Radiation detector, detector module and method of manufacturing a radiation detector

Abstract

The present disclosure relates to a radiation detector that can suppress deterioration of an SN ratio of a read signal. The radiation detector includes a TlBr crystalline body, and a first electrode and a second electrode provided on respective electrode formation surfaces. At least one of the first electrode and the second electrode includes a first layer and a second layer. The first layer formed on the electrode formation surface includes metallic thallium or a first alloy including metallic thallium and another metal. The second layer on the first layer includes an alloy of a first metal and a second metal. A diffusion coefficient of metallic thallium with respect to the layer composed of the alloy of the first metal and the second metal is smaller than a diffusion coefficient of metallic thallium with respect to the layer composed of the second metal.

Description

Technical Field

[0001] This invention relates to a radiation detector, a detector module, and a method for manufacturing a radiation detector.

[0002] This invention claims priority to Japanese Patent Application No. 2020-206683, filed on December 14, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] A radiation detector is a device used to detect radiation such as X-rays and gamma rays. It can be used in devices such as PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography), gamma cameras, Compton cameras, and imaging spectrometers.

[0004] As radiation detectors, structures using thallium halide crystals (e.g., thallium bromide, thallium iodide, thallium chloride, and mixed crystals thereof) are well known. As an example, Patent Documents 1 and 2 disclose a radiation detector having a parallel plate-like structure in which a thallium bromide (TlBr) crystal is disposed between a first electrode and a second electrode. One of the first and second electrodes is used as an anode electrode, and the other as a cathode electrode. Radiation detectors using TlBr crystals have the advantages of being inexpensive, easy to manufacture, and highly sensitive. Furthermore, there are cases where more than one electrode is further disposed between the first and second electrodes to control the electrolytic or electrostatic shielding electric field.

[0005] The radiation detector described in Patent Document 1 uses a metal thallium electrode made solely of thallium (Tl) metal as its electrode. By using the metal thallium electrode, the polarization of TlBr crystals can be suppressed, enabling the radiation detector to operate stably for a long period of time.

[0006] If a thallium metal electrode is used as the electrode in a radiation detector, it will corrode and deteriorate rapidly in the atmosphere, causing a degradation in the detector's characteristics. This degradation can also occur when a metal layer, such as gold, is deposited onto the thallium metal electrode. To suppress this degradation, the thallium metal electrode needs to be sealed with resin or similar materials after the radiation detector is fabricated to improve its moisture resistance and prevent oxidation and reactions with the atmospheric environment.

[0007] However, in cases where a radiation detector is mounted on a readout circuit board as a two-dimensional detector, the resin seal prevents electrical conduction between the electrodes of the radiation detector and the electrode pads of the readout circuit board. This hinders the practical application of radiation detectors using TlBr crystals.

[0008] An invention that can eliminate this problem is disclosed in Patent Document 2. The electrode of the radiation detector disclosed in this patent document has an alloy layer of thallium and other metals (e.g., lead, silver, bismuth, or indium), and further has a low-resistivity metal layer (e.g., gold) disposed on this alloy layer. By having a thallium alloy layer on the electrode, the degradation of detector characteristics caused by polarization due to TlBr crystallization can be suppressed, and the corrosion of the electrode in the atmosphere can be suppressed.

[0009] [Existing Technical Documents]

[0010] [Patent Literature]

[0011] [Patent Document 1] Japanese Patent No. 5083964

[0012] [Patent Document 2] Japanese Patent No. 6242954 Summary of the Invention

[0013] [The problem the invention aims to solve]

[0014] Based on their research and review of the aforementioned prior art, the inventors discovered the following problem: Specifically, the inventors found that the radiation detector disclosed in Patent Document 2 has the following problem. In the radiation detector disclosed in Patent Document 2, the electrodes of the radiation detector are electrically connected to the electrode pads of the readout circuit board using a conductive adhesive. When reading a signal from the radiation detector towards the readout circuit board, the signal-to-noise ratio (SN ratio) of the read signal is very poor. Since the impedance values ​​of both the thallium alloy layer constituting the electrodes and the low-impedance metal layer are very low, the reason for the deterioration of the SN ratio of the read signal is likely located on or near the surface of the low-impedance metal layer. Therefore, the inventors completed the present invention by analyzing the surface of the low-impedance metal layer or the area near its surface with X-rays to identify the cause of the deterioration of the SN ratio of the read signal and by conducting careful research to eliminate this cause.

[0015] The present invention was developed to solve the aforementioned problems, and its object is to provide a radiation detector, a detector module, and a method for manufacturing a radiation detector that can suppress the degradation of the signal-to-noise ratio of the read signal.

[0016] [Technical means to solve the problem]

[0017] The radiation detector of this embodiment includes: a thallium bromide crystal; and a first electrode and the aforementioned second electrode respectively disposed on electrode forming surfaces disposed at different positions on the thallium bromide crystal. At least one of the first electrode and the second electrode contains a first layer and a second layer. The first layer is a first layer disposed on a corresponding electrode forming surface in the electrode forming surface, and contains metallic thallium or a first alloy containing metallic thallium and a metal different from metallic thallium. In addition, the second layer is a layer disposed on the first layer, and contains a second alloy containing a first metal and a second metal. In particular, the first metal and the second metal are selected such that the diffusion coefficient of metallic thallium to the layer composed of the second alloy is smaller than the diffusion coefficient of metallic thallium to the layer composed of the second metal.

[0018] [Invention Effects]

[0019] According to the present invention, a radiation detector that can suppress the deterioration of the signal-to-noise ratio of the read signal can be obtained. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of the radiation detector 1A according to the first embodiment.

[0021] Figure 2 This is a cross-sectional view of the radiation detector 1B, a modified example of the first embodiment.

[0022] Figure 3 This is a flowchart illustrating the manufacturing method of a radiation detector.

[0023] Figure 4 This is a cross-sectional view of the radiation detector 1C according to the second embodiment.

[0024] Figure 5 This is a cross-sectional view of the radiation detector 1D, a modified example of the second embodiment.

[0025] Figure 6 This is a cross-sectional view of the radiation detector 1E according to the third embodiment.

[0026] Figure 7 This is a cross-sectional view of the radiation detector 1F, a modified example of the third embodiment.

[0027] Figure 8 This is a three-dimensional view of the schematic structure of detector module 2.

[0028] Figure 9 This is a cross-sectional view of the structure of detector module 2.

[0029] Figure 10 This is a cross-sectional view of the main structure of detector module 2.

[0030] Figure 11This is a three-dimensional view of the radiation detector 100.

[0031] Figure 12 To read a partial 3D view of the circuit board 200.

[0032] Figure 13 A diagram showing the layered structure of sample A.

[0033] Figure 14 A diagram showing the layered structure of samples B through D.

[0034] Figure 15 A graph showing the μXPS analysis results for sample A without a Bi layer.

[0035] Figure 16 The graph shows the μXPS analysis results of sample B with a Bi layer immediately after Au evaporation, without heating.

[0036] Figure 17 This is a graph showing the μXPS analysis results after one week for sample C with a Bi layer, without heating after Au evaporation.

[0037] Figure 18 The graph shows the μXPS analysis results after one week for sample D with a Bi layer, after heating following Au evaporation.

[0038] Figure 19 The graph shows the XRD analysis results of samples C and D, which have a Bi layer, after Au evaporation and one week. Detailed Implementation

[0039] [Description of embodiments of the present invention]

[0040] First, individual embodiments of the present invention will be listed for description.

[0041] (1) One embodiment of the radiation detector includes: a thallium bromide crystal; and a first electrode and the aforementioned second electrode respectively disposed on electrode forming surfaces disposed at different positions on the thallium bromide crystal. At least one of the first electrode and the second electrode contains a first layer and a second layer. The first layer is a first layer disposed on a corresponding electrode forming surface in the electrode forming surface, and contains metallic thallium or a first alloy containing metallic thallium and a metal different from metallic thallium. In addition, the second layer is a layer disposed on the first layer, containing a second alloy containing a first metal and a second metal. In particular, the first metal and the second metal are selected such that the diffusion coefficient of metallic thallium to the layer composed of the second alloy (the diffusion coefficient of metallic thallium when diffusing within the layer composed of the second alloy) is smaller than the diffusion coefficient of metallic thallium to the layer composed of the second metal (the diffusion coefficient of metallic thallium when diffusing within the layer composed of the second metal).

[0042] Furthermore, the other electrode among the first and second electrodes may also be constructed, for example, solely from a layer of a low-resistivity metal such as gold or platinum. Additionally, even if the other electrode contains the aforementioned first and second layers, different electrode structures may be employed between the first and second electrodes.

[0043] (2) In one embodiment of this invention, the first layer may comprise: a thallium layer containing metallic thallium or a first alloy; and a first metal layer disposed on the thallium layer. This first metal layer contains a first metal. Alternatively, in another embodiment of this invention, the first layer may comprise an alloy of metallic thallium and the first metal, serving as the first alloy. In another embodiment of this invention, the first layer may comprise an alloy of metallic thallium and the first metal, serving as the first alloy, and may contain an excess of the first metal. In another embodiment of this invention, the first layer may comprise an alloy of metallic thallium and any one or more metals selected from lead, silver, bismuth, and indium, serving as the first alloy. In another embodiment of this invention, the first metal is preferably any one of bismuth, lead, tin, and antimony. In another embodiment of this invention, the second metal is preferably any one of gold and platinum.

[0044] (3) In one embodiment of this invention, the radiation detector further includes a conductive intermediate layer disposed between the first layer and the second layer to improve the adhesion between the first layer and the second layer. In another embodiment of this invention, the intermediate layer may contain any one of chromium, nickel, and titanium.

[0045] (4) In one embodiment, the radiation detector further includes a conductive substrate layer disposed between the electrode forming surface corresponding to any one electrode and the first layer to improve the adhesion between the corresponding electrode forming surface and the first layer. In another embodiment, the substrate layer may contain any one of chromium, nickel, and titanium.

[0046] (5) The detector module of this embodiment includes: a radiation detector having the aforementioned structure; and a readout circuit board. The readout circuit board is a readout circuit board electrically connected to the first electrode or the second electrode of the radiation detector. Furthermore, this readout circuit board has a circuit that processes a signal output from the radiation detector corresponding to radiation detection. Alternatively, in one embodiment, the first electrode or the second electrode of the radiation detector may be electrically connected to an electrode pad on the readout circuit board using a conductive adhesive. In another embodiment, it is preferable to fill the space between the radiation detector and the readout circuit board with resin. In yet another embodiment, it is preferable to cover the radiation detector on the readout circuit board with resin.

[0047] (6) One embodiment of the radiation detector manufacturing method includes: a first step of preparing thallium bromide crystals; and a second step of forming a first electrode and the aforementioned second electrode on electrode forming surfaces disposed at different positions on the thallium bromide crystals. The second step includes a first layer forming step and a second layer forming step, which are steps for forming at least one of the first electrode and the aforementioned second electrode. In the first layer forming step, a first layer is formed, which is disposed on the electrode forming surface corresponding to any of the electrodes in the electrode forming surface. This first layer contains metallic thallium or contains a first alloy composed of metallic thallium and a metal different from metallic thallium. The second layer forming step is to form a second layer on the first layer. This second layer contains a second alloy of the first metal and the second metal. In particular, the first metal and the second metal are selected such that the diffusion coefficient of metallic thallium to the layer composed of the second alloy is smaller than the diffusion coefficient of metallic thallium to the layer composed of the second metal.

[0048] (7) As one embodiment of this embodiment, in the first layer forming step, a thallium layer containing metal thallium or a first alloy may be formed, and then a first metal layer containing a first metal may be stacked on the thallium layer to form the first layer. In the second layer forming step, a second layer containing an alloy of the second metal and the first metal diffused from the first layer may be formed by forming an upper layer of the second metal on the first layer and then heating the laminate composed of the first layer and the upper layer. As one embodiment of this embodiment, in the first layer forming step, a first layer containing an alloy of metal thallium and the first metal may be formed as the first alloy. In the second layer forming step, a second layer containing an alloy of the second metal and the first metal diffused from the first layer may be formed by forming an upper layer of the second metal on the first layer and then heating the laminate composed of the first layer and the upper layer. In one embodiment, the first layer may be formed in the first layer forming process, comprising an alloy of thallium and a first metal as the first alloy, and the first metal may be excessively contained therein. In another embodiment, the first layer may be formed in the first layer forming process, comprising an alloy of thallium and any one or more metals selected from lead, silver, bismuth, and indium as the first alloy.

[0049] (8) As one embodiment of this invention, the first metal may be any one of bismuth, lead, tin, and antimony. Alternatively, as another embodiment of this invention, the second metal may be any one of gold and platinum.

[0050] (9) In one embodiment of this invention, the radiation detector manufacturing method further includes an intermediate layer forming step after the first layer forming step and before the second layer forming step, which is used to form an intermediate layer with conductivity that improves the adhesion between the first layer and the second layer. In another embodiment of this invention, the intermediate layer may contain any one of chromium, nickel, and titanium.

[0051] (10) As one embodiment of this invention, the radiation detector manufacturing method further includes a substrate layer forming step before the first layer forming step, which forms a conductive substrate layer disposed between the corresponding electrode forming surface and the first layer to improve the adhesion between the corresponding electrode forming surface and the first layer. As one embodiment of this invention, the conductive substrate layer preferably contains any one of chromium, nickel, and titanium.

[0052] As explained above, each of the forms listed in this [Description of Embodiments of the Invention] can be applied to all the remaining forms or all combinations of these remaining forms.

[0053] [Detailed Description of Embodiments of the Invention]

[0054] Hereinafter, with reference to the accompanying drawings, the specific structure of the radiation detector, detector module, and radiation detector manufacturing method of this embodiment will be described in detail. Furthermore, the scope of this invention is not limited to the structure of these foregoing embodiments. Various modifications can be made within the same meaning and scope as indicated in the claims, and all such modifications are also included in this invention. Additionally, in the description of the drawings, the same reference numerals are used for the same elements, and repeated descriptions are omitted.

[0055] Furthermore, as explained below... Figure 1 , Figure 2 and Figures 4-7 The radiation detectors 1A to 1F shown have identical electrode structures for their first and second electrodes in thallium bromide (TlBr) crystals. However, different electrode structures can also be used for these first and second electrodes. That is, the first electrode is unaffected by the electrode structure of the second electrode and can be any of the first electrodes 10A to 10F described later. The second electrode is unaffected by the electrode structure of the first electrode and can be any of the second electrodes 20A to 20F described later. Furthermore, either the first or second electrode can have a structure similar to... Figure 1 , Figure 2 and Figures 4-7 The diagram shows different electrode configurations (e.g., constructed solely from layers of low-resistivity metals such as gold or platinum).

[0056] (First Embodiment)

[0057] Figure 1 This is a cross-sectional view of the radiation detector 1A according to the first embodiment. The radiation detector 1A has a plate shape in which a first electrode 10A and a second electrode 20A are provided on a thallium bromide (TlBr) crystal 30. On one of the two parallel surfaces of the TlBr crystal 30, the first electrode 10A is formed by, for example, vapor deposition, and on the other surface (the second electrode forming surface), the second electrode 20A is formed by, for example, vapor deposition.

[0058] The first electrode 10A has a first layer 12 and a second layer 16. The first layer 12, formed on the first electrode forming surface of the TlBr crystal 30, contains metallic thallium or a thallium alloy (first alloy). The second layer 16, formed on the first layer 12, contains an alloy of the first metal and a second metal (second alloy). The second layer 16 has a lower impedance compared to the first layer 12.

[0059] The second electrode 20A has a first layer 22 and a second layer 26. The first layer 22, formed on the second electrode forming surface of the TlBr crystal 30, contains metallic thallium or a thallium alloy. The second layer 26, formed on the first layer 22, contains an alloy of the first metal and the second metal. The second layer 26 has a lower impedance compared to the first layer 22.

[0060] The thickness of the first layers 12 and 22 is, for example, tens of nm to hundreds of nm. When the first layers 12 and 22 contain a thallium alloy (Tl alloy), this Tl alloy is an alloy of metallic thallium (metallic Tl) and other metals. The other metallic elements constituting the Tl alloy along with metallic Tl can be arbitrary, but are preferably one or more elements selected from lead (Pb), silver (Ag), bismuth (Bi), and indium (In).

[0061] Examples of Tl alloys include Tl-Pb, Tl-Ag, Tl-Bi, Tl-In, Tl-Pb-Bi, and Tl-Pb-In. Tl alloys contain Tl as a metallic element, and are not materials containing only Tl as a compound (e.g., Tl oxide, Tl fluoride, Tl nitric acid, etc.). The proportion of metallic Tl in a Tl alloy is the level of metallic Tl detectable by X-ray fluorescence (XRF) analysis. Furthermore, the surface of the Tl alloy layer may oxidize upon contact with air, but the interior of the Tl alloy layer will not be oxidized.

[0062] One of the first electrode 10A and the second electrode 20A is used as the anode electrode, and the other is used as the cathode electrode. Because thallium halide crystals exhibit ionic conductivity, if a voltage is applied to the TlBr crystal 30, then Tl... + Ions will accumulate towards the cathode electrode, Br - Ions accumulate towards the anode electrode. The radiation detector 1A detects radiation by using a current flowing between the two electrodes, caused by the movement of electron-hole pairs generated by the incident radiation due to the applied voltage.

[0063] Br accumulated under the anode electrode - Ions combine with the metallic Tl contained in the anode electrode to form TlBr, releasing electrons in the process. Tl accumulates under the cathode electrode. + The ions combine with the released electrons to form metallic Tl. The metallic Tl and TlBr generated through these reactions are not ions and do not carry a charge. Therefore, polarization suppression of TlBr crystals 30 can be achieved.

[0064] The thickness of the second layers 16 and 26 is, for example, tens of nm to hundreds of nm. The first metal constituting the alloy of the second layers 16 and 26 is preferably any one of bismuth (Bi), lead (Pb), tin (Sn), and antimony (Sb), and the second metal is preferably any one of gold (Au) and platinum (Pt). In the second layers 16 and 26, the second metal and the alloy of the first and second metals may be mixed, or the layers of the second metal and the alloy of the first and second metals may be stacked. In the second layers 16 and 26, the alloy of the first and second metals may be formed on top of the layers of the second metal, under the layers of the second metal, or sandwiched between the layers of the second metal.

[0065] The diffusion coefficient of metal Tl to the alloy layer of the first and second metals in the second layers 16 and 26 is smaller than the diffusion coefficient of metal Tl to the second metal layer. Therefore, even if metal Tl present in the first layers 12 and 22 diffuses over time immediately after fabrication, the diffusion of metal Tl can be suppressed by the alloy layer of the first and second metals in the second layers 16 and 26, thus preventing metal Tl from precipitating onto the surface of the second layers 16 and 26.

[0066] If metallic Tl precipitates onto the surface of the second layer, 16 and 26, the precipitated metallic Tl will oxidize to form thallium oxide (TlO2). This thallium oxide reacts with moisture in the atmosphere to form highly corrosive thallium hydroxide (TlOH). This will become a significant cause of deterioration in the signal-to-noise ratio (SN ratio) of the signal to be read.

[0067] However, in the radiation detector 1A of this embodiment, since the metal T1 can be suppressed from precipitating onto the surface of the second layer 16, 26 and thus suppressing the corrosion of the first electrode 10A and the second electrode 20A, the deterioration of the signal-to-noise ratio of the signal to be read can be suppressed.

[0068] Figure 2 This is a cross-sectional view of a radiation detector 1B, a modified example of the first embodiment. The radiation detector 1B has a flat plate structure in which a first electrode 10B and a second electrode 20B are provided on a thallium bromide (TlBr) crystal 30. The first electrode 10B is formed, for example, by vapor deposition on one of the two parallel surfaces of the TlBr crystal 30 (the first electrode forming surface), and the second electrode 20B is formed, for example, by vapor deposition on the other surface (the second electrode forming surface).

[0069] The first electrode 10B comprises a base layer 11, a first layer 12, an intermediate layer 15, and a second layer 16. The second electrode 20B comprises a base layer 21, a first layer 22, an intermediate layer 25, and a second layer 26. If compared with the radiation detector 1A ( Figure 1 If we compare the structures of the two, the difference lies in the structure of the radiation detector 1B. Figure 2 In the structure of the first electrode 10B, the first electrode 10B also has a base layer 11 and an intermediate layer 15, and the second electrode 20B also has a base layer 21 and an intermediate layer 25.

[0070] Substrate layer 11 is inserted to improve the adhesion between the first electrode forming surface of TlBr crystal 30 and the first layer 12. Substrate layer 21 is inserted to improve the adhesion between the second electrode forming surface of TlBr crystal 30 and the first layer 22. Substrate layers 11 and 21 are conductive. Substrate layers 11 and 21 are thin films with an island-like structure, and their thickness is, for example, several nm to tens of nm. The material of substrate layers 11 and 21 can be arbitrary, but is preferably composed of any metal selected from chromium (Cr), nickel (Ni), and titanium (Ti).

[0071] Intermediate layer 15 is inserted to improve the adhesion between layer 12 and layer 26. Intermediate layer 25 is inserted to improve the adhesion between layer 12 and layer 26. Intermediate layers 15 and 25 are conductive. The thickness of intermediate layers 15 and 25 is, for example, several nm to several hundred nm. The material of intermediate layers 15 and 25 can be arbitrary, but is preferably composed of any metal selected from chromium (Cr), nickel (Ni), and titanium (Ti).

[0072] Radiation detector 1B ( Figure 2 Besides achieving the same performance as the radiation detector 1A ( Figure 1 In addition to having the same effect, by setting the base layer 11, 21 and the intermediate layer 15, 25, the film structure of the first electrode 10B and the second electrode 20B can be made more stable.

[0073] Secondly, regarding the manufacture of radiation detector 1B ( Figure 2 An example of the method will be used to illustrate this. Figure 3 This is a flowchart illustrating a method for manufacturing a radiation detector. This method includes a TlBr crystal fabrication step S1, a substrate layer formation step S2, a first layer formation step S3, an intermediate layer formation step S4, and a second layer formation step S5. By sequentially performing these steps, a radiation detector 1B can be manufactured. Figure 2 ).

[0074] In the TlBr crystal fabrication process S1, the TlBr crystal wafer is prepared to be cut into TlBr crystals 30 of appropriate size (e.g., rectangles with one side length of 10mm to 20mm), and the surface of the TlBr crystals 30 is ground. Alternatively, the wafer can be cut after grinding. In addition, the TlBr crystals 30 are degreased and cleaned.

[0075] In the substrate layer formation process S2, any one of Cr, Ni, and Ti is used as an evaporation source, and a relatively thin substrate layer 11 is formed on the polished surface (first electrode forming surface) of the TlBr crystal 30 by vapor deposition. By setting the substrate layer 11, the adhesion between the first electrode forming surface of the TlBr crystal 30 and the first layer 12 can be improved.

[0076] In the first layer formation process S3, a first layer 12 containing metal Tl or a Tl alloy is formed on the base layer 11 by vapor deposition. When forming the first layer 12 containing the Tl alloy, metal Tl and other metals, used as raw materials, are placed in a tungsten boat or an alumina crucible in an appropriate weight ratio beforehand, and the pressure is reduced to 10... -3 Heating is performed in a vacuum chamber at a pressure below Pa. This alloys metal Tl and other metals. Furthermore, using this alloy as an evaporation source, a first layer 12 is formed on the substrate 11 by vapor deposition. By heating the TlBr crystals 30 before, during, or after the vapor deposition of the first layer 12, the adhesion and electrical stability of the first layer 12 can be improved.

[0077] In the intermediate layer formation process S4, after the TlBr crystals 30 formed up to the first layer 12 have cooled, any one of Cr, Ni, and Ti is used as an evaporation source, and an intermediate layer 15 is formed on the first layer 12 by vapor deposition. By setting the intermediate layer 15, the adhesion between the first layer 12 and the second layer 16 can be improved.

[0078] In the second layer forming process S5, a pre-prepared alloy of the first metal and the second metal is used as an evaporation source, and the second layer 16 is formed on the intermediate layer 15 by vapor deposition. Alternatively, the second layer 16 can also be formed by vapor deposition by stacking a layer of the first metal and a layer of the alloy of the first metal and the second metal on the intermediate layer 15.

[0079] As described above, a first electrode 10B is formed on one side of the TlBr crystal 30 (the first electrode forming surface). After the TlBr crystal 30 on which the first electrode 10B is formed is sufficiently cooled, a base layer 21, a first layer 22, an intermediate layer 25, and a second layer 26 are sequentially formed in the same manner on the other polished surfaces of the TlBr crystal 30 opposite to the surface on which the first electrode 10B is formed (the second electrode forming surface), thereby forming a second electrode 20B. As described above, a radiation detector 1B can be manufactured. Figure 2 ).

[0080] (Second Implementation)

[0081] Figure 4This is a cross-sectional view of the radiation detector 1C according to the second embodiment. The radiation detector 1C has a flat plate structure in which a first electrode 10C and a second electrode 20C are provided on a thallium bromide (TlBr) crystal 30. The first electrode 10C is formed, for example, by vapor deposition on one of the two parallel surfaces of the TlBr crystal 30 (the first electrode forming surface), and the second electrode 20C is formed, for example, by vapor deposition on the other surface (the second electrode forming surface).

[0082] The first electrode 10C comprises a first layer 13 and a second layer 16. The first layer 13, formed on the first electrode forming surface of the TlBr crystal 30, has a thallium layer 18 containing metallic thallium or a thallium alloy (first alloy) stacked on it, and a first metal layer 19 containing a first metal on the thallium layer 18. The second layer 16 formed on the first layer 13 contains an alloy of the first metal and a second metal (second alloy). The second layer 16 has a lower impedance compared to the first layer 13.

[0083] The second electrode 20C comprises a first layer 23 and a second layer 26. The first layer 23, formed on the second electrode forming surface of the TlBr crystal 30, is stacked with a thallium layer 28 containing metallic thallium or a thallium alloy, and a first metal layer 29 containing a first metal on this thallium layer 28. The second layer 26 formed on the first layer 23 contains an alloy of the first metal and a second metal. The second layer 26 has a lower impedance compared to the first layer 23.

[0084] If compared with radiation detector 1A ( Figure 1 If we compare the structures of the two, the difference lies in the structure of the radiation detector 1C ( Figure 4 The structure is such that a thallium layer 18 and a first metal layer 19 are stacked in the first layer 13 of the first electrode 10C, and a thallium layer 28 and a first metal layer 29 are stacked in the first layer 23 of the second electrode 20C.

[0085] The thicknesses of thallium layers 18 and 28 and the first metal layers 19 and 29 are, for example, tens to hundreds of nm. Thallium layers 18 and 28 correspond to radiation detector 1A (…). Figure 1 The first layers 12 and 22 of the structure. The first metal contained in the first metal layers 19 and 29 is the same as the first metal described in the first embodiment. Radiation detector 1C ( Figure 4 The second layer 16, 26 of the structure corresponds to the radiation detector 1A. Figure 1 The second layer of the structure is 16 and 26.

[0086] Even in the radiation detector 1C, the diffusion coefficient of metal Tl to the alloy layer of the first and second metals in the second layers 16 and 26 is smaller than the diffusion coefficient of metal Tl to the second metal layer. Therefore, even if metal Tl present in the first layers 13 and 23 diffuses over time immediately after fabrication, the diffusion of metal Tl can be suppressed by the alloy layer of the first and second metals in the second layers 16 and 26, thus preventing metal Tl from precipitating onto the surface of the second layers 16 and 26. Furthermore, because corrosion of the first electrode 10C and the second electrode 20C can be suppressed, the deterioration of the signal-to-noise ratio (SN ratio) of the signal to be read can be prevented.

[0087] Figure 5 This is a cross-sectional view of a modified example of the second embodiment of the radiation detector 1D. The radiation detector 1D has a flat plate structure in which a first electrode 10D and a second electrode 20D are provided on a thallium bromide (TlBr) crystal 30. The first electrode 10D is formed, for example, by vapor deposition on one of the two parallel surfaces of the TlBr crystal 30 (the first electrode forming surface), and the second electrode 20D is formed, for example, by vapor deposition on the other surface (the second electrode forming surface).

[0088] The first electrode 10D comprises a base layer 11, a first layer 13, an intermediate layer 15, and a second layer 16. The second electrode 20D comprises a base layer 21, a first layer 23, an intermediate layer 25, and a second layer 26. (If compared with a radiation detector 1C...) Figure 4 If we compare the structures of the two, the difference lies in the structure of the radiation detector 1D ( Figure 5 The structure of the first electrode 10D is further provided with a base layer 11 and an intermediate layer 15, and the second electrode 20D is further provided with a base layer 21 and an intermediate layer 25.

[0089] 1D radiation detector Figure 5 The base layers 11 and 21 of the structure correspond to the radiation detector 1B. Figure 2 The basal layer 11, 21 of the structure. Radiation detector 1D ( Figure 5 The intermediate layers 15 and 25 of the structure correspond to the radiation detector 1B. Figure 2 The middle layers 15 and 25 of the structure.

[0090] 1D radiation detector Figure 5 Besides achieving the same level as the radiation detector 1C ( Figure 4 In addition to having the same effect, by setting the substrate layers 11 and 21 and the intermediate layers 15 and 25, the film structures of the first electrode 10D and the second electrode 20D can be made more stable.

[0091] Secondly, regarding the manufacture of radiation detector 1D ( Figure 5An example of the method will be illustrated. Radiation detector 1D ( Figure 5 It can also be done through, for example Figure 3 The manufacturing process is carried out in the sequence of steps shown in the flowchart. However, if it is related to the radiation detector 1B ( Figure 2 If we compare the manufacturing methods of the 1D radiation detector, the radiation detector... Figure 5 In the manufacturing method of TlBr, although the contents of the TlBr crystal formation process S1, the base layer formation process S2 and the intermediate layer formation process S4 are the same, the contents of the first layer formation process S3 and the second layer formation process S5 are different.

[0092] In the first layer formation process S3, a thallium layer 18 containing metal Tl or a Tl alloy is formed on the base layer 11 by vapor deposition. Then, a first layer 13 is formed by stacking the thallium layer 18 and the first metal layer 19 by forming a first metal layer 19. When forming the thallium layer 18 containing the Tl alloy, metal Tl and other metals used as raw materials are placed in a tungsten boat or an alumina crucible in an appropriate weight ratio beforehand, and the pressure is reduced to 10... -3 Heating is performed in a vacuum chamber below Pa. This alloys metal Tl and other metals. Furthermore, using this alloy as an evaporation source, a thallium layer 18 is formed on the substrate layer 11 by vapor deposition. Additionally, by heating the TlBr crystals 30 before, during, or after vapor deposition of the thallium layer 18, the adhesion and electrical stability of the thallium layer 18 can be improved.

[0093] In the second layer formation process S5, after the second metal layer is formed on the intermediate layer 15 by vapor deposition, a heat treatment is performed. For example, heating is performed at a temperature of 140°C for 3 hours. Through this heat treatment, the first metal diffused from the first metal layer 19 of the first layer 13 is alloyed with the vapor-deposited second metal to form a second layer 16 containing an alloy of the first metal and the second metal.

[0094] As described above, a first electrode 10D is formed on one side (the first electrode forming surface) of the TlBr crystal 30. After the TlBr crystal 30 on which the first electrode 10D is formed is sufficiently cooled, a second electrode 20D is formed. That is, on the other polished surfaces (the second electrode forming surfaces) of the TlBr crystal 30 opposite to the surfaces on which the first electrode 10D is formed, a base layer 21, a first layer 23, an intermediate layer 25, and a second layer 26 are sequentially formed in the same manner, thereby forming the second electrode 20D. As described above, a radiation detector 1D can be obtained. Figure 5 ).

[0095] Furthermore, in the second layer formation process S5, after the second metal layer is formed on both intermediate layers 15 and 25 by vapor deposition, a heat treatment can be performed. Through this heat treatment, an alloy of the first metal and the second metal can be formed simultaneously on both second layers 16 and 26.

[0096] (Third Implementation)

[0097] Figure 6 This is a cross-sectional view of the radiation detector 1E according to the third embodiment. The radiation detector 1E has a flat plate structure in which a first electrode 10E and a second electrode 20E are provided on a thallium bromide (TlBr) crystal 30. The first electrode 10E is formed, for example, by vapor deposition on one of the two parallel surfaces of the TlBr crystal 30 (the first electrode forming surface), and the second electrode 20E is formed, for example, by vapor deposition on the other surface (the second electrode forming surface).

[0098] The first electrode 10E comprises a first layer 14 and a second layer 16. The first layer 14, formed on the first electrode forming surface of the TlBr crystal 30, contains an alloy of metallic thallium and a first metal. The first layer 14 preferably contains a first metal with a more excessive stoichiometric composition than the alloy of metallic thallium and the first metal. The second layer 16, formed on the first layer 14, contains an alloy of the first metal and a second metal. The second layer 16 has a lower impedance compared to the first layer 14.

[0099] The second electrode 20E comprises a first layer 24 and a second layer 26. The first layer 24, formed on the second electrode forming surface of the TlBr crystal 30, contains an alloy of metallic thallium and a first metal. Preferably, the first layer 24 contains a first metal with a more excessive stoichiometric composition than the alloy of metallic thallium and the first metal. The second layer 26, formed on the first layer 24, contains an alloy of the first metal and a second metal. The second layer 26 has a lower impedance compared to the first layer 24.

[0100] If compared with radiation detector 1A ( Figure 1 If we compare the structures of the two, the difference lies in the structure of the radiation detector 1E ( Figure 6 In the structure of ), the first layer 14, 24 contains an alloy of metal thallium and a first metal, and contains an excess of the first metal.

[0101] The thickness of the first layers 14 and 24 is, for example, tens of nm to hundreds of nm. The first layers 14 and 24 contain an alloy of thallium and a first metal, and contain a first metal in excess of the stoichiometric composition of this alloy. The first metal contained in the first layers 14 and 24 is the same as the first metal described in the first embodiment. Radiation detector 1E ( Figure 6 The second layer 16, 26 of the structure corresponds to the radiation detector 1A. Figure 1The second layer of the structure is 16 and 26.

[0102] Even in the radiation detector 1E, the diffusion coefficient of metal Tl to the alloy layer of the first and second metals in the second layers 16 and 26 is smaller than the diffusion coefficient of metal Tl to the layer of the second metal. Therefore, even if metal Tl present in the first layers 14 and 24 diffuses over time immediately after fabrication, the diffusion of metal Tl can be suppressed by the alloy layer of the first and second metals in the second layers 16 and 26, thus preventing metal Tl from precipitating onto the surface of the second layers 16 and 26. Furthermore, because corrosion of the first electrode 10E and the second electrode 20E can be suppressed, the deterioration of the signal-to-noise ratio (SN ratio) of the signal to be read can be prevented.

[0103] Figure 7 This is a cross-sectional view of a modified example of the third embodiment of the radiation detector 1F. The radiation detector 1F has a flat plate shape with a first electrode 10F and a second electrode 20F provided on a thallium bromide (TlBr) crystal 30. The first electrode 10F is formed, for example, by vapor deposition on one of the two parallel surfaces of the TlBr crystal 30 (the first electrode forming surface), and the second electrode 20F is formed, for example, by vapor deposition on the other surface (the second electrode forming surface).

[0104] The first electrode 10F comprises a base layer 11, a first layer 14, an intermediate layer 15, and a second layer 16. The second electrode 20F comprises a base layer 21, a first layer 24, an intermediate layer 25, and a second layer 26. If compared with the radiation detector 1E ( Figure 6 If we compare the structures of the two, the difference lies in the structure of the radiation detector 1F ( Figure 7 In the structure of the first electrode 10F, the first electrode 10F also has a base layer 11 and an intermediate layer 15, and the second electrode 20F also has a base layer 21 and an intermediate layer 25.

[0105] Radiation detector 1F ( Figure 7 The base layers 11 and 21 of the structure correspond to the radiation detector 1B. Figure 2 The base layer 11, 21 of the structure. Radiation detector 1F ( Figure 7 The intermediate layers 15 and 25 of the structure correspond to the radiation detector 1B. Figure 2 The middle layers 15 and 25 of the structure.

[0106] Radiation detector 1F ( Figure 7 Besides achieving the same level as the 1E radiation detector, Figure 6 In addition to having the same effect, by setting the base layer 11, 21 and the intermediate layer 15, 25, the film structure of the first electrode 10F and the second electrode 20F can be made more stable.

[0107] Secondly, regarding the manufacture of radiation detector 1F ( Figure 7 An example of the method will be illustrated. Radiation detector 1F ( Figure 7 It can also be done through, for example Figure 3 The manufacturing process is carried out in the sequence of steps shown in the flowchart. However, if it is related to the radiation detector 1B ( Figure 2 If we compare the manufacturing methods of the radiation detector 1F, the radiation detector 1F ( Figure 7 In the manufacturing method of TlBr, although the contents of the TlBr crystal formation process S1, the base layer formation process S2 and the intermediate layer formation process S4 are the same, the contents of the first layer formation process S3 and the second layer formation process S5 are different.

[0108] In the first layer formation process S3, a first layer 14 containing an alloy of thallium and a first metal is formed on the base layer 11 by vapor deposition, and the first metal is present in excess. During this vapor deposition, the raw materials, metal Tl and the first metal, are placed in a tungsten boat or an alumina crucible in an appropriate weight ratio (a weight ratio in which the first metal is in excess compared to the alloy ratio necessary for forming the thallium and first metal alloy), and the vapor deposition is reduced to 10... -3 Heating is performed in a vacuum chamber at a pressure below Pa. This prepares an alloy of metal Tl and a first metal, along with excess first metal. Using this alloy and excess first metal as an evaporation source, a first layer 14 is formed on the substrate 11 by vapor deposition. Furthermore, by heating the TlBr crystals 30 before, during, or after vapor deposition of the first layer 14, the adhesion and electrical stability of the first layer 14 can be improved.

[0109] In the second layer formation process S5, after the second metal layer is formed on the intermediate layer 15 by vapor deposition, a heat treatment is performed. For example, a heat treatment is performed at a temperature of 140°C for 3 hours. Through this heat treatment, the first metal diffused from the first layer 14 is alloyed with the vapor-deposited second metal to form a second layer 16 containing an alloy of the first metal and the second metal.

[0110] As described above, a first electrode 10F is formed on one side (the first electrode forming surface) of the TlBr crystal 30. After the TlBr crystal 30 on which the first electrode 10F is formed is sufficiently cooled, a second electrode 20F is formed. That is, on the other polished surfaces (the second electrode forming surfaces) of the TlBr crystal 30 opposite to the surfaces on which the first electrode 10F is formed, a base layer 21, a first layer 24, an intermediate layer 25, and a second layer 26 are formed sequentially in the same manner, thereby forming the second electrode 20F. As described above, a radiation detector 1F can be obtained. Figure 7 ).

[0111] Furthermore, in the second layer formation process S5, after the second metal layer is formed on both intermediate layers 15 and 25 by vapor deposition, a heat treatment can be performed. Through this heat treatment, an alloy of the first metal and the second metal can be formed simultaneously on both second layers 16 and 26.

[0112] (Implementation of the detector module)

[0113] Figure 8 This is a perspective view of the schematic structure of detector module 2. Detector module 2 includes: one or more radiation detectors 100; and a readout circuit board 200. The radiation detector 100 has the same structure as any of the aforementioned radiation detectors 1A to 1F. Furthermore, in the radiation detectors 1A to 1F suitable for the radiation detector 100, the first electrode and the second electrode may have different electrode structures. In addition, either the first electrode or the second electrode may have a structure similar to that of the respective... Figure 1 , Figure 2 and Figures 4-7 The diagram shows different electrode configurations (e.g., constructed only by layers of low-resistivity metals such as gold or platinum). The readout circuit board 200 is electrically connected to the electrodes of the radiation detector 100, and is equipped with circuitry that takes into account the signal output from the radiation detector 100 corresponding to the detection of radiation (e.g., gamma rays) by the radiation detector 100 and processes that signal.

[0114] Figure 9 This is a cross-sectional view of the detector module 2. The readout circuit board 200 has one or more radiation detectors 100 mounted on its first surface and one or more signal processing circuits 202 mounted on its second surface. Additionally, the readout circuit board 200 has one or more connectors 204 mounted on its first surface. The board 201 is, for example, a flexible printed circuit board. Electrode pads are provided on the first surface of the board 201, and these electrode pads are electrically connected to the electrodes of the radiation detectors 100. The board 201 has through electrodes used to electrically connect the electrode pads to the signal processing circuits 202. The signal processing circuits 202 receive signals output from the radiation detectors 100 and arriving via the through electrodes, and then process these signals. The connectors 204 are electrically connected to the signal processing circuits 202 via wiring formed on the board 201. Connector 204 receives control signals from the outside to control the operation of signal processing circuit 202, and outputs the signals obtained by the signal processing circuit 202 to the outside.

[0115] Figure 10 This is a cross-sectional view of the main structure of detector module 2. Figure 11 This is a three-dimensional view of the radiation detector 100. Figure 12This is a partial perspective view of the circuit board 200. The following uses... Figures 10-12 The structure of detector module 2 will be described below.

[0116] The radiation detector 100 includes: a first electrode 110 containing a first layer 112 and a second layer 116; a second electrode 120 containing a first layer 122 and a second layer 126; and a TlBr crystal 130. In such cases... Figures 10-12 The structure shown has a radiation detector 100 with 4×4 first electrodes 110 arranged in a two-dimensional array on the lower surface of the TlBr crystal 130 (the surface opposite to the readout circuit board 200), and a common second electrode 120 on the upper surface of the TlBr crystal 130. The second electrode 120 is preferably configured to cover almost the entire upper surface of the TlBr crystal 130. The number of pixels in the radiation detector 100 is the same as the number of first electrodes 110, which is 16. A bias line 320 is electrically connected to the second electrode 120 on the upper surface of the TlBr crystal 130 via a conductive adhesive 312. This bias line 320 can be in the shape of a wire or a thin film.

[0117] The readout circuit board 200 has 4×4 electrode pads 203 arranged in a two-dimensional array on the upper surface of the board 201 (the surface facing the radiation detector 100), and a signal processing circuit 202 is provided on the lower surface of the board 201. The first electrode 110 of the radiation detector 100 and the electrode pads 203 of the readout circuit board 200 are electrically connected in a one-to-one manner by a conductive adhesive 311.

[0118] Because TlBr crystals have a low melting point and a high coefficient of thermal expansion, conductive adhesives 311 and 312 are preferably low-temperature heat-curing adhesives with a temperature below 160°C. For example, Ni-filled conductive adhesives, Ag-filled conductive adhesives, C-filled conductive adhesives, or low-temperature solder pastes of the Sn-Bi type can be used as conductive adhesives 311 and 312. The application of conductive adhesives 311 and 312 can be performed using a dispenser or a printing method.

[0119] The space between the radiation detector 100 and the readout circuit board 200 is filled with an insulating underfill material 331. The underfill material 331 covers the first electrode 110 of the radiation detector 100, the electrode pad 203 of the readout circuit board 200, and the conductive adhesive 311. This underfill material 331 is provided to improve the strength and temperature resistance of the detector module 2. The underfill material 331 is preferably a resin material with low thermal expansion. The underfill material 331 may be a material containing silica, or it may be a material containing only epoxy resin and no silica.

[0120] The radiation detector 100 on the readout circuit board 200 is covered by an insulating protective film 332. The protective film 332 preferably covers the entire upper surface of the readout circuit board 200. This protective film 332 is provided for moisture protection. The protective film 332 is preferably a resin material that can be coated into a thin film, for example, with a thickness of 10 μm to 200 μm; furthermore, it is preferably a resin material that cures at room temperature or at a temperature below 100°C. As the protective film 332, for example, acrylic resin, polyolefin resin, polyurethane resin, or silicone resin can be used.

[0121] The radiation detector 100 is covered by a bottom filler 331 and a protective film 332 to prevent contact with the atmosphere. Therefore, the detector module 2 not only improves its strength and temperature resistance but also ensures long-term reliability.

[0122] (Modified Example)

[0123] However, the present invention is not limited to the aforementioned embodiments and various modifications can be made. For example, when forming the Tl-Bi alloy layer in the first layer, one of Tl and Bi can be vapor-deposited first, followed by vapor deposition of the other, and then heat treatment can be performed, instead of using a pre-made alloy of Tl and Bi as the vapor deposition source to form the Tl-Bi alloy layer. Thus, a Tl-Bi alloy layer can also be formed. Furthermore, when forming the Au-Bi alloy layer in the second layer, one of Au and Bi can be vapor-deposited first, followed by vapor deposition of the other, and then heat treatment can be performed to form the Au-Bi alloy layer, instead of using a pre-made alloy of Au and Bi as the vapor deposition source to form the Au-Bi alloy layer.

[0124] The electrode of either the first electrode or the second electrode may also be constructed, for example, by a layer of a low-resistivity metal such as gold or platinum. Figures 8-12 The detector module 2 shown can also be configured such that the second electrode 120 of the common electrode is formed only by a layer of a low-resistivity metal such as Au or Pt, depending on the method of use.

[0125] [Example]

[0126] (First Embodiment)

[0127] Perform compositional analysis on samples A through D as described below. Figure 13 This diagram illustrates the layered structure of sample A. Sample A has a structure in which a TlBi alloy layer and a gold (Au) layer are sequentially formed on a glass substrate simulating TlBr crystals. In sample A, there is no bismuth (Bi) layer between the TlBi alloy layer and the Au layer. Figure 14The diagram shows the layered structure of samples B to D. Samples B to D have a structure in which a TlBi alloy layer, a bismuth (Bi) layer, and a gold (Au) layer are sequentially formed on a glass substrate simulating TlBr crystals.

[0128] When performing compositional analysis on various samples, microprobe X-ray photoelectron spectroscopy (μXPS) and X-ray diffraction (XRD) are used. The μXPS device measures the energy of photoelectrons emitted from the sample surface when X-rays are incident on the sample, thereby obtaining information about the sample's composition and chemical bonding state. Furthermore, by using it in conjunction with, for example, an Ar sputtering device, the μXPS device can obtain information about the composition and chemical bonding state at various locations along the depth direction of the sample. The XRD device calculates the relationship between the diffraction angle and diffraction intensity based on the diffraction light produced when X-rays of known wavelengths are incident on the sample, and then analyzes the sample's composition.

[0129] Figure 15 This graph displays the μXPS analysis results for sample A, which lacks a Bi layer. The horizontal axis shows the Ar sputtering time (i.e., the depth position of the sample), and the vertical axis shows the composition percentage (atomic %). In sample A, a large amount of metallic Tl is deposited on the Au layer surface, along with abundant oxygen (O). If the metallic Tl deposited on the Au layer surface oxidizes to form thallium oxide (TlO2), this thallium oxide reacts with atmospheric moisture to form highly corrosive thallium hydroxide (TlOH). This significantly degrades the signal-to-noise ratio (SN ratio) of the signal to be read.

[0130] Figure 16 This chart shows the μXPS analysis results immediately after Au deposition, without heating, for sample B, which has a Bi layer. In this sample B, the amount of metallic Tl precipitated onto the Au layer surface immediately after Au deposition is small.

[0131] Figure 17 This is a graph showing the μXPS analysis results of sample C, which has a Bi layer, one week after Au deposition without heating. The μXPS analysis results of sample B (immediately after Au deposition) are also shown. Figure 16 μXPS analysis results of sample C (after 1 week) Figure 17 In contrast, in sample C, a large amount of metallic Tl precipitated onto the Au layer surface during the period from Au deposition to one week. Therefore, even in sample C, as in sample A, thallium hydroxide (TlOH) was generated, which became a significant cause of the deterioration in the signal-to-signal ratio of the signal to be read.

[0132] Figure 18 The graph shows the μXPS analysis results after one week for sample D, which has a Bi layer, after heating following Au deposition. Sample D is an alloy of Bi and Au diffused from the Bi layer by heating at 140°C for 3 hours. The μXPS analysis results for sample C (without heating, after one week) are also shown. Figure 17 μXPS analysis results of sample D (after heating and 1 week) Figure 18 In comparison, in sample D, even after one week from the start of Au deposition, the amount of metal Tl deposited onto the Au layer surface is not significant. Therefore, in sample D, the generation of thallium hydroxide (TlOH) can be suppressed, thus preventing the deterioration of the signal-to-noise ratio (SN ratio) of the signal to be read.

[0133] Furthermore, the μXPS analysis of samples C and D was performed after Au deposition and storage under reduced pressure for one week. This is because during this one-week storage period, the precipitation of metallic Tl towards the Au layer surface is stable, and the subsequent change in the amount of metallic Tl precipitation on the Au layer surface is small. Additionally, sample D simulates the formation of the first layer (TlBi alloy layer and Bi layer) and the second layer (Au layer) on TlBr crystals after heating, using a radiation detector 1C (…). Figure 4 ).

[0134] Figure 19 This chart shows the XRD analysis results of samples C and D, which have Bi layers, one week after Au deposition. The horizontal axis of the chart shows the diffraction angle, and the vertical axis shows the diffraction intensity (photoelectron count). Since both samples C (unheated) and D (heated) used an alloy of molten Bi and metallic Tl as the evaporation source before deposition onto the glass substrate, the presence of the Bi-Tl alloy (Bi₂Tl) was considered to be of the same degree. However, compared to sample C (unheated), it was found that in sample D (heated), the amounts of Bi and Au as individual elements were reduced, and an alloy of Bi and Au (Au₂Bi) was formed upon heating.

[0135] μXPS analysis results of samples A through D ( Figures 15-18 ) and XRD analysis results of samples C and D ( Figure 19 It was learned that a heated radiation detector 1C (with a first layer (TlBi alloy layer and Bi layer) and a second layer (Au layer) formed on TlBr crystals) Figure 4By forming an alloy (Au2Bi) in the second layer, the precipitation of metallic Tl towards the surface of the second layer can be suppressed, thereby inhibiting electrode corrosion and thus suppressing the degradation of the signal-to-noise ratio (SN ratio) of the signal to be read. This is not only applicable to radiation detectors 1C ( Figure 4 ), in other structures of the radiation detector 1A ( Figure 1 ), radiation detector 1B ( Figure 2 ), radiation detector 1D ( Figure 5 ), radiation detector 1E ( Figure 6 ) and radiation detector 1F ( Figure 7 The same applies.

[0136] (Second Embodiment)

[0137] The defect rate was determined by fabricating the following detector module. The fabricated detector module has the following structure: four radiation detectors are mounted on a readout circuit board, and each radiation detector has a first electrode structure with 64 (=8×8) electrodes, for a total pixel count of 256. In each radiation detector, the TlBr crystal has a 20mm×20mm flat plate shape, and the first electrodes have a 2.5mm spacing. The structure of each radiation detector is similar to that of radiation detector 1C (…). Figure 4 The defect rate of the detector module that forms an alloy of Bi and Au through heat treatment after Au vapor deposition in the second layer formation process is reduced by about 1 / 4 compared to the defect rate of the detector module that does not undergo heat treatment after Au vapor deposition.

[0138] [Symbol Explanation]

[0139] 1A~1F…Radiation detector, 2…Detector module, 10A~10F…First electrode, 11…Base layer, 12~14…First layer, 15…Intermediate layer, 16…Second layer, 18…Thallium layer, 19…First metal layer, 20A~20F…Second electrode, 21…Base layer, 22~24…First layer, 25…Intermediate layer, 26…Second layer, 28…Thallium layer, 29…First metal layer, 30…Thallium bromide (TlBr) crystals, 100… Radiation detector, 110…first electrode, 112…first layer, 116…second layer, 120…second electrode, 122…first layer, 126…second layer, 130…thallium bromide (TlBr) crystal, 200…reading circuit board, 201…board, 202…signal processing circuit, 203…electrode pad, 204…connector, 311, 312…conductive adhesive, 320…bias line, 331…bottom filler, 332…protective film.

Claims

1. A radiation detector, comprising: Thallium bromide crystals; and The first electrode and the second electrode are respectively disposed on the electrode forming surface at different positions on the thallium bromide crystal. The electrode of at least one of the first electrode and the second electrode comprises: The first layer, disposed on the corresponding electrode forming surface in the electrode forming surface, contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal; and The second layer, which is a layer disposed on the first layer, contains a second alloy of the first metal and the second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. The first layer includes: A thallium layer containing the metallic thallium or the first alloy; and A first metal layer is disposed on the thallium layer and contains the first metal.

2. A radiation detector, comprising: Thallium bromide crystals; and The first electrode and the second electrode are respectively disposed on the electrode forming surface at different positions on the thallium bromide crystal. The electrode of at least one of the first electrode and the second electrode comprises: The first layer, disposed on the corresponding electrode forming surface in the electrode forming surface, contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal; and The second layer, which is a layer disposed on the first layer, contains a second alloy of the first metal and the second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. The first layer contains an alloy of the metal thallium and the first metal as the first alloy.

3. The radiation detector as described in claim 2, wherein, The first layer contains an alloy of the metal thallium and the first metal as the first alloy, and contains an excess of the first metal.

4. A radiation detector, comprising: Thallium bromide crystals; and The first electrode and the second electrode are respectively disposed on the electrode forming surface at different positions on the thallium bromide crystal. The electrode of at least one of the first electrode and the second electrode comprises: The first layer, disposed on the corresponding electrode forming surface in the electrode forming surface, contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal; and The second layer, which is a layer disposed on the first layer, contains a second alloy of the first metal and the second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. The first metal is any one of bismuth, lead, tin, and antimony.

5. The radiation detector as claimed in any one of claims 1 to 4, wherein, The first layer comprises an alloy of the metal thallium with any one or more of the metals lead, silver, bismuth and indium as the first alloy.

6. The radiation detector as claimed in any one of claims 1 to 4, wherein, The second metal is either gold or platinum.

7. The radiation detector as claimed in claim 5, wherein, The second metal is either gold or platinum.

8. The radiation detector according to any one of claims 1 to 4 and 7, wherein, It also has a conductive intermediate layer disposed between the first layer and the second layer to improve the adhesion between the first layer and the second layer.

9. The radiation detector as claimed in claim 8, wherein, The intermediate layer contains any one of the following metals: chromium, nickel, and titanium.

10. The radiation detector according to any one of claims 1 to 4, 7, and 9, wherein, It also has a conductive substrate layer disposed between the corresponding electrode forming surface and the first layer to improve the adhesion between the corresponding electrode forming surface and the first layer.

11. The radiation detector of claim 10, wherein, The base layer contains any one of the metals selected from chromium, nickel, and titanium.

12. A detector module comprising: The radiation detector according to any one of claims 1 to 11; and A reading circuit board is electrically connected to the first electrode or the second electrode of the radiation detector and is provided with a circuit for inputting a signal output from the radiation detector corresponding to the detection of radiation and processing the signal.

13. The detector module of claim 12, wherein, The first electrode or the second electrode of the radiation detector is electrically connected to the electrode pad on the readout circuit board via a conductive adhesive.

14. The detector module as claimed in claim 12 or 13, wherein, The space between the radiation detector and the readout circuit board is filled with resin.

15. The detector module as claimed in claim 12 or 13, wherein, The radiation detector on the readout circuit board is covered with resin.

16. The detector module of claim 14, wherein, The radiation detector on the readout circuit board is covered with resin.

17. A method for manufacturing a radiation detector, comprising: Step 1: Prepare thallium bromide crystals; and In the second step, a first electrode and a second electrode are formed on electrode forming surfaces located at different positions on the thallium bromide crystal, respectively. The second step includes a first layer forming step and a second layer forming step as steps for forming at least one of the first electrode and the second electrode. The first layer forming process forms a first layer, which is disposed on the corresponding electrode forming surface in the electrode forming surface, and contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal. The second layer forming process forms a second layer, which is disposed on the first layer and contains a second alloy of a first metal and a second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. In the first layer forming process, a thallium layer containing the metal thallium or the first alloy is formed, and a first metal layer containing the first metal is stacked on the thallium layer, thereby forming the first layer. In the second layer forming process, after forming an upper layer made of the second metal on the first layer, the laminate made of the first layer and the upper layer is heated to form the second layer containing an alloy of the second metal and the first metal diffused from the first layer.

18. A method for manufacturing a radiation detector, comprising: Step 1: Prepare thallium bromide crystals; and In the second step, a first electrode and a second electrode are formed on electrode forming surfaces located at different positions on the thallium bromide crystal, respectively. The second step includes a first layer forming step and a second layer forming step as steps for forming at least one of the first electrode and the second electrode. The first layer forming process forms a first layer, which is disposed on the corresponding electrode forming surface in the electrode forming surface, and contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal. The second layer forming process forms a second layer, which is disposed on the first layer and contains a second alloy of a first metal and a second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. In the first layer forming process, a first layer is formed, which comprises an alloy of the metal thallium and the first metal as the first alloy. In the second layer forming process, after forming an upper layer made of the second metal on the first layer, the laminate made of the first layer and the upper layer is heated to form the second layer containing the alloy of the second layer and the first metal diffused from the first layer.

19. The method for manufacturing a radiation detector as described in claim 18, wherein, In the first layer forming process, a first layer is formed, which contains an alloy of the metal thallium and the first metal as the first alloy, and contains an excess of the first metal.

20. A method for manufacturing a radiation detector, comprising: Step 1: Prepare thallium bromide crystals; and In the second step, a first electrode and a second electrode are formed on electrode forming surfaces located at different positions on the thallium bromide crystal, respectively. The second step includes a first layer forming step and a second layer forming step as steps for forming at least one of the first electrode and the second electrode. The first layer forming process forms a first layer, which is disposed on the corresponding electrode forming surface in the electrode forming surface, and contains thallium metal or a first alloy containing thallium metal and a metal different from thallium metal. The second layer forming process forms a second layer, which is disposed on the first layer and contains a second alloy of a first metal and a second metal. The first metal and the second metal are selected such that the diffusion coefficient of thallium metal with respect to the layer composed of the second alloy is smaller than the diffusion coefficient of thallium metal with respect to the layer composed of the second metal. The first metal is any one of bismuth, lead, tin, and antimony.

21. The method for manufacturing a radiation detector as described in any one of claims 17 to 20, wherein, In the first layer forming process, a first layer is formed, which comprises an alloy of the metal thallium with any one or more metals selected from lead, silver, bismuth and indium as the first alloy.

22. The method for manufacturing a radiation detector as described in any one of claims 17 to 20, wherein, The second metal is either gold or platinum.

23. The method for manufacturing a radiation detector as described in claim 21, wherein, The second metal is either gold or platinum.

24. The method for manufacturing a radiation detector as described in any one of claims 17 to 20 and 23, wherein, After the first layer formation process and before the second layer formation process, an intermediate layer formation process is provided, which forms a conductive intermediate layer to improve the adhesion between the first layer and the second layer.

25. The method for manufacturing a radiation detector as described in claim 24, wherein, The intermediate layer contains any one of the following metals: chromium, nickel, and titanium.

26. The method for manufacturing a radiation detector as described in any one of claims 17 to 20, 23, and 25, wherein, Before the first layer forming process, a substrate layer forming process is also provided, which forms a conductive substrate layer. The conductive substrate layer is disposed between the corresponding electrode forming surface and the first layer to improve the adhesion between the corresponding electrode forming surface and the first layer.

27. The method for manufacturing a radiation detector as described in claim 26, wherein, The conductive substrate contains any one of the metals selected from chromium, nickel, and titanium.

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