Piezoelectric Acoustic Pressure Sensors with Enhanced Sensitivity and Stiffness Based on Stress Concentration Structures and Wedge-Shape Electrodes

This paper demonstrates a piezoelectric acoustic pressure sensor that successfully combines high sensitivity with high stiffness. A concave hexagonal membrane structure was utilized to enhance the stress generated by acoustic pressure, resulting in a higher output charge density than traditional circular design. Furthermore, wedge shape electrodes and series connections were optimized to address the challenge of stress concentration in very limited areas, thereby maximizing the output voltage. Lead zirconate titanate (PZT) thin film was chosen due to its high piezoelectric constant and large dielectric constant, which enables sufficient capacitance for implementing a series connection of electrodes in a limited area. Meanwhile, the increased stiffness offers a high acoustic overload point or a wide bandwidth with a flat band response. Experimental results indicate that the concave hexagonal sensor exhibits a higher sensitivity of 22.5 μV/Pa at 1 kHz and a higher characteristic frequency of 270 kHz, compared to 15 μV/Pa and 146 kHz for circular sensors. The concave hexagonal pressure sensor with both high sensitivity and high stiffness demonstrates that the stress concentration strategy can be an insightful technique for advanced pressure sensor development.