Overall elastic domain of thin polysilicon films

We present a numerical study aimed to define the overall elastic domain of thin polysilicon films subjected to in-plane loadings. Homogenized properties are obtained for digital polycrystalline microstructures, generated in a representative volume element (RVE) through Voronoi tessellations. To locate the elastic limit, three micromechanical sources of dissipation are allowed for: (i) trans-granular cracking, as due to tensile stresses attaining the local strength inside silicon grains; (ii) inter-granular failure, as due to coupled normal-shear tractions attaining a local effective strength along grain boundaries; (iii) trans-granular phase transformation, as due to compressive stresses attaining a critical threshold inside silicon grains. Results of the homogenization procedure show that Rankine-type overall domains are too crude approximations to the polysilicon elastic envelope, since corners arise because of switching among the three dissipative modes allowed for. Outcomes of the analysis allow also to estimate the size of the RVE required to get objective overall polysilicon properties: according to data already available in the literature, it is shown that the RVE has to gather at least a few hundreds of grains.