High k<inf>t</inf>2.Q silicon Fin Bulk Acoustic Resonators (FinBAR) FOR chip-scale multi-band spectrum analysis

Abstract

This paper reports on the silicon (Si) Fin Bulk Acoustic Resonator (FinBAR) technology that enables extreme frequency scaling and integration of multi-band signal processors over the ultra-and super-high-frequency regimes (UHF and SHF). High-aspect-ratio Si fins are covered by aluminum nitride (AlN) films to enable efficient electromechanical transduction of bulk acoustic resonance harmonics with large coupling coefficient (k%). The low phononic dissipation of single crystal Si, along with suppression of piezoelectric charge redistribution loss result in unprecedentedly high quality-factors (Q). Having a frequency defined lithographically by the width of the Si fin, FinBARs with frequencies spread over UHF and SHF can be co-integrated to enable a single-chip multi-band spectrum analyzer. Benefiting from low temperature sensitivity of elastic constants in N-doped Si, FinBARs demonstrate significantly lower temperature instability compared to uncompensated AlN FBARs. FinBAR prototypes, with different fin widths are presented operating in 3rd and 9th width extensional modes at 0.93 GHz, 1.65 GHz, 2 GHz, and 6 GHz, with Qs of 8450, 6400, 4800, and 2300 respectively, k t 2 over 0.2%-1.2%, and temperature coefficient of frequency (TCFi) of −17.6 ppm/°C. The resulting record f ×Q of 1.4 × 1013, the large k2t ×Q of 58, and lithographical frequency scalability demonstrate the promising potential of FinBAR technology to realize multi-band acoustic signal processors for the emerging 5G systems.