Superconductor-insulator-normal tunnel junctions for on-chip measurement of the temperature

We describe SIN (superconductor-insulator-normal) tunnel junctions made by thin-films of Nb/AlOx/Cu and we report on the measurements of their I-V characteristics between 10 K and 0.3 K. The junctions show a strong dependence of the subgap conductance on the temperature, which makes them suitable for the on-chip measurement of the temperature. In this paper we also describe the design of an on-chip electronic refrigerator based on this type of junction.