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

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, and S. P. Zhao

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. The formation of tunnel barriers in these Nb/ALD-Al₂O₃/Nb trilayers was strongly indicated at room temperature by using the current-in-plane tunneling technique. 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 I_cR_N 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. 

Keywords - Atomic layer deposition, Josephson junction.  

IEEE/CSC & ESAS European Superconductivity News Forum (ESNF) No. 22 October/November 2012.  ESNF Reference No.ST323 Category 6.
The published version of this preprint appeared in IEEE Transactions on Applied Superconductivity 23, 1100705 (June 2013).