Thick-polysilicon-based surface micromachined capacitive accelerometer with force-feedback operation

This paper describes the concept, the design and measurement results of a surface micromachined accelerometer. For the accelerometer presented here a polysilicon high rate deposition process was used to fabricate polysilicon layers with a thickness of 10 micrometers . The sensor is designed as an interdigital finger structure forming a differential capacitor, where the moveable fingers are mounted on a moveable mass and the fixed electrodes are anchored on the substrate. The air gap between the fingers is 1 micrometers . A force-feedback operation mode is realized to increase the sensor performance. A two chip solution with sensing element and signal processing circuit on separate chips was chosen as first approach towards a monolithic integrated accelerometer. The evaluation circuit was realized in BiCMOS technology. Sensors with a closed-loop sensitivity of 8mV/g and a bandwidth of about 10kHz have been fabricated. A resolution of 0.1g and a linearity error of less than 1% could be achieved for a measurement range of +/- 100 g.