The effect of Ni/Ti layered stack thickness on the interface amorphization behavior

Abstract A promising approach for synthesizing the NiTi alloy films with shape memory effect, which are of interest for modern nano- and microelectromechanical applications, is their thermally-activated formation from Ni/Ti layered structures. In such layered stacks composed of individual metal layers, their interfaces can partially blur already during deposition due to the diffusion-stipulated solid-state amorphization. In the present work, we intended to examine the effect of Ni/Ti bilayer thickness (modulation period, Δ) on the initial amorphization in 60-nm-thick films by means of structural and electrical resistivity measurements. It was revealed that as the Δ decreases from 60 nm to 20 nm it yields a larger amorphization effect, which resulted in (a) decrease of crystallinity (82% → 75%), (b) increment of electrical resistivity (81.78 μΩ·cm → 93.14 μΩ·cm); and (c) decrease of the temperature coefficient of resistivity (2380 ppm °C −1 → 1890 ppm °C −1 ). Considering the necessity of finding a compromise between a small modulation period (which enhances amorphization) and a large modulation period (which increases the effective diffusion length), the most promising candidate for advanced MEMS applications seems to be the films with an intermediate modulation period.