Cmos-Mems Resonators with Sub-100-Nm Transducer Gap Using Stress Engineering

A clamped-clamped beam (CC-beam) resonator based on a 0.35-m 2-poly-4-metal CMOS-MEMS process platform with an unprecedented sub-100-nm structure-to-electrode gap has been demonstrated. Particularly, using a floating electrode connected to a doubly-clamped arc beam that displaces due to thermally-induced stress after release brings the design rule defined capacitive transduction gap of 500 nm to below 100 nm-a value that is never been seen in CMOS-MEMS resonators. Unlike the previously demonstrated approach of that uses an additional voltage to pull the resonator structure closer to the electrode, this work yields a reduced gap spacing controllable by adjusting the initial gap spacing or the arc beam dimensions readily right after release without the need for additional voltages. The resultant sub-100-nm capacitive transducer gap successfully lowers the motional impedance for a 2.27-MHz CC-beam resonator by 157.4 times, from 62.1 MO to 394.5 kO, under a DC bias 3.6V. While being demonstrated on a CC-beam resonator, the generic gap-narrowing scheme allows deployment to other resonator topologies. © 2022 IEEE.