Low-noise superconducting quantum interference device with a highdV/dΦ optimized by thermally controlling critical current

摘要

The transfer function dV/dΦ and the noise characteristics of a low-Tc superconducting quantum interference device (SQUID) have been improved by annealing to adjust the critical current, thereby optimizing the McCumber parameter βc. A SQUID structure suitable for annealing and using surface nitridation and planarization has also been developed. By annealing a SQUID that initially has a βc greater than 1, the I-V characteristics can be changed from characteristics with hysteresis to characteristics without hysteresis. A SQUID with βc=0.81, close to the hysteresis limitation, had a large dV/dΦ (3.7 mV/Φ) and good noise characteristics (1.5 μΦ0/√(Hz) at 100 Hz and 3.0 μΦ0/√(Hz) at 1 Hz). These characteristics can be attained even when using a simple measuring circuit connected directly to preamplifier without adaptive components such as flux modulation or additional positive feedback (APF)