Characteristics of superconductor-insulator-normal tunnel junctions for on-chip electronic refrigeration

In this paper we discuss some points concerning the design of an on-chip electronic refrigerator based on low-resistance tunnel junctions. We describe our Nb/AlO x /Cu (SIN) and Nb/AlO x /Cu/Al (SINS') junctions and we report on the measurements of theirI-V characteristics between 10 K and 0.3 K, showing that the junctions of the first type are suitable for the refrigerator fabrication.