FABRICATION AND PROPERTIES OF VERTICALLY STACKED NB/AL-ALOX/NB JOSEPHSON TUNNEL JUNCTIONS

We present three novel processes for the fabrication of two or more vertically stacked Josephson tunnel junctions all based on the Nb/Al - AlOx/Nb technology. The dynamical properties of stacks of up to five, high-quality and low current density Josephson junctions have been investigated. In particular, we report the generation of two families of Fiske resonances in two-fold stacks of electrically small junctions and on synchronized motion of fluxons having the same polarities but moving in opposite directions. Finally, we show why stacked junctions are very promising for application to the voltage standard maintenance.