STACKED NB AL-ALOX/NB LONG JOSEPHSON TUNNEL-JUNCTIONS/

We developed a technique for fabrication of small stacked tunnel junct ions with up to ten tunnel barriers in a stack. This technique allowed us to fabricate long stacked tunnel junctions in order to study the f luxon motion in closely spaced Josephson tunnel barriers. Up to three long junctions were fabricated in a stack of the overlap geometry with maximum length of 800 mum. The distance between the individual tunnel barriers in each stack was 30 nm. Flux-flow steps in the current - vo ltage (I-V) characteristics were investigated at 4.2 K as a function o f the external magnetic field.