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

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 mmx10 mm SrTiO3 bicrystal substrate with 30 degrees 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 mu V 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-Phi) characteristic showed a pronounced distortion on the negative slope. Numerical simulations were performed to explain the distorted V-Phi characteristic. Measurements of magnetocardiograms demonstrate the suitability of this sensor for biomagnetic applications. (C) 1998 American Institute of Physics.