JPH0360406A - Production of oxide superconducting thin film - Google Patents

Abstract

PURPOSE:To efficiently and surely add a low-melting-point element by forming the amorphous film of the elements constituting an oxide superconducting material in a specified ratio on a substrate, adding a low melting-point element into the film by a gas-phase diffusion reaction and crystallizing the film. CONSTITUTION:The amorphous film of the elements constituting the superconducting material in a specified stoichiometric ratio is formed on a substrate by vapor deposition, etc. The film is formed at low temp. at this time, because the film is crystallized when the substrate temp. is high. The film and the bulk compd. contg. Pb, for example, etc., are then enclosed in a closed vessel and heat-treated at a specified temp. The low-melting-point element is vaporized from the compd. in the heat treatment, the vapor is infiltrated into the film by the diffusion reaction from the surface when the amorphous film is crystallized, and a specified compd. phase is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing an oxide superconducting thin film, and particularly to an improvement in the method of adding a low melting point element to an oxide superconducting thin film.

[Prior Art] In recent years, the development of oxide superconducting materials has progressed at a remarkable speed, and in particular, Y-based, Bi-based, and TI-based materials are being put to practical use. In order to put the above substances into practical use, various methods of forming wire rods and thin films are being considered, among which:
The following three methods are known as methods for producing thin film materials.

Namely, (1) a method of performing crystallization and oxygen treatment after film formation, (2) a method of performing oxygen treatment after film formation and crystallization treatment, and (2) a method of performing oxygen treatment after film formation.
There is a method in which film formation, crystallization, and oxygen treatment are performed simultaneously.

In method (2) above, after forming a film on a substrate in a vacuum chamber, the film is transferred to an electric furnace or the like and subjected to heat treatment and oxygen treatment separately. Thereafter, oxygen treatment is performed, and in (2), film formation, crystallization, and oxygen treatment are all completed at once in a vacuum chamber.

Using each of the above methods, Y-Ba-Cu-0 system super 2
For 14 materials, we have successfully created single crystal thin films showing critical temperatures of 90 degrees, and for [3l-3r-Ca-Cu-0 system and Tl-Ba-Ca-Cu-0 system, the critical temperatures are 105 and lloK class thin films have been obtained.

[Problems to be Solved by the Invention] However, there are problems as described below, particularly in the production of thin film materials from superconducting substances having high critical temperatures, such as B1 series and T1 series.

In other words, in the case of old superconducting materials, (a) a single-phase film cannot be obtained unless the substrate temperature is formed in the range of 650 to 75°C (1'C), and (b) a temperature of around IIIH°C. A single-phase film cannot be obtained unless it is annealed.For this reason, it is necessary to raise the substrate temperature, so when making a single-phase bulk sample, it is necessary to improve the superconducting properties, that is, hlgh-Tc. This is because the addition of PB, which is an effective method for phase generation, cannot be carried out effectively.This is because the substrate temperature is high, so even if PB is added, it evaporates, and PB is essentially added into the film. due to inability to do so.

Therefore, it is not possible to effectively add Pb to obtain a thin film having a critical temperature of 10K level in Bt-based superconducting materials, which is a problem in device fabrication. It is similarly difficult to add low-melting-point elements to the Tl system, and Tl20ff is highly toxic, so performing high-temperature heat treatment in multiple stages requires sufficient safety for exhaust equipment, etc., and industrialization is difficult. This is a difficult point in the process.

As described above, in order to obtain a high temperature phase of a superconducting material, a high substrate temperature is required, and therefore there are various difficulties when adding a low melting point element to a film.

The present invention has been made to solve the above-mentioned difficulties.
The object of the present invention is to provide a method for manufacturing an oxide superconducting thin film having a high critical temperature by effectively, safely, and reliably adding a low melting point element.

[Means for Solving the Problems] In order to achieve the above object, the method for producing an oxide superconducting thin film of the present invention comprises forming an amorphous film on a substrate in a predetermined ratio of elements constituting an oxide superconducting substance. Afterwards, a low melting point element is added to this film by vapor phase diffusion reaction to cause crystallization.

The oxide superconducting material in the present invention is not limited to Bt-based materials, but includes other superconducting thin materials whose properties can be improved by adding a low melting point element. Further, the film needs to be formed in an amorphous state on the substrate, and its properties cannot be improved even if a low melting point element is added into the crystallized film by an air diffusion reaction.

In the present invention, the addition of the above-described low melting point element and the crystallization of the film are performed simultaneously in the west of the closed container.

Although the sputtering method is suitable for forming the film body, other methods can be used as long as the constituent elements in the film are chemically the same.

The above low melting point elements include Li, Na5S%K
, Zn, Ga, Sas Rb, Cd, Ins
Examples include 5nSSbb Tes T1% Pbs old, but of course it is also applicable to other low melting point elements. These elements are usually heated in the form of a compound, solid solution, sintered body, or molded body together with a membrane in a closed container.

For addition of pb to Bt system, for example, pbo
s Pbo 4, Pb-9r-Ca, etc. can be used.

In addition, although the above-mentioned vapor phase diffusion reaction is carried out at high temperature, in order to efficiently add a low melting point element into the film, it is necessary to
It is preferable to carry out the reaction in a temperature range of 0°C. The treatment time is selected from about 1 to 20 hours in the above temperature range depending on the temperature. As the treatment time becomes longer, the big-Tc phase decomposes and disappears.

[Function] In the present invention, the elements constituting the superconducting material are blended in a predetermined ratio during the film formation of Alumofus 7, and the low melting point elements are added by vapor phase diffusion reaction during heat treatment. A predetermined amount of the element can be efficiently added to the film body, thereby making it possible to improve the superconducting properties.

[Example] An embodiment of the present invention will be described below.

First, constituent elements of a superconducting material are formed into an amorphous film on a substrate in a predetermined stoichiometric ratio by sputtering, vapor deposition, or the like. If the substrate temperature is high, the film crystallizes at a low temperature, for example, 500℃ or less in the case of the old system, especially 4
The film is formed at around 00°C.

In the case of the old thread superconducting material, the above constituent elements are old and Sr.

These are Ca and Cu, and pb, which is a low melting point component among the constituent elements, and oxygen may be added thereto.

The above substrates include MgO, A1203, YSZ (
Yttrium stabilized zirconium) and (Ag.

A commonly used material such as a metal such as N1 or a buffer layer provided on a metal substrate can be used.

Next, the above-mentioned film body and a bulk material compound containing PB are sealed in a closed container, and heat-treated at a temperature of 800 to 880°C. During this heat treatment, a low melting point element from the compound becomes a gas phase, and when the amorphous film crystallizes, it penetrates into the film by a diffusion reaction from the surface and forms a predetermined compound phase.

Examples 1 to 3 1 was deposited on a Mg0 substrate by sputtering under the following conditions.
A film of 31-Sr-Ca-Cu-based material was formed with the composition shown in the table.

Film forming method: R['Sputtering gas pressure =-
0.1~50mTorr rf power-100mm sputtering time...3hr Substrate temperature...400 Substrate surface...MgO(100) Film thickness...3000~40006 Film body obtained in this way The X-ray diffraction chart is shown in Figure 3. As is clear from this figure, it is clear that the film is in an amorphous phase, and when the substrate temperature is increased from 400°C, the semiconductor peak and u change between 500 and 700°C.
The nknown peak appears at 800°C, and a Low Tc phase appears.

The above membrane body and the PB compound were placed in a sealed container, and 850
The film was annealed at temperatures of 855° C. and 855° C., and at the same time as crystallization, PB was added into the film by a vapor phase diffusion reaction method.

The high-Tc (direct rise temperature) phase fraction, direct rise temperature (Tc: onset and end poi) of this superconducting thin film are
nt) are shown in the table.

(Margins below) Figures 1 and 2 are X of Examples 1 and 2, respectively.
This shows a line diffraction chart. In both figures, S, L, and H represent one S (2201) phase, one L (2212) phase, and one H phase, respectively.
Indicates the (2223) phase.

Comparative Examples 1-2 The same table shows the opposite results when a film of Bl-based superconducting material was formed on lJ and E with the composition shown in the table as in Examples, and then annealed at 850°C and 855°C. . In this case, PB was not added by the vapor phase diffusion method.

Comparative Example 3 A film having the same composition and the same method as in Example 1 was formed on a substrate, and then annealed at 800° C. for 1 hour to crystallize the film. Then, p at 850°C for 5 hours by vapor phase diffusion reaction method
b was added into the membrane body. Figure 4 shows the X-ray diffraction chart after annealing, and it is clear that only the low-Tar phase is formed, while in Figure 5, which shows the state after PB addition, the high-Tc phase is not present. It does not appear, indicating that impurities are generated.

Comparative Example 4 A superconducting thin film was manufactured under the same conditions as in Example 2 except that the annealing conditions were changed to 855° C. for 20 hours. The X-ray diffraction chart in this case is hL-gh-Tc as shown in FIG.
This shows that the phase pcak has disappeared.

[Effects of the Invention] As described above, according to the method for producing an oxide superconducting thin film of the present invention, a low melting point element can be effectively added to the thin film, thereby reducing the fraction of the old gh-Te phase. As a result, the critical temperature can be increased. In particular, for thin films of old thread superconducting materials, annealing treatment can be performed at low temperatures and in a short period of time.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are X-ray diffraction charts of membrane bodies prepared according to Example 1 and Example 2 of the present invention, respectively;
FIG. 3 is an X-ray diffraction chart of the film body after film formation of Examples 1 to 3 of the present invention, FIGS. 4 and 5 are X-ray diffraction charts of Comparative Example 3 after annealing and after PB addition, FIG. 6 is an X-ray diffraction chart of Comparative Example 4.

Claims (3)

[Claims] (1) After forming an amorphous film of the elements constituting the oxide superconducting material on a substrate in a predetermined ratio, a low melting point element is added to this film by a vapor phase diffusion reaction and crystallized. A method for producing an oxide superconducting thin film. (2) Low melting point elements are Li, Na, S, K, Zn, Ga,
Se, Rb, Cd, In, Sn, Sb, Te, Tl, P
2. The method for producing an oxide superconducting thin film according to claim 1, wherein the oxide superconducting thin film is at least one element selected from B, Bi, and Bi. (3) The method for producing an oxide superconducting thin film according to claim 1 or 2, wherein the gas phase diffusion reaction is carried out at 800 to 880°C.