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Multilayer Josephson Memory Device

IP.com Disclosure Number: IPCOM000078902D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Laibowitz, RB: AUTHOR [+2]

Abstract

While high-quality Josephson devices can be made using metals such as Pb and Sn (and alloys based on these metals), these metallurgically soft materials can suffer degradation both thermally and in normal handling procedures. Processing steps necessary for the fabrication of arrays must be carried out above room temperature, and the arrays must be able to be cycled from 4 degrees K to room temperature. Thus, it is very advantageous to be able to use metals such as Al and Nb in the fabrication of Josephson devices.

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Multilayer Josephson Memory Device

While high-quality Josephson devices can be made using metals such as Pb and Sn (and alloys based on these metals), these metallurgically soft materials can suffer degradation both thermally and in normal handling procedures. Processing steps necessary for the fabrication of arrays must be carried out above room temperature, and the arrays must be able to be cycled from 4 degrees K to room temperature. Thus, it is very advantageous to be able to use metals such as Al and Nb in the fabrication of Josephson devices.

The T(c) of Al is too low for practical consideration, while an all Nb device suffers from the poor quality of the oxide (Nb oxide) barrier that can be formed on an Nb film. The major problem now recognized is that depositing an Nb top electrode on a tunnel barrier of Nb oxide degrades the oxide barrier, resulting in a lower quality junction. In the past, it has been proposed to use a multilayer of Nb/Al as the base electrode, oxidizing the Al to form a barrier of Al(2)O(3) and then depositing Nb on the Al(2)O(3) to complete the device. (See IBM Technical Disclosure Bulletin, Vol. 13 No. 5, October 1970, p. 1197-1198). The Al becomes superconducting by its proximity to the Nb and must be kept thin. While these devices do work, the Nb top electrode still reacts with the Al(2)O(3), degrading the junction.

A new configuration is proposed which uses only metallurgically hard materials such as Nb and Al, a good barrier such as Al(2)O(3) and which in no...