Title: A Low Power/Low Voltage Electrostatic Actuator for RF MEMS Applications
Abstract: We have designed and fabricated a low power / low voltage electrostatic actuator, and demonstrated its application to a large tuning-ratio tunable capacitor for RF MEMS applications.Using adhesive bonding and deep silicon reactive ion etching techniques, the entire MEMS device is made of single crystal silicon, and is suspended over a glass substrate.A coat of aluminum is sputtered on after the dry release in an oxygen plasma to provide good electrical conductivity for the integrated RF devices.An electrostatic deflection of 23 l.trn has been demonstrated with an applied voltage of 5.2 V, and has resulted in the tunable capacitor having a maximum continuous tuning ratio in excess of 4.5 to 1. Alternative devices with a required low tuning voltage of 3 V have also been demonstrated to provide a tuning ratio of 2 to 1.The power consumption of this actuator is linearly proportional to the actuation frequency, and is in the range of 10's of nano-Watts when the device is actuated at a frequency of a few kHz.less than lo), and a low electrical self-resonance caused by large parasitics.Drastic measures are often required for the solid-state components to improve on one single parameter; for example, the use of light power to increase the tuning ratio [2].Recent efforts within the MEMS field [3-91 have shown promising results in the realization of MEMS-based high performance tunable capacitors.Many shortcomings of solid-state varactors have indeed been overcome in these MEMS-based devices.Parameters already improved using the MEMS approaches include equivalent series resistance and Q factor, capacitance tuning-ratio, associated parasitic capacitance, and intrinsic inductance and electrical selfresonance.This paper addresses the low actuation power and voltage requirement of the tunable capacitor device, and discusses in detail a massively parallel electrostatic actuator for RF MEMS applications.