Preparation and properties of Nb Josephson junctions with thin Al layers

Josephson tunnel junctions of the types Nb/Al-oxide-Nb and Nb/Al-oxide-Al/Nb, where Al represents thin (∼50Å) films of Al, were prepared by D.C. magnetron sputtering. The tunnel barrier was formed by in-situ thermal oxidation. Individual junctions were defined using photolithography coupled with the plasma etching technique. Junctions with critical current density up to 1300 A/cm
²
and V
m
= i
c
R(2mV) between 15mV and 47mV at 4.2K were obtained.