JPH0629585A - Superconducting radiation detector - Google Patents

Abstract

PURPOSE:To enhance resistance against a thermal cycle and to improve a detecting accuracy by forming upper and lower electrodes made of superconductors of tantalum in a superconducting radiation detector in which the upper and lower electrodes are formed through a barrier layer. CONSTITUTION:A lower electrode pattern 2 is formed on a board 1, an insulating film 3 having openings 3a, 3b exposed with the pattern 2 is formed thereon, and a barrier layer 4 to be formed by thermal oxidation is provided on the pattern 2 in the opening 3a. An upper electrode pattern 5 isolated by an opening 5a to be used also as lead wiring is formed on the layer 4 in the opening 3a and the pattern in the opening 3b, and a Josephson junction is formed of the patterns 2, 5 and the layer 4. In such a superconducting radiation detector, the patterns 2, 5 are formed of tantalum thereby to obtain excellent thermal cycle resistance and energy resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting radiation detector, and more particularly to a superconducting radiation detector for irradiating an object to be measured with radiation such as X-rays and measuring characteristic X-rays emitted from the object to be measured. The present invention relates to a superconducting radiation detector that can be applied to a conduction radiation detector and the like, and in particular can be made strong against a thermal cycle and can have good energy resolution and detection accuracy.

In recent years, the most typical application example of radiation such as X-rays, γ-rays and α-rays is utilization of synchrotron radiation. This synchrotron radiation emits an electromagnetic wave having a very directional tangential direction when an electron moving at a speed close to the speed of light emitted from a circular accelerator bends its orbit by a magnetic field. Moreover, wavelength continuity,
The synchrotron radiation having excellent characteristics such as the deflecting property and the pulse property can be applied to various technologies in various fields as shown in the application example of the synchrotron radiation of FIG. Furthermore, not only synchrotron radiation but also ordinary X-rays are widely used for medical treatment and physical property analysis.

Various types of radiation detectors used in such fields, such as characteristics and shapes, are used according to the application. In many cases, the excellent radiation energy detection results in excellent radiation resolution. Has become an important element for the vessel. This is a very important factor because it means that the radiation detector has high detection accuracy. Thus, as a detector with high energy resolution, Si
A semiconductor detector using Ge or Ge is known. The resolution of these detectors is approaching the limit due to statistical fluctuations in the number of electron-hole pairs created in the detector by radiation. Further, in the above-mentioned application fields, more severe detection accuracy is required, and Si and G are accompanied by this.
The advent of detectors with higher energy resolution than semiconductor detectors using e, etc. has been earnestly desired.
There is a need for a new principle-based detector with a smaller resolution limit due to statistical fluctuations.

In recent years, attention has been paid to a superconducting radiation detector using a superconductor, which has a remarkably superior energy resolution than that of a semiconductor detector such as Si or Ge. Hereinafter, this will be specifically described. First, the principle of the superconducting radiation detector will be described. When energy (E) radiation is incident on the radiation detector, many valence electron pairs are generated and collected as signals. The relative resolution P caused by the fluctuation of the number N of generated valence pairs is expressed by the following equation (1). This has been reported in, for example, energy dispersive X-ray analysis; Yoichi Koshi, Kimitaka Sato, The Spectroscopy Society of Japan Series of Measurement Methods, Academic Society Publishing Center.

[0005]

[Equation 1]

Here, ε is the minimum energy required to excite one electron by radiation, and F is called the Fano factor, and the excitation defined by <(N- <N>) ² > / <N> To the extent that the fluctuation of the number of electrons is smaller than the fluctuation of Poisson distribution, E represents the energy of radiation. If the Poisson distribution is followed, F = 1; otherwise, F <1. From this, it can be seen that how to increase the number N of valence electron pairs with respect to the incident radiation or finding a material having a small ε value is a factor for improving the energy resolution of the radiation detector. Then, if the energy gap Eg of the material forming the detector is small, it can be said that the valence pair can be generated with a small ε value.
However, in the case of a semiconductor detector, the fact that the minimum energy ε value required to excite one electron is small in proportion to the small energy gap Eg value does not apply. Known to be. About this, for example, CA Klein, J. Appl. Phy
As reported in s.39,2090 (1968), the minimum energy required to excite one electron is expressed by the following equation (2).

[0007]

[Equation 2]

That is, no matter how small the energy gap Eg value is, the minimum energy ε value required to excite one electron is not less than several hundred meV, and the number of collected electrons is limited by this. Shows. Therefore, in a semiconductor, a valence electron cannot be excited with a phonon of several tens of meV as the maximum energy emitted.

By the way, in the case of a superconductor, since the energy gap is as small as a few meV, other than the incident radiation, the emitted phonons also destroy other electron pairs from the electron pairs destroyed by the radiation. Then, quasi-particles can be generated, that is, the number of valence pairs N can be increased, and a detector with high energy resolution can be produced. Computer simulation of the cascade excitation process of quasiparticles and phonons, which consists of direct excitation of electrons by radiation, phonon emission by quasiparticles, and quasiparticle generation by phonons in superconductors, is three orders of magnitude higher than that of semiconductors. A large number of quasiparticles are generated and ε = 0.6
The values of 96 meV and F = 0.2 are obtained from theoretical studies. About this, for example M.Kurakado and H.Ma
zaki, Phys. Rev. B22 (1980) 168. In the Sn / SnOx / Sn junction experiment described later, ε = 2.
4 meV is obtained. About this, for example MK
urakado, Nucl. Nucl. Instrum & Methods 196, 275 (19
82). Here, the relationship between the energy resolution and the incident energy when assuming theoretical values for Case 1 and experimental values of ε and F = 1 for Case 2 is shown in FIG.
Shown in. In FIG. 7, ε = 3.76e of Si semiconductor, which is the semiconductor detector with the best energy resolution at present, is shown in FIG.
The relationship of energy resolution obtained by substituting V and F = 0.08 (both are experimental values) is also shown for comparison. Josephson is a detector that has about 10 times better energy resolution than semiconductors. It shows what can be achieved by joining.

Next, FIG. 8 shows a tunnel process in a Josephson structure composed of a superconductor / insulator / superconductor when irradiated with radiation. In FIG. 8, since the voltage (V _B ) is applied, the band of the superconductor on one side is eV _B.
It shows the state of rising. When radiation is incident on the superconductor on one side, electron pairs are destroyed and quasi-particles are generated. The generation of these quasiparticles is due to direct excitation of radiation or excitation by phonons, and these quasiparticles tunnel through the insulator. The improvement of energy resolution depends on how efficiently the generated quasiparticles tunnel the barrier (insulator). This phenomenon is essentially a non-equilibrium state, and how efficiently tunneling is primarily determined by the relationship between the quasiparticle tunneling time and the quasiparticle recombination time with phonon emission. It will be. These values differ greatly depending on the superconducting material, and this effect will be described later. Furthermore, in order to minimize the influence of thermally excited quasiparticles, it is considered necessary to make the measurement at a low temperature (<4.2K>).

Next, FIG. 9 shows the current-voltage characteristics when the Josephson junction is irradiated with radiation. That is, when the voltage V _B is smaller than the value 2Δ / e corresponding to the gap energy 2Δ, only the quasi-particles excited on the energy gap and their vacancies contribute to the current. If the voltage V _B applied to the junction is kept constant (constant voltage method), a current change ΔI occurs, while if the current I _B passed to the junction is kept constant (constant current method, voltage change ΔV is Occurs,
These can be taken out as signals. Any change is an amount proportional to the incident energy.

[0012]

2. Description of the Related Art As described above, it has been shown that the radiation detector has a performance that exceeds that of a semiconductor detector. Next, the development status of the conventional superconducting radiation detector will be described. The experiment of injecting the radiation into the joint was carried out by Wood et al. About 20 years ago. For example, CH Wood and BL Whi
te, Appl. Phys. Lett. 15 (1969) 237. The bonding material was Sn / SnOx / Sn, and the signal due to α-ray incidence was in a level that could be discriminated. Then the same S
Kurakado using n / SnOx / Sn junction
A series of experiments, etc. were carried out vigorously. About this, for example, M. Kurakado, S. Tachi, R. Katano and H. M
azaki, Bull, Inst. Chem Res. 59 (Kyoto Univ. 1981) 1
06; M.Kurakado and H.Mazaki, Nucl.Instrum & Methods
185, 141 (1981); M. Kurakado and H. Mazaki, Nucl. Inst
rum & Methods 185, 149 (1981); M.Kurakado, J. App
l. Phys. 55 (1984) 3185. Here, they show that the generation of excess quasiparticles by radiation is essential for the signal generation from the junction, rather than the signal due to radiation incidence merely due to the temperature rise.

Then, the neutrino mass determination and the solar
Measurement of energy distribution in eutrinos, dark matter and magnetic monopoles
Related to astrophysics and particle physics such as child detection
Then, research and development of superconducting radiation detectors were conducted all over the world.
It's starting. 1986 Kuraus et al. And Tswelle
Separately for Twerenbold, etc. ⁵⁵Mnk from Fe
X-ray detection of α and Mnkβ was successful. The former Claus, etc.
For example, see H. Kraus, Th. Peterrins, F. Pro.
bst, F. V. Feilitzsch, R. L. Moessbauer, V. Zacek a
Reported in nd B. Umlauf, Europhys. Lett. 1 (1986) 161.
As for the latter Twelenbold etc.,
For example D. Twerenbold. Burophys. Lett, 1 (1986) 209 in
It has been reported. The bonding material here is Sn / SnOx /
Sn is the measured temperature in order to eliminate thermal effects as much as possible.
The degree is 0.3K. Here, in Fig. 10, elements such as Claus
The structure and the obtained pulse height spectrum are shown in Fig. 11.
The element structure such as Nambold and the wave height spectrum are shown. Twe
According to the results of Lembold et al., The incident X-ray of 5.9 KeV was
The full width at half maximum is 90 eV.
It is 65 eV when the effect of gee diffusion is removed,
The full width at half maximum excluding the spread due to
You're getting value. After that, reduce the wiring width to 4 μm.
, And the realization of the wave height spectrum of Rossmund, etc.
As shown in the test results, 48e for 5.9 KeV X-rays
V, which is the full width at half maximum when the spread due to noise is removed
Has obtained a value of 37 eV. About this,
W. Rothmund and A. Zehnderp Superconductive Parti
cle Detectors, edited by A. Barone (Worid Scjentifi
c, Singapore).

[0014]

As described above, it has been proved that the conventional superconducting radiation detector is superior in energy resolution to the semiconductor detector and is superior in performance such as detection accuracy. Is still an order of magnitude larger than the theoretical energy resolution value of 2.5 eV expected from the Sn energy gap value, and it is considered that there is room for improvement in terms of the device structure. Further, Sn has a fatal defect that it is weak in a thermal cycle between room temperature and helium temperature, and easily deteriorates even at room temperature.

Therefore, development by bonding using a material resistant to heat cycle is being carried out. For example, as shown in FIG. 13, Barone et al. Uses a Pb / NbOx / Nb junction in which Nb, which is resistant to thermal cycles, is used as a lower electrode in the device structure. About this, for example A. Barone, G.
Darbo, S. De. Stefano, G. Gallinasro, G. Gallinar
o, A. Siri, R. Vaglio and S. Vitale, Nucl. Instru
m & Methods, A234 (1985) 61; A. Barone, S. De. Stefa
no, and KB Gray, Nucl. Instrum & Methods.A235 (1
985) 254. As shown in FIG. 13, it was shown that the wave height spectrum becomes sharper by narrowing the wiring width.

Nb / A, which has a proven record in digital applications
Attempts are also being made to use an lOx-Al / Nb junction for the detector. About this, for example M. Kurakado and A.
Matsumura, JJ Appl, Phys. 28 (1989) L459 and K. Ish
ibashi, K. Takano, Y. Oae, T. Sakae, Y. MATSUMOTO,
A. Katase, S. Takada, H. Ako h and H. Nakagawa, IEE
E Trans. Magn, MAG-25 (1989) 1354 or P. Gar
e, R. Engelhardt, A. Peacock, D. Twerenbold, J. Luml
ey and RE Somekh, Applied Superconductivity Con
It was reported in ference (1988). However, the performance obtained in these experiments is not as good as that of the Sn / SnOx / Sn junction. K to improve performance
Urakado et al. obtains a half value width of 160 eV with respect to 5.9 KeV X-ray incidence by single-crystallizing the lower electrode Nb. This is reported in, for example, Masahiko Kuramato, Tohru Takahashi, Atsushi Matsumura, IEICE Technical Report SCB90-19 pp7.

As described above, the Nb-based superconducting radiation detector has the advantage that it can be made stronger against thermal cycles than the Sn-based superconducting radiation detector, but has an energy resolution higher than that of the Sn-based system. Was 250 eV, which is worse than 150 eV of Si semiconductor, and there was a problem in terms of detection accuracy. Therefore, it is an object of the present invention to provide a superconducting radiation detector that can be strengthened in a thermal cycle and that can have good energy resolution and good detection accuracy.

[0018]

In order to achieve the above object, a superconducting radiation detector according to the present invention has a lower electrode made of a superconductor, a barrier layer formed on the lower electrode, and a barrier layer on the barrier layer. In a superconducting radiation detector having a Josephson junction structure composed of an upper electrode made of a superconductor formed in the above, the lower and upper electrodes are made of tantalum.

In the present invention, the barrier layer may be made of a tantalum oxide film, and the formation method is not a deposition method but a heat treatment of Ta of the lower electrode. preferable. With deposition methods such as evaporation,
In the current process, it is extremely difficult to uniformly form a barrier layer with a thickness less than the required thickness (20 Å or less) so that a current path does not occur. By appropriately adjusting the above, it is possible to form a film having a uniform film thickness and a film thickness required for the barrier layer or less without generating a current path.

In the present invention, the barrier layer may be formed of a two-layer film including a metal thin film and an oxide film of the metal which substantially functions as a barrier and is formed on the metal thin film, The metal may be any one of aluminum, zirconium, and hafnium. In the three modes, AlOx-Al and ZrO are included.
x-Zr and HfOx-Hf are mentioned. As a forming method, a metal thin film is formed as thin and uniform as possible on the Ta lower electrode by a deposition method such as a vapor deposition method, and for the same reason as in the case of TaOx, an oxide film of the metal is formed by heat treatment instead of the deposition method. Good. According to the configuration of these three aspects,
The barrier properties can be made better than in the case of the TaOx barrier layer. The TaOx is an insulating Ta ₂
It is composed of a mixture of O ₅ , conductive TaO, etc., and its structure contains a conductive oxide, whereas AlOx.
Is composed of a mixture of Al (OH) ₃ , Al ₂ O ₃ , AlO (OH), ZrOx is composed of ZrO ₂ , and its hydrate (ZrO ₂ .nH ₂ O), and HfOx is Hf.
Consists of O ₂ and its hydrate (HfO ₂ · nH ₂ O), etc., each of which is composed of an insulating oxide, and contains a structure / substance such as a conductive oxide that causes a current path. Therefore, the barrier property is better than that of TaOx containing a conductive oxide. Of the three types of barrier layers, the former AlOx-Al is the latter two ZrOx-Z.
r and HfOx-Hf are preferable in terms of process controllability, and the latter two ZrOx-Zr and HfOx-Hf are preferable in terms of barrier heat resistance than the former AlOx-Al. Further, it is preferable that the metal film of Al, Zr, Hf or the like has a film thickness of 1 nm or more and 50 nm or less. It is preferable that the thickness of the metal film is 1 nm or more. If the metal film is formed thinner than 1 nm by a deposition method such as vapor deposition, it is difficult to form a uniform film in the current process, and a current path portion is generated. This is because it is not preferable, and the thickness of the metal film is preferably 50 nm. When the metal film is formed to have a thickness of more than 50 nm, the normal-conducting portion unnecessary for the Josephson junction is extremely increased and the proximity effect is remarkably generated. This is not preferable because the barrier properties deteriorate.

[0021]

As described above, this superconducting radiation detector utilizes the non-equilibrium superconducting phenomenon, and in order to achieve high performance, incident radiation and the quasiparticles excited by the accompanying phonons are It depends on how to efficiently tunnel the barrier without loss on the way. We focused on the fact that the lifetime of quasiparticles and phonons of superconductors are important factors for efficiently tunneling excited quasiparticles through a barrier.

Conventionally, the high-performance result is obtained in the case of Sn / SnOx / Sn junction, and the result is still insufficient in the thermally stable Nb system such as thermal cycle. Showed that there is no. The reason for this was considered to be that the excited quasiparticles are essentially different in the rate of tunneling through the barrier efficiently, that is, without recombination. We thought that a material with a large quasi-particle recombination time would be suitable for this device. Therefore, the recombination time of typical materials was investigated. The result is shown in FIG. This has been reported in, for example, Isei Iguchi, Journal of the Physical Society of Japan, Vol. 35, No. 4, PP314. However, this result is the value in the thermal equilibrium state, and it is unknown whether this value is held even in the actual non-equilibrium state. So-called soft metals such as Al, Sn, and Pb have a long quasi-particle recombination time. On the other hand, Nb is smaller than Sn by one digit or more. Furthermore, it was considered that phonon generation can be performed more efficiently with a longer phonon lifetime. Also in this respect, Nb is two orders of magnitude smaller than Sn. It can be said that Sn and Pb are preferable materials as the material for the radiation detector unless it is considered that they do not have thermal cycle resistance.

By the way, Ta (superconducting transition temperature 4.5
K) has a phonon lifetime slightly smaller than that of Sn, but has a quasi-particle lifetime of about the same value as Sn, and is therefore expected to have excellent energy resolution. At the same time, it has a high melting point like Nb. It is expected that it may have excellent heat cycle resistance. Therefore, in the present invention, when Ta, which is thermally stable and has a long quasi-particle relaxation time, is used for the junction electrode in the present invention, higher resolution can be obtained than in the case of the conventional Nb system. You can Moreover, since it is composed of a thermally stable Ta electrode, the conventional S
Better results were obtained for thermal cycling than for the n-system.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 2 is a sectional view showing a structure of a Josephson junction in a superconducting radiation detector according to Embodiment 1 of the present invention. In FIG. 2, 1 is a substrate such as Si,
Reference numeral ₂ is a lower electrode pattern made of Ta formed on the substrate 1, and 3 is an insulating film such as SiO ₂ having openings 3a and 3b where the Ta lower electrode pattern 2 is exposed. Reference numeral 4 denotes a barrier layer made of TaOx formed by thermally oxidizing the Ta lower electrode pattern 2 in the opening 3a,
Reference numeral 5 denotes an upper electrode pattern formed also on the barrier layer 4 in the opening 3a and on the lower electrode pattern 2 in the opening 3b and also serving as a lead wiring. The upper electrode pattern 5 is separated by the opening 5a. And the current flows through the opening 5a.
The upper electrode pattern 5 on the right side → the barrier layer 4 → the lower electrode pattern 2 → the opening 5a flows in the order of the upper electrode pattern 5 on the left side. The Josephson junction is composed of the Ta upper electrode pattern 5, the TaOx barrier layer 4, and the Ta lower electrode pattern 2.

Next, FIG. 3 is a diagram for explaining a method of manufacturing the Josephson junction in the superconducting radiation detector according to the first embodiment of the present invention. 3, the same reference numerals as those in FIG. 2 indicate the same or corresponding portions, and 2a is a lower electrode T
a film. Next, a method of manufacturing the Josephson junction will be described. First, as shown in FIG.
A Ta film 2 having a thickness of about 200 nm is deposited on the substrate 1 as a lower electrode for bonding by sputtering. The film forming conditions at this time are A
The r pressure is 1.3 Pa, the applied current of DC magnetron sputtering is 2.0 A, and the applied voltage is 300 V.

Next, as shown in FIG. 3B, a resist mask is formed by performing a resist patterning by a photoresist process so that a region corresponding to the lower electrode remains, and then CF ₄ is used by using this resist mask. The Ta film 2a is etched by reactive etching (RIE) using + 5% O ₂ gas to form the lower electrode pattern 2. The etching conditions at this time were applied power of 50 W and pressure of 8 Pa.
And Then, after removing the resist mask, SiO ₂ is deposited on the entire surface by sputtering to form an insulating film 3 having a thickness of about 400 nm. The film-forming conditions at this time are applied power of 900
W and Ar pressure is 1.3 Pa.

Next, as shown in FIG. 3 (c), resist patterning is performed by a photoresist process so as to leave the region other than the region corresponding to the barrier layer to form a resist mask, and this resist mask is used. CHF ₃
The insulating film 3 is etched by RIE using + 30% O ₂ gas to form an opening 3a in which the lower electrode pattern 2 is exposed. At this time, the joint area is determined. The etching conditions at this time are an applied power of 100 W and a pressure of 2 Pa.

Then, the resist mask is left as it is,
The opening 3a is formed by anodic oxidation using a 0.1% citric acid aqueous solution.
The Ta lower electrode pattern 2 portion exposed inside is oxidized to form a barrier layer 4 of a junction made of TaOx. Then, the resist mask is removed. Next, as shown in FIG. 3D, the contact portion is perforated by the same process as when the opening 3a is formed to expose the lower electrode pattern 2 which is separated from the opening 3a. To form.

Next, Ta, which serves as an upper electrode that also serves as an extraction wiring layer, is deposited in a thickness of 400 nm to form a Ta film. The film forming conditions are the same as those for the Ta film 2a which will be the lower electrode. Then, an upper electrode pattern 5 having an opening 5a for etching and separating the Ta film is formed by reactive etching (RIE) using CF ₄ + 5% O ₂ gas, thereby forming the upper electrode pattern 5. A device having a Josephson junction composed of the Ta upper electrode pattern 5, the TaOx barrier layer 4, and the Ta lower electrode pattern 2 as shown in (3) can be obtained.

Ta lower electrode pattern 2, Ta of this embodiment
A detector having a junction composed of the Ox barrier layer 4 and the Ta upper electrode pattern 5 has an energy resolution of 60 eV.
Then, it was possible to improve it to 250 eV in the case of the conventional Nb system. In the case of the conventional Sn / SnOx / S junction, the element deterioration was caused by the thermal cycle of room temperature and helium temperature, but in the present example, it was possible to prevent the deterioration.

In the examples, the case where the TaOx barrier layer 4 is formed by forming the Ta lower electrode pattern 2 by anodic oxidation has been described, but the present invention is not limited to this and, for example, RF in an oxygen gas atmosphere. It may be formed by oxidation, thermal oxidation, or the like. (Embodiment 2) Next, FIG. 4 is a sectional view showing the structure of a Josephson junction in a superconducting radiation detector according to Embodiment 2 of the present invention. In FIG. 4, 11 is a substrate such as Si, 12 is a lower electrode pattern made of Ta formed on the substrate 11, 13a is an Al film pattern formed on the lower electrode pattern 12, and 13b is AlOx film pattern
13B is an AlOx film pattern formed on 13b, where 13 is A
Al that substantially functions as a barrier with the film pattern 13a
This is a barrier layer composed of the Ox film pattern 13b. Next, 14 is an upper electrode pattern made of Ta formed on the barrier layer 13, and 15 has an opening 15a where the Ta upper electrode pattern 14 is exposed and an opening 15b where the Ta lower electrode pattern 12 is exposed. It is an insulating film such as SiO ₂ . 16 is a T formed on the Ta upper electrode pattern 14 in the opening 15a and the Ta lower electrode pattern 12 in the opening 15b.
The lead-out wiring layer pattern 16 is composed of a. The lead-out wiring layer pattern 16 is separated by the opening 16a, and the current flows through the lead-out wiring layer pattern 16 on the right side of the opening 16a.
→ Upper electrode pattern 14 → Lower electrode pattern 12 → Opening 15
b The flow of the lead wiring layer pattern 16 on the left side flows. The Josephson junction is the Ta upper electrode pattern.
14, a barrier layer 13 including an Al film pattern 13a and an AlOx film pattern 13b, and a Ta lower electrode pattern 12.

Next, FIG. 5 is a diagram for explaining a method of manufacturing a Josephson junction in a superconducting radiation detector according to the second embodiment of the present invention. 5, the same reference numerals as those in FIG. 4 indicate the same or corresponding portions, and 12a is a lower electrode T
a film, 13c and 13d are an Al film and an AlOx film, respectively, and 14a is a Ta film. Next, a method of manufacturing the Josephson junction will be described.

First, as shown in FIG. 5C, a Si substrate
11 / Ta / AlOx-A continuously without breaking vacuum
1 / Ta is deposited to form a Ta film 12a having a film thickness of 200 nm, an Al film 13c having a film thickness of 6 nm, an AlOx film 13d having a film thickness of 1 nm, and a Ta film 14a having a film thickness of 200 nm. Ta is the same film forming condition as in Example 1. Al is formed by DC magnetron sputtering, Ar pressure is 1.3 Pa, applied current is 0.3 A, and applied voltage is 270 V.
AlOx is formed by introducing O ₂ gas and oxidizing the Al surface. Next, resist patterning is performed by a photoresist process so that a region corresponding to the bonded portion remains, and a resist mask is formed. Then, using this resist mask, Ta film 14 is formed by RIE using CF ₄ + 5% O ₂ gas.
The upper electrode pattern 14 is formed by etching a. At this time, AlOx 13d is not etched. Then A
AlOx 13d and Al film 13c are etched by r etching to form AlOx film pattern 13b and Al film pattern
13a is formed. At this time, the barrier layer 13 including the AlOx film pattern 13b and the Al film pattern 13a is formed to determine the junction area. Then, the resist mask is removed.

Next, as shown in FIG. 5C, a resist mask is formed by a photoresist process so that a region corresponding to the lower electrode remains, and then a resist mask is used to form CF ₄ +5. The lower electrode pattern 12 is formed by etching the Ta film 12a by RIE using% O ₂ gas. Next, as shown in FIG. 5D, SiO ₂ is deposited on the entire surface by sputtering to obtain a film thickness of 400 n.
m insulating film 15 is formed. The film forming conditions at this time are as in Example 1.
It is the same as the case of SiO ₂ .

Next, as shown in FIG. 5E, the insulating film 15 is etched by a photoresist process and RIE to form an opening 15a exposing the upper electrode pattern 14, and the lower electrode pattern 12 is formed. The exposed opening
Form 15b. Then, a Ta film having a thickness of 600 nm is formed on the entire surface.
And then Ta is etched by a photoresist process and RIE or the like to form a lead wiring layer pattern 16 having an opening 16a for separation, thereby forming Ta as shown in FIGS. 4 and 5 (f). Upper electrode pattern 1
4. A device having a Josephson junction composed of the barrier layer 13 composed of the Al film pattern 13a and the AlOx film pattern 13b and the Ta lower electrode pattern 12 can be obtained.

Ta lower electrode pattern 12, Al of this embodiment
A detector having a junction composed of the barrier layer 13 composed of the film pattern 13a and the AlOx film pattern 13b and the Ta upper electrode pattern 14 can have an energy resolution of 60 eV, which is better than 250 eV in the case of the conventional Nb system. It was In the case of the conventional Sn / SnO / S junction, the element deterioration was caused by the thermal cycle of the room temperature and the helium temperature, but in the present example, it was possible to prevent the deterioration.

In the second embodiment, the lead wiring layer is made of T.
Although the case where a is used has been described, Nb, NbN or the like other than Ta may be used. Further, in Example 1, TaOx was used for the barrier layer 4, and in Example 2, AOx was used for the barrier layer.
Although the case of using lOx-Al has been described, the present invention is not limited to this, and for example, ZrOx-Zr or HfOx-Hf having excellent heat resistance of the barrier may be used.

[0038]

EFFECTS OF THE INVENTION According to the present invention, it is possible to strengthen the thermal cycle and to exhibit high resolution, high sensitivity and high speed response.

[Brief description of drawings]

FIG. 1 is a diagram showing lifetimes of quasiparticles and phonons of a typical superconductor for explaining the principle of the present invention.

FIG. 2 is a sectional view showing a structure of a Josephson junction in the superconducting radiation detector according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a method of manufacturing the Josephson junction in the superconducting radiation detector according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a Josephson junction in a superconducting radiation detector according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a method of manufacturing a Josephson junction in a superconducting radiation detector according to the second embodiment of the present invention.

FIG. 6 is a diagram showing an application example of synchrotron radiation light.

FIG. 7 is a diagram showing energy resolution and incident energy of a superconducting radiation detector and a Si (Li) semiconductor detector.

FIG. 8 is a diagram showing a tunnel process when a Josephson junction is irradiated with radiation.

FIG. 9 is a diagram showing current-voltage characteristics when a Josephson junction is irradiated with radiation.

FIG. 10 is a diagram showing a device structure such as Klaus and the result of a wave height spectrum experiment.

FIG. 11 is a diagram showing an element structure of Twelenbold or the like and a result of a wave height spectrum experiment.

FIG. 12 is a diagram showing experimental results of wave height spectra of Rosmund and others.

FIG. 13 is a diagram showing an element structure of Barone and the like and a result of a wave spectrum experiment.

[Explanation of symbols]

 1, 11 substrate 2, 12 lower electrode pattern 2a, 12a Ta film 3,15 insulating film 3a, 3b, 5a opening 4,13 barrier layer 5,14 upper electrode pattern 13a Al film pattern 13b AlOx film pattern 13c Al film 13d AlOx film 15a, 15b, 16a Opening 16 Lead-out wiring layer pattern

Claims (5)

[Claims] 1. A Josephson junction structure comprising a lower electrode made of a superconductor, a barrier layer formed on the lower electrode, and an upper electrode made of a superconductor formed on the barrier layer. The superconducting radiation detector, wherein the lower and upper electrodes are made of tantalum. 2. The superconducting radiation detector according to claim 1, wherein the barrier layer is made of a tantalum oxide film. 3. The barrier layer is composed of a two-layer film including a metal thin film and an oxide film of the metal formed on the metal thin film and substantially functioning as a barrier. Superconducting radiation detector. 4. The superconducting radiation detector according to claim 3, wherein the metal is one of aluminum, zirconium and hafnium. 5. The metal film has a film thickness of 1 nm or more and 50 nm.
5. The superconducting radiation detector according to claim 3, comprising: