AVS 50th International Symposium
    Microelectromechanical Systems (MEMS) Tuesday Sessions
       Session MM-TuM

Paper MM-TuM6
Chemical Control of Mechanical Energy Dissipation in Micromechanical Silicon Resonators

Tuesday, November 4, 2003, 10:00 am, Room 320

Session: Development and Characterization of MEMS and NEMS Materials
Presenter: Y. Wang, Cornell University
Authors: Y. Wang, Cornell University
J.A. Henry, Cornell University
M.A. Hines, Cornell University
Correspondent: Click to Email
Why are we unable to predict the dynamical performance of nanoscale devices from the well-known properties of macroscopic materials? For example, the quality (or Q) of micromechanical resonators plummets as the size of the device is reduced. We will show that the role of surface effects on energy loss cannot be ignored at this length scale. To investigate the role of surface dissipation, we have fabricated silicon torsional resonators with predominantly Si(111) faces. The resonators' surfaces are then chemically modified and characterized by infrared spectroscopy. Resonators terminated by an atomic layer of hydrogen have the lowest energy loss but the quality of the resonator decreases with time even in high vacuum (10@super -8@ Torr). Quantitative analysis of the time-dependent frequency shift suggests that the increased losses observed in vacuum are correlated with chemical adsorption. The quantitative effects of a variety of adsorbates will also be discussed. When the H-monolayer is replaced by one type of self-assembled monolayer (SAM), a small decrease in initial quality is observed; however, SAMs-terminated devices are much more stable with time. This stability is attributed, in part, to increased chemical resistance; however, aggressively oxidizing environments still lead to performance degradation. A second type of SAM leads to much higher energy losses. The chemical origins of this difference will be discussed.