Tunable high temperature superconductor microstrip resonators

Electrically tunable high-temperature superconductor microstrip resonators incorporating YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconductor and SrTiO/sub 3/ ferroelectric films have been fabricated and characterized. The resonators consist of two collinear microstrip line sections separated by a 5- mu m gap. The capacitance of the gap influences the frequencies of the odd-order coupled resonances. Inductively choked DC bias lines are attached to each line section so that a bias voltage can be applied to the gap. When the gap is filled with a ferroelectric material, the odd resonances can be tuned. Frequency shifts of 300 MHz have been observed with a bias voltage of 50 V for resonances at 5.6 GHz and 11.6 GHz. The tunability is independent of temperature from 4 K to 80 K. An upper bound for the loss tangent of the SrTiO/sub 3/ capacitor is extracted from the resonance Q, and tan delta <0.07 at 4 K is found.<>