Josephson tunnel junctions with refractory electrodes

Fabrication of high quality Josephson tunnel junctions with refractory electrodes is made difficult by the electrode's short coherence lengths and the sensitivity of the their superconducting properties to tunnel barrier processing. Several innovative procedures have been developed to address this problem. In this review, we describe these tunnel barrier processes and the junction characteristics that were obtained using them. In particular, attention is focused on the junction's subgap conductance and the reproducibility of the maximum Josephson current because of their importance as device design parameters for integrated circuits.