Fabrication and characterization of superconducting Pb alloy deposited at −80 °C

In lead alloy Josephson junction integrated circuits, two major problems often lead to device failures. In the region of electrode crossings, poor step coverage can cause shorts between the base electrode and the counterelectrode as well as opens in the counter electrode. Hillock formation on the lead alloy as a result of thermal cycling can rupture the thin oxide barrier. Deposition of the base electrode of the Pb alloy Josephson junction at −196 °C yields films with very fine grains which significantly reduce the problem of hillock formation, at the expense of very stringent requirements on the chamber pressure of the vacuum system. These problems have been alleviated in the present work by depositing the base electrode of the lead alloy Josephson junction on a rotating substrate holder, held at −80 °C, with relatively modest vacuum requirements.