A current density distribution approach to the optimisation of RF-MEMS variable capacitors

An argument for the geometry based frequency range extension of tunable MEMS capacitors is presented. It is shown that, besides reducing the length of the feed arms, the parasitic inductances in a parallel-plate MEMS capacitor can be reduced further by optimising the plate geometry. Extension of the self resonance frequency is demonstrated with reduced circumference of the plate, due to high-frequency currents travelling around the edge of the plate and acting as a major component affecting the self-resonance frequency (SRF) of the capacitor. Full-wave 2.5-D electromagnetic simulation results using Agilent EEsof's ADS Momentum [1] are presented that demonstrate the improvement in selfC, C, resonance frequency of circular and symmetrically fed structures. It is shown that efforts in shortening current paths by means of slots did not yield significant further improvement.