Fabrication process of dc-SQUIDs based on Bi-2212 intrinsic Josephson junctions by dilute hydrochloric acid solutions

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We have previously reported on an acid-treatment process for the fabrication of Bi2Sr2CaCu2Ox (Bi-2212) stacks. In this process, we found interesting phenomena that Bi-2212 single crystal dipped into acid solution of pH>1.4 was varied to transparent material. In this study, we tried to fabricate dc-SQUID with an in-plane loop having two stacks of IJJs by this acid-treatment process. The SQUID without a shunt resistor showed large hysteretic current-voltage characteristics at liquid N2 temperature. In addition, we fabricated dc-SQUIDs attached to the shunt resistor, which exhibited nonhysteretic current - voltage characteristics. The SQUIDs showed periodic modulation of the critical current Ic(B) as a function of magnetic field at 77K. Although there are many problems to be solved, the proposed acid treatment process may be useful for dc-SQUID based on Bi-2212 IJJs.