JP2002196081A - Superconductive image detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize detection sensitivity of a superconductive tunnel junction(STJ) to improve both enhancement of detection performance and a stable operation, and to provide image detection of high performance. SOLUTION: A phonon, a quasiparticle or the like is generated by making a radiation incident into a substrate. An incident position and energy of the radiation are measured based on a propagation time difference and energy detected by plural STJs integrated in a periphery of the substrate. Micro strip coils different each other are integrated in the respective STJs to be coupled electromagnetically onto the respective STJs, and a current flowing in the each micro strip coil is regulated to unify the detection sensitivity of the each STJ in an induced magnetic field. Since a Josephson current is restrained thereby to get uniform, a dispersion on manufacturing an element such as a characteristic in the STJ and an incident angle of an external magnetic field is regulated individually.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting image detector for detecting an incident distribution of radiation, and more particularly to a superconducting image detector capable of individually adjusting a magnetic field applied to a superconducting junction element as a detecting element.

[0002]

2. Description of the Related Art Superconducting tunnel junctions (hereinafter, STJ, Su)
Radiation detectors using perconductive tunnel junctions have better radiation resistance than conventional semiconductors, are energy dispersive, have high energy resolution (up to several eV), and have a wide measurement range (infrared, visible, X-ray, α
Line, high energy radiation) and high counting rate (~ 10kCP)
S), etc., so that precise trace spectroscopy analysis of various elements and molecules using excitation phenomena by irradiation of light, electrons and ions (fluorescence X-ray method, electron beam excitation X-ray method, ion beam impact X-ray Application) is expected. 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 the excited electrons due to the radiation incident on its own electrode by utilizing the tunnel effect. However, if the junction area is increased to increase the detection area, the electric capacity of the junction increases. S
/ N ratio deteriorates. Therefore, the size of the joint is generally about several hundred micrometers.

[0004] As an idea for obtaining a large sensitive area using an STJ, 1) STJ elements are arranged in an array on a two-dimensional plane to have a large area. By measuring the output waveforms of these STJs, it is possible to identify the STJ on which the radiation is incident, to detect the position and energy of the incident radiation, and 2) to detect the phonon by radiation excitation incident on a wide area substrate. A method of simultaneously detecting the position and energy of radiation incident on a two-dimensional plane from a waveform of a detection signal and time information at that time, which is detected by an STJ arranged in the surrounding area (for example, Japanese Patent Application Laid-Open No. 8-262144). Has been proposed.

In the latter method, the case where an insulating material such as sapphire is used as a substrate and the case where Nb
A method is known in which a superconducting electrode such as that described above is formed, and an excitation signal due to radiation generated in the electrode is detected by surrounding STJs. In these methods, the incident position and the 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.

Referring to FIG. 3, a conventional superconducting image detector will be described. FIG. 3 shows a plane through the STJ of a superconducting image detector having a plurality of STJ detecting elements. 1a,
1b is two STJs among a plurality of STJs, 2 and 3 are superconducting thin films, 4 is a tunnel barrier insulating thin film, 9
Denotes a substrate that generates phonons or quasiparticles upon incidence of infrared rays, visible rays, X-rays, α-rays, high-energy radiation, particle beams, and the like (collectively referred to as 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, 1b in the figure). FIG. 3B shows a base electrode 3A, which also serves as the substrate-side superconducting thin film 3 in FIG.

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 propagates in the substrate 9 as lattice waves. When this reaches a plurality of STJ superconducting thin films 4,
The superconducting electrons in the superconducting thin film are excited to generate quasiparticles 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.

In the conventional example shown in FIG. 1B, radiation 11 incident on the base electrode 3A of the superconductor excites electrons in the superconductor, and the generated quasiparticles measure the time difference between arrival at a plurality of STJs and the energy. To measure the incident position and energy of the radiation 11. Hereinafter, the same elements are denoted by the same reference numerals, and description thereof will be omitted.

[0009]

The radiation detector using the STJ element operates under the condition that the Josephson current and the Fiske step current of the element are suppressed in an extremely low temperature environment (up to 1K). High strength (100 Gauss)
It was necessary to apply a uniform parallel 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.

However, the magnetic field dependence of the STJ exposed to an external magnetic field depends on the characteristics of the STJ (current density, junction shape, leakage current), the variation in the fabrication of the element such as the incident angle of the external magnetic field, and the installation state of the element. It is known to be greatly affected by Fig. 4 shows STJ by applying external magnetic field Φ.
FIG. 4 is a diagram showing an effect (Franforfar pattern) of suppressing the Josephson current of FIG.

As shown in FIG. 1, 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 specific STJ. When a magnetic field of 3.5Φ0 is applied, the Josephson current rises from zero to 0.1 Ic (0). This makes the detection sensitivity different from other STJ detection elements. In addition, 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 characteristics also causes the detection sensitivity of the STJ to be not uniform.

In particular, in the incident radiation detection method using a plurality of STJs for extracting image information, it is difficult to obtain accurate position measurement and energy resolution if there is a difference in detection performance between the respective STJs. I was 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]

In order to solve the above-mentioned problems, the present invention has been proposed by the present inventors in Japanese Patent Application No. 11-21928.
An image is obtained by detecting an STJ element having a structure in which a superconducting coil formed by a microstrip line is directly coupled to an STJ on a substrate provided with a ground plane, which was filed in Japanese Patent Application No. 6 (JP-A-2000-150975). Detector that adjusts the Josephson current and Fiske step current suppression effect of each STJ in each STJ, and measures the position and energy of incident radiation under the best detection conditions I will provide a.

That is, according to the present invention, a plurality of superconducting tunnel junctions are integrated around an area of a substrate or a superconducting thin film which generates phonons or quasiparticles by the incidence of radiation, and different microstrip coils are provided for each STJ. Is a structure integrated so as to be electromagnetically coupled on each STJ, extracting a voltage signal between each STJ,
A current is passed through the microstrip line to extract the voltage signal between the tunnel junctions while suppressing the Josephson current and Fiske step of the tunnel junctions, and image the radiation position and energy of radiation incident on the substrate or superconducting thin film. Provide an image detector. 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]

FIG. 1 shows an embodiment of a 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 a 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. Microstrip coil 10a
10 to 10d are shown. In the figure, 5 is a bias line, 6 is a microstrip coil current line, 7 is S
A terminal for voltage detection between TJ and 8 is a connection terminal for connecting the bias line and the superconducting thin film 2. When the number of STJs is two, the dimension is one-dimensional x-direction.
When the number is more than three, image detection in three-dimensional xyz directions can be performed.

FIG. 2 is a diagram for explaining 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 the superconductor base electrode 3A on the radiation incident surface. 1A and 1B show cross sections. Magnetic fields Φa, Φ applied to each STJ
b,... indicate the respective microstrip coils 10a to 10
This is a magnetic field induced by the current b. This magnetic field is applied to the superconductor layer opposite to each other by flowing a mirror current to localize each magnetic field near each STJ and in parallel with the junction of the STJs.

The microstrip coil currents Ima, Imb, Imc, I that induce the respective magnetic fields Φa, Φb,.
The md (see FIG. 1) can be individually adjusted with a device not shown. After the image detector is created, the Josephson current of each STJ in the 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 passed through each microstrip coil, and each S
Maximize TJ sensitivity. This makes it possible to compensate for non-uniformity caused by 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]

According to the present invention, it is possible to individually adjust variations in the fabrication of elements such as the characteristics of the STJ and the angle of incidence of an external magnetic field, so that the detection performance of the image radiation detector using the STJ can be improved and stable operation can be achieved. In both cases, improvements could be achieved, and a high-performance radiation detector could be realized.

[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 illustrating 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 Substrate 10a to 10d Microstrip coil Φ, Φa to Φb Externally applied magnetic field 11 Radiation

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Ako 1-1-4, Umezono, Tsukuba, Ibaraki Pref. Electronic Technology Research Institute (72) Inventor Kyosuke Maehata 6-10- Hakozaki, Higashi-ku, Fukuoka, Fukuoka 1 Kyushu University Faculty of Engineering (72) Inventor Kenji Ishibashi 6-10-1 Hakozaki, Higashi-ku, Fukuoka City, Fukuoka Prefecture (72) Inventor Toru Taino 6-10-1 Hakozaki, Higashi-ku, Fukuoka City, Fukuoka Kyushu Univ. Faculty of Engineering F-term (reference) 2G065 AA04 AA18 AB02 AB04 BA31 BA34 2G088 FF02 FF06 FF14 FF15 GG22 JJ05 JJ09 4M113 AA01 AC24 AC30 AD51

Claims (2)

[Claims] A plurality of superconducting tunnel junctions are integrated around an area of a substrate or a superconducting thin film which generates phonons or quasiparticles upon incidence of radiation, and a different microstrip coil is provided for each superconducting tunnel junction. A structure integrated so as to be electromagnetically coupled on a superconducting tunnel junction. A voltage signal between each superconducting tunnel junction is taken out, and an incident position and energy of radiation incident on a substrate or a superconducting thin film are determined. A superconducting image detector characterized by detecting. 2. The superconducting image detector according to claim 1, wherein a magnetic field applied to each superconducting tunnel junction is adjusted by adjusting a current flowing through the microstrip coil.