JPS63298920A - Manufacture of membranous superconductor - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a compound membranous superconductor of a good property easily by applying oxygen ions on a specific complex compound membrane attached to the surface of a base body in order to oxidize the metallic main component in the membrane. CONSTITUTION:For the formation of a membranous superconductor, first a complex compound membrane of oxide including A element, B element, and Cu at the mol ratio of elements, 0.5 <= (A+B)/Cu <= 2.5 is attached on a base body in a physical gaseous phase growing method. In this case, A is at least one of Sc, Y, and lanthan family elements, B is at least one of IIa group elements such as Ba, Sr, Ca, Be, and Mg. Then, the complex compound membrane is treated further by oxygen ions which are grown by the discharge of a gas including oxygen. In this case, the base body is heated at a temperature between 400 deg.C and 800 deg.C.

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,! 1uller, Zetshrift Fairphysik
f Qrphysik B)-Condensed M
atter 64.189-193 (1986) I
Additionally, it has recently been proposed that the Y-Ba-Cu-0 system is a higher temperature superconducting material. (Literature) [M,
L Wu et al.

Physical Review Letters (Physical R
View Letters) Vol, 58 No9
．． 908-910 (1987) ]]Y-Ba-Cu
The details of the superconducting mechanism of -0 materials are not clear, but the transition temperature may be higher than the liquid nitrogen temperature, and the properties mentioned above are more promising than conventional binary compounds as high-temperature superconductors. Although good superconducting properties can be obtained by heat-treating a composite compound film in an oxygen atmosphere, etc., it is difficult to set the conditions.
There are problems in that it takes a long time to process and, furthermore, a high-temperature furnace or the like is required due to the high-temperature process at 800° C. or higher.

Means for Solving the Problems The basic composition of the thin film superconductor formed by the manufacturing method of the present invention is a ternary compound on the surface of the substrate, which is an oxide containing A, B, and Cu, with a molar ratio of the elements. The superconductor of this product is characterized by having a coating 12 deposited thereon. This invention was based on the discovery that it can be formed by doing this.

Here, A is at least one of Sc, Y, and lanthanum series elements (atomic number 57-71), B is Bar
Sr.

Indicates at least one element of Group IIa elements such as Ca + B e * M g.

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 involves decomposing the superconductor material into ultrafine particles in the atomic state, depositing them on the substrate, and then irradiating them with oxygen ions, so the composition of the formed superconductor is essentially that of conventional sintering. It is homogeneous compared to the body. 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 of, for example, liquid nitrogen temperature (-195 degrees Celsius), the adhesion between the substrate 11 and the coating 12 is particularly poor (and the coating 12 is often The inventors have confirmed that the thermal expansion coefficient α of the substrate 1 is greater than 1 as a result of investigating the detailed thermal characteristics of the substrate for various materials.
It was confirmed that if it was 0-6/e, the coating would not be damaged and could be put to practical use. For example, the present inventors have confirmed that if quartz glass with α of 1Q-6/i is used as the substrate, the coating 12 will have numerous cracks and become a discontinuous coating, making it unsuitable for 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
-AI203), spinel, strontium titanate,
It was confirmed that single crystals such as silicon and gallium arsenide are 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. 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, first, a composite compound film of AB-Cu-0 is deposited on a substrate by physical vapor deposition such as sputtering deposition 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) acuao+a, 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. Component A is also used in this double pressure or reduced pressure chemical vapor deposition method, plasma chemical vapor deposition method, and photochemical vapor deposition method.

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.

At temperatures below 100°C, the adhesion of the composite oxide film to the substrate surface becomes poor. At temperatures above 1000°C, the deviation from the structural ratio of components A, B, and Cu in the composite oxide film increases. .

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 or composed of microcrystals.

However, surprisingly, this type of coating exhibits semiconducting properties, and no superconductivity is observed even at liquid He temperatures (4°K). It was also confirmed that if discharged in the air, the film would have high resistance, making it extremely unstable and unreliable.

The present inventors have discovered that by further treating this type of composite compound film with oxygen ions generated by discharging a gas containing at least oxygen, superconductivity occurs and long-term stability is greatly improved. In this case, it has been found that superconducting properties can be improved by heating the substrate. The optimum heat treatment temperature was 400-800°C.

If the temperature is higher than this, the resistivity will increase and the properties of the film will become unstable, and it will not exhibit steep superconductivity.

(Specific Example) YgBaa sintered by high-frequency Brenner magnetron sputtering using a sapphire single crystal R-plane as the base 11
A cueota 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 z B a 4 Cu e 014 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 0.5 Pa.
The temperature of the substrate was 700°C. The formed film was further heated to 500° C. and subjected to oxygen ion treatment. 5
The processing time was 10 minutes in a vacuum chamber of X10-'Torr.

In FIG. 2, a sapphire R-face is used as the substrate 11, and the main component is Y 2 B a 4 Cu e by sputtering vapor deposition.
2 shows an X-ray diffraction spectrum of the ternary compound coating 12 in an example when the ternary compound coating 12 of No. 014 was attached. In FIG. 2, spectrum a is obtained from coating 12, and spectrum b is obtained from a structure exhibiting superconductivity. As shown in the figure (the coating spectrum a is similar to spectrum b, superconductivity occurred).

The superconducting transition temperature of the coating was 90°.

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

The present inventors experimentally investigated in detail the effectiveness of crystalline substrates other than sapphire. Magnesium oxide, Y2Ba4Cu a O+ a on spinel single crystal substrate
It was confirmed that by depositing structural films by the sputtering deposition method as in the case of sapphire single crystals and subjecting these films to the oxygen ion treatment of the present invention, they all exhibit superconductivity.

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 in a single crystal substrate to increase the single crystallinity, a tetragonal perovskite structure is easily formed, with good reproducibility. In many cases, superconductors cannot be obtained. Therefore, as described in the embodiments of the present invention (
However, it is more reproducible to select a substrate temperature in a low range, form a composite compound film containing perovskite or microcrystalline structure, crystallize it by heat treatment, and then treat it with oxygen ions (the inventors have experimentally demonstrated that a superconductor can be obtained). I confirmed it.

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. The present inventors have confirmed that oxygen ion treatment of Time)
A polycrystalline porcelain substrate is effective.

In sputtering deposition of this type of oxide film, for example, A
A mixed gas of r and 02 is used as the sputtering gas.

Additionally, the present inventors have experimentally confirmed that inert gases such as Ar, 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.

Especially in the case of DC sputtering, it is necessary to lower the resistivity of the sputtering target to below 10-3 Ωcm+.
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.

Oxygen treatment was performed on the composite compound film obtained by the above-described method using an apparatus having the configuration shown in FIGS. 3, 4, and 5.

First, oxygen gas or a mixed gas containing oxygen is introduced into the ion source 31 shown in FIG. 3, and a high frequency signal is applied to electrodes 32 and 33 facing each other with this gas in between to generate plasma. Magnetic field generation source 3 for forming a magnetic field in this plasma
By applying a voltage between the substrate table 36 on which the substrate 35 on which the composite compound film is formed and the plasma of the ion source are placed, oxygen ions are generated efficiently from the ion source. The composite compound coating 12 on the substrate 11 on the substrate stand 36 is irradiated. At this time, the inventors have discovered that by heating the substrate to 400° C. to 800° C. with the heater 37, the oxygen ion treatment time can be shortened and the superconducting properties of the film can be improved. Furthermore, it has been confirmed that when the voltage applied between the plasma and the characteristic sample stage is 10 KV or less, the surface of the coating 12 is sputtered, but the interior of the coating can be effectively treated with oxygen ions.

FIG. 4 shows that oxygen gas or a mixed gas containing oxygen is introduced into a vacuum chamber 41, this gas is irradiated with microwaves to generate a discharge, and a magnetic field 42 is applied to the plasma to ionize oxygen ions. An ion source with increased efficiency is used as an ion source. In this case, usually the microwave source 4
In 3, when microwaves of 2.45 GHz are used and the magnetic field strength is set to about 875 Gauss, electron cyclotron resonance occurs, which increases the efficiency of oxygen ionization. The structure is such that oxygen ions extracted from this ion source are irradiated onto the composite compound coating placed on the sample stage 36. In this case, we discovered that high-energy oxygen ions efficiently ionized by microwaves efficiently oxidize the composite compound film, improving its superconducting properties.

In addition to this, oxygen gas or a mixed gas containing oxygen is introduced into the vacuum chamber, high frequency waves are applied to the parallel electrodes to cause a discharge in this gas, and a composite compound film is placed in this discharge plasma for oxygen treatment. You can also do that. The inventors confirmed that this method improves the superconducting properties of the coating.

However, in this method, the coating is irradiated with a substance other than ions, changing the surface condition, so the above-mentioned oxygen treatment method is more preferable. For this reason, it has been confirmed that oxygen treatment using ordinary ion implantation technology using an accelerating voltage of several tens of kilovolts or higher is sufficiently 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) acu60z is not formed in the composite compound film deposited on the substrate by sputtering vapor deposition or the like. In this case, for example, a complex oxide is formed in which the oxide of element A is dispersed in a BCubs tetragonal perovskite structure network. The generation of structures exhibiting superconductivity is related to the oxidation treatment of the coating. In this case, it has been found that for the coatings of the invention, injection voltages of 50 KV or higher allow for less damaging processing.

It has been found that in the above oxygen treatment method, the efficiency of oxygen treatment can be improved by irradiating the composite compound film with oxygen ions and simultaneously irradiating it with a light beam with a short wavelength of 500 nm or less. In particular, it was confirmed that the effect of ultraviolet irradiation was greater. Furthermore, we have discovered that the effect of oxygen treatment can be further improved if hydrogen ions are generated in a similar manner and irradiated onto the composite compound film prior to this oxygen treatment. In this case, the coating is 300~6
It was also confirmed that the effect of hydrogen ions becomes stronger when heated to 00°C. In other words, treatment with these oxygen ions and hydrogen ions improves the superconducting properties of the composite compound film, and also significantly improves reliability and long-term stability. .

The details of changes in superconducting properties due to changes in constituent elements A and B of this type of ternary compound superconductor (A, B) acue01 are not clear. However, it is true that A indicates trivalence and B indicates divalence. The explanation has been given using an example of Y as element A, but SC, La, and even lanthanum series elements (atomic numbers 57 to 71) change the superconducting transition temperature, but do not change the essential characteristics of the invention. .

Also, in the B element, 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 present invention.

Effects of the Invention Particularly, the superconductor according to the present invention has a major feature in that the superconductor is made into a thin film and treated with oxygen 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 commonly used thermal annealing, the oxygen ion treatment according to the present invention has better controllability and can be performed in a shorter time. 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 the drawing]

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 ion processing apparatus used in the present invention. 11... Substrate, 12... Ternary compound coating, 31...
・Ion source. Name of agent: Patent attorney Toshio Nakao and 1 other person! figure

Claims (16)

[Claims] (1) Oxygen ions are irradiated onto a composite compound film consisting 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, comprising oxidizing the main metal component in the coating. 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 oxygen ion irradiation. (3) The method for manufacturing a thin film superconductor according to claim 1, wherein plasma generated by discharging a gas containing at least oxygen in a vacuum chamber is used as the oxygen ion source. (4) The method for manufacturing a thin film superconductor according to claim 3, characterized in that a plasma processing device using plasma decomposition using microwaves is used as the oxygen ion source device. (5) The method for manufacturing a thin film superconductor according to claim 4, characterized in that electron cyclotron resonance is used. (6) A patent claim characterized in that oxygen ions generated by electric discharge in a vacuum chamber are accelerated and 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 producing a thin film superconductor according to item 3. (7) The method for manufacturing a thin film superconductor according to claim 2, characterized in that the composite compound film during oxygen ion irradiation is heated from 400°C to 800°C or less. (8) An electrode set at a predetermined potential is installed between the plasma generated by applying a high frequency voltage to oxygen gas and the sample stage, and irradiation with oxygen ions is described in claim 6. A method for producing thin film superconductors. (9) The method for manufacturing a thin film superconductor according to claim 6, characterized in that a DC voltage of 10 KV or less is applied between the plasma and the sample stage. (10) A method for manufacturing a thin film superconductor according to claim 6, characterized in that the composite compound coating is placed in plasma generated by applying a high frequency voltage to oxygen gas. (11) The method for producing a thin film superconductor according to claim 3, characterized in that the light beam is irradiated at the same time as the oxygen ion irradiation. (12) The method for manufacturing a thin film superconductor according to claim 11, characterized in that ultraviolet rays are irradiated simultaneously with irradiation of oxygen ions. (13) The method for producing a thin film superconductor according to claim 1, wherein oxygen ion irradiation is performed successively using the same device after forming the composite compound film. (14) The method for manufacturing a thin film superconductor according to claim 6, characterized in that a voltage of 50 KV or more is applied between the oxygen ion source and the sample stage. (15) A method for producing a thin film superconductor according to claim 1, which comprises discharging a hydrogen-containing gas and irradiating the composite compound coating with hydrogen ions. (16) The method for producing a thin film superconductor according to claim 15, characterized in that the temperature of the composite compound coating is 400°C to 600°C.