Dc SQUIDs made of intrinsic Josephson junctions

We have fabricated and studied a dc superconducting quantum interference device (dc SQUID) based on intrinsic Josephson junctions in Bi2Sr2CaCu2Oy single crystals. The dc SQUIDs with in-plane loop geometry and two stacks of intrinsic Josephson junctions (IJJs) were successfully fabricated using a double-side etching process. Such a layout allowed us to define the SQUID inductance and the number of junctions in the stack independently. At 4.2 K, the SQUIDs showed hysteretic current-voltage characteristics with typical multiple resistive branches. When the operating temperature was elevated in order to reduce the hysteresis, clear periodic and symmetric flux-voltage characteristics due to the quantum interference between the weakest junctions in the stacks were observed. Both the number of junctions and the asymmetry in the critical currents are discussed as important factors in the operation of IJJ-SQUID.