Fabrication of DC SQUIDs based on Bi2Sr2CaCu2Oy intrinsic Josephson junctions

We report on the first observation of clear voltage modulation in dc SQUID based on intrinsic Josephson junctions of Bi2Sr2CaCu2Oy. Stacked series array of intrinsic Josephson junctions and dc SQUID based on it have been made from Bi2Sr2CaCu2Oy single crystals using a double-side etching process. The number of junctions in the stack is rather controllable by monitoring the junction resistance at room temperature. The current-voltage characteristics of the SQUIDs with stacks of 20-50 IJJs at 4.2 K exhibit additional closely spaced branches together with typical multiple quasi-particle branches with voltage spacing of similar to 20 mV. On applying magnetic field clear periodic modulation of the lowest critical current and voltage of the SQUID are observed and the flux period obtained from the voltage-flux characteristics agrees with one flux quantum. The maximum voltage modulation and transfer function are about 80 mu V and 0.75 mV/Phi(0) at 26 K, respectively. The property of dc SQUID with shunt resistances is also discussed.