Capacitively-driven and piezoresistively-sensed CMOS-MEMS resonators

A foundry-oriented capacitively-driven CMOS-MEMS resonator using differentially piezoresistive sensing has been demonstrated for the first time to enable feedthrough cancellation with more than 20 dB noise floor reduction as compared to purely capacitive transduction. The resonators are formed by high-Q SiO₂ structure (Q >; 5,500) using metal wet etching and XeF₂ release processes while polysilicon (originally CMOS gate poly) embedded inside the resonator structure serves as piezoresistive element for vibratory detection. In addition, such composite structure enabling electrical isolation accomplishes decoupling of capacitive and piezoresistive transductions, allowing the selection (or switching) of the preferred transduction scheme using the same resonator device. The resonators with capacitive drive and differentially piezoresistive sense configuration have been demonstrated with Q >; 4,000 and more than 28 dB signal-to-feedthrough ratio. CMOS-MEMS oxide resonators with differentially piezoresistive sensing provide an excellent alternative to purely capacitive transduction for integrated oscillator applications.