S parameter measurements on single superconducting thin-film three-terminal devices made of high-T c and low-T c materials

Abstract

We have investigated three-terminal single-layer thin-film superconducting devices made of YBaCuO and Nb. The devices incorporate regions of weak superconductivity in multiple parallel links that are influenced by current in a separate control line. These experiments were designed to study the possible application of this device as an rf amplifier. With the device biased, rf power was applied to the control line and the transmission coefficient, S21, was measured. The reverse transmission coefficient, S12, was also measured for comparison. Upon biasing into a flux flow state, the S21 of the device at rf frequencies was found to increase 10–15 dB over the zero bias value and over the reverse feed (S12 ) value. The device behaved linearly up to power inputs of +5 dBm (1-dB compression point). The bandwidth was limited only by the impedance transformer.