TABLE OF CONTENTS Mechanical properties of thin films and the interface between film and substrate will be considered in this chapter. Among these properties are flow strength, fracture strengths of film and of interface between film and substrate, friction and resistance to wear, elastic moduli, stress relaxation and piezoelectric properties. The mechanical properties of thin films affect their behavior in a variety of applications. In particular, the plastic flow and fracture, that occur during the operation of conductor lines upon electromigration induced stress development, certainly are affected by the mechanical properties of the film as well as the mechanical constraints provided by the substrate and cladding; adhesion of film to substrate is affected by the film's mechanical properties as well as the substrate/film interface strength; wear of thin film head and recording media thin film over-layers depend upon their mechanical properties, etc.
Microstructure has marked effects on the strengths of bulk materials. It would be expected that thin films exhibit the same effects on their various strengths. For example, for ductile bulk materials, the yield strength increases as the dislocation density increases, as the grain size decreases, as the solute content in solution increases (for most types of solute), and as the spacing between noncoherent particles dispersed within the bulk decreases. The yield strength of ductile thin films exhibits similar qualitative behavior with these structural variations only when the thin films are not constrained by a substrate or other more rigid layer
