Size dependent morphologies of brittle silicon nitride thin films with combined buckling and cracking

We report on size-dependent morphological characteristics of buckle-driven delaminations in large-scale brittle silicon nitride films in accompany with ridge cracking. The buckling morphologies fall into four distinct categories in a phase diagram. They start as straight-sided blisters with or without ridge cracks from the film edge and then spread as telephone cord blisters with or without ridge cracks into the central region of the sample gradually. The buckle-delamination size is found to decrease with the increase of residual stress, different from the previous reports. Theoretic analysis based on Föppl-von Kármán plate theory with strong mixed-mode interfacial adhesion elucidates this abnormal behavior and explains why the ridge-cracked straight-sided blister always appears with much smaller delamination size in comparison with the coexisting uncracked telephone cord blister with large delamination size. The ridge-cracked buckle-delaminations destabilized into bubble-like blisters are also recovered by dynamic simulations based on phase field modeling, in good agreement with the experimental observations.

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