DIRECT-COUPLED HIGH T(C) DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE MAGNETOMETERS ON SRTIO3 SUBSTRATE - THEORETICAL DESCRIPTION AND COMPARISON WITH EXPERIMENT

A comprehensive quantitative comparison between the measured performan ce of direct-coupled high T-c superconducting quantum interference dev ice (SQUID) magnetometers with 30 degrees bicrystal junctions and a nu merical simulation is presented. It is shown that the characteristics of the SQUID magnetometer are considerably affected by resonances due to the large dielectric constant of the SrTiO3 substrate. In the reali zed magnetometer layout, the strip line resonance occurring in the SQU ID inductance increases the voltage modulation depth and the output vo ltage noise of the SQUID, while the flux noise of the SQUID is nearly unchanged. It is also shown that the distortion of the voltage versus Aux characteristic is caused by the LC resonance in the pickup loop of the magnetometer in combination with a capacitive feedback. Good agre ement between experiment and simulation has been obtained.