Radiation detector and radiation ct device

Abstract

To provide a technique advantageous for suppressing an influence of reduction in carrier transport characteristics at an end of a semiconductor substrate.SOLUTION: A radiation detector has a plurality of pixels arranged on a semiconductor substrate that converts incident radiation into electric charges. The plurality of pixels includes first pixels arranged along an outer edge of the semiconductor substrate, and second pixels arranged closer to a center of the semiconductor substrate than the first pixels. The first pixels each include a plurality of first electrodes on one principal surface of two principal surfaces of the semiconductor substrate. The second pixels each include a second electrode on one principal surface. An area of the second electrode is larger than an area of each of the plurality of first electrodes.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a radiation detector and a radiation CT apparatus. [Background technology]

[0002] It is known that a semiconductor substrate that converts incident radiation into electric charges is used in a radiation detector. Patent Document 1 discloses a radiation detector that suppresses a decrease in charge collection efficiency due to the spread of an electric field at the edge of the semiconductor substrate, which results in a decrease in image quality. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent No. 7,223,982 Summary of the Invention [Problem to be solved by the invention]

[0004] The edge of the semiconductor substrate may have defects due to the mechanical processing performed when cutting out the semiconductor substrate, which may deteriorate the carrier transport properties. At the edge of the semiconductor substrate, it is necessary to arrange electrodes taking into consideration not only the spread of the electric field but also the deterioration of the carrier transport properties.

[0005] An object of the present invention is to provide a technique that is advantageous in suppressing the influence of the deterioration of carrier transport properties at the edge of a semiconductor substrate. [Means for solving the problem]

[0006] In view of the above problems, a radiation detector according to an embodiment of the present invention is a radiation detector having a plurality of pixels arranged on a semiconductor substrate that converts incident radiation into electric charges, the plurality of pixels including a first pixel arranged along an outer edge of the semiconductor substrate and a second pixel arranged closer to the center of the semiconductor substrate than the first pixel, the first pixel having a plurality of first electrodes on one of two main surfaces of the semiconductor substrate, the second pixel having a second electrode on the one main surface, and an area of ​​the second electrode being larger than an area of ​​each of the plurality of first electrodes. Effect of the Invention

[0007] According to the present invention, it is possible to provide a technique that is advantageous in suppressing the influence of the deterioration of the carrier transport properties at the edge of the semiconductor substrate. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram showing an example of the configuration of a radiation detector according to the present embodiment. [Diagram 2] 2 is a diagram showing an example of the configuration of electrodes disposed on a semiconductor substrate of the radiation detector of FIG. 1; [Diagram 3] 2 is a diagram showing an example of the configuration of electrodes disposed on a semiconductor substrate of the radiation detector of FIG. 1; [Figure 4] 2 is a diagram showing an example of the configuration of electrodes disposed on a semiconductor substrate of the radiation detector of FIG. 1; [Diagram 5] 2 is a diagram showing an example of the configuration of electrodes disposed on a semiconductor substrate of the radiation detector of FIG. 1; [Figure 6] A diagram showing the charge distribution induced on a conductor by a point charge. [Figure 7] 13 is a diagram showing a potential distribution when the width of the electrode and the thickness of the semiconductor substrate are changed. [Figure 8] FIG. 2 is a diagram showing an example of the configuration of the radiation detector shown in FIG. 1; [Figure 9] FIG. 2 is a diagram showing an example of the configuration of the radiation detector shown in FIG. 1; [Figure 10] FIG. 2 is a diagram showing an example of the configuration of a radiation CT apparatus using the radiation detector of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] Furthermore, radiation in the present invention may include α-rays, β-rays, γ-rays, and other beams produced by particles (including photons) emitted by radioactive decay, as well as beams having the same or greater energy, such as X-rays, particle beams, and cosmic rays.

[0011] A radiation detector according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 10. FIG. 1 is a diagram showing a configuration example of a radiation detector 100 according to the present embodiment. In the radiation detector 100, a plurality of pixels are arranged on a semiconductor substrate 110 that converts incident radiation into electric charges. For the semiconductor substrate 110, a single crystal substrate of a semiconductor that directly converts incident radiation into electric charges, such as cadmium zinc telluride or cadmium telluride, is used. Note that in this embodiment, cadmium zinc telluride (CdZnTe) and cadmium telluride (CdTe) will be mainly described, but the present invention is not limited to this form and can be applied to a single crystal substrate of a semiconductor that can directly detect radiation such as X-rays. For example, this embodiment can be applied to a single crystal substrate of a semiconductor such as lead iodide (PbI2), mercury iodide (HgI2), bismuth iodide (BiI3), or thallium bromide (TlBr). A plurality of electrodes 112 are arranged on one of the two main surfaces of the semiconductor substrate 110, and an electrode 111 is arranged on the other main surface. The electrode 111 may be integrated as shown in Fig. 1. However, this is not limited thereto, and the electrode 111 may be divided into a plurality of electrodes.

[0012] FIG. 2 is a diagram showing an example of the arrangement of electrodes 112 arranged on a semiconductor substrate 110. As described above, in the radiation detector 100, a plurality of pixels 115 are arranged on the semiconductor substrate 110. Here, the pixel 115 arranged on the semiconductor substrate 110 corresponds to one pixel in a radiographic image generated using the radiation detector 100. As shown in FIG. 2, the radiation detector 100 includes electrodes 112 having different sizes depending on the pixel 115. More specifically, the plurality of pixels 115 include a pixel 115a arranged along the outer edge of the semiconductor substrate 110 and a pixel 115b arranged closer to the center of the semiconductor substrate 110 than the pixel 115a. The pixel 115a includes a plurality of electrodes 112a, and the pixel 115b includes an electrode 112b. In this case, the area of ​​the electrode 112b is larger than the area of ​​each of the plurality of electrodes 112a.

[0013] The end of the semiconductor substrate 110 may have defects due to mechanical processing such as a dicing process when cutting out the semiconductor substrate 110, and the carrier transport properties may be degraded. For this reason, the signal output from the pixel 115a arranged along the outer edge of the semiconductor substrate 110 may have a smaller signal intensity than the pixel 115b arranged closer to the center of the semiconductor substrate 110 than the pixel 115a, even if the amount of incident radiation is the same. As a result, the image quality of the radiation image obtained by the radiation detector 100 may be degraded. In order to suppress the influence of the degradation of the carrier transport properties at the end of the semiconductor substrate 110, in this embodiment, the area of ​​the electrode 112a arranged in the pixel 115a is smaller than the area of ​​the electrode 112b arranged in the pixel 115b. The reason for reducing the area of ​​the electrode 112a arranged in the pixel 115a will be explained below.

[0014] In the radiation detector 100, as described above, the end (outer edge) of the semiconductor substrate 110 that converts radiation into electric charges has reduced carrier transport properties (mobility μ, lifetime τ). In many semiconductor materials, the μτ product, which indicates the carrier transport properties, is larger for electrons than for holes. This results in a significant decrease in the hole collection efficiency, causing a decrease in signal intensity at the end of the semiconductor substrate 110. Therefore, it is necessary to reduce the contribution of holes to the signal at the end of the semiconductor substrate 110 and suppress the decrease in signal intensity caused by the decrease in hole collection efficiency.

[0015] 6(a) and 6(b) show the charge distribution induced on the conductor by a point charge -q induced on the semiconductor substrate 110 by the incidence of radiation. FIG. 6(a) shows the case where there is one continuous conductor (electrode), and FIG. 6(b) shows the case where there is a segmented conductor (electrode). As shown in FIGS. 6(a) and 6(b), the charge distribution induced by the point charge -q becomes narrower and steeper as the point charge -q approaches the conductor. The charge distribution shown in FIGS. 6(a) and 6(b) is integrated to obtain the induced charge q induced on the conductor by the point charge -q. Here, the charge generated by the incidence of radiation on the semiconductor substrate 110 is an electron-hole pair, but the holes are omitted in FIGS. 6(a) and 6(b). An induced charge -q is induced in the conductor by the holes, but in Figures 6(a) and 6(b), the holes move away from the conductor, resulting in the induced charge -q becoming broader, and the difference between the induced charge q and the induced charge -q becomes the signal charge.

[0016] As shown in Fig. 6(a), when the conductor is continuous, the charge induced on the conductor always remains q even if the position of the charge approaches the conductor. On the other hand, as shown in Fig. 6(b), when the conductor is segmented, the charge distribution induced by the point charge -q is the same as that shown in Fig. 6(a), but the induced charge induced in each segmented conductor depends on the position of the point charge -q. In other words, the movement of the point charge -q changes the induced charge in the segmented conductor and causes a current to flow. Furthermore, when the point charge -q approaches the conductor infinitesimally, the induced charge -q occurs only in the conductor directly below the point charge -q. In other words, by miniaturizing (segmenting) the conductor, the increase or decrease in the induced charge induced in the conductor differs depending on the position of the point charge, and the apparent potential based on this is called a weighting potential.

[0017] FIG. 7 shows the weighted potential distribution when the width W of the electrode 112 and the thickness L of the semiconductor substrate 110 are changed. As described above, in order to reduce the contribution ratio of holes to the signal and obtain sufficient signal strength from electrons, the integral electrode 111 functions as a cathode and the segmented electrode 112 functions as an anode. The weighted potential is determined by the structure of the electrode 112 and the thickness of the semiconductor substrate 110, regardless of the voltage applied between the electrodes 111 and 112 or the material of the semiconductor substrate 110. It should be noted that the weighted potential is a pseudo potential for calculating induced charges and is different from the potential (electric field) applied between the electrodes 111 and 112. The actual movement of carriers is determined by the potential (electric field) applied between the electrodes 111 and 112.

[0018] As shown in FIG. 7, when the electrodes are continuous (infinity), the change in potential between the cathode and the anode is constant. On the other hand, when the anode (electrode 112) is segmented and the W / L ratio is small, the change in the weighted potential near the anode becomes large. The difference in potential between the position where the electron / hole is generated and the anode becomes the signal component contributed by the electron, and the difference in potential between the position where the electron / hole is generated and the cathode becomes the signal component contributed by the hole. As described above, the μτ product, which indicates the transport characteristics of the carrier, is larger for electrons than for holes. Therefore, even if the electrons are generated at a position away from the anode, they are collected by the anode. On the other hand, since the μτ product is small for holes, holes generated in a region close to the anode are difficult to collect by the cathode, but the change in potential for holes generated near the cathode is small, so the contribution to the signal strength is small. As a result, by reducing the W / L ratio, it is possible to reduce the contribution ratio of holes to the signal and obtain sufficient signal strength from electrons.

[0019] Therefore, in order to increase the induced charge generated by electrons at the end of the semiconductor substrate 110 where the transport properties of carriers are degraded, the area of ​​the electrode 112a arranged in the pixel 115a arranged at the end of the semiconductor substrate 110 is reduced as shown in Fig. 2. This makes it possible to suppress degradation of image quality caused by degradation of the transport properties of carriers at the end of the semiconductor substrate 110.

[0020] As shown in Fig. 2, the electrodes 112a and 112b may each be a square. In this case, the length of each side of the multiple electrodes 112a arranged in the pixel 115a (width W shown in Fig. 7) may be 0.2 times or less the thickness of the semiconductor substrate 110 (thickness L shown in Fig. 7). This is because, as shown in Fig. 7, when the W / L ratio is 0.2 or less, the gradient of the potential distribution near the anode becomes steep.

[0021] A plurality of pixels 115a may be arranged along the outer edge of the semiconductor substrate 110. For example, as shown in FIG. 2, the pixels 115a may be arranged so as to surround the pixel 115b around the entire circumference along the outer edge of the semiconductor substrate 110. In FIG. 2, one row of pixels 115a is arranged so as to surround the pixel 115b, but two or more rows of pixels 115a may be arranged so as to surround the pixel 115b. In this case, the area of ​​the region surrounded by a virtual line connecting the outer edges of the plurality of electrodes 112a arranged in the pixel 115a may be the same as the area of ​​the electrode 112b arranged in the pixel 115b. As a result, the pixels 115 may be arranged at a constant pitch regardless of the pixel 115a and the pixel 115b. This may make the process of generating a radiographic image easier than when the pixels 115a and the pixels 115b are arranged at different pitches. The same applies to the arrangement of the electrodes 112 shown below. However, the present invention is not limited to this, and the pitch at which the pixels 115a are arranged and the pitch at which the pixels 115b are arranged may be different from each other. When the pixel 115 has one electrode 112b like the pixel 115b, the pitch at which the pixels 115 are arranged may be defined as the interval between the geometric center positions of the electrode 112b in orthogonal projection onto the main surface of the semiconductor substrate 110. When the pixel 115 has multiple electrodes 112a like the pixel 115a, the pitch at which the pixels 115 are arranged may be defined as the interval between the geometric center positions of the area surrounded by a virtual line connecting the outer edges of the multiple electrodes 112a arranged in the pixel 115a.

[0022] Also, for example, as shown in FIG. 3, the electrode 112a of the pixel 115a arranged at the corner of the semiconductor substrate 110 may be smaller than the electrode 112b of the other pixel 115b. That is, in an orthogonal projection onto the main surface of the semiconductor substrate 110, the semiconductor substrate 110 may have a rectangular shape, and the pixels 115a may be arranged at both ends of the pixels 115 arranged along one side of the semiconductor substrate 110 among the multiple pixels 115. Defects when cutting out the semiconductor substrate 110 exist along the sides of the semiconductor substrate 110, and the pixel 115 arranged at the corner of the semiconductor substrate 110 may be affected by defects on two sides. For this reason, it is possible to suppress the effect of the deterioration of the transport properties of the carriers by reducing the area of ​​the electrode 112 of the pixel 115 arranged at the corner of the semiconductor substrate 110 that is most affected by the defects.

[0023] In the configurations shown in FIGS. 2 and 3, an example in which two types of electrodes 112 are arranged is shown, but the present invention is not limited thereto. As shown in FIG. 4, the pixels 115 may include a pixel 115c arranged between the pixel 115a and the pixel 115b. The pixel 115c includes a plurality of electrodes 112c, and the area of ​​each of the plurality of electrodes 112c is larger than the area of ​​each of the plurality of electrodes 112a of the pixel 115a and smaller than the area of ​​the electrode 112b of the pixel 115b. That is, the area of ​​the electrode 112 included in the pixel 115 may be reduced stepwise or continuously from the center of the semiconductor substrate 110 toward the outer edge. In the example shown in FIG. 4, an example in which three types of electrodes 112 are arranged are shown, but four or more types of electrodes 112 may be arranged.

[0024] 5 is a modified example of the arrangement of the electrodes 112 shown in FIG. 3. Among the pixels 115 arranged along one side of the semiconductor substrate 110, pixel 115d is arranged between pixels 115a arranged at both ends. The pixel 115d includes a plurality of electrodes 112d, and the area of ​​each of the plurality of electrodes 112d is larger than the area of ​​each of the plurality of electrodes 112a included in the pixel 115a, and is smaller than the area of ​​the electrode 112b included in the pixel 115b. In other words, the pixels 115a and 115d having smaller areas of the electrodes 112a and 112d are arranged along the outer edge of the semiconductor substrate 110 so as to surround the pixel 115b arranged closer to the center of the semiconductor substrate 110 than the pixels 115a and 115d. By making the area of ​​the electrodes 112a, 112d of the pixels 115a, 115d along the outer edge of the semiconductor substrate 110 smaller than the area of ​​the electrode 112b of the pixel 115b not along the outer edge of the semiconductor substrate 110, the influence of the deterioration of the carrier transport properties at the edge of the semiconductor substrate 110 is suppressed. Furthermore, since the pixel 115a arranged at the corner of the semiconductor substrate 110 may be affected by defects on two sides as described above, the area of ​​the electrode 112a of the pixel 115a is made even smaller than the area of ​​the electrode 112d of the pixel 115d. This makes it possible to further suppress the deterioration of the image quality of the radiation image caused by the deterioration of the carrier transport properties at the edge of the semiconductor substrate 110.

[0025] In the configuration shown in Fig. 5, the pixel 115a having nine electrodes 112a may be arranged along the outer edge of the semiconductor substrate 110 as in the configuration shown in Fig. 3, but in that case, the number of electrodes 112 arranged in one radiation detector 100 will be very large. The segmented electrodes 112a must be electrically independent from each other as shown in Fig. 6(b). Therefore, if the number of electrodes 112 increases, the circuit scale of the readout circuit and the like will increase. Similarly, if the electrodes of all pixels are configured in the same way as the pixel 115a, the circuit scale of the readout circuit and the like will also increase.

[0026] For example, as shown in Fig. 8(a), a plurality of capacitors 141 for storing signals generated by a plurality of pixels 115 may be arranged in the radiation detector 100, with one capacitor connected to each of all of the electrodes 112. Also, for example, as shown in Fig. 8(b), a plurality of amplifiers 142 for amplifying signals generated by a plurality of pixels 115 may be arranged in the radiation detector 100, with one amplifier connected to each of all of the electrodes 112. In this case, a shaper circuit, a discriminator circuit, and the like for discriminating peak values ​​and performing photon counting may be connected downstream of the amplifier 142.

[0027] 5, pixels 115 along the outer edge of the semiconductor substrate 110 may have different numbers of electrodes 112, such as pixel 115a having nine electrodes 112a and pixel 115d having three electrodes 112d. With the configuration as shown in FIG. 5, it is possible to suppress the influence of a decrease in the transport properties of carriers at the edge of the semiconductor substrate 110 while suppressing an increase in the circuit size.

[0028] Also, as shown in FIG. 5, each of the multiple electrodes 112d may be rectangular. Also, the electrode 112a arranged in the pixel 115a may be rectangular. Similarly, the electrode 112b arranged in the pixel 115b may be rectangular. In this case, the short side of each of the multiple electrodes 112d (electrodes 112a) may be arranged along the outer edge of the semiconductor substrate 110. Since defects may exist along the outer edge (side) of the semiconductor substrate 110 as described above, the effect of the weighted potential distribution described above can be obtained by shortening the part of the electrode 112d arranged along the outer edge of the semiconductor substrate 110. Also, from the weighted potential distribution shown in FIG. 7, the length of each short side of the electrode 112d may be 0.2 times or less the thickness of the semiconductor substrate 110.

[0029] 9(a) and 9(b), the radiation detector 100 may include a mounting substrate 120. Of the two main surfaces of the semiconductor substrate 110, the surface having the electrodes 112 is disposed opposite the mounting substrate 120.

[0030] 9(a), the electrodes 112 of the semiconductor substrate 110 and the terminals 121 of the mounting substrate 120 may be electrically connected via bumps 151 such as solder balls. Also, the electrodes 111 of the semiconductor substrate 110 and the terminals 122 of the mounting substrate 120 may be electrically connected by wires 152.

[0031] The mounting substrate 120 may be provided with the above-mentioned capacitor 141, amplifier 142, and the like. The mounting substrate 120 may also be provided with a signal generating unit 123 that generates a signal for one pixel (e.g., pixel 115a) based on the signal values ​​of the signals read out from the multiple electrodes 112 (e.g., electrode 112a) included in one pixel 115 (e.g., pixel 115a). As described above, since the electrodes 112 are electrically independent from each other, it is necessary to add up the signal values ​​of the signals of the pixel 115 including the multiple electrodes 112 to obtain one signal after the signals are read out.

[0032] 9(b), for example, a readout circuit 130 for reading out a signal generated in the semiconductor substrate 110 may be disposed between the semiconductor substrate 110 and the mounting substrate 120. A terminal 132 of the readout circuit 130 and a terminal 121 of the mounting substrate 120 may be electrically connected via a bump 153 such as a solder ball. In this case, the above-mentioned capacitor 141 and amplifier 142 may be disposed in the readout circuit 130.

[0033] As described above, it is possible to realize the radiation detector 100 that suppresses the effects of the deterioration of the carrier transport properties at the edge of the semiconductor substrate 110. As a result, deterioration of the image quality of the obtained radiation image is suppressed.

[0034] 10 is a block diagram of a radiation CT apparatus in this embodiment. The radiation detector 100 described above is applicable to a detector of a radiation CT apparatus. The radiation CT apparatus 30 in this embodiment includes a radiation generating unit 310, a wedge 311, a collimator 312, a radiation detecting unit 320, a top plate 330, a rotating frame 340, a high voltage generating device 350, a data acquisition system (DAS) 351, a signal processing unit 352, a display unit 353, and a control unit 354.

[0035] Radiation generating unit 310 is composed of, for example, a vacuum tube that generates X-rays. A high voltage and a filament current are supplied to the vacuum tube of radiation generating unit 310 from high voltage generator 350. X-rays are generated by irradiating thermal electrons from a cathode (filament) toward an anode (target).

[0036] Wedge 311 is a filter that adjusts the amount of radiation irradiated from radiation generating unit 310. Wedge 311 attenuates the amount of radiation so that the radiation irradiated from radiation generating unit 310 to the subject has a predetermined distribution. Collimator 312 is composed of a lead plate or the like that narrows down the irradiation range of the radiation that has passed through wedge 311. The radiation generated by radiation generating unit 310 is shaped into a cone beam via collimator 312 and irradiated to the subject on top board 330.

[0037] The radiation detection unit 320 is configured using the above-mentioned radiation detector 100. The radiation detection unit 320 detects radiation that has passed through the subject from the radiation generation unit 310, and outputs a signal corresponding to the radiation dose as the DAS 351.

[0038] The rotating frame 340 has an annular shape and is configured to be rotatable. A radiation generating unit 310 (wedge 311, collimator 312) and a radiation detecting unit 320 are arranged facing each other inside the rotating frame 340. The radiation generating unit 310 and the radiation detecting unit 320 are rotatable together with the rotating frame 340.

[0039] The high voltage generator 350 includes a boost circuit, and outputs a high voltage to the radiation generation unit 310. The DAS 351 includes an amplifier circuit and an A / D conversion circuit, and outputs a signal from the radiation detection unit 320 to the signal processing unit 352 as digital data.

[0040] The signal processing unit 352 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and is capable of performing image processing on digital data. The display unit 353 includes a flat display device, and is capable of displaying radiation images. The control unit 354 includes a CPU, a ROM, a RAM, and the like, and controls the operation of the entire radiation CT apparatus 30.

[0041] The disclosure of the present specification includes the following radiation detector and radiation CT device.

[0042] (Item 1) A radiation detector in which a plurality of pixels are arranged on a semiconductor substrate that converts incident radiation into electric charges, the plurality of pixels include a first pixel arranged along an outer edge of the semiconductor substrate and a second pixel arranged closer to a center of the semiconductor substrate than the first pixel; the first pixel includes a plurality of first electrodes on one of the two main surfaces of the semiconductor substrate; the second pixel includes a second electrode on the one principal surface; A radiation detector, wherein the area of ​​the second electrode is larger than the area of ​​each of the plurality of first electrodes.

[0043] (Item 2) 2. The radiation detector according to item 1, wherein each of the plurality of first electrodes is square.

[0044] (Item 3) 3. The radiation detector according to item 2, wherein the length of each side of the plurality of first electrodes is 0.2 times or less the thickness of the semiconductor substrate.

[0045] (Item 4) 2. The radiation detector according to item 1, wherein each of the plurality of first electrodes is rectangular.

[0046] (Item 5) 5. The radiation detector according to item 4, wherein the length of the short side of each of the plurality of first electrodes is 0.2 times or less the thickness of the semiconductor substrate.

[0047] (Item 6) 6. The radiation detector according to item 4 or 5, wherein the short sides of each of the plurality of first electrodes are arranged along an outer edge of the semiconductor substrate.

[0048] (Item 7) 7. The radiation detector according to any one of items 1 to 6, wherein an area of ​​a region surrounded by a virtual line connecting the outer edges of the plurality of first electrodes is the same as an area of ​​the second electrode.

[0049] (Item 8) the plurality of pixels includes a third pixel disposed between the first pixel and the second pixel, the third pixel includes a plurality of third electrodes on the one principal surface; 8. The radiation detector according to claim 1, wherein the area of ​​each of the third electrodes is larger than the area of ​​each of the first electrodes and smaller than the area of ​​the second electrode.

[0050] (Item 9) 9. The radiation detector according to item 8, wherein the plurality of third electrodes function as anodes.

[0051] (Item 10) 8. The radiation detector according to claim 1, wherein a plurality of the first pixels are arranged along an outer edge of the semiconductor substrate.

[0052] (Item 11) When orthogonally projected onto the main surface, the semiconductor substrate has a rectangular shape, 8. The radiation detector according to any one of items 1 to 7, wherein the first pixel is disposed on both ends of a pixel among the plurality of pixels that is disposed along one side of the semiconductor substrate.

[0053] (Item 12) a fourth pixel of the plurality of pixels is disposed between the first pixels disposed at both ends of the pixels disposed along the one side, the fourth pixel includes a plurality of fourth electrodes on the one principal surface; Item 12. The radiation detector according to item 11, wherein an area of ​​each of the plurality of fourth electrodes is larger than an area of ​​each of the plurality of first electrodes and smaller than an area of ​​the second electrode.

[0054] (Item 13) 13. The radiation detector according to item 12, wherein the plurality of fourth electrodes function as anodes.

[0055] (Item 14) 14. The radiation detector according to any one of items 1 to 13, wherein the plurality of first electrodes and the second electrode function as an anode.

[0056] (Item 15) 15. The radiation detector according to any one of claims 1 to 14, further comprising a plurality of capacitors for storing signals generated in the plurality of pixels, one capacitor being connected to each of the plurality of first electrodes and the second electrodes.

[0057] (Item 16) 15. The radiation detector according to any one of claims 1 to 14, further comprising a plurality of amplifiers for amplifying signals generated by the plurality of pixels, one amplifier being connected to each of the plurality of first electrodes and the second electrodes.

[0058] (Item 17) 17. The radiation detector according to any one of items 1 to 16, further comprising a signal generating unit that generates a signal for the first pixel based on a signal value of each signal read out from the plurality of first electrodes.

[0059] (Item 18) 18. The radiation detector according to any one of items 1 to 17, wherein the semiconductor substrate is a single crystal substrate of cadmium zinc telluride.

[0060] (Item 19) 18. The radiation detector according to any one of items 1 to 17, wherein the semiconductor substrate is a single crystal substrate of any one of cadmium telluride, lead iodide, mercury iodide, bismuth iodide, and thallium bromide.

[0061] (Item 20) 20. The radiation detector according to any one of items 1 to 19, wherein the plurality of pixels are arranged at a constant pitch.

[0062] (Item 21) A radiation detector according to any one of items 1 to 20, a radiation generating unit that irradiates the radiation detector with radiation; a signal processing unit that processes a signal output from the radiation detector; A radiation CT apparatus comprising:

[0063] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0064] 100: radiation detector, 110: semiconductor substrate, 112: electrode, 115: pixel

Claims

1. A radiation detector in which a plurality of pixels are arranged on a semiconductor substrate that converts incident radiation into electric charges, the plurality of pixels include a first pixel arranged along an outer edge of the semiconductor substrate and a second pixel arranged closer to the center of the semiconductor substrate than the first pixel; the first pixel includes a plurality of first electrodes on one of two main surfaces of the semiconductor substrate; the second pixel includes a second electrode on the one principal surface; an area of ​​the second electrode is larger than an area of ​​each of the plurality of first electrodes; a plurality of capacitors for storing signals generated by the plurality of pixels, one capacitor connected to each of the plurality of first electrodes and the second electrodes;

2. 2. The radiation detector according to claim 1, wherein each of the plurality of first electrodes is square.

3. 3. The radiation detector according to claim 2, wherein the length of each side of the plurality of first electrodes is 0.2 times or less the thickness of the semiconductor substrate.

4. 2. The radiation detector according to claim 1, wherein each of the plurality of first electrodes is rectangular.

5. 5. The radiation detector according to claim 4, wherein the length of the short side of each of the plurality of first electrodes is 0.2 times or less the thickness of the semiconductor substrate.

6. 5. The radiation detector according to claim 4, wherein the short sides of the plurality of first electrodes are arranged along the outer edge of the semiconductor substrate.

7. 2. The radiation detector according to claim 1, wherein an area of ​​a region surrounded by an imaginary line connecting outer edges of the plurality of first electrodes is equal to an area of ​​the second electrode.

8. the plurality of pixels includes a third pixel disposed between the first pixel and the second pixel, the third pixel includes a plurality of third electrodes on the one main surface; 2. The radiation detector according to claim 1, wherein the area of ​​each of the plurality of third electrodes is larger than the area of ​​each of the plurality of first electrodes and smaller than the area of ​​the second electrode.

9. The radiation detector according to claim 8 , wherein the plurality of third electrodes function as anodes.

10. 2. The radiation detector according to claim 1, wherein a plurality of the first pixels are arranged along an outer edge of the semiconductor substrate.

11. In the orthogonal projection onto the main surface, the semiconductor substrate has a rectangular shape. The radiation detector according to claim 1, characterized in that the first pixels are arranged at both ends of a pixel among the plurality of pixels that is arranged along one side of the semiconductor substrate.

12. A fourth pixel is positioned between the first pixels, which are located at both ends of the pixels arranged along one of the aforementioned edges, The fourth pixel is provided with a plurality of fourth electrodes on one of its main surfaces. The radiation detector according to claim 11, characterized in that the area of ​​each of the plurality of fourth electrodes is larger than the area of ​​each of the plurality of first electrodes and smaller than the area of ​​the second electrode.

13. The radiation detector according to claim 12, characterized in that the plurality of fourth electrodes function as anodes.

14. The radiation detector according to claim 1, characterized in that the plurality of first electrodes and the second electrodes function as anodes.

15. The radiation detector according to claim 1, further comprising a plurality of amplifiers for amplifying signals generated by the plurality of pixels, such that one amplifier is connected to each of the plurality of first electrodes and the second electrodes.

16. The radiation detector according to claim 1, further comprising a signal generation unit that generates a signal for the first pixel based on the signal values ​​of the signals read from the plurality of first electrodes.

17. The radiation detector according to claim 1, characterized in that the semiconductor substrate is a single crystal substrate of cadmium zinc telluride.

18. The radiation detector according to claim 1, characterized in that the semiconductor substrate is a single crystal substrate of cadmium telluride, lead iodide, mercury iodide, bismuth iodide, or thallium bromide.

19. The radiation detector according to claim 1, characterized in that the plurality of pixels are arranged at a constant pitch.

20. A radiation detector according to any one of claims 1 to 19, A radiation generating unit that irradiates the aforementioned radiation detector with radiation, A signal processing unit that processes the signal output from the radiation detector, A radiation CT scanner characterized by being equipped with the following features.

Images