Noise resolution of RuO2-based resistance thermometers

Low-frequency noise was measured for RuO2-based thick film resistors at liquid helium temperatures down to 0.36 K. The 1∕f-type spectrum and squared voltage dependence of power spectral density observed at low voltages attribute the noise as coming from equilibrium resistance fluctuations. Measurements carried out at different temperatures show that the magnitude of noise intensity (index) increases significantly as temperature goes down. Due to this fact, the resolution of RuO2 thermometers increases above the instrument resolution. The quantity which describes a sensor resolution is defined and calculated for RuO2 thick film sensor. Some remarks on measurement strategy and sensor optimization are supplied.