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Process for Improving the Barrier Quality of Josephson Junctions

IP.com Disclosure Number: IPCOM000049802D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Gasser, M: AUTHOR [+2]

Abstract

Ultra high vacuum processes currently employed for the formation of Nb(2)0(5) tunnel barriers on Nb base electrodes involve an AR-RF (radio frequency) cleaning of the base electrode, this step being followed by an Ar/0(2)-RF oxidation. Due to leakage currents, these barriers lead to junctions of poor quality. The process proposed here introduces an additional step during which a transition layer containing carbon is formed before the oxidation takes place.

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Process for Improving the Barrier Quality of Josephson Junctions

Ultra high vacuum processes currently employed for the formation of Nb(2)0(5) tunnel barriers on Nb base electrodes involve an AR-RF (radio frequency) cleaning of the base electrode, this step being followed by an Ar/0(2)- RF oxidation. Due to leakage currents, these barriers lead to junctions of poor quality. The process proposed here introduces an additional step during which a transition layer containing carbon is formed before the oxidation takes place.

The tunnel barrier fabrication steps can be carried out as indicated below: 1. Ar-RF surface cleaning.

2. Ar/CH(4)-RF discharge.

3. Ar/O(2)-RF oxidation.

Starting with a cleaned surface, the CHL-contaminated Ar plasma treatment results in the formation of a niobium carbide surface compound. This process is reproducible, the compound thickness being time- and RF voltage-dependent. During the subsequent RF oxidation step, the topmost layers are transformed to Nb(2)O(5), forming a sandwich. Using this structure as a tunnel barrier in Nb/Pb or Nb/Nb Josephson junctions leads to significant improvements of the I-V characteristic and particularly to reduced leakage currents.

Different kinds of plasma containing carbon and resulting in carbon compound transition layers can be employed. For example, an Ar plasma containing CO and leading to a surface layer of Nb+C+O has been successfully tested.

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