Multijunction SQUID Based on Intrinsic Josephson Junctions

We have numerically and experimentally investigated multijunction superconducting quantum interference device (SQUID) based on intrinsic Josephson junctions (IJJs) of in order to improve the flux to voltage transfer coefficient. Numerical simulations suggest that the modulation depth of critical current decreases with an increase in the number of junctions in the stack and the SQUID consisting of few junctions will yield the best performance. The SQUIDs with in-plane loop geometry incorporating two stacks of IJJs were successfully fabricated from (BSCCO). The advantages of this layout are that the multijunction SQUID can be achieved without an increase in device size and the stack of IJJs is less affected by an applying magnetic field. At 4.2 K, the SQUIDs showed hysteretic current-voltage characteristics with typical multiple resistive branches. As the temperature was increased, the hysteresis disappeared and the SQUID showed clear periodic voltage-flux characteristics due to the quantum interference between the weakest junctions in the stacks.