JPH06350147A - Superconducting circuit - Google Patents

Abstract

PURPOSE:To acquire a highly stable and highly reliable superconducting circuit wherein a circuit can be prepared readily by forming a circuit of a superconductor thin film formed of carbon cluster C60 doped with alkaline metal or alkaline earth metal on a substrate and by coating the circuit with an insulating protection film. CONSTITUTION:Pattern formation is performed for an electrode 4 on a surface of a substrate 3 and a circuit 1 comprosed of a carbon cluster superconductor thin film is formed in contact with the electrode 4. The circuit 1 comprosed of the carbon cluster superconductor thin film is coated with an insulating protection film 2 and an entire thereof is coated with a protection film 5. As for the carbon cluster superconductor thin film circuit 1, carbon cluster C60 doped with alkaline metal or alkaline earth metal is used. The insulating protection film 2 covering the circuit 1 prevents gaseous impurities such as oxygen and nitrogen in air from entering the circuit. Furthermore, the protection film 5 covering an entire of the superconductive circuit further surely cuts off impurities such as water and oxygen in air into the circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel superconducting circuit effectively used in various circuits, devices and the like using a superconductor thin film.

[0002]

2. Description of the Related Art Superconducting thin films as conventional superconducting circuits include non-transition element superconducting thin films, transition element superconducting thin films,
Compound superconductor thin films, oxide high temperature superconductor thin films, etc. have been used. As a non-transition element superconductor thin film, Al
(Critical temperature Tc [hereinafter appropriately referred to as “Tc”] = 5.7
K), Pb (Tc = 7.5K), Sn (Tc = 6K)
As a transition element superconductor thin film, Nb (Tc = 10
K), Mo (Tc = 8.5K), La (Tc = 6.5)
K), etc., and as a compound superconductor thin film, NbN (T
c = 17K), Nb ₃ Sn (Tc = 18K), Nb ₃ G
e (Tc = 23K) and the like are known.

As an oxide high-temperature superconductor thin film, Y
₁ Ba ₂ Cu ₃ O, Tl ₂ Ba ₂ Ca ₂ Cu ₃ O, etc. have been proposed.

[0004]

However, the superconductor thin film used in the conventional superconducting circuit has the following problems. A non-transition element superconductor thin film can be easily formed by vapor deposition or the like, but its Tc is low, so that it lacks stability and reliability when formed into a circuit.

Since many transition element superconducting thin films have a high melting point and have a strong action of occluding gaseous impurities such as oxygen and nitrogen, care must be taken in forming the thin film. Further, the Tc of this transition element superconductor thin film was the highest at 10K of Nb, and likewise the stability and reliability when formed into a circuit was similar to the above non-transition element superconducting thin film. The compound superconductor thin film has a relatively high Tc of NbN and Nb ₃ Ge, but it is a complicated process such as ultra-high vacuum or high temperature process because it is necessary to control the composition as well as to combine during film formation. was there.

Further, the oxide high temperature superconductor thin film is made of Y ₁ B.
Although a ₂ Cu ₃ O and Tl ₂ Ba ₂ Ca ₂ Cu ₃ O have been studied, it is necessary to control the composition and crystal orientation because of the large number of elements and the anisotropic crystal structure. However, there are drawbacks such that the circuit is complicated to produce and the substrate is limited to a substrate having a predetermined plane orientation for controlling the crystal orientation.

Therefore, an object of the present invention is to provide a superconducting circuit which is excellent in stability and reliability and which can be easily manufactured.

[0008]

In the superconducting circuit of the present invention for solving the above-mentioned problems, a circuit composed of a carbon cluster superconductor thin film and an insulating protective film for covering the circuit are formed on a substrate. It is characterized by that. Further, in the above superconducting circuit, it is preferable that the carbon cluster superconductor thin film comprises carbon cluster C ₆₀ doped with an alkali metal or an alkaline earth metal.

[0009]

According to the superconducting circuit of the present invention having the above-mentioned structure, the circuit formed on the substrate is made of the carbon cluster superconductor thin film, so that the critical temperature Tc of the circuit is made higher than that of the conventional superconductor thin film. You can The carbon cluster superconductor thin film has a so-called fullerene structure in which a plurality of carbon atoms are connected in a spherical shape or a spheroidal shape, so that it can be expected to have three-dimensional properties, and its applicability is not limited by the dimension and is a three-dimensional circuit. Can be easily formed. Since the structure of this carbon cluster is cubic and has no anisotropy, it is not limited to a substrate having a predetermined plane orientation in which a circuit is formed, such as an oxide high-temperature superconductor thin film. Since the insulating protective film is formed so as to cover the circuit composed of the carbon cluster superconductor thin film,
It is possible to block ingress of moisture, oxygen, carbon dioxide gas, etc. in the atmosphere into the circuit.

Further, when the carbon cluster superconductor is composed of the carbon cluster C ₆₀ doped with an alkali metal or an alkaline earth metal, the Tc of the circuit can be further increased. For example, 16 to 19 for K-doped C ₆₀
10 to 31 K for K and Rb-doped C ₆₀ , Cs-doped C ₆₀
Is 8 to 29K, and Rb2Cs-doped C ₆₀ is 33K. Then, the thin film formation of the carbon cluster C ₆₀ and the doping process of the alkali metal and the alkaline earth metal are performed by 2
It can be carried out at a low temperature of 00 ° C. or lower.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a plan view of a superconducting circuit according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II of FIG. The illustrated superconducting circuit is on the surface of the substrate 3,
The electrode 4 is patterned, and the circuit 1 made of a carbon cluster superconductor thin film is formed so as to contact the electrode 4. The circuit 1 made of this carbon cluster superconductor thin film is covered with an insulating protective film 2. The entire superconducting circuit 1 is covered with a protective film 5.

The substrate 3 is made of a flat plate having a rectangular planar shape, and its material is, for example, glass, quartz, diamond, etc., as well as silicon, GaAs, InP, Zn.
Various materials such as semiconductors such as Se and ceramics such as MoS, BN and Al ₂ O ₃ are used. The electrode 4 is gold, silver,
A metal such as aluminum is used and is formed at two adjacent positions among the four corners of the surface of the substrate 3. The electrode 4 is formed by a vapor deposition method using a mask pattern, a lift-off method, or the like. Further, the electrode 4 is connected to a lead wire 6 which serves as a voltage extracting terminal and a current extracting terminal of the circuit.

The circuit 1 made of a carbon cluster superconductor thin film is patterned on the substrate 3 in various shapes so that a part thereof is connected to the electrode 4. The carbon cluster superconductor which constitutes this circuit 1 is C _2n (however, 10
A superconductor obtained by doping carbon cluster molecules having a π-electron conjugated system represented by ≦ n ≦ 300) with various impurities serving as dopants.

A carbon cluster is a molecule composed of 60 carbon atoms having a so-called soccer ball-like structure, C
₆₀ , C ₇₀ which is a molecule composed of 60 carbon atoms having a rugby ball structure, and a mixture of these C ₆₀ and C ₇₀ are preferably used. Carbon clusters are made from graphite or carbon as a raw material, and the soot obtained by arc discharge, resistance heating, laser beam heating, magnetron sputtering, etc. is purified to a high purity of 99.9% or more by solvent extraction, column chromatography purification, etc. It is manufactured by purification.

The dopants are alkali metals such as K, Rb and Cs, and alkaline earth metals such as Ca.
Etc. are illustrated. In the carbon cluster superconductor thin film circuit 1 of this example, the carbon cluster C ₆₀ doped with an alkali metal or an alkaline earth metal is used. The carbon cluster superconductor thin film circuit 1 may be prepared by forming a carbon cluster C ₆₀ thin film and then doping it with an alkali metal or an alkaline earth metal, or simultaneously using the carbon cluster C ₆₀ and an alkali metal or an alkaline earth metal. A method of vaporizing and forming a film is used.

More specifically, a method such as vacuum deposition, MBE, ion plating or laser deposition is used to form the carbon cluster C ₆₀ thin film. The thickness of the carbon cluster C ₆₀ thin film formed by these methods is preferably 100 so that the circuit characteristics can be exhibited.
It is formed in the range of up to 1000 nm. For the doping of alkali metal or alkaline earth metal, vapor phase doping, ion implantation or the like is used.

The insulating protective film 2 covering the circuit 1 made of the carbon cluster superconductor thin film is formed by an E gun (electron gun) or the like. As the insulating protective film 2, for example, S
Elements such as i, nitrides such as Si ₃ N ₄ , SiO, B
₂ O ₃ , BaO, GeO, TeO ₂ , WO ₂ or W
O _{3 and} other oxides, KF, RbF, CsF, CaF _{2 and} MgF _{2 and} other halides, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PV
Polymers such as F) or polyparaxylylene (parylene) are used. The thickness of the insulating protective film 2 is preferably 500 to 5000 nm so that invasion of gaseous impurities such as oxygen and nitrogen in the atmosphere into the circuit can be reliably prevented.
Or more.

Further, the protective film 5 covering the entire superconducting circuit is for more reliably blocking the intrusion of impurities such as moisture and oxygen in the air into the circuit. Tetrafluoroethylene (PTF
Polymers such as E), polyvinylidene fluoride (PVF) or polyparaxylylene (parylene) are used. The thickness of the protective film 5 is such that the invasion of gaseous impurities such as oxygen and nitrogen in the atmosphere into the circuit can be prevented more reliably.
It is preferably formed in the range of several μm to several mm.

According to the above-mentioned superconducting circuit, since the circuit 1 made of the carbon cluster superconductor thin film is formed on the substrate 3, the critical temperature Tc of the circuit 1 can be increased. For example, K-doped C ₆₀ Then Tc = 16 ~ 19K, R
For b-doped C ₆₀ , Tc = 10 to 31 K, Cs-doped C ₆₀
Tc = 8 to 29K, and Rb ₂ Cs-doped C ₆₀ has Tc
= 33K. Since all of these carbon cluster superconductor thin films are cubic crystals and have no anisotropy, the substrate 3 forming the circuit 1 is not limited unlike the oxide high temperature superconductor. In particular, the C ₆₀ carbon cluster superconductor is
A three-dimensional property having a soccer ball-like structure can be expected, and its applicability is not limited by the dimension, and a three-dimensional circuit can be easily formed. Thin film creation and of C _60,
The alkali metal or alkaline earth metal doping process can be performed at a low temperature of 200 ° C. or lower, and a relatively simple apparatus can be used. Further, the insulating protective film 2 that covers the circuit 1 is formed subsequently after forming the superconductor circuit 1 in vacuum. Therefore, the superconducting circuit 1 can be manufactured without exposing the circuit 1 of the carbon cluster superconductor to the atmosphere even once, and a stable and highly reliable one can be obtained in the atmosphere. As the protective material, an inorganic insulating protective film 2 such as a single element, a nitride, an oxide or a halide is provided, and then the entire circuit is coated with an organic polymer protective film 5. Further, the infiltration of carbon dioxide gas and the like can be blocked, and the carbon cluster superconductor circuit 1 can be further stabilized.

As described above, the superconducting circuit using the carbon cluster superconducting thin film 1 of the present invention has a critical temperature (Tc) higher than that of the conventional circuit using the superconducting thin film of Pb, Pb alloy, Nb, NbN or the like. Since the critical magnetic field (Hcz) is high, it can be used in a stable characteristic region, and a highly reliable circuit can be produced. In addition, since there is no anisotropy of superconducting characteristics based on the anisotropy of the crystal structure unlike the high temperature oxide superconductor, it is easy to create a circuit. The thin film circuit manufacturing process does not use high melting point low vapor pressure metal, which is difficult to deposit,
Further, the raw materials and the composition are simple, and further, the film can be formed at a low temperature, which is simple.

From the above, various circuits using thin film superconductivity,
It can be effectively used for devices. For example, a strip path, a high frequency circuit element such as a resonator or an antenna, a circuit element (electromagnetic wave detection, an amplifier, a generator, etc.) combined with a superconducting quantum interferometer (SQUID) or a Josephson junction, a logic circuit element or a memory circuit. When used as an element or the like, its characteristics are remarkably exhibited.

The present invention is not limited to the above-mentioned embodiment, and, for example, a multi-layer circuit in which carbon cluster superconductor thin films 1 and insulating protective films 2 are alternately laminated is formed. It is possible to make various design changes within a range that does not change. Next, an example of making a superconducting circuit according to an embodiment of the present invention will be described with reference to FIG. Preparation Example First, as shown in FIG. 3, four electrode patterns were formed on the substrate 3 by a vapor deposition method using a mask pattern or a lift-off method. This substrate 3 was set in a vacuum apparatus, and as shown in the figure, a C ₆₀ vapor-deposited thin film 1 '(carbon cluster thin film) having a required circuit pattern was formed on the substrate 3 by a mask pattern method or a lift-off method. . The vapor deposition conditions at this time are as follows: vacuum degree 10 ⁻⁸ Torr,
Substrate 3 temperature 100 ° C, C ₆₀ deposition film temperature 300-400 ° C
, And formed a 2000 Å film thickness of C ₆₀ . Then, in C ₆₀ formed into a circuit pattern, an Rb alkali dispenser manufactured by SAES Getter was used to form Rb.
Doping with (rubidium), as shown in the figure,
An Rb ₃ C ₆₀ superconductor thin film (carbon cluster superconductor) circuit 1 was prepared.

The composition of Rb with respect to C ₆₀ is determined by placing a monitor having a C ₆₀ thin film of the same thickness on the glass substrate 3 with four gold vapor deposition terminals near the substrate 3 for forming a circuit. The resistance is controlled by measuring the resistance. The resistivity of this monitor drops with Rb doping, reaches a local minimum, and begins to rise. In order to obtain the composition of Rb ₃ C ₆₀ , it is advisable to stop the heating of the alkali dispenser and stop the doping at the time when the resistance becomes minimum.

Next, the substrate 3 having the obtained superconducting circuit 1 formed thereon is coated with a protective film material through a mask for a protective film without taking out from the vacuum apparatus, and as shown in FIG. To form. The insulating protective film 2 completely covers the superconducting circuit 1 and is formed so that moisture, oxygen, etc. in the atmosphere do not enter the superconducting circuit. Here, the insulating protective film 2 is formed by depositing Si with an E gun,
The film thickness was set to 0Å. Further, a lead wire 6 is attached on the electrode 4 which is not covered with the insulating protective film 2 as shown in the figure.

Then, the obtained superconducting circuit board 3 with the Si protective film is taken out from the vacuum apparatus, immediately set in a polyparaxylylene (parylene) coating apparatus, and the parylene protective film 5 is vacuum-deposited as shown in FIG. went. The film thickness of the parylene protective film 5 was 25 μm. The superconducting characteristics of the obtained superconducting circuit in the atmosphere were evaluated to be 25K.
Shows zero resistance at 10K and Nb of conventional material Nb
It was more than 17K for N and 23K for Nb ₃ Ge.

[0026]

As described above, the superconducting circuit using the carbon cluster superconductor thin film of the present invention has the conventional Pb and Pb
Compared to a circuit using a superconductor thin film of alloy, Nb, NbN, etc., it has a higher critical temperature (Tc) and critical magnetic field (Hcz), can be used in a stable characteristic region, and has a highly reliable circuit. . In addition, since carbon clusters are cubic and do not have anisotropy of superconducting properties based on anisotropy of crystal structure unlike oxide high-temperature superconductors, the substrate is not limited and circuits can be easily formed. The manufacturing process of a carbon cluster superconductor thin film circuit is simple because it does not use a high melting point and low vapor pressure metal, which is difficult to deposit, has a simple raw material and composition, and can form a film at a low temperature. Since the insulating protective film is formed so as to cover the carbon cluster superconductor circuit,
It is possible to prevent ingress of nitrogen, oxygen, moisture, etc. in the atmosphere into the circuit, and further improve the stability and reliability of the circuit.

When the carbon cluster superconductor thin film is made of carbon cluster C ₆₀ doped with an alkali metal or an alkaline earth metal, the Tc of the circuit can be further increased, and the stability and reliability are excellent. . Since the melting point of the carbon cluster C ₆₀ thin film formation and the alkali metal and alkaline earth metal doping processes are relatively low, the process can be performed at a low temperature of 200 ° C. or less, and a relatively simple apparatus can be used. .

[Brief description of drawings]

FIG. 1 is a plan view showing a superconducting circuit according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a schematic view showing a manufacturing process of a superconducting circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 carbon cluster superconductor (circuit) 2 insulating protective film 3 substrate

Front page continuation (72) Inventor Koji Tada 1-3-3 Shimaya, Konohana-ku, Osaka Sumitomo Electric Industries, Ltd. Osaka Works

Claims (2)

[Claims] 1. A superconducting circuit in which a circuit made of a carbon cluster superconductor thin film and an insulating protective film for covering the circuit are formed on a substrate. 2. The superconducting circuit according to claim 1, wherein the carbon cluster superconductor thin film comprises carbon cluster C ₆₀ doped with an alkali metal or an alkaline earth metal.