An analysis of the membrane deflection experiment used in the investigation of mechanical properties of freestanding submicron thin films

In this paper we investigate, both experimentally and theoretically, the competition between different failure mechanisms (stretching, bending and curvature localization) in freestanding submicron thin films commonly used in microelectromechanical systems. Microstructures made of elastic-brittle materials such as ultrananocrystalline diamond, diamond like carbon and silicon nitride, as well as elastic–plastic materials such as gold, aluminum, and copper, are tested by means of the membrane deflection experiment developed at Northwestern University. Evidence of competition between different failure modes has been found for the investigated elastic-brittle materials. The phenomenon is dependent on specimen size and shape. By contrast, in the case of elastic–plastic materials, failure due to stretching was found to be the dominant mechanism. An analytical model is proposed to rationalize the experimental data and to provide dimensionless parameters able to describe the competition between different failure mechanisms. These dimensionless parameters are particularly useful in the design of specimens employed in the MDE technique.