Strontium titanate DC electric field switchable and tunable bulk acoustic wave solidly mounted resonator

A voltage switchable/tunable strontium titanate solidly mounted BAW resonator was implemented using an acoustical Bragg reflector of alternating high and low acoustic impedance layers. In the absence of any bias the device is merely capacitive, but under a DC bias the material becomes piezoelectrically active, leading to a BAW resonance that is effectively turned on and off by the applied field. In the resonant state a voltage-dependent frequency trimming of 1 % is observed, from 7.05 GHz to 6.98 GHz with an applied bias of 0–9 V, respectively. The quality factor at the resonant frequency was approximately 100, limited by the simplicity of the device design. The Q was relatively constant with applied bias, with an effective electromechanical coupling coefficient that varied linearly with applied bias up to a maximum of 3.3 %.