Tunable Solidly Mounted Thin Film Bulk Acoustic Resonators Based on Ba_xSr_1−xTiO₃ Films

Electrically tunable solidly mounted thin film bulk acoustic resonators based on Ba_xSr_1-xTiO₃ 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_0.25Sr_0.75TiO₃ 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 BaTiO₃ 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%.