JPH03250774A - Oxide superconductor and manufacture thereof - Google Patents

Abstract

PURPOSE:To inhibit a reduction in a critical current density and to make it possible to maintain a high current density in a magnetic field by a method wherein a substrate having points and/or line defects is used and a superconductive film is formed on the substrate. CONSTITUTION:Points or line defects 3 and 4 are introduced in the surface of a substrate 1 and thereafter, an oxide superconductive film 2 is formed on this surface. It is desirable that the depth, width and length of recessed parts consisting of the points or the line defects 3 and 4 are respectively 50nm to 1mum, 10nm to 1mum and 50nm to 1mum. The film having defects is formed on the surface, in which the recessed parts consisting of the points or the line defects 3, 4 and the like or projecting parts are introduced, of the substrate 1 in the direction normal to the surface of the substrate 1. Accordingly, as the defects in the direction normal to the surface of the substrate 1 are dispersed, can be introduced in the film and a trap site for a line of magnetic flux in the case a magnetic field is applied is included, a reduction in a critical current density in the magnetic field can be inhibited. Thereby, a high critical current density is obtained in the magnetic field.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oxide superconductor and a method for manufacturing the same.
More specifically, the present invention relates to an oxide superconductor having a high critical current density (Jc) in a magnetic field and a method for manufacturing the same.

[Conventional technology]

Y-Ba-Cu-0 with layered perovskite structure
System + B1-8r-Ca-Cu-○ system, TQ-I3a
-Ca-Cu-0-based oxide superconducting materials have a critical temperature (Jc) equal to or higher than the liquid nitrogen temperature (77K), and are therefore expected to have wide applications in superconducting magnets, coils, and electronic devices.

Film-forming methods for oxide superconductors include R,F sputtering, MBE (monocular beam epitaxy), laser deposition, and CVD; for example, Appl, Phys, Lett, 53 (16)
.

1557 (1988). Here 5r
By using a TiOff (100)-plane single crystal substrate, an epitaxially grown film and a C-axis oriented film can be formed, and a high critical current density Jc can be obtained in a zero magnetic field.

[Problem to be solved by the invention]

However, although it is relatively easy to obtain a high Jc in a zero magnetic field in the film formation method using a single crystal substrate as described above, there is a problem in that the Jc decreases in a magnetic field.

An object of the present invention is to provide an oxide superconductor having a high current density in a magnetic field and a method for manufacturing the same.

[Means to solve the problem]

In order to achieve the above objective, as a result of various experiments and studies on substrate materials, substrate modification, and film formation methods for forming oxide superconducting films, we found that, for example, 5rTiO, dots or lines were first applied to the substrate surface by electron beam irradiation, etc. It has been found that after introducing defects, it is sufficient to form an oxide superconducting film on this surface using a thin film forming technique such as sputtering or vapor deposition.

The substrate material is not limited as long as it can withstand the heat during synthesis of the oxide superconducting layer.

The depth of the concave portion consisting of point or line defects is 5゜nm to 1μ
m, 1 lil is 100 m to 1 μm, length is 50 nm to
1 μm is desirable.

A hemispherical protrusion may be provided instead of the recess, and the height in this case is preferably 25 nm to 1 μm.

The hemispherical protrusion is preferably made of a material different from the substrate material.

[Effect]

When an oxide superconducting film is synthesized on a MgO (100) or 5rTiO (100) single crystal substrate, it is possible to form a superconducting film whose crystals are oriented relatively close to the lattice constant of the substrate under the influence of the substrate. On the surface of the substrate where concave parts such as point or line defects are introduced, the crystal growth of the oxide superconductor does not occur in the defect part, so crystals grow from the periphery of the defect part to form a film with a shape that includes the defect part. do. Therefore, a film having defects in a direction perpendicular to the substrate surface is formed. therefore,
By introducing dispersed point and line defects into a single crystal substrate,
Defects in the direction perpendicular to the substrate surface can be dispersed and introduced into the film. Furthermore, since this film contains trap sites for magnetic flux lines when a magnetic field is applied, it has the function of suppressing a decrease in Jc in a magnetic field.

In addition, the crystal growth of superconducting films on crystalline and amorphous bodies that mismatch the lattice constant of the oxide superconductor as a substrate is
Forms a non-oriented film without being affected by the substrate. therefore,
On a single crystal substrate on which crystalline and amorphous precipitates are formed, an oriented film in which crystal grains are not oriented with respect to the substrate surface can be synthesized.

Point and line defects are introduced onto the substrate using electron beam irradiation.

This can be done by various sputtering methods, ion implantation methods, polishing methods, acid and alkali treatment methods, etc. In addition, various sputtering methods and vapor deposition methods can be used to form precipitates on the substrate.

This can be done by a normal film forming method such as a PVD method such as a laser deposition method or a chemical vapor deposition method (CVD).

The oxide superconducting film on the substrate having the point and line defects or the substrate having the precipitates can be formed by various sputtering methods, vapor deposition methods,
It can be formed by a film forming method using a normal thin film forming technique such as a laser deposition method or a CVD method.

〔Example〕

Hereinafter, the present invention will be explained in more detail by showing examples.

<Example 1> An embodiment of the invention is shown in FIG. 5rTiO.

(100) Focused ion beam (F I
By method B), Ga ions are irradiated with an acceleration voltage of 30 keV and a dose of 1011 to 101 G/cm2 to remove defects 4 and/or
Alternatively, the line defects 3 were introduced in a dispersed manner.

Next, Y-B a -Cu-0(
An oxide superconducting film (hereinafter referred to as YBCO) was formed. In the deposited YBCO film 2, point defects 5 and/or line defects 6 were formed in a direction perpendicular to the substrate surface, corresponding to the point and/or line defects of the substrate.

Table 1 Sputtering conditions YIB a, Cu3oc-s-7,s deposited in Figure 2
An X-ray diffraction pattern of an oxide superconducting film is shown. Y B C
○Only the diffraction peak based on the (00n) plane of the oxide superconductor is clearly observed, indicating that it is C-axis oriented.

Furthermore, the Tc and Jc of this film were measured using a four-terminal method. The temperature T c (zero) at which the resistance becomes zero is 8
5, Jc was 2×105 A/cm (77, OT). FIG. 3 shows the rate of decrease in Jc when a magnetic field is applied. The film obtained in this experiment had a smaller rate of decrease in Jc in a magnetic field than a conventional epitaxially grown film without defects.

As described above, when a superconducting film is formed on a substrate with point and/or line defects, it is possible to synthesize the crotches containing the point and/or line defects formed perpendicularly to the substrate surface, and the film becomes more sensitive to the magnetic field. It is clear that a high Jc can be maintained.

<Example 2> 5iTiO, (100), 5rTiO, (100).

Single-crystal substrates made of MgO (100), LaAQO, and (100) are dotted and/or
Alternatively, line defects were introduced in a distributed manner. Example 1 A YBCO film was formed on the substrate under the conditions shown below. The composition of the YBCO film is the same as in Example 1. The Tc of this YBCO film and the Jc when a magnetic field was applied were measured using a four-terminal method. Although superconducting films were formed on any substrate using any treatment method, L a A with electron beam irradiation
The best characteristics for Q03 board, specifically Tc=
90, J c / J c (0) = in the magnetic field IT
0.7 was obtained.

As described above, it is clear that by using a substrate into which point and/or line defects are introduced, an oxide superconducting film that can suppress a decrease in Jc due to a magnetic field can be formed.

<Example 3> S rTj O, (100) single crystal substrate, M, BE method.

AQ was deposited in the form of islands by RF sputtering and CVD. A YBC◯ film was formed on the substrate under the conditions shown in Example 1. An outline of the present invention is shown in FIG. 5rT
On the i03 (100) single crystal substrate 1, a YBCO film is formed with the C axis of the YBCO film oriented in a direction perpendicular to the substrate surface.

In AQ precipitate 30-J2, the YBC◯ film forms a non-oriented film. Reference numeral 40 indicates a non-oriented YBaCuO crystal. The Tc of the oxide superconducting film shown in FIG. 4 was evaluated using the four-terminal method and the JC when a magnetic field was applied.

The best dispersion was obtained when A and Q were deposited using the MBE method, and the properties were the best when this substrate was used.

Tc is 86, Jc/, dc(o)= in the magnetic field IT
0.6 was obtained.

As described above, if a substrate having island-shaped precipitates is used, the substrate surface I
It can be seen that a YBC* film in which non-oriented crystals are formed in the form of islands in a direction perpendicular to this can be synthesized, and that the decrease in Jc due to the magnetic field can be suppressed.

<Example 4> S rT i O, (l OO
) Y was deposited on the single crystal substrate 1 under the sputtering conditions shown in Example 1.
A BCO film was formed. A schematic diagram of the YBCO film is shown in FIG. 5rTjO, the (OOn) plane of the YBC○ film grows on the (1,00) plane of the substrate, and the (110) plane 31 and (103) plane 41 of the YBaCu○ film grow on the different phase of the substrate.
is growing as a crystal.

The Tc of this oxide superconducting film was evaluated using the four-terminal method and the Jc when a magnetic field was applied. Tc is 85, magnetic field IT
Jc/Jc(o)-0,4 was obtained.

From the above results, it is clear that an oxide superconducting film having a high Tc and a high Jc even in a magnetic field can be formed by using a substrate in which different phases are dispersed.

<Example 5> 5rTi○a+Mg○, B a T 1 on Si substrate
0:i +LaAQO3, MgAQ20. After forming a thin film (approximately 0.2 μm) with a uniform surface orientation by sputtering, point and/or line defects were introduced in a dispersed manner by the FIB method shown in Example 1. Next, a YBC◯ film was formed under the sputtering conditions shown in Example 1. In the crystal, as in Example 1, point and/or line defects were formed in a direction perpendicular to the substrate surface corresponding to point and/or line defects on the substrate surface. The Tc of this oxide superconducting film and the Jc in a magnetic field were measured using a four-terminal method. Tc is 84, Jc in magnetic field IT
/Jc(o)=0.6 was obtained.

From the above results, even in the case of a multilayer film, by introducing point and line defects into the superconducting film in a distributed manner, it is possible to achieve high Jc even in a magnetic field.
It is clear that it is possible to maintain

<Example 6> After precipitating AQ in the form of islands on a 5rTi◯ (100) single crystal substrate under the conditions shown in Example 3, a YBCO film was formed under the conditions shown in Example 1. When the substrate heating temperature during the formation of the YBCO film was set to 660'C or higher, AQ melted and reacted with the YBCO film, resulting in a Tc of 74 and a decrease in superconducting properties. Therefore, Y
It is preferable to form a BCO film.

<Example 7> In the YBCO film formed under the conditions shown in Example 1,
The size of defects in the YBCO film was changed by adjusting the size of defects in the substrate. The superconducting properties of this oxide superconducting film were evaluated by measuring Tc and Jc in a magnetic field using a four-terminal method. The Tc remained unchanged at 85, regardless of the size of the film defects. However, the rate of decrease in Jc in the magnetic field IT increases when the size of the defect becomes larger than 500 nm, and 500 nm or less is preferable.

〔Effect of the invention〕

If a superconducting film is formed on the substrate using a substrate having points and/or line defects according to the present invention.

A superconducting film having point and/or line defects in the direction perpendicular to the substrate surface can be synthesized. Since this film has sites that trap lines of magnetic flux, it is possible to suppress a decrease in Jc when a magnetic field is applied. Furthermore, by using a substrate on which precipitates are formed in the form of islands, it is possible to form an oxide superconducting film in which non-oriented crystal grains grow in a direction perpendicular to the substrate surface.
It is effective in improving Jc in a magnetic field. Furthermore, when an oxide superconducting film is synthesized on a substrate in which portions with different plane orientations are dispersed, a high Jc can be maintained in a magnetic field because the superconducting film has phases with different plane orientations.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an oxide superconducting film formed on a substrate having point and/or line defects according to one embodiment of the present invention, and FIG.
The figure shows an X-ray diffraction pattern of an oxide superconducting film exhibiting C-axis orientation according to the present invention, and FIG. 3 shows the rate of decrease in critical current density (J c / J c ( o))
FIG. 4 is a schematic diagram of an oxide superconducting film formed on a substrate with island-shaped precipitates according to the present invention, and FIG. FIG. 2 is a schematic diagram of an oxide superconducting film. 1... Single crystal substrate, 2... Oxide superconducting film, 3...
- Line defect on the board, 4... Point defect on the board. 5... Point defect in superconducting film, 6... Line defect in superconducting film.

Claims (1)

[Claims] 1. In an oxide superconductor having an oxide superconducting layer on a substrate, a layer having a depth of 50 nm to 1 μm and a width of 10 nm is provided on the surface of the substrate.
It has a large number of recesses of nm to 1 μm and a length of 50 nm to 1 μm or hemispherical projections of 25 nm to 1 μm in height,
An oxide superconductor characterized in that point and/or line defects are introduced in the oxide superconducting layer in a direction perpendicular to the substrate surface. 2. Many recesses with a depth of 50 nm to 1 μm, a width of 10 nm to 1 μm, and a length of 50 nm to 1 μm, or a height of 25 nm.
An oxide superconducting layer is formed on a substrate having hemispherical projections of ~1 μm by a thin film forming technique selected from sputtering, vapor deposition, and laser deposition, and the superconducting layer is formed in a direction perpendicular to the substrate surface. 1. A method for producing an oxide superconductor, the method comprising introducing point and/or line defects into the oxide superconductor. 3. The oxide superconductor according to claim 1, wherein the substrate surface has a hemispherical different phase. 4. Having an intermediate layer grown in a uniform plane orientation on the substrate, with a depth of 50 nm to 1 μm and a width of 10 nm to 1 μm on the surface of the intermediate layer.
m and a large number of recesses with a length of 50 nm to 1 μm or hemispherical protrusions with a height of 25 nm to 1 μm, an oxide superconducting layer on the intermediate layer, and a surface of the intermediate layer of the superconducting layer. An oxide superconductor characterized in that point and/or line defects are introduced in a direction perpendicular to the oxide superconductor. 5. The method of manufacturing an oxide superconductor according to claim 2, wherein the recessed portion is formed on the surface of the substrate by at least one of electron beam irradiation, sputtering, and ion implantation. 6. In claim 1, the oxide superconducting layer is Y_1B.
a_2Cu_3O_6_. ＿５＿〜＿７＿． An oxide superconductor characterized by being made of a _5-based oxide superconducting material.