On the lower thickness boundary of sputtered TiNi films for shape memory application

Fu, Yong Qing, Zhang, Sam, Wu, M. J., Huang, Wei Min, Du, Hejun, Luo, Jikui, Flewitt, Andrew and Milne, William (2006) On the lower thickness boundary of sputtered TiNi films for shape memory application. Thin Solid Films, 515 (1). pp. 80-86. ISSN 0040 6090

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Abstract

In this paper, we study the effects of film thickness on phase transformation of constrained Ti50.2Ni49.8 films deposited onto silicon substrates. When the film is too thin, surface oxide and interfacial diffusion layers exert dominant constraining effect that renders high residual stress and low recovery capabilities in the film. The surface oxide and inter-diffusion layer restricts the phase transformation, alters stoichiometry of the remaining TiNi film, and reduces volume of the material available for phase transformation. As a result, a lower thickness boundary (about 100 nm) exists for TiNi films to remain “shape remembering”. Results indicate that a maximum recovery stress and actuation speed can be realized with a thickness of about 800 nm. Based on the curvature measurement results, the relationship between the relative stress and strain of the films (during phase transformation with change of temperature) can be derived.

Item Type:	Article
Uncontrolled Keywords:	TiNi; Thin film; Thickness; Sputtering; Shape memory
Subjects:	F200 Materials Science
Department:	Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User:	Becky Skoyles
Date Deposited:	27 Mar 2015 09:53
Last Modified:	12 Oct 2019 19:06
URI:	http://nrl.northumbria.ac.uk/id/eprint/21876

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