Integrated Monolayer Planar Flux Transformer and Resonator Tank Circuit for High- $T_{c}$ RF-SQUID Magnetometer

The authors propose a new design for monolayer superconducting planar flux transformer integrated with a coplanar resonator serving as a gigahertz range tank circuit for high- T c rf-SQUID magnetometers. Based on the proposed design, which is optimized using the finite element method, the transformer-resonator configuration is made of 200-nm-thick monolayer YBCO film on a crystalline LaAlO 3 substrate. In this optimized design, the SQUID magnetometer is coupled through flip-chip configuration with the configuration providing high coupling coefficient between the devices. The design permits coupling of the rf signals to the SQUID efficiently, whereas the transformer is designed to couple the dc to low-frequency magnetic field signals to the SQUID without disturbing the rf excitation. By means of split-ring resonator structure and also a SrTiO 3 layer on the back side of the configuration, tuning the resonance frequency with high precision could be made possible using minimum change in the design. Loaded quality factor and the coupling coefficient of the designed resonator are obtained to be high to meet the SQUID system requirements very well. Also, lower field-to-flux transformation coefficient is achieved by using our single-turn transformer design compared to that of the bare SQUID.