Fabrication of TiNi shape memory alloy microactuators by ion beam sputter deposition

Abstract

TiNi shape memory alloy has been recently investigated for use in micro actuators because of the high power to volume ratio. Conventional sputtering methods, such as RF and DC sputtering and magnetron sputtering, have previously been used by other workers in order to deposit TiNi thin films. As-deposited films produced by these methods are amorphous, and are then crystallised typically by annealing at 500°C for 1 hour in order to exhibit the shape memory effect. These deposition methods have invariably used alloyed targets to grow thin films. In this thesis, an Ion Beam Sputter Deposition (IBSD) method has been used by which argon ions are used to bombard nonalloyed targets. The thin films grown by this technique demonstrate the characteristics of the shape memory effect. Films have been characterised by electrical resistivity, resistance and thermal measurements, giving physical properties in excellent agreement with those quoted in the literature. Compositional and density measurements were done by X-ray reflectometry and were consistent with equi-atomic composition and nominal density for TiNi. In addition thermal modelling was used to investigate implications of heating and cooling rates for microactuator operation. Finally, a novel fabrication process is proposed, combining ion beam milling and Focused Ion Beam (FIB) trepanning for the process of micro actuator production