A new condenser microphone design, which can be fabricated using the sacrificial layer technique, is proposed and tested. The microphone backplate is a 1 mu m PECVD silicon nitride film with a high density of acoustic holes (120-525 holes mm-2), covered with a thin Ti/Au electrode. Microphones with a 1.5*1.5 mm diaphragm show a flat frequency response between 100 Hz and 14 kHz and a sensitivity of about 2 mV Pa-1 using a bias voltage of 16 V. These values are comparable to those of other silicon microphones with highly perforated backplates. The major advantage of the new microphone design is that it can be fabricated on a single wafer so that no bonding techniques are required.
Scheeper, P. R., Olthuis, W., & Bergveld, P. (1992). A silicon condenser microphone with a silicon nitride diaphragm and backplate. Journal of micromechanics and microengineering, 2(3), 187-189. https://doi.org/10.1088/0960-1317/2/3/016