Assessing micromechanical sensor characteristics via optical and electrical metrology

This paper presents a custom instrument for the static and dynamic electrical characterization of capacitive MEMS sensors. Such a tool is useful for the validation of Finite Element Models (FEM) of MEMS prior to device operation, for the estimation of process parameters and consequent variance in the device performance, and for endurance tests. The core of the instrument consists of the capacitive sensing electronics, which in this work features a novel demodulation scheme, based on active Schottky diodes rectifying. As an example, a complete electro-mechanical characterization of a micro-machined charge sensor is performed for three different packaging conditions. A data reduction procedure is used to estimate the mechanical device parameters (flexure stiffness, natural frequency, and quality factor) and unknown process parameters like the over etching. The results are cross-validated using stroboscopic image captures, obtained through a Planar Motion Analyzer and then compared to FEM simulations.