The measurement of the mechanical properties of materials with submicrometer dimensions is extremely challenging, from the preparation and manipulation of specimens to the application of small loads and extraction of accurate stresses and strains. A new concept of on-chip nanomechanical testing platform has been developed in order to measure the mechanical properties of submicrometer freestanding thin films allowing various loading configurations and specimen geometries. The basic idea is to use internal stress present in one film to provide the actuation for deforming another film attached to the first film on one side and to the substrate on the other side. The measurement of the displacement resulting from the release of both films gives access to the stress and the strain applied to the test specimen provided the Young’s modulus and mismatch strain of the actuator film are known.
Classical microelectromechanical-systems-based microfabrication procedures are used to pattern the test structures and release the films from the substrate. A suite of test structures with various combinations of dimensions allow the characterization of a large variety of materials and mechanical properties. It enables high throughputs of data while avoiding any electrical signal or external actuation. This characterization technique has been successfully applied to the analysis of the intrinsic mechanical properties such as the Young’s modulus, yield stress or fracture stress, fracture strain, and strain hardening, but also piezoresistance effects, of ductile and brittle materials. The technique can also be directly applied to relaxation/creep with ageing/environmental effects. The specimen thickness varies between typically 1 μm down to a few tens of nm, the width between 25 nm and several μm, and the length between a few μm to several hundreds of μm.
The interest of this characterization methodology is not limited to the fundamental analysis of materials intrinsic properties but it can bring original solutions to monitor the functional properties of materials during their manufacturing process and their life time.
ICTEAM, Université catholique de Louvain (UCL)