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TiNi shape memory alloy thin film rotating micro-actuators

Authors Ma, Cho Chiu
Issue Date 1999
Summary Titanium nickel (TiNi) shape memory alloy (SMA) thin film is a promising candidate for micro-actuation because of its large deformation and recovery force, good electrical and mechanical properties, long fatigue life, and high corrosion resistance. The work output per volume of thin film SMA micro-actuators exceeds that of the other micro-actuation mechanisms such as electrostatic, magnetic, thermal bimorph, piezoelectric, and thermo-pneumatic. In this research, techniques for depositing and characterizing TiNi thin films are evaluated, and micro-machining and design issues for SMA actuators are discussed. A micro-machined shape memory-actuated rotating micro-actuator also is presented. TiNi thin films were deposited by RF magnetron sputtering and patterned by HF-HNO3 wet etching. The as-sputtered thin films were amorphous. They were heat-treated at 750℃ for 30 minutes and followed by aging at 500℃ for 100 hours. The compositions were determined by X-ray fluorescence (XRF). The depth profile, the transformation temperatures, the lattice constants and the micro-structures were characterized by X-ray photo-emission spectroscopy (XPS), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM), respectively. It was clear that the transformation temperatures increased with increasing applied stress and aging time. In addition, in situ TEM observation showed that the R-phase and the martensitic phase transformation took place upon cooling. An SMA rotating actuator had been fabricated by controlling the conditions of sputtering and annealing, and demonstrated to have a two-way shape memory effect, with flat frequency response up to 2Hz and maximum amplitude of 4μm. The rotating micro-actuator was found to be very attractive to perform work in Micro-Electra-Mechanical Systems (MEMS).
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 1999
Language English
Format Thesis
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