Evaluation of mechanical materials properties by means of surface micromachined structures

Abstract

For all micromechanical devices, mechanical properties such as elasticity constants, internal stresses, fracture limits and, for ductile materials, yield limits and strain-hardening behaviour, are of paramount importance in design and use. Furthermore, mechanical integrity aspects are important also for devices with non-mechanical functions. During the last two decades, a diversified and somewhat scrubby flora of methods, instrumentation and microstructures for mechanical microcharacterisation has evolved. Early results were difficult to reproduce and verify, but lately an increasing degree of agreement between reported results is discernible. This paper reviews some recent development of techniques using surface micromachined structures, with special emphasis on stress–strain, internal stress, and fracture property characterisation of brittle and ductile materials. Particular attention is given to evaluation issues such as analytical and numerical modelling (FEA), identification and elimination of error sources, and proper statistical treatment of the results (such as Weibull analysis of fracture results).