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Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.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 frequency 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 AlN 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.
Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators (FBARs) based on SiO 2 / Mo Bragg reflectors are explored, which can withstand high temperatures for the deposition of Ba x Sr 1 x TiO 3 (BST) films at 800 C 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 shifted upwards at low dc bias (<45 V) while downwards at higher dc bias. calculated relative tunability of shifts at series resonance frequency 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 AlN 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.