Electron cooling by arrays of submicron tunnel junctions

We cooled down the electrons of a 3 ?m3 copper strip by using an on-chip electronic microcooler made by a superconductor-insulator-normal-insulator-superconductor (SINIS) structure. We obtained an electron temperature drop ?T?-10 mK at a temperature of the bath slightly above Tb=500 mK and we estimated a cooling power slightly larger than 20 pW at this temperature. In contrast to previous experiments, we obtained this result operating with a simple 3He refrigerator. The copper strip temperature change was sensed by measuring the voltage change across a current-biased SINIS junction, with a temperature responsivity ?V/?T?-500 ?V/K. On-chip microcooler and thermometer have been fabricated by two-angle shadow mask evaporation and e-beam lithography. © 1999 American Institute of Physics.