Optimal Orientations of Lithium Niobate for Lateral-and Thickness-Field-Excitation PMUTs
Xiaoxi Zhao (TU Delft - Electronic Instrumentation)
Michiel Pertijs (TU Delft - Electronic Instrumentation)
Tomás Manzaneque
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Abstract
This work identifies the optimal orientation of lithium niobate (LiNbO3, LN) for piezoelectric micromachined ultrasonic transducers (PMUTs) operating in lateral-field excitation (LFE) and thickness-field excitation (TFE) modes. Geometry-independent material figures of merit (FoMs), representing the round-trip signal-to-noise ratio (SNR), are evaluated by sweeping rotated material tensors across the full orientation space. Finite element method (FEM) simulation is then used to quantify the electromechanical coupling kt2 under consistent device stacks and electrode layouts. The FoMs peak at 140°Y-cut LiNbO3 (≈120% of PZT-5H); the best commercial TFE option, 128°Y-cut, attains ~65% of that maximum. Under the shared baseline design, the highest kt2 is achieved with X-cut LiNbO3 (≈7.2%) using elongated rectangular membranes, about 70% of the PZT-5H reference. Our results provide clear design guidance for LiNbO3 PMUTs to maximize performance: optimal cut, in-plane rotation, and membrane geometry.