Performance evaluation of CMOS-MEMS thermal-piezoresistive resonators in ambient pressure for sensor applications

In this work, we report a thermally driven and piezoresistively sensed (a.k.a. thermal-piezoresistive) CMOS-MEMS resonator with high quality factor in ambient pressure and with decent power handling capability. The combination of (i) no need of tiny capacitive transducer's gap spacing thanks to thermal-piezoresistive transduction, (ii) the use of high-Q SiO
₂
/polysilicon structural materials from CMOS back-end-of-line (BEOL), and (iii) the bulk-mode resonator design leads to resonator Q more than 2,000 in ambient pressure and 10,000 in vacuum. Key to attaining sheer Q in ambient pressure relies on significant attenuation of the air damping effect through thermal-piezoresistive transduction as compared to conventional capacitive resonators which necessitate tiny transducer's gap for reasonable electromechanical coupling. With such high Q and inherent circuit integration capability, the proposed CMOS-MEMS thermal-piezoresistive resonators can potentially be implemented as high sensitivity mass/gas sensors based on resonant transducers. The resonators with center frequency around 5.1 MHz were fabricated using a standard 0.35 μm 2-poly-4-metal (2P4M) CMOS process, thus featuring low cost, batch production, fast turnaround time, easy prototyping, and MEMS/IC integration.