SQUID noise thermometers with lithographically defined metal sensing elements

Abstract

We present SQUID noise thermometers for sub-kelvin thermometry that employ lithographically defined metal thin-film resistors as the temperature sensors. The resistors with values of about 1 milliohm are lithographically fabricated using Au, PdAu and superconducting Nb wiring. In order to ensure constant resistance values in the whole temperature range of operation, the resitive structures are designed to avoid superconducting proximity effects. The thin-film resistor circuits can be easily combined with different types of multi-purpose dc SQUID current sensors to adapt noise temperatures, uncertainties and measurement speeds as well as robustness against magnetic fields in different measurement setups.