A NEW CONDENSER MICROPHONE IN SILICON

A diaphragm, machined in lightly doped silicon, is the principal component of a new capacitive microphone designed to operate with an external bias voltage. The new concept aims towards a microphone design which can be highly miniaturized and fabricated at low cost with IC- compatible technology. The significant points of the new concept are low stray capacitances ( < 0.5 pF), a large number of ventilation holes in the back plate allowing a small air gap (4 μm), and an integrated back chamber. The microphone frequency response has been calculated using a mechano-acoustical lumped parameter model. Finally, microphone chips with an overall size of 3 × 4 × 1.3 mm3 have been fabricated and preliminary measurements have demonstrated open- circuit sensitivities between 1.4 and 13 mV/Pa, corresponding to bandwidths between 16 and 4 kHz. © 1990.