Characteristics of vertically stacked Nb/Al/AlN/Nb Josephson junctions

Vertically stacked Josephson junctions have been fabricated with Nb/Al/AlN as a base unit. The reactively sputtered AlN layer is deposited much more quickly than the lengthy thermal oxidation of Al. AlN is therefore a favorable candidate for stacked junctions consisting of many layers. Lift-off patterning the junctions avoids the problem of anodizing or etching through many layers. The superconducting layer thickness is chosen to be small with respect to the London penetration depth to allow coupling of the magnetic field in the adjacent insulating layers. Current versus voltage characteristics of these devices will be presented. In addition, critical current as a function of applied magnetic field will be presented.