Texture development and phase transformation behavior of sputtered Ni-Ti films

It is essential to identify and control the preferential orientation of Ni-Ti shape memory alloy (SMA) films since it is a crucial factor in determining the shape memory behavior. In the present work, in situ studies by synchrotron radiation scattering enabled to identify the different steps of the structural evolution of Ni-Ti films during co-sputtering deposition. For micro-electromechanical systems (MEMS) integration, there is a need for an electrically and thermally insulating or sacrificial layer. Widening the scope of previous experiments concerning the influence of the deposition parameters on the structure of the Ni-Ti films, the incorporation of a TiN buffer layer has been tested. Here, it is established a relationship between the TiN substrates and Ni-Ti texture development (B2 phase). Ni-Ti films mainly containing grains with (110) or (211) planes of the B2 phase parallel to the film surface could be produced using TiN buffer layers with distinct thickness values. The electrical resistivity measurements performed during temperature cycling have shown that the crystallographic orientations of the Ni-Ti films influence their phase transformation characteristics. The resistivity increase during R-phase transformation, especially visible on cooling, is higher for Ni-Ti films with a higher fraction of grains of the B2 phase with (211) parallel to the film surface.