Pressure effects on the dynamic properties of hydrogenated amorphous silicon disk resonators

Abstract

Microelectromechanical-system resonators have great potential as sensors for the detection of chemical and biological species in air and in liquids due to their high frequency, low dissipation and possibility of miniaturization. In this work, the influence of a fluidic environment on the quality factors and resonance frequency is studied. The changes in the dynamic behavior of thin-film hydrogenated amorphous silicon microelectromechanical disk resonators of ∼50–350 µm characteristic length and spanning a resonance frequency range between 0.1 and 20 MHz are described as a function of air pressure up to atmospheric conditions. The results show that fluidic damping behavior is dependent on the frequency of operation with respect to the penetration depth of the propagation of shear waves resulting from fluid–structure interaction. The use of higher harmonics is suggested for reduced damping in fluidic applications, independent of the particular mode shape. Significant increases in the effective stiffness are observed due to elastically clamped air associated with squeeze-film effects. Linear variation of the resonance frequency up to 40% was observed when varying the pressure. It is observed that inertial effects from the surrounding media are less prominent at higher orders and at higher frequency modes.