Tunable Bulk Acoustic Wave Resonators Based on Ba0.25Sr0.75TiO3 Thin Films and a HfO2/SiO2 Bragg Reflector

A switchable and tunable bulk acoustic wave resonator based on a paraelectric phase Ba0.25Sr0.75TiO3 thin film and an all-dielectric HfO2/SiO2 Bragg reflector is presented. The achieved tuning range (3.8%) and effective electromechanical coupling coefficient (7.1%) are the highest reported for solidly mounted tunable bulk acoustic wave resonators. The non-conductive Bragg reflector stack provides excellent integration possibilities.