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

Abstract

This paper reports a new application of micromachined thermally-isolated diaphragm structures for audio frequency filters. A pair of electrothermal elements that consist of a heater and a temperature sensor integrated in the same dielectric diaphragm have been used as a basic filter component. The electrothermal response of the diaphragm structure has one-pole, low-pass filtering characteristics. Various filter configurations using the fabricated electrothermal structures with driving circuitry have been tested. Measured responses of the filters show that cut-off frequencies can be electrically tuned, ranging from 30 to 300 Hz. Design parameters and guidelines have been identified and analyzed with respect to filter characteristics. The results have demonstrated the possibility that the thermally-isolated diaphragm structures can be used for audio frequency filter applications. (C) 2001 Elsevier Science B.V. All rights reserved.