Low-noise YBa2Cu3O7−x single layer dc superconducting quantum interference device (SQUID) magnetometer based on bicrystal junctions with 30° misorientation angle

Abstract

We have fabricated and characterized a low-noise direct-coupled magnetometer based on a 100 pH YBa2Cu3O7−x dc superconducting quantum interference device (SQUID) on a 10 mm×10 mm SrTiO3 bicrystal substrate with 30° misorientation angle. The thin films were deposited by hollow cathode discharge sputtering and patterned using conventional photolithography and Ar ion beam etching. The SQUID magnetometer was operated using direct-coupled flux-locked-loop electronics with bias reversal. The sensor had a usable voltage swing of 39 μV and a white magnetic field noise of 32 fTHz−1/2 with a 1/f corner at 2 Hz, including electronics and environmental noise. The voltage versus flux (V−Φ) characteristic showed a pronounced distortion on the negative slope. Numerical simulations were performed to explain the distorted V−Φ characteristic. Measurements of magnetocardiograms demonstrate the suitability of this sensor for biomagnetic applications.