Thermo-mechanical characterization of optical thin films filters deposited onto shape memory alloy micro-actuators

Abstract

Different optical thin films filters have been deposited by plasma techniques onto shape memory alloy micro-actuators controlled by the heating of laser irradiations. Thermomechanical cycles have been performed to investigate the stability of these optical filters. Excellent properties have been obtained with amorphous hydrogenated silicon/silica and amorphous hydrogenated silicon/plasma polymerized methacrylic acid-based filters; no degradation was observed after up to 50 000 cycles. Other silver/plasma polymerized methacrylic acid-based filters, which have a better selectivity and permit the use of more laser sources of different wavelengths for optical actuation, showed lower stability. The optical-filtering properties are lost during the thermomechanical cycles, due to a rearrangement of the silver atoms with heating. Thus, there is a trade-off between wavelength selectivity and the stability of the structures used for the optical control of the micro-actuators.