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High Frequency RF Oxidation Techniques to Fabricate Thermally Stable Josephson Junctions

IP.com Disclosure Number: IPCOM000050001D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Brosious, PR: AUTHOR [+2]

Abstract

Oxide growth in an RF oxygen glow discharge has been an important step in the fabrication processes of Josephson junction devices. The current techniques make use of a relatively low RF frequency which requires a high RF voltage and oxygen gas pressure to maintain RF discharge. Under this condition, the lead impurity is sputtered away from a lead-precoated cathode and backscattered in the tunnel barrier during oxide growth. Tunneling currents are reduced by nearly three orders of magnitude with increasing backscattered lead, converting the tunnel barrier from more like In(2)O(3) to more like PbO.

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High Frequency RF Oxidation Techniques to Fabricate Thermally Stable Josephson Junctions

Oxide growth in an RF oxygen glow discharge has been an important step in the fabrication processes of Josephson junction devices. The current techniques make use of a relatively low RF frequency which requires a high RF voltage and oxygen gas pressure to maintain RF discharge. Under this condition, the lead impurity is sputtered away from a lead-precoated cathode and backscattered in the tunnel barrier during oxide growth. Tunneling currents are reduced by nearly three orders of magnitude with increasing backscattered lead, converting the tunnel barrier from more like In(2)O(3) to more like PbO. Further complication arises from the fact that lead appears highly mobile within an ultra-thin barrier oxide even at room temperature, which leads to an increase in the Josephson current density not only upon heat treatment at elevated temperatures, but also during storage at room temperature for a long period of time. Therefore, it is highly desirable to avoid backscattered lead and achieve thermal stability in the current density for lead alloy based junction devices by finding a method to fabricate junctions which are more like a pure In(2)O(3) barrier.

Lead contamination can be prevented by removing lead completely from a cathode and precoating it with a fresh oxide. A photoresist, such as an oxide, can be used to precoat a cathode and to fabricate a junction which shows a zero annealing factor in tunneling currents. A similar result is obtained when a cathode is first precoated with lead and RF-oxidized to convert it to yellow PbO. One may achieve this goal by using other insulators, such as SiO or SiO(2).

Another fabricatio...