High quality refractory Josephson tunnel junctions utilizing thin aluminum layers

Preparation of high quality all-refractory Josephson tunnel junctions based on Nb/Al-oxide-Nb and Nb/Al-oxide-Al/Nb structures is reported. Critical currents up to 1300 A/cm2 and Vm values up to 35 mV were obtained. The specific capacitance of these junctions is 0.06±0.02 pF/μm2. Junctions were fabricated using standard photolithography and a new plasma etching process coupled with anodization of Nb.