JPH01275405A - Production of superconductor structure - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a superconductor due to moisture, etc., and to obtain the title structure having stable superconducting characteristics by vapor-depositing an insulating film on the surface of the superconductor using a multiple oxide by an ion beam sputtering method. CONSTITUTION:An insulating film such as a film of AlN, Al2O3, Si3N4, SiO2, TiN, TiO2 or BN is vapor-deposited on the surface of a superconductor using a multiple oxide such as Bi-Sr-Ca-Cu-O or Tl-Ba-Ca-Cu-O by carrying out ion beam sputtering with one or more among Al, Ti, Si and B as the materials of a target for sputtering and an inert gas such as Ar or a gaseous mixture of the inert gas with O2 or N2 as gas for ion beams.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a superconductor structure applied to an electronic device, particularly a composite compound superconductor structure.

Conventional technology Conventionally, niobium nitride (NbN) and niobium germanium (Nb3) have been used as A15 type binary compounds as superconductors.
Ge) and the like were known, but the superconducting transition temperature Tc of these materials was at most 24. In addition, as a velorskite compound, B a-P b-B i
-0 series (Japanese Unexamined Patent Publication No. 60-173885) is known, but the TC of this material is as low as 13, making it difficult to put it to practical use in electronic devices and the like. However, Tc is 3
A B a-L a-Cu -0-based high-temperature superconductor exhibiting a temperature of 0 to 40 K was proposed [J, G-Bednorz and
K., A., Muller.

Zeit Schrift Fair Physique
shrift fur physik B)-C
Ondensed Matter 64,189-
193 (1986)], then the proposed Y-Ba
-Cu-0 series has been reported to have a Tc exceeding 90K [M, Ni, Wu et al., Physical Review Letters (
Physical Review Letters)
Vol, 58. No. 9,908-910 (1987
)], its practical application has become promising as it has become higher than the boiling point (77K) of liquid nitrogen. Also, recently B 1-Sr
-Ca-Cu-0 system or T I -B a-Ca-
It has been reported that the Cu-0 system may exhibit zero resistance at a temperature of 120 nm, and it has become promising to put into practical use an element that can stably operate in liquid nitrogen.

Problems to be Solved by the Invention Superconductors formed from composite compound materials such as Y-Ba-Cu-0 and Bi-Sr-Ca-Cu-0 deteriorate in superconducting properties when left in the atmosphere. It has been found that stabilization of its properties is strongly desired for practical use. The present inventors believe that superconducting properties can be stabilized by coating the surface of this type of material with an optimal material using an optimal method, and that it is possible to change the composition of the superconductor by using ion beam sputtering, which causes less surface damage. discovered that it was possible to stabilize the characteristics without
Based on this, we invented a new method for manufacturing superconducting structures using a new composite compound material.

Means for Solving the Problems The method of manufacturing a superconductor structure using a composite compound according to the present invention includes, for example, Bi-Sr-Ca as a composite compound.
It is characterized in that an insulating film is deposited on the surface of a superconductor made of -Cu -0 based oxide by ion beam sputtering.

Function: The method of manufacturing a superconductor structure according to the present invention forms an insulating protective film by ion beam sputtering without damaging the surface of a composite compound superconductor and without changing the composition of the superconductor. Its great feature is that it can do this. Further, as surface treatment, the superconductor is irradiated with oxygen ions to compensate for oxygen deficiencies on the surface, and then a protective film can be formed. Therefore, a superconductor structure with extremely high precision and excellent stability can be easily realized by the manufacturing method of the present invention.

Example Embodiments of the present invention will be described using the drawings.

In FIG. 1, an example of the superconductor structure according to the present invention is such that the molar ratio of the B1-3r-Ca-Cu-0-based oxide or element is 0.5≦(A+B)/Cu≦2. The structure consists of an oxide superconductor 11 containing elements A, B, and Cu, which are 5, and an insulating protective film 12 deposited on the surface of the superconductor by ion beam sputtering. Here, A represents at least one element selected from Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B represents at least one element selected from the a-group elements.

The present inventors have found that the superconducting properties of this type of composite compound superconductor in particular deteriorate significantly when left in the atmosphere. We discovered that coating the surface of superconductors is effective.

Furthermore, when coating the superconductor surface with a protective film, care must be taken not to damage the superconductor surface or change the composition of the superconductor surface, especially the oxygen concentration, so as not to change the superconducting properties. The present inventors have discovered that this must be the case. Based on these findings, the method for manufacturing a superconductor structure according to the present invention attempts to prevent this type of oxide superconductor from deteriorating.

Deterioration of a superconductor is a phenomenon in which, for example, when it is left in the atmosphere, its transition temperature becomes lower. Although the details of the cause of this deterioration are not clear, it is thought that the superconductor has been altered by moisture, carbon dioxide, etc. in the atmosphere. Surface coatings are usually used to prevent atmospheric moisture. In this case, the present inventors have discovered that if the protective film material and protective film forming method are not appropriately selected, the superconducting properties will be degraded when the protective film is coated. In other words, if aluminum nitride, aluminum oxide, silicon nitride, silicon oxide, titanium nitride, titanium oxide, boron nitride, etc. are used as the material for the protective film to be coated, the coating will not change the properties, and the product can be left in the atmosphere. There was no noticeable deterioration in properties, confirming that the material was suitable. In addition, methods for forming the protective film include sputtering methods that damage the surface, and plasma CVD methods.
It was confirmed that this method is inappropriate because it not only damages the surface, but also reduces and removes the oxygen on the superconductor surface, changing the composition of the surface. In addition, when forming the protective film, the present inventors also found that the composite compound superconductor 11
It has been found that when the temperature is set at 200° C. or higher, oxygen escapes and the characteristics deteriorate, so it is desirable to use a method that does not involve heating. It was confirmed that the ion beam sputtering method of the present invention causes little surface damage and can form a dense film even at a substrate temperature of 100° C. or lower, and is effective as a method for forming a protective film.

In addition, when oxygen ions are irradiated as a pretreatment before forming the protective film, 1, M! Replenishes the deficient t0 oxygen on the surface of the conductor,
Superconducting properties can be improved.

When a composite compound superconductor is put into practical use, this type of #i!
The conductor is made into a thin film and used as a fIlt layer on E of the substrate.

Therefore, a superconductor is often a coating formed on a substrate, and this type of coating is formed on the surface of the coated superconductor.

That is, the superconductor structure according to the present invention, as shown in FIG. 2, consists of a thinned superconductor 11 having a coating film 12 and a base 2I that supports it. ' In this case, we found that there is an optimal material for the substrate. That is, in FIG. 2, superconductor coating 11 is formed on the surface of base 21 by, for example, a sputtering method. In this case, the purpose of the base 21 is to hold the composite compound coating 11 exhibiting superconductivity. This coating 11 is usually formed at a high temperature of several hundred degrees Celsius, and since the superconductor is operated at a low temperature of, for example, liquid nitrogen temperature (-195 degrees Celsius), the adhesion between the substrate 21 and the coating 11 is particularly poor, and the coating 11 is often
The present inventors confirmed that 1 was damaged. Roughly speaking, the present inventors investigated the detailed thermal characteristics of the substrate for various materials, and found that the linear thermal expansion coefficient α>I O-'/
℃, it was confirmed that the above film would not be damaged and could be put to practical use.

In order to further understand the content of the present invention, more specific examples will be shown below.

(Specific Example) Using a M g O single crystal (100) plane as the substrate 21,
Using a high frequency Brenner magnetron scatterer, the sintered YB a2c u a, 50x target was
A crystalline YBa2Cu30v-delta coating 11 was deposited on the substrate by sputtering deposition in a mixed gas atmosphere of 2.

In this case, the mixed gas pressure was 0.4 Pa, the sputtering power was 130 W, the sputtering time was 1 hour, the film thickness was 0.5 μm, and the substrate temperature was 640° C. After the coating 11 was deposited, it was cooled to room temperature in an oxygen atmosphere of 500 Pa, and then taken out into the atmosphere. The coating 11 thus obtained exhibited superconductivity, with a transition temperature of 89 K on set and 75 K on offset.

Further, the surface of the coating 11, which was kept at 60° C. without being left in the atmosphere, was coated with 20% oxygen by ion beam sputtering method using an easily controllable Kaufman type ion source using aluminum as a target. An aluminum oxide protective film 2 was formed in a partial pressure atmosphere of . At this time, Ar gas was used as the ion beam gas. The ion acceleration energy was 1 kV, the beam current was 50 mA, and the degree of vacuum during film formation was 3X 10-' Tor.
It was r.

Y-Ba coated with aluminum oxide in this way
-When measuring the superconducting properties of the -Cu-0 superconductor structure, the transition temperature is 89) and 74
K, there was almost no change in the superconducting properties. Moreover, no change in this property was observed even when this was left in the atmosphere. FIG. 3 shows the Auger electron spectroscopy interface characteristics of a superconductor structure in which this Y-Ba-Cu-0 thin film is coated with aluminum oxide. As can be seen from the figure, the respective constituent elements are not observed in the superconducting film or the coating protective film. Therefore, it can be seen that the protective film is coated without changing the composition of the superconductor.

From the above, it has been found that aluminum oxide is effective as a protective film for a composite compound superconductor, and ion beam sputtering is effective as a method for forming the protective film.

When coating an insulating film, a mixing layer in which the insulating film material and the superconductor material are mixed is generally formed on the surface of the superconductor. The present inventors have discovered that when the accelerating voltage of the ion beam irradiating the target exceeds 10 kV, the mixing layer has a negative effect on the superconducting properties, but when the accelerating voltage is 10 kV or less, the superconducting properties are not affected.

Next, a second specific example will be described. A superconductor film 11 prepared under the same conditions as in the first specific example was used, and this film 11 was mounted on a sample stand and maintained at 60°C. The superconducting critical temperature of this superconducting film was 91 K at onset and 73 K at offset. A magnetic field that satisfies electron cyclotron resonance conditions is applied to a plasma generation chamber into which microwaves have been introduced, and a mixed gas of Ar and nitrogen is introduced from the gas inlet of the plasma generation chamber to generate plasma with a high degree of dissociation. The Ar ions and nitrogen ions inside were drawn out from the outlet, and an aluminum target placed at the outlet was sputtered to form aluminum nitride on the superconducting film 11. However, the degree of vacuum during film formation was 2X10-3 Torr, and the ion current density was 3 mA/cm.
2. The microwave power was 150W. At this time, the formed superconductor structure exhibits a superconducting critical temperature of 90 K (oncela) and an offset of 74, and has superconducting properties of C
There was no significant change. When using the method described above, that is, ECR plasma, as an ion source for an ion beam, the ions have a high degree of activity, so the dense insulating film at low temperatures has little effect on the superconductor coated. This is a more effective method in that it can be obtained without any additional costs.

In addition, in the examples, Bi-Sr-C was used as the superconductor.
a-Cu-0 series, T I -B a-Ca-Cu-0 series, or replacing the B element with a lanthanum series element other than Y or Sc, or replacing the B element with Sr, Ca, etc.
Even if they are replaced with group a elements, the essential characteristics of the invention do not change except that the superconducting transition temperature changes.

Effects of the Invention The method for manufacturing a superconductor structure according to the present invention uses an ion beam sputtering method to coat a protective film without damaging the surface of the superconductor or changing the composition of the surface, and further A major feature is that the superconductor is made into a thin film. By forming the protective film, it is possible to prevent deterioration of superconducting properties due to moisture intrusion and external damage, and therefore, a stable and highly reliable superconductor structure can be realized in the present invention.

Using the present invention, it is possible to integrate devices such as Si or CaAs, and it can also be put to practical use as an elemental material for various superconducting devices such as Josephson elements. In particular, the transition temperature of this type of compound superconductor may be room temperature, so the practical scope of the present invention is wide and the industrial value of the present invention is extremely high.

[Brief explanation of the drawing]

1 and 2 are basic configuration diagrams of a superconductor structure according to an embodiment of the present invention, and FIG. 3 is an Auger electron spectroscopy analysis interface characteristic diagram of a superconductor structure formed according to the present invention. 11... Composite compound superconductor, 12... Protective film, 2
1... Base. Name of agent: Patent attorney Toshio Nakao (1 person Figure 1 Figure 3 Sponsorship time C minutes)

Claims (1)

[Scope of Claims] (1) A method for manufacturing a superconductor structure, which comprises depositing an insulating film on the surface of a superconductor using a composite compound by ion beam sputtering. (2) A method for manufacturing a superconductor structure according to claim 1, characterized in that the superconductor structure is made of a multilayered superconductor in which a superconductor film is laminated on a base. (3) Production of a superconductor structure according to claim 1, characterized in that an oxide of Bi-Sr-Ca-Cu-O or Tl-Ba-Ca-Cu-O is used as the composite compound. Method. (4) Claim 1, characterized in that an oxide containing element A, element B, and Cu whose molar ratio of elements is 0.5≦(A+B)/Cu≦2.5 is used as the composite compound. A method for manufacturing a superconductor structure as described in . Here, A represents at least one element among Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B represents at least one element among group IIa elements. (5) Aluminum as a sputtering target,
2. The method of manufacturing a superconductor structure according to claim 1, wherein the superconductor structure is made of at least one of silicon, titanium, and boron. (6) The method for manufacturing a superconductor structure according to claim 1, characterized in that an inert gas alone or a mixed gas of an inert gas and oxygen or nitrogen is used as the ion beam gas. (7) A method for manufacturing a superconductor structure according to claim 1, wherein the superconductor structure is formed in a gas atmosphere containing at least one of oxygen and nitrogen. (8) The method for manufacturing a superconductor structure according to claim 1, wherein plasma generated by discharging a gas containing at least an inert gas in a vacuum chamber is used as the ion source. (9) Claim 8, characterized in that ions generated by electric discharge in a vacuum chamber are accelerated and irradiated by applying a DC voltage between the plasma in the vacuum chamber and the sputtering target. A method for manufacturing a superconductor structure. (10) The method for manufacturing a superconductor structure according to claim 9, characterized in that the applied DC voltage is 10 kV or less. (11) The superconductor according to claim 8, wherein the ion source device is a plasma processing device that generates plasma by applying a magnetic field and microwaves so as to satisfy electron cyclotron resonance absorption conditions. Method of manufacturing structures. (12) A method for manufacturing a superconductor structure according to claim 1, characterized in that the surface of the composite compound superconductor is subjected to oxygen ion irradiation treatment. (13) A method for manufacturing a superconductor structure according to claim 1, characterized in that the temperature of the composite compound superconductor during the deposition of the insulating film is set to 100° C. or lower. (14) The method for manufacturing a superconductor structure according to claim 2, wherein the substrate is made of a material having a coefficient of linear expansion α>10^-^6/°C.