On the Small-Signal Capacitance of RF MEMS Switches at Very Low Frequencies

This paper presents on-wafer capacitance measurements of silicon-based RF MEMS capacitive switches down to frequencies below 1 Hz. The capacitance-voltage (C-V) curve measured at very-low frequency (0.01-10 Hz) deviates from the commonly measured and well-understood high-frequency C-V curve, especially near the pull-in and pull-out voltages. This behavior is explained from the mechanical action of the top electrode. An electrostatic transducer model is used to express the coupling between mechanical and electrical behavior of the device under study. The mechanical action and air damping play an important role at the lower measurement frequencies, as confirmed by vibrometer measurements, FEM modeling and experiments at reduced pressure.