Improved model for the adhesion of μcantilevers: Theory and experiments

A nonlinear method is proposed to calculate the adhesion energy (strain energy release rate) of stiction-failed μcantilever beams with large deflections. The proposed method uses a nonlinear theory for the deflection of a beam and an energy method for calculating the beam's strain energy. It is shown that current models used to predict μcantilevers' profile breakdown when the beam deflection exceeds 27% of the thickness due to the onset of longitudinal stresses in the μcantilevers. Because the present model captures longitudinal stresses in the μcantilevers and consequently their contribution to the strain energy, mode I and mode II contributions to the adhesion energy can be discerned. A set of experiments are performed using the peel test scheme with poly-Si μcantilever stiction failed on a poly-Si substrate. Results processed using the present model indicate that the adhesion energy of the μcantilevers actually increases with increased height of the μcantilever's base. This increase in the adhesion energy is attributed to the manner of loading that the μcantilevers experience which leads to increased contact area and the concomitant increase of adhesion.