Electrostatic micromechanical actuator with extended range of travel

The practical design issues of an electrostatic micromechanical actuator that can travel beyond the trademark limit of conventional actuators are presented in this paper. The actuator employs a series capacitor to extend the effective electrical gap of the device and to provide stabilizing negative feedback. Sources of parasitics-from layout and two-dimensional nonuniform deformation-that limit the actuation range are identified and their effects quantified. Two "folded capacitor" designs that minimize the parasitics and are straightforward to implement in multiuser microelectromechanical processes are introduced. The effects of residual charge are analyzed, and a linear electrostatic actuator exploiting those effects is proposed. Extended travel is achieved in fabricated devices, but is ultimately limited by tilting instabilities. Nevertheless, the resultant designs are smaller than devices based on other extended-travel technologies, making them attractive for applications that require high fill factors.