Characterization of TiNi, TiNiPd thin films by ion beam analysis techniques

Abstract

Ti-based shape memory alloy (SMA) thin films have the potential to become high performance actuator materials for microelectromechanical systems. The major challenge in fabricating Ti-based SMA thin films is composition control, since a small compositional deviation can result in very large changes in the phase transformation temperatures. Owing to extreme reactivity of titanium, oxygen contamination is a major problem during the sputter deposition of TiNi and TiNiPd SMA thin films as it alters the Ni/Ti ratio. Oxygen as a contaminant has deleterious effects both on shape memory properties and mechanical properties of these alloys. Not much work in this field has been focussed on identification, determination and elimination of oxygen contamination. Rutherford Backscattering Spectrometry (RBS)is a useful technique for accurate determination of stoichiometry and depth profiling of these alloy films. RBS is less sensitive to light elements. For this reason RBS has been complemented by Heavy Ion Elastic Recoil Detection Analysis (HIERDA) for the determination of oxygen. TiNi and TiNiPd films were deposited by DC- Magnetron Sputtering on unheated Silicon substrates by using Ti_1.08Ni_0.92 and Ti_1.08 Ni _0.74 Pd _0.18 alloy targets. RBS measurements were carried out with 2 MeV He ions whereas HIERDA used 77 MeV I¹⁰⁺ ions with a ToF-E detector. It was found that oxygen contamination is almost negligible in TiNiPd films compared to TiNi films deposited under similar conditions. Palladium is effective as a catalyst in removing the oxygen from the deposition system resulting in reduced oxygen pick-up. This paper presents the stoichiometric analysis and depth profiling of these films by RBS and HIERDA technniques