Stacked Nb/Al AlO X/Nb long Josephson tunnel junctions

We developed a technique for fabrication of small stacked tunnel junctions with up to ten tunnel barriers in a stack. This technique allowed us to fabricate long stacked tunnel junctions in order to study the fluxon 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 μm. The distance between the individual tunnel barriers in each stack was 30 nm. Flux-flow steps in the current - voltage (I-V) characteristics were investigated at 4.2 K as a function of the external magnetic field.