JPS63239742A - Manufacture for film superconductor - Google Patents

Abstract

PURPOSE:To secure such a superconductor that is homogeneous and excellent in accuracy as compared with the conventional sintered body securable, by sticking a specific complex compound coat onto a substrate, and having this coat subjected to heat treatment in addition. CONSTITUTION:A complex compound coat 12 consisting of (A, B)3Cu2O7-delta in the base is stuck on a surface 13 of the heated substrate 11 by means of vapor deposition, by way of example, and it is subjected to heat treatment at an oxidizing atmosphere. A, said herein, shows at least one type of Sc, Y and lanthanum series elements (atomis number 57-71), and B shows at least one type of IIa group elements such as Ba, Sr, Ca, Be, Mg, etc. With this constitution, such a superconductor that is homogeneous and excellent in accuracy as compared with the conventional sintered body is securable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing superconductors. In particular, it relates to a method for manufacturing compound thin film superconductors.

Conventional technology Niobium nitride (NbN) and germanium niobium (NbsGe) are used as A15 type binary compounds as high-temperature superconductors.
were known, but the superconducting transition temperature of these materials was at most 24°. On the other hand, perovskite-based ternary compounds are expected to have even higher transition temperatures, and Ba-
A La-Cu-0-based high-temperature superconductor was proposed [J,
G. Bend.

rz and K, A, Muller, Ze tshrift f.
Mouth Rphysik B) - Condensed Mat
ter 64.189-193 (1986)]. Additionally, ]Y-Ba-Cu-0 was recently proposed to be a higher temperature superconducting material. (Reference) [M, K
, Wu et al.

Physical Review Letters
Review Letters) Vol, 58 No.
9.908-910 (1987) ]]Y-Ba-C
Although the details of the superconducting mechanism of the u-0 material are not clear,
The transition temperature can be higher than liquid nitrogen temperature,
However, Y-Ba-Cu-0 materials are expected to have more promising properties as high-temperature superconductors than conventional binary compounds. Can only be obtained in block form. On the other hand, when this type of material is to be put to practical use, there is a strong demand for processing it into a thin film, but with conventional techniques, it is considered very difficult to process the material into a thin film.

The present inventors have discovered that when a thin film of this type of material is deposited by an ion process, a thin film-like high temperature superconductor is formed, and based on this discovery, they have invented a method for producing a thin film superconductor.

Means for Solving the Problems The basic structure of the thin film superconductor formed by the manufacturing method of the present invention is that the main components (A, B) are
It is characterized by a layered structure to which the original compound coating 12 is attached. The present inventors have developed this type of layered structure superconductor by depositing a composite compound film whose main components are (A, B) sCuzo7-δ on a heated substrate, for example, by a process called vapor deposition, and then depositing it in an oxidizing atmosphere. The present invention was based on the discovery that it can be formed by heat treatment. Here, A is Sc, Y, and lanthanum series elements (atomic number 57-
At least one of 71), B is B a, Sr, C
Indicates at least one element of group Ila elements such as a, Be, and Mg.

Function: The method for producing a thin film superconductor according to the present invention has a major feature in that the superconductor is made into a thin film.

In other words, because film thinning involves decomposing the superconductor material into ultrafine particles in the atomic state and then depositing them on the substrate, the composition of the formed superconductor is essentially more homogeneous than that of conventional sintered bodies. . Superconductors of very high precision are therefore realized using the method of the invention.

Example Embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, a ternary compound film 12 is formed by, for example, a sputtering method. In this case, the substrate 11 is intended to hold a ternary compound coating 12 exhibiting superconductivity. The superconductor of the invention therefore essentially consists of a layered structure. This layered structure is usually formed at a high temperature of several hundred degrees Celsius, and since superconductors are operated at a low temperature of, for example, liquid nitrogen temperature (-195 degrees Celsius), the adhesion between the substrate 11 and the coating 12 is particularly poor (and the layered structure is often formed). The inventors have confirmed that the thermal expansion coefficient α of the substrate is greater than 10-6'e. If there is, there is no damage to the layered structure (it has been confirmed that it is practical. For example, α<10
If quartz glass with a ratio of ~6/fi is used as the substrate, the coating 12 will have numerous cracks and become a discontinuous coating, making it difficult to put it into practical use (
The present inventors have confirmed that this is true.

Furthermore, the present inventors have discovered that there is an optimal material for the layered structure substrate 1 shown in FIG. 1 from the viewpoint of functionality.

That is, the highly crystalline ternary compound coating 12 is applied to the substrate 11.
A single crystal substrate is effective for forming it on the surface 13 of. As a result of detailed investigation into the optimal substrate material, the present inventors found that the substrate 11 was made of magnesium oxide, sapphire (α
-Al2O3), spinel, strontium titanate, silicon, gallium arsenide, and other single crystals were confirmed to be effective. However, since this is for effectively growing a highly crystalline coating 12 on the surface 13, it is sufficient if at least the substrate surface 13 is a single crystal.

The present inventors have confirmed that so-called sintered porcelain is more effective as a substrate than a single crystal when processing this type of superconductor into an arbitrary shape, such as a cylinder, and have also found the most suitable porcelain material. I found it. That is, the present inventors have found that alumina, maglucium oxide, zirconium oxide, steatite, forsterite, beryllia, spinel, etc. are used as the porcelain substrate to provide optimal adhesion of the superconducting coating 12 to the substrate 11 during processing of the substrate. confirmed. In this case as well, it is preferable that even the surface of the substrate is made of this type of porcelain, as in the case of single crystals.

To form a thin film superconductor, first (A, B) 3cug07
- A six-component composite compound coating is deposited on the substrate by physical vapor deposition methods such as sputtering or thermal evaporation, e.g. electron beam evaporation, laser beam evaporation. In this case, the composite compound coating is component A.

The present inventors have confirmed that the amount of oxygen is not particularly important, as long as the stoichiometric ratio of B and Cu matches.

As a result, methods for forming composite compound films are not limited to physical vapor deposition, but also chemical vapor deposition, such as atmospheric or reduced pressure chemical vapor deposition, plasma chemical vapor deposition, photochemical vapor deposition, and photochemical vapor deposition. The present inventors have confirmed that a chemical vapor phase growth method is also effective if matched.

The present inventors have confirmed that when a composite compound coating is applied to the surface 13 of the substrate 11, there is an optimum temperature range for the substrate. In other words, the optimum temperature range for the substrate is 1
00-1000°C.

Note that below 100°C, the adhesion of the composite oxide film to the substrate surface deteriorates. Moreover, at temperatures above 1000° C., the deviation from the stoichiometric ratio of components A, B, and Cu in the composite oxide film increases (becomes large).

Furthermore, the present inventors have found that a temperature range of 200 to 500°C for the substrate when depositing the composite compound film is optimal in terms of the functionality of this type of vapor deposition equipment and the reproducibility of the properties of the composite oxide film. confirmed. In this case, the formed composite compound film is amorphous or composed of microcrystals such as (A,B)3Cu20y-a which exhibit superconductivity.

However, surprisingly, this type of coating exhibits semiconducting properties, and no superconductivity is observed even at liquid He temperatures (4°K).

The present inventors have discovered that superconductivity can be generated by further heat-treating this type of composite compound or film in an oxidizing atmosphere such as air at normal pressure, a mixed gas of argon and oxygen, or pure oxygen. In this case, the optimal heat treatment temperature is 70
0 to 1000°C, heat treatment time is 1 to 100 hours,
In particular, it is characterized by a long heat treatment time, which is unconventional for thin film materials, and by slow cooling after heat treatment. If the heat treatment time is less than 1 hour, superconducting properties cannot be obtained with good reproducibility of semiconductor properties. Moreover, when the time exceeds 100 hours, the resistivity becomes high and the characteristics of the film become unstable. Does not exhibit steep superconductivity. For example, an annealing time of 20 hours or more is required to obtain superconductivity.

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

(Specific Example) Using a magnesium oxide single crystal (100) plane as the substrate 11, (Y, B a ) 3Cu 20 ? was sintered by high-frequency planar magnetron sputtering. The target was deposited by sputtering in an Ar gas atmosphere to form a layered structure on the substrate as a crystalline (Y,Ba)sCuzot film.

In this case, the Ar gas pressure was 0.5 Pa, the sputtering power was 150 W, the sputtering time was 10 hours, the film thickness was 6 μI, and the substrate temperature was 250° C. The formed layered structure was further heat-treated at 900° C. for 70 hours in air, and then slowly cooled for 24 hours.

FIG. 2 shows an example 3 in which a sapphire R surface is used as the substrate 11 and a ternary compound coating 12 whose main components are (Y, Ba) 3 cu 207 is deposited by sputtering deposition method.
The X-ray diffraction spectrum of the original compound 1112 is shown. Second
In the figure, spectrum a is obtained from the coating 12, and spectrum b is obtained from the layered perovskite structure exhibiting superconductivity. As shown in the figure (the coating spectrum a is similar to the spectrum b of layered perovskite, superconductivity occurred).

The superconducting transition temperature of the coating was 45°.

In this example, the film thickness of the coating 12 is 6 μm, but it has been confirmed that superconductivity occurs even when the film thickness is as thin as 0.1 μm or less, or as thick as 10 μm or more.

The present inventors experimentally investigated in detail the effectiveness of crystalline substrates other than sapphire. A film with the (Y, Ba)3cug07 structure was deposited on a magnesium oxide, spinel single crystal substrate by sputtering vapor deposition in the same manner as for the sapphire single crystal, and these films were heated in air for 90 minutes.
It was confirmed that all of the samples exhibited superconductivity when they were heat-treated at 0° C. for 70 hours and then slowly cooled for 24 hours. Similar results were also obtained for strontium titanate, silicon, and gallium arsenide single crystals.

The (Y,Ba)3cuzo7-based superconducting material is said to have a two-layer perovskite structure, and the structure is complex. When the substrate temperature is raised to above the epitaxial temperature on a single crystal substrate to enhance the single crystal coating, a tetragonal perovskite structure is likely to be formed (in many cases, a layered perovskite structure cannot be obtained with good reproducibility. Therefore, it is difficult to carry out the present invention. As mentioned in the example, the present inventors have found that a layered perovskite structure can be obtained with better reproducibility by selecting the substrate temperature in a rather low range, forming a composite compound film with an amorphous or microcrystalline structure, and then crystallizing it by heat treatment. was confirmed experimentally.

In this case, the substrate having a single crystal structure is effective in assisting the solid phase epitaxial growth of the coating during the heat treatment process. In particular, if an amorphous film is formed on the substrate in advance and then heat treated, the crystalline film will be more effectively taxially formed on the surface of the crystalline substrate, and this will be effective in forming a thin film with excellent superconducting properties. The present inventors confirmed that. Note that when crystallinity of the superconducting film is not particularly required (when steep superconducting dislocations are not required), a polycrystalline ceramic substrate is effective.

In sputtering deposition of this type of oxide film, for example, A
Although a mixed gas of r and 02 is used as a sputtering gas, the present inventors have found that the presence of 02 gas increases the resistivity and makes it difficult to form a superconductor. Experimentally, A
The present inventors have confirmed that inert gases such as r, Xe, Ne, and Kr, or mixed gases of these inert gases, are effective as sputtering gases.

The present inventors have confirmed that all sputtering vapor deposition methods, such as high-frequency bipolar sputtering, direct current bipolar sputtering, and magnetron sputtering, are effective.

Particularly in the case of DC sputtering, it is necessary to lower the resistivity of the sputtering target to 10 -3 Ωcm or less; if the resistivity is higher than this, sufficient sputtering discharge will not occur. Note that the resistivity of the target is usually adjusted by adjusting the sintering conditions of the target.

Particularly in this type of apparatus, the present inventors have confirmed that DC sputtering is effective for precise control of sputtering power, etc., and that DC magnetron sputtering or a DC magnetron sputter gun is particularly effective.

In addition, as a method for forming a composite compound film on the surface of a substrate, the main component of the metal is deposited on the substrate by physical vapor deposition, and the film is further irradiated with an oxygen beam or oxygen ions during film formation. It is also possible to oxidize the main component. In addition to sputtering, the physical vapor deposition method includes thermal evaporation, for example, sputtering deposition using the main alloy component of the composite oxide film as a target while irradiating with an electron beam. In this case, the film formation rate is more than an order of magnitude faster than sputtering vapor deposition using a composite oxide target, and it is industrially more effective.

The detailed characteristics of this type of coating, such as its crystal structure, are such that because the coating is constrained on the substrate, there are large strains and defects within the coating that do not exist in ordinary sintered bodies. For this reason, it is not possible to infer the method of manufacturing the coating from the method of manufacturing the sintered body. Although the details of the physical meaning of the heat treatment of the film are not clear, it can be roughly considered as follows.

That is, the compound (A*B)sCuto7 is not formed in the composite compound film deposited on the substrate by sputtering vapor deposition or the like. In this case, for example, BCLI03
A composite oxide is formed in which the oxide of element A is dispersed in a network of a tetragonal perovskite structure. Superconductivity results from the generation of layered perovskite structures, and this process is associated with heat treatment.

Note that the reason why superconductivity cannot be obtained when the heat treatment time is 1 hour or less is considered to be due to insufficient formation of the layered helobskite structure. Although the heat treatment was carried out using an ordinary heater heating furnace, it is also possible to apply an engineering heat treatment method using laser light, infrared rays, etc., or a heating method using an electron beam.

Details of changes in superconducting properties due to changes in constituent elements A and B of this type of ternary compound superconductor ABzCusOr are not clear. However, it is true that A indicates trivalence and B indicates divalence. Although Y was explained as an example of element A, Sc, La, and even lanthanum series elements (
Even if the atomic number is 57 to 71), the superconducting transition temperature changes, but the essential properties of the layered structure of the invention do not change.

Also, regarding B elements, changes in group IIa elements such as Sr, Ca, and Ba change the superconducting transition temperature by about 10'', but this does not essentially change the characteristics of the layered structure of the present invention.

The superconducting material shown here has a two-layer perovskite structure, but this type of perovskite-structure superconducting material having a multilayer (zero layer) structure such as a three-layer structure or a four-layer structure (A, B) n++ Cu nosn++ can also be formed by the same manufacturing method as the present invention, and can be put to practical use as a superconducting material.

Effects of the Invention Particularly, the superconductor according to the present invention has a great feature in that the superconductor is made into a thin film. In other words, in thin film formation, the superconductor material is decomposed into ultrafine particles in the atomic state and then deposited on the substrate, so the composition of the formed superconductor is essentially more homogeneous than that of conventional sintered bodies. be. Therefore, a superconductor with very high precision is realized with the present invention.

As explained above (according to the method for manufacturing a thin film superconductor of the present invention), for example, since it is formed in the form of a thin film on a crystalline substrate, it is essentially more precise than a sintered body, and is made of Si or Ga.
It is possible to integrate devices such as As, and
It is used in the production of various superconducting devices such as Josephson elements. In particular, the transition temperature of this type of compound superconductor may be room temperature, so the range of conventional practical use is wide, and the industrial value of the present invention is high.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a thin film superconductor formed by a method for producing a thin film superconductor according to an embodiment of the present invention, and FIG. 2 is a diagram of basic characteristics of the thin film superconductor of the present invention. 11...Substrate, 12...Ternary compound coating.

Claims (16)

[Claims] (1) Main components (A, B)_3Cu_2O_7 on the substrate
A method for producing a thin film superconductor, comprising: depositing a composite compound film of ____δ, and further heat-treating the film. Here, A represents at least one kind of Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B represents at least one kind of group IIa elements. δ is 0≦
δ≦7. (2) The method for manufacturing a thin film superconductor according to claim 1, wherein the substrate is made of a material having a coefficient of linear expansion α>10^-^6/°C. (3) The substrate is magnesium oxide, sapphire (α-A
2. The method for producing a thin film superconductor according to claim 1, wherein the thin film superconductor is made of at least one of single crystals such as 1_2O_3), spinel, strontium titanate, silicon, and gallium arsenide. (4) The base material is alumina, magnesium oxide, zirconium oxide, steatite, forsterite, beryllia,
A method for manufacturing a thin film superconductor according to claim 1, characterized in that the thin film superconductor is made of porcelain such as spinel. (5) A method for producing a thin film superconductor according to claim 1, characterized in that the composite compound film is deposited on the substrate by a physical vapor deposition method such as sputtering vapor deposition or thermal vapor deposition. (6) The composite compound coating is deposited on the substrate by a chemical vapor deposition method such as normal pressure or reduced pressure chemical vapor deposition method, plasma chemical vapor deposition method, or photochemical vapor deposition method. A method for manufacturing a thin film superconductor according to claim 1. (7) The method for producing a thin film superconductor according to claim 5, characterized in that in sputtering deposition, the substrate temperature is set within a range of 100 to 1000°C during film deposition. (8) The method for producing a thin film superconductor according to claim 5, characterized in that in sputtering deposition, the substrate temperature is set within a range of 200 to 500°C during film deposition. (9) The method for producing a thin film superconductor according to claim 1, wherein normal pressure air or pure oxygen is used as an atmosphere in the heat treatment. (10) In sputtering deposition, the main components are (A,
B) The method for manufacturing a thin film superconductor according to claim 5, characterized in that a composite compound target of _3Cu_2O_7_-_δ is sputter-deposited. (11) In sputtering deposition, Ar, Xe, N
6. The method for producing a thin film superconductor according to claim 5, wherein the thin film superconductor is deposited by sputtering using at least one of E, Kr, or a mixed gas thereof. (12) The method for producing a thin film superconductor according to claim 5, wherein the sputtering deposition is performed by at least one of bipolar sputtering, DC bipolar sputtering, and magnetron sputtering. (13) The method for producing a thin film superconductor according to claim 5, wherein the electrical resistivity of the composite compound target is set to 10^-^3 Ωcm or less in sputtering deposition. (14) In the physical vapor deposition method, the main metal component of the composite compound film is deposited on the substrate, and then oxygen beam or oxygen ions are irradiated during film formation to oxidize the main metal component on the surface of the substrate. A method for producing a thin film superconductor according to claim 5. (15) The thin film superconductor according to claim 5, wherein the thin film superconductor according to claim 5 is deposited by sputtering using the main alloy component of the composite compound film as a target while irradiating oxygen ions onto the substrate in the physical vapor deposition method. manufacturing method. (16) By solid phase epitaxial method on a crystalline substrate,
A method for producing a thin film superconductor, which comprises depositing a composite oxide film whose main components are (A, B)_3Cu_2O_7.