JP2008268038A - Semiconductor radiation detector and industrial X-ray CT apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor radiation detector having reduced thickness while holding sufficient assembly strength. <P>SOLUTION: The semiconductor radiation detector includes a flexible substrate, a shielding plate opposing to the flexible substrate, a semiconductor crystal between a pair of the flexible substrate and the shielding plate, and a base plate provided on a side face side of the semiconductor crystal to form the semiconductor radiation detector having reduced thickness while holding sufficient assembly strength. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor radiation detector and an industrial X-ray CT apparatus.

  Non-Patent Document 1 discloses a semiconductor radiation detector using a semiconductor crystal in which an electrode is formed on a surface substantially parallel to the incident direction of radiation. This detector has a semiconductor crystal in which a bias electrode is formed on one of two opposing surfaces of a Si crystal and a signal extraction electrode is formed on the other surface. Then, the semiconductor crystal is bonded to a flexible substrate (FPC) provided on the upper surface of the heavy metal base plate to constitute a semiconductor radiation detector. This detector is used in an industrial X-ray CT apparatus.

  Also, as described in Patent Document 1, for the purpose of improving the performance of industrial X-ray CT apparatus, a detector for industrial X-ray CT apparatus is manufactured using a compound semiconductor CdTe having a density higher than that of Si. Attempts have also been made.

JP-A-2005-274169 H.Miyai, et. Al .: “A High Energy X-Ray Computed Tomography Using Silicon Semiconductor Detectors,” 1996 IEEE Nuclear Science Symposium Conference Record, Vol.2, pp816-820, Anaheim, CA, USA (1996)

  The maximum energy of X-rays generated from an X-ray generator (accelerator) used in an industrial X-ray CT apparatus varies depending on the object to be imaged and ranges from 12 MeV to 1 MeV. When the X-ray energy is low, the radiation shielding effect by the base plate may be low. Therefore, the base plate can be thinned and the detector array pitch can be narrowed. The image resolution of the X-ray CT apparatus can be improved. However, the base plate also has a role of fixing to the sensor holder. For this reason, if the base plate is made thin, the base plate bends when it is assembled into the sensor holder, etc., so that stress is applied to the semiconductor crystal and the detector performance may be deteriorated.

  An object of the present invention is to realize a semiconductor radiation detector having a reduced thickness while maintaining assembly strength.

  The present invention includes a flexible substrate, a shielding plate facing the flexible substrate, a semiconductor crystal between a pair of the flexible substrate and the shielding plate, and a base plate provided on a side surface of the semiconductor crystal. And

  According to the present invention, it is possible to realize a semiconductor radiation detector having a reduced thickness while maintaining assembly strength.

  An industrial X-ray CT apparatus using a semiconductor radiation detector is a very useful nondestructive inspection apparatus for observing and measuring the internal shape of an object. For this reason, it has recently been used mainly by automobile companies for measuring the shape of developed products and measuring the distribution of casting nests. In order to take a tomographic image of a large cast product or the like, an X-ray CT apparatus using an accelerator that emits high-energy X-rays with high transmission power as an X-ray source has been developed. Non-Patent Document 1 discloses an industrial X-ray CT apparatus using an electron linear accelerator as an X-ray source and using a strip-shaped Si crystal as a semiconductor radiation detector. This X-ray CT apparatus is a so-called third generation CT apparatus that takes a tomographic image by rotating the device under test once around an axis perpendicular to the X-ray fan beam.

FIG. 7 shows a configuration of an industrial X-ray CT apparatus which is a third generation CT apparatus. The industrial X-ray CT apparatus 13 detects an X-ray transmitted through the DUT 14, the electron linear accelerator 1 (X-ray source) that outputs the X-ray fan beam 2, the scanner 3 for installing the DUT 14. In order to improve the S / N ratio of the semiconductor radiation detectors 4-1 to 4-512 and the semiconductor radiation detector 4, the collimator 7 for suppressing the incidence of scattered X-rays on the adjacent detectors, the semiconductor radiation detector 4, a signal processing device 10 that amplifies the output signal and converts it into a digital signal, a control device 6 that collects digital data from the signal processing device 10 and controls the entire device, and an image reconstruction device that performs image reconstruction 11. Control of the operation of the electronic linear accelerator 1, the scanner 3, and the signal processing device 10 according to a control command from the display device 8 and the control device 6 for displaying an image created by image reconstruction and other information. A controller 9. The industrial X-ray CT apparatus 13 in this figure is a third-generation X-ray CT apparatus that rotates a test object and images one cross section. In addition to the rotation function, the scanner 3 has a function of moving up and down in order to perform cross-sectional imaging of each height of the DUT 14.

  The electronic linear accelerator 1 is connected to a controller 9 by a control cable 16, and generation / stop of the X-ray fan beam 2 is controlled by the controller 9. Similarly, the scanner 3 is connected to the controller 9 via a control cable 15 to adjust the rotation and vertical position of the scanner.

  The semiconductor radiation detector 4 uses a Si crystal or CdTe crystal, which will be described later, and is arranged in a row so as to anticipate the generation point of the fan beam 2. The semiconductor radiation detector 4 is fixed to the sensor holder 5. The narrow hole of the collimator 7 is located on a straight line between the generation point of the fan beam 2 and the semiconductor radiation detector 4. Each detector detects X-rays incident through the hole of the collimator 7.

  In FIG. 7, 512 detectors are installed, and the imaging resolution improves as the number of detectors increases. In synchronization with the rotation of the scanner 3, the electron linear accelerator 1 emits an X-ray pulse to the device under test 14 at a constant angle. The X-ray detector 4 detects X-rays transmitted through the device under test 14. A signal corresponding to the X-ray dose output from the semiconductor radiation detector 4 is amplified by the signal processing device 10 and converted into a digital signal. Thereafter, the signal is sent to the image reconstruction device 7 via the control device 6 via the signal cable 17 and used for the reconstruction of the CT image.

  Here, as a comparative example, the structure of a semiconductor radiation detector will be described.

  In a semiconductor radiation detector using a silicon (Si) crystal, a detection efficiency of about 20% can be obtained with high energy X-rays of 1 to 10 MeV. The detection efficiency differs depending on the detector size and X-ray energy. Currently, semiconductor radiation detectors using silicon crystals are used in high energy CT devices.

  FIG. 6 shows an elevational view (shown on the upper side of FIG. 6) and a plan view (shown on the lower side of FIG. 6) showing the structure of the semiconductor radiation detector 4 and the structure of a comparative example. As shown in the figure, X-rays enter the Si crystal 50 from the left side of the figure. In the elevation view of FIG. 6, the surface on which the X-rays enter the Si crystal 50 is the front side of the semiconductor radiation detector. In addition, the surface where the flexible substrate 53 is bonded to the base plate 54 (the surface where the Si crystal 50 can be seen) is defined as the upper side of the semiconductor radiation detector.

  The Si crystal 50 is bonded to the flexible substrate 53, and the size of the Si crystal is 3 mm long × 40 mm wide × 0.4 mm high.

  The base plate 54 is made of a tungsten alloy, and fixes the semiconductor radiation detector to the sensor holder, and at the same time, shields X-rays and counter-electrons that enter and scatter from the adjacent semiconductor radiation detector to generate a crosstalk current. Play a role to prevent. For this reason, it is necessary to use a metal material having a high density for the base plate 54.

The thickness of the strip-shaped semiconductor radiation detector is determined by the thickness of the base plate, the flexible substrate, the Si crystal, and the adhesive that bonds them. Therefore, the thickness of the semiconductor radiation detector becomes the thickness of the base plate 54 (0.5 mm) + the thickness of the flexible substrate 53 (0.1 mm) + the thickness of the Si crystal 50 (0.4 mm). Including the thickness, it becomes 1.2 mm. The arrangement pitch of the semiconductor radiation detectors is about 1.3 mm.

  Electrodes 51 and 52 are deposited on the upper and lower surfaces of the Si crystal 50 to form a silicon semiconductor sensor. The electrode 52 on the flexible substrate 53 side and the printed wiring terminal 57 are connected to each other at the bonding portion 58 with a conductive adhesive. The upper electrode 51 is electrically connected to the lower electrode 61 around the inside of the Si crystal 50, and the electrode 61 is connected to the printed wiring terminal 56 at the bonding portion 59. The side surface of the Si crystal 50 is a dicing surface cut out from the Si wafer by dicing. Compared with the electrode surface, the dicing surface has a lot of microscopic irregularities, so it is expected that the dicing surface is unstable to outside air such as moisture. In view of this, a silicon resin protective film 64 is applied to block outside air.

The left side of the figure shows a cross-sectional structure along the plane AA ′. The Si crystal of this detector has a pn diode structure in which the vicinity of the electrode 52 is doped p-type with an n-type semiconductor. At the same time, the peripheral portion 62 of the Si crystal is doped n ⁺ . Therefore, as described above, the electrode 51 and the electrode 61 can be conducted, and in this detector, the wiring of the two electrodes can be drawn from the flexible substrate 53 side. The dicing surface of the Si crystal 50 is held at the conductive position with the surface electrode 51 by the peripheral portion 62. A bias voltage of about 30 to 50 V is usually applied between the electrodes 51 and 52.

  FIG. 8 shows a structure when the semiconductor radiation detector 4 is installed in the sensor holder 5. This figure shows the positional relationship between the sensor holder 5 and the semiconductor radiation detectors 4-1, 4-2, 4-3. Each detector inserts and fixes a base plate 54 of the detector into a slit provided above and below the sensor holder 5. Then, a detector is installed so that the hole 12 of the collimator 7 and the front side surface of the Si crystal 50 (that is, an area of 3 mm in length × 0.4 mm in height) coincide. In this figure, the Si crystal of the semiconductor radiation detector 4-1 is installed so as to coincide with the hole 12-1 of the collimator 7 on the front side of the sensor holder 5. The Si crystals of the semiconductor radiation detectors 4-2 and 4-3 are also installed so as to coincide with the holes 12-2 and 12-3, respectively. The minimum pitch at which detectors can be installed is limited by the thickness of the detector.

  The maximum energy of X-rays generated from an X-ray generator (electronic linear accelerator) of an industrial X-ray CT apparatus varies depending on the object to be imaged and ranges from 12 MeV to 1 MeV. When the X-ray energy is low, the radiation shielding effect by the base plate is small. Therefore, the base plate can be thinned, the detector array pitch can be narrowed, and as a result, the image resolution of the CT apparatus can be improved. However, the base plate also has a function of fixing to the sensor holder. For this reason, if the base plate is made thin, it will bend when it is assembled into the sensor holder, etc., so that the semiconductor crystal may be stressed and the detector performance may deteriorate. For this reason, in order to maintain the assembly strength, it is necessary to set the thickness of the base plate to 0.5 mm.

  Further, it is difficult to make the thickness of the Si crystal 50 thinner than 0.4 mm from the viewpoint of strength. For this reason, in the structure of FIG. 6, it was difficult to make the thickness of the detector 1.2 mm or less.

  On the other hand, in a 1 MeV CT apparatus often used for industrial use, the maximum energy of recoil electrons is about 1 MeV when X-rays enter an adjacent detector and are Compton scattered inside. The electron range of 1 MeV in heavy metal is about 0.3 mm. Therefore, the thickness of the shielding plate necessary for shielding radiation should be about 0.3 mm. If crosstalk to adjacent detectors is allowed to increase slightly, 0.1 to 0.2 mm can be allowed. Therefore, if the base plate is made thinner, the arrangement pitch of the detectors can be reduced, and high resolution of the X-ray CT image can be realized.

  Therefore, according to the present invention, a shielding plate that shields radiation is provided separately from the base plate, with the thickness of the base plate being a thickness that can maintain the assembly strength of the sensor holder.

  FIG. 1 shows a structural diagram of a semiconductor radiation detector according to the present invention. In this embodiment, the Si substrate and the flexible substrate to which the Si crystal is bonded are securely held, and a base plate for storing the Si crystal is provided. Moreover, in order to shield the radiation which flows in from the adjacent radiation detector, the shielding board is provided separately.

  The Si crystal 20 is bonded to the flexible substrate 21 as in the comparative example. Although electrodes similar to those in the comparative example are provided on both sides of the Si crystal, the display thereof is omitted in this figure. Wiring patterns 25 and 27 are wired on the flexible substrate 21, and external connection terminals 26 and 28 are provided at ends of the flexible substrate 21 for supplying a bias voltage to the detector and extracting a signal current. The thickness of the flexible substrate is 0.1 mm.

The flexible substrate 21 is affixed to a base plate 22 having the shape shown in FIG. The difference from the comparative example is that the Si substrate 20 is stored in the cut portion (concave portion) of the base plate 22 instead of attaching the flexible substrate to the upper side of the base plate (that is, placing the Si crystal on the upper side of the base plate). As described above, the flexible substrate 21 is attached to the lower side of the base plate 22. The base plate 22 is manufactured in a U-shape. The thickness of the base plate 22 is 0.5 mm as in the comparative example. The bonding surface between the flexible substrate 21 and the base plate 22 is the same as the bonding surface between the Si crystal 20 and the flexible substrate 21. For this reason, the wiring patterns 25 and 27 on the flexible substrate 21 are configured to be insulated from the base plate 22. The periphery of the Si crystal 20 is protected by applying a silicon resin 24 as in the comparative example.

  On the left side of FIG. 1, a view of the semiconductor radiation detector 404 viewed from the X-ray incident direction is described. The semiconductor crystal is disposed so as to be sandwiched between the flexible substrate and the shielding plate, and a base plate is disposed on the side surface side of the semiconductor crystal.

  The radiation shielding plate 23 is made of heavy metal and is provided at a position facing the flexible substrate 21. Since the base plate 22 has a thickness of 0.5 mm and the Si crystal has a thickness of 0.4 mm, there is no possibility that the shielding plate 23 and the Si crystal 20 come into contact with each other. The base plate may be made thinner, but it needs to be thicker than the Si crystal.

  In FIG. 1, the shielding plate 23 plays a role of shielding radiation. Therefore, the base plate 22 does not need to be made of expensive heavy metal, can be manufactured with high accuracy, and can use a strong material (for example, a metal such as stainless steel or brass, an engineering plastic, or a ceramic). In this embodiment, stainless steel is used.

  The thickness of the shielding plate 23 can be freely changed according to the X-ray energy and the required resolution. This is because the mechanical strength of the semiconductor radiation detector is secured by the base plate 22. In this embodiment, the thickness of the shielding plate 23 is set to 0.2 mm. Therefore, the thickness of the semiconductor radiation detector is the thickness of the flexible substrate 21 (0.1 mm) + the thickness of the base plate 22 (0.5 mm) + the thickness of the shielding plate 23 (0.2 mm). Then, it becomes 0.8mm.

  As described above, the Si crystal 20 is provided between the pair of flexible substrates 21 and the shielding plate 23, and the Si crystal is formed in the cut portion of the base plate 22 so that the base plate 22 is located on the side surface side of the Si crystal 20. 20 is stored. Therefore, the thickness of the semiconductor radiation detector can be reduced by the thickness of the Si crystal. The base plate holds the semiconductor crystal and the flexible substrate, and ensures the strength of the semiconductor radiation detector. And since it was set as the structure which sticks a shielding board to a base board, the thickness of a shielding board can be changed freely and there exists an effect which can make a semiconductor radiation detector thin.

  FIG. 3 is a diagram showing a configuration of an example of an industrial X-ray CT apparatus using the semiconductor radiation detector according to the present embodiment. Compared with FIG. 7, the semiconductor radiation detector 404 shown in the present embodiment is used. The configuration other than the semiconductor radiation detector 404 is the same as that shown in FIG.

  FIG. 4 shows a structure in which the semiconductor radiation detector 404 is installed in the sensor holder 5. This figure shows the positional relationship between the sensor holder 5 and the semiconductor radiation detectors 404-1, 404-2, 404-3. In FIG. 4, three of the plurality of detectors are representatively shown.

  Each detector inserts and fixes the base plate 22 in the slits provided above and below the sensor holder 5. Then, the detector is installed with the collimator hole 420 aligned with the front side surface of the Si crystal. In this figure, the Si crystal 20 of the semiconductor radiation detector 404-1 is installed so as to coincide with the hole 420-1 of the collimator 7 on the front side of the sensor holder. The other semiconductor radiation detectors 404-2 and 404-3 are also installed so as to coincide with the holes 420-2 and 420-3, respectively.

  The minimum pitch at which detectors can be installed is limited by the thickness of the detector. However, in the present embodiment, the thickness of the shielding plate 23 can be freely changed without changing the dimensions of the detector body (the thickness of the base plate and the flexible substrate combined). For this reason, the thickness and pitch of the detector can be flexibly changed according to the specifications of the CT apparatus. In particular, a high-resolution industrial X-ray CT apparatus in which the pitch between adjacent detectors is narrowed can be realized.

  In order to further improve the density resolution of the tomographic image, it is desirable that the detection efficiency (sensitivity) of the detector itself is high. Therefore, if CdTe has a density twice or more that of silicon, it is considered that the detection efficiency can be improved about twice.

  As the electrodes provided in the CdTe crystal, two electrodes are deposited on the upper and lower sides of the CdTe crystal. This is because, unlike a Si crystal, wiring by a process cannot be performed inside the crystal. Therefore, in the CdTe crystal, it is necessary to directly draw out signal lines from upper and lower electrodes by bonding. Other structures are the same as those of the semiconductor radiation detector using Si.

  FIG. 5 shows a structural diagram of a semiconductor radiation detector 404 according to another embodiment. In this embodiment, the flexible substrate 21 is about twice as long as the flexible substrate of FIG. Then, after bonding to the lower portion of the base plate 22 (downward in FIG. 5), the remaining portion is bent and attached to the upper portion of the base plate 22. With this structure, the two flexible substrates sandwiching the upper and lower sides of the Si crystal 20 are constituted by a single flexible substrate. The flexible substrate 21 may be divided into two pieces having the same length and installed on the upper and lower sides of the base plate 22.

  The Si crystal 20 is surrounded by the base plate 22 and the flexible substrate 21 and is blocked from the outside air. The base plate 22 is made of stainless steel as in the first embodiment. Therefore, the silicon resin applied around the Si crystal in Example 1 becomes unnecessary. The shielding plate 23 is bonded below the base plate 22. Of course, as in the first embodiment, the shielding plate 23 may be installed above the base plate.

  Moreover, the thickness of the shielding plate 23 can be halved, and the shield plate 23 can be divided and installed on the upper side and the lower side of the Si crystal 20. If installed on both sides, the outer peripheral side of the semiconductor radiation detector is surrounded by the shielding plate and the base plate. Therefore, it can be covered with metal except for the front side of the Si crystal on which X-rays enter, and the detector can be handled easily.

  According to the present embodiment, as in the first embodiment, the base plate holds the semiconductor crystal and the flexible substrate, and ensures the assembly strength of the detector. Further, since the shielding plate is attached to the flexible substrate, the thickness of the shielding plate can be freely changed, and the detector can be thinned.

  The configuration of Example 2 can be similarly used for CdTe crystals. Further, the semiconductor radiation detector of the present embodiment can be applied to an industrial high energy X-ray CT apparatus, similarly to the detector of the first embodiment.

  Furthermore, the present invention can also be applied to an X-ray detector such as NaI which has a scintillator that emits fluorescence when incident on X-rays, and has a photodiode that receives fluorescence on the back or side. If the scintillator and the photodiode are installed on the flexible substrate, the same structure as in the first and second embodiments can be applied.

  The present invention can be used for an X-ray detection unit of an industrial X-ray CT apparatus, and can be used for inspection of a cast hole of a cast product, three-dimensional shape data acquisition, density distribution measurement, and the like.

It is a figure which shows the structure of one Example of this invention. It is a figure which shows the shape of the base board of one Example of this invention. It is a block diagram of the industrial X-ray CT apparatus using one Example of this invention. It is a figure when the semiconductor detector of this invention is installed in the sensor holder of an industrial X-ray CT apparatus. It is a figure which shows the structure of Example 2 of this invention. It is a figure which shows the structure of the semiconductor radiation detector which concerns on a comparative example. It is a block diagram of the industrial X-ray CT apparatus which has the structure of CT apparatus of a 3rd generation system. It is a figure when the semiconductor radiation detector which concerns on a comparative example is installed in the sensor holder of an industrial X-ray CT apparatus.

Explanation of symbols

20 Si crystal 21 Flexible substrate 22 Base plate 23 Shield plate 24 Silicon resin 25, 27 Wiring pattern 26, 28 Connection terminal

Claims (5)

A semiconductor radiation detector for use in an industrial X-ray CT apparatus,
A semiconductor radiation comprising: a flexible substrate; a shielding plate facing the flexible substrate; a semiconductor crystal between the pair of the flexible substrate and the shielding plate; and a base plate provided on a side surface of the semiconductor crystal. Detector. A semiconductor radiation detector for use in an industrial X-ray CT apparatus,
A first flexible substrate, a second flexible substrate facing the first flexible substrate, and a semiconductor crystal between the pair of flexible substrates, and a base plate provided on a side surface of the semiconductor crystal are provided. A semiconductor radiation detector. A semiconductor radiation detector according to claim 2, wherein
The semiconductor radiation detector, wherein the first flexible substrate and the second flexible substrate are constituted by a single flexible substrate.   4. The semiconductor radiation detector according to claim 1, wherein the semiconductor crystal is a Si crystal or a CdTe crystal.   4. An industrial X-ray CT apparatus, wherein the semiconductor radiation detector according to claim 1 is used as an X-ray detector.

Images