JP2819871B2 - Manufacturing method of superconducting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device and a method for manufacturing the same. More specifically, the present invention relates to a superconducting device having an oxide superconducting thin film formed on a substrate and an insulating thin film formed on the thin film, and a method for manufacturing the same.

[0002]

2. Description of the Related Art When an oxide superconductor is used in a superconducting device, it is necessary to reduce the thickness of the oxide superconductor and form a structure in which the oxide superconductor is laminated with a thin film of an insulator, a semiconductor, or the like. For example,
When a superconductor-insulator-superconductor junction called a Josephson junction is realized by using an oxide superconductor, the first oxide superconducting thin film, the insulator thin film, and the second oxide superconducting thin film are formed as follows. They must be stacked in order.

In the above Josephson junction, the thickness of the insulator thin film is determined by the coherence length of the superconductor. Oxide superconductors have a very short coherence length, so in a Josephson junction using oxide superconductors,
The thickness of the non-superconductor thin film must be about several nm.

[0004] However, when the oxide superconducting thin film comes into contact with air, the superconductivity and crystallinity of the portion of about 1 nm from the surface deteriorate. Usually, when another thin film is laminated on the oxide superconducting thin film, a different film forming apparatus is used, so that the oxide superconducting thin film inevitably comes into contact with air during transportation. Therefore, conventionally, before stacking another thin film on the oxide superconducting thin film, one oxide superconducting thin film is
Heat treatment was performed by heating to about 700 ° C. in a high vacuum of about × 10 ⁻⁹ Torr.

[0005]

The oxide superconducting thin film subjected to the above-mentioned heat treatment has improved surface crystallinity, and a thin film laminated thereon can be epitaxially grown. However, when the oxide superconducting thin film is heated in a high vacuum as described above, oxygen in the oxide superconducting crystal constituting the thin film is lost, and the superconducting properties of the thin film deteriorate, or the thin film loses superconductivity. No longer shown.

On the other hand, when heat treatment is performed in oxygen, no problem occurs in the superconductivity of the thin film, but the crystallinity of the thin film surface is not improved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a superconducting device having a novel configuration and a method for manufacturing the same, which has solved the above-mentioned problems of the prior art.

[0008]

According to the present invention SUMMARY OF THE INVENTION In the superconducting device including an oxide superconducting thin film formed on a substrate, and an insulating thin film laminated on the oxide superconductor thin film, said oxide superconductor The body breaks down when exposed to air
The insulator thin film is constituted by the amorphous oxide
Superconducting device is provided, characterized in that there.

[0009]

According to the present invention, an oxide superconducting thin film formed on a substrate and an oxide superconductor formed on the oxide superconducting thin film and constituting the oxide superconducting thin film are equal to each other. In a method for manufacturing a superconducting device having an amorphous oxide insulator thin film made of a constituent element, the method comprises the steps of: forming the oxide superconducting thin film, forming the oxide superconducting thin film into an amorphous state; Pressure of 1 × 10 ⁻⁵ to 1 × 10 ⁻⁴ Torr in a changing gas atmosphere
A method for manufacturing a superconducting device is provided, which includes a step of performing a heat treatment at r.

[0010]

According to the superconducting device of the present invention, the constituent elements of the amorphous oxide insulator thin film formed on the oxide superconducting thin film are the constituent elements of the oxide superconductor forming the oxide superconducting thin film. Its main feature is that This amorphous oxide is formed by reacting when the oxide superconducting thin film comes into contact with air, and conventionally, it was considered that the oxide superconducting thin film was deteriorated by contacting with air. Although the exact composition and the like of this amorphous oxide is not clear, it is considered that the crystal of the oxide superconductor collapsed and became amorphous. The superconducting device of the present invention includes this amorphous oxide thin film formed to an appropriate thickness as an insulator layer. Therefore, in the superconducting device of the present invention, the insulator layer can be easily formed, and the insulator layer does not adversely affect the oxide superconducting thin film.

On the other hand, the method of the present invention is a method for producing the above-described superconducting device, which comprises forming a superconducting oxide thin film and then performing a heat treatment in a gas atmosphere for amorphizing the oxide superconductor. Features. As a gas for making the oxide superconductor amorphous, for example, H ₂ O, CO _{2 and the} like can be mentioned.
In the method of the present invention, the heat treatment is performed in the above-mentioned gaseous atmosphere. The pressure at that time is preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻⁴ Torr, and the heating temperature is preferably 400 to 600 ° C. When the heating temperature is high, the decomposition of the oxide superconducting thin film on the surface is promoted, and the amorphization proceeds rapidly. However, the interdiffusion between the layers is avoided, and the interface between the amorphous oxide thin film and the oxide superconducting thin film is prevented. In order to form sharply, it is preferable to process at a temperature of 600 ° C. or less. At a temperature lower than 400 ° C., amorphization does not sufficiently proceed.

In the method of the present invention, it is preferable that after the heat treatment is performed in the above-described gas atmosphere, the heat treatment of the oxide superconducting thin film is further performed in an oxygen atmosphere. This is because the superconducting properties of the oxide superconducting film may be degraded if the heat treatment is performed in the above gas atmosphere, and the superconducting properties of the oxide superconducting thin film are restored by the heat treatment in the oxygen atmosphere. The pressure during this treatment is preferably from 50 to 200 Torr, and the heating temperature is preferably from 400 to 500 ° C.

Although the method of the present invention can be applied to any oxide superconductor, a Y ₁ Ba ₂ Cu ₃ O _{7 -X-} based oxide superconductor can stably provide a high-quality thin film with good crystallinity. It is preferred. In addition, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention.

[0015]

EXAMPLE A Josephson element was manufactured as an example of the superconducting device of the present invention by the method of the present invention. An MgO single crystal substrate was used for the substrate, and Y ₁ Ba ₂ Cu ₃ O _7-X was used for the oxide superconductor. The manufacturing procedure will be described with reference to FIG.

First, a first Y ₁ Ba ₂ Cu _{3 is formed} on an MgO (100) substrate 4 by a sputtering method as shown in FIG.
An O _7-X superconducting thin film 1 was formed. The main film forming conditions are shown below.

Next, the oxide superconducting thin film 1 was treated under the following conditions to form an amorphous oxide insulator layer 2 having a thickness of 3 nm on the surface as shown in FIG. 1 (b).

After the above treatment, the substrate was allowed to cool until the substrate temperature reached 400 ° C., and was treated in an oxygen atmosphere under the following conditions.

Further, a second Y ₁ Ba ₂ Cu ₃ O is formed on the amorphous oxide insulator layer 2 on the surface of the thin film 1 as shown in FIG.
_{The 7-X} superconducting thin film 3 was formed by a laser ablation method. The main film forming conditions are shown below.

In the Josephson device fabricated as described above, the second Y ₁ Ba ₂ Cu ₃ O _7-X superconducting thin film 3 was also composed of c-axis oriented crystals. In addition, the first and second Y ₁ Ba ₂
The superconducting critical temperatures of Cu ₃ O _7-X thin films are 85K and 82K, respectively.
It was K.

[0021]

As described above, according to the method for manufacturing a superconducting device of the present invention, the surface of a single-crystal oxide superconductor having an arbitrary size can be made amorphous, Unlike the case of crystal, various performances can be easily manufactured, and an element with a much larger area can be manufactured, and an element capable of flowing a large amount of current can be manufactured. is there. Moreover, since the surface of the single crystal is made amorphous by only a few nm, the device has excellent reproducibility of element characteristics and stable characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic view showing steps in the case of manufacturing a superconducting device of the present invention by a method of the present invention.

[Explanation of symbols]

 1, 3 superconductor thin film, 2 insulator thin film, 4 substrate

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 39/00 H01L 39/22-39/24

Claims (3)

(57) [Claims] 1. An oxide superconducting thin film formed on a substrate, and an amorphous oxide formed on the oxide superconducting thin film and comprising the same constituent element as the oxide superconductor constituting the oxide superconducting thin film In the method for manufacturing a superconducting device having an insulator thin film, the oxide superconducting thin film is formed, and then the oxide superconducting thin film is subjected to a pressure of 1 × in a gas atmosphere for amorphizing the oxide superconductor. 10 ^-5 ~
A method for manufacturing a superconducting device, comprising a step of performing a heat treatment at 1 × 10 ⁻⁴ Torr. 2. The heating temperature during the heat treatment is 400 to
The method of claim 1, wherein the temperature is 600C. 3. The method according to claim 1, wherein after the heat treatment, the oxide superconducting thin film is further heat-treated in an oxygen atmosphere.