JPH03171685A - superconducting element - Google Patents

Abstract

PURPOSE:To obtain a superconductive element which is able to operate at a high temperature and stable in operation by a method wherein two terminals connected to two connection sections formed of normal conductor on an superconductive electrode are provided. CONSTITUTION:A first superconductive electrode 11 of a Y1Ba2Cu3O7-x thin film formed on an MgO substrate 3, an Au film 4, and a second superconductive electrode 12 of a Y1Ba2Cu3O7-x thin film are provided. Two metal electrode 5 and 6 are arranged on the second electrode 12, and metal electrodes 7 and 8 connected to terminals 17 and 18 serving as connection sections are provided onto the ends of the second superconductive electrode 12 where the Au film 4 is not provided. The metal electrodes 5 and 6 are covered with an insulating film excluding their upper sides and connected to terminals 27 and 28 with metal films 15 and 16. As a superconductive element of this design is provided with a tunnel type junction structure and four terminals, it operates stably and is handled easily.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting elements. In more detail, high speed using Josephson bonds formed in oxide superconductors,
The present invention relates to superconducting elements that can be used in high-sensitivity electromagnetic wave detectors, etc.

Conventional technology A Josephson mixer, which is an example of a superconducting element using Josephson coupling, is a high-speed, high-sensitivity, low-noise electromagnetic wave detector that can be used as a receiver in the submillimeter wave and far infrared regions. IOTI{z( l XIOl3H
It has been confirmed that it responds to up to z).

FIG. 3 shows a schematic cross-sectional view of a conventional Josephson mixer. In the Josephson mixer shown in FIG. 3, the point contact type Josephson mixer 1 is built into the rear part of the antenna 20 and is integrated. In the Josephson mixer 1, the Nb wire 21, which is a metal superconductor whose tip is processed to be extremely thin, is made of Nb.
It is formed in contact with the line 22. From antenna 20,
A signal wave with frequency fs and a local oscillation wave with frequency fL are mixed manually, and the output of Josephson mixer 1 outputs a signal with a frequency expressed as f + p = fs nf, (n is a natural number). Ru. Thereby, high frequency signal waves can be converted to lower frequencies that are easier to process.

In Joseph Numiwasa, a value of about 100 can be selected as the value of n mentioned above, and the frequency r1 of the local oscillation wave
, can receive signal waves with a frequency approximately 100 times that of .

Since the Josephson mixer described above uses a metal superconductor such as Nb, its operating temperature is low and liquid He had to be used. Recently, Josephson mixers using composite oxide superconductors with high critical temperatures have been considered.

Problems to be Solved by the Invention When a composite oxide superconductor is used for a superconducting electrode of a superconducting element, connection of terminals becomes a problem. That is, unlike metal-based superconductors, it is difficult to directly connect terminals to complex oxide superconductors.

Therefore, a connection part is formed using metal or the like on the superconducting electrode of the composite oxide superconductor, and a terminal is connected to the connection part.

In a superconducting device in which multiple terminals are connected to one superconducting electrode, such as the above-mentioned Josephson mixer, conventional
Multiple terminals were connected to each connection part. Therefore, a normal conduction current may flow between the terminals, and the Josephson effect may not occur.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a superconducting element which solves the problems of the prior art described above and which operates at high temperatures and whose operation is stable.

Means for Solving the Problems According to the present invention, a superconducting electrode is formed between a pair of superconducting electrodes made of an oxide superconductor and the superconducting electrode pair so that the superconducting electrodes of the superconducting electrode pair do not directly contact each other. In the superconducting element, each of the superconducting electrodes has two normal conductors formed on the superconducting electrode.
SUMMARY OF THE INVENTION A superconducting element is provided, characterized in that it includes two terminals, one terminal connected to each connecting portion.

Function The superconducting element of the present invention has a tunnel-type structure of a Njosefson bond in which a thin normal conductor is sandwiched between a pair of oxide superconducting electrodes, and each superconducting electrode is made of a normal conductor.
Its main feature is that it has two terminals, one connected to each connection part.

As an application example of the superconducting element of the present invention, a Josephson mixer can be considered, for example. Josephson mixers are generally four-terminal devices with each superconducting electrode having two terminals. In the Josephson mixer according to the present invention, only one terminal is connected to one connection provided on each superconducting electrode. Therefore, unnecessary normal conduction current does not flow between terminals connected to the same superconducting electrode, and the device operates reliably.

The superconductor used for the superconducting electrode of the superconducting element of the present invention is:
Although it can be selected arbitrarily, it is preferable to use a composite oxide superconductor because of its high critical temperature. Among composite oxide superconductors, Y-Ba-Cu10 series, Bi-Sr
-Ca-Cu-0 system, TI -Ba-Ca-Cu-
Complex oxide superconductors such as ○-based superconductors are particularly preferable because they have a high critical temperature.

In the superconducting element of the present invention, when a composite oxide superconductor is used for the superconducting electrode, the normal conductive portion is preferably made of Au. The reasons for this are that it is easy to form an Au thin film on the composite oxide superconductor, that Au is difficult to oxidize, and that the state of the interface with the composite oxide superconductor is eroded.

In addition, composite oxide superconductors have a short coherence length,
When forming a tunnel-type Josephson coupling, the thickness of the non-superconducting portion is very important. In the superconducting element of the present invention, when a composite oxide superconductor is used for the superconducting electrode and 80 is used for the normal conducting part, the thickness of the Au film is preferably 1 to 5 Q nm. This is because if the thickness of the Au film is outside the above range, no Josephson bond will exist.

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.

Embodiment FIG. 1 shows a sectional view of a Josephson mixer as an example of a superconducting element of the present invention. The Josephson mixer in Figure 1 is M
A first superconducting electrode l1 made of a YIBa2Cu30t-x thin film formed on a gO substrate 3, and a first superconducting electrode 1
Au film 4 formed in the center of
The second superconducting electrode 12 is also formed of a Y+Ba2Cu30,-8 thin film and is formed so as not to be in direct contact with the superconducting electrode 11. Two metal electrodes 5 and 6, each forming a connection part, are arranged on the second electrode. Moreover, metal electrodes 7 and 8, which are connection parts to which terminals 17 and 18 are connected, are provided at the ends of the first superconducting electrode 11 where the ^U film 4 is not formed.

The metal electrodes 5 and 6 are covered with an insulating film 9 except for their upper surfaces, and are connected to terminals 27 and 28 near the metal electrodes 7 and 8 by metal films 15 and 16 formed on the insulating film 9, respectively.

In the Josephson mixer of this embodiment, the thickness of the first and second superconducting electrodes is 4001 m at maximum,
The thickness of the Au film was 1Q nm. Further, the metal electrodes 5 and 6 on the second superconducting electrode 12
The electrode had a two-layer structure in which the lower layer in contact with 2 was Ag and the upper layer was Au. This two-layered metal electrode does not have an adverse effect on the composite oxide superconductor and has good adhesion to the composite oxide superconductor.

The procedure for manufacturing the above Josephson mixer will be described with reference to FIGS. 2(a) to 2(g). First, MgO substrate 3
On top is the first Y, Ba2Cu307-X superconducting thin film 111.
, ^U membrane 4, second Y. Ba2Cu301-X superconducting thin film 112 and metal film 114 are laminated in order so as to completely cover the surface of each underlying film. lth YIBa2
Cu30t-x superconducting thin film 111 and second Y+Ba
The 2Cu307-x superconducting thin films 112 are each formed to a thickness of about 400 nm by sputtering.

Further, the Au film 4 is formed to a thickness of about 1Q nm by a vacuum evaporation method.

The metal film 114 has a thickness of 150 nm and is formed by vacuum evaporation.
On top of the Ag film, an Au film with a thickness of 150 nm is formed by vacuum evaporation. Thereafter, a photoresist film 8 is formed on the metal film 114 as shown in FIG. 2(a). Next, as shown in FIG. 2(b), a pattern is formed so that portions 81 and 82 that will become metal electrodes remain.

Then, the metal film 114 is etched by Ar ion etching to completely remove the portions not covered by the photoresist films 8l and 82, forming metal electrodes 5 and 6 as shown in FIG. 2(C). Next, as shown in FIG. 2(d), a photoresist film 83 is formed on the second Y, Ba2Cu307-X superconducting thin film 112 so as to cover the metal electrodes 5 and 6.

Then, by Ar ion etching, the second Y1Ba2
(1: A part of the u30t-x superconducting thin film 112, the Au film 4, and the lth Y.Ba2Cu,07-X superconducting thin film 111 are etched as shown in FIG. 2(e), and the first superconducting electrode 11 and The shape of the second superconducting electrode l2 is determined.

Next, as shown in FIG. 2(f), the first superconducting electrode 11
The parts other than the ends 37 and 38 and the upper surfaces of the metal electrodes 5 and 6 are covered with an insulating film 9. Finally, as shown in FIG. The Josephson mixer according to the present invention is then completed.

FIG. 4 shows the current-voltage characteristics of the above Josephson mixer. The Josephson mixer of the present invention operated stably even at 9Gl{z.

Effects of the Invention As explained above, since the superconducting element of the present invention has a tunnel junction structure and four terminals, it operates more stably than the conventional one and is easier to handle.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a Josephson mixer as an example of the superconducting element of the present invention, FIG. 2 is a diagram showing the manufacturing procedure of the Josephson mixer of FIG. 1, and FIG. 4 is a conceptual diagram of the Josephson mixer shown in FIG. 1. FIG. 4 is a graph showing the current-voltage characteristics of the Josephson mixer shown in FIG. [Main reference numbers] 1... Josephson mixer, 3... substrate, 4... Au film, 5, 6... metal electrode, 9... insulating film, 11, l2... superconductor electrode

Claims (1)

[Claims] A superconducting element comprising a pair of superconducting electrodes made of an oxide superconductor and a normal conducting part formed between the superconducting electrodes so that the superconducting electrodes of the superconducting electrode pair do not come into direct contact with each other, A superconducting element characterized in that each of the superconducting electrodes includes two terminals each connected to two connecting portions formed of a normal conductor on the superconducting electrode.