Micro-actuation design in VO2-based bimorph cantilevers

The temperature-dependent actuation of cantilever-type bimorphs based on VO2 active layers exhibiting a reversible phase transformation (known as the 'metal-to-insulator transition' (MIT)) between a semiconducting monoclinic phase, and a metallic tetragonal (rutile) phase, can be optimized for specific applications by convenient selection of several parameters, among which the nature of the passive layer material, the cantilever geometry (layers thickness, beam length), and also the deposition temperature (at which the active and passive layers are joined), or the temperature at which the as-manufactured bimorph is annealed (in both cases the curvature being zero), are of special importance. In this sense, a model for the thermally controlled actuation of such bimorphs, in which the thermo-elastic parameters of the two layers materials, and also the evolution of these parameters during the phase transformation are taken into account, has been developed. The analysis projects significant differences in the actuation, in terms of the deposition temperature position relative to the thermal range of the phase transformation in the active layer. The model is useful in predicting the profile of the temperature-controlled actuation for custom-engineered devices based on this transformation. Nevertheless, the model provides a very useful tool for the design of experiments and actuators based on such MIT bimorphs.