Lithium Niobate Microphone With High SNR Potential

A bimorph lithium niobate (LN) transducer has been proposed as a microphone. Surface electrodes sense the lateral in-plane electric field in thin LN films resulting from out of plane deformation due to acoustic pressure. The bimorph is implemented using LN films with opposing polarization, achieved with a wafer bonding approach. The article summarizes our work on a LN microphone using a LN diaphragm with 300 μm thickness and quarter inch diameter. Laser doppler vibrometer (LDV) measurements are performed using piezoelectric excitation of the diaphragm to characterize mode shapes of the diaphragm. Pitch-catch acoustic measurements are performed in air using tone burst waveforms. We characterized acoustic sensitivity and noise floor. Lumped element and finite element analysis (FEA) are used to predict the acoustical performance. This is the first work demonstrating LN material in microphone applications. We ultimately envision using a bimorph LN film with 2 μm thickness in total on silicon substrate, where an approximately 1 mm by 1 mm diaphragm is formed via a backside through wafer etch. A rigorous lumped element model is used to simulate the LN MEMS microphone with 73.58 dB signalto- noise ratio (SNR). Improving MEMS microphone SNR beyond the current state of art is challenging. LN microphones may be a viable path.