Thin-film processing of TiNi shape memory alloy

Abstract

The deposition and processing of thin-film Nitinol, a shape memory alloy (SMA), are discussed and demonstrated. By using sputter-deposition techniques, 0.5 to 8.0-μm-thick films of Nitinol (an alloy of nickel and titanium) were deposited, patterned and etched. Although the processing of the individual constituents of the alloy are well understood, the processing of the shape memory alloy is not a simple extension or combination of the constituent metals processing. Requisite deposition conditions for the film to retain the shape memory effect of the bulk material and avoid stress-induced cracking are discussed. An appropriate wet-etch for patterning the thin-film Nitinol is presented. Results from surface micromachined test structures are presented, which verify the shape recovery property of the thin-film Nitinol using resistive heating as the source of heat energy for the shape recovery. Finally, we discuss an isotropic, dry-etch technique developed for the release of the thin-film test structures that also has potential use in other thin-film applications.