Acoustic resonator devices having multiple resonant frequencies and methods
of making the same are described. In one aspect, an acoustic resonator device includes
an acoustic resonant structure that includes first and second electrodes and first
and second piezoelectric layers. The first and second electrodes abut opposite
sides of a resonant volume free of any interposing electrodes. The first and second
piezoelectric layers are disposed for acoustic vibrations in the resonant volume
and have different respective acoustical resonance characteristics and respective
piezoelectric axes oriented in different directions. The acoustic resonant structure
has resonant electric responses at first and second resonant frequencies respectively
determined at least in part by the acoustical resonance characteristics of the
first and second piezoelectric layers.
