Estimating the In-Plane Young's Modulus of Polycrystalline Films in MEMS

Polycrystalline films in microelectromechanical systems (MEMS) sometimes have a crystallographic fiber texture that causes their in-plane Young's modulus to differ from the bulk isotropic value, which influences device behavior, lifetime, and reliability. We estimate the in-plane Young's modulus of electrodeposited nickel bridges in radio-frequency MEMS devices by measuring the crystallographic texture using X-ray diffraction and then computing a texture-weighted average of the single-crystal elastic coefficients. The nickel bridges have a 001 fiber texture and are predicted to have an in-plane Young's modulus of 195-200 GPa, about 5-7% less than the bulk isotropic value of 210 GPa. The method presented here takes into account the full distribution of crystallite orientations to predict the in-plane Young's modulus. The method is rapid, general, and capable of estimating the in-plane Young's modulus of polycrystalline film components in individual MEMS devices in an array, making it ideal for MEMS design, analysis, and quality control.