Optimization of thermal deflection in NiTi-based bimorph microactuators

The optimization of the microactuation of shape memory alloy films in bimorph architectures was analysed for various film thickness and substrates material architectures, based on a known model that uses the fraction of phases during the martensitic transformation to evaluate the properties of the shape memory alloy film. It was shown by appropriately selecting the substrate material it is possible to maximize the deflection of the tip of a cantilever-type microactuator. For NiTi films, the increase of the active material thickness, as expected, leads to increased actuation, however the thermoeleastic properties of the substrate contribute to the stress achieved at the onset of the martensitic phase transformation, with higher values corresponding to larger actuation. Also depending on the thermoelastic constants of the substrate, the curvature of the cantilever-type microactuator can be toward the deposited film or toward the substrate. Si, Mo and Ti generated bending toward the shape memory alloy film, while Ni, stainless steel and Upilex S ended up bending toward the substrate. The result are important for the prediction of complex actuation complex architectures with potential to be used in micro-electromechanical systems.