DIRECTLY COUPLED DC-SQUIDS OF YBCO STEP-EDGE JUNCTIONS FABRICATED BY A CHEMICAL ETCHING PROCESS OPERATING AT 77-K

High T-c directly coupled DC-SQUIDs have been successfully fabricated bin chemically etched MgO substrate steps. The chemical etching was pe rformed in a mixed acid solution of H3PO4 and H2SO4 for the best contr ol of etched surface and roughness. YBCO thin films were deposited epi taxially on the step-edged MgO substrate by a KrF laser ablation metho d. 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 an the YBCO thin film deposited rand patterned on chemically e tched show no sign of appreciable degradation. The result is a good qu ality junction even at at relatively low step angle. Directly coupled DC-SQUIDs that are fabricated with this. process show sweeping voltage s of 160 mu V at 4.2 K, and 6 mu V at 77 K, respectively.