MEMS Acoustic Sensor for Low Frequency Applications

This work presents the design of a piezoelectric based MEMS acoustic sensor for low frequency applications. The sensor design is based on MEMS-CAD-tool Coventorware. The frontside of the device consists of piezoelectric ZnO layer sandwiched between two gold electrodes, placed on a Si-diaphragm. The thickness of the diaphragm has been optimized using Coventorware upto the sound pressure level (SPL) of 120 dB. The optimized diaphragm size and thickness were found to be 4 mm × 4 mm and 10 µm, respectively. The backside consists of cavity and micro-channel structures. The microchannel is required for connecting the cavity to the outside environment. The design of the microchannel decides the low cut-off frequency of the sensor and it was found to be 5.7 Hz. Harmonic analysis was performed to determine the resonance frequency of the structure and it was found to be 9.6 kHz. The maximum sensitivity of the device obtained from simulation is 3.25 mV/Pa. A proposed fabrication process flow has also been suggested. The sensor can be utilized in the detection of low frequency noise and seismic waves created by earthquakes, volcanic eruptions etc.