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Multilayer Structures for High Temperature Superconducting Josephson Junctions

IP.com Disclosure Number: IPCOM000035253D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Kleinsasser, AW: AUTHOR [+2]

Abstract

Fabrication of thin film Josephson tunnel junctions using high Tc oxide superconductors as electrodes is expected to be extremely difficult for several reasons. One is the very short coherence length (a few nm) which is expected for these high Tc materials, which makes them difficult to tunnel into (this currently limits the use of NbN as a counterelectrode in all NbN junctions, since it is difficult to grow a NbN electrode on top of an insulating tunnel barrier with adequate material perfection within a coherence length or so of the interface). Another is that the films tend to require high temperature (e.g., 900oC) anneal steps in order to have good superconducting properties, making fabrication of multilayer devices difficult.

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Multilayer Structures for High Temperature Superconducting Josephson Junctions

Fabrication of thin film Josephson tunnel junctions using high Tc oxide superconductors as electrodes is expected to be extremely difficult for several reasons. One is the very short coherence length (a few nm) which is expected for these high Tc materials, which makes them difficult to tunnel into (this currently limits the use of NbN as a counterelectrode in all NbN junctions, since it is difficult to grow a NbN electrode on top of an insulating tunnel barrier with adequate material perfection within a coherence length or so of the interface). Another is that the films tend to require high temperature (e.g., 900oC) anneal steps in order to have good superconducting properties, making fabrication of multilayer devices difficult.

The magnitude of the coherence length is also critical in bridge structures, since it sets the limits for allowable device sizes. For example, an alternative to the Josephson tunnel junction is the weak link. All superconducting weak links are ideally of the order of a coherence length long - a real limitation at high temperatures. Superconductor - normal - superconductor (SNS) devices should also have lengths of the order of a coherence length; however, the normal coherence length can be appreciably longer.

For high temperature superconductors the coherence length is of the order of a few nm. For a similar normal metal, it will be larger by a factor of about...