Design of a Time-Based Micro-g Accelerometer

Closed-loop pull-in time operated devices are a good alternative for high sensitivity accelerometers. This paper proposes the use of time measurement as the transduction mechanism for the realization of a high-precision accelerometer. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. The main design challenges for a pull-in time parallel-plate capacitive microelectromechanical system (MEMS) accelerometer are related to the damping and the associated tradeoff between sensitivity and noise is discussed. Parallel-plate MEMS structures designed and fabricated in a 25 μm-thick SOI micromachining process (SOIMUMPS) are used to demonstrate the accelerometer time-based approach and experimental results demonstrate a sensitivity of 0.25 μs/μg.