FEM Frequency Response Analysis of Mass Loading in MEMS Resonators and Sensors
Abstract
This project focuses on a series of thermally actuated MEMS resonators we have designed as gas sensors and investigates the behavior of their frequency response as mass loading occurs on the shuttle due to gas absorption. These Silicon MEMS resonators contain a shuttle mass in the center, free to move in a cavity, and tethered to substrate with two springs implemented with folded beams on either side. The resonators were simulated in COMSOL Multiphysics, an advanced finite element (FEM) simulation software, for varied added shuttle masses. To simplify the simulation computations the resonator is driven by a sinusoidal displacement at all four spring fingers whereas the real device uses thermal expansion from an AC input to drive the resonator. Both real time responses (transient and sinusoidal steady state) and modal analyses were performed and compared. Trends in resonant frequencies versus mass loadings were extracted and compared with simple textbook bulk model. COMSOL simulations also yield stress distributions to highlight potential breakage conditions on overdriven resonators. Separately, tests were done on the fabricated MEMS resonator samples containing deposited gold films and correlated to FEM simulated frequency shifts with mass loading.