TUNABILITY AND LOSS TANGENT OF FERROELECTRIC SRTIO3 FILMS IN YBA2CU3OY SUPERCONDUCTING RESONATOR

Using a high-temperature superconducting resonator, measurements of th e dielectric properties of ferroelectric SrTiO3 films at microwave fre quency (similar to 5 GHz) are performed. The variation in dielectric c onstant, epsilon, of SrTiO3 film under the influence of an applied do voltage, U-b, at liquid-nitrogen temperature affects the value of the capacitance, C, and loss tangent, tan delta, of the SrTiO3 ferroelectr ic capacitor. In order to evaluate the values of C and tan delta of th e SrTiO3 capacitor, we used the YBa2Cu3Oy resonator which has a planar ferroelectric capacitor in the break of the microstrip line. The coup lings of each microwave input and output port are designed in the reso nator, including the bias circuits of the zero-field points. SrTiO3 fe rroelectric capacitors with values of the capacitance of about 0.5 pF and tan delta less than 0.01 successfully control the tunability of th e resonance frequency in the resonator with a factor of similar to 1.5 .