Self-aligned contact process for Nb/Al-AlOx/Nb Josephson junctions

High quality Nb/Al-AlOx/Nb Josephson junctions have been fabricated by a novel process named the self-aligned contact process. After the definition of the junction area by a reactive ion etching (RIE) technique, the exposed Nb layer and the junction edge are anodized to protect against electrical shorts and an Al film is deposited as the etching stopper layer. After base electrode patterning by RIE, an insulation layer is deposited. The contact hole, with the diameter of the junction, for connecting a counter electrode and a wiring layer, can be made without registration because of the deposited Al film. The junctions fabricated by this process have exhibited excellent current-voltage characteristics (Vm =70 mV at the critical current density jJ =1.8 kA/cm2, Vm =11 mV at jJ =20 kA/cm2).