Mechanical behavior of freestanding and passivated Al thin films

Abstract

In this research, the mechanical behavior of freestanding and passivated Al thin films is studied. Tensile test, membrane deflection test, and cantilever beam bending test are carried out and the Young's modulus measured from different test methods is compared to precisely measure the mechanical properties of electron beam evaporated freestanding Al thin films. While results from tensile test and membrane deflection test show a high level of repeatability, there is a difference between the Young's modulus measured by the two test methods. Finite element analysis is utilized to disclose the effects of various experimental errors in membrane deflection test that could explain the discrepancy. The Young's modulus measured by cantilever bending test exhibits poor accuracy, and there is high deviation between the measured values. The mechanical behavior of passivated Al thin films deposited via direct current magnetron sputtering is investigated by performing tensile experiments. The yield strength of passivated Al thin films is much larger than that of unpassivated films. While strain hardening behavior is observed in unpassivated films, passivated films show softening behavior. It is also found that a thin passivation layer prevents necking from occurring in Al thin films.