JPH03224278A - Substrate with composite-oxide superconducting thin film layer and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the surface smoothness of the title substrate by forming a composite-oxide super-conducting thin film layer on an intermediate layer containing a specific oxide. CONSTITUTION:An intermediate layer containing at least one or more thin films of an oxide including copper is formed on a single-crystal substrate. A composite-oxide superconducting thin film is formed on the intermediate layer which is good in lattice matching with the oxide super-conducting thin films. Therefore, the critical current density can be increased significantly due to the improved surface smoothness of the substrate by super--conducting thin film which is epitaxially grown to a good state and, at the same time, the influence of the material used for the substrate to the super-conducting layer when the material is thermally diffused is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a substrate having a composite oxide electrically conductive thin film layer.

In particular, the present invention relates to the structure and method of manufacturing a novel composite oxide superconducting substrate that has a composite oxide thin film with a unique structure on a base substrate and stably exhibits good superconducting properties.

Conventional technologyThe superconducting phenomenon, which is said to be a phase transition of electrons, has been known for a long time.
It was thought that this phenomenon could only be observed at extremely low temperatures requiring cooling with liquid helium. However, 19
In 1986, Bednotes and Muller showed a superconducting state at 30 (La, Ba) 2Cub.

was discovered, and in 1987, Chu et al. discovered YBa2Cu:+oy with a critical temperature in the 90s.
In 1988, Maeda et al. discovered a Bi-based composite oxide superconducting material that exhibited a critical temperature of 100 K or higher. These composite oxide-based superconducting materials can achieve superconductivity using inexpensive liquid nitrogen, and are therefore expected to put superconducting technology into practical use.

These composite oxide-based high-temperature superconducting materials were initially obtained as sintered bodies using powder metallurgy, but since sintered bodies can only have particularly low critical current densities, they have been produced as thin films using various vapor deposition methods. Methods for film formation have been widely studied.

Generally, composite oxide-based superconducting thin films are SrT+03, M
A film is formed on a single crystal substrate such as gO by various physical vapor deposition methods such as vacuum evaporation, sputtering, ion blating, and MBE, and chemical vapor deposition such as MO-CVD.

By forming a thin film of composite oxide superconducting material,
Although the critical current density has been significantly improved, the superconducting thin films obtained to date are not microscopically uniform in film quality and the critical current density is low, so it is difficult to actually fabricate electronic circuit elements. Have difficulty.

Therefore, in order to actually utilize composite oxide superconducting thin films in the production of various devices, it is necessary not only to further increase the critical current density, but also to provide a superconducting thin film with uniform film quality on a large area substrate, preferably a single crystal. It is necessary to deposit a superconducting thin film.

The following are possible reasons why the properties of the composite oxide Mi conductive thin film formed on a single crystal substrate of an oxide such as MgO or 5rTiG3 are excellent; When a superconducting thin film is directly formed, the constituent elements of the substrate are likely to diffuse into the oxide superconductor and the properties of the superconducting thin film are likely to deteriorate, but single crystals such as MgO1SrTi03 have little adverse effect even in this case.

Second, a composite oxide superconductor deposited on a specific surface of a single crystal such as MgO1SrTi03 tends to become an oriented polycrystal or single crystal. That is, MgO1Sr
When a single crystal substrate such as TiO+ is used, it is easy to grow a composite oxide superconducting thin film by so-called epitaxial growth. Therefore, the obtained superconducting thin film is composed of a single crystal with excellent superconducting properties or a polycrystal with very uniform crystal orientation. Furthermore, although the superconducting properties of composite oxide superconductors have anisotropy, this anisotropy can also be controlled.

However, composite oxide superconducting thin films formed on oxide single-crystal substrates using conventional methods are susceptible to the effects of unevenness on the substrate surface and the lattice constant between the crystals of the material composing the substrate and the oxide superconductor crystals. Due to the mismatch, the surface was not smooth, which was inconvenient for application to devices and the like. Possible reasons why the surface of an oxide superconducting thin film is not smooth are as follows: ■ The surface of an oxide single crystal substrate is not smooth at the atomic level. Polishing the surface makes it smooth to some extent, but electron diffraction (RHEED)
When observed, it is difficult to obtain a streak pattern indicating surface smoothness, and only a smooth pattern is obtained.

■ Because the lattice constants of the oxide superconductor and the oxide single crystal substrate are different, the unevenness that was absorbed by the film stress at the early stage of growth becomes unable to withstand the film stress as the film thickness increases, and the surface Causes unevenness.

Furthermore, since composite oxide superconducting thin films formed by various conventional vapor deposition methods have poor superconducting properties in as-devo,
In order to achieve excellent superconducting properties, it was necessary to subject the composite oxide thin film to a boss annealing process after film formation.

However, it is known that the substrate material diffuses into the thin film during the boss annealing process, resulting in a significant decrease in the quality of the thin film in the region near the substrate.

US Pat. No. 4,837,609 proposes interposing W, Mo, and Ta between a composite oxide superconducting material and a silicon single crystal.

Furthermore, Japanese Patent Laid-Open No. 63-239.840 proposes oxidizing a metal copper substrate to form a CuO layer, and depositing a composite oxide superconducting material on this CuO layer.

Problems to be Solved by the Invention An object of the present invention is to solve the problems of the prior art described above, and to provide a substrate having a superconducting thin film layer with a smooth surface and excellent characteristics;
The object of the present invention is to provide a method for producing the same.

Means for Solving the Problems The present invention provides a substrate having a composite oxide superconducting thin film layer, which comprises a substrate, an intermediate layer formed on the substrate, and a composite oxide superconducting thin film formed on the intermediate layer. A substrate having a composite oxide superconducting thin film layer constituted by a composite oxide superconducting thin film layer is characterized in that the intermediate layer includes at least one thin film of an oxide containing copper.

The substrate is preferably an oxide single crystal substrate, particularly an oxide single crystal substrate of MgO1SrTiQ3 or YSZ.

The composite oxide superconducting thin film used in the present invention can be made of any known composite oxide superconducting material. The following can be mentioned as already known composite oxide superconducting materials.

(1) Bit (Sr,-,,CaX)mCu
, o, +.

(Here, x, m, n, p and y are numbers in the following range: 6≦m≦10.4≦n≦8, p=6+m+n.

Q<x<l, -2≦y≦2) (2) Ln, Ba2 Cu3
Ch-z (where Ln is la, NdXSm,
represents at least one element selected from the group consisting of Eu, Gd, DyXHQ%Y1ε, Tm5Yb and Lu, Z is a number satisfying the formula: 0≦Z<l) (3) (La+-x ( 2% Lcuo4-y
(Here, α represents Sr or Ba, and X and y are o
≦x<l, 0≦y<1) The present invention is particularly suitable for the substrate having a Bi-based composite oxide superconducting thin film (1).

A feature of the present invention is that the intermediate layer includes at least one thin film of an oxide containing copper.

Examples of the intermediate layer of this copper-containing oxide include the following: (i) A copper oxide or a copper composite oxide having a perovskite-type or layered perovskite-type crystal structure.

Specifically, composite oxides represented by the following formula can be mentioned: ■ Ln+ Ba, Cu307-2 (here, Ln
are La, Ce, Pr, Nd, Sm, Eu.

Gd5TbSDy, llo, YSEr, TmXY
(La+-x αH)zcuO<-.

(Here, α represents Sr or 8a, and X and y are 0
≦x<l, O≦y<1 is the number that increases z) (ii) Composite of the present invention, a two-layer film of a Cu layer (on the substrate side) and a CuO layer (on the composite oxide superconducting thin film side) A substrate having an oxide superconducting thin film layer can be manufactured using normal thin film forming means. That is, various physical vapor deposition methods such as vacuum evaporation method, sputtering method, ion blating method, MBE method, and MO-CVD
A predetermined element or molecule is evaporated from an evaporation source using a chemical vapor deposition method such as 5rTi0
3. An intermediate layer and a composite oxide superconducting thin film layer can be formed by depositing on a single crystal substrate such as MgO.

First Embodiment In the first embodiment of the present invention, a Cu oxide or a composite oxide containing Cu having a perovskite or layered perovskite crystal structure is selected as the intermediate layer formed on the substrate. .

The composite oxide superconducting thin film in which this first embodiment is most effectively exhibited is a thin film composed of a Bl-based composite oxide superconducting material expressed by the following formula:=B14(Sr+-
11, Ca x) a CuhOp+y (where m, n
, p, x and y are numbers in the following ranges: 6≦m≦10, 4≦n≦8, p=6+m+n.

0<x<L -2≦y≦2) Particularly preferable compositions include the following ranges (a) 7≦m≦9.5≦n≦7.0.4 <x<Q,
5(b) 6≦m≦7.4≦n≦5.0.2 <x<0.
4(C)9≦m≦10.7≦n≦8.0.5<X<0.
7 In addition, the middle layer in this case is the following formula ■ or ■
A complex oxide represented by: ■ LnlBa
2Cu3 Ch-z (where Ln is La, CeXP
r, Nd, Sm5Bu, Gd.

Represents at least one element selected from the group consisting of Tb5Dy, Ha, YXEr, Tm, Yb and Lu, 2 is a number satisfying 0≦z<l)■ (La, -
, α, )2CuOs-y (where α is Sr or Ba
, and X and y represent numbers in the following ranges: 0≦X<l, 0≦y<1) This special case has the following advantages. That is, conventionally, when producing a Bi-3r-Ca-Cu-based composite oxide superconducting thin film, [
100] surface, sputtering method, vacuum evaporation method, MO
- Films were formed by CVD method etc., but MgO and Bi -
It has a low lattice matching with the 3r-Ca-Cu-based composite oxide, and it is not possible to epitaxially grow the Bl-based composite oxide, which has particularly strong anisotropy, and the formation of a low critical temperature phase cannot be prevented. There wasn't.

On the other hand, in the substrate having a composite oxide superconducting thin film layer according to the present invention, the oxide superconducting thin film layer is formed by forming an intermediate layer having a perovskite type or layered perovskite type crystal structure on the substrate. A Cu-0 lattice plane consisting of Cu atoms and zero atoms having high crystal consistency with the Bii composite oxide is formed on the surface that will be the actual film forming surface. By forming a Bii composite oxide thin film on this intermediate layer, epitaxial growth of the B1-based composite oxide is promoted. As a result, the critical current density of the superconducting thin film can be improved.

It is preferable to use a single crystal substrate of MgO1SrTi03YSZ as the substrate.

The composite oxide (1) or (2) used as the intermediate layer can itself be a superconducting material, but in this embodiment, the substrate and B! It is used as an intermediate layer material with excellent lattice matching with any type of composite oxide. That is,
This intermediate layer [1) or (2) is made of MgO or 5rT10.
can be easily epitaxially grown on single crystal substrates to form perovskite or layered perovskite crystals. This perovskite-type or layered perovskite-type crystal contains a unique Cu-0 plane structure that contributes to superconducting phenomena, and also has a structure similar to the Cu-0 plane that contributes to superconducting phenomena in B1-based composite oxide superconductors. have,
Moreover, this Cu-0 plane and the Cu of Bii oxide superconductor
It has very good lattice matching with the O-plane. Therefore, a Bi-based superconducting thin film is epitaxially grown on this composite oxide intermediate layer (1) or (2), and the critical current density of the obtained superconducting thin film is improved.

The intermediate layer and the composite oxide superconducting thin film layer can be formed by any known film forming method such as a sputtering method, a vacuum evaporation method, an MO-CVD method, or the like. In addition, MBE method and VPE
Alternatively, the interface between the intermediate layer and the composite oxide superconducting thin film layer can be formed mainly of Cu atoms and zero atoms by sequentially stacking monoatomic layers on a substrate by a method or the like.

Another special embodiment of this first embodiment is to
This is the case when forming a BCO thin film. In this case, it is preferable that the intermediate layer be a composite oxide thin film of La and Cu.

In other words, YB, a typical composite oxide superconducting material
Considering the case where a2Cu:+Oy (hereinafter referred to as YBCO) is formed on an MgO single crystal substrate, which is also a typical substrate material, the lattice mismatch between MgO and YBCO is as much as 9.2%. Further, it is considered that the crystal growth of YBCO depends exclusively on the fact that YBCO itself has a structure that is easy to crystallize. However, when the substrate material diffuses to the superconducting thin film side by Bost annealing, YBCO
can no longer maintain a structure effective for superconducting phenomena.

Further, the film forming conditions for producing a YBCO thin film with good crystallinity are limited to extremely narrow and specific conditions.

On the other hand, in the substrate having a composite oxide superconducting thin film of the present invention, a composite oxide thin film of La and Cu (La-C) is formed on the substrate.
u-0 is formed, and a superconducting thin film is formed on this La-Cu-0 composite oxide thin film. This La-Cu-o1 composite oxide thin film has extremely good crystallinity (La-CuO and YB
The lattice mismatch with CO is about 2.1 layers, and MgO and YB
Since the degree of lattice mismatch with CO is smaller, YBC
The O thin film becomes very easy to crystallize, and Cu on the MgO substrate
To reliably form a perovskite structure including the −0 plane. Furthermore, since La is a lanthanide element like Y and has the same Cu-0 plane, even if mutual diffusion occurs at the interface between the t, a-cu-o composite oxide and YBCO, it will not affect the superconducting properties. The impact will be very small.

Therefore, it is possible to easily produce a YBCO thin film with extremely good crystallinity, and since the thickness of the part of the thin film that becomes substantially superconducting increases, the absolute value of the usable current density can be increased. I can do it.

In order for the La-Cu-0 composite oxide to form the desired crystal structure and effectively prevent diffusion of the substrate material, the La-Cu-0
The film thickness of the -0 composite oxide is preferably 100 Å or more.

Second Embodiment In the second embodiment of the present invention, an intermediate layer consisting of a Cu layer and a CuO layer, that is, a buffer layer (hereinafter referred to as a Cu/CuO buffer layer) is provided between the substrate and the composite oxide superconducting thin film. C
A u layer (referred to as 'uO thin film) is formed. In this case, a Cu layer is formed on the substrate side, a CuO layer is formed on this Cu layer, and a composite oxide superconducting thin film is formed on this CuO layer.

In this second embodiment, both the Cu thin film and the Cu◯ thin film are preferably single crystal, and the composite oxide superconducting thin film is also preferably single crystal.

The Cu/[:uo buffer layer absorbs the surface irregularities of the oxide single crystal substrate and absorbs the difference in crystal lattice constant between the composite oxide superconducting thin film and the substrate, so this second embodiment The composite oxide superconducting thin film obtained by this method has a smooth surface and high quality.

This second embodiment is applicable to any known composite oxide superconductor having a Cu-0 plane in its crystal, and examples thereof include the following system: La-3r-Cu- 〇 system, Y-Ba-Cu-0 system, B+ -3r -Ca-Cu-0 system, TI -Ba
-Ca-Cu-0 system Bi-3r-Ca-Cu-0 system, Bi-Pb
Sr-Ca-Cu-0-based complex oxides, such as the following: 814 (Sr l-X , C'l x) a Cu
n0p-y (where m% nS0% X and y are numbers in the following ranges: 6 layers m≦10, 4≦n≦8, p=6+m+n.

Q<x<1, -2≦y≦2) Particularly preferable compositions include the following range: (a) 7 layers m≦9.5≦n≦7.0.4 <x<
0.6 (b) 6 layers m≦7.4≦n≦5.0.2<X<Region 4 (c) 9 layers m≦1O17≦n≦8.0.5 < x
<0.7 The substrate is preferably an oxide single crystal substrate such as MgO1SrTiO3 or YSZ because it is easy to epitaxially grow a Cu/CuO buffer layer and/or a composite oxide superconducting thin film.
It is preferable to use the plane and the (110) plane as the film-forming plane.

The Cu/CuO thin film serving as the buffer layer is preferably single crystal.

The advantages of using a Cu/CuO thin film as a buffer layer include the following: (1) C
uO has a very good lattice match with composite oxide superconducting thin films.
Complex oxide superconductors are easily epitaxially grown on CuO thin films. In addition, in complex oxide superconducting thin films, the Cu-0 plane in the crystal is greatly involved in superconducting properties, but C
In a composite oxide superconducting thin film grown on uO, the Cu-0 plane in the crystal reflects the structure of the CuO crystal, and it tends to become a layered crystal in a preferable direction.

(2) In particular, Bi-based composite oxide superconducting thin films are characterized by having a layered structure, and it is known that the diffusion of elements between the B1-0 layers is small. Even if an 81-series complex oxide superconductor thin film is formed on this Cu/CuO buffer layer, the Cu/CuO in the buffer layer will not diffuse into the superconductor and will not disrupt the stoichiometry. do not have.

(3) A Cu thin film easily grows epitaxially on a single crystal substrate, and has a surface smoothness such that a streak pattern is obtained when observed by RHEED. Further, CuO easily grows epitaxially on this Cu thin film and has similar surface smoothness.

The film thickness of the above Cu/CuO buffer layer is Cu thin film, C
The thickness of both uO thin films is preferably 10 Å or more and 1000 Å or less, particularly preferably 10 Å or more and 100 Å or less. This is because if the thickness of each film is less than 10, the effect will not be sufficient, and if the thickness of each film exceeds 1000, the crystallinity of each thin film will be disturbed, which will have a negative effect on the superconducting thin film. . Each film thickness is 10 Å or more 100
When the thickness is Å or less, both the Cu thin film and the CuO thin film have the best crystallinity, and more excellent effects can be obtained.

The Cu/CuO buffer layer and composite oxide superconducting thin film of this second embodiment are formed by MBE (molecular beam epitaxy).
It can be formed using a method such as a method, a sputtering method, an ion beam sputtering method, an ion blating method, or the like.

Although the present invention has been described above with reference to two special embodiments, the present invention can be easily applied to other composite oxide superconducting thin films.

Examples of the present invention will be shown below, but the present invention is not limited to the following examples.

Example 1 A La-3r-Cu-based composite oxide intermediate layer was formed on the substrate by RF sputtering using the (100) plane of a SrTiO3 single crystal substrate as the film-forming surface under the film-forming conditions shown in Table 1 below. was formed, and a Bi-3r-Ca-Cu based composite oxide superconducting thin film layer was formed thereon.

In addition, as a comparative example, a sample was prepared in which a superconducting thin film layer was directly formed on a Sr'riOz single crystal substrate under the conditions listed in Table 1 (2) above.

The samples of Examples and Comparative Examples formed as described above were post-annealed. That is, each sample was heated to 890° C. at a heating rate of 3° C./min in an 02 air flow, maintained at this temperature for 1 hour, and then cooled to room temperature at a cooling rate of 3° C./min.

The composition (atomic ratio) of the intermediate layer and superconducting thin film layer of the obtained sample was as follows: Intermediate layer: La:Sr:Cu = 1.85:0.15
: 1 superconducting thin film layer Bi :Sr:Ca:Cu = 2:2:2:3
The superconducting critical temperature Tc and critical current density Jc were measured and evaluated for each sample of the example and the comparative example. The results are shown in Table 2.

Table 2*: Temperature at which the electrical resistance of the sample begins to decreaseKimoto: Temperature at which the electrical resistance of the sample can no longer be measured**Critical current density at near 7K As shown in Table 2, the temperature at which the electrical resistance of the sample begins to decrease is as shown in Table 2. It was confirmed that superconducting substrates achieve extremely high critical current densities without sacrificing other properties.

Further, when the crystallinity of each sample was evaluated by electron beam diffraction, it was revealed that the superconducting thin film layer of the sample according to the example of the present invention was epitaxially grown.

Example 2 Using the (100) plane of an Mg0 single crystal substrate as the film formation surface, an intermediate layer made of Y-Ba-Cu-based composite oxide was formed on the substrate by simultaneous vacuum evaporation, and Bi- 3r
A -Ca-Cu based composite oxide superconducting thin film layer was formed.

In this example, commercially available metal Y5 metal B1,
Using metal Ca, metal Cu, BaF2, and SrF2, BaF2 and SrF2 were prepared using an electron gun, and
Each metal element was evaporated using a cell.

The film forming conditions are shown in Table 3 below.

In addition, as a comparative example, a sample was prepared in which a superconducting thin film layer was directly formed on an MgO single crystal substrate under the conditions listed in Table 3 (2) above.

The samples of Examples and Comparative Examples formed as described above were post-annealed. That is, each sample was heated to 890° C. at a heating rate of 3° C./min in an 02 air flow, maintained at this temperature for 1 hour, and then cooled to room temperature at a cooling rate of 3° C./min.

The compositions (atomic ratio) of the intermediate layer and superconducting thin film layer of the obtained sample were as follows: Intermediate layer Y:Ba:Cu = 1:2:3Superconducting thin film layer B+:Sr:Ca:Cu = 2 :2:2:3 The superconducting critical temperature Tc and critical current density Jc of each sample of Example and Comparative Example were measured and evaluated. The results are shown in Table 4.

Table 4 *: Temperature at which the electrical resistance of the sample begins to decrease Kimoto: Temperature at which the electrical resistance of the sample can no longer be measured * Book * Critical current density at near 7K As shown in Table 4, the composite oxide of the present invention It has been established that substrates with superconducting thin films have extremely high critical current densities.

Further, when the crystallinity of each sample was evaluated by electron beam diffraction, it was confirmed that the superconducting thin film layer of the sample according to the example of the present invention was epitaxially grown.

Example 3 Bi25r2Ca2Cu according to the present invention was deposited on the (100) plane of an MgO single crystal substrate using the MBE apparatus shown in FIG.
, O.

An oxide superconducting thin film was formed.

The device shown in Figure 1 has a chamber 1 that can be evacuated to a high vacuum.
, a plurality of Knudsen cells (K-cells) 2 which can control and heat the temperature of the evaporation source 10 housed therein, and which can control the amount of evaporation of the evaporation source 10 with a shutter 8; The substrate holder 3 has a substrate holder 3 which can be heated by controlling the temperature, and an oxygen supply vibro which is opened near the substrate 5 and which supplies oxygen excited by microwave discharge from a microwave power source 7 to the vicinity of the surface of the substrate 5.

First, Cu was deposited on an MgO (100) single crystal substrate under the following conditions.
A thin film was formed.

Evaporation source Evaporation source temperature Substrate temperature Vapor deposition rate Chamber internal pressure Cu: 1400 °C = 500 °C: 05 people/sec: I The epitaxial film was of good quality.

Next, the CuO thin film was coated with the above C in an oxygen atmosphere under the following conditions.
Film formed on u thin film: Evaporation source 2Cu Evaporation source temperature: 1400°C Substrate temperature: 500°C Vapor deposition rate: 0.58/sec Microwave output crab 100W O2 partial pressure: 5 Xl0-'Torr film thickness: 20 Finally, Bi, 5r2 (
:A2Cu30x thin film was grown: Evaporation source and evaporation source temperature: Bi: 530°C Sr: 900°C Ca: 950°C Cu: 1400°C Substrate temperature Near 00°C Vapor deposition rate: 0.58/sec Microwave emission crab 100 W 02 Partial pressure: 5 Xl0-6 Torr Film thickness: 500 people The results of RHEED observation of this superconducting thin film are shown in Figure 2. The diffraction pattern in Figure 2 is streaky, indicating that it is a single crystal film with a smooth surface.

Further, the measurement results of the superconducting properties of the above superconducting thin film are shown below. For comparison, Bi25r2Ca2Cu, 0.0. The measurement results of the superconducting properties of thin films are also shown as a comparative example.

Comparative Example of the Present Invention As described above, the composite oxide superconducting thin film of the present invention produced by the method of the present invention has far superior properties compared to conventional ones.

Example 4 Using an MgO single crystal substrate with a diameter of 15 mmφ as a substrate,
A La-Cu oxide thin film was formed using the RF sputtering method using the (100) plane as the film-forming surface under the film-forming conditions shown in Table 4 below, and then a Y-BaCu oxide thin film was formed thereon. A film was formed to prepare sample (2). In addition, sample (2) was prepared in which a Y -Ba-[:u oxide thin film was directly formed on an MgO single crystal substrate.

The obtained samples ■ and ■ were heated to 900°C in a 0□ air flow at a temperature increase rate of 3°C/min, maintained at this temperature for 1 hour, and then cooled to room temperature at a cooling rate of 3°C/min. .

The superconducting critical temperature (Tc-o and T
c-1) and critical current density Jc were measured.

The measurement results are shown in Table 5.

Table 5*: rTc-o J represents the temperature at which the electrical resistance of the sample begins to decrease, and rTc-i'' represents the temperature at which the electrical resistance of the sample can no longer be measured.

This is the critical current density at Kimoto near 7K.

As shown in Table 5, it was confirmed that the substrate having the composite oxide superconducting thin film according to the present invention achieved extremely high critical current density without sacrificing other properties.

Furthermore, when the crystal characteristics of each sample were observed by electron beam diffraction, it was found that in the sample according to the example of the present invention, the superconducting thin film layer was epitaxially grown, but in the comparative example, it was not epitaxially grown.

As described above, it has been confirmed that according to the present invention, a composite oxide superconducting thin film having a high critical current density can be formed with good reproducibility.

As described in detail of the invention, the substrate having the composite oxide superconducting thin film according to the present invention has the following characteristics: by providing an intermediate layer with good lattice matching between the oxide single crystal substrate and the oxide superconducting thin film,
The superconducting thin film can be epitaxially grown well, the surface smoothness is improved, and the critical current density is significantly increased. Furthermore, thermal diffusion of the substrate material into the superconducting material layer has little effect, and a composite oxide superconducting thin film with good crystallinity can be formed uniformly and stably in the thickness direction.

The oxide superconducting thin film of the present invention is extremely useful when used in devices such as switching elements of Machiso, memory elements of Anatsuka, and superconducting quantum interferometers (SQUID).

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a thin film forming apparatus used in an embodiment of the present invention, and FIG. 2 is a conceptual diagram of a thin film forming apparatus used in an embodiment of the present invention.
There is a RHEED pattern of an O)l thin film grown at 500A. [Main reference numbers] 1...Chamber, 2...K-senohe 3...Substrate holder, 4...Heater, 5...Substrate, 6...Oxygen supply pipe, 7... microwave power source, 8... shutter, 10... evaporation source,

Claims (3)

[Claims] (1) A substrate having a composite oxide superconducting thin film layer composed of a substrate, an intermediate layer formed on the substrate, and a composite oxide superconducting thin film layer formed on the intermediate layer, wherein the intermediate layer 1. A substrate having a composite oxide superconducting thin film layer, the substrate comprising at least one thin film of an oxide containing copper. (2) The substrate according to claim 1, wherein the copper-containing oxide thin film is a copper oxide or copper-containing composite oxide thin film having a perovskite-type or layered perovskite-type crystal structure. (3) The above copper-containing oxide thin film is in contact with the substrate.
2. The substrate according to claim 1, comprising two layers: a layer of U and a layer of CuO in contact with the Cu layer and the composite oxide superconducting thin film.