ABSTRACT

The adhesion of a thin film to the substrate is an important issue controlling the reliability of the film's performance. This subject has been most recently reviewed by Mittal [1] and Valli [2]. The mechanics for the adhesion and development of measuring techniques were mainly focused on interface fracture or bonding failure [3, 4]. Our present work studies the adhesion at the interfaces from a different point of view, i.e. it considers the load transfer across the interface. Adhesion is then defined, instead as a detaching force, as the degree of load which can be elastically transferred from one side of the interface to the other side. Any partial or nonelastic transfer is considered as an imperfection of the adhesion, though it may not lead to any permanent damage such as crack formation or detachment. In fact, detachment may be considered to represent the final stage of interface deformation. As in bulk materials, information on the nonelastic response exists in the stress-strain curve long before the material fails. Most information on mechanical properties is extracted in the region immediately following elastic deformation. Analogously, there exist a wide range of mechanical responses between elastic film/substrate bending and complete film detachment in which

2. DYNAMICAL RESPONSE OF THE FILM/SUBSTRATE COMPOSITE

The dynamic mechanical properties of thin film layered materials consisting of a substrate of thickness ds and a perfectly adhering film of thickness df are usually determined by a cantilever method. Since such an oscillating cantilever comprises a parallel composite, its eigenfrequency fc is given by [5]

(1)

where the subscripts s and f denote substrate and film quantities, and E and p represent the elastic modulus and density, respectively.