Performance of Electro-Thermally Driven ${\rm VO}_{2}$-Based MEMS Actuators

Abstract

The integration of VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films in a MEMS actuator device is presented. The structural phase transition of VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was induced electro-thermally by resistive heaters monolithically integrated in the MEMS actuator. The drastic mechanical displacements generated by the large stress induced during the VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film phase transition have been characterized for static and time-dependent current pulses to the resistive heater, for air and vacuum environments. A comprehensive and simplified finite element model is developed and validated with experimental data. It was found that the cut-off frequency of the 300 μm-long VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based MEMS actuator operated in vacuum (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> =29 Hz) was mostly limited by conductive heat loss through the anchor, whereas convection losses were more dominant in air (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> =541 Hz). The cut-off frequency is found to be strongly dependent on the dimensions of the cantilever when operated in air but far less dependent when operated in vacuum. Total deflections of 68.7 and 28.5 μm were observed for 300 and 200 μm-long MEMS cantilevers, respectively. Full actuation in air required ~ 16 times more power than in vacuum.