title: An elevated temperature study of a Ti adhesion layer on polyimide.
abstract: Titanium layers are used to promote adhesion between polymer substrates for flexible electronics and the Cu or Au conducting lines. Good adhesion of conducting lines in flexible circuits is critical in improving circuit performance and increasingcircuit lifetime. Nominally 50 nm thick Ti films on polyimide (PI) are investigated by fragmentation testing under uniaxial tensile load in the as-deposited state, at 350 °C, and after annealing. The cracking and buckling of the films show clear differences between the as-deposited and the thermally treated samples, cracks are much straighter and buckles are smaller following heat treatment. These changes are correlated to a drop in adhesion of the samples following heat treatment. Adhesion values are determined from the buckle dimensions using a total energy approach as described in the work of Cordill et al. (Acta Mater. 2010). Cross-sectional transmission electron microscopy of the Ti/PI interface found evidence of a ~ 5 nm thick interlayer between the largely columnar Ti and the amorphous PI. This interlayer is amorphous in the as-deposited state but nano-crystalline in those coatings tested at elevated temperature or annealed. It is put forward that this alteration of the interfacial structure causes the reduced adhesion.
authors.affiliation: Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstraβe 12, A-8700 Leoben, Austria ; Physics Department, Durham University, South Road, Durham, DH1 3LE, UK.
authors.forename: A A
authors.initials: AA
authors.lastname: Taylor
authors.forename: M J
authors.initials: MJ
authors.lastname: Cordill
authors.forename: L
authors.initials: L
authors.lastname: Bowles
authors.forename: J
authors.initials: J
authors.lastname: Schalko
authors.forename: G
authors.initials: G
authors.lastname: Dehm
keywords: Adhesion layer; Electron microscopy; Fragmentation testing; Interfaces; Temperature; Titanium