Periodic Poling of Lithium Niobate for Fabrication of Piezoelectric Micromachined Ultrasonic Transducers (PMUTs)

Abstract

This work explores the periodic poling of x-cut thin film Lithium Niobate (LN) for use in Piezoelectric Micromachined Ultrasonic Transducers (PMUTs). In recent years, LN has demonstrated significant potential for PMUTs owing to its high sensitivity, low noise, and excellent thermal stability. However, state-of-the-art LN-based PMUTs still suffer from low device admittance, posing challenges for readout circuit design. To address this, we propose LN PMUTs using large electrode arrays to increase conductance. To enable large piezoelectric transcuction with such configuration, ferroelectric domain engineering on thin-film LN is needed. COMSOL simulations were performed to optimize electrode geometry and insulation requirements, ensuring sufficient electric field strength for domain inversion without dielectric breakdown. Structures were fabricated using standard cleanroom techniques, with Silicon Dioxide as the passivation layer. High-voltage pulses were applied using a precision source measure unit, and domain inversion was confirmed through the observation of characteristic current spikes. Our results demonstrate the feasibility of periodic poling using top-side overlapping electrodes, and show increased material conductivity post-poling, consistent with domain wall formation. This approach enables the future fabrication of PMUTs with improved performance using periodically poled Lithium Niobate.