The frequency switchable multi-layered BST/BaTiO₃ epitaxial film resonator

The frequency switchable filters are suitable for selecting the vacant frequency bands. Usual polarity unidirectional single-layered resonators excite 1^st mode whereas polarity inverted two-layered resonators excite 2^nd mode. We previous reported the frequency switchable two-layered PZT/PbTiO₃ epitaxial film resonators[1]. However, PbTiO₃ films grown on PZT/PbTiO₃ films are difficult to obtain since Curie temperature and deposition temperature in PbTiO₃ are higher than those of PZT. (Ba_x, Sr_1-x)TiO₃ (BST) films exhibit electrostrictive effect in paraelectric phase. In ferroelectric BaTiO₃, on the other hand, polarity inversion is impossible to be obtained without the application of higher than coercive electric field to films. Therefore, in this study, we considered that polarity inverted structure is easily obtained by application of less than coercive electric field of BaTiO₃ to two-layered BaTiO₃/BST epitaxial films. [1]T. Mori, et al., Proc. IUS 2016.