Influence of electrodes and Bragg reflector on the quality of thin film bulk acoustic wave resonators

It is considered that the acoustic wave attenuation in the metal and piezoelectric films, the wave scattering loss, and the electrode electrical loss are the possible quality factor detractors in FBAR devices. Due to the small acoustic wave attenuation of the Mo electrode, the composite Mo-AlN-Mo resonator with thick electrodes provides higher Q than that with thin Mo electrodes. In such Mo electroded resonators, a relatively high effective coupling coefficient is retained. In Q value detractors, the acoustic wave scattering loss originating from surface roughness is thought to be fatal in terms of FBAR quality. The thickness of the low impedance SiO₂ layer of the Bragg reflector also affects the Q value and effective coupling constant due to the low material Q of the SiO₂ film.