An audio frequency filter application of micromachined thermally-isolated diaphragm structures

This paper reports a new application of micromachined thermally-isolated diaphragm structures for audio frequency filters. We have used a pair of electrothermal elements that consist of a heater and a temperature sensor integrated in the same dielectric diaphragm for a good thermal coupling. The filters using the fabricated electrothermal structures with driving circuitry have been tested. Measured responses of the filters show that a cutoff frequency can be electrically tuned ranging from 30 Hz to 300 Hz. Design parameters with respect to filter characteristics have been analyzed and design guidelines have been identified. The results have demonstrated the possibility that the thermally-isolated diaphragm structures can be used for audio frequency filter applications.