J. Sok et al., TUNABILITY AND LOSS TANGENT OF FERROELECTRIC SRTIO3 FILMS IN YBA2CU3OY SUPERCONDUCTING RESONATOR, Superconductor science and technology, 11(9), 1998, pp. 875-879
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
.