Wrinkling of anisotropic crystal films on soft substrates


Se Hyuk Im and Rui Huang, ruihuang@mail.utexas.edu. Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, TX 78712
Complex wrinkle patterns have been observed in various systems, typically with integrated hard and soft materials. The underlying mechanism of wrinkling has been generally understood as a stress-driven instability, similar to the classical Euler buckling of a compressed column. Much of the theoretical studies on wrinkling have considered isotropic elastic thin films on soft substrates. For elastic substrates, analytical solutions have been obtained by linear perturbation analysis and the method of energy minimization. Dynamics of wrinkle evolution have also been investigated for elastic films on viscous and viscoelastic substrates. This paper considers wrinkling of anisotropic crystal thin films on soft substrates. Recent experiments have observed wrinkles in single-crystal Si and SiGe films on polydimethylsiloxane (PDMS) as well as on a glass substrate at a high temperature, exhibiting certain directional characteristics most likely due to the anisotropic material properties. This paper develops an anisotropic model for wrinkling of crystal thin films on viscoelastic substrates. Analytical solutions are obtained by a linear perturbation analysis for the early stage evolution and by energy minimization for the equilibrium state. Numerical simulations show evolving wrinkle patterns, with specific orientations.