VHF CMOS-MEMS oxide resonators with Q > 10,000

A fully differential CMOS-MEMS oxide resonator fabricated using 0.18 μm CMOS-MEMS platform via metal wet-etching post process has been demonstrated with Q >; 10,000, first time ever in any CMOS-MEMS resonators, and more than 25 dB signal-to-feedthrough ratio at 47.9 MHz. Key to attaining such performance attributes to (1) the bulk-mode vibration to enable exceptional Q and much higher frequencies and (2) the oxide-rich structure with embedded metal electrodes for capacitive transduction, where SiO₂ offers better mechanical properties than metals to minimize intrinsic energy loss and where flexible electrical routing facilitates fully differential configuration to suppress capacitive feedthroughs. In addition, a previously developed metal wet-etching technique capable of releasing large device areas has been successfully transferred from 0.35 μm 2-Poly-4-Metal (2P4M) CMOS process to a new 0.18 μm 1-Poly-6-Metal (1P6M) technology node, therefore greatly lowering the motional impedance of the capacitively-transduced resonators due to smaller electrode-to-resonator gap spacing and larger transduction areas. This technology paves a way to realize fully-integrated CMOS-MEMS oscillators and filters which might benefit future single-chip transceivers for wireless communications.