Controlling Levitation and Enhancing Displacement in Electrostatic Comb Drives of MEMS Actuators

Capacitive comb actuators are widely used as MEMS motors due to their long range of linear motion, low power consumption, and ease of fabrication. Here, we present data from a thin comb capacitive actuator where fringe fields contribute significantly to the device performance. We characterize the observed levitation effect and discuss two methods to control the out-of-plane forces: 1) by means of alternating the comb polarity; and 2) by using an additional electrode below the comb. Considering two alternative designs, it is shown how the levitation force can be mitigated. One design decreases the out-of-plane motion by a factor of two, but also reduces the lateral range. An alternative design proved successful in decreasing out-of-plane motion by 75%, while enhancing the in-plane displacement of the linear comb actuator by over 35%.