LOW-NOISE YBA2CU3O7-X SINGLE-LAYER DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (SQUID) MAGNETOMETER BASED ON BICRYSTAL JUNCTIONS WITH 30-DEGREES MISORIENTATION ANGLE

We have fabricated and characterized a low-noise direct-coupled magnet ometer based on a 100 pH YBa2Cu3O7-x dc superconducting quantum interf erence device (SQUID) on a 10 mmx10 mm SrTiO3 bicrystal substrate with 30 degrees misorientation angle. The thin films were deposited by hol low cathode discharge sputtering and patterned using conventional phot olithography and Ar ion beam etching. The SQUID magnetometer was opera ted using direct-coupled flux-locked-loop electronics with bias revers al. The sensor had a usable voltage swing of 39 mu V and a white magne tic 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) c haracteristic showed a pronounced distortion on the negative slope. Nu merical simulations were performed to explain the distorted V-Phi char acteristic. Measurements of magnetocardiograms demonstrate the suitabi lity of this sensor for biomagnetic applications. (C) 1998 American In stitute of Physics.