Effect of surface chemistry on the quality factors of micromechanical resonators

Abstract

Single monolayers of molecules were found to strongly affect the quality factors of MHz-range torsional silicon resonators. By changing a single monolayer of molecules on the surface of a 5-µm-wide, 250-nm-thick silicon resonator less than 0.07% of the total mass the quality factor of the resonator was increased by 70%. In contrast, the standard commercial coating, a thin layer of silicon oxide, dissipates at least 75% of the mechanical energy in similarly sized resonators. Since the relative importance of these surface chemical losses scales with the resonator's surface-to-volume ratio, the development of low-loss, stable surface chemistries will be important for the production of high-performance micro-and nano-mechanical devices.

Permanent reduction of dissipation in nanomechanical Si resonators by chemical surface protection

“…Although it is possible to remove the oxide layer by annealing to 800°C in ultra-high vacuum (UHV) [18,19] or using chemical etching, the oxidefree silicon surface is unstable in air, and the oxide layer regrows within minutes under ambient atmosphere [12]. In a series of investigations, Henry, Hines and coworkers found that some permanent improvement in the mechanical quality factor is possible by monolayer coating of the surface with alkanes [20][21][22]. It is, however, unknown whether these improvements extend to low temperatures, where many of the most sensitive measurements are carried out.…”