JPS63306677A - Superconducting device and manufacture thereof - Google Patents

Abstract

PURPOSE:To form the composition of a formed superconductor substantially homogeneous and a fine structure homogeneous by forming a fine pattern in a previous stage for forming a superconductor, and reducing the thickness of a superconducting material in coincidence with its shape. CONSTITUTION:A photoresist pattern is formed by a photophosphorus process using a photomask on a single crystalline material, such as the round face of a sapphire substrate 11 in a DC SQUID shape, i.e., in the shape in which two arms are formed in a ring having two contractions. Subsequently, a thin tantalum oxide film 12 is adhered by magnetron sputtering over the whole surface. Here, the substrate 11 is again set in a magnetron sputtering device, with sintered YBa2Cu3O7-delta(0<=delta<=7) as a target oxygen argon mixture gas (0.1Pa of pressure) is deposited by sputtering, and a thin superconducting film 13 having 1mum of thickness is formed. The formed layer structure is heat treated in the air, and gradually cooled to obtain a DC SQUID 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a superconducting device and a method for manufacturing the same. In particular, it relates to composite oxide thin film superconducting devices.

Conventional technology As high temperature superconductors, niobium nitride (NbN) and germanium niobium (Wb, Ge
), but the superconducting transition temperature of these materials was at most 24°.

On the other hand, peropskite-based ternary compounds are expected to have even higher transition temperatures, and Ba-La-Cu-0-based high-temperature superconductors have been proposed (J, G, Bednorz
and K. A. Muller, 7 Zeitschrif'
t fur Physik,)-conaensea
Matter 64, 189-193 (1986))
. Furthermore, it has recently been proposed that the Y-Ba-Cu-o system is a higher temperature superconducting material. (M, K, Wu et al. Physical Repureters (Physical R
View Letters) Vol.

68, Ks, 908-910 (1987)
) The details of the superconducting mechanism of Y--Ba-1u-0-based materials are not clear, but the transition temperature may be higher than the liquid nitrogen temperature, making them more promising as high-temperature superconductors than conventional two-element compounds. characteristics are expected.

Problems to be Solved by the Invention However, with current technology, this type of high-temperature superconductor material can only be formed through a process called sintering, so it can only be obtained in the form of ceramic powder or blocks. On the other hand, in order to construct electronic circuits and optical circuits using this type of material, there is a strong demand for superconductor thin film processing and superconductor microfabrication, but with conventional technology, thin film processing is extremely difficult. Moreover, the above-mentioned superconductors are porous and highly hydrophilic, making this type of processing extremely difficult.

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 that superconductivity is selectively exhibited depending on the substrate surface condition. Based on this, we discovered a new superconducting device and its manufacturing method.

Means to Solve the Problems The superconducting device of the present invention forms a part covered with a thin layer made of a material different from that of the substrate on one principal surface of a substrate having in-plane anisotropy, and a superconducting thin film is formed on this part. It is made up of
The main component of the superconducting thin film material is an A-8-1u-o based composite oxide material (Mu is at least one of scandium, yttrium, lanthanum series elements, B is at least one of the h group elements, A, B elements and This is carried out by treatment with a concentration of Cu element.

Function The present invention makes it possible to control superconductivity by making the superconductor into a thin film and by differentiating the interface during thin film formation.The present invention also makes it possible to control the superconductivity due to the fact that the superconductor is made into a thin film and the difference in the interface during thin film formation. The major feature of this technology is that it enables new superconducting devices. That is,
In film thinning, 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. Moreover, in the process of decomposition, deposition, and recrystallization, depending on the crystalline state of the interface, a good superconductor is formed on a single crystal such as magnesium oxide, strontium titanate, or sapphire, but a good superconductor is formed on a substrate. For example, it has been discovered that films deposited on an amorphous thin layer of tantalum oxide have extremely low critical temperatures and do not exhibit superconductivity. By depositing superconductors over the entire surface, the difference in the interface becomes the difference in electrical conductivity, so a superconducting device with extremely high precision can be realized.

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

FIG. 1 is a schematic plan view for explaining an apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a mou 5' in the same figure.

The base plate 11 is often made of a single crystal material, and R-plane sapphire was used here. Next, a photoresist pattern is formed on the substrate 11 by a photolithography process using a photomask in the shape of a DC SQUID, that is, a circular ring having two constrictions and two arms. Subsequently, a tantalum oxide thin film was deposited over the entire surface by magnetron sputtering. The target is tantalum. The substrate temperature is maintained at 100°C in an oxygen/argon mixed atmosphere, and the film is grown to a film thickness of 3 Q nm. When the photoresist pattern is removed, the tantalum oxide pattern 1 is removed according to the shape of the SQUID.
2 was formed.

The width of the constriction was approximately 1 μm, as designed by the photomask.

Here, the substrate 11 is again set in the magnetron sputtering device, and the sintered YBa2Cu, o, -δ (0≦δ
≦7) as a target, using an oxygen-argon mixed gas (pressure O, 1 PIL), keeping the substrate temperature at 450°C, and sputtering power at 200W, Shanter evaporation was performed for 2 hours, and the film thickness was 1 μm.
A superconducting thin film 13 was formed. The formed layered structure was heat treated in air at 90 to 1000°C for about 10 hours, and then slowly cooled to create a DC SQUID 10. As a result of electrical measurements,
It was confirmed that the SQUID constriction part 1.2 functions as a Josephson junction. Furthermore, the superconducting currents in the two constrictions are almost equal, proving that it is easy to produce a SQUID device. When the material structure of the obtained superconducting thin film 13 was analyzed for crystallinity by X-ray diffraction, it was found that the entire surface was perovskite crystal.

FIG. 3 is an enlarged view of the X section in FIG.

2o is a portion where the above-mentioned resist pattern was formed and removed. The thin film 13 is formed with a polyconjunctival membrane 31 and a uniconjunctival membrane 32 . In other words, upon closer examination, even with the same perovskite structure, microscopic differences in crystallinity can be seen depending on the location. It was found that the exposed portion was a single-crystalline film 32. The mechanism of superconductivity in this type of composite oxide has not yet been elucidated.
Although an exact explanation cannot be given, if superconducting current flows along the layers of layered peropskite, it can be thought that the superconducting current will be larger in the single crystal where the layers are aligned, and the current will be smaller in the polycrystalline part. Alternatively, it can be considered that the superconductivity becomes almost zero and almost no superconductivity is exhibited. Because of this phenomenon, it is thought that even if a superconducting thin film is provided over the entire surface, electrical characteristics equivalent to those obtained by forming it only on areas without tantalum oxide are obtained. Considering this as an extension of conventional technology, the conventional method is to form a superconducting thin film over the entire surface of a substrate and then pattern it by photoetching, but this composite oxide is extremely hydrophilic, perhaps due to oxygen defects. is strong, and it is soluble in solutions containing -0 and 10H groups, so it is actually difficult to perform microfabrication using conventional techniques. In the present invention, the microfabrication is completed at a stage before the formation of the complex oxide exhibiting such abnormal hydrophilicity, so there is a great effect that the process can be carried out stably and with good reproducibility.

In this way, the superconducting thin film on the part without the thin layer can be used as an electrical wiring, and in addition to the SQUID, it can also be used as a Gisefson element or a superconducting circuit wiring, taking advantage of its low resistance feature. It is also possible to use thin layers for optical waveguide.
In that case, two circuits, one electrical and one optical, can be integrated and formed.

Although the explanation has been limited to the example of 8-sided sapphire as the material of the substrate 11, other planes may be used, and magnesium oxide or strontium titanate may also be used, since the lattice constants match well and a good superconducting device can be formed. It was confirmed.

Furthermore, although we have described the case of tantalum oxide (T!L205) as the material for the thin layer, examples of nitrides such as TiN
, TaN, MoN, NbN, WN,
MnN, etc., and carbides such as TaC, Tie, N
bC, MoC.

WO, MnC, etc. are used as oxides such as Wb205°Ti.
e2. Ta205. Al□O,, ZrO2, Y2O
The present inventors have confirmed that 5 and the like are effective.

The effect of these thin layers is to control the crystallinity of the composite oxide film and to prevent mutual diffusion during high-temperature processing. The material is not limited to the above-mentioned materials as long as the properties are satisfied.

In addition, the present inventors have confirmed that this composite oxide film only needs to match the stoichiometric ratios of the components B and Cu, and the amount of oxygen is not particularly important.

As a result, methods for forming composite oxide films are not limited to physical vapor deposition, but also chemical vapor deposition, such as atmospheric or low pressure chemical vapor deposition, plasma chemical vapor deposition, etc. , photochemical vapor deposition also uses the components Mu, B and Cu.
The present inventors have confirmed that it is effective as long as the stoichiometric ratios of .

In this case, the present inventors have confirmed that there is an optimal temperature range for heating the substrate. That is, the optimum temperature range is 10o~10oO<0>C. Note that below 10 o'C, the adhesion of the composite compound coating to the substrate surface becomes poor.

Moreover, at 10 Oo'C or more, the deviation from the stoichiometric ratio of the components M, B, and Cu in the composite oxide film increases,
The inventors have discovered that superconducting properties cannot be obtained even after successive heat treatment steps.

Furthermore, the present invention has shown that a temperature range of 200 to 500°C for the substrate when depositing the composite oxide film is optimal in terms of the functionality of this type of vapor deposition apparatus and the reproducibility of the properties of the composite oxide film. They confirmed.

The present inventors have discovered that superconductivity can be generated by further heat-treating this type of composite oxide 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 900
The heat treatment time is 1 to 10 hours at ~100 to 1000° C., and is particularly characterized by the long heat treatment time, which is unconventional for thin film materials, and the slow cooling after the heat treatment. If the heat treatment time is less than 1 hour, semiconductor-like properties will occur, and superconducting properties will not be obtained with good reproducibility. Further, if the cooling time exceeds 10 hours, the resistivity increases and the properties of the film become unstable, and the rapid cooling does not exhibit superconductivity. For example, an annealing time of 10 hours or more is required to obtain superconductivity.

Also in the process of forming this type of superconducting sintered body, a long-time heat treatment of 1 to 10 hours, similar to the heat treatment used in the present invention, is used. However, in the case of a bulk material such as a sintered body, a heat treatment time of about 100 hours, for example, is not particularly long and is usually widely used. On the other hand, in the case of a film, the size of the material itself is, for example, 1 μm or less, which is three to four orders of magnitude larger than the bulk. Therefore, the heat treatment time is also three orders of magnitude shorter than that of bulk materials, considering the movement of substances. Therefore, if the heat treatment process is similar to that for bulk materials, superconducting properties should be obtained with a short heat treatment of several minutes or less. Furthermore, it was thought that this type of heat treatment would be unnecessary if an oxidizing atmosphere was used during film formation. However, it has been experimentally confirmed that a long heat treatment is required as described above. This unexpectedness is thought to be due to the essential difference in properties between the bulk material and the thin film material.

That is, the detailed characteristics of this type of coating, such as the crystal structure, are such that because the coating is constrained on the substrate, there are large strains and defects in the coating that do not exist in ordinary sintered bodies. Therefore, the conventional method for manufacturing a sintered body cannot be directly applied to the method for manufacturing the coating. Furthermore, 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, a composite oxide film deposited on a substrate by sputtering vapor deposition or the like does not form a crystal structure exhibiting superconductivity. In this case, for example, a composite oxide is formed in which the oxide of the human element is dispersed in a network of a BCuO3 tetragonal perovskite structure. Superconductivity results from the development of a layered peropskite structure, and this process is associated with heat treatment.

Note that the reason why superconductivity was not obtained when the heat treatment time was 1 hour or less is considered to be due to insufficient formation of the layered perovskite structure.

Although an example of heat treatment in an oxygen atmosphere has been described here, it has also been confirmed that the amount of oxygen in the film can be controlled by irradiating the film with a beam of oxygen atoms or a beam of oxygen ions.

Furthermore, as a result of examining the crystallinity of the oxide thin film deposited on the tantalum oxide thin layer before and after this heat treatment, it was found that before the heat treatment it had a mixed orientation close to amorphous, but after the treatment it became polycrystalline and became a single crystal. It was confirmed that the crystallinity of the thin film on sapphire was clearly different from that of the thin film shown on sapphire.

When forming a composite oxide film on the surface of a substrate by sputtering vapor deposition, as described above, it is important to control the stoichiometric ratio of the components B and Cu in the film. The present inventors investigated in detail the optimum conditions for sputtering deposition, and surprisingly found that the composition of the sputtering target may be the same as the main component of the target superconductor. The amount of oxygen can be adjusted during sputtering or by heat treatment after sputtering, so it is particularly important for the target composition. Furthermore, in the sputtering deposition of this type of oxide film, for example, a mixed gas of Ar and O2 is used as the sputtering gas, but the presence of O2 gas increases the resistivity of the formed compound film and prevents the formation of a superconductor. The present inventors have found that there are cases where this is necessary. Experimentally, Mr.
The present inventors have confirmed that inert gases such as Xs, Ha, and Kr, or mixed gases of these inert gases, are effective as sputtering gases.

The present inventors have confirmed that sputtering vapor deposition methods such as high-frequency two-hole sputtering, direct current two-hole sputtering, and magnetron sputtering are all effective. Particularly in the case of DC sputtering, it is necessary to lower the resistivity of the sputtering target to less than 10@-5 Ω; if the resistivity is higher than this, sufficient sputtering discharge will not occur. Note that the resistivity of the target is usually adjusted by the sintering conditions of the target. Alternatively, the resistance can be lowered by forming the target as an alloy with copper. In addition, a so-called multi-source sputtering method in which sputter deposition is performed using multiple targets is also possible, and by adjusting the power supplied to each target, it is possible to achieve uniform film thickness and film quality.

Note that active adjustment of the chemical composition of the film and the formation of artificial chemical composition fluctuations such as an artificial lattice are made possible by multi-source sputtering. 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 oxide film on the substrate surface, the main metal component is deposited on the substrate by physical vapor deposition, and the coating is irradiated with an oxygen beam or oxygen ions during film formation, so that the coating is formed on the substrate surface. It is also possible to oxidize the metal main component. In addition to sputtering, thermal evaporation, such as electron beam evaporation, is also effective as a physical vapor deposition method. In the sputtering method, while irradiating the substrate with an oxygen ion beam, the main alloy component of the composite oxide film is sputter-deposited using a target. 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.

Effects of the Invention The present invention is characterized in that a fine pattern is formed before forming a superconductor, and the superconducting material is thinned to match the shape. 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. The fine structure can also be formed uniformly. Therefore, a superconducting device with very high precision is realized with the present invention.

In particular, the transition temperature of this type of oxide 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 the drawing]

FIG. 1 is a schematic plan view of an apparatus according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of the same apparatus, and FIG. 3 is an enlarged view of the portion marked with a circle X in FIG. 10...Superconducting device, 11...Substrate,
12... Tantalum oxide pattern, 13...
...Superconducting thin film, 31... Polycrystalline film, 32
...Single crystalline film. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 figure

Claims (20)

[Claims] (1) A thin layer made of a material different from that of the substrate is selectively formed on one main surface of a substrate having in-plane anisotropy, and a superconducting thin film is formed on the substrate and the thin layer. superconducting device. (2) The superconducting device according to claim 1, wherein a single crystal of magnesium oxide, strontium titanate, or sapphire is used as the substrate. (3) The superconducting device according to claim 1, wherein an oxide, nitride, or carbide is used as the thin layer. (4) A-B-Cu-O composite oxide material as the main component of the superconducting thin film (A is at least one of scandium, yttrium, and lanthanum series elements; B is at least one of group IIa elements; however, A, 2. The superconducting device according to claim 1, wherein the concentrations of B element and Cu element are 0.5≦(A+B/Cu)≦2.5). (5) The superconducting device according to claim 4, wherein A is a composite oxide material of yttrium and B is a composite oxide material of barium. (6) A superconducting device according to claim 1, characterized in that a superconducting thin film formed on a portion of the substrate not covered by the thin layer is used as electrical wiring. (7) The superconducting device according to claim 1, wherein light is guided in the thin layer portion. (8) A thin layer made of a material different from that of the substrate is selectively formed on one main surface of a substrate having in-plane anisotropy, and A-B-Cu-O based composite oxide is applied over the entire main surface. materials (A is at least one of scandium, yttrium, and lanthanum series elements; B is at least one of group IIa elements; however, the concentrations of A, B elements, and Cu element are 0.5≦(A+
A method for manufacturing a superconducting device, which comprises forming a thin film containing B/Cu)≦2.5) as a main component and treating it in an oxidizing atmosphere. (9) A method for manufacturing a superconducting device according to claim 8, characterized in that the thin film is deposited on the substrate by a physical vapor deposition method such as sputtering deposition or thermal evaporation. (10) Thin films are grown by atmospheric or low pressure chemical vapor deposition;
9. The method of manufacturing a superconducting device according to claim 8, wherein the superconducting device is deposited on the substrate by a chemical vapor deposition method such as a plasma chemical vapor deposition method or a photochemical vapor deposition method. (11) When forming a thin film on a heated substrate,
9. The method for manufacturing a superconducting device according to claim 8, wherein the heating is performed within a range of 0 to 1000°C. (12) When forming a thin film on a heated substrate,
9. The method for manufacturing a superconducting device according to claim 8, wherein heating is performed within a range of 0 to 500°C. (13) The method for manufacturing a superconducting device according to claim 8, characterized in that normal pressure air or pure oxygen is used as the atmosphere. (14) In sputtering deposition, the main component is A-B-
10. The method of manufacturing a superconducting device according to claim 9, wherein a composite compound target, which is a Cu-O-based composite oxide, is deposited by sputtering. Here, A is at least one of scandium, yttrium, and lanthanum series elements, B is at least one of group IIa elements,
The concentration of A, B elements and Cu element is 0.5≦A+B/Cu≦
2.5. (15) In sputtering deposition, Ar, Xe, N
15. The method for manufacturing a superconducting device according to claim 14, characterized in that sputtering is carried out using at least one gas of e.g., Kr, or a mixture thereof. (16) The method for manufacturing a superconducting device according to claim 9, wherein the sputtering deposition is performed by at least one of DC dipole sputtering and high-frequency dipole sputtering. (17) The method for manufacturing a superconducting device according to claim 9, wherein the sputtering vapor deposition is performed by simultaneously sputtering a plurality of targets. (18) The method for manufacturing a superconducting device according to claim 9, characterized in that the electrical resistivity of the target for forming the composite oxide thin film is set to 10^-^3 Ωcm or less. (19) In the physical vapor deposition method, the main metal component of a composite oxide thin film is deposited on a 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 manufacturing a superconducting device according to claim 9, characterized in that: (20) In the physical vapor deposition method, the main alloy component of the composite oxide film is sputtered and deposited as a target while irradiating the substrate with an oxygen ion beam. A method for manufacturing a superconducting device.