Measuring time-dependent mechanics in metallic MEMS

The reliability of metallic microelectromechanical systems (MEMS) depends on time-dependent deformation such as creep. The interaction between microstructural length scales and dimensional length scales, so-called ‘size-effects’, play a prominent role in this. As a first critical step towards studying these size effects in time-dependent deformation, a purely mechanical experimental methodology has been developed, which is discussed here. It is found most suitable for the investigation of creep due to the simplicity of sample handling and preparation and setup design, whilst maximizing long term stability and displacement resolution. The methodology entails the application of a constant deflection to a µm-sized free-standing aluminum cantilever beam for a prolonged period of time. After this load is removed, the deformation evolution is immediately recorded by acquiring surface height profiles through confocal optical profilometry. Image correlation and an algorithm based on elastic beam theory are applied to the full-field beam profiles to yield the tip deflection as function of time. From a discussion on the sources of experimental error, it is concluded that the methodology yields the tip deflection as function of time with ∼3 nm precision.