The use of silicon technology for an electret microphone construction

The authors present a subminiature electret microphone which has been realized in silicon using wafer processing techniques. The microphone consists of two conducting plates which form a capacitor. The lower plate (backplate) is rigid and fabricated in silicon. The upper plate (diaphragm) consists of a 6-μm-thick metallized Mylar foil. In the air cavity between both plates a 1-μm-thick silicon dioxide electret is present. The fabrication process, such as the construction of the silicon backplate, the realization of the electret, and the diaphragm attachment, are described. The microphones measure 3-mm×3-mm×3-mm and show a sensitivity of 1.4 mV/μbar and a frequency response within ±1 dB up to 15 kHz