Versatile and reliable Coulomb-blockade thermometry

Coulomb blockade thermometers (CBTs) are very well-established, broadly covering the Kelvin to micro Kelvin temperature range [1,2]. They can be conveniently integrated on-chip and provide accurate and fast electron temperature readout based on a simple two-terminal device not requiring any tuning. Furthermore, CBTs can operate as primary thermometers, thus reading absolute temperature without relying on another thermometer for calibration. As CBT arrays, they can exhibit even better accuracy, immunity to voltage noise, resilience to nanofabrication issues, and extending the temperature range.

Here, we present a new approach to CBTs as a primary thermometers in the universal regime at arbitrary bias and independent of heating effects. Based on a simple numerical solution of the master equation, we extract the charging energy Ec independently at each phonon/refrigerator temperature Tp with high precision, revealing a characteristic temperature dependence of the dielectric constant of the AlOx tunnel junctions with surprisingly strong temperature dependence at the 10% level below about 100 mK. With Ec at hand, we obtain for each bias voltage the electron temperature Te, which may be heated above Tp. Our new method allows the study of heat flow and device parameters in an unprecedented way, opening new avenues for thermal analysis and versatile, reliable and precision thermometry at low temperatures.