Capacitive MEMS Accelerometer With Perforated and Electrically Separated Mass Structure for Low Noise and Low Power

Abstract

A capacitive MEMS accelerometer with superior features, namely low cost, low noise, and low-power consumption, for a large sensor network was developed. To achieve both low noise and low-power consumption, a sensor architecture with a unique perforated and electrode-separated mass structure was devised. The MEMS elements were fabricated by using silicon-on-insulator wafers with 60- $\mu \text{m}$ -thick device layer and 380- $\mu \text{m}$ -thick handle layer for providing mechanical and electrical features independently. Two layers of perforation (which penetrates through the inertial mass) were designed by finite-element simulation for low mechanical noise. This design makes it possible to fabricate the inertial mass by a deep reactive ion etching process and to seal the MEMS element by a low-cost getter-less commercial packaging. A separated-servo-mass architecture is implemented with differential amplifiers for low electrical noise and low-power consumption by isolating the pick-off nodes for signal detection and the servo nodes for servo control electrically while maintaining the mechanical rigidity of the entire mass. A single-axis accelerometer implemented with the MEMS element and readout circuits demonstrated excellent performance with a low noise floor of less than 30 nG/ $\surd $ Hz and a low-power consumption of 20 mW in a getter-less vacuum ceramic package.