Evaluation of MEMS Capacitive Accelerometers

Capacitive based microelectromechanical systems (MEMS) accelerometers are devices that measure acceleration based on a change in capacitance due to a moving plate or sensing element. These devices have been implemented in many commercial applications, such as automobile air bags, navigation, and instrumentation. These devices have been employed in these and many other applications because they generally offer more sensitivity (more mV/g) and more resolution than similar piezoresistive accelerometers. For most commercial applications, the maximum g-sensing level (MGSL) employed in capacitive accelerometers is 500 gn. However, in many applications, there can be high-frequency components to an acceleration profile that are much higher than the MGSL of an accelerometer. For example, in vibration monitoring of a hard drive, the peak acceleration can be as high as 10 kgn. The response and recovery times of an accelerometer to such shock over range are important in many critical applications. In this article, three commercial MEMS-based capacitive accelerometers (Silicon Designs, Inc. 1220, Analog Devices ADXL, 181-1000, and Endevco 7290A-100) are evaluated below and above their respective MGSLs. The output of these devices is compared to that of an Endevco piezoresistive 7270-A accelerometer and an Endevco 2270 comparison standard accelerometer. The emphasis on this investigation is to determine the response of these devices to high-g shock levels and to evaluate their failure modes