Effects of anisotropic elasticity on stress concentration in micro mechanical structures fabricated on (001) single-crystal silicon films

Abstract

Anisotropy in the elastic properties of single-crystal materials is often neglected when designing microelectromechanical systems (MEMS) made of single-crystal silicon. In this report, the effects of anisotropic elasticity in single-crystal silicon on the stress concentration were analyzed and compared to isotropic simulation results. Semicircular notched beams, quarter-circle curved beams, and notched curved beams were analyzed using two-dimensional finite element method structural simulation. Two different material configurations on the (001) plane and isotropic material constants were compared for each model to clarify the anisotropy effects. The stress concentration factor of a circular notch was modified from the isotropic estimation by 7%–9% with the introduction of the anisotropic effect and became crystal-orientation dependent. Both the peak stress and stress distribution were dependent on the model configuration against the crystal axis. The results for other models were explicitly explained also by the rotation of the principal stress axis around the curved surface. A simple estimation method to select crystal orientation was proposed to minimize or maximize the stress concentration factor using elastic anisotropy. These findings will be useful for reducing the peak stress in MEMS structures and improving their reliability.