Thickness effect on the fracture and delamination of titanium films

• Crack behavior changes with film thickness despite film adhesion staying constant.
• Ti–PI interlayer and TiOx surface layer thicknesses do not change with film thickness.
• Film and interface characterization provides understanding of mechanical properties.

Titanium adhesion layers are a common component of many coated products; they play a particularly important role in promoting the adhesion of Cu and Au conduction lines to polymer substrates for flexible electronic circuitry. In this work a full microstructural and mechanical characterization is performed on Ti layers of three different thicknesses—8, 12 and 50 nm—deposited onto polyimide. Observed differences in the mechanical behavior of the coatings were found to relate to the changing chemistry and grain size of the coatings. In particular, the observation, using transmission electron microscopy, that the two thinner coatings were comprised of 50% or less metallic Ti illustrates the potential pitfalls of altering something so simple as the coating thickness.