Modeling of an out-of-plane capacitive MEMS transducer with dynamically coupled electrodes

This paper presents a system-level, physic-based compact model of a novel out-of-plane capacitive MEMS transducer based on a combination of plate- and comb-capacitor drives. Unlike conventional plate-capacitor-like transducers both electrodes of this novel device are movable. This feature results in a device dynamics analogous to a weakly coupled two-degree-of-freedom oscillator system. An analysis of the governing electro-mechanical and fluid-mechanical coupling effects is presented together with an analytical description of the dynamics of the coupled electrodes. The proposed model can be simulated with the help of standard circuit simulation software enabling both transient and small signal analysis. Dynamic measurements performed on prototype devices in a low-pressure environment are used to calibrate and validate the model. Sensitivity enhancement and resonance frequency shift due to electrostatic spring softening are self-consistently included in the model since the interaction among mechanical, electrical, and fluidic domain is implemented on a physical basis. The presented study provides accurate physical understanding of the device, which can be employed to analyze and improve the transducer characteristics. The energy-coupled and modular modeling approach enables the extension of the model to investigate the performance of the device under the impact of the surrounding atmosphere and the effects of device packaging.