JPH01249607A - Production of oxide superconducting film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an oxide superconductor film.

[Conventional technology and its issues]

In recent years, 1-a-3r-Cu-0 system, Y-Ba-Cu-○ system, Bi-3r-Ca-Cu-0 system, Tp, -3r-
Oxide superconductors such as Ca-Cu-0 have been discovered. These oxide superconductors have a high critical temperature (hereinafter abbreviated as Tc) and become superconducting at liquid N2 temperature, so they are much more economical than conventional metal superconductors that exhibit superconductivity at liquid He temperature. As a wire material for electric cables, magnetic conductors, etc., or as transistors, Josephson elements, 5Q
Electronic devices such as UIDs and infrared sensors are widely used in various fields.

By the way, the crystal structure of the above-mentioned oxide superconductor has transition element ions such as Cu in the center of the cube, and Ba in the corners, as illustrated in Fig. 1 for the superconductor YBatCux07-δ. , Y, and other active metal ions with a large radius, and oxygen ions arranged face-centered. Oxide superconductors with such a crystal structure have strong electrical crystal anisotropy because the electron cloud of the central transition element ion is not spherically symmetric, and the critical current value is small in the C-axis direction.
It shows a large value in the direction parallel to the plane perpendicular to the axis, that is, the plane including the a and b axes.

For this reason, in the production of oxide superconductors, vapor phase deposition methods such as PVD and CVD, which are easy to orient crystals, are often used.

However, in order to achieve crystal orientation using the above-mentioned vapor phase deposition method, it is necessary to perform vapor phase precipitation while holding the substrate at a high temperature of about 600'C or higher, and for this reason, a diffusion reaction occurs between the substrate and the superconductor during manufacturing. This causes deterioration of the properties of the superconductor, and since the substrate is heated to high temperatures, a reverse spuck phenomenon occurs, and the amount of evaporation at this time differs depending on the component of the superconductor, making composition control difficult, and further impeding the growth of the superconductor. The film speed is about 1/10 of that when the substrate is at room temperature, that is, 0.1 to 0.5/11
There were various problems such as an extremely low level of performance.

[Means and effects for solving the problems] The present invention was made in view of the above circumstances, and its purpose is to provide a method for rapidly producing an oxide superconductor film having high crystal orientation and excellent superconducting properties. Our goal is to provide the following.

That is, in the present invention, an oxide superconductor material is formed in a film shape with a predetermined crystal orientation on a substrate, and then the same oxide superconductor material as described above is formed in a non-oriented state on the oriented film body.
trm or less, and then heat-treating the two-layered film body in an oxygen-containing atmosphere at a temperature below the melting point, which is repeated as many times as desired.

In the present invention, an oxide superconductor material is deposited on a substrate with a crystal structure shown in FIG. 1 having a predetermined crystal orientation in which the crystal plane including the highly conductive ab axis is parallel to the substrate surface (hereinafter referred to as ab orientation). Then, the oxide superconductor material is formed into a film in a non-oriented state at high speed, and then the formed film is heated at a temperature below the melting point in an atmosphere containing 02. By performing a treatment, the crystals of the upper non-oriented film are rearranged in the ab orientation using the lower oriented film as a seed crystal, and the amount of 0□ etc. is adjusted to form a superconductor.

A superconductor film having a desired thickness can be manufactured by repeating the above steps of forming a non-oriented film and then heat-treating this film body as many times as desired.

In the present invention, the non-oriented film body has 0. ! The heat treatment temperature in the superconducting atmosphere must be lower than the melting point of the superconductor material; if it exceeds the melting point, harmful reactions such as heterophase precipitation may occur, which is not preferable. In addition, in the above heat treatment, 02 is an essential component for crystallization, and the 02 partial pressure is usually lower than the equilibrium 02 partial pressure.
The heat treatment is performed in an atmosphere containing No. 2.

In the method of the present invention, since the film formation rate is slow, it is preferable to form the crystal-oriented film as thin as about 0.1 to 1-1, and the non-oriented film to be formed on the oriented film. If the thickness is too large, sufficient a-b orientation will not be achieved in the subsequent heat treatment process, so the thickness must be 3 or less.
Particularly preferred is a thickness of about 1 to 2p.

In the present invention, an oxide superconductor substance is a substance that can be made into a superconductor by performing a prescribed heat treatment in an oxygen-containing atmosphere, and a superconductor that reacts with the superconductor or vaporizes and dissipates by the heat treatment. Also included are oxide superconductor precursors containing elements or compounds other than the constituent elements.

In the present invention, the non-oriented film formed on the oriented film refers to a film with low orientation, an amorphous film, or a mixture of both. Amorphous films include a wide range of crystal structures, from those with a crystalline structure that is slightly less oriented than films to those in which each crystal grain is randomly oriented, and an amorphous film is a film that is compositionally the same as a superconductor except for oxygen. It has a crystal structure that does not show a clear crystal analysis pattern in X-ray diffraction, and is composed of fine crystal grains with a diameter of several hundred angstroms or less and a completely glassy state.

In the present invention, methods for forming the oxide superconductor into a film include magnetron sputtering method, vapor deposition method, MB
A PVD method such as the E method, a spinco-1 method, a spray coating method, and even a thick film method such as a screen printing method can be applied.

In the present invention, any material can be used for the substrate depending on the purpose and application, but it is essential that the substrate has crystal lattice conditions that can give the superconductor a predetermined crystal orientation. It is necessary to select the material by considering reactivity with the substance, thermal expansion matching property, etc.

〔Example〕

The present invention will be explained in detail below using examples.

Example 1 SrO (100) was deposited as an oxidation-resistant buffer layer on a susaios tape by an RF magnetron sputtering device.
A tape coated with an alignment film to a thickness of 0.5 Irm was used as a base, and the base was coated on this base with a thickness of 700 Irm using the above device.
While heating to °C, 50 mTorr (A r +02
) Sputtering was performed at an output of 150 W for 1 hour under a low vacuum to form a film of DyBa2ctl*o7 to a thickness of 0.5 mm. The above DyBa2Cu307 film was found to have perfect ab orientation by X-ray analysis, and Dy:
The atomic ratio of Ba:Cu is 1:2.01! , 05.

Next, without heating the substrate, sputtering was performed at an output of 300 W for 1 hour using the oxide of [)yBa2cu+ot as a target on the oriented film of D y B a 2 Cu 30. 2.
5- formed to a thickness. The above film was found to be an amorphous body by X-ray analysis and ICP analysis, and the atomic ratio of Dy:Ba:Cu was 1:1.98:3. o It was confirmed that it was 1.

After that, the above film of D V Ba 2 Cu 307 was heated at 900°C for 1 hour in a 0□ air flow, and then heated at 2° (:/m
A superconductor film was produced by performing a heat treatment of slow cooling at a speed of 1.5 in.

Example 2 A superconductor film was produced by the same method as in Example 1 except that the amorphous film formation step and the heat treatment step were repeated twice.

Example 3 A superconductor film was manufactured by the same method as in Example 1 except that the thickness of the amorphous film was changed to 1.5 μm.

Comparative Example 1 In Example 1, the steps after the step of forming the amorphous film were omitted.

Comparative example 2 In Example 1, the heat treatment step was omitted.

Comparative Example 3 A superconductor film was manufactured by the same method as in Example 1, except that the oriented film was formed by sputtering at an output of 150 W for 3 hours, and the formation of the amorphous film was omitted.

Comparative Example 4 A superconductor film was manufactured by the same method as in Comparative Example 3, except that the oriented film was formed by sputtering at an output of 300 W for 3 hours.

Comparative Example 5 In Example 1, the amorphous film was formed at 300 W at 1.4
A superconductor film was produced by the same method as in Example 1 except that H sputtering was performed to make the film thickness 3.5-.

Comparative Example 6 In Example 1, the amorphous film was formed at 300 W at 2.2
A superconductor film was produced by the same method as in Example 1 except that H sputtering was performed to make the film thickness 5.5-.

Tc and J were measured for each superconductor film thus obtained. The results are shown in Table 1 together with the main manufacturing conditions and film formation speed.

As is clear from Table 1, the method of the present invention (Examples 1 to 3)
), the film can be formed quickly and high values of superconducting properties such as TC%JC have been obtained. On the other hand, those in which heat treatment was omitted (Comparative Examples 1.2) had extremely low TC values, and those in which oriented films were directly formed by sputtering (Comparative Examples 3 and 4) had slow film formation speeds. Compared to the invention method product (Example 2), the speed is about 1/4 or 2/5, respectively, and it reacts with the high temperature substrate during sppacking. was also low. In addition, in the case where the orientation film was formed thickly at once (Comparative Examples 5 and 6), crystal orientation was not sufficiently achieved in the subsequent heat treatment step, resulting in a low Jc value.

In the cow example, the same substrate used in Example 1 was heated to 500'C.
While heating each nitrate of Y, Ba, and Cu to Y+B
a: A 5% aqueous solution of Cu dissolved in water at an atomic ratio of 11:3 was sprayed on an 02 air stream for 1.5 minutes to form a YBazCu30. After forming a film, this film was heated to 850°C in the atmosphere and then slowly cooled at a rate of 3°C/min to produce a superconductor film.

A superconductor film having a thickness of 6 μm was produced by repeating the same procedure as in Example except that the aqueous solution spraying step and heat treatment step were repeated three times.

Comparative Example 7 A superconductor film was produced in the same manner as in Example 3, except that the aqueous solution was sprayed for 4.5 minutes to give a film thickness of 6.

T and Jc were measured for each superconductor film thus obtained. The results are shown in Table 2 along with the main manufacturing conditions.

As is clear from Table 2, the method of the present invention (Example 4.5)
In all cases, the film formation rate was fast and a high value of 1゛6, Jc was obtained.

On the other hand, in the comparative method (Comparative Example 7), since the amorphous film was formed thickly at once, the crystal orientation was not sufficiently achieved in the subsequent heat treatment step, resulting in a low value of Jc.

〔effect〕

As described above, according to the method of the present invention, the crystal orientation is high <1゜. Since an oxide superconductor film having excellent characteristics such as , Jc, etc. can be rapidly produced, this method has a significant industrial effect.

[Brief explanation of the drawing]

Figure 1 shows an example of the crystal structure of an oxide superconductor.
It is a crystal structure of zCu307-δ.

Claims (1)

[Claims] After forming a film of an oxide superconductor material with a predetermined crystal orientation on the substrate, the same oxide superconductor material as above is formed on the oriented film body in a non-oriented state with a thickness of 3 μm or less. 1. A method for producing an oxide superconductor film, comprising repeating the step of forming the above-mentioned two-layer film at a temperature below the melting point in an oxygen-containing atmosphere as many times as desired.