We have realized the Josephson fluxon–antifluxon transistor (JFAT) in high temperature superconductivity using an asymmetric control line on top of either bicrystal junctions or Co-doped YBa2Cu3Ox superconductor–normal–superconductor (SNS) junctions. We have measured current gains as high as 6 for 30 μm-wide bicrystal JFATs (30 K) and as high as 3 for Co-doped SNS JFATs (50 K). An improvement in gain over the Josephson vortex flow transistor, due to improved coupling efficiency, is demonstrated. There is also a reduction of control line inductance that should lead to an improvement in gate speed.

SrTiO3 (STO) thin films are promising for a variety of applications requiring tunability. We describe the growth and characterization of STO thin films including their dielectric properties. We also present attempts at reducing the loss tangent of these films, and we discuss their integration with high-temperature superconductor (HTS) microwave filters for trimming purposes.