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 non-linear behaviour, parallel-plate MEMS capacitors generate 5/sub th/ order tones along with 3/sub rd/ order IMD products. It is shown that MEMS linear models, restricted to small displacements of the MEMS membrane, neglect 5/sub th/ order distortion while underestimate 3/sub rd/ order tones, when high voltages are considered. A numerical non-linear model for simulating intermodulation is presented and validated by means of measurements for the general 2-tone case. Generation of 3/sub rd/ and 5/sub th/ 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).