. Specifically, each of the element electrodes 24 _{1 to} 24 ₈ of the first electrode section 24 and each of the pad electrodes 26 _{1 to} 26 ₈ provided on the surface of the wiring board 21 are two bumps made of a conductive adhesive. 28 is fixed. As a result, the stress caused by the thermal expansion of the wiring board 21 is less likely to be transmitted to the semiconductor crystal body 23 than in the conventional bonding method by sticking, and deterioration of detection characteristics can be suppressed (detailed later).

As the conductive adhesive forming the bumps 28, a so-called conductive paste or anisotropic adhesive made of metal powder selected from Au, Ag, Cu, and alloys thereof, a carbon filler, and a resin can be used. . As the conductive adhesive, a material having a deviation elasticity smaller than the Young's modulus of the semiconductor crystal 23 in a solidified state after bonding is used. The Young's modulus of the semiconductor crystal body 23 is 54 × 10 ⁹ Pa for CdTe and 167 × 10 ⁹ Pa for silicon. On the other hand, as the conductive adhesive, for example, a commercially available product having a deviation elasticity after solidification of 1.0 × 10 ⁹ Pa may be used.

  Further, the thickness of the bump 28 is set to 100 μm, for example. The thicker the bump is, the higher the effect of absorbing stress, which will be described later, but it is preferable to set the bump in the range of 10 μm to 200 μm, for example.

  A bonding process between the semiconductor detection element 22 and the wiring substrate 21 will be described with reference to FIG. First, two bumps 28 are formed on each pad electrode 26 of the wiring board 21 by applying a conductive paste such as a gravure printing method. Next, the semiconductor detection element 22 is positioned with respect to the wiring substrate 21 placed on a stage (not shown). Next, the semiconductor detection element 22 is disposed on the wiring board 21 and temporarily joined.

  Next, while holding the semiconductor detection element 22 from above and pressing it with a jig, the wiring board 21 and the semiconductor detection element 22 are heated, for example, at a temperature of 120 ° C. for 60 minutes, or at a temperature of 150 ° C. for a heating time of 2 The main bonding is performed by heating under the conditions of min to 4 min. Next, when cooling, after the conductive paste starts to solidify, the holding jig is separated from the semiconductor detection element 22 and further cooled to room temperature. As described above, the semiconductor detection element 22 and the wiring substrate 21 are joined.

5 and 6 are diagrams for explaining the operation of the first embodiment. FIGS. 5A and 6A are views showing a state of the wiring board and the semiconductor detection element at the start of solidification of the bumps in the main joining step, and FIGS. 5B and 6B. FIG. 3 is a diagram showing a state after solidification. 5 is a part of the cross-sectional view in the X-axis direction shown in FIG. 3 (part including the device electrodes 24 ₁ and 24 ₂ as an example), and FIG. 6 is a part of the cross-sectional view in the Y-axis direction shown in FIG. As an example, a portion including the device electrode 24 ₁ is shown.

Referring to FIG. 5A, when returning from the temperature of the main bonding in the bonding process described above to room temperature, the wiring board 21 and the semiconductor crystal body 23 are in the directions of arrows 21a and 23a, respectively, at the start of the solidification of the bumps 28. Try to shrink. Since the thermal expansion coefficient of the wiring board 21 is larger than the thermal expansion coefficient of the semiconductor crystal 23, the wiring substrate 21 at this point because it expands more than the semiconductor crystal 23, the bumps 28, device electrodes 24 ₁ and 24 wider towards the gap between the pad electrode 26 ₁ and 26 ₂ than the distance between _2, which is on the outside of the X-axis direction in the pad electrode 26 _1, 26 ₂ side.

  Referring to FIG. 5B, after the bumps 28 are solidified, the amount of shrinkage of the wiring substrate 21 from the solidification start time of the bumps of FIG. Bigger than. If the bump 28 is an ideal rigid body, a compressive stress generated by contraction of the wiring board 21 is applied to the semiconductor crystal body 23 via the bump. However, since the bump 28 has elasticity that is lower than the Young's modulus of the semiconductor crystal body 23, the stress from the wiring substrate 21 is absorbed. That is, since the bump itself substantially absorbs the difference in bending amount between the state where the bump shown in FIG. 5A is bent and the state where the bump shown in FIG. Suppresses applied stress. Thereby, deterioration of the detection characteristics of the semiconductor crystal body 23 can be suppressed. This effect is the same in the cross section in the Y-axis direction shown in FIGS. 6A and 6B, and the semiconductor crystal produced by the difference in the thermal expansion coefficient in the Y-axis direction by the bump 28 absorbing the deformation. The stress applied to the body 23 is suppressed.

In the contact region between the bump 28 and the semiconductor crystal 23 (via the device electrodes 24 ₁ and 24 ₂ ), compressive stress due to contraction of the bump 28 itself is applied to the semiconductor crystal 23. Since the area in contact with the body 23 is extremely smaller than the sticking, the stress applied to the semiconductor crystal body 23 can also be suppressed in this respect.

  According to the first embodiment, a substrate having a larger thermal expansion coefficient than the conventional one is used for the wiring substrate 21. A bump 28 made of a conductive adhesive is used for the semiconductor detection element 22 and the wiring substrate 21. The bump is made of a material whose elasticity is less than the Young's modulus of the semiconductor crystal 23 in a state after solidification. Therefore, the bump absorbs the stress caused by the difference in thermal expansion coefficient between the wiring substrate 21 and the semiconductor crystal 23 and thus the semiconductor. The stress applied to the crystal body 23 is suppressed. Therefore, even if the wiring substrate 21 having a large difference in thermal expansion coefficient from that of the semiconductor crystal 23 is used, it is possible to suppress the deterioration of the detection characteristics of the semiconductor crystal 23. Furthermore, since a glass epoxy substrate or a flexible printed circuit board with a low manufacturing cost can be used, the manufacturing cost can be reduced as compared with an alumina substrate or a glass substrate.

  Furthermore, a dimensional change due to thermal expansion of the wiring board 21 occurs due to a temperature change in a temperature range of 0 ° C. to 50 ° C., for example, in a storage environment. Application of the generated stress to the semiconductor crystal body 23 can be suppressed. Therefore, deterioration of the detection characteristics of the semiconductor crystal body 23 can be suppressed not only during the manufacturing but also after the manufacturing, and the long-term reliability of the radiation detector and the PET apparatus 10 is improved.

(Second Embodiment)
Next, a PET apparatus according to the second embodiment of the present invention will be described. The PET apparatus according to the second embodiment is a modification of the PET apparatus according to the first embodiment, and has the same configuration except that the semiconductor detection element 22 of the semiconductor detection unit 20 shown in FIG. 3 is different. Have.

  FIG. 7 is a perspective view showing the configuration of the semiconductor detection unit of the PET apparatus according to the second embodiment of the present invention. In the figure, portions corresponding to the portions described above are denoted by the same reference numerals, and description thereof is omitted.

Referring to FIG. 7, in the semiconductor detection element 42, a groove 43 a extending in the X axis direction at a predetermined interval and extending in the Y axis direction is formed on the first electrode portion 44 side of the semiconductor crystal body 43. In the semiconductor detection element 42, element electrodes 24 _{1 to} 24 ₈ are further formed on the surface of the convex portion 43b between the adjacent groove portions 43a and 43a. The material of the semiconductor crystal 43 is the same as that of the semiconductor crystal 23 in FIG. The width of the groove 43a is set to 0.1 mm, for example, and the depth is set to 0.3 mm. In this case, the width and interval of the element electrodes 24 are the same as those shown in the first embodiment.

Thus, by providing the groove 43a on the first electrode portion 44 side, when gamma rays are incident on the semiconductor crystal body 43 and an electron-hole pair is generated, electrons are transferred to the closest device electrodes 24 _{1 to} 24 ₈ . Can concentrate. As a result, the peak value of the detection signal is increased, and the position detection resolution of the gamma ray is improved. Furthermore, the following effects are produced by providing the groove 43a.

FIG. 8 is a diagram for explaining the operation of the second embodiment, and is a diagram showing a state after the bumps are solidified in the main bonding step between the wiring board and the semiconductor detection element. 8 shows a part of the cross-sectional view in the X-axis direction shown in FIG. 7 (a part including element electrodes 24 ₁ and 24 ₂ as an example).

Referring to FIG. 8, the region 43c above the groove 43a of the semiconductor crystal body 43 is thinner than the region 43d where the device electrodes 24 ₁ and 24 ₂ are in contact with each other, so that the mechanical strength is reduced. Is inferior to the region 43d. In the state after the bumps 28 are solidified, the stress caused by the difference in thermal expansion coefficient between the wiring substrate 21 and the semiconductor crystal body 43 is suppressed by the bumps 28. However, there is a possibility that stress that cannot be completely absorbed by the bumps 28 remains in the semiconductor crystal body 43. This stress is applied in a direction that narrows the distance between the device electrodes 24 ₁ and 24 _2, and thereby a tensile stress is applied to the region 43 c as indicated by an arrow 43 e. Since the region 43c is a region between the device electrode 24 ₁ and the device electrode 24 ₂ , the electron-hole pair generated by the incidence of gamma rays at this position is detected more than the electron-hole pair generated in the region 43d. The need for purpose is low. Therefore, stress can be concentrated on the region 43c and stress application to the region 43d can be avoided, and as a result, deterioration of detection characteristics can be further suppressed.

  In addition, although it is preferable to form the groove part 43a over the whole Y-axis direction of the semiconductor crystal body 43 as mentioned above, you may provide a groove part in a part of Y-axis direction. In this case, the same effect as described above is produced. However, although the degree of the effect is reduced, it may be appropriately applied depending on the degree of difference between the thermal expansion coefficient of the wiring substrate 21 and the thermal expansion coefficient of the semiconductor crystal body 43.

  According to the second embodiment, by providing the groove 43a on the first electrode portion 44 side of the semiconductor crystal 43, the stress caused by the difference in thermal expansion coefficient between the wiring substrate 21 and the semiconductor crystal 43 is applied to the region 43c. By concentrating, application of stress to the region 43d with which the element electrode 24 is in contact can be avoided. As a result, the deterioration of detection characteristics can be further suppressed.

  In the first and second embodiments described above, as shown in FIGS. 3 and 7, the number of bumps per set of the element electrode 24 and the pad electrode 26 is two, but three That's all. However, each pad needs to be separated. Furthermore, as shown below, the number of bumps per set of element electrodes and pad electrodes may be one.

  FIG. 9 is a schematic plan view showing a modification of the semiconductor detection unit. In the figure, portions corresponding to the portions described above are denoted by the same reference numerals, and description thereof is omitted.

Referring to FIG. 9, a semiconductor detection unit 50 is a modification of the semiconductor detection unit 20 of the first embodiment shown in FIG. In the semiconductor detection unit 50, the semiconductor detection element 22 and the wiring substrate 21 are joined by one bump 28 per set of element electrodes 24 _{1 to} 24 ₈ and pad electrodes 26 _{1 to} 26 ₈ . In the case of a single bump 28, the compressive stress generated by the thermal expansion in the Y-axis direction is not applied to the bump 28 and the semiconductor crystal 23, thereby further suppressing the deterioration of detection characteristics due to the stress applied to the semiconductor crystal 23. it can. In the semiconductor detection unit 40 shown in FIG. 7 as well, one set of element electrode 44 and pad electrode 26 may be joined by one bump as described above.

  Next, another modification of the semiconductor detection unit will be described.

  FIG. 10 is a schematic plan view showing another modification of the semiconductor detection unit, and FIG. 11 is a cross-sectional view taken along line AA shown in FIG. In the figure, portions corresponding to the portions described above are denoted by the same reference numerals, and description thereof is omitted.

Referring to FIGS. 10 and 11, the semiconductor detection unit 60, a slit-shaped opening 21a is provided between the pad electrode 26 _{1-26 8} wiring board 21 is adjacent. The opening 21 a penetrates in the thickness direction of the wiring board 21. The width of the opening 21a (X-axis direction length) is set smaller than the gap between the pad electrodes 26 ₁ to 26 _8. However, the width is set such that the flatness of the wiring board 21 is not impaired. By providing such an opening 21a, a dimensional change due to thermal expansion of the wiring board 21 can be suppressed. Therefore, it is possible to reduce the numerical change caused by the difference in thermal expansion coefficient between the wiring substrate 21 and the semiconductor crystal body 23. As a result, the stress applied to the semiconductor crystal body 23 can be further suppressed by reducing the stress caused by the difference in thermal expansion coefficient between the wiring substrate 21 and the semiconductor crystal body 23. As a result, the deterioration of the detection characteristics of the semiconductor crystal body 23 can be further suppressed. In addition, the effect is further enhanced by applying this modification to the semiconductor detection unit 40 shown in FIG.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the present invention described in the claims. It can be changed.

  For example, in the above-described first embodiment, the PET apparatus has been described as an example, but the present invention can be applied to a SPECT (Single Photon Emission Computed Tomography) apparatus. In the above description, the case where the semiconductor detection unit detects gamma rays has been described as an example. However, it goes without saying that the present invention can also be applied to a semiconductor detection unit for X-rays or other radiation.

It is a figure for demonstrating the problem of the conventional semiconductor detector. It is a block diagram which shows the structure of the PET apparatus which concerns on the 1st Embodiment of this invention. It is a disassembled perspective view which shows the structure of the semiconductor detection part of 1st Embodiment. It is a schematic plan view of the semiconductor detection part of 1st Embodiment. It is FIG. (1) for demonstrating the effect | action of 1st Embodiment. It is FIG. (2) for demonstrating the effect | action of 1st Embodiment. It is a perspective view which shows the structure of the semiconductor detection part of the PET apparatus which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the effect | action of 2nd Embodiment. It is a schematic plan view which shows the modification of a semiconductor detection part. It is a schematic plan view which shows the other modification of a semiconductor detection part. It is the sectional view on the AA line shown in FIG.

Explanation of symbols

10 PET device 11, 11 ₁ to 11 ₈ detector 12 information processing unit 13 display unit 14 control unit 15 input unit 16 detecting circuit 20,40,50,60 semiconductor detector 21 wiring board 22, 42 semiconductor detection device 23, 43 semiconductor crystal 24, 44 first electrode portion 24 _{1-24 8} element electrode 25 second electrode 26, 26 ₁ to 26 ₈ pad electrode 28 bumps 29a, 29b connector 30,30a wiring patterns 43a groove 43b protrusions

Claims (8)

A radiation detector comprising a wiring board and a semiconductor detection element that generates electron-hole pairs by incidence of radiation on the wiring board,
The semiconductor detection element includes a substantially plate-like semiconductor crystal body and a plurality of semiconductor crystal bodies that are orthogonal to the thickness direction of the semiconductor crystal body and arranged on the first main surface on the wiring board side so as to be spaced apart from each other at substantially equal intervals. A first electrode portion made of the element electrode and a second electrode portion made of a metal film substantially covering the second main surface on the second main surface on the opposite side,
The wiring board is provided with a pad electrode corresponding to the element electrode of the first electrode portion on the surface, and has a thermal expansion coefficient of 8.0 × 10 ⁻⁶ [1 / ° C.] or more,
In the semiconductor detection element, each of the element electrodes and each of the pad electrodes are fixed by a bump-like adhesive portion made of a conductive adhesive having elasticity that is smaller than the Young's modulus of the semiconductor crystal. A radiation detector, characterized in that the adhesive portion is disposed in a part of a region where the element electrode and the pad electrode face each other.   The radiation detector according to claim 1, wherein the first main surface of the semiconductor crystal body is substantially flat.   2. The radiation according to claim 1, wherein the first main surface of the semiconductor crystal is formed with a groove for suppressing stress caused by thermal expansion of the wiring board between adjacent element electrodes. Detector.   The radiation detector according to any one of claims 1 to 3, wherein the bump-shaped adhesive portion includes a plurality of bumps disposed in the region so as to be separated from each other.   The radiation detector according to any one of claims 1 to 4, wherein the bump-shaped adhesive portion is formed of a single bump disposed in the region.   The radiation detector according to claim 1, wherein the wiring board is a glass epoxy board or a flexible printed board.   The radiation detector according to claim 1, wherein the wiring board has an opening penetrating in the thickness direction of the wiring board between adjacent pad electrodes. A radiation detector according to any one of claims 1 to 7, which detects radiation generated from a subject containing a radioisotope,
A radiation examination apparatus comprising: information processing means for acquiring distribution information of the radioisotope in a subject based on detection information including an incident time and an incident position of radiation acquired from the radiation detector.

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