On-chip micro-refrigerators for sub-Kelvin cooling

Thin-film tunnel junctions made of a normal metal, an insulating layer and a superconductor (this structures are also called NIS junctions), are able to cool down the metal electrons by means of the tunneling mechanism. This fact opens the possibility to refrigerate small detectors by means of a local cooling of the chip. Another important application of the NIS junctions is high sensitive thermometry. These NIS coolers, together with their relative thermometers, are fabricated by using micro and nano-electronic techniques. This fact makes them very compact devices, allowing sub-Kelvin cooling with no moving parts. The present status of the art on Peltier refrigeration by NIS junctions will be reviewed in this work