화학공학소재연구정보센터
Thin Solid Films, Vol.519, No.1, 122-128, 2010
Texture development, microstructure and phase transformation characteristics of sputtered Ni-Ti Shape Memory Alloy films grown on TiN < 111 >
Near equiatomic Ni-Ti films have been deposited by magnetron co-sputtering on TiN films with a topmost layer formed by < 111 > oriented grains (TiN/SiO2/Si(100) substrate) in a chamber installed at a synchrotron radiation beamline. In-situ X-ray diffraction during Ni-Ti film growth and their complementary ex-situ characterization by Auger electron spectroscopy, scanning electron microscopy and electrical resistivity measurements during temperature cycling have allowed us to establish a relationship between the structure and processing parameters. A preferential development of < 110 > oriented grains of the B2 phase since the beginning of the deposition has been observed (without and with the application of a substrate bias voltage of -45 and -90 V). The biaxial stress state is considerably influenced by the energy of the bombarding ions, which is dependent on the substrate bias voltage value applied during the growth of the Ni-Ti film. Furthermore, the present work reveals that the control of the energy of the bombarding ions is a promising tool to vary the transformation characteristics of Ni-Ti films, as shown by electrical resistivity measurements during temperature cycling. The in-situ study of the structural evolution of the growing Ni-Ti film as a consequence of changing the Ti:Ni ratio during deposition (on a TiN < 111 > layer) has also been performed. The preferential growth of < 110 > oriented grains of the Ni-Ti B2 phase has been as well observed despite the precipitation of Ti2Ni during the deposition of a Ti-rich Ni-Ti film fraction. Functionally graded Ni-Ti films should lead to an intrinsic "two-way" shape memory effect which is a plus for the miniaturization of Ni-Ti films based devices in the field of micro-electro-mechanical systems. (C) 2010 Elsevier B.V. All rights reserved.