Frequency-switchable polarity-inverted BAW resonators based on electric-field-induced piezoelectric PMN-PT/PZT epitaxial film stacks

Spontaneous polarization of tetragonal ferroelectrics cannot be inverted unless the applied electric field is greater than the coercive field. In the case of the cubic phase, on the other hand, polarization and piezoelectricity can be induced merely by applying an electric field. In this study, we proposed polarity-inverted cubic/tetragonal multilayer film resonators which allow switching between the fundamental and high-order mode resonances through the independent control of the polarization of the cubic layer. Frequency switching in bulk acoustic wave (BAW) resonators based on all-epitaxial cubic 0.95Pb(Mg_1/3Nb_2/3)O₃ (PMN)-0.05PbTiO₃ (PTO)/tetragonal Pb(Zr,Ti)O₃ (PZT) bilayer film stacks is demonstrated theoretically and experimentally. Under a negative voltage application, which is less than the coercive field of the tetragonal PZT layers, a fundamental mode resonance (327 MHz) is observed, whereas a second-mode resonance (779 MHz) is observed under a positive voltage application in BAW resonators. A theoretical simulation based on Mason's equivalent circuit model, taking account of the polarity-inverted bilayer structure, shows good agreement with the experimental results.