Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

摘要

Tunable and switchable Ba0.5Sr0.5TiO3 film bulk acoustic resonators (FBARs) based on SiO2/Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of BaxSr1-xTiO3 (BST) films at 800 ℃.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias (＜ 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frcquency is around -2.3％ and the electromechanical coupling coefficient is up to approximately 8.09％ at 60-V dc bias,which can be comparable to A1N FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum (Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.