P. M. Chan, J. C. Y. Chung, City University of Hong Kong, Hong Kong, Hong Kong
The application of nickel-titanium (NiTi) shape memory alloy (SMA) thin film in optical devices is introduced. An uncooled imaging sensor design that utilizes the thermo-mechanical properties of NiTi SMAs for detecting far infrared (IR) radiation is fabricated. NiTi SMA thin films have been prepared by d.c. magnetron sputter deposition and made into two-dimensional cantilever arrays by photolithography. The thickness and the composition of the film are approximately 5 μm and 49.75 at.%Ti respectively. After the crystallization and aging processes, the NiTi SMA thin films exhibited phase transition at near room temperatures which corresponds to the R-phase transition. Upon the absorption of IR radiation, NiTi SMA thin film is heated up and results in the reverse R-phase transition. Illumination of the micro-array can increase the temperature locally and cause bending of the two-way shape memory (TWSM) thin film. The projected images are further modified with the aid of an optical readout technique that eliminates cross talk problem.
