Resonant-mode effect on fluidic damping of piezoelectric microcantilevers vibrating in an infinite viscous gaseous environment

High quality factors are preferable for resonating microcantilever sensors in order to improve sensitivity and resolution. In this paper we investigate the performance of microcantilevers in different resonant modes vibrating in infinite gaseous environments. Aluminum nitride based piezoelectric microcantilevers are fabricated and tested under controlled pressure from high vacuum to atmospheric pressure in N2 environment, using a custom-built vacuum chamber. From the experiment results it can be seen that the torsional modes exhibit larger quality factors than those of the flexural and lateral ones, and the lateral modes have the lowest Q factors, which are limited mainly by the high intrinsic damping. Finally, analytical models for the fluidic damping characteristics of beam-shaped resonators at different resonant modes are derived and show good agreement with experimental results in the higher pressure regime.