Ion Implantation in Superconducting Niobium and Nb sub 3 Sn Thin Films: Adjustment of Josephson Microbridges and SQUID Devices

摘要

The principles of operation of Josephson junctions and SQUIDS are resumed. An ion implantation technique for the adjustment of the critical current is presented. High quality superconducting thin films were obtained by electron gun evaporation of niobium on heated substrates. Polycrystalline Nb sub 3 Sn was made by annealing (1000 K, 10 exp -6 Torr) a multilayer structure of successively evaporated niobium and thin films. Selected ions (helium, neon, argon) were implanted at doses ranging from 10 exp 13 to 10 exp 17 cm exp -2 . After implantation the critical temperature, the critical current and the normal resistivity were measured on special photoetched geometries. The variations of these electrical properties depend on the nuclear energy loss. The critical temperature of Nb sub 3 Sn is decreased by ion implantation and can be increased again by a new annealing. The parameters of the ion implantation were defined in order to obtain a critical temperature slightly higher than the operating temperature. The geometries of the microbridges and the implanted areas where then chosen to obtain appropriate criticals currents (approximately 10 mu A) at the operating temperature. The obtained microbridges were used as junction elements in superconducting quantum interference devices. (Atomindex citation 11:497927)