Characterization and Modeling of Surface Roughness on a Silicon/PZT Unimorph Cantilever using Finite Element Method

Abstract

Silicon etching using deep reactive ion etching (DRIE) at large etch depth results in rougher surfaces due to increased response in process pressure, amount of coil power, increased amount of helium leak at the backside, and even post process handling. To account for the effects of surface roughness on the characteristics of a silicon cantilever beam, a numerical model based on the finite element method (FEM) modeling was developed using actual roughness data from fabricated samples. The acquired roughness data was integrated to the silicon cantilever beam model coupled with multiphysics to simulate a piezoelectric energy harvester. Simulation result shows that roughness parameter ranging from 1.488-3.138 μm can shift the resonant frequency by 5.53% to 9.48% or 308.31 Hz to 551.21 Hz of the device but does not have significant effect on the output power. The significant shift in the resonant frequency implies that careful consideration of surface roughness from fabrication processes must be considered when designing energy harvesters.