Photolithographic fabrication of lead alloy Josephson junctions

Abstract

Techniques for the photolithographic fabrication of thin-film Josephson junctions are presented in detail, including metal liftoff processes, lead alloy composition, and formation of tunneling junction barriers using plasma oxidation in an rf discharge. A comparison with earlier rf plasma oxidation studies on Pb(In) –oxide–Pb junctions shows the tunneling resistance of Pb(In,Au) –oxide–Pb(Au) junctions to be nearly two decades lower for a given oxygen pressure in the rf discharge; this difference was attributed to the use of different alloys and sputtering parameter measurement techniques in the respective studies. Typically, tunneling resistance decreased by only 2% after ten thermal cycles, but decreased at an accelerated rate with subsequent cycling. Room-temperature storage often induced downward resistance changes on the order of 30% per month. Junctions stored at −15°C generally showed little change after a period of three months.