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

PR Cantwell and H Kim and MM Schneider and HH Hsu and D Peroulis and EA Stach and A Strachan, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, 21, 840-849 (2012).

DOI: 10.1109/JMEMS.2012.2191939

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.

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