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

摘要

Atomic layer deposition (ALD) provides a promising approach for deposition ofultrathin low-defect-density tunnel barriers, and it has been implemented in ahigh-vacuum magnetron sputtering system for in situ deposition of ALD-Al2O3tunnel barriers in superconductor-insulator-superconductor (SIS) Josephsonjunctions. A smooth ALD-Al2O3 barrier layer was grown on a Al-wetted Nb bottomelectrode 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 theintegrity of the ALD-Al2O3 barrier layer. However, the IcRN product of thejunctions is much smaller than the value expected from the Ambegaokar-Baratoffformula suggesting a significant pair-breaking mechanism at the interfaces.