Microstructures of lead alloy Josephson junction electrode materials: PbInAu and PbSb

The microstructures of PbInAu and PbSb films similar to those used as electrodes for Josephson junctions were investigated. These films were deposited mainly by evaporation to completion of alloys. The depth profiles of various elements in these alloy films were determined by a combination of sputter etching and Auger electron spectroscopy. The surface morphologies and microstuctures were examined by scanning and transmission electron microscopies respectively. X-ray energy spectroscopy and transmission electron diffraction techniques were used to identify different crystalline phases. No apparent difference was found in the morphologies or microstructures of PbInAu films deposited on substrates with or without a thin layer of oxidized chromium film. The result suggests that the improved cyclability of the PbInAu film deposited on an oxidized chromiun layer may be due to the increased adhesion of the film composite to the substrate. For the PbSb films, antimony was found to segregate and form Sb-rich grains dispersed between Pb-rich grains. We believe that the better thermal cyclability of PbSb films is largely due to this dispersion hardening process.