Generation of third and higher-order intermodulation products in MEMS capacitors, and their effects

In this work, the intermodulation distortion (IMD) produced by RF MEMS capacitors is studied. It is demonstrated that due to their nonlinear behaviour, parallel-plate MEMS capacitors generate 5th order tones along with 3rd order IMD products. It is shown that MEMS linear models, restricted to small displacements of the MEMS membrane, neglect 5th order distortion while underestimate 3rd order tones, when high voltages are considered. A numerical nonlinear model for simulating intermodulation is presented and validated by means of measurements for the general 2-tone case. Generation of 3rd and 5th IMD products is also demonstrated in MEMS driven by digitally-modulated communication signals. A measurement system is proposed in order to characterize IMD generation in RF MEMS capacitors excited by two RF tones as well as by digitally-modulated signals (QPSK).