JPH02154485A - Josephson element - Google Patents

Abstract

PURPOSE:To perform a high temperature oxide superconducting S-N-S Josephson junction having no parasitic resistance in a boundary and an optimum current density by composing a normal conducting part of a S-N-F Josephson junction of ion damaged oxide high temperature superconductor. CONSTITUTION:In an S-R-S Josephson junction in which oxide high temperature conductors 1 are used at both electrodes, the normal conducting part 7 of the junction is composed of ion damaged oxide high temperature superconductor 1. The superconductivity of the oxide superconductor 1 can be destroyed by damaging it by ion implanting. An ion implanting amount is regulated to make the damaged part 7 metallic or insulative. An N-S boundary 5 between the thus formed normal conductive damaged part 7 and the superconductor does not form a high resistance contaminant layer due to the presence in the film from the first. Thus, an ideal clean N-S boundary is obtained, and no parasitic resistance is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thin film 5-N-8 Josephson junction having an oxide superconductor as an electrode.

(Prior art) Y-Ba-Cu-0,B1-8r-Ca-Cu-0,T
High-temperature oxide superconductors such as l-Ba-Ca-Cu-0 have loherence lengths of only about a few tens of nanometers, and it is difficult to artificially create tunnel-type and S-5-S microbunosode type Josephson junctions. It is very difficult. That point 5-N-
It is known that type 8 Josephson junctions are relatively easy to make because the length of the junction made of the intermediate normal conductor can be selected regardless of the loherence length of the superconducting electrode.

The conventionally used 5-N-
A plan view and a cross-sectional view of 8 junctions are shown. 1 in Figure 3. is a high temperature oxide superconductor as described above; 2. is a normal conductor, 3° is the joint length of a joint made of a normal conductor, and 4. represents the substrate, and 5° represents the N-8 interface between the normal conductor and the superconductor. In such a 5-N-8 junction, even with a junction length of about 1 micron, the
．． The Josephson effect can be observed in 2.

(Problems to be Solved by the Invention) Such a 5-N-8 junction operates. Alternatively, in order to create a large Josephson current, the N-8 interface between the normal conductor and the superconductor must be clean. If a large surface resistance exists at this N-8 interface, the Josephson current will decrease and the IcRN product, which is the output voltage of the junction, will also decrease, and in the worst case, the Josephson effect itself will be lost. On the other hand, it is known that the surfaces of high-temperature oxide superconductors are highly susceptible to contamination. This contamination layer has a thickness of several 100 nm and may have metallic, semiconducting or insulating properties.

The presence of such a contamination layer causes a large parasitic resistance at the N-8 interface, significantly degrading the characteristics of the 5-N-8 junction.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a 5-N-5 structure in which an oxide high temperature superconductor is used for both electrodes.
The present invention provides a Josephson element in which a normal conduction part of a Josephson junction is made of the ion-damaged oxide high-temperature superconductor.

(Operation) The present invention will be explained in detail using FIG. 2. In Figure 2, 1 is a high-temperature oxide superconductor film, 4 is a substrate, 5 is an N-8 interface, and 6 is a high-temperature oxide superconductor film.
is an ion beam, and 7 is a portion of the high temperature superconductor film 1 that has been damaged by the ion beam. The superconductivity of oxide superconductors can be destroyed by damaging them through ion implantation. By adjusting the amount of ion irradiation, this damaged area can be made metallic or insulating. For example, 130 for YBa2Cu2O7-8
In KeV silicon ion implantation, the implantation amount is 5 x 10
At 16.2 IXIOlon/cm, an insulating damaged area is created, which is metallic. B1-8r-Ca-Cu-○ and Tl-
It is known that in Ba-Ca-Cu-0 based materials, superconductivity is destroyed at an even lower ion implantation dose. N- between the normal conducting damaged part and the superconductor created in this way
8 interface, no high-resistance contaminant layer is formed because it was present in the film from the beginning. Therefore, the ideal clean N-8
An interface is obtained. The area irradiated by the ion beam can be sufficiently controlled in submicron terms using, for example, a focused ion beam source or a mask made using phosphorography technology.

(Example) An example of the present invention will be described with reference to FIG. This figure is a plan view of this embodiment. 11 is the YBa2Cu307-6 superconductor film, 3 is the junction length, 5 is the N-8 interface, and 7 is the YBa2Cu30-t that has become normal conductive due to ion damage.
8 membrane, 8 is a pad part of an electrode. The ion-damaged area has been transformed into a metal by ion irradiation. When silicon ions are used, this can be achieved at approximately 5×10 ion/cm with an acceleration energy of 130 KeV. Since the gear density in this damaged area hardly changes, even if the bond length is approximately 0.5 microns, operation as a Josephson bond at 4.2 mm is sufficiently possible.

The pad portion may be patterned using ordinary lithography, but it can also be easily formed by insulating the peripheral portion by sufficiently increasing the amount of ion irradiation.

In this example, Y-Ba-Cu-0 material was selected to demonstrate the ion damage conditions, but B1-8r-Ca-
Cu-○, Tl-Ba-Ca-Cu-0. B1-Pb-
The same applies to other oxide superconductors such as Ba-0.

(Effects of the Invention) As explained above, the present invention provides high-temperature oxide superconducting 5-N with optimal current density without parasitic resistance at the interface.
−5 Josephson junction is created. Furthermore, if a focused ion beam source or the like is used, it is possible to easily create a bond by direct ion writing, which does not require a complicated sockeye beam.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the effect of the present invention, and FIG. 3 (aXb) is a plan view and a cross-sectional view of a conventional 5-N-8 junction, respectively. 1 High temperature oxide superconductor film 11YBa2Cu307-8 film 3 Bonding length 4 Substrate 5 N-8 interface 6 Ion beam 7 Ion damaged part 8 Pad part

Claims (1)

[Claims] S-N-S where oxide high temperature superconductors are used for both electrodes
1. A Josephson element, characterized in that, in a Josephson junction, a normal conduction part of the junction is made of the ion-damaged oxide high-temperature superconductor.