An array of 100 Al–Al2O3–Cu SIN tunnel junctions in direct-write trilayer technology

Abstract

We present superconductor–insulator–normal metal (SIN) tunnel junction thermometers made of arrays of4–100 Al–Al2O3–Cu SIN tunnel junctions fabricated in direct-write technology. The technology is based onin situ evaporation of the superconductive electrode followed by the oxidation and thenormal counter-electrode as a first step and deposition of normal metal absorber as asecond one.This approach allows one to realize any geometry of the tunnel junctions and of theabsorber with no limitation related to the size of the junctions or the absorber, which is notpossible using the shadow evaporation technique.Measurements performed at 300 mK showed the high quality ofthe fabricated tunnel junctions, low leakage currents, and that anRd/Rn ratio of 500 has been achieved at that temperature.The junctions were characterized as temperature sensors, andvoltage versus temperature dependence measurements showed adV/dT of0.5 mV K−1 for each single junction, which is typical for this kind of tunnel junction. A temperature resolutionof ± 5 µK has been achieved which is much better than the previously reported value of ± 30 µK for this type of thermometer.