Mechanical quality factor of microcantilevers for mass sensing applications

Abstract

Mechanical quality factor (Q-factor) is essential to detect-limitation of a resonant based mass sensor because it determines signal to noise ratio. This paper studies the effects of different energy dissipation mechanisms, including air damping, support loss and thermoelastic damping (TED), on Q-factor of a microcantilever under atmospheric pressure conditions. The contribution of each mechanism was analyzed at various cantilever geometry. And the precondition to Z.Hao's model, which describes the support loss effect by elastic wave theory, was discussed. It was found that in 5 μm-thick silicon cantilevers, air damping was the predominant reason to energy dissipation when cantilever length was larger than 140 μm. The support loss and TED became noteworthy at shorter cantilevers when cantilever length to thickness ratio (L/t) was less than 20. Q-factor of a microcantilever thus can be improved by increasing the cantilever thickness to suppress air damping, but not infinitely because the support loss became comparable to air damping when cantilever thickness was increased. Moreover, it was found that the Q-factor of a multi-layered microcantilever was degraded markedly with the increase of layer numbers.