Nb/Al/Nb junctions with a wide range of characteristic voltages for superconducting electronic applications

Josephson devices for superconducting electronic applications, such as RSFQ logic circuits and programmable voltage standards, require nonhysteretic junctions with a high speed or a high voltage resolution and hence with characteristic voltages spanning over several orders of magnitude. We present here our recent results on Nb/Al/Nb junctions where, by changing some fabrication parameters such as the thickness and deposition rate of the Al barrier, it is possible to obtain junctions with very different electrical properties. These junctions have characteristic voltages varying from a few tens of μV up to more than 1 mV, with critical current densities from 10³ up to 10⁶ A/cm².