Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb

摘要

We have successfully fabricated Cu/AlOx-Al/Nbnormal-metal/insulator/superconductor tunnel junction devices with a high valueof the superconducting gap (up to $\sim 1$ mV), using electron-beam lithographyand angle evaporation techniques in the sub-micron scale. The subgapconductance of these junctions shows the expected strong temperaturedependence, rendering them suitable for thermometry all the way from 100 mK to6 K. In addition, some direct electronic cooling of the normal metal was alsoseen at bias values near the gap edge. The device performance was stronglyinfluenced by the details of the Al layer geometry, with lateral spilling ofthe aluminium giving rise to strong extra subgap features, and the thickness ofAl layer affecting the proximised superconducting gap value of thesuperconducting Al/Nb bilayer.