The role of microstructure in MEMS deformation and failure

MEMS technologies create complex devices with critical dimensions on the order of 1-100 μm from a limited, but expanding materials base. Two standard MEMS technologies of interest to Sandia National Laboratories are surface micromachining (SMM) and LIGA-based high aspect ratio microfabrication. SMM techniques produce complex devices on the surface of a silicon wafer with critical dimensions of about 2 μm using a patterned multilayer film deposition process. LIGA (Lithographie, Galvanoformung, Abformung) is a process in which structural material is electrodeposited into a polymethyl-methacrylate (PMMA) mold realized by deep x-ray photolithography. The resolution of the LIGA process can be as precise as 1 μm, but typical component sizes range in the 100's of microns. In both technologies, material microstructural features, e.g. grains and defects, scale with component sizes. Consequently, issues surrounding the mechanical response of components fabricated from these technologies are often caused by this microstructure-component size scale equivalence. The objective of this paper is to present an overview of select mechanical properties results and associated microstructure evaluations expected to be useful for developing damage mechanics models that accurately predict the lifetime of MEMS devices. A companion paper (IMECE2002-32393) discusses experimental results and observations from micromechanical evaluation studies of SMM-MEMS. This paper discusses experimental results and observations on LIGA fabricated materials and some complementary, straightforward polycrystal elastic deformation simulations of SMM polysilicon. Copyright © 2002 by ASME.