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 um-thick SOI micromachining process (SOIMUMPS) are used to demonstrate the accelerometer time-based approach and experimental results demonstrate a sensitivityof 0.25 us/ ug.Fundação para a Ciência e a Tecnologia (FCT)ADI - Agência de Inovaçã

Fast step-response settling of micro electrostatic actuators operated at low air pressure using input shaping

Squeeze-film damping is highly inadequate in low-pressure systems or in systems where air pressure and/or gap dimensions are poorly defined. Input shaping has been used to circumvent the oscillations typically associated with under-damped mass-spring-damper systems and drastically decrease the settling time. The proposed method does not rely on feedback but solely on the system dynamics. The required input signal is derived analytically from the differential equation describing the system. The resulting device response is simulated and experimentally verified on an electrostatically actuated microstructure. Settling occurs even faster than for an equivalent critically damped system.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

Auto-calibration of capacitive MEMS accelerometers based on pull-in voltage

This paper describes an electro-mechanical auto-calibration technique for use in capacitive MEMS accelerometers. Auto-calibration is achieved using the combined information derived from an initial measurement of the resonance frequency and the measurement of the pull-in voltages during device operation, with an estimation of process-induced variations in device dimensions from layout and deviations in material properties from the known nominal value. An experiment-based analytical model is used to compute the required electrostatic forces required to simulate external accelerations allowing the electro-mechanical calibration of the accelerometer. Measurements on fabricated devices confirm the validity of the proposed technique and electro-mechanical calibration is experimentally demonstrated.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

Squeezed film damping measurements on a parallel-plate MEMS in the free molecule regime

This paper provides experimental validation of the predictions by two recent models for squeezed film damping in the free molecule regime. Measurements were carried out using a parallel-plate microstructure with a 2.29 ?m gap operated at pressures from 105 to 101 Pa (corresponding to Knudsen numbers from 0.03 to 300). Experiments are in good agreement with the modelling based on molecular dynamics at Knudsen numbers over 10. The result also indicates that modelling based on the modified Reynolds equation including inertia effects underestimates the damping due to end effects; however, it correctly predicts the trend for lower Knudsen numbers.Department of MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc