Tunable Solidly Mounted Thin Film Bulk Acoustic Resonators Based on Ba$_{x}{{\hbox{Sr}}_{1-x}}{\hbox{TiO}}_{3}$ Films

Electrically tunable solidly mounted thin film bulk acoustic resonators based on Ba
_x
Sr
_1-x
TiO
₃
films are reported for the first time. The films are acoustically isolated from the silicon substrate by a Bragg reflector stack. Applying DC bias induces piezoelectric effect and an acoustic resonance at approximately 4 GHz. Under 10 V applied DC bias the resonance frequency of the resonators based on Ba
_0.25
Sr
_0.75
TiO
₃
films is tuned 1.2% to lower frequencies. The Q-factor of these resonators is approximately 120, and the electromechanical coupling coefficient is 0.5%. The resonant frequency of the BaTiO
₃
based resonators shifts upwards 1.3% under 10 V DC bias, and the -factor is approximately 30, with an electromechanical coupling coefficient of 6.2%.