Lead-alloy Josephson-tunneling gates with improved stability upon thermal cycling

Abstract

An investigation has been carried out in order to explore means to improve the stability of the in-line Josephson-tunneling gates, which are fabricated using Pb films containing In and/or Au additions as electrodes. The investigation has revealed that incorporation of several modifications in a previously reported gate-fabrication process results in at least a fourfold increase in the stability during thermal cycling from 298 to 4.2 °K. For a total of 38 gates fabricated using the modified process, only about 30% were found to have failed after 500 cycles. In comparison, the same percentage failure was observed after only 120 cycles, even for the most stable set of 19 gates which were fabricated using the previous method. Evaluation of the results indicates that the observed improvement in the stability could be attributed to the use of reduced electrode film thicknesses and an alteration of the base-electrode fabrication process. In this paper the process modifications which resulted in the improved stability and corresponding junction characteristics and cycling data are described.