4.3.3 - Application-specific programming of MEMS microphones

Abstract

The paper presents a novel method to trim MEMS microphones towards specific applications. This method allows tuning the acoustical parameters of programmable MEMS microphones after fabrication. Depending on the customer , either a high signal to noise ratio (SNR) or a low total harmonic distortion (THD) at high sound pressure levels (SPL) can be achieved. A high SNR of up to 66 dB(A) was reached by programming high bias voltages. Low bias voltages and a correction by gain factors allow the use at high sound pressure levels. Within a MEMS microphone fabrication batch the standard deviation of sensitivity was reduced by a factor of 5. A comparison of the two programmed settings shows that with the high SNR setting the SNR is better by 1 dB. The THD @ 127 dB SPL has the value of 1.0 % for the high SPL setting in comparison to 2.2 % for the high SNR setting.