Delamination of Stiff Films on Pressure Sensitive Ductile Substrates

Abstract

Stiff thin films supported by pressure sensitive ductile solids are an ubiquitous architecture appearing in a wide range of applications. The film rupture and delamination of films are important reliability issues of such an architecture. In this study, we investigate the synergistic effects of plastic deformation of substrates and fracture properties of film/substrate interface on the delamination of films. The focus of this study is on the interplay between the debonding of the interface and the plastic deformation of substrates. Finite deformation analyses are carried out for a stiff film deposited on a soft substrate with the substrate subjected to stretching. The fracture process of film/substrate interface is represented by a cohesive zone model, and the substrate is modeled as an elastic–plastic solid with pressure sensitive and plastically dilatant plastic flow. It is found that increasing the degree of pressure sensitivity of substrate can generate large plastic deformation, promoting crack tip blunting and thereby retarding delamination of film/substrate interface. Whereas, the increase in the degree of plastic dilatancy of substrate gives rise to the limited plastic deformation and leads to poor resistance to interface delamination. The strain hardening of substrate also affects the film/substrate debonding; the substrate with weakly post-yield strain hardening behavior contributes to enhanced resistance to interface delamination. It is further identified that the fracture properties of interface play an important role in activating plastic deformation of substrates. The film/substrate interface with high stiffness, large cohesive strength and high toughness enables the substrate to undergo significant plastic deformation, which suppresses the film/substrate delamination.