Surface oxide effects on failure of polysilicon MEMS after cyclic and monotonic loading

Polycrystalline silicon (polysilicon) microelectromechanical systems (MEMS) devices subjected to constant tensile stresses do not display delayed fracture in humid ambients unless they also contain thick (>45 nm) surface oxide layers, which are then susceptible to moisture-assisted stress corrosion. Polysilicon MEMS devices with typical (similar to 3 nm thick) native oxides do not show any thickening of the surface oxide layer after 3 x 10(7) fatigue cycles, excluding stress corrosion of the surface oxide as a cause of fatigue failure. Possible origins of polysilicon fatigue are discussed. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.