Bulk Lateral MEM Resonator on Thin SOI With High $Q$ -Factor

The fabrication, design, and characterization of high-quality factor microelectromechanical (MEM) resonators fabricated on thin-film silicon-on-insulators (SOIs) are addressed in this paper. In particular, we investigate laterally vibrating bulk-mode resonators based on connected parallel beams [parallel beam resonators (PBRs)]. The experimental characteristics of PBRs are compared to disk resonators and rectangular plate resonators. All the reported MEM resonators are fabricated on 1.25-$\mu\hbox{m}$ SOI substrates by a hard mask and deep reactive-ion etching process, resulting in transduction gaps smaller than 200 nm. Additionally, this fabrication process allows the growth of a thermal silicon dioxide layer on the resonators, which is used to compensate the resonance-frequency dependence on temperature. Quality factors $Q$, ranging from 20 000 at 32 MHz up to 100 000 at 24.6 MHz, are experimentally demonstrated. The motional resistances $R_{\rm m}$ are compared for different designs, and values as low as 55 $ \hbox{k}\Omega$ at 18 V of bias voltage are obtained with the thin SOI substrate. The thermal sensitivity of the resonance frequency is investigated from 200 K to 360 K, showing values of $-$15 ppm/K for the PBRs, with a possible compensation of 2 ppm/K when using 20 nm of $\hbox{SiO}_{2}$. $\hfill$[2008-0112]