Shaped comb fingers for tailored electromechanical restoring force

Abstract

Electrostatic comb drives are widely used in microelectromechanical devices. These comb drives often employ rectangular fingers which produce a stable, constant force output as they engage. This paper explores the use of shapes other than the common rectangular fingers. Such shaped comb fingers allow customized force-displacement response for a variety of applications. In order to simplify analysis and design of shaped fingers, a simple model is developed to predict the force generated by shaped comb fingers. This model is tested using numerical simulation on several different sample shaped comb designs. Finally, the model is further tested, and the use of shaped comb fingers is demonstrated, through the design, fabrication, and testing of tunable resonators which allow both up and down shifts of the resonant frequency. The simulation and testing results demonstrate the usefulness and accuracy of the simple model. Finally, other applications for shaped comb fingers are described, including tunable sensors, low-voltage actuators, multistable actuators, or actuators with linear voltagedisplacement behavior. [879] Index Terms-Tunable resonators, variable gap electrodes. I. INTRODUCTION T HE 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 interdigitated conductive combs. Because of its capability of force generation or varying capacitance, 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 radio frequency (RF) filters [6]. Consequently, any improvement to this basic actuator could have far-reaching effects.

Design and fabrication of a SU-8 based electrostatic microactuator

“…Johnson and Warn (1995) then reported a physical analysis. Ye and Jensen proposed optimal shaped comb designs such as quadratic or cubic force profiles under constant bias voltage to produce highly linear forcedisplacement behavior (Ye 1998;Jensen et al 1998). Zhou and Dowd (2003) presented tilted folded-beam suspension to extend the stable travel range of combdrive microactuators using the low voltage.…”

A Survey of Modeling and Control Techniques for Micro- and Nanoelectromechanical Systems

“…Though simulated results reportedly showed improved performance, practical implementation of this rigorously mathematical technique may be quite challenging. Recently, MEMS actuator designs are being modified to give better open-loop performance, [105]. An improved modeling technique that resulted in open-loop control of a tunneling accelerometer for very high resolution acceleration measurement was reported in [106].…”

System integration of high voltage electrostatic MEMS actuators

“…A typical MEMS electrostatic actuator is the Straight Comb [11]. This MEMS device can be used for diverse applications.…”