A new technology for the fabrication of silicon condenser microphones is presented. The technology, which is based on the use of polyimide, can be performed entirely as a post process on substrates already containing integrated circuits. Microphones with an open-circuit sensitivity of 8.1 mV Pa¿1, and a flat frequency response (±2 dB) between 100 Hz and 15 kHz have been fabricated with this technology. The bias voltage used in these measurements is 15 V, and the measured noise level with zero bias is 24 dB SPL, which is sufficient for most acoustic applications, including hearing aids.
Pedersen, M., Olthuis, W., & Bergveld, P. (1997). A silicon condenser microphone with polyimide diaphragm and backplate. Sensors and actuators. A: Physical, A63(2), 97-104. https://doi.org/10.1016/S0924-4247(97)01532-X