IMPROVING FRACTURE PROPERTIES OF MEMS COMPONENTS BY SURFACE CONTROL

This thesis studies the mechanical reliability of nanostructures. The strength statistics of Si nanobeams, their dependence on surface morphology and degrada-tion due to air exposure are characterized and necessary conditions for maximum strength and durability are determined. Due to their small sizes and use of low defect materials, nanostructures have the potential to be used in applications requiring very high stresses at low failure probabilities. Fracture strength of 190-nm thick Si beams have been shown to be as high as 13 GPa, approximately 30 times higher than the strength of macroscale samples. Testing similarly prepared beams etched with relatively smooth mor-phologies (0.4 nm rms) we showed that the strengths were further improved to 16 GPa, approaching theoretical strengths predicted by previous atomistic calcula-tions. To explain this influence, a series of fracture mechanics based Monte Carlo simulations were performed. Chemically modified surfaces of the tested beams were measured, statistically characterized and equivalent surfaces were generated