SHAPE MEMORY EFFECT IN ULTRA-THIN NICKEL TITANIUM ALLOY FILMS DEPOSITED BY BIASED TARGET ION BEAM DEPOSITION
Area of Honors:
Bachelor of Science
Mark William Horn, Thesis Supervisor Dr. Sean N Brennan, Honors Advisor
niti nickeltitanium btibd biased target ion beam deposition thin film fast actuation mems shape memory alloys
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 . Biased target ion beam deposition (BTIBD) is a novel technique that can produce high quality films with thicknesses less than 1000 Å . 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.