Thermometers based on NIS junctions of temperature range 1.5–9.0 K

The paper presents a study of structures based on tunnelling transitions of normal metal-insulator-superconductor (NIS) Al/AlO$_x$/Nb and Al/AlN/NbN, in which the role of superconductor is performed by niobium (Nb) or niobium nitride (NbN), which are able to operate as thermometers in the temperature range of 1.5–10 K. SNEAP (Selective Niobium Etching and Anodisation Process) technology was used to form tunnel transitions. The $R_d/R_n(T)$ dependences of the test samples were obtained; the experimental data agree with the theoretical model. The values of fluctuation sensitivity of the order of 1 $\mu$K/$\sqrt{Hz}$ close to the theoretically expected values have been measured. Normal metal-insulator-superconductor (NIS) and superconductor-insulator-normal metal-insulator-superconductor (SINIS) structures made of Al and Nb or Al and NbN can be used as on-chip thermometers. Bolometers, electronic cooling systems and on-chip thermometers can be developed based on the studied structures, integrated directly into or placed next to the working structures for precise monitoring of thermal effects.