In this work, a vanadium dioxide (VO2)-based micro-electro-mechanical actuator has been successfully designed, fabricated, characterized and controlled to achieve accurate displacements through the monolithic integration of a localized heater and self-sensing mechanism. VO2 is a solid-to-solid phase transition material whose electrical, structural, and optical properties change abruptly as a function of temperature. Recent integration of this material in micro-actuators has shown strain energy densities, displacements, actuation speeds, and repeatability values comparable or, in some cases, superior to state-of-the-art micro-actuator technologies. Previous studies on VO2 micro-actuators focus on open-loop manipulation of the device deflection, whose performance is highly susceptible to environmental disturbances and noises. In order to obtain accurate deflection control in micro-actuators, a closed-loop configuration is generally employed, which involves the use of external or internal displacement sensors. The incorporation of these sensors in micro-actuators usually increase design complexity, fabrication cost, and system footprint. Due to the multifunctional nature of VO2, a self-sensing technique is achieved, where the micro-actuator deflection is estimated through VO2 resistance measurements. In addition, the resistance-deflection hysteretic behavior is largely reduced due to the strong correlation between the electrical and structural transition, which greatly simplifies the self-sensing model. The closed-loop deflection control of these devices using self-heating actuation is also studied through voltage and current control, which reduces the need for additional heating components.
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