Determination of intermodulation distortion in a contact-type MEMS microswitch

Finite-element simulations have been used to predict intermodulation distortion in a gold-on-gold contact-type microelectromechanical systems microswitch. The simulations are used to find the variation in switch resistance with input power that is a result of temperature-dependent electrical resistivity and thermal conductivity. This resistance variation leads to intermodulation distortion. In a similar way, a closed-form expression is found for the variation of resistance with contact force. It is found that this also produces a variation in resistance due to the input voltage variation at high frequencies, which also leads to intermodulation distortion. The sideband power due to thermal effects was found to be -103dBc for a 1-W input signal leading to a third-order intermodulation intercept point of +81.3dBm. The sideband power due to contact force effects was found to be less than -140dBc for a 1-W signal. The methods for prediction of intermodulation distortion used in this paper are applied to measured data for the variation of resistance with switch current and gate voltage, leading to predictions of intermodulation levels based on real switch parameters. The effect of contact force on intermodulation can become significant if the difference frequency of the excitation is near the natural frequency of the device.