Size-effects in time-dependent mechanics of metallic MEMS

Micro-electromechanical systems (MEMS) integrate electrical and mechanical functionality at the μm-scale for innovative high-tech consumer applications, like capacitive switches for low-power wireless communications. However, commercialization of metallic MEMS devices still face challenges, e.g., compromised mechanical reliability due to poorly understood time-dependent micromechanics at this microscale. This project aims to increase the fundamental understanding of the responsible micro-mechanisms in aluminum-copper thin films through micromechanical experiments.

PhD researcher: ir. Lambert Bergers
Supervisors: Dr.ir. J.P.M.Hoefnagels, Prof.Dr.ir.M.G.D.Geers
Funding: FOM - M2i: Size-dependent materials properties program.

Intrinsic effects, e.g. grain size, alloy structure, and extrinsic effects, e.g. structure size, affect the time-dependent deformation. Alloy structure variations are investigated by aging Al-(1wt%)Cu cantilevers in thin metal films at elevated temperatures and measuring Cu content with energy dispersive spectroscopy, whilst grain size variations are revealed using electron backscatter diffraction.

Mechanical characterization at the micro-scale is not trivial. First a novel micro-beam bending methodology is developed employing optical profilometry for 3D deformation measurements of time-dependent reversible deflections. Digital image correlation corrects drift artifacts, allowing nm-precise extraction of the beam deflection over 24 hours. Second, a custom high-precision tensile tester is developed with nN force and nm-deformation measurement reproducibility. The setup fits in the SEM allowing in-situ testing for direct correlation of the mechanical behavior to the evolving microstructure.