YBCO step-edge SQUIDs by magnetron sputtering technique

Summary

YBCO step-edge junction d.c. SQUIDs have been realized by using the Inverted Cylindrical Magnetron Sputtering (ICMS) technique. This last represents a novel technology for high-T _c Josephson junctions (HTSC). Steps are obtained by standard ion milling procedure on LaAlO₃ (100) substrates using Nb-masks patterned by reactive ion etching. Measurements of currentvs. voltage, maximum d.c. Josephson currentvs. magnetic field and SQUID voltage response measurements have been performed, also as a function of the temperature. Operating temperature as high as 77K has been achieved. At 4.2K the SQUIDs show a maximum voltage of flux transfer function ∂V/∂φ _max = 870μV/Φ ₀and a good periodicity of theV-ϕ modulation up to 20Φ without any sign of hysteresis. The ratio between the step height (h) and the film thickness (d) seems to play a fundamental role in determining Josephson properties of the bridges, these conditions being more severe with respect to most of the data available in literature.