Performance of High-Sensitivity Nano-SQUIDs Based on Niobium Dayem Bridges

Measurements and noise performances of integrated nano superconducting quantum interference devices (nano-SQUIDs) are presented. The nano-sensors are based on nanometric niobium constrictions (Dayem bridges) inserted in a square loop having a side length of 200 nm. Integrated micrometric niobium coils located close to the sensor allow both an easy tuning/calibration and the optimization of the working point. Improved measurements of voltage-flux characteristic, flux to voltage transfer factor and noise performances are reported. In small signal mode, the sensors have shown a magnetic flux noise spectral density of 1.5 muPhi₀/Hz^1/2. Furthermore, preliminary measurements concerning the critical current vs. temperature dependence and the switching probability of the critical current are shown.