Switched Mode Thin Film Bulk Acoustic Wave Resonators

The development of wireless communication systems with more complexity, greater functionality, and multi-band operation imposes new challenges on the RF front end design. Ferroelectric barium strontium titanate (Ba_(x)Sr_(1-x)TiO₃, BST) incorporated into a multi-layer structure, allows for the design of a new class of switched mode thin film bulk acoustic wave resonators. These devices can selectively resonate the different harmonics of the acoustic resonator. A switched mode dual resonance ferroelectric thin film bulk acoustic resonator (FBAR) is presented in this work. The device is capable of alternating between two modes of the resonant structure (at 2 GHz or 3.6 GHz) only by switching the polarity of the applied DC bias controlling voltage across the ferroelectric thin films.