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Employing novel surface micromachining techniques, a highly miniaturized, robust device has been fabricated. The accelerometer fulfills all requirements of state-of-the-art airbag systems. The present paper reports on the manufacturing and assembly process as well as the performance of the sensor. The capacitive sensing element consists of a moveable proof mass of polysilicon on a single crystalline silicon substrate. A lateral acceleration displaces the proof mass and a capacitive signal is generated at a comb electrode configuration. An external IC circuit provides the signal evaluation and conditioning in a closed loop mode, resulting in low temperature dependency of sensor characteristics and a wide frequency response. The sensor is fabricated by standard IC processing steps combined with additional surface micromachining techniques. A special deposition process in an epitaxial reactor allows the fabrication of moveable masses of more than 10 µm thickness.

For side airbag systems it is necessary to measure the acceleration within a time of less than 3 ms in order to inflate the side airbag in time. A new generation of side airbag sensors that uses a linear accelerometer is presented. The evaluation circuit includes amplification, temperature coefficient compensation, two wire unidirectional current interface, and a zero-offset compensation. The sensing element for the measurement of acceleration is a surface micromachined accelerometer. In order to minimise the production costs the surface micromachined sensor element and the corresponding evaluation ASIC are packaged into a standard PLCC28 housing. For the entire function only few external components are necessary. During the power-on cycle an internal selftest is carried out and the result is transmitted to the airbag control unit. Most important results of the characterisation are presented.