JPH09249498A - Oxide superconductor multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-quality superconductive multilayer film free from internal stress because of being composed of layers with low lattice inconsistency, and to obtain a superconductive wire capable of injecting large current thereinto. SOLUTION: This oxide superconductor multilayer film, which has laminated structure composed of oxide superconductor thin film layers and non- superconductor thin film layers, consists of a combination of materials so as to result in strain-free interfaces between both kinds of the thin film layers. This oxide superconductor multilayer film is obtained, for example, by alternately laminating oxide superconductor thin film of the compositional chemical formula, M'Ba2 Cu3 O7-δ (M' is a rare earth element such as Nd, Sm or E, or an alloy thereof; δ is oxygen deficit) and oxide thin film of the compositional chemical formula, M*Ba2 Cu3 O7-δ (M* is an element such as Pr or Sc, or an alloy thereof; δ is oxygen deficit). The latter thin film is made by laser deposition or sputtering process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting thin film having a laminated structure of a superconducting thin film and a non-superconducting thin film, and comprising a combination of material systems in which the interface between the two thin film layers is strain-free. The present invention relates to a technique effectively applied to an integrated circuit in an electronic device for communication, information processing, and information processing.

[0002]

2. Description of the Related Art A multilayer film composed of a superconductor and a normal conductive metal is a composite material system important for large current application or high frequency current application because the magnetic field penetration length can be effectively utilized. Therefore, a method for producing a multilayer structure has been widely studied even in a metal superconductor system having a low critical temperature Tc.
In addition, especially in oxide superconductors having a high critical temperature Tc, the crystal structure itself is layered, and many studies have been conducted on multilayer films in view of the relationship with the superconducting mechanism.

Furthermore, it is expected that this technique will serve as a basis for realizing a laminated tunnel junction which is a basic element for electronic applications. By the way, in order to realize a multilayer thin film, it is advantageous in terms of crystal growth to combine materials of the same kind. Therefore, a superconductor having a 123 structure, which is represented by YBa ₂ Cu ₃ O _7-δ (δ is an oxygen deficiency amount), does not exhibit superconductivity even though it has almost the same crystal structure.
rBa ₂ Cu ₃ O _7-δ was selected and many production results have been reported. However, YBa ₂ Cu ₃ O _{7-δ, which has been} established as a high-quality thin film deposition method as a superconductor layer, has been used for the most part in the past.
Was selected and produced.

The layer-by-layer technology of the oxide superconducting lattice thin film relating to the above-mentioned prior art is described in Hideomi Koinuma, Mamoru Yoshimoto, Applied Physics Vol. 60, No. 5 (1991) 433-4.
It is disclosed on page 42.

Further, high quality YBa ₂ Cu ₃ O _7-δ and PrB
The layering technique with a ₂ Cu ₃ O _7-δ is described in Naoto Bando, Takahito Terashima, Applied Physics Volume 60, No. 5 (1991) 474-4.
It is disclosed on page 77.

In addition, YBa ₂ Cu ₃ O _7-δ / PrBa ₂ C
u ₃ O _7-δ / YBa ₂ Cu ₃ O _7-δ Josephson composite fabrication technology is described by Jiro Yoshida, Tatsunori Hashimoto, Applied Physics Vol. 61, Vol.
(1992) pages 494-497.

[0007]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

In conventional YBa ₂ Cu ₃ O _7-δ , many screw dislocations due to strain were observed, and there was a problem in surface flatness, which is an essential condition for realizing a multilayer film. In addition, PrBa ₂ Cu ₃ O _7-δ
The lattice matching with is not so good. It is known that in an oxide superconductor, the amount of oxygen deficiency increases due to lattice strain and the superconducting characteristics are deteriorated. In fact, the Tc of the a-axis oriented film on the SrTiO ₃ single crystal substrate is kept low due to the effect of strain. In this way, YBa ₂ Cu ₃ O _7-δ and PrB
In the multilayer film of a ₂ Cu ₃ O _7-δ , stress is accumulated inside and it is difficult to obtain high quality superconducting properties.

That is, since the oxide superconductor has a low carrier concentration, its electrical characteristics strongly depend on the content of oxygen supplying hole carriers. By the way, this amount of oxygen is strongly related to the lattice strain. Therefore, in the state where strain is applied, oxygen deficiency occurs and the superconducting characteristics deteriorate.

By the way, when different materials are combined, an internal strain generally occurs from the bonding interface due to the difference in lattice constant or thermal expansion coefficient. As a result, not only the mechanical strength is weakened, but also the superconductivity of the oxide superconducting material is reduced. Therefore, the present inventor has found that, in the case of producing such a laminated structure, it is important to reduce this strain as much as possible in order to realize high-performance superconductivity.

An object of the present invention is to provide a high-quality superconducting multilayer film which has no internal stress because it is composed of layers having a small lattice mismatch.

Another object of the present invention is to provide a superconducting wiring which can carry a large current.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0014]

The following is a brief description of an outline of a typical invention among the inventions disclosed by the present application.

(1) An oxide superconductor having a laminated structure of an oxide superconducting thin film layer and a non-superconducting thin film layer, and a combination of material systems in which the interface between the two thin film layers is strain-free or strain close thereto. It is a body multilayer film.

(2) Compositional chemical formula M'Ba ₂ Cu ₃ O
An oxide superconductor thin film represented by _7-δ (where M ′ is a rare earth element such as Nd, Sm, Eu or alloys thereof, and δ is an oxygen deficiency amount), and a chemical composition formula M * Ba ₂ Cu ₃ O _{7- δ}
(Where M * is an element such as Pr or Sc or an alloy thereof, and δ is an oxygen deficiency amount) is an oxide superconductor multilayer film having a laminated structure in which oxide thin films are alternately deposited.

(3) The oxide thin film of (2) above is a thin film produced by a laser deposition method or a sputtering method.

According to the above-mentioned means, the oxide superconductor thin film layer and the non-superconductor thin film layer have a laminated structure, and the interface of the two thin film layers is made of a combination of material systems in which the interface is strain-free, Since the strain at the interface between the two thin film layers is reduced to or close to no strain, high-performance superconductivity can be realized.

For example, non-superconductor PrBa ₂ Cu ₃ O
A superconductor having a lattice constant close to that of the _7-δ layer, for example NdBa ₂ Cu ₃ O _7-δ, can be selected to realize an oxide superconductor multilayer film having a small internal stress and a high critical temperature Tc. .

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below along with its embodiments (examples).

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
2 is a cross-sectional view showing the configuration of the oxide superconductor multilayer film of FIG.
Is NdBa ₂ Cu ₃ O _7-δ (NBCO), 2 is PrBa ₂
Cu ₃ O _7-δ (PBCO).

As shown in FIG. 1, the oxide superconductor multilayer film of Embodiment 1 of the present invention has a chemical composition formula of NdBa ₂ Cu ₃ O.
_7-δ (where δ is an oxygen deficiency) an oxide superconductor thin film and an oxide thin film represented by a chemical composition formula PrBa ₂ Cu ₃ O _7-δ (δ is an oxygen deficiency) are alternately deposited. Composed of structure.

The method for producing the oxide superconductor multilayer film according to the first embodiment will be described below.

A NdBa ₂ Cu ₃ O _7-δ thin film is formed on the entire surface of the SrTiO ₃ single crystal substrate by the laser ablation method. The thin film production conditions are NdBa ₂ C as a target.
u ₃ O _{7- δ} polycrystal was used, the substrate temperature was 750 ° C., the oxygen partial pressure was 200 mTorr, the growth time was 0.5 minutes, and the thin film was 8 n.
m. The laser used was a KrF excimer laser having a wavelength of 248 nm and an energy density of 5 J / cm ² .

After that, a PrBa ₂ Cu ₃ O _7-δ thin film is prepared. PrB in the same chamber as the target
An a ₂ Cu ₃ O _7-δ polycrystal is used. Thin film manufacturing conditions are N
Almost the same as dBa ₂ Cu ₃ O _7-δ , the substrate temperature is 750 ° C,
The oxygen partial pressure is 200 mTorr, the growth time is 0.5 minutes, and the film thickness is 8 nm (see FIG. 1). A multilayer film was produced by repeating this alternately. In the case of Embodiment 1, this was repeated 6 times.

FIG. 2 shows the θ-2θ characteristic of the X-ray diffraction of the multilayer film. For comparison, the results of the NdBa ₂ Cu ₃ O _{7 -δ} simple substance film are also shown. It can be seen that the c-axis orientation is obtained, the intensity ratio between the diffraction peaks is the same as that of the NdBa ₂ Cu ₃ O _7-δ simple film, and the lattice matching is good. In addition, no separation of diffraction peaks or peaks of satellite reflection was observed despite the multilayer film. This shows that a multi-layer film having good crystallinity and having no interface strain is formed.

From the results of Rutherford backscattering (RBS) (FIG. 3), the Χmin indicating the disorder of crystallinity is 2.2.
It can be seen from the fact that it is as low as a high-quality film.

FIG. 4 shows the temperature dependence of the electric resistance of the obtained sample. For comparison, the results of the NdBa ₂ Cu ₃ O _7-δ simple substance film are also shown. It can be seen that all of them are superconducting at 80 K or less, and that good quality thin films can be produced. If a solid phase reaction occurs between Nd and Pr to form a thin film, the critical temperature Tc will decrease. Therefore, this high critical temperature Tc indicates compositional separation between layers.

(Embodiment 2) Hereinafter, Embodiment 2 of the present invention
A method for producing the oxide superconductor multilayer film of 1 will be described.

Basically, an element is formed by the same steps as those in the first embodiment. A SmBa ₂ Cu ₃ O _7-δ thin film is formed on the entire surface of the SrTiO ₃ single crystal substrate by the sputtering method. The thin film manufacturing conditions are SmBa ₂ Cu ₃ as a target.
O _7-δ polycrystal is used, the substrate temperature is 740 ° C., the atmospheric pressure is 84 mTorr, the oxygen gas flow rate is 0.5 sccm, the argon gas flow rate is 10 sccm, and the growth time is 1 minute.
It is. The RF power used is 80W.

After that, S is sputtered on the entire surface of the substrate.
A cBa ₂ Cu ₃ O _7-δ thin film is prepared. ScBa ₂ Cu ₃ O _7-δ polycrystal was used as a target, and the substrate temperature was 74.
0 ° C., atmosphere pressure 84 mTorr, oxygen gas flow rate 0.5 s
In ccm, the flow rate of argon gas is 10 sccm, and the growth time is 1 minute. A multilayer film was produced by repeating this alternately.

In the case of the second embodiment, the process was repeated 15 times. FIG. 5 shows the rocking curve of the (005) X-ray diffraction peak. The full width at half maximum is 0.07 °, which shows that a high quality film with few defects is formed.

From the above description, in the first and second embodiments, the oxide represented by the chemical composition formula M'Ba ₂ Cu ₃ O _7-δ (where M'is Nd, Sm, Eu or alloys thereof). Superconductor thin film and chemical composition formula M * Ba ₂ C
An oxide superconductor multilayer film in which an oxide thin film represented by u ₃ O _7-δ (where M * is Pr, Sc, or an alloy thereof) is alternately deposited has been described. The elements of M'in the chemical formula are Nd, Sm, Eu
It may be easily inferred from the above description that it may be a rare earth element or the like or an alloy thereof.

Although the invention made by the present invention has been specifically described based on the embodiments (examples), the present invention is not limited to the above-mentioned embodiments (examples), and the gist thereof is not limited. It goes without saying that various changes can be made without departing from the scope.

[0035]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

According to the present invention, a high-quality superconducting multilayer film having no internal stress can be obtained because it is composed of layers having a small lattice mismatch. Therefore, it is possible to obtain superconducting wiring through which a large current can flow, which is a basic technique for realizing a superconducting circuit.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an oxide superconductor multilayer film according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a θ-2θ characteristic of an X-ray diffraction of an oxide superconductor multilayer film of Embodiment 1 of the present invention.

FIG. 3 is a diagram showing results of Rutherford backscattering (RBS) of the oxide superconductor multilayer film according to the first embodiment.

FIG. 4 is a diagram showing temperature dependence of electric resistance of the oxide superconductor multilayer film according to the first embodiment.

FIG. 5 is a diagram showing a rocking curve of a (005) X-ray diffraction peak of the oxide superconductor multilayer film of Embodiment 1 of the present invention.

[Explanation of symbols]

1 ... NdBa ₂ Cu ₃ O _7-δ (NBCO), 2 ... PrBa
₂ Cu ₃ O _7-δ (PBCO).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 39/24 ZAA H01L 39/24 ZAAZ (72) Inventor's statement Founding 1-14 Shinonome, Koto-ku, Tokyo No. 3 International Superconducting Industrial Technology Research Center, Superconducting Engineering Laboratory (72) Inventor Naoki Koshizuka 1-14-3 Shinonome, Koto-ku, Tokyo International Superconducting Industrial Technology Center, Superconducting Engineering Laboratory (72) Inventor Yoichi Enomoto 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Technology Center Research Institute of Superconductivity Engineering

Claims (3)

[Claims] 1. A laminate structure comprising an oxide superconductor thin film layer and a non-superconductor thin film layer, wherein the interface between the two thin film layers is made of a combination of material systems with no strain or strain close to it. Oxide superconductor multilayer film. 2. An oxide superconductor represented by a chemical composition formula M'Ba ₂ Cu ₃ O _7-δ (where M'is a rare earth element such as Nd, Sm, Eu or their alloys, and δ is an oxygen deficiency amount). The thin film and the chemical composition formula M * Ba ₂ Cu ₃ O _7-δ (where M
* Is an oxide superconductor multilayer film having a laminated structure in which elements such as Pr and Sc or alloys thereof, and δ are oxide thin films represented by oxygen deficiency) are alternately deposited. 3. The oxide superconductor multi-layer film according to claim 2, wherein the oxide thin film is a thin film produced by a laser deposition method or a sputtering method.