JPH01246142A - Production of thin film superconductor - Google Patents

Abstract

PURPOSE:To obtain the title high-quality superconductor excellent in reliability and long-term stability by irradiating oxygen ions on a composite compound film consisting of Bi, alkaline earth group IIa element(s) and Cu. CONSTITUTION:A composite compound film consisting of at least Bi, alkaline earth group IIa element(s) and Cu is irradiated with oxygen ions to oxidize the metallic chief component in said film. For example, a Bi-Sr-Ca-O-based composite compound film 2 is formed on a substrate 1 by sputterling vapor deposition to make a base plate 25. This base plate 25 is mounted on a table 26 heated by a heater 27 in a vacuum chamber; an oxygen gas g is introduced into an ion source 21 followed by discharge between electrodes 22 and 23 to generate oxygen ions, which are irradiated on the composite compound film 2 on the base plate 25.

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 (NbGe) are used as A15 type binary compounds.
), 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 a Ba-La-Cu-0-based high-temperature superconductor has been proposed [J, G, Bend
orz and K, A, Muller, Zet Schrift Fair Tour Seek (Ze tshr
if f rphysik B)-Condens
ed Matter 64.189-193 (198
6) ].

Furthermore, it has been discovered that materials of the B I -S r -Ca -Cu -0 series exhibit a transition temperature of 100°C or higher.

Although the details of the superconducting mechanism of this type of material are not clear,
The transition temperature can be higher than room temperature, and it is expected to have more promising properties as a high-temperature superconductor than conventional binary compounds.

Problem to be Solved by the Invention As mentioned above, B l -S r -Ca -Cu -0
The composite compound film of the system can obtain good superconducting properties by heat-treating it in an oxygen atmosphere or the like. However, there are problems in that it is difficult to set the conditions, 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 that the substrate surface is composed of an oxide containing at least bismuth (B1), alkaline earth (group II a), and Cu. The present inventors have discovered that this type of superconductor is characterized by depositing the composite compound coating on a heated substrate by a process called vapor deposition, and then adding oxygen ions to the superconductor. The inventors discovered that the main metal component in the film is oxidized and formed by irradiating the film with . Here, alkaline earth is B a * S
r + Indicates at least one or two or more elements of group II a elements such as Ca, Be, and Mg.

Function The method for producing a thin film superconductor according to the present invention is based on bismuth (
B1), the major feature is that the oxide superconductor containing alkaline earth metals and Cu is made into a thin film. In other words, in thinning the superconductor material, the material of the superconductor is decomposed into ultrafine particles in the atomic state and then deposited on the substrate, and then the main metal component in the broken film is oxidized by oxygen ion irradiation, so the formed superconductor The composition is essentially more homogeneous than that of conventional sintered bodies, and a highly precise superconductor can be obtained. Therefore, the present invention is applicable to B, which is said to have a transition temperature of 100 or more.
By applying this method to the production of thin films of I-Sr-Ca-Cu-0 type materials, high-quality superconductors can be realized and are very effective.

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

To form a thin film superconductor, first B I -S r -C
A -Cu-0 composite compound film is deposited by sputtering or thermal evaporation, for example, by physical vapor deposition such as electron beam evaporation or laser beam evaporation, or by chemical vapor deposition, such as normal pressure or reduced pressure chemical vapor deposition. , plasma chemical vapor deposition, photochemical vapor deposition, or the like.

The present inventors have confirmed that there is an optimal temperature range for the substrate when depositing a composite compound coating on the surface of the substrate. In other words, the optimum temperature range for the substrate is 100 to 1
000°C is desirable. Note that below 100°C, the adhesion of the composite oxide film to the substrate surface deteriorates. Also, 1
At temperatures above 000°C, the composite oxide film itself will melt.

Furthermore, the present inventors have found that a temperature range of 700 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 has a very low zero resistance temperature near IOK.

The present inventors further treated this type of composite compound film with oxygen ions generated by discharging a gas containing at least oxygen, so that the main high-metal components in the composite compound film were oxidized and superconductivity occurred at high temperatures. I discovered that. In this case, it has been found that superconducting properties can be improved by heating the substrate. The optimal heat treatment temperature is room temperature ~
The temperature was 800°C. At temperatures higher than this, the properties of the film become unstable and do not exhibit steep superconductivity.

(Specific Example) Using a magnesium oxide single crystal (100) plane as the substrate 1, a sintered B I - S r - Ca - Cu -0 target was sintered in a mixed gas atmosphere of Ar and O by high frequency planar magnetron sputtering. Crystalline B1-5 r -Ca - is deposited on the substrate 1 by sputtering.
Cu-0 was deposited as yA2 to form a layered structure.

In this case, the sputtering gas pressure was Q, 5 Pa, the sputtering power was 150 W, the sputtering time was 1 hour, the film thickness was 0.5 μm, and the substrate temperature was 600° C. The formed film was further maintained at 400°C and subjected to oxygen ion treatment. The processing time was 10 minutes in a vacuum chamber of 5×10 −4 Torr. FIG. 2 shows the characteristic curve of the coating after treatment. A thin film with good properties such as a zero resistance temperature of 100 or higher was obtained.

In this example, the film thickness of the coating 11'i12 is 0.5 μm, but if the film thickness is as thin as 0.1 μm or less, it may be 10 μm.
It was confirmed that superconductivity occurs even when the thickness is thicker than m.

The present inventors experimentally investigated in detail the effectiveness of crystalline substrates other than magnesium oxide.

Sapphire, B1-5r-C on spinel single crystal substrate
It was confirmed that a-Cu-0 films were similarly deposited by the sputtering deposition method, and that these films exhibited superconductivity at high temperatures by subjecting them to the oxygen ion treatment of the present invention. 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 that is not yet well understood. Even if the substrate temperature is raised to above the epitaxial temperature of a single crystal substrate to improve single crystallinity, it is often difficult to obtain a superconductor with good reproducibility. . Therefore, as described in the Example of the present invention at °C1, it is better to select the substrate temperature in a low range, form a composite compound film containing a microcrystalline structure, crystallize it by heat treatment, and then treat it with oxygen ions to obtain a superconductor with better reproducibility. The present inventors have experimentally confirmed that

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 is effective in forming a thin film with excellent superconducting properties. Note that when crystallinity of the superconducting film is not particularly required (when steep superconducting dislocations are not required), a polycrystalline ceramic substrate is effective.

In sputtering deposition of this type of oxide film, for example, A
A mixed gas of r and O is used as the sputtering gas. Also, experimentally, Ar, Xs, and Ne.

The present inventors have confirmed that an inert gas such as Kr or a mixed gas of these inert gases is effective as a sputtering gas.

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

Particularly in 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.

The composite compound film obtained by the above-described method was subjected to oxygen treatment using an apparatus having the configuration shown in FIGS. 3 and 4.

First, oxygen gas or a mixed gas g containing oxygen is introduced into the ion source 21 shown in FIG. 3, and a high frequency signal is applied to electrodes 22 and 23 facing each other with this gas in between to generate plasma. A magnetic field generation source 24 for forming a magnetic field in this plasma is arranged, and the efficiently generated oxygen ions are placed between the substrate table 26 on which the substrate 25 on which the composite compound film is formed and the plasma of the ion source. By applying a voltage, oxygen ions are extracted from the ion source and irradiated onto the composite compound coating 2 on the substrate 25 on the substrate stand 26 .

At this time, the inventors have discovered that by heating the substrate from room temperature to 800° C. with the heater 27, the oxygen ion treatment time is shortened and the superconducting properties of the film are improved. Furthermore, it was confirmed that when the voltage applied between the plasma and the characteristic sample stage was 10 KV or less, the surface of the coating 2 was sputtered, but the interior of the coating could be effectively treated with oxygen ions.

In Figure 3, oxygen gas or a mixed gas containing oxygen is introduced into a vacuum chamber 31, 11 fl of microwaves are irradiated to this gas to generate a discharge, and a magnetic field 32 is applied to the plasma to generate oxygen ions. An ion source with high ionization efficiency is used. In this case, if a 2.45 GHz microwave is normally used for the microwave source 33 and the magnetic field strength is set to about 875 Gauss, electron cyclotron resonance will occur, thereby increasing 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, and high frequency waves are applied parallel to this gas! Oxygen treatment can also be performed by applying a voltage to a pole to cause a discharge, disposing a composite compound film in this discharge plasma, and treating the composite compound film with oxygen. 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 a normal ion implantation technique using an accelerating voltage of several IQKV or higher is sufficiently effective.

Regarding the detailed characteristics of this type of coating, such as its crystal structure, since the n-hole is restrained on the substrate, there are large strains and defects in the coating that do not exist in ordinary sintered bodies. For this reason, it is not possible to infer the manufacturing method of the film 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, the generation of a structure exhibiting superconductivity is due to the oxidation treatment of the film. Related. In this case, in the coating of the present invention, 50
It has been found that injection voltages of 7 or higher allow 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. In other words, these oxygen ion treatments improved the superconducting properties of the composite compound film, and significantly improved its reliability and long-term stability.

Group II a elements (
A change in Sr, Ca, Ba, etc.) changes the transition temperature by about 10 degrees, 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 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 oxidation treatment using oxygen ions according to the present invention can be performed at low temperatures, with good controllability, and in a short 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 S1 or Ga
It is possible to integrate devices such as As,
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 cross-sectional view of a thin film superconductor formed by the method for producing a thin film superconductor according to an embodiment of the present invention, FIG. 2 is a characteristic curve diagram thereof, and FIGS. 3 and 4 are ion processing equipment used in the present invention. FIG. 1...Substrate, 2...Bi-5r-Ca-Cu-0
Film, g... gas containing oxygen. Name of agent Patent attorney Toshio Nakao One idiot Figure 1 Figure 2 7X 屓 (k,)

Claims (6)

[Claims] (1) A composite compound film whose main components are at least bismuth (Bi), an alkaline earth group IIa element, and Cu is irradiated with oxygen ions to oxidize the main metal components in the film. A method for manufacturing thin film superconductors. Here, alkaline earth refers to at least one or two or more elements of 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) 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. (5) 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. (6) The method for producing a thin film superconductor according to claim 1, characterized in that after forming the composite compound film, oxygen ion irradiation is performed using the same device.