  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.
