Mastering parasitics in complex MEMS circuits

Because of the tight coupling between closely spaced 3-D elements, parasitic effects often degrade the overall performance of complex MEMS circuits. A single-pole-double-throw (SPDT) switch in CPW technology consisting of a T-junction with one series-resistive and one shunt-capacitive MEMS switches per arm has been fabricated and tested. Parasitic coupling is shown to significantly affect the isolation of the isolated arm. While full-wave EM simulators would lead to unaffordable computational efforts to master such phenomena, a simple yet accurate planar approach recently presented is employed to effectively model and predict the behaviour of both the whole SPDT and its components. Having identified the portions of the circuit responsible for the spurious coupling, the planar approach has been used to modify the geometry of the shunt MEMS so as to minimize the parasitics, yielding a significantly improved performance of the SPDT.