Supercurrent decay in nano-superconducting quantum interference devices for intrinsic magnetic flux resolution

Supercurrent decay measurements of nano-superconducting quantum interference devices SQUIDs based on niobium constrictions Dayem bridges are reported. Such measurements provide useful information for applications that employ the SQUID as a trigger where the sensor works on the zero voltage state. The nanodevice consists of a niobium thin film 30 nm thick ring with a hole side length of 200 nm including two Dayem bridges of 120200 nm2. The measurements of the switching current distribution from the zero voltage state and the related escape rate, as function of the bias current, have been performed by a low noise fly time technique. The experimental data have shown an intrinsic current fluctuation less than 0.2% of the critical current at liquid helium temperature, corresponding to an intrinsic sensor magnetic flux resolution of a few m0. The theoretical predictions based on the thermal escape process theory in the moderately damping limit are in a reasonable agreement with the experimental data.