JP2702711B2 - Manufacturing method of thin film superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a superconductor. In particular, the present invention relates to a method for manufacturing a compound thin film superconductor. As a conventional art high-temperature superconductor, but such niobium nitride (NbN) and germanium niobium (Nb ₃ Ge) is known as A15 type binary compounds, superconducting transition temperatures of these materials are met at most 24 ° K Was. On the other hand, a perovskite-based ternary compound is expected to have a higher transition temperature, and a Ba-La-Cu-O-based high-temperature superconductor has been proposed [JGBendorz and KAMu.
ller, Zeit Schrift Fair Physik (Ze ts
hrift frphysik B) -Condensed Matter 64,189-193
(1986)]. Furthermore, it has recently been suggested that the Y-Ba-Cu-O system is a higher temperature superconducting material. (Literature) [M.
K. Wu et al., Physical Review Letters (Physical R
eview Letters) Vol, 58 No9, 908-910 (1987)] The details of the superconducting mechanism of the Y-Ba-Cu-O material are not clear, but the transition temperature may be higher than the liquid nitrogen temperature. As a high-temperature superconductor, more promising properties are expected than conventional binary compounds. Problems to be Solved by the Invention However, Y-Ba-Cu-O-based materials can be formed only in the process of sintering with current technology, and thus can be obtained only in the form of ceramic powder or blocks.
On the other hand, when this kind of material is put to practical use, it is strongly desired to process it into a thin film. However, it is considered very difficult to form a thin film with the conventional technology. The present inventors have discovered that a thin film of a high-temperature superconductor is formed when a thin film of such a material is deposited by an ion process, and based on this, invented a method of manufacturing a thin film superconductor. Means for Solving the Problems The basic configuration of the thin film superconductor formed by the manufacturing method of the present invention is an oxide containing at least A, B, and Cu on the surface of the substrate, and the molar ratio of the elements is Characterized in that a ternary compound coating 12 is applied. The present inventors have found that this kind of long conductor is formed on a heated substrate by depositing the above-mentioned composite compound film by, for example, a process called vapor deposition and then heat-treating it in an oxidizing atmosphere. It is in accordance with the invention. Where A is Sc, Y and lanthanide elements (atomic number
57-71) At least one kind of B is Ba, Sr, Ca, Be, Mg
Indicate at least one element from group IIa elements. Action The method for manufacturing a thin film superconductor according to the present invention is characterized in that the superconductor is thinned. In other words, the thinning is performed by decomposing the material of the superconductor into ultrafine particles, which are in an atomic state, and then depositing the superconductor on the substrate. Therefore, the composition of the formed superconductor is essentially homogeneous compared to a conventional sintered body. .
Thus, very high precision superconductors are realized using the method of the present invention. Embodiment An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the ternary compound film 12 is formed by, for example, a sputtering method. In this case, the base 11 is intended to hold the ternary compound coating 12 exhibiting superconductivity. The coating 12 is usually formed at a high temperature of several hundred degrees Celsius, and since the superconductivity is operated at a low temperature of, for example, liquid nitrogen temperature (-195 ° C), the adhesion between the substrate 11 and the coating 12 is deteriorated, and the coating 12 is often damaged. The present inventors have confirmed that this is done. Furthermore, the present inventors have examined the detailed thermal properties of the substrate for various materials. As a result, if the linear thermal expansion coefficient of the substrate is α> 10 ^{−6 /} ° C.,
It was confirmed that the film was practically used without any damage to the film. For example, if quartz glass with α <10 ^{−6 /} ° C is used for the substrate,
The present inventors have confirmed that No. 12 had a discontinuous coating with numerous cracks and was difficult to be put to practical use. Furthermore, the present inventors have found that the base 11 of FIG. 1 has an optimal material from the viewpoint of functionality. The present inventors have confirmed that when processing this type of superconductor into an arbitrary shape, for example, a cylindrical shape, the sintered ceramics provided by the contract are more effective than a single crystal as the base, and the optimum ceramic material I found That is, as a porcelain base,
The present inventors have confirmed that the adhesion of the superconducting film 12 to the substrate 11 is optimal for alumina, magnesium oxide, zirconium oxide, steatite, forsterite, beryllia, spinel, etc., such as processing of the substrate. In this case, it is preferable that even the surface of the base is made of this kind of porcelain. To form a thin film superconductor, first, a composite compound coating of AB-Cu-O is deposited on a substrate by physical vapor deposition such as sputtering evaporation or thermal evaporation such as electron beam evaporation or laser beam evaporation. In this case, although the crystal structure and the composition formula of the superconductor AB-Cu-O have not yet been clearly determined, it is also referred to as oxygen-deficient perovskite (A, B) ₆ Cu ₆ O ₁₄ . The present inventors have found that the element ratio in the prepared coating is It was confirmed that the superconductivity phenomenon was found even if there was a slight difference in the critical temperature within the range. The method of forming the composite compound film is not limited to the physical vapor deposition method, but may be a chemical vapor deposition method such as a normal or reduced pressure chemical vapor deposition method, a plasma chemical vapor deposition method, a photochemical vapor deposition method. The present inventors have confirmed that the vapor phase growth method is also effective if the ratios of the components A, B, and Cu are matched. The present inventors have confirmed that there is an optimal temperature range for the substrate when the composite compound coating is applied to the surface 13 of the substrate 11. That is, the optimal substrate temperature range is 100
~ 1000 ° C. If the temperature is lower than 100 ° C., the adhesion of the composite oxide film to the surface of the substrate is deteriorated. At 1000 ° C. or higher, the deviation from the structural ratio of components A, B, and Cu in the composite oxide film becomes large. Furthermore, the present inventor has found that the temperature of the substrate when depositing the composite compound film is particularly preferably in the range of 200 to 500 ° C. in view of the function of this type of vapor deposition apparatus and the reproducibility of the characteristics of the composite oxide film. Confirmed. In this case, the formed composite compound film is composed of amorphous or microcrystal. Surprisingly, however, this type of coating exhibits semiconducting properties, and superconductivity is not seen at liquid He temperatures (4 ° K). The present inventors have found that superconductivity is generated by further heat-treating this kind of composite compound film in an oxide 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 700
~ 1000 ℃, heat treatment time is 0.1 ~ 10 hours. Also, 10
If the time is longer than this, the resistivity increases, the characteristics of the coating become unstable, and no steep superconductivity is exhibited. The cooling time after the heat treatment, for example, a cooling time of 2 hours or more is suitable for obtaining superconductivity. In the sputtering deposition, as a target,
The inventors of the present invention used sintered AB-Cu-O ceramics, and found that when the substrate temperature was in the range of 200 to 500 ° C., the metal components of the target almost coincided with the components in the formed thin film. Confirmed. Therefore, the composition of the target should be within the optimal range of the coating. The present inventors have confirmed that In this case, even if the target is a granular or powdery sintered body in addition to a plate-like or cylindrical ceramic, it is effective for sputtering deposition. In the case of powder, for example, a stainless steel dish is filled with powder and used. Hereinafter, more specific reference examples will be shown in order to further understand the contents of the present invention. (Reference Example) A sintered Y ₂ Ba ₄ Cu ₆ O ₁₄ target was sputter-deposited by high frequency planar magnetron sputtering in an Ar gas atmosphere using a magnesium oxide single crystal (100) plane as the substrate 11, and was deposited on the substrate. It was deposited as a crystalline Y ₂ Ba ₄ Cu ₆ O ₁₄ coating to form a layered structure. In this case, Ar gas pressure is 0.5 Pa, sputtering power is 1
50 W, sputtering time 6 hours, film thickness 5.2 μm,
The substrate temperature was 250 ° C. The formed film was further heat-treated at 900 ° C. for 2 hours in an oxygen atmosphere and then cooled for 3 to 4 hours. FIG. 2 shows a ternary compound film 1 whose main component is Y ₂ Ba ₄ Cu ₆ O ₁₄ by sputtering vapor deposition using a sapphire R surface as a substrate 11.
2 shows an X-ray diffraction spectrum of a ternary compound coating 12 in Example when 2 was attached. In FIG. 2, spectrum a is obtained from the coating 12, and spectrum b is obtained from a structure exhibiting superconductivity. As the figure shows,
In the coating spectrum a, superconductivity occurred similarly to the spectrum b. The superconducting transition temperature of the coating was 90 K. In this example, the film thickness of the film 12 was 5.2 μm, but it was confirmed that superconductivity was generated when the film thickness was as thin as 0.1 μm or less or as thick as 10 μm or more. The present inventors have examined experimentally the effectiveness of crystalline substrates other than sapphire in detail. Magnesium oxide,
A film having a Y ₂ Ba ₄ Cu ₆ O ₁₄ structure is deposited on a spinel single crystal substrate by sputtering in the same manner as in the case of a sapphire single crystal, and these films are heat-treated at 900 ° C. for 2 hours in air and then 3 to 4 times. It was confirmed that all samples exhibited superconductivity after time exclusion. Also, strontium titanate, silicon,
Similar results were obtained for gallium arsenide single crystals. The superconductor of the present invention has a complicated crystal structure and is not yet well understood. If the temperature of the single crystal substrate is raised to the temperature equal to or higher than the epitaxial temperature and the single crystal film is increased, a tetragonal perovskite structure is easily generated, and a superconductor cannot be obtained with good reproducibility in many cases. Therefore, as described in the examples of the present invention, it is clear that the superconductor can be obtained with higher reproducibility by selecting the substrate temperature in a rather low range, forming an amorphous or microcrystalline structure composite compound film, and then crystallization by heat treatment. The present inventors have confirmed experimentally. In this case, the substrate having a single crystal structure is subjected to a heat treatment process.
It is effective for assisting solid phase epitaxial growth of the coating. In particular, an amorphous film is formed on the substrate in advance,
The present inventors have confirmed that when this is heat-treated, the crystalline film is more effectively solid-phase epitaxially grown on the surface of the crystalline substrate, and is effective for forming a thin film having excellent superconducting properties. The present inventors have found that it is effective to use a polycrystalline porcelain substrate as the substrate. This polycrystalline porcelain substrate is particularly effective when the crystallinity of the superconducting film is not so required (when a sharp superconducting transition is unnecessary). In sputtering deposition of this kind of oxide film, for example,
A mixed gas of Ar and O ₂ is used as a sputtering gas. The present inventors have experimentally confirmed that an inert gas such as Ar, Xe, Ne, or Kr or a mixed gas of these inert gases is effective as a sputtering gas. The present inventors have confirmed that high-frequency bipolar sputtering, DC bipolar sputtering, and magnetron sputtering are all effective for the sputtering deposition method. In particular, in the case of DC sputtering, it is necessary to reduce the resistivity of the sputtering target to 10 ⁻³ Ωcm or less. If the resistivity is higher than this, sufficient sputtering discharge does not occur. Adjustment of the resistivity of the target is usually performed according to the target sintering conditions. In particular, in this type of apparatus, the present inventors have confirmed that DC sputtering is effective for precise control of sputtering power and the like, and DC magnetron sputtering or a DC magnetron sputtering gun is particularly effective. In addition, as a method of forming a composite compound film on the substrate surface, a metal main component is attached to the substrate by physical vapor deposition, and the film is irradiated with an oxygen beam or oxygen ions during the film formation, and the metal surface is formed on the substrate surface. It is also possible to oxidize the main component. In the physical vapor deposition method, in addition to sputtering, thermal vapor deposition, for example, while irradiating an electron beam, is performed by vapor deposition using the alloy main component of the composite oxide film as a target. In this case, the composite oxide target has a feature that the film formation speed is at least one order of magnitude faster than the sputtering deposition, and is industrially more effective. Regarding the detailed characteristics such as the crystal structure of this type of film, since the film is constrained on the substrate, there are large strains and defects in the film that are not present in a normal sintered body. For this reason, it is not possible to analogize the method for producing a coating from the method for producing a sintered body. Although the details of the physical meaning of the heat treatment of the coating film are not clear, the following may be considered. That is, the compound compound (A, B) ₆ Cu ₆ O ₁₄ is not formed in the composite compound film deposited on the substrate by sputtering deposition or the like. In this case, for example, a complex oxide in which an oxide of the element A is dispersed in a network having a perovskite structure of BCuO ₃ tetragonal is formed. The generation of a structure exhibiting superconductivity is related to the heat treatment. That is, the heat treatment time is 1
It is considered that the reason why superconductivity is not obtained in less than the time is that the formation of this structure was insufficient. The heat treatment was performed in a normal heater heating furnace, but an engineering heat treatment method using laser light, infrared light, or the like, a heating method using an electron beam, or the like can be applied. The details of the change in the superconducting characteristics due to the change in the constituent elements A and B of this type of ternary compound superconductor (A, B) ₆ Cu ₆ O ₁₄ are not clear. However, it is true that A is trivalent and B is divalent. Although Y has been described as an example of the A element, Sc, La, and even lanthanum-based elements (atomic numbers 57 to 71) do not change the essential characteristics of the invention to the extent that the superconducting transition temperature changes. . Also, in the case of element B, the change of the group IIa element such as Sr, Ca, and Ba changes the superconducting transition temperature by about 10 ° K, but does not essentially change the characteristics of the present invention. Advantageous Effects of the Invention The superconductor according to the present invention is particularly characterized in that the superconductor is thinned. In other words, the thinning is performed by decomposing the material of the superconductor into ultrafine particles, which are in the atomic state, and then depositing the superconductor on the substrate. Therefore, the composition of the formed superconductor is essentially more uniform than that of a conventional sintered body. is there. Thus, a very accurate superconductor is realized in the present invention. As described above, according to the method for manufacturing a thin film superconductor of the present invention, since it is formed in a thin film on a sintered porcelain body, it is inherently higher in accuracy than a sintered body and can be integrated with a device such as Si or GaAs. It can be used in the manufacture of various superconducting devices such as Josephson devices.
In particular, there is a possibility that the transition temperature of this type of compound superconductor may be room temperature, so that the conventional practical range is wide, and the industrial value of the present invention is high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic configuration diagram of a thin film superconductor formed by a method of manufacturing a thin film superconductor according to one embodiment of the present invention, and FIG. 2 is a basic characteristic diagram of the thin film superconductor of the present invention. is there. 11: Base, 12: Ternary compound coating.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hideaki Adachi               1006 Kadoma Kadoma Matsushita Electric Industrial               Inside the corporation (72) Inventor Tsuneo Sanroku               1006 Kadoma Kadoma Matsushita Electric Industrial               Inside the corporation (72) Inventor Shinichiro Hatta               1006 Kadoma Kadoma Matsushita Electric Industrial               Inside the corporation                (56) References JP-A-63-250882 (JP, A)                 JP-A-64-18920 (JP, A)                 JP-A-63-237313 (JP, A)                 JP-A 64-3001 (JP, A)

Claims (1)

(57) [Claims] On a substrate, a composite oxide film composed of at least three or more elements having copper and oxygen as main components is adhered,
A method of manufacturing a thin film superconductor, further comprising using a sintered ceramic material as a base in a thin film superconductor obtained by heat-treating the coating in an atmosphere containing oxygen. 2. 2. The method according to claim 1, wherein the base is made of a material having a coefficient of linear expansion α> 10 ⁻⁶ / ° C. 3. 2. The method for manufacturing a thin film superconductor according to claim 1, wherein the substrate is made of a porcelain such as alumina, magnesium oxide, zirconium oxide, steatite, forsterite, beryllia, and spinel. 4. 2. The method for producing a thin film superconductor according to claim 1, wherein the composite compound film is deposited on the substrate by a physical vapor deposition method such as sputtering vapor deposition or thermal vapor deposition. 5. Patent for depositing a composite compound film on a substrate by chemical vapor deposition such as normal pressure or reduced pressure chemical vapor deposition, plasma chemical vapor deposition, photochemical vapor deposition, etc. A method for manufacturing a thin film superconductor according to claim 1. 6. 5. The method for manufacturing a thin film superconductor according to claim 4, wherein the substrate temperature is set in the range of 100 to 1000 [deg.] C. during the film deposition in the sputtering deposition. 7. 5. The method for producing a thin film superconductor according to claim 4, wherein the substrate temperature is set in the range of 200 to 500 [deg.] C. during the film deposition in the sputtering deposition. 8. 2. The method for manufacturing a thin film superconductor according to claim 1, wherein in the heat treatment, atmospheric pressure air or pure oxygen is used as an atmosphere. 9. In sputtering deposition, at least the element A,
The molar ratio of the elements in the oxide containing B element and Cu is 5. The method for producing a thin film superconductor according to claim 4, wherein said composite target is deposited by sputtering. 10. In sputtering deposition, Ar, Xe, Ne, Kr,
5. The method for producing a thin film superconductor according to claim 4, wherein sputtering deposition is performed using at least one of O ₂ or a mixed gas thereof. 11. Sputtering deposition at least bipolar sputtering,
5. The method for manufacturing a thin film superconductor according to claim 4, wherein the method is performed by one of DC bipolar sputtering and magnetron sputtering. 12. 5. The method for producing a thin film superconductor according to claim 4, wherein in the sputtering deposition, the electric resistivity of the composite compound target is set to 10 ^-3 Ωcm or less. 13. In the physical vapor deposition method, a metal main component of a composite compound film is deposited on a substrate, and further irradiated with an oxygen beam or oxygen ions during the film formation to oxidize the metal main component on the substrate surface. Claim 5
The method for producing a thin-film superconductor according to the above item. 14． 5. The method for producing a thin film superconductor according to claim 4, wherein in the physical vapor deposition method, sputtering is performed by irradiating oxygen ions onto the substrate while using the alloy main component of the composite compound film as a target. . 15. A composite oxide film composed of at least three or more elements containing copper and oxygen as main components is deposited on a crystalline substrate formed by a sintered porcelain, and the film is heat-treated in an oxygen-containing atmosphere. A solid-phase epitaxial growth to improve the crystallinity of the thin-film superconductor.