Design of Multi-actuation RF MEMS Switch Using CMOS Process

Abstract

This work demonstrates a capacitive RF (radio frequency) MEMS (micro-electromechanical systems) switch, which is actuated by electro-thermal force and electrostatic force at the same time, and than latching the switching status by electrostatic force only. Since thermal actuator need relative low voltage compare to electrostatic actuator, for electrostatic force need almost no power to maintain the switching status. The benefit of this mechanism is very low actuation voltage and low power consumption. This RF MEMS switch has considered the issues for integrated circuit compatible including process and package between MEMS device and IC (integrated circuit). So it fabricated by standard 0.35 mum 2P4M (double polysilicon four metal) CMOS (complementary metal oxide semiconductor) process and then post- processed by wet etching. The structure of the switch consists of a set of CPW (coplanar waveguides) transmission lines and a suspended membrane. Both the CPW and the membrane are the metal layers in CMOS structure. Besides, electro-thermal actuators are designed by polysilicon layer because of the higher resistance than metal. So one of the main advantages of the RF switch is only CMOS process layers are needed for both electro-thermal and electrostatic actuations in switch. Moreover, the bimorph thermal actuator is designed by a stacked step structure including two metal layers, so no additional MEMS processes are needed. Measured results show that the actuation voltage of the switch is around 7 V. The insertion loss of the RF switch in the ON state is -2.5 dB at 5 GHz, and the isolation of the OFF state is -4.1 dB relatively.