J. Gohng et al., DIRECTLY COUPLED DC-SQUIDS OF YBCO STEP-EDGE JUNCTIONS FABRICATED BY A CHEMICAL ETCHING PROCESS OPERATING AT 77-K, IEEE transactions on applied superconductivity, 7(2), 1997, pp. 3694-3697
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.