Temperature-Compensated CMOS-MEMS Oxide Resonators

Integrated CMOS-MEMS clamped-clamped beam resonators using metal wet etching technique are demonstrated with passive temperature compensation through the use of SiO₂ and large stopband rejection via circuit integration. Such performance is enabled by the high- Q structural material (i.e., SiO₂) and embedded electrodes (i.e., metal) for capacitive transduction without the need of complex post-CMOS processes. In virtue of exceptional selectivity of metal wet etchant to SiO₂ among CMOS layers, the use of release holes needed for most of isotropic etching processes could be eliminated, hence substantially preserving the integrity of resonator structures. In this paper, CMOS-MEMS clamped-clamped beams with SiO₂-rich structural design are fabricated and tested in vacuum under a two-port measurement configuration, exhibiting the lowest temperature coefficient of frequency (TC_f) in CMOS-MEMS-based resonators with a turnover point at room temperature. Such a resonator monolithically integrated with readout circuitry using a standard CMOS 0.35 μm 2P4M process is tested with significantly enhanced performance, showing resonator Q´s up to 6100, stopband rejection ~60 dB, and low noise floor at center frequency ~8 MHz, therefore benefiting future timing references and RF-MEMS building blocks for next-generation wireless communication applications.