Non-monotonic pressure dependence of resonant frequencies of microelectromechanical systems supported on squeeze films

The resonant frequencies of released microcantilevers, microbeams, and microplates are among the most important response characteristics for microelectromechanical systems such as resonators, sensors, and radio frequency (RF) switches. It is generally believed that the resonance frequencies of such structures decrease monotonically as the surrounding gas pressure is increased from vacuum conditions. However, we find that for microbeams supported on gas films the natural frequencies of the device can first increase and then decrease with increasing gas pressure from vacuum, with the extent of non-monotonicity depending on device geometry. This anomalous property of a wide class of microelectromechanical systems is explained in terms of the competing inertial and compressive effects of the supporting squeeze film. (Some figures in this article are in colour only in the electronic version)