This work demonstrates a linear PMUT array based on a bilayer X-cut lithium niobate (LiNbO3) structure. Leveraging LiNbO3's high piezoelectric coefficients and the bilayer's ability to harness the sign-changing in-plain strain associated to plate bending, the device achieves high transmit sensitivity (0.48 kPa/V at 10 mm), high current receive sensitivity (0.56 nA/Pa), high voltage receive sensitivity ($2.26 \mu ~\mathrm{V} / \text{Pa}$), and a low noise-equivalent pressure ($0.18 \text{mPa} / \sqrt{\text{Hz}}$). The array operates at 1 MHz with a fractional bandwidth of $82.5 \%(-6 ~\text{dB})$ and has an active area of $0.173 ~\text{mm}^{2}$. Figures of merit (FoMs) that capture the sensitivity-bandwidth-area trade-offs are reported and benchmarked with other PMUT technologies. The results position bilayer LiNbO3 as a promising route to compact, high-performance ultrasonic transducers.

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 k_t² 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 k_t² 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.