An Electrothermally Actuated VO2-Based MEMS Using Self-Sensing Feedback Control

A self-sensing approach is used to accurately control the large displacements observed in VO₂-based microelectromechanical systems actuators. The device is operated electrothermally using integrated resistive heaters. The coupling of the abrupt electrical and mechanical changes in VO₂ films across its phase transition allow for the estimation of the device´s deflection by monitoring the film´s resistance. Furthermore, the typical hysteretic behavior observed in VO₂ films is significantly reduced in the present device and the need for optical testing equipment is eliminated. The displacement-resistance relationship is modeled by a memoryless Boltzmann function consisting of four parameters, which are optimized to fit the experimental data with an average error of 1.1 μm throughout the complete actuation range of 95 μm. The estimated deflection is used as feedback to achieve closed-loop micropositioning control of the device, which is designed from the system dynamics obtained experimentally. Closed-loop sinusoidal and step reference response experiments are performed in order to show the effectiveness of the self-sensing feedback technique used. In the closed-loop sinusoidal frequency response, a cutoff frequency of 43 Hz is observed with a maximum actual deflection error of 0.19 dB up to the phase margin frequency of 30 Hz. In the step response, an average actual displacement steady-state error of ±1.15 μm is obtained with response times ranging from 5 to 12 ms.