Differentially Driven Dual-Electrode Air-Coupled AlN PMUTs with Enhanced Transmission Efficiency

In this work, a novel transduction mechanism based on differential driving through a dual-electrode aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducer (PMUT) device is introduced to enhance its output acoustic pressure. The proposed PMUT of 65-kHz was designed to possess center and side electrodes on both top and bottom conductive layers, which enables two electrode ports operated with differential driving. The presented device was fabricated through an in-house five-mask platform. Such driving condition leads to significant nonlinearity to the PMUT during mechanical and acoustic measurements. The proposed single-cell PMUT under 10-cycle sinusoidal waves implementing differential driving configuration achieves a sound pressure level (SPL) of 97.8 dB at 30 cm. Such differentially driven dual-electrode AlN PMUTs attain relatively competitive transmission efficiency as compared to other PMUTs using higher piezoelectric coefficient material, which shows great potential for rangefinders.