Self-Calibrating Micromachined Microphones with Integrated Optical Displacement Detection

Abstract

An optical displacement detection method for micromachined microphones is described and experimental results are presented. The microphone membrane is fabricated on a transparent substrate and the back electrode is patterned in the form of diffraction fingers. This structure forms a phase sensitive diffraction grating, providing the displacement sensitivity of an optical interferometer. The diffraction fingers are also used for electrostatic actuation, providing sensitivity adjustment and self calibration capabilities. The optical detection and electrostatic actuation capabilities are demonstrated on aluminum microphone membranes microfabricated on quartz substrates.