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 (∼3 nm thick) native oxides do not show any thickening of the surface oxide layer after 3 × 107 fatigue cycles, excluding stress corrosion of the surface oxide as a cause of fatigue failure. Possible origins of polysilicon fatigue are discussed.