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Method of Producing Nb Josephson Tunnel Junctions

IP.com Disclosure Number: IPCOM000051464D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Broom, RF: AUTHOR [+3]

Abstract

Successful preparation of niobium-niobium oxide Josephson tunnel juncti requires high voltage sputter cleaning of the Nb base electrode before oxidation in order to produce desired I-V characteristics. It has been found that good results are obtained under the following conditions: A low flow rate of the Ar gas used for the RF-plasma, and a cathode coating which has a high sputter rate and which reacts chemically with the dominant plasma impurities.

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Method of Producing Nb Josephson Tunnel Junctions

Successful preparation of niobium-niobium oxide Josephson tunnel juncti requires high voltage sputter cleaning of the Nb base electrode before oxidation in order to produce desired I-V characteristics. It has been found that good results are obtained under the following conditions: A low flow rate of the Ar gas used for the RF-plasma, and a cathode coating which has a high sputter rate and which reacts chemically with the dominant plasma impurities.

The Ar always contains trace amounts of H(2)O, O(2), CO(2) and hydrocarbon, etc. Similar impurities are provided by desorption from the walls of the vacuum chamber. Because the Nb is very reactive, and the energy of the ionized Ar atoms is high, the impurities combine rapidly with the Nb surface to form a contaminated layer despite the constant removal rate of the surface by sputtering. However, during sputter cleaning, material is also removed from the entire surface of the RF cathode supporting the samples. If the above-mentioned conditions are met, this material has a substantial gettering action. Reactive impurities combine with the sputter atoms and eventually diffuse to the walls of the system where they are trapped. The RF-plasma is self-cleaning provided the flow rate is low.

Good tunnel characteristics are obtained with an Ar flow rate of about 0,5 sccm in a system volume of approximately 30 1, and a Pb or Si coating on the cathode.

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