Directly coupled DC-SQUIDs of YBCO step-edge junctions fabricated by a chemical etching process operating at 77 K

High T/sub c/ directly coupled DC-SQUIDs have been successfully fabricated on chemically etched MgO substrate steps. The chemical etching was performed in a mixed acid solution of H/sub 3/PO/sub 4/ and H/sub 2/SO/sub 4/ for the best control of etched surface and roughness. YBCO thin films were deposited epitaxially on the step-edged MgO substrate by a KrF laser ablation method. Characteristics of the directly coupled DC-SQUID have been studied following the patterning and fabrication of the device. The chemically etched steps show sharper edges at the bottom of the step as well as the top unlike those made by ion milling. AFM and Raman Spectroscopy studies on the YBCO thin film deposited and patterned on chemically etched show no sign of appreciable degradation. The result is a good quality junction even at a relatively low step angle. Directly coupled DC-SQUIDs that are fabricated with this process show sweeping voltages of 160 /spl mu/V at 4.2 K, and 6 /spl mu/V at 77 K, respectively.