Microfabrication-based nanomechanical laboratory for testing the ductility of submicron aluminium films

The measurement of the mechanical properties of materials with submicron dimensions is extremely challenging, from the preparation and manipulation of specimens, to the application of small loads and extraction of accurate displacements. Here, we present results obtained on 250 nm-thick aluminium films using a novel versatile concept of micro and nano-machines allowing multiple loading configurations and geometries. The focus is put on the fracture strain defined either as the strain at necking under uniaxial tension or the local strain at cracking initiation. The ductility of free-standing thin metallic films is one of the mechanical properties which is rarely measured and discussed in the literature. The necking and fracture strains are found equal to 0.08 and 0.3, respectively. Depending on the application, such as the development of flexible electronics or the reliability of interconnects, and on the loading conditions, one or both of these ductility indices can be key in the definition of fail-safe designs. This study enlightens also the interest and potential of the new nanomechanical testing concept. (c) 2007 Elsevier B.V. All rights reserved.