Silicon Crystal Effects in Modeling of MEMS Silicon Resonators

S. Ghaffari, C.H. Ahn, E.J. Ng, T.W. Kenny
Stanford University, US

Keywords: silicon anisotropy, modeling, MEMS, resonators, frequency response, quality factor


Silicon has found considerable application in precision MEMS devices because it provides desirable high frequency and quality factor characteristics. Usually, MEMS resonators are built from single crystal silicon with proven long-term stability. It is experimentally shown that a change in crystal orientation can make up to 20% difference in quality factor (Q) of resonators. Also, frequency splitting is observed in flexural disk resonators for anisotropic devices and also polysilicon devices where it is not expected. Modeling of crystal properties can be used both for prediction and explanation of these experimental results. Especially for more complex geometries where an analytical solution does not exist, modeling can explain, predict or direct experimental results. We extend previous work by incorporating silicon crystal properties into the modeling of disk resonators and tuning forks and demonstrate that the frequency splitting and quality factor of those devices can be accurately predicted.