Magnetic Field Investigations of Small Sputtered Step-Edge Junctions

Abstract
YBa₂Cu₃O₇ step-edge junctions are fabricated on SrTiO₃-substrates. The steps of 300nm height are milled by argon-ion-beam-etching (IBE). The films are deposited by high-pressure on-axis magnetron sputter technique patterned to microbridges with widths down to 0.5µm by electron beam lithography and argon ion etching. For ratios of film thickness to step height of t/h≈1/2 the current-voltage characteristics show Shapiro steps under microwave irradiation and RSJ-(resistively shunted junction)-like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer-pattern. The period of the variation ΔB₀ follows a 1/w²-dependence in agreement with the theoretical prediction for planar thin Josephson junctions : ΔB₀=1.84Φ₀/W². Junctions with widths of 0.7µm possess a large magnetic field stability with ΔB₀≈100G. Small junctions (w<1µm) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the superconducting electrodes. The developed preparation technique for "field-stable" Josephson junctions will be used for wafer scaling on 2-inch substrates and for the production of magnetically stable rf-SQUIDs.