Tunable composite piezoelectric resonators: A possible “Holy Grail” of RF filters?

The availability of RF filters able to be tuned over a frequency span covering several communication standards has been recently described as a “Holy Grail” sought after by filter manufacturers and system designers [1]. In this paper, we develop the idea of tuning a composite Bulk Acoustic Wave (BAW) resonator made of two piezoelectric thin films by modifying the external electrical boundary condition applied to one of these films [2]. We show that an AlN/AlN composite resonator configuration is hardly suitable for the synthesis of a tunable channel selection filter while the use of piezoelectric materials with larger piezoelectric properties, such as KNbO3 or LiNbO3 offers theoretically the possibility to synthesize a front-end filter capable of being tuned over several communication standards.