Niobium dc SQUIDs with Nanobridge Junctions

DC SQUIDs with outer loop size similar to 10 mu m x 10 mu m have been fabricated with nanobridge Josephson junctions in thin Niobium films (25, 100 and 200nm) using either electron beam or focused ion beam techniques. Such SQUIDs are ideally suited to incorporate into the centre strip of a superconducting coplanar waveguide. The current-voltage characteristics and magnetic field modulation of the SQUIDs are compared for the two methods. The temperature dependence of the critical current is quite linear for the e-beam devices whilst the focused ion beam devices fit an exponential. Here we also investigate trimming methods to reduce the critical currents of the nanojunctions fabricated in the thicker films, in order to improve the SQUID parameters at lower temperatures. (C) 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of Guest Editors.