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In order to obtain the high-fidelity model of latching failure threshold power of the capacitive RF MEMS switch, it is necessary to find out the rough dielectric layer effect on its down-state capacitance degradation. The comparative modeling method between the 3-D electromagnetic simulation and the equivalent circuit simulation is proposed. First, the simulation curve of the switch isolation (S21) is attained at different roughness levels with the HFSS 3-D electromagnetic model. And then the simulation curve of the S21 of the ADS equivalent circuit model is consistent with the simulation result of the 3-D electromagnetic as far as possible by tuning the down-state capacitance in the equivalent circuit. Hence, the relationship between the dielectric layer roughness and the down-state capacitance is identified. By changing the roughness level of dielectric layer and repeating the above steps, the relationship between the dielectric layer roughness and the down-state capacitance degradation is identified. Rationality and feasibility of the method is verified by comparing the calculated values of the down-state capacitance with the measured values in a relevant literature. And analytical equation of the latching failure threshold power of the capacitive RF MEMS switch with perfect smooth dielectric layer is modified, according to the relationship between the dielectric layer roughness and the down-state capacitance degradation, which is also suitable for predicting the power handling capacity of the switch with rough dielectric layer.
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