Sensitivity Analysis of Novel PolyMUMPs-Based Ultrasonic MEMS Microphones

MEMS (micro-electro-mechanical-systems) microphones have been widely studied over the past decades. Studies have focused on the audible frequency range, while microphones operating in the ultrasonic range beyond 20 kHz (inaudible range) have rarely been explored. The aim of this work is to design a capacitive-based ultrasonic MEMS microphone having a flat response of up to 100 kHz. One major application for this is leak detection from highly pressurized pipes. The proposed microphone structure accounts for the limitations associated to the PolyMUMPs standard surface micro-machining process to enable its potential for future fabrication. Equations governing static and dynamic behavior are derived and solved using MATLAB by implementing the Galerkin method. The finite element simulations are conducted using COMSOL to present the sensitivity analysis while the model is further validated by obtaining the sensitivity curve of an audible MEMS microphone available in the literature. The sensitivity of the proposed microphone is -78 dB with a flat response within ±2 dB at up to 100 kHz. Considering the sensitivity of the benchmark ultrasonic bulk microphone B&K 4138 being equal to -60 dB, it can be concluded that although the proposed PolyMUMPs-based device has lower sensitivity, it eliminates the need for the costly additional back-etch processing required to create a larger back chamber.