Shape memory NiTi thin films deposited on polyimide at low temperature

Abstract

In this work, we present the deposition of NixTi1−x shape memory alloy (SMA) thin films at a substrate temperature of 350°C. Deposition at 350°C preserves the mechanical properties of the polymer and widens the scope for potential applications such as electrically excitable soft bodied robots, in flexible deformable devices and for miniaturized biomedical active probes.Essential for this result is the application of an ion-bombardment to the growing film. For the ion bombardment on the growing film, RF bias plasma was generated at the sample stage. The films were deposited through magnetron sputtering from NiTi and Ti targets onto polyimide spin coated silicon wafers. The crystal structure, surface morphology and microstructure were studied using X-ray diffraction, atomic force microscopy and transmission electron microscopy. As deposited films on spin coated polyimide were crystalline. The presence of solid state transformation responsible for shape memory effect has been demonstrated through electrical resistance vs temperature measurements and temperature dependent X-ray diffraction for approximately stoichiometric films. Transmission electron microscopy observations revealed that all films have an amorphous base and a columnar poly-crystalline top and the formation of nuclei is dependent on chemical composition and thickness.