Ion beam oxidation for Josephson circuit applications

Niobium-niobium oxide-lead Josephson tunnel junctions have been fabricated using reactive ion beam oxidation. High quality junctions were obtained using a low beam voltage without cooling the sample to 77 K during oxidation. A Vm∼20 mV was achieved routinely at a beam voltage of 100 V and Vm≳30 mV at 67 V. Furthermore, excellent critical current uniformity was demonstrated using a 10-cm Kaufman ion source with substrate motion implemented. A standard deviation in the critical current of 0.5% was obtained among three hundred and fifty 30×30 μm windowed junctions laid out over an area of 1.1×0.34 cm.