Sensitivity study of comb-drive actuator with folded suspension

Comb-drive electrostatic actuators are widely used in micron scale devices. The main failure mechanisms of this kind of actuator include electrostatic instability as well as the inability to meet performance requirements imposed by their particular applications. In the present work, the sensitivity of the comb-drive actuators of different configurations to the actuator geometry and ambient temperature are studied both theoretically and experimentally. Displacement-voltage dependence, stability range and natural frequencies are used as output parameters. Models of the actuator include definitions based on an extensible elastica theory as well as reduced order models. The influence of secondary compliances of the structure is studied using the Finite Element Method. Results produced by the models, and proven experimentally, show that the location of the instability point is sensitive to geometric imperfections and secondary compliances while the influence of temperature is relatively minor. Highly uncertain fabrication tolerances may lead to a significant reduction in the stiffness of the device. Stiffness parameters are extracted by fitting the static and dynamic responses as well as direct measurements of the device geometry.