JPH0653630B2 - Thin film type superconducting element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to rare earth elements (Ln), alkaline earth metal elements (M),
The present invention relates to a thin film type superconducting element in which a composite oxide superconductor composed of copper (Cu) and oxygen (O) is formed as a thin film on an electrically insulating substrate.

[Conventional technology]

Since Bednorz et al. In 1986 showed the existence of a superconducting material having a high critical temperature (Tc) in a LA-Ba-Cu-O system composite oxide, Tc increased sharply, and in February 1987 98K
Was recorded. As a result, there is a possibility of practical application of a superconductor using liquid nitrogen as a refrigerant.

As substances with high Tc that have been discovered so far,
Ln-M-Cu-O based complex oxide superconductor (where Ln is La, Nd, P
At least one of m, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least one of Ba, Sr, and Ca) is known. For example, it is a superconductor having a composition of LnM ₂ Cu ₃ O _7-k (0 <k ≦ 0.5).

Ln-M-Cu-O composite oxide superconductors are applied in various forms such as sintered bodies, thin films, single crystals, and wire rods. When using this material as an electronic device, thin film or single It is generally used as a crystal. High for single crystals
The production of crystals with Tc is difficult, and it is expected that thin films will precede the deviceization.

[Problems to be solved by the invention]

By the way, when a thin film is produced, a substrate is always required, so the coefficient of thermal expansion between the thin film and the substrate is an important factor. In particular, when the Ln-M-Cu-O-based composite oxide is formed as a thin film on a substrate at a high temperature, the film is formed at a high substrate temperature or after a low substrate temperature, Since the method of heat treatment at a high temperature is adopted, it is desirable that the thermal expansion coefficient of the substrate and that of the thin film are closer to each other than those of other thin films. According to the data measured by the present inventors, Ln-M-Cu-O
It has been found that the coefficient of thermal expansion of the system composite oxide is close to that of metals, an order of magnitude greater than that of silica glass, which is often used as a substrate for oxide thin films, and several times greater than that of alumina substrates. . For this reason, when a thin film is formed on a quartz glass substrate or an alumina substrate, a crack is generated in the thin film during film formation or during cooling to liquid nitrogen temperature, which easily causes deterioration of the superconductor. Furthermore, the quartz glass substrate and the alumina substrate easily react with the Ln-M-Cu-O-based composite oxide at high temperature, and there is a problem in this respect as well.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a stable thin film type superconducting element in which characteristic deterioration due to thermal strain and reaction between a substrate and a superconductor do not occur at high temperatures.

[Means for solving problems]

This invention is a substrate of oxide having a composition of Y ₂ MCuO ₅ , LnM ₂ Cu ₃ O _7-k (where Ln is La, Nd, Pm, Sm, Eu, Gd, Dy,
At least one of Ho, Er, Tm, Yb, Lu, Y; M is Ba, S
At least one of r and Ca; k is a thin film of a superconductor having a composition of 0 <k ≦ 0.5), thereby achieving the above object.

[Action]

According to this invention, since the oxide made of the constituent element which is the same as or similar to the constituent element of the Ln-M-Cu-O-based composite oxide superconductor is used as the substrate material, both the superconductor and the substrate are The coefficient of thermal expansion can be very close. This allows
Almost no thermal stress or strain is generated between the substrate and thin film from high temperature to low temperature. Further, there is no problem of reaction between the substrate and the superconductor at high temperature, and good superconducting characteristics can be stably obtained.

〔Example〕

 Examples will be described below with reference to the drawings.

(Example 1) Y ₂ O ₃ , Ba ₂ CO ₃ , CuO was used as a starting material, weighed so that Y ₂ BaCuO ₅ was obtained, and after mixing with a ball mill,
The powder was calcined and pulverized again with a ball mill to granulate this powder, and then it was molded into a disk-shaped pellet having a diameter of 25 mm and a thickness of 1.5 mm, and fired in the atmosphere to obtain a sintered body. This sintered body was cut into a square with a side length of 15 mm and a thickness of 1 mm, and a mirror-polished product was used as a substrate to form a superconductor thin film by the sputtering method as follows. The film composition of the sputter gate is
A sintered body having a composition of LaBa ₂ Cu ₄ O _6.8 and having a diameter of 6 inches so as to be LaBa ₂ Cu ₃ O _7-k was used. Here, Cu is Cu in consideration of the fact that the composition of the target is not directly incorporated in the film formation.
₄ As the sputtering gas, a mixed gas of O ₂ : Ar = 1: 1 (volume ratio) is used, and the gas pressure thereof is 0.5 Pa. The sputtering power is 300 W, the substrate temperature is 650 ° C., and the distance between the target and the substrate is 28 mm.

After the sputtering, the oxygen was quickly switched to 1 atm of pure oxygen so that oxygen was sufficiently taken into the film during the cooling process of the substrate after the film formation (k≈0.1), and the film was cooled from 650 ° C. to room temperature therein. Using the mask for electrode formation on the film thus manufactured, Au was attached by the vapor deposition method, and the temperature change of the resistance was examined by the 4-terminal method. Fig. 2 shows the structure of the substrate, superconductor thin film, and electrodes. In FIG. 2, 1 is a substrate made of La ₂ BaCuO ₅ , 2 is a superconductor thin film made of LaBa ₂ Cu ₃ O _7-k , 31-
34 is an Au electrode, 4 is a constant current power source, and 5 is a voltmeter.

To compare the characteristics, a superconductor thin film and an Au electrode were formed on a quartz glass substrate and an alumina substrate under the same conditions, and the temperature change of resistance was measured by the above method.

FIG. 1 is a plot of the resistance of these samples as a function of temperature. However, in this figure, instead of plotting the resistance directly, the resistance R (T) at temperature T and 30
It is shown as a ratio to the resistance R (300K) at 0K.
From FIG. 1 it can be seen that the method of the present invention results in a high critical temperature Tc. This is because when a film is formed on a quartz glass substrate or an alumina substrate, the film and the substrate have large thermal expansion coefficients, so that countless small cracks occur in the film.

(Example 2) Instead of the Y ₂ BaCuO ₅ substrate shown in Example 1, a Y ₂ SrCuO ₅ substrate was used, and after the film formation and the electrode formation in the same procedure as in Example 1, the temperature change of the resistance was performed. It was measured. The results are shown in FIG.

(Example 3) Instead of the Y ₂ BaCuO ₅ substrate shown in Example 1, a Y ₂ CaCuO ₅ substrate was used, and after the film formation and the electrode formation by the same procedure as in Example 1, the temperature change of the resistance was changed. It was measured. The results are shown in FIG.

From FIGS. 3 and 4 and Table 1 described later, the effect of the present invention is recognized as in the case of the first embodiment.

Instead of LaBa ₂ Cu ₃ O _7-k superconducting thin film shown in (Example 4) Example 1, replacing La in addition to the rare earth element (Ln), the substrate material
Table 1 shows the critical temperature Tc when Ba is replaced with other alkaline earth metal elements Sr and Ca. Further, the case where an alumina substrate is used is also shown as the substrate A for comparison.

Although the alkaline earth metal element M of the substrate material is described as a single element of each of Ba, Sr, and Ca in the above-mentioned examples, a plurality of alkaline earth metal elements, for example, one may be added as an additive. , Can be appropriately adopted within the scope of the technical idea of the present invention.

〔The invention's effect〕

According to the present invention, LnM ₂ Cu ₃ O _7-k (where Ln is La, Nd, Pm, Sm, Eu, G) on the oxide substrate having a composition of Y ₂ MCuO _5.
At least one of d, Dy, Ho, Er, Tm, Yb, Lu, Y; M
Is at least one of Ba, Sr, and Ca; k is 0 <k ≦ 0.
Since the superconductor having the composition 5) is formed as a thin film, the thermal expansion coefficients of both the superconductor and the substrate can be made extremely close to each other. As a result, thermal stress and thermal strain hardly occur between the substrate and the thin film from high temperature to low temperature. Further, there is no problem of reaction between the substrate and the superconductor at high temperature, and good superconducting characteristics can be stably obtained.
As described above, it is possible to provide a thin film type superconducting element having excellent characteristics and reproducibility and stable.

[Brief description of drawings]

FIG. 1, FIG. 3 and FIG. 4 are diagrams showing temperature-resistance ratio characteristic curves of thin film type superconducting elements in different embodiments of the present invention, and FIG. 2 is a schematic configuration for measuring the characteristic curves. It is a figure. In the figure, 1: substrate, 2: superconductor thin film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01L 39/12 ZAA C 9276-4M (72) Inventor Yukinori Kawamura Kanata Pref. Tanabe Nitta, Kawasaki-ku, Kawasaki-shi No. 1 in Fuji Electric Co., Ltd. (72) Inventor Kazuro Mukai 1-1 No. Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (1)

[Claims] 1. Rare earth element (Ln), alkaline earth metal element
(M), copper (Cu), oxygen (O) complex oxide superconductor,
In a thin film type superconducting device formed as a thin film on an electrically insulating substrate, LnM ₂ Cu ₃ O is formed on an oxide substrate having a composition of Y ₂ MCuO _5.
7-k (where Ln is La, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb,
At least one of Lu and Y; M is at least one of Ba, Sr, and Ca; k is a thin-film superconductor having a composition of 0 <k ≦ 0.5) Superconducting element.