JP3543111B2 - Superconducting image detector - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a superconducting image detector that detects an incident distribution of radiation, and more particularly to a superconducting image detector that can individually adjust a magnetic field applied to a superconducting junction element that is a detecting element.
[0002]
[Prior art]
Radiation detectors using superconductive tunnel junctions (hereinafter referred to as STJs) have better radiation resistance than conventional semiconductors, and have high energy resolution (up to several eV) despite being energy dispersive. Various elements utilizing excitation phenomena caused by irradiation of light, electrons and ions due to its characteristics such as wide measurement range (infrared, visible, X-ray, α-ray, high-energy radiation) and high counting rate (up to 10 kCPS) It is expected to be applied to precise microspectroscopy of molecules (fluorescence X-ray method, electron beam excitation X-ray method, ion beam impact X-ray method, etc.). In addition, since the detection of extremely weak photons and energy analysis can be performed simultaneously, it is planned to be mounted on artificial satellites as a high-performance eye to solve the mysteries of the universe.
[0003]
The STJ can detect excited electrons due to radiation incident on its own electrode using the tunnel effect. However, if the junction area is increased to increase the detection area, the electric capacity of the junction increases. The S / N ratio deteriorates. Therefore, the size of the joint was generally about several hundred micrometers.
[0004]
As an idea to get a large sensitive area using STJ,
1) STJ elements are arranged in an array on a two-dimensional plane to have a large area. By measuring each output waveform in these STJs, it is possible to identify the STJ on which the radiation has entered, and to detect the position and energy of the incident radiation,
2) The phonon caused by radiation excitation incident on the substrate having a large area is detected by the STJ arranged around the substrate, and the position and energy of the radiation incident on the two-dimensional plane are obtained from the waveform and time information of the detection signal at that time. A method for simultaneous detection (for example, Japanese Patent Application Laid-Open No. 8-262144) has been proposed.
[0005]
Also in the latter method, a case where an insulating material such as sapphire is used as a substrate, a case where a superconducting electrode such as Nb is formed on such a substrate, and an excitation signal due to radiation generated in this electrode is transmitted to a surrounding STJ. Methods for detecting are known. In these methods, the incident position and energy can be measured simultaneously by observing the time and intensity of the signal waveform in three or more (X, Y, and Z directions) STJs of the signal due to the incident radiation. If this is displayed three-dimensionally, an incident image having color information (energy) can be obtained.
[0006]
A conventional superconducting image detector will be described with reference to FIG. FIG. 3 shows a plane through an STJ of a superconducting image detector having a plurality of STJ detecting elements. 1a and 1b are two STJs out of a plurality of STJs, 2 and 3 are superconducting thin films, 4 is a tunnel barrier insulating thin film, 9 is infrared, visible, X-ray, α-ray, high energy A substrate that generates phonons, quasiparticles, or the like upon incidence of radiation, particle beams, or the like (collectively, radiation) Φ represents a magnetic field generated by an external magnetic field generator (not shown), for example, an electromagnet, and applied in parallel to a junction of a plurality of STJs (1a and 1b in the figure). FIG. 3B shows an example of a base electrode 3A, which also serves as the substrate side superconducting thin film 3 in FIG.
[0007]
In the conventional example shown in FIG. 1A, when the radiation 11 is incident on the substrate 9, phonons are generated on the substrate 9, and the energy of the phonons is transmitted as a lattice wave in the substrate 9. When this reaches the superconducting thin film 4 of a plurality of STJs, it excites superconducting electrons in the superconducting thin film, quasiparticles are generated in the STJ, and this current is detected by the tunnel junction. When the time difference at which the lattice wave reaches a plurality of STJs and the energy at that time are measured, the incident position and energy of the radiation 11 can be detected from these measured values.
[0008]
In the conventional example shown in FIG. 2B, the radiation 11 incident on the base electrode 3A of the superconductor excites electrons in the superconductor, and the generated quasiparticles measure the difference in arrival time between the plurality of STJs and the energy of the radiation 11 by measuring the energy. The incident position and energy of are measured. Hereinafter, the same elements are denoted by the same reference numerals, and description thereof will be omitted.
[0009]
[Problems to be solved by the invention]
A radiation detector using an STJ element operates in a very low temperature environment (up to 1K) under conditions where the Josephson current and Fiske step current of the element are suppressed. It was necessary to apply a magnetic field Φ. However, in order to obtain image information, it is necessary to arrange a plurality of STJs at spatially separated places, and it has been difficult to apply an equivalent magnetic field to all the elements.
[0010]
However, the magnetic field dependence of the STJ exposed to an external magnetic field is greatly affected by the characteristics of the STJ (current density, junction shape, leakage current), variations in element fabrication such as the incident angle of the external magnetic field, and the state of element installation. Is known to be. FIG. 4 is a diagram showing the effect (Franforfar pattern) of suppressing the Josephson current of the STJ by applying an external magnetic field Φ.
[0011]
As shown in the figure, even if an external magnetic field of 4Φ0 (actually 100Φ0) is applied to each STJ in order to reduce the Josephson current to zero, non-uniform application of the external magnetic field causes, for example, a specific STJ to be applied to a particular STJ in FIG. When a magnetic field of 5Φ0 is applied, the Josephson current rises from zero to 0.1 Ic (0). This makes the detection sensitivity different from other STJ detection elements. Further, since characteristic curves and the like are different from each other due to individual characteristics due to the manufacture of the STJ and variations in installation, the difference in the characteristics also causes the detection sensitivity of the STJ to be not uniform.
[0012]
In particular, in the method of detecting incident radiation using a plurality of STJs for extracting image information, it is difficult to obtain accurate position measurement and energy resolution if each STJ has a difference in detection performance. It is possible to increase the number of STJs to guarantee this, but it is not advisable because it complicates the processing of the detector itself and data.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has been developed on STJ on a substrate provided with a ground plane, which was filed by the present inventors in Japanese Patent Application No. 11-219286 (Japanese Patent Application No. 2000-150975). An STJ element having a structure in which a superconducting coil made of a microstrip line is directly coupled to an STJ for obtaining a detection image, and the effect of suppressing the Josephson current and the Fiske step current of each STJ is reduced. To provide a detector that measures the position and energy of the incident radiation under the best detection conditions.
[0014]
That is, according to the present invention, a plurality of superconducting tunnel junctions are integrated around a substrate or a superconducting thin film region which generates phonons or quasiparticles upon incidence of radiation, and a different microstrip coil is provided for each STJ. Is a structure integrated so as to be electromagnetically coupled on top of each other, taking out a voltage signal between each STJ, flowing a current through a microstrip line, and suppressing a Josephson current and a Fiske step of a tunnel junction. Provided is an image detector for extracting a voltage signal between tunnel junctions and detecting the radiation position and energy of radiation incident on a substrate or a superconducting thin film. The current flowing through the microstrip coil is adjusted so that the Josephson current of each STJ and the effect of suppressing the Fiske step become equal.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an embodiment of the superconducting image detector according to the present invention. In the embodiment shown in the figure, four STJs, 1a to 1d are integrated at four corners of the substrate 9 on which radiation is incident, and a superconductor magnetically coupled to each STJ via an insulator is provided above each STJ via an insulator. The figure provided with microstrip coils 10a to 10d is shown. In the figure, 5 is a bias line, 6 is a current line of a microstrip coil, 7 is a voltage detection terminal between STJs, and 8 is a connection terminal for connecting the bias line and the superconducting thin film 2. When the number of STJs is two, images can be detected in the one-dimensional x direction, when there are three STJs, in the two-dimensional xy direction, and when there are four or more STJs, the image can be detected in the three-dimensional xyz direction.
[0016]
FIG. 2 is a diagram illustrating the principle of the present invention. FIG. 1A corresponds to the embodiment of FIG. 1, and FIG. 2B is an embodiment in which the superconducting thin film 3 of FIG. 1A also serves as a superconductor base electrode 3A on the radiation incident surface. 1A and 1B show cross sections. The magnetic fields .PHI.a, .PHI.b,... Applied to the respective STJs are magnetic fields induced by the currents of the microstrip coils 10a to 10b. It is localized near the STJ and is applied in parallel with the junction of the STJ.
[0017]
The microstrip coil currents Ima, Imb, Imc, Imd (see FIG. 1) that induce the respective magnetic fields Φa, Φb,... Can be individually adjusted by devices not shown. After the image detector is created, the Josephson current of each STJ in a state where the Josephson current and the Fiske step are suppressed is measured to be zero, and in some cases, the microstrip coil current is set to a set value near zero. The same current as this measurement current is applied to each microstrip coil to maximize the sensitivity of each STJ. This makes it possible to compensate for the non-uniformity generated in the fabrication of elements such as STJs and microstrip coils, and to maximize the detection sensitivity of each STJ. Furthermore, the detection sensitivity of the STJ can be maximized even with respect to the environmental magnetic field where the detector is installed.
[0018]
【The invention's effect】
According to the present invention, it is possible to individually adjust variations in device fabrication such as STJ characteristics and an incident angle of an external magnetic field, and therefore, it is possible to improve both the detection performance and the stable operation of an image radiation detector using an STJ. This has enabled the realization of a high-performance radiation detector.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a structural diagram of the present invention.
FIG. 2 is a diagram illustrating the principle of the present invention.
FIG. 3 is a diagram illustrating the principle of a conventional image detector.
FIG. 4 is a diagram for explaining the effect of suppressing a Josephson current by applying a magnetic field.
[Explanation of symbols]
1a to 1d STJ
2, 3 Superconducting thin film 3A Base electrode 4 Tunnel barrier insulating thin film 9 Substrates 10a to 10d Microstrip coils Φ, Φa to Φb Externally applied magnetic field 11 Radiation

Claims (2)

A substrate that generates phonons upon incidence of radiation,
A plurality of superconducting tunnel junctions integrated around a region of the substrate to detect the arrival of the phonons;
A superconducting tunnel junction on each superconducting tunnel junction, and a structure in which different microstrip coils are electromagnetically coupled,
By adjusting the currents flowing through the plurality of microstrip coils, respectively, the magnetic field applied to the corresponding superconducting tunnel junction is adjusted, and the voltage signal of each superconducting tunnel junction is respectively taken out. A superconducting image detector for detecting an incident position and energy of radiation incident on a substrate based on a voltage signal of the superconducting image. A superconducting thin film that generates quasiparticles upon incidence of radiation,
A plurality of superconducting tunnel junctions that form a superconducting tunnel junction by integrating a superconducting thin film via an insulating film around a region of the superconducting thin film, and detect arrival of generated quasiparticles;
A structure in which a different microstrip coil electromagnetically coupled to the superconducting tunnel junction is integrated on each of the superconducting tunnel junctions,
By adjusting the current flowing through each of the plurality of microstrip coils, the magnetic field applied to the corresponding superconducting tunnel junction is adjusted, and the voltage signal of each superconducting tunnel junction is extracted, and the extracted voltage is extracted. A superconducting image detector for detecting an incident position and energy of incident radiation based on a signal.

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