JP6970801B2 - Radiation detector manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a radiation detector.

The radiation detector detects radiation such as X-rays and gamma rays, and is used in PET (Positron Emission Tomography) devices, SPECT (Single Photon Emission Computed Tomography) devices, gamma cameras, Compton cameras, imaging spectrometers, and the like. Can be.

As a radiation detector, one using a halogenated thallium crystal (for example, thallium bromide, thallium iodide, thallium chloride, and a mixed crystal thereof) is known, and as an example, a first electrode and a second electrode are used. A parallel plate-like structure in which thallium bromide (TlBr) crystals are provided between them is known (see Patent Documents 1 and 2). One of the first electrode and the second electrode is used as an anode electrode, and the other is used as a cathode electrode. A radiation detector using TlBr crystals has the advantages of being inexpensive and easy to manufacture and having high sensitivity. In some cases, one or more electrodes may be provided between the first electrode and the second electrode in order to control electrolysis or electrostatically shield the electric field.

The radiation detectors described in Patent Documents 1 and 2 use a thallium electrode made of only thallium (Tl) metal as a first electrode and a second electrode. It is said that the use of a thallium electrode can suppress the polarization of TlBr crystals and enable long-term stable operation of the radiation detector.

Japanese Patent No. 5083964 Japanese Unexamined Patent Publication No. 2006-80206

When a thallium electrode is used as the first electrode and the second electrode in a radiation detector using a TlBr crystal, the thallium electrode rapidly corrodes and deteriorates in the atmosphere, and the characteristics of the radiation detector deteriorate. This also occurs when a metal layer such as gold is deposited and formed on the thallium electrode. In order to suppress this deterioration, it is necessary to seal the thallium electrode with a resin or the like after manufacturing the radiation detector to improve the moisture resistance and prevent oxidation and reaction with the atmosphere.

However, for example, when a radiation detector is mounted on a read circuit board as a two-dimensional detector, electrical conduction between the electrodes of the radiation detector and the pad of the read circuit board can be obtained by sealing with resin. It disappears. This hinders the practical application of radiation detectors using TlBr crystals.

The present invention has been made to solve the above problems, and is capable of suppressing deterioration of detector characteristics due to polarization of TlBr crystals and suppressing corrosion of electrodes in the atmosphere. Radiation detection. It is an object of the present invention to provide a method of manufacturing a vessel.

The method for manufacturing a radiation detector of the present invention is a method for manufacturing a radiation detector including a first electrode, a second electrode, and a tallium bromide crystal provided between the first electrode and the second electrode. Then, (1) the first step of cutting out the talium bromide crystal from the talium bromide crystal wafer, and (2) the talium metal and other metal elements are placed in a boat and heated in a vacuum chamber, and these tallium metals and other metal elements are heated. In the second step of alloying the metal element, and (3) on the electrode forming surface on which the first electrode or the second electrode should be formed in the tallium bromide crystal cut out in the first step, in the boat in the second step. The present invention comprises a third step including an alloy layer forming step of forming an alloy layer by vapor deposition using the metal alloyed with the above as an evaporation source. The alloy layer preferably contains one or more metal elements of lead, silver, bismuth and indium as other metal elements.
In the present invention, it is preferable that the first step includes a polishing step of polishing the thallium bromide crystal wafer or the electrode-forming surface of the thallium bromide crystal. It is preferable that the third step includes a heating step of heating the thallium bromide crystal before, before, or during the vapor deposition of the alloy layer on the electrode forming surface of the thallium bromide crystal.

In the present invention, in the third step, after the alloy layer forming step, a low resistance metal layer is formed by depositing on the electrode forming surface of the thallium bromide crystal to form a low resistance metal layer made of a metal having a lower resistance than the alloy layer. It is preferable to include a step. The low resistance metal layer is preferably made of gold.

In the present invention, the third step is an intermediate layer for forming a conductive intermediate layer by vapor deposition on the electrode forming surface of the thallium bromide crystal after the alloy layer forming step and before the low resistance metal layer forming step. It is preferable to include a forming step. The intermediate layer is preferably made of any metal of chromium, nickel and titanium.

In the present invention, it is preferable that the third step includes a base layer forming step of forming a conductive base layer by vapor deposition on the electrode forming surface of the thallium bromide crystal before the alloy layer forming step. The underlayer is preferably made of any metal of chromium, nickel and titanium.

According to the present invention, it is possible to manufacture a radiation detector capable of suppressing deterioration of detector characteristics due to polarization of TlBr crystals and suppressing corrosion of electrodes in the atmosphere.

FIG. 1 is a diagram showing a cross-sectional configuration of the radiation detector 1A of the first embodiment. FIG. 2 is a diagram showing a cross-sectional configuration of the radiation detector 1B of the second embodiment. FIG. 3 is a diagram showing a cross-sectional configuration of the radiation detector 1C of the third embodiment. FIG. 4 is a diagram showing a cross-sectional configuration of the radiation detector 1D of the fourth embodiment. FIG. 5 is a diagram showing a cross-sectional configuration of the radiation detector 1E according to the fifth embodiment. FIG. 6 is a diagram showing a cross-sectional configuration of the radiation detector 1F of the sixth embodiment. FIG. 7 is a graph showing the content weight ratios of Pb metal and Tl metal in the alloy layer when the weight ratios of Pb metal and Tl metal as raw materials before alloying are taken as each value. FIG. 8 is a graph showing the content weight ratios of Bi metal and Tl metal in the alloy layer when the weight ratios of Bi metal and Tl metal as raw materials before alloying are taken as respective values. FIG. 9 is a diagram showing a spectrum of 137Cs gamma rays obtained by using the radiation detector of the example.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. The present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

FIG. 1 is a diagram showing a cross-sectional configuration of the radiation detector 1A of the first embodiment. The radiation detector 1A is a flat plate-shaped detector including a first electrode 10A, a second electrode 20A, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10A and the second electrode 20A. Is. Of the two parallel surfaces of the TlBr crystal 30, the first electrode 10A is formed by, for example, vapor deposition on one surface, and the second electrode 20A is formed, for example, by vapor deposition on the other surface.

The first electrode 10A has an alloy layer 12. The second electrode 20A has an alloy layer 22. The thickness of the alloy layers 12 and 22 is, for example, several tens of nm to several hundreds of nm. The alloy layers 12 and 22 are made of an alloy of thallium (Tl) metal and other metal elements. Other metal elements contained in the alloy together with the Tl metal may be arbitrary, but preferably one or more elements selected from lead (Pb), silver (Ag), bismuth (Bi) and indium (In). Is.

The alloy layers 12 and 22 are made of, for example, alloys such as Tl-Pb, Tl-Ag, Tl-Bi, Tl-In, Tl-Pb-Bi, and Tl-Pb-In. The alloy layers 12 and 22 contain Tl as a metal, and do not contain Tl only as a compound (for example, Tl oxide, Tl fluoride, Tl nitrate, etc.). The Tl metal content ratio in the alloy layers 12 and 22 is at a level at which Tl metal is detected by analysis by the fluorescent X-ray analysis (XRF) method. The surfaces of the alloy layers 12 and 22 may be oxidized by contact with air, but the inside of the alloy layers 12 and 22 is not oxidized.

One of the first electrode 10A and the second electrode 20A is used as an anode electrode, and the other is used as a cathode electrode. Since the halogenated thallium crystal exhibits ionic conductivity, when a voltage is applied to the TlBr crystal 30, Tl ⁺ ions are accumulated under the cathode electrode and Br ⁻ ions are accumulated under the anode electrode. The radiation detector 1A can detect radiation incident by the current flowing between both electrodes by moving the electron-hole pair generated by the incident radiation by the applied voltage.

^{The Br-} ions accumulated under the anode electrode combine with the Tl metal contained in the anode electrode to form TlBr, at which time electrons are emitted. ^{The Tl +} ions accumulated under the cathode electrode combine with the emitted electrons to form a Tl metal. The Tl metal and TlBr produced by these reactions are not ions and have no charge. Therefore, the polarization of the TlBr crystal 30 can be suppressed.

Since the first electrode 10A and the second electrode 20A are not electrodes made of only Tl metal but electrodes made of an alloy of Tl metal and other metal elements, corrosion in the atmosphere is suppressed and the electrodes are sealed with a resin or the like. You don't have to. Therefore, the radiation detector 1A can be mounted on the read circuit board.

The first electrode 10A and the second electrode 20A made of an alloy of Tl metal and other metal elements have stronger adhesion to TlBr crystal 30 than electrodes made only of Tl metal, and are peeled off from TlBr crystal 30 at high temperature. Is suppressed. For example, even if the radiation detector 1A becomes hot when the radiation detector 1A is mounted on the reading circuit board, the reliability of the radiation detector 1A can be ensured.

Further, in a radiation detector having an electrode made of only Tl metal, it is necessary to perform aging (an operation of changing the polarity of the voltage and alternately applying it between the electrodes) in order to stabilize the characteristics. On the other hand, a radiation detector having an electrode made of an alloy of Tl metal and another metal element does not need to perform such aging and has good energy resolution from the beginning.

FIG. 2 is a diagram showing a cross-sectional configuration of the radiation detector 1B of the second embodiment. The radiation detector 1B includes a first electrode 10B, a second electrode 20B, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10B and the second electrode 20B. Compared with the configuration of the first embodiment shown in FIG. 1, in the configuration of the second embodiment shown in FIG. 2, a low resistance metal layer 14 is formed on the surface of the alloy layer 12 in the first electrode 10B by, for example, thin film deposition. The difference is that the low resistance metal layer 24 is formed on the surface of the alloy layer 22 in the second electrode 20B by, for example, thin film deposition.

The low resistance metal layer 14 is made of a metal having a lower resistance than the alloy layer 12. The low resistance metal layer 24 is made of a metal having a lower resistance than the alloy layer 22. The low resistance metal layers 14 and 24 may be a single layer or a plurality of layers. The thickness of the low resistance metal layers 14 and 24 is, for example, several tens of nm to several hundreds of nm. The metal of the low resistance metal layers 14 and 24 may be arbitrary, but gold (Au) is preferably used. By providing a low resistance metal layer made of a low resistance metal on the surface of the alloy layer, oxidation of the surface of the alloy layer is suppressed and, for example, the resistance between the pad and the electrode on the read circuit board is reduced. be able to.

FIG. 3 is a diagram showing a cross-sectional configuration of the radiation detector 1C of the third embodiment. The radiation detector 1C includes a first electrode 10C, a second electrode 20C, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10C and the second electrode 20C. Compared with the configuration of the second embodiment shown in FIG. 2, in the configuration of the third embodiment shown in FIG. 3, the intermediate layer 13 is formed between the alloy layer 12 and the low resistance metal layer 14 in the first electrode 10C. Is different, for example, in that the intermediate layer 23 is formed between the alloy layer 22 and the low resistance metal layer 24 in the second electrode 20C, for example, by thin film deposition.

The intermediate layer 13 is inserted to increase the adhesive force between the alloy layer 12 and the low resistance metal layer 14. The intermediate layer 23 is inserted to increase the adhesive force between the alloy layer 22 and the low resistance metal layer 24. The intermediate layers 13 and 23 have conductivity. The thicknesses of the intermediate layers 13 and 23 are, for example, several nm to several hundred nm. The materials of the intermediate layers 13 and 23 may be arbitrary, but are preferably made of any one of chromium (Cr), nickel (Ni) and titanium (Ti).

FIG. 4 is a diagram showing a cross-sectional configuration of the radiation detector 1D of the fourth embodiment. The radiation detector 1D includes a first electrode 10D, a second electrode 20D, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10D and the second electrode 20D. Compared with the configuration of the first embodiment shown in FIG. 1, in the configuration of the fourth embodiment shown in FIG. 4, a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10D. The difference is that the base layer 11 is formed by, for example, thin-film deposition (resistance heating method), and the first electrode 10D is formed in the gaps of the island-shaped structure. Further, in the second electrode 20D, an underlayer 21 which is a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, thin film deposition (resistance heating method), and the second electrode 20D is formed in the gap of the island-like structure. Is different in that is formed.

FIG. 5 is a diagram showing a cross-sectional configuration of the radiation detector 1E according to the fifth embodiment. The radiation detector 1E includes a first electrode 10E, a second electrode 20E, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10E and the second electrode 20E. Compared with the configuration of the second embodiment shown in FIG. 2, in the configuration of the fifth embodiment shown in FIG. 5, a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10E. The difference is that the base layer 11 is formed by, for example, thin-film deposition (resistance heating method), and the first electrode 10E is formed in the gaps of the island-shaped structure. Further, in the second electrode 20E, an underlayer 21 which is a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, thin film deposition (resistance heating method), and the second electrode 20E is formed in the gap of the island-like structure. Is different in that is formed.

FIG. 6 is a diagram showing a cross-sectional configuration of the radiation detector 1F of the sixth embodiment. The radiation detector 1F includes a first electrode 10F, a second electrode 20F, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10F and the second electrode 20F. Compared with the configuration of the third embodiment shown in FIG. 3, in the configuration of the sixth embodiment shown in FIG. 6, a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10F. The difference is that the base layer 11 is formed by, for example, thin-film deposition (resistance heating method), and the first electrode 10F is formed in the gaps of the island-shaped structure. Further, in the second electrode 20F, an underlayer 21 which is a thin film having an island-like structure is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, thin film deposition (resistance heating method), and the second electrode 20F is formed in the gap of the island-like structure. Is different in that is formed.

In the fourth to sixth embodiments, the base layer 11 is inserted in order to increase the adhesive force between the TlBr crystal 30 and the alloy layer 12. The base layer 21 is inserted in order to increase the adhesive force between the TlBr crystal 30 and the alloy layer 22. The base layers 11 and 21 have conductivity. The thickness of the base layers 11 and 21 is, for example, several nm to several tens of nm. The material of the base layers 11 and 21 may be arbitrary, but is preferably made of any one of chromium (Cr), nickel (Ni) and titanium (Ti).

Next, an example of a method for manufacturing the radiation detector 1F of the sixth embodiment will be described. Other metal elements contained in the alloy together with the Tl metal will be described as lead (Pb).

First, a wafer of TlBr crystals is cut into an appropriate size (for example, a rectangle having a side length of about 10 to 20 mm) to obtain TlBr crystals 30, and the surface of the TlBr crystals 30 is polished. The wafer may be polished and then cut. Further, as raw materials, Tl metal and Pb element are placed in a tungsten boat at an appropriate weight ratio, ^{and the boat is heated in a vacuum chamber reduced to 10 -3} Pa or less to alloy the Tl metal and Pb element.

Using any of the metals Cr, Ni and Ti as an evaporation source, the underlayer 11 is thinly formed by vapor deposition on the polished surface of the TlBr crystal 30. Then, using the alloyed metal in the boat as an evaporation source, the alloy layer 12 is formed by vapor deposition on the base layer 11. By providing the base layer 11, the adhesive force between the TlBr crystal 30 and the alloy layer 12 can be enhanced.

After cooling the TlBr crystals 30 formed up to the alloy layer 12, the intermediate layer 13 is thinly formed on the alloy layer 12 by vapor deposition using any of Cr, Ni and Ti as an evaporation source. Then, using gold (Au) as an evaporation source, a low resistance metal layer 14 is formed on the intermediate layer 13 by vapor deposition. By providing the intermediate layer 13, the adhesive force between the alloy layer 12 and the low resistance metal layer 14 can be enhanced. With the above, the first electrode 10F is formed on one surface of the TlBr crystal 30.

After the TlBr crystal 30 on which the first electrode 10F was formed was sufficiently cooled, the underlying layer 21 and the like were similarly applied to the other polished surface of the TlBr crystal 30 facing the surface on which the first electrode 10F was formed. The alloy layer 22, the intermediate layer 23, and the low resistance metal layer 24 are sequentially formed by vapor deposition to form the second electrode 20F. The radiation detector 1F can be manufactured as described above.

By heating the TlBr crystal 30 before, before, or during the vapor deposition of the alloy layer 12, the adhesive force and electrical stability of the alloy layer 12 can be improved. Further, a method in which the Pb metal is first attached to the TlBr crystal 30 by thin-film deposition and then the Tl metal is attached by thin-film deposition, or a method in which the Tl metal is first attached to the TlBr crystal 30 by thin-film deposition and then Pb. The alloy layer 12 can also be formed by a method of forming a metal by thin film deposition.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the first electrode may be an electrode having an alloy layer made of an alloy of thallium metal and another metal element, and the second electrode may be an electrode made of only thallium metal. In this case, for example, the first electrode may be connected to the pad of the reading circuit board with the first electrode exposed, the second electrode may be directly connected to the pad of the reading circuit board, and the second electrode may be sealed with a resin or the like. As the sealing resin, for example, an epoxy resin may be used. In this case, by providing the base layer between the second electrode and the TlBr crystal, the adhesive force between the TlBr crystal and the thallium metal can be improved as in the case of the alloy layer. The first electrode may be an electrode having an alloy layer made of an alloy of tallium metal and another metal element, and the second electrode may be made of gold.

FIG. 7 is a graph showing the content weight ratios of Pb metal and Tl metal in the alloy layer when the weight ratios of Pb metal and Tl metal as raw materials before alloying are taken as each value. The weight ratios of the Pb metal and the Tl metal before alloying were (a) 80:20, (b) 60:40, (c) 40:60, and (d) 20:80.

FIG. 8 is a graph showing the content weight ratios of Bi metal and Tl metal in the alloy layer when the weight ratios of Bi metal and Tl metal as raw materials before alloying are taken as respective values. The weight ratios of Bi metal and Tl metal before alloying were (a) 80:20, (b) 60:40, (c) 40:60, and (d) 20:80.

The content-weight ratio of each metal in the alloy layers shown in FIGS. 7 and 8 was measured using a fluorescent X-ray analyzer (ZSX Primus) manufactured by Rigaku Corporation. As shown in FIGS. 7 and 8, the weight ratio of each metal in the alloy layer does not necessarily match the weight ratio of each metal as a raw material before alloying. Therefore, in order to set the content weight ratio of each metal in the alloy layer to a desired value, it is preferable to mix and alloy the raw materials before alloying at the weight ratio of each metal according to the desired value.

FIG. 9 is a diagram showing a spectrum of 137Cs gamma rays obtained by using the radiation detector of the example. FIG. 9A shows a spectrum 5 minutes after the start of operation, and FIG. 9B shows a spectrum 6 hours after the start of operation. The radiation detector used here has the configuration of the first embodiment, and the alloy layer contains Tl metal and Pb metal in a weight ratio of 60:40 and has a thickness of 100 nm. The equipment used for the spectrum measurement was a preamplifier (clear pulse 580HP), a shaping amplifier (ORTEC673) and a multi-channel analyzer (laboratory equipment 2100C / MCA). As shown in this figure, it was confirmed that the radiation detector of the present embodiment can operate continuously for 6 hours without sealing the electrodes with resin. In the radiation detector of the comparative example having an electrode made of only Tl metal, the electrode was corroded and blackened within one hour from the start of operation, and the characteristics deteriorated. As described above, the radiation detector of the present embodiment can suppress the corrosion of the electrodes in the atmosphere.

In addition, the adhesive force of the electrode to the TlBr crystal in the radiation detector was investigated. The electrode of the embodiment has the configuration of the second embodiment, and is made of gold and has a low resistance of 100 nm on a 100 nm-thick alloy layer containing a Tl metal and a Pb metal in a weight ratio of 60:40. It is provided with a metal layer. In the electrode of the comparative example, a low resistance metal layer having a thickness of 100 nm made of gold is provided on a layer having a thickness of 100 nm made of only Tl metal. The radiation detector was placed in an atmosphere at each temperature of 150 ° C., 175 ° C. and 200 ° C. for 1 minute, and the presence or absence of peeling of the electrode with respect to the TlBr crystal was examined. In the comparative example, the electrode was peeled off at a temperature of 150 ° C., whereas in the example, the electrode was not peeled off even at a temperature of 200 ° C. As described above, in the radiation detector of the present embodiment, the electrode is suppressed from peeling from the TlBr crystal at a high temperature, and the reliability can be ensured.

1A-1F ... Radiation detector, 10A-10F ... 1st electrode, 11 ... Underlayer, 12 ... Alloy layer, 13 ... Intermediate layer, 14 ... Low resistance metal layer, 20A-20F ... Second electrode, 21 ... Underlayer , 22 ... Alloy layer, 23 ... Intermediate layer, 24 ... Low resistance metal layer, 30 ... Thallium bromide crystal.

Claims (10)

A method for manufacturing a radiation detector including a first electrode, a second electrode, and a thallium bromide crystal provided between the first electrode and the second electrode.
The first step of cutting out the thallium bromide crystal from the thallium bromide crystal wafer, and
The second step of putting thallium metal and other metal elements in a boat and heating them in a vacuum chamber to alloy these thallium metals and other metal elements, and
The metal alloyed in the boat in the second step is evaporated onto the electrode forming surface on which the first electrode or the second electrode should be formed in the thallium bromide crystal cut out in the first step. A third step including an alloy layer forming step of forming an alloy layer by vapor deposition using it as a source, and
Radiation detector manufacturing method. The alloy layer contains, as the other metal element, one or more metal elements of lead, silver, bismuth and indium.
The radiation detector manufacturing method according to claim 1. The first step includes a polishing step of polishing the electrode-forming surface of the thallium bromide crystal wafer or the thallium bromide crystal.
The radiation detector manufacturing method according to claim 1 or 2. The third step includes a heating step of heating the thallium bromide crystal before, before, or during the vapor deposition of the alloy layer on the electrode forming surface of the thallium bromide crystal.
The radiation detector manufacturing method according to any one of claims 1 to 3. In the third step, after the alloy layer forming step, a low resistance metal layer is formed by depositing on the electrode forming surface of the thallium bromide crystal to form a low resistance metal layer made of a metal having a lower resistance than the alloy layer. Including the process,
The radiation detector manufacturing method according to any one of claims 1 to 4. The low resistance metal layer is made of gold.
The radiation detector manufacturing method according to any one of claims 5. The third step is an intermediate layer for forming a conductive intermediate layer by vapor deposition on the electrode forming surface of the thallium bromide crystal after the alloy layer forming step and before the low resistance metal layer forming step. Including forming process,
The radiation detector manufacturing method according to claim 5 or 6. The intermediate layer is made of any metal of chromium, nickel and titanium.
The radiation detector manufacturing method according to claim 7. The third step includes a base layer forming step of forming a conductive base layer by vapor deposition on the electrode forming surface of the thallium bromide crystal before the alloy layer forming step.
The radiation detector manufacturing method according to any one of claims 1 to 8. The underlayer is made of any metal of chromium, nickel and titanium.
The radiation detector manufacturing method according to claim 9.

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