YBa2Cu3O7−x dc squid magnetometers with bicrystal junctions for biomagnetic multichannel applications

Abstract We have fabricated magnetometers based on direct-coupled YBa 2 Cu 3 O 7− x superconducting quantum interference devices (SQUID) with SQUID inductances of 50 pH and 100 pH on 10×10 mm 2 24° SrTiO 3 bicrystal substrates. The thin films were deposited by hollow cathode discharge sputtering and patterned using conventional photolithography and Ar ion beam etching. The optimization of the fabrication process was performed utilizing design of experiment methodology. The SQUID magnetometers were operated with an improved direct-coupled flux-locked loop electronics with a preamplifier voltage noise of 0.44 nV Hz −1/2 and bias reversal ( f b =0.1–500 kHz). The best sensor had a white noise of 41 fT Hz −1/2 and a 1/ f corner at 2 Hz, including electronics and environmental noise. High-quality magnetocardiograms recorded in the Berlin magnetically shielded room (BMSR) illustrate that the sensors are suitable for biomagnetic multichannel systems.