CHARACTERIZATION OF A TUNABLE THIN-FILM MICROWAVE YBA2CU3O7-X SRTIO3 COPLANAR CAPACITOR/

We have fabricated and characterized electrically tunable high tempera ture superconductor coplanar microstrip resonators incorporating tunab le SrTiO3 ferroelectric thin films. The low frequency capacitance of t he SrTiO3 capacitor is measured directly. High frequency capacitance a nd loss information are extracted from the observed resonances and com pared with the low frequency data. Hysteresis loops display an onset o f ferroelectricity at 160 K. The spontaneous charge and coercive volta ge (at 10 kHz) as a function of temperature are extracted from these l oops.