JP2006125969A - X-ray detection element and x-ray detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a semiconductor element for detecting an X-ray from being affected by atmospheric humidity by storing the semiconductor element in a vessel and blocking the inside of the vessel from the atmosphere. <P>SOLUTION: The vessel 10 is formed of a pedestal 14 and a cap 16. A proximity of the outer periphery of the pedestal 14 and a flange 18 of the cap 16 are closely jointed to each other. A circular opening 22 is formed in the cap 16, and a beryllium window 24 is closely jointed so as to cover the opening 22. An APD 12 is mounted on a substrate 26, and the substrate 26 is stuck to the inner surface of the pedestal 14. Two through holes 28 are formed in the pedestal 14, and a first lead terminal 30 and a second lead terminal 32 pass the through holes 28, respectively. The through parts are closely sealed by a glass hermetic seal 38. The inside of the vessel 10 is a sealed space blocked from the atmosphere, and the sealed space is filled with dry nitrogen gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray detection element using a semiconductor element that detects an X-ray by applying a bias voltage of 200 V or more, and an X-ray detection apparatus using such an X-ray detection element.

  A SiPIN photodiode is known as a semiconductor element that directly converts X-rays into electrical signals. When this semiconductor element is used as an X-ray detection element, it is usual to cool the semiconductor element to a low temperature in order to reduce background noise. When the semiconductor element is used after being cooled, it is necessary to seal the entire X-ray detection device from the atmosphere in order to avoid adverse effects such as condensation.

  On the other hand, an avalanche photodiode (hereinafter abbreviated as APD) is known as another example of a semiconductor element that directly converts an X-ray into an electric signal. The APD is characterized in that a high bias voltage is applied to give an amplifying action inside the device, and the background noise is very low compared to the X-ray detection signal. Therefore, it is common knowledge that APDs do not need to be cooled and therefore do not require strict sealing.

This APD is often used for detection of visible light, but the bias voltage of the APD for visible light is about 100V. On the other hand, the APD for X-ray detection uses a high bias voltage of 200 V to 1 kV, more preferably a bias voltage of 600 V to 1 kV, in order to increase detection efficiency. For example, the following Patent Document 1 discloses the use of an APD as an X-ray detection element.
JP 2004-37360 A

  According to Patent Document 1, in a system for detecting fluorescent X-ray holography, measurement can be completed in a shorter time than before by using an APD having a high count rate (count rate).

  In the case of a semiconductor element using a high bias voltage of 200 V or more, instantaneous current leakage is likely to occur from a high voltage portion due to the influence of humidity. The magnitude of such an abnormal signal due to current leakage may be approximately the same as that of a normal X-ray detection signal (an electric signal obtained by converting X-ray energy). Hard to stick. In particular, when using a bias voltage of 600 V or more, the influence is remarkable.

  A comparison of the magnitudes of the normal X-ray detection signal and the abnormal signal will be described with numerical values. For example, the combined capacitance C of the capacitor connected between the semiconductor element and the amplifier circuit is set to 100 pF, the amplitude V of the normal X-ray detection signal from the semiconductor element before amplification is set to 0.1 mV, and the rise of the signal Is 10 nanoseconds, the instantaneous current dI flowing at this time is dI = C × (dV / dt) = 1 μA. Therefore, the magnitude of the normal X-ray detection signal in this case is 1 μA. On the other hand, when the humidity is high, an instantaneous leakage current of about 1 μA may occur. Depending on the mounting state of the semiconductor element, for example, if a semiconductor element is placed in an environment with a humidity of 70% with a bias voltage of several hundred volts applied, a leakage current of about 1 μA may occur. In that case, it becomes impossible to distinguish between a normal X-ray detection signal and an abnormal signal due to leakage current.

  Particularly in the case of APD, the output signal rises at a high speed, and it is necessary to prepare an amplifier circuit in the subsequent stage of the APD with a signal band suitable for such a high-speed signal change. That is, the signal rise time of the amplifier circuit itself needs to be about 1 to 10 nanoseconds. Such a high-speed rising signal is very similar to the rising of an abnormal signal caused by a leakage current (current generated by a short circuit or discharge at a high voltage site). For this reason, the amplification circuit cannot distinguish between a normal X-ray detection signal and an abnormal signal. On the other hand, in the semiconductor element for X-ray detection other than APD, the rise of the signal is not so fast (for example, on the order of several hundred nanoseconds in the case of a SiPIN diode), so that the signal band of the subsequent amplifier circuit is low. Just a frequency band. Therefore, in such a semiconductor element, noise in a high frequency band caused by leakage current is cut off by the amplifier circuit and hardly affected.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an X-ray detection element and an X-ray detection apparatus that are not affected by humidity.

  In order to achieve the above-described object, in the X-ray detection element of the present invention, a semiconductor element for detecting X-rays is accommodated in a container, and the inside of the container is shielded from the atmosphere, so that the semiconductor element is in the atmosphere. It is not affected by humidity. The X-ray detection element of the present invention has the following configurations (a) to (d). (A) A semiconductor element that detects X-rays when a bias voltage of 200 V or higher is applied. (A) A container for housing the semiconductor element, the inside of which is a sealed space cut off from the atmosphere. (C) An X-ray transmission window formed in the container, the X-ray transmission window being arranged in a positional relationship such that the X-rays transmitted through the X-ray transmission window hit the semiconductor element. (D) A first terminal and a second terminal that are electrically connected to the semiconductor element and are partially exposed to the outside of the container.

  A typical example of the semiconductor element is an avalanche photodiode. This avalanche photodiode detects X-rays by applying a high bias voltage of 200 V to 1 kV, and the present invention is effective when applied to an X-ray detection element using such an avalanche photodiode. In particular, when a high bias voltage of 600 V to 1 kV is applied, the background level increases due to the influence of humidity as compared with a conventional X-ray detection element using a semiconductor element in the atmosphere. There is almost no.

  The inside of the container is preferably filled with a dry gas such as dry nitrogen gas or dry air. Alternatively, the inside of the container may be evacuated to form a sealed space.

  The X-ray detection apparatus of the present invention includes the X-ray detection element as described above, and has a high voltage application portion (at least wiring connecting the high voltage generator and the high voltage application terminal of the X-ray detection element and its The high voltage application terminal itself is cut off from the atmosphere. For example, the high voltage application portion can be covered with an electrically insulating resin. Thereby, the abnormal signal resulting from the discharge in the high voltage application part can be eliminated.

  According to the present invention, since the semiconductor element that detects X-rays is shielded from the atmosphere, it is not affected by humidity. Further, even in the X-ray detection apparatus provided with this semiconductor detection element, the high voltage application portion is shielded from the atmosphere, so that it is not affected by humidity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an embodiment of the X-ray detection element of the present invention. The X-ray detection element includes a container 10, and an APD 12 is accommodated inside the container 10. The container 10 includes a disk-shaped base 14 and a bottomed cylindrical cap 16 with a flange 18. The material of the base 14 and the cap 16 is Kovar (alloy of Fe53% -Ni28% -Co18%). The vicinity of the outer periphery of the base 14 and the flange 18 of the cap 16 are hermetically joined to each other by welding. A circular opening 22 is formed at the bottom 20 of the cap 16 (the upper end surface portion in FIG. 2). A beryllium window 24 is hermetically bonded by welding to cover the opening 22. This beryllium window 24 corresponds to an X-ray transmission window. The positional relationship between the beryllium window 24 and the APD 12 is such that the X-rays that have passed through the beryllium window 24 strike the detection surface of the APD 12.

  The APD 12 is mounted on the substrate 26, and the substrate 26 is bonded to the inner surface of the base 14. The material of the substrate 26 is ceramic. Two through holes 28 are formed in the base 14, and the first lead terminal 30 and the second lead terminal 32 pass through the through holes 28, respectively. The gap between the outer peripheral surfaces of the two terminals 30 and 32 and the inner wall surface of the through hole 28 is hermetically sealed with a glass hermetic seal 38. One end of each of the two terminals 30 and 32 protrudes into the container 10, while the other end is exposed to the outside of the container 10. The first electrode of the APD 12 is connected to the first lead terminal 30 by the first bonding wire 34, and the second electrode of the APD 12 is connected to the second lead terminal 32 by the second bonding wire 36.

  The inside of the container 10 is a sealed space cut off from the atmosphere (existing in a space outside the container 10), and this sealed space is filled with dry nitrogen gas. Therefore, the APD 12 is not affected by atmospheric humidity. Instead of dry nitrogen gas, other dry gases (such as dry air) may be used.

  FIG. 2 shows the appearance of the X-ray detection element of FIG. It can be seen that the beryllium window 24 is exposed at the opening 22 of the cap 16. A pair of lead terminals 30 and 32 are visible below the pedestal 14.

  FIG. 3 is an exploded perspective view of the X-ray detection apparatus including the X-ray detection element of FIG. The two lead terminals of the X-ray detection element 40 are fixed to the first surface (upper surface in FIG. 3) of the printed wiring board 42 by soldering. A first shield block 44 is fixed to the second surface (the lower surface in FIG. 3) of the printed wiring board 42 with screws 46. A second shield block 48 is fixed to the first surface of the printed wiring board 42 with screws inserted from the second surface side. A shield lid 50 is fixed to the upper surface of the second shield block 48 with screws 52. A shield front plate 54 is fixed to the front end face of the first shield block 44 and the front end face of the second shield block 48 with screws 56. A through hole 60 is formed in the shield front plate 54, and the cap of the X-ray detection element 40 enters the through hole 60, and the beryllium window 24 of the X-ray detection element is exposed to the outside at the through hole 60. become.

  The first shield block 44, the second shield block 48, the shield lid 50, and the shield front plate 54 are all made of metal, and a shield case is constituted by these components. Electrical components and wiring to which a high voltage is applied are housed in the internal space of the shield case. This shield case is at the ground potential and provides the electrical stability of the X-ray detection device, and also plays the role of ensuring the mechanical strength of the X-ray detection device. The X-ray detection element 40 is also mechanically protected by this shield case.

  A high voltage generation circuit 58 is fixed to the first surface of the printed wiring board 42. The high voltage generation circuit 58 is outside the second shield block 48. The output terminal of the high voltage generation circuit 58 is on the back side of the printed wiring board 42.

  4 is a plan view of the X-ray detection apparatus of FIG. However, the shield front plate 54 is shown in a sectional view, and the shield lid 50 is shown with a part cut away. The shield front plate 54 is fixed to the first shield block 44 by screws 56. The cap 16 of the X-ray detection element 40 enters the through hole 60 of the shield front plate 54, and the beryllium window 24 of the X-ray detection element 40 is exposed to the outside. A printed wiring board 42 is fixed to the upper surface of the first shield block 44 with screws 46. Most of the surface area of the upper and lower surfaces of the printed wiring board 42 is covered with a conductor layer 64 for supplying a ground potential. This conductor layer 64 is shown by cross hatching in FIG. A second shield block 48 is fixed to the upper surface of the printed wiring board 42. A shield lid 50 is fixed to the upper surface of the second shield block 48 with screws 52. The shield lid 50 is shown with a part cut away, and the inside of the second shield block 48 is partially shown. In a region outside the second shield block 48, a high voltage generation circuit 58 and an external electric circuit 62 are fixed on the upper surface of the printed wiring board 42. In a region inside the second shield block 48, a pair of lead terminals of the X-ray detection element 40, a DC cut capacitor 66, and an internal electric circuit 68 are fixed on the upper surface of the printed wiring board 42.

  FIG. 5 is an enlarged plan view showing the vicinity of the X-ray detection element 40 in FIG. This is a state before the shield front plate 54 (see FIG. 4) is attached. 6A is a cross-sectional view taken along line AA in FIG. 6B is a cross-sectional view taken along line BB in FIG. In FIG. 6A, the first lead terminal 30 (terminal for applying a high voltage) of the X-ray detection element 40 is soldered to the wiring 70. The wiring 70 is connected to one terminal of the DC cut capacitor 66, and the other terminal of the DC cut capacitor 66 is connected to the internal electric circuit 68 (see FIG. 4) via the wiring 72. Further, as shown in FIG. 5, a wiring 74 is branched from the wiring 70 described above. As shown in FIG. 6B, the branched wiring 74 described above passes through the through hole of the printed wiring board 42 and extends to the back side of the printed wiring board 42, and on the back side, the high voltage generating circuit 58 is provided. (See FIG. 4). Returning to FIG. 5, the second lead terminal 32 (terminal to be grounded) of the X-ray detection element 40 is soldered to the conductor layer 64 of the printed wiring board 42.

  In FIG. 6A, the first lead terminal 30, the wiring 70, and the DC cut capacitor 66 are portions to which a high voltage is applied, and this portion is covered with an electrically insulating resin 76. In FIG. 6B, the wiring 74 is also a portion to which a high voltage is applied, and this portion is also covered with the resin 78 on the front side and the resin 80 on the back side of the printed wiring board 42. These resins 78 and 80 are also electrically insulating. Further, in FIG. 3, the space between the high voltage generation circuit 58 and the printed wiring board 42 is also filled with resin. Thus, by covering the portion to which the high voltage is applied with the electrically insulating resin, the discharge (causing noise) from the high voltage application portion due to moisture in the atmosphere is eliminated.

  FIG. 7 is an electric circuit of the X-ray detection apparatus including the X-ray detection element 40. The high voltage generation unit 82 includes a high voltage generation circuit 58. The output terminal of the high voltage generator 82 is connected to the first lead terminal 30 of the X-ray detection element 40 via the resistor 84. The first lead terminal 30 is connected to the preamplifier circuit 86 via a DC cut capacitor 66. The preamplifier circuit 86 is included in the internal electric circuit 68 of FIG. A bias voltage of 200 V to 1 kV is applied to the first lead terminal 30 by the high voltage generator 82. The second lead terminal 32 of the X-ray detection element 40 is grounded. A region 88 surrounded by oblique lines is a portion to which a high voltage is applied, and this portion is covered with an electrically insulating resin as shown in FIGS. 6 (A) and 6 (B).

  In this X-ray detection device, the periphery of the X-ray detection element is filled with a dry gas such as dry nitrogen gas or dry air, and a portion to which a high voltage is applied is covered with an electrically insulating resin. Therefore, even if the atmospheric humidity changes, it will not be affected. That is, noise does not change even when the humidity changes, and current leakage due to discharge or the like at the high voltage application site does not occur even if the humidity increases.

It is sectional drawing of one Example of the X-ray detection element of this invention. It is a perspective view of the X-ray detection element of FIG. It is a disassembled perspective view of the X-ray detection apparatus containing the X-ray detection element of FIG. It is a top view of the X-ray detection apparatus of FIG. It is the top view which expanded and showed the vicinity of the X-ray detection element in FIG. It is the sectional view on the AA line and BB line of FIG. It is an electric circuit of the X-ray detection apparatus containing an X-ray detection element.

Explanation of symbols

10 containers 12 APD
14 pedestal 16 cap 18 flange 22 opening 24 beryllium window 26 substrate 30 first lead terminal 32 second lead terminal 38 glass hermetic seal 40 X-ray detection element

Claims (5)

An X-ray detection element having the following configuration.
(A) A semiconductor element that detects X-rays when a bias voltage of 200 V or higher is applied.
(A) A container for housing the semiconductor element, the inside of which is a sealed space cut off from the atmosphere.
(C) An X-ray transmission window formed in the container, the X-ray transmission window being arranged in a positional relationship such that the X-rays transmitted through the X-ray transmission window hit the semiconductor element.
(D) A first terminal and a second terminal that are electrically connected to the semiconductor element and are partially exposed to the outside of the container. An X-ray detection element having the following configuration.
(A) An avalanche photodiode that detects X-rays.
(A) A container for housing the avalanche photodiode, the container being a sealed space that is shielded from the atmosphere.
(C) An X-ray transmission window formed in the container, wherein the X-ray transmission window is disposed in a positional relationship such that the X-ray transmitted through the X-ray transmission window hits the avalanche photodiode.
(D) A first terminal and a second terminal that are electrically connected to the avalanche photodiode and are partially exposed to the outside of the container.   The X-ray detection element according to claim 1 or 2, wherein the inside of the container is filled with a dry gas.   4. The X-ray detection element according to claim 1, wherein the semiconductor element detects an X-ray when a bias voltage of 600 V or more is applied thereto. 5. . An X-ray detection apparatus having the following configuration.
(A) The X-ray detection element according to any one of claims 1 to 4.
(A) A high voltage generator for supplying a bias voltage of 200 V or more to the first terminal of the X-ray detection element.
(C) Grounding means for supplying a ground potential to the second terminal of the X-ray detection element.
(D) Sealing means for cutting off the wiring connecting the high-voltage generator and the first terminal and the first terminal itself from the atmosphere.

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