Electrical frequency switching in bulk acoustic wave resonators based on lead zirconate titanate (PZT)/PbTiO3 epitaxial bilayer films is demonstrated and analyzed. In general, the coercive field of PbTiO3 is higher than that of PZT. Independent polarity inversion of the PZT layers is achieved by applying an intermediate electric field between the coercive fields of PZT and PbTiO3 to the bilayer films. The resonant frequency is switched between the fundamental mode resonance (0.56 GHz) and second mode resonance (1.58 GHz) by applying a negative or a positive electric field to the resonators. The second mode operation can be achieved in the absence of an external electric field. A theoretical model simulated by Mason's equivalent circuit model including the effect of the polarity-inverted structure agreed well with the experimental results. The electromechanical coupling coefficients kt2 of both the PZT layer and the PbTiO3 layer of the polarity-inverted bilayer were estimated to be 17.6% (kt = 0.42) by comparing the experimental results with the theoretical simulations.
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