Modelling and Simulation of the Effect of Air Damping on the Frequency and Quality factor of a CMOS-MEMS Resonator

This paper reports analytical modeling and finite element analysis (FEA) of the effect of two types of air damping (squeeze film and slide film damping) on resonance frequency and quality factor of a multi-layer CMOS-MEMS resonator designed for application as a mass sensitive gas sensor. The sensing principle is based on change in frequency or amplitude of the resonator due to adsorption/absorption of trace gases onto an active material to be deposited on the resonator membrane plate. The effect of air damping for mode 1 and mode 2 are investigated and the damping coefficient is found to increase from 0.922 × 10−6 Ns/m to 1.768 × 10−6 Ns/m for mode 1 and from 0.914 × 10−6 Ns/m to 1.708 × 10−6 Ns/m for mode 2 with increase in the overlap area of the fingers from 40 μm to 75 μm, respectively. The quality factor (Q) of the CMOS-MEMS resonator is found to decrease with increasing damping coefficient for both modes of vibration while the frequency remained unaffected. Analytical and simulation results shows good agreement for damping coefficient (1.43 % and 1.22 %), resonant frequency (3.45 % and 4.4 %) and quality factor (2.27 % and 0.88 %) for mode 1 and 2, respectively.