Fabrication of Nb/Al2O3/Nb Josephson Junctions using Atomic Layer Deposition

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 \textit{in situ} deposition of ALD-Al$_{2}$O$_{3}$ tunnel barriers in superconductor-insulator-superconductor (SIS) Josephson junctions. A smooth ALD-Al$_{2}$O$_{3}$ 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-Al$_{2}$O$_{3}$/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-Al$_{2}$O$_{3}$ barrier layer. However, the I$_{c}$R$_{N}$ 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.