JPH03204983A - Superconductive junction - Google Patents

Abstract

PURPOSE:To obtain a superconductive junction which is formed of an oxide superconductor, operable at a high temperature, and excellent in performance by a method wherein a non-superconductor is formed of the oxide of an element selected from Ia elements, IIa elements, lanthanoid elements, and Y. CONSTITUTION:A non-superconductor 3 is formed of the oxide of a Ia element such as Li, Rb, Cs, or the like, or a IIa elements such as Mg, Ca, Sr, Ba, or the like, or a lanthanoid element such as La, Ce, Pr, Nd, or the like, or Y. The above elements are basic, so that the elements concerned are a little reac tive to oxide superconductors 1 and 2 which are also basic and hardly deterio rate the oxide superconductors 1 and 2 at an interface between them. In a tunnel type junction, a non-superconductive layer can be epitaxially grown at a temperature close to a board temperature that an oxide superconductive thin film is formed, so that a first and a second oxide superconductive thin films can be excellent in characteristic and the interface between the oxide superconductive thin film and a non-conductor layer can be excellent in perfor mance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting junctions. More specifically, the present invention relates to a superconducting junction with a novel configuration using an oxide superconductor.

Although there are various configurations for realizing a superconducting junction called a Josephson junction, the most preferred structure is a tunnel-type junction in which a thin non-superconductor is sandwiched between a pair of superconductors. Generally, such a superconducting junction is realized in the form of an element, and the above pair of superconductor and non-superconductor is a so-called thin film.

For example, when realizing a tunnel-type superconducting junction using an oxide superconductor as a superconductor, a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film are laminated in order on a substrate. do.

The thickness of the non-superconductor in a tunnel-type superconducting junction is determined by the coherence length of the superconductor.

Oxide superconductors have very short coherence lengths, so
In a tunnel-type superconducting junction using an oxide superconductor, the thickness of the non-superconductor must be on the order of several nanometers.

Problems to be Solved by the Invention Since it is difficult to uniformly form a thin film of a non-superconductor as described above, there are few examples of producing a tunnel-type superconducting junction using an oxide superconductor.

Furthermore, in conventional tunnel-type superconducting junctions, the interface between the oxide superconductor and the non-superconductor film was not in good condition, and desired characteristics could not be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and provide a superconducting junction using an oxide superconductor that operates at high temperatures and has excellent performance.

Means for Solving the Problems According to the present invention, in a superconducting junction having a structure in which a non-superconductor is sandwiched between a pair of oxide superconductors, the non-superconductor is an element of group Ia of the periodic table, an element of group fJa, or a lanthanoid. A superconducting junction characterized by being an oxide of any element selected from the elements and Y is provided.

Function The superconducting junction of the present invention has a so-called tunnel type structure using an oxide superconductor, and the non-superconductor is a group Ia element of the periodic table, which is a basic element, an a group element, a lanthanide element, and Y. Its main characteristic is that it is an oxide of any element selected from among the following. Specifically, non-superconductors include oxides of Group Ia elements such as I, Rb, and Cs, and fla such as Mg, Ca, Sr, and Ba.
Group Ia element compounds, oxides of lanthanoid elements such as La, Ce, Pr, and Nd, and oxides of Y are used.

The above elements are basic and have low reactivity with the oxide superconductor, which is also basic, and do not deteriorate the oxide superconductor, especially at the interface. In addition, the lattice constants of oxide crystals of the above elements are 3.5 to 4.4, which is close to that of oxide superconductor crystals, so that the non-superconductor layer formed of the oxides of the above elements It is also easy to epitaxially grow oxide superconductor crystals.

Furthermore, since the oxides of the above elements have weaker oxygen-taking properties, they hardly take oxygen from the adjacent oxide superconductor. Further, in the tunnel junction of the present invention, the non-superconductor layer can be epitaxially grown at a temperature close to the substrate temperature when forming the oxide superconductor thin film.

In the superconducting junction of the present invention, due to the characteristics of the non-superconducting layer as described above, the characteristics of the first and second oxide superconducting thin films and the interface state between the oxide superconducting thin film and the non-superconducting layer are excellent. Become something.

When the above-mentioned oxide superconductor and non-superconductor are used, the thickness of the non-superconductor layer is preferably about 1 to 4 Qnrn, more preferably 2 to 5 nm. Such a superconducting junction of the present invention can be produced using a sputtering method, a physical vapor deposition method such as an MBE method, or a chemical vapor deposition method such as an MO-CVD method.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

EXAMPLE A cross-sectional view of an example of a superconducting junction according to the present invention is shown in FIG. FIG. 1 shows an element using superconducting bonding, which includes a first oxide superconducting thin film 1 formed on an MgO single crystal substrate 4 and a portion of the first oxide superconducting thin film 1 excluding the right end. The formed non-superconducting thin film 3, the second oxide superconducting thin film 2 formed on the non-superconducting thin film 3, and the terminals 5 and 6 connected to the first and second oxide superconducting thin films, respectively. Equipped with.

The above superconducting junction device was fabricated by the MBE method using the superconductors and non-superconductors shown in Table 1 below. In both superconducting junction elements, the thickness of oxide superconducting thin films 1 and 2 is 400 nm, and the thickness of non-superconducting thin film 3 is 5 nm.
And so.

Table 1■ Table 1■ In addition, the element profiles of each of the fabricated superconducting junction devices were measured using a micro Auger electron spectrometer (AES).
) was measured. As a result, all of the above superconducting junction devices exhibited a sharp profile, and the diffusion of the non-superconducting layer was within 10 nm. Also, RHEED
When the crystallinity was examined, it was found to be an excellent epitaxial thin film.

As described in detail, the superconducting junction of the present invention has a tunnel type structure in which the non-superconducting layer is formed of a material having a crystal structure and lattice constant similar to those of the superconductor. Therefore, even when an oxide superconductor is used, a non-superconductor layer having an appropriate thickness can be formed satisfactorily.

The present invention provides a high-performance superconducting junction element and further promotes the application of superconducting technology to electronic devices.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a superconducting junction element using an example of the superconducting junction of the present invention. [Main reference numbers] 1.2... Oxide superconductor, 3... Non-superconductor, 4... Substrate, 5.6... Terminal

Claims (1)

[Claims] In a superconducting junction having a structure in which a non-superconductor is sandwiched between a pair of oxide superconductors, the non-superconductor is a member of the periodic table Ia.
A superconducting junction characterized in that it is an oxide of any element selected from Group elements, Group IIa elements, lanthanide elements, and Y.