Dielectric material selection for high capacitance ratio and low loss in MEMS capacitive switch using ashby's methodology

Abstract

The performance of the RF MEMS capacitive switch is majorly decided on capacitance ratio and loss in the dielectric layer as they decide the isolation (in dBs) in off condition. The capacitances in a MEMS capacitive switch in pull-up and pull-down states are used for deciding the capacitance ratio. In this article, we have presented a method to find out the best dielectric material using Ashby's methodology for high capacitance ratio and low loss thus high isolation in switch off condition. Firstly, a database of 10 mostly employed dielectric materials have been created, and then, material indices are derived using material properties such as dielectric constant, resistivity, conductivity, and loss tangent which have been used in the selection of dielectric material. Through the study it is observed that to have a high capacitance ratio and low loss in dielectrics, the down capacitance should always be much greater than pull-up capacitance and tangent loss must be kept at possible minimum. This method will be highly useful in the selection of the best dielectric material by switch designers.