Fabrication of a ${rm Bi}_{2}{rm Sr}_{2}{rm CaCu}_{2}{rm O}_{8+x}$ Intrinsic DC-SQUID With a Shunt Resistor

摘要

We fabricated ${rm Bi}_{2}{rm Sr}_{2}{rm CaCu}_{2}{rm O}_{x}$ (Bi-2212) SQUIDs with two stacks of intrinsic Josephson junctions by an acid-treatment process. The stacks were fabricated from a single crystal of Bi-2212. The in-plane loop of a dc-SQUID was surrounded by an acid-treated product, which was produced by immersing the Bi-2212 single crystal in dilute hydrochloric acid $({rm pH}=1.65)$. The critical aspect of this process is that the surrounding acid-treated product (BiOCl) is transparent. The SQUID exhibited a large hysteresis with a ratio of the critical current to the return current of 0.4 at 77 K. Applying a magnetic field modulated the critical current of a dc-SQUID for fields of up to about 10 G. In addition, we fabricated dc-SQUIDs attached to a shunt resistor, which exhibited nonhysteretic current-voltage characteristics. Appling a magnetic field modulated the voltage; the maximum voltage modulation was about 30 $mu{rm V}$ at 77 K.