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Fabrication of Nb/Al2O3/Nb Josephson Junctions using in situ Magnetron Sputtering and Atomic Layer Deposition

IEEE Trans. Appl. Supercond. Vol. 23, No. 3, (2013)

Rongtao Lu*, Alan J. Elliot*, Logan Wille*, Bo Mao*, Siyuan Han*, Judy Z. Wu*, John Talvacchio, Heidi M. Schulze, Rupert M. Lewis, Daniel J. Ewing, H.F. Yu, G.M. Xue, S.P. Zhao 
* KU Physics and Astronomy Authors

ABSTRACT

Atomic layer deposition (ALD) provides a promising approach for deposition of ultrathin low-defect-density tunnel barriers, and it has been implemented in a high-vacuum magnetron sputtering system for in situ deposition of ALD-Al2O3 tunnel barriers in superconductor-insulator-superconductor (SIS) Josephson junctions. A smooth ALD-Al2O3 barrier layer was grown on a Al-wetted Nb bottom electrode and was followed with a top Nb electrode growth using sputtering. Preliminary low temperature measurements of current-voltage characteristics (IVC) of the Josephson junctions made from these trilayers confirmed the integrity of the ALD-Al2O3 barrier layer. However, the IcRN product of the junctions is much smaller than the value expected from the Ambegaokar-Baratoff formula suggesting a significant pair-breaking mechanism at the interfaces.

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