Effect of Stress on Pull-in Voltage of RF MEMS SPDT Switch

Abstract

RF MEMS switches are well known to exhibit performance superior to solid-state devices. However, electromechanical issues, such as repeatability and higher pull-in voltage, are a matter of concern. MEMS switches generally consist of metallic beams which curl up or down based on stresses in the structure. Stress-induced curling-up phenomenon, in such structures, increases the gap between the actuating electrode and the freely suspended metallic structure which in turn increases the pull-in voltage. This article focuses on simulations and curve fitting to analyze the effect of stress on pull-in voltage. The pull-in voltage of the switch is proportional to stress, and accordingly, its dependence on in-built stress and Young's modulus is analyzed. In addition to mechanical analysis, RF response of the single pole double throw (SPDT) switch is discussed as a case study. Measured stress and pull-in voltage of the SPDT switch is 50 MPa and 16 V. In the presence of stress, the curled-up cantilever switch shows measured isolation better than 31 dB for dc to 10-GHz range.