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 Bi₂Sr₂CaCu₂O_y. Stacked series array of intrinsic Josephson junctions and dc SQUID based on it have been made from Bi₂Sr₂CaCu₂O_y 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 ∼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 μV and 0.75 mV/Φ₀ at 26 K, respectively. The property of dc SQUID with shunt resistances is also discussed.