SHAPE MEMORY EFFECT IN ULTRA-THIN NICKEL TITANIUM ALLOY FILMS DEPOSITED BY BIASED TARGET ION BEAM DEPOSITION

Open Access
Author:
Tang, Yuan
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Mark Horn, Thesis Supervisor
  • Sean Brennan, Honors Advisor
Keywords:
  • niti
  • nickeltitanium
  • btibd
  • biased target ion beam deposition
  • thin film
  • fast actuation
  • mems
  • shape memory alloys
Abstract:
The need for high performance microelectromechanical systems (MEMS) has driven the industry to research ultra-thin shape memory alloy (SMA) films, specifically for microactuators capable of rapid actuation [1]. Biased target ion beam deposition (BTIBD) is a novel technique that can produce high quality films with thicknesses less than 1000 Å [2]. Nickel-titanium (NiTi) thin films with different composition ranges (Ni-poor/Ti-rich, near equiatomic NiTi, and Ni-rich), various thicknesses, and post-deposition annealing were deposited using BTIBD by Dr. Huilong Hou at the Penn State University [2 – 4]. The shape memory effect in NiTi films can be detected by measuring the thin film stress as a function of temperature. Stress measurements during heating and cooling were made on a variety of films using laser-based system that measures substrate. Additionally, cyclic tests, up to 100 heating-cooling cycles, were conducted to evaluate the stability of the phase transformation in subset of the deposited films. In several films that were 800 nm thick, thermal stress measurements showed a distinct hysteresis indicative of a functional shape memory effect in these films. These same films also showed that the effect was repeatable even after 100 temperature cycles.