Fabrication of $\hbox {Nb/Al}_{2}\hbox {O}_{3}/\hbox {Nb}$ Josephson Junctions Using In Situ Magnetron Sputtering and 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 in situ deposition of ALD-Al₂O₃ tunnel barriers in superconductor-insulator-superconductor Josephson junctions. A smooth ALD-Al₂O₃ barrier layer was grown on an Al-wetted Nb bottom electrode and was followed with a top Nb electrode growth using sputtering. Preliminary low temperature measurements of current-voltage characteristics 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.