Direct-coupled high tc DC superconducting quantum interference device magnetometers on SrTiO3 substrate:: Theoretical description and comparison with experiment

A comprehensive quantitative comparison between the measured performance of direct-coupled high T-c superconducting quantum interference device (SQUID) magnetometers with 30 degrees bicrystal junctions and a numerical 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 realized magnetometer layout, the strip line resonance occurring in the SQUID inductance increases the voltage modulation depth and the output voltage 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 agreement between experiment and simulation has been obtained.