Adhesion and interfacial structure of magnetron sputtered TiNi films on Si/SiO2 substrate

Shape memory alloy TiNi films were prepared on Si and Si/SiO2 by co-sputtering of TiNi target (Ti 50 at.% and Ni 50 at.%) and Ti target (99.999 at.%). When comparing Si/TiNi with Si/SiO2/TiNi, the addition of SiO2 sandwich layer did not result in significant change in the crystalline structures and shape memory properties. The SiO2 sandwich layer served as an effective diffusion barrier in preventing formation of interfacial titanium silicide at the expense of film adhesion. As revealed by X-ray photoelectron spectroscopy, under the same conditions, the interfacial diffusion zone in Si/TiNi system was approximately 120 nm while in Si/SiO2/TiNi system the diffusion zone was only approximately 30 nm—a four-fold reduction in inter diffusion. Meanwhile, the scratch adhesion testing registered a sharp drop in adhesion of the film from 170 mN in Si/TiNi system to 60 mN in Si/SiO2/TiNi system.