Design and Simulation of Shaped Comb Fingers for Compensation of Mechanical Restoring Force in Tunable Resonators Extended Abstract

INTRODUCTION The comb-drive actuator is one of the main building blocks of microelectromechanical systems (MEMS). Its working principle is based on an electrostatic force that is generated between biased conductor plates as one moves relative to the other. Because of its capability of force generation, it finds wide application in micro-mechanical systems. Sample applications include polysilicon microgrippers [1], scanning probe devices [2], force-balanced accelerometers [3], actuation mechanisms for rotating devices [4], laterally oscillating gyroscopes [5], and RF filters [6]. Consequently, any improvement to this basic actuator could have far-reaching effects. Specifically, we are interested in shaped comb finger designs which would generate force-deflection profiles that have linear shapes. These linear relationships could partially compensate for the mechanical restoring force due to the action of a linear suspension spring. This electrostatic weakening or stiffening of the mechanical spring can decrease the drive voltage of actuators or change the resonant frequency of resonators. Several previous researchers have investigated various comb shapes. Hirano et al. [7] reported techniques for fabricating fingers which could dramatically reduce the separation gap after only a short motion. These fingers were designed for maximum possible force output at a nearly constant rate. Rosa et al. [8] continued this search for high-force actuators by designing and testing actuators with angled comb fingers. Ye et al. [9] studied directly the force-deflection behavior of a number of finger designs using a two-dimensional numeric electrostatic solution. They reported designs with linear, quadratic, and cubic behavior. This work focuses on designing, modeling, and testing of shaped comb fingers with linear force profiles for use in tunable resonators. A tunable resonator designed using the principles outlined here has been designed with stiffness tuning of up to 50% at 100 V tuning voltage, compared to 4.9% stiffness tuning (for a weaker spring) in an earlier work [6]. This extended abstract describes the key points of the work.