Fabrication of a subminiature silicon condenser microphone using the sacrificial layer technique

The application of the sacrificial layer technique for the fabrication of a subminiature silicon condenser microphone with a plasma-enhanced chemical vapor deposited silicon nitride diaphragm has been investigated. Square diaphragms with dimensions from 0.6 to 2.6 mm and a thickness of 1 mu m have been realized. Measurements on a microphone with a 2*2 mm diaphragm and a 1 mu m airgap have shown that a sensitivity of 1.4 mV/Pa for low frequencies can be achieved with a low bias voltage (-2 V). The sensitivity decreases for high frequencies. This effect is probably due to the small airgap. Therefore, microphones with wider airgaps have to be developed to achieve a flat frequency response for the entire audio frequency range.<>