A Super-High-Frequency Non-Released Silicon Fin Bulk Acoustic Resonator
This paper reports, for the first time, on a high quality-factor (Q) super-high-frequency bulk acoustic wave resonator realized from integration of aluminum nitride (AlN) on sidewalls of a non-released single crystal silicon (Si) micro-fin. The non-released Fin Bulk Acoustic Resonator (FinBAR) enables monolithic integration of filters for realization of single-chip RF front-end (RFFE) modules. Benefiting from the low acoustic-loss of Si fin and large longitudinal piezoelectric coefficient of AlN, the FinBAR technology provides the high kt²×Q required for implementation of wideband filters. Furthermore, having a frequency defined by the Si fin width, the FinBAR technology provides extreme lithographical scalability over the wide 3–30 GHz spectrum; hence facilitating chip-scale integration of multi-band spectral processors for carrier-aggregated RFFE. Proof of concept non-released FinBARs are fabricated through process optimization of magnetron sputtering to yield (0002)-textured AlN films on the sidewalls with perpendicular c-axis. The fin geometry is engineered to enable highly efficient acoustic energy localization in the active region to enhance resonator’s kt²×Q. A non-released FinBAR at 4.2 GHz, with a Q of 1,573 and kt² of 2.75% is demonstrated. The effects of c-axis misorientation of the sidewall transducer film and the non-released architecture of Si micro-fin on the resonator performance are discussed in detail.