Structure and Thermal Stability in Titanium-Nickel Thin Films Sputtered at Elevated-Temperature on Inorganic and Polymeric Substrates

Abstract

AbstractDeposition of crystalline titanium-nickel shape-memory alloys on polymeric substrates is complicated by the elevated temperatures that must be withstood either during deposition or during post-deposition crystallization anneals. In this paper we report results on thin films of titanium-nickel, with Ni-rich compositions, which were prepared by dc magnetron sputtering onto quartz substrates, and onto thin polyimide membranes, at various elevated substrate temperatures between 623K and 703K. All of the as-deposited films possessed ordered bcc microstructures and had nano-scale grain sizes. Films deposited at the higher end of the temperature range displayed familiar two-step transformation behavior in electrical resistivity experiments, with transformation temperatures that were stable with respect to annealing for 22-hrs at 700K. Classic shape-memory was observed for a bilayer consisting of an 7.6 μm thick Kapton® polyimide sheet onto which 3 μm of near-equiatomic TiNi had been sputtered at 703K. By applying a pattern-etch technique to the metallized polymer we were able to fabricate a prototype electrically-excitable thin-film actuating element, potentially applicable to microelectromechanical and biomechanical systems.