Perspectives of Overdamped Josephson Junctions in Voltage Standard Applications

ABSTRACT

We discuss the main characteristics that must be satisfied by Josephson junctions for metrological applications and, specifically, in the development of voltage standards of new generation. Data reported in the literature for the most established technologies, like SNS (Superconductor-Normal conductor-Superconductor), SINIS (Superconductor-Insulator-Normal conductor-Insulator-Superconductor) and others, are analyzed and compared. The properties of Nb/Al-AlO_x/Nb overdamped SNIS (Superconductor-Normal conductor-Insulator-Superconductor) Josephson junctions developed at INRiM are also presented, since these junctions can optimize crucial parameters such as the current density and the characteristic voltage. Operation at temperatures above 4.2 K is also discussed, in view of using cryocooler setups to replace liquid helium refrigeration systems.