Mechanical properties of compressively prestressed thin films extracted from pressure dependent ripple profiles of long membranes

We report the determination of mechanical properties of compressively prestressed thin films from the postbuckling behavior of long rectangular membranes under differential pressure. Such structures show buckling profiles with ripples of pressure-dependent wavelength λ and amplitude Δw. At sufficiently high loads they undergo a symmetry transition to a ripple-free deflection profile. A model based on the energy minimization method (EMM) was developed to describe the mechanical behavior of these compressively prestressed membranes. For this purpose a new set of trial functions was constructed enabling the complex behavior including the symmetry transition to be described. Values for Young´s modulus E and the prestrain ε₀ can be extracted from the comparison of experimental load-deflection data and EMM simulations. The model was applied to ripple data of a PECVD silicon nitride. Young´s modulus and the prestrain were found to be E=160 GPa and ε₀=-7.0×10^-4 respectively.