Energy dissipations in MEMS resonators: Fluid damping of flexural resonators and thermoelastic damping.

摘要

Micro/nano resonators are important components in many Micro/Nano-Electrical-Mechanical system (MEMS/NEMS) applications. Quality factor (Q) and resonant frequency are two key parameters MEMS resonators. Precise Q-factor and the resonant frequency prediction are very desirable in MEMS design. Q-factor of a MEMS resonator is determined by the system damping of the device. Therefore it is crucial to identify and understand the dominant damping physics for micro resonators.;Vacuum and fluid (such as air or liquid) are two most important operating circumstances for MEMS resonators. Applications requiring a resonator operated in fluid include resonator-based mass-sensing and AFM-based imaging. In our research, we investigate the fluid-resonator interaction in detail by exploring how factors such as resonant frequency, device dimensions and geometric shape affect the this interaction. Both the damping effect and the loading effect are considered. Three aspect of this research, experiment, numerical simulation, and analysis, are combined closely to form a supporting loop, providing a platform for understanding and predicting the resonator behavior in fluid.;For MEMS resonators operated in vacuum, we will focus on the thermoelastic damping (TED) to understand the Q-factor upper limit. We experimentally show how TED affects the Q-factor for flexural resonators. Theoretically we develop a TED-approximation for longitudinal resonators. A new procedure to derive the exact solution of TED for flexural resonators is also presented.;Lastly macroscopic damping of the thin coating film of MEMS resonators is discussed. Useful relation are developed to aid MEMS designers in achieving Q-factor prediction and control in the design phase.