JPS63299019A - Manufacture of thin film superconductive material - Google Patents

Abstract

PURPOSE:To obtain a superconductive material of a high accuracy by decomposing a specific raw material for the superconductive material into minute particles of an atomic state, depositing them on a substrate and irradiating hydrogen ions. CONSTITUTION:Hydrogen ions are irradiated to a complex compond film of an oxide containing an element A, an element B and Cu constituted with the mol ratio of the elements of 0.5<=(A+B)/Cu<=2.5. Here, A denotes at least one element of Sc, Y and an element of lanthanum family (atomic numbers 57-71), and B at least one element from the IIa group. Since the raw material of the superconductive material is deposited on the substrate after being decomposed into tiny particles of the atomic state, the composition of the superconductive material formed becomes uniform. Furthermore, hydrogen ion treatment has a good controllability, enabling the treatment within a short period of time, and compensates crystal defect to obtain a desired crystal structure. This makes it possible to obtain the superconductive material of a high accuracy.

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 As high-temperature superconductors, niobium nitride (NbN) and germanium niobium (N b s ) are used as A15 type binary compounds.
G e ), etc. 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-La-Cu-0-based high-temperature superconductors have been proposed [J, G, Bend.

rz and K, A, Muller,
a rphysik B)-Condensed M
atter 64.189-193 (1986)]
. Additionally, ]Y-Ba-Cu-0 was recently proposed to be a higher temperature superconducting material. (Literature) (l1
1. K., Wu et al.

Physical Review Letters (Physical R
View Letters) Vol, 5B No9
．． 908'-910(19B?)]]Y-Ba-Cu
- The details of the superconducting mechanism of OJi materials are not clear, but the transition temperature may be higher than the liquid nitrogen temperature, and it has more promising properties as a high-temperature superconductor than conventional binary compounds. Composite compound materials can be made into thin films through ion processes to form high-temperature superconductors, but heat treatment is required to achieve good superconducting properties. This heat treatment is performed to control the crystallinity of the composite compound film and the amount of oxygen, but these optimization conditions cannot always be obtained at the same temperature, and the treatment requires a long time, and The problem was that the setting of conditions such as cooling was complicated and the reproducibility was poor.

Means for Solving the Problems The basic composition 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 substrate surface, and the molar ratio of the elements is A+B 0.5≦ It is characterized in that a ternary compound film 12 of □≦2.5 Cu is attached. The present inventors have discovered that this type of superconductor can be produced by depositing the above-mentioned composite compound film on a heated substrate through a process called vapor deposition, and then irradiating it with hydrogen ions either subsequently or after heat treatment. This invention was discovered after discovering that it can be formed. Here A is Sc,
Among Y and lanthanum series elements (atomic number 57-7.1), B is Ba, Sr, Ca, Be,
A small group of Group IIa elements such as Mg (also refers to one type of element).

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, thinning is achieved by decomposing the superconductor material into ultrafine particles in the atomic state, depositing them on a substrate, and then irradiating the formed superconductor with hydrogen ions after heat treatment or oxygen treatment. The composition of the body is essentially homogeneous compared to 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. This coating 12 is usually formed at a high temperature of several hundred degrees Celsius, and since the superconductor is operated at a low temperature, for example, liquid nitrogen temperature (-195 degrees Celsius), the adhesion between the base 11 and the coating 12 is particularly poor, and the coating 12 is often damaged. The present inventors have confirmed that. Furthermore, as a result of investigating the detailed thermal characteristics of the substrate for various materials, the present inventors found that the linear thermal expansion coefficient α of the substrate
10-6/l: It was confirmed that the coating was not damaged and could be put to practical use. For example, the inventors of the present invention have confirmed that if quartz glass with a diameter of 10-67 mm is used as the substrate, the coating 12 will have numerous cracks and become a discontinuous coating, making it difficult to put it to practical use.

Furthermore, the present inventors have discovered that there is an optimal material for the base body 11 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
It was confirmed that single crystals such as -A120g), strontium titanate, silicon, and gallium arsenide are effective. However, although this is to effectively grow a highly crystalline coating 12 on the surface 13,
It suffices if at least the substrate surface 13 is single crystal.

The present inventors confirmed that when processing this type of superconductor into an arbitrary shape, such as a cylinder, sintered porcelain is more effective than a single crystal as a base material, and also found that the most suitable porcelain material I found out. In other words, the present inventors have found that alumina, maglucium oxide, derconium 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, a composite compound film of AB-Cu-0 is first deposited on a substrate by physical vapor deposition such as sputtering or thermal evaporation, such as electron beam evaporation or laser beam evaporation.

In this case, the superconductor A-B-Cu-0 is also said to be an oxygen-deficient perovskite (A, B) ecusota, although its crystal structure and composition formula have not yet been clearly determined.

The present inventors have confirmed that if the element ratio in the produced film is within the range of , superconductivity can be observed even if there is a slight difference in critical temperature. The method for forming this composite compound film is not limited to physical vapor deposition, but also chemical vapor deposition, such as atmospheric or low pressure chemical vapor deposition, plasma chemical vapor deposition, and photochemical vapor deposition. The vapor phase growth method also uses component A.

The present inventors have confirmed that it is effective if the ratios of B and Cu match.

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 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 inventors have found that a temperature range of 500 to 900° 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, microcrystalline, or single crystalline.

However, surprisingly, this type of coating exhibits semiconducting properties, and superconductivity may not be observed at liquid He temperatures (4°K). It was also confirmed that when the film was discharged into the air, the resistance became high and the film was extremely unstable and unreliable.

The present inventors discovered that by further heat-treating this type of composite compound film in an oxidizing atmosphere such as air at normal pressure, a mixed gas of argon and oxygen, or pure oxygen, superconductivity occurs and long-term stability is also improved. In this case, the optimal heat treatment temperature is 700 to 1000°C and the heat treatment time is 0.1 to 10 hours.In addition, when the heat treatment time exceeds 10 hours, the resistivity increases and the properties of the film deteriorate. It becomes unstable and does not exhibit steep superconductivity.

On the other hand, the present inventors have also discovered that the superconducting properties can be improved by irradiating the film with hydrogen ions. In this case, it has been found that the coating is more effective when heated to 300 to 600°C. At 600° C. or higher, hydrogen ions stop reacting with the coating composite compound and no effect can be obtained.

(Specific Example) Y2Ba4 sintered by high-frequency Brenner magnetron sputtering using a sapphire single crystal R-plane as the base 11
A cuao+a target was sputter-deposited in a mixed gas atmosphere of Ar and 02, and crystalline Y was deposited on the above substrate.
It was deposited as a 2 Ba 4 Cue Os 4 coating to form a layered structure.

In this case, the gas pressure was 0.5 Pa, the sputtering power was 150 W, the sputtering time was 1 hour, and the film thickness was 0.
．． The thickness was 5 μm, and the substrate temperature was 800°C. The formed coating may be heat-treated for 2 hours at 900°C in air or oxygen atmosphere, then cooled slowly for 3 to 4 hours, and then heated to 450°C and irradiated with hydrogen ions accelerated at a voltage of 2KV. did.

In FIG. 2, a sapphire R-face is used as the base 11, and the main component is Y t Ba a Cu e by sputtering deposition method.
The X-ray diffraction spectrum of the ternary compound coating 12 in the example when the ternary compound coating 12 No. 01 was attached is shown. In FIG. 2, spectrum a is obtained from a coating 12 treated according to the method of the present invention, and spectrum b is obtained from a structure exhibiting superconductivity. As the figure shows,
The coating spectrum a was similar to the spectrum b, and superconductivity occurred.

The superconducting transition temperature of the coating was 90°.

In this example, the film thickness of the coating 12 is 0.5 μm,
It was confirmed that superconductivity occurs when the film thickness is as thin as 0.1 μm or less, and when it is thicker than 10 μm.

The present inventors experimentally investigated in detail the effectiveness of crystalline substrates other than sapphire. A film having a Y2Ba4Cu60I4 structure is deposited on a magnesium oxide, spinel single crystal substrate by sputtering deposition method in the same manner as in the case of a sapphire single crystal, and by subjecting these films to the hydrogen ion treatment of the present invention, both exhibit superconductivity. This was confirmed.

Similar results were also obtained for strontium titanate, silicon, and gallium arsenide single crystals.

The superconductor of the present invention has a complex crystal structure and is not yet well understood. If the substrate temperature is raised to above the epitaxial temperature of a single crystal substrate to increase single crystallinity, a tetragonal perovskite structure is likely to be generated (and a superconductor cannot be obtained with good reproducibility in many cases. Therefore, the embodiments of the present invention As stated in (
However, it is better to select the substrate temperature in a low range, form a composite compound film containing orthorhombic perovskite or microcrystalline structure, crystallize it by heat treatment, and optimize the amount of oxygen and crystal defects by hydrogen treatment. The present inventors have experimentally confirmed that this can be obtained.

In this case, it is effective to heat-treat the single-crystal structure substrate to facilitate solid-phase epitaxial growth of the film. In particular, by forming an amorphous film on a substrate in advance and heat-treating it, the crystalline film is effectively solid-phase epitaxially formed on the surface of the crystalline substrate, and then the present invention can be continued without breaking the vacuum of the film forming apparatus. The present inventors have confirmed that hydrogen ion treatment is effective in forming a thin film with excellent superconducting properties. In addition, when crystallinity of the superconducting film is not particularly required (when steep superconducting dislocations are not required)
A polycrystalline porcelain substrate is 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. However, although the resulting film containing more oxygen than necessary exhibits good crystallinity, its superconducting properties may not be optimal.

The inventors have discovered that the crystallinity of this thin composite compound coating can be improved by heat-treating it at 800° C. or higher. The hydrogen treatment of the present invention is particularly effective when applied to a film that has been heat treated at 800° C. or higher. As mentioned above, hydrogen treatment can be carried out by introducing a desired gas into a commonly used vacuum chamber, applying high frequency waves to this gas from parallel electrodes to cause a discharge, and placing a composite compound coating in this discharge plasma. It was confirmed that this method improves superconducting properties. However, in this method, the coating is irradiated with particles other than ions, changing the surface condition of the coating, so it is desirable to separate the ion source and the ion irradiation section.

FIG. 3 shows a method for realizing this condition.

Hydrogen gas or a gas containing hydrogen is introduced into the ion source 31, and a high frequency voltage is applied to electrodes 32 and 33 facing each other across the gas to generate plasma. A magnetic field generation source 34 for forming a magnetic field in this plasma is disposed, and a voltage is applied between the plasma of the ion source and the substrate table 36 on which the substrate 35 on which the composite compound film is formed is disposed. By applying , oxygen ions are extracted from the ion source and irradiated onto the composite compound film on the substrate stage. At this time, the inventors have discovered that by heating the substrate to 300 to 600° C. with the heater 37, the efficiency of the hydrogen ion treatment can be increased, the treatment time can be shortened, and the superconducting properties of the film can be improved.

Also, the voltage applied between the plasma and the characteristic sample stage is 5KV.
In the following cases, the surface of the film was sputtered, but it was confirmed that the inside of the film could be effectively treated with hydrogen ions.

Figure 4 shows hydrogen gas or hydrogen-containing gas introduced into a vacuum chamber 41, irradiated with microwaves to generate a plasma, and a magnetic field 42 applied to the plasma to increase the ionization efficiency of hydrogen ions. The ion source was used as an ion source. In this case, a 2.45 GHz microwave is normally used as the microwave source 43, and the magnetic field strength is set to 8.
When the temperature is set to about 75 Gauss, electron cyclotron resonance occurs, which increases the efficiency of hydrogen ionization. This ion source 4
It has a structure in which hydrogen ions extracted from 4 are irradiated onto a composite compound coating placed on a sample stage. In this case, we discovered that high-energy hydrogen ions efficiently ionized by microwaves efficiently hydrogenate the composite compound film and improve its superconducting properties.

In the hydrogen treatment method described above, by irradiating the film with hydrogen ions and at the same time irradiating it with short wavelength light of 500 nm or less, crystal defects caused by hydrogenation can be efficiently compensated for, and it has been shown that ultraviolet irradiation is particularly effective. confirmed.

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 hydrogen treatment of the film are not clear, it can be roughly considered as follows. That is, in a composite compound film deposited on a substrate by sputtering vapor deposition or the like, (A, B) e Cu
e No compound called OIa is formed. in this case,
For example, a composite oxide is formed in which an oxide of element A is dispersed in a BCuOs tetragonal perovskite structure network. The generation of structures exhibiting superconductivity is related to heat treatment. That is, 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 this structure. Furthermore, it is necessary to appropriately contain oxygen in order to obtain good superconducting properties; if it is too large, it becomes an insulator, and if it is too small, it is unstable and decomposes due to moisture or the like. When the hydrogen treatment according to the present invention is performed, the oxygen content can be easily controlled to an appropriate value, and the treatment can be carried out in a short time, which is convenient for producing superconducting thin films.

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.

This kind of ternary compound superconductor (A, B)acue014
The details of changes in superconducting properties due to changes in constituent elements A and B are not clear. However, it is true that A indicates trivalence and B indicates divalence. Although the explanation has been given using an example of Y as element A, SC, La, and even lanthanum series elements (atomic numbers 57 to 71) are also 0, and the fact that the superconducting transition temperature changes does not change the essential characteristics of the invention. do not have.

Also, regarding B elements, changes in Na group 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 present invention.

Effects of the Invention Particularly, the superconductor according to the present invention is characterized in that the superconductor is made into a thin film and treated with hydrogen ions.

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. Furthermore, compared to the conventional treatment using only heat, the hydrogen ion treatment according to the present invention has better controllability and can be performed in a shorter time, and can compensate for crystal defects and realize a desired crystal structure. Therefore, a superconductor with very high precision is realized with the present invention.

As explained above, according to the method for producing a thin film superconductor of the present invention, it is formed in the form of a thin film on a crystalline substrate, so it is essentially more accurate 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, FIG. 2 is a basic characteristic diagram of the thin film superconductor of the present invention, FIGS. 3 and 4 1 is a schematic configuration diagram of an apparatus for a hydrogen treatment apparatus of the present invention. 11... Substrate, 12... Ternary compound coating, 31.3
4...Ion source, 32.33.High frequency electrode, 34
．． 42... Magnetic field generation source, 35... Substrate, 36...
Board stand, 37...heater. Name of agent: Patent attorney Toshio Nakao and one other person Fig. 1 Fig. 2 Magnesium oxide... M2O2UQ 2θ (Friend 0ff 2θ (7) Fig. 3 Fig. 4

Claims (15)

[Claims] (1) Irradiating hydrogen ions to a composite compound film composed of an oxide containing element A, element B, and Cu, with a molar ratio of elements of 0.5≦(A+B)/Cu≦2.5. A method for producing a thin film superconductor characterized by: 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. (2) The method for producing a thin film superconductor according to claim 1, which comprises heating the composite compound film during hydrogen ion irradiation. (3) The method for producing a thin film superconductor according to claim 1, wherein plasma generated by discharging a gas containing at least hydrogen in a vacuum chamber is used as the hydrogen ion source. (4) The method for producing a thin film superconductor according to claim 3, wherein plasma generated by applying a high frequency voltage including microwaves to a gas is used as the hydrogen ion source device. (5) A method for manufacturing a thin film superconductor according to claim 4, characterized in that plasma is irradiated with hydrogen ions generated by applying a magnetic field. (6) The method for producing a thin film superconductor according to claim 2, characterized in that the composite compound coating during hydrogen ion irradiation is heated from 300°C to 600°C or less. (7) A patent characterized in that hydrogen ions generated by gas discharge in a vacuum chamber are irradiated by applying a voltage between the plasma in the vacuum chamber and a sample stage on which a composite compound coating is installed. A method for manufacturing a thin film superconductor according to claim 3. (8) Claim 7, characterized in that an electrode set at a predetermined potential is installed between the plasma generated by applying a high frequency voltage to hydrogen gas and the sample stage, and hydrogen ions are irradiated. A method for manufacturing thin film superconductors. (9) The method for manufacturing a thin film superconductor according to claim 7, characterized in that a DC voltage of 5 KV or less is applied between the plasma and the sample stage. (10) A method for manufacturing a thin film superconductor according to claim 4, characterized in that a composite compound coating is placed in plasma generated by applying a high frequency voltage. (11) A method for manufacturing a thin film superconductor according to claim 3, characterized in that hydrogen ions are irradiated with light at the same time. (12) The method for manufacturing a thin film superconductor according to claim 1, wherein after forming the composite compound film, hydrogen ion irradiation is performed successively using the same device. (13) The method for producing a thin film superconductor according to claim 1, which comprises forming the composite compound film, then heat-treating it in an oxygen-containing atmosphere, and then irradiating it with hydrogen ions. (14) Heat treatment at 800℃ or higher, hydrogen ion irradiation at 60℃
14. The method for manufacturing a thin film superconductor according to claim 13, wherein the method is performed for a film at a temperature of 0° C. or lower. (15) The method for manufacturing a thin film superconductor according to claim 1, characterized in that the composite compound film created is irradiated with hydrogen ions while being irradiated with hydrogen ions.