In-Plane Q Anisotropy of Higher-Order XBARs in 128°Y-Cut Lithium Niobate
Abstract
128∘Y-cut lithium niobate (LN) laterally field-excited higher-order antisymmetric bulk acoustic resonators (XBARs) have attracted interest for high-frequency acoustic devices thanks to their high electromechanical coupling coefficient (k2), high quality factor (Q) from low metal coverage ratio, and thickness-defined resonant frequency. So far, the in-plane orientation of these resonators is commonly chosen to maximize k2, thereby maximizing bandwidth. More recently, in-plane-rotated XBARs in 128∘Y-cut LN have been built to provide greater design flexibility in filter synthesis. However, the in-plane anisotropy of Q has been far less explored. This leaves an important gap in understanding whether the propagation direction that determines k2 also affects Q. In this work, we investigate the anisotropic Q of higher-order antisymmetric modes (namely, A3, A5, and A7) in 500-nm-thick 128∘Y-cut LN on Si. By characterizing resonator performance in various in-plane orientations, we observe that both Bode Q and Q3dB, fp show minimum values at 90∘ to the material x-axis and maximum values around 0∘, following a trend similar to k2. The A3, A5, and A7 modes around 10.4, 17, and 24 GHz exhibit averaged Bode Q/Q3dB, fp values of 735/556, 204/149, and 59/37, respectively. At 90∘, the average Bode Q values are reduced to 66, 9, and 12. Finite element analysis (FEA) results suggest that the orientation-dependent degradation of Q near 90∘ is associated with stronger transverse displacement near the inactive and anchor regions, resulting in enhanced energy leakage. These results reveal an orientation-dependent loss pathway in 128∘Y-cut LN XBARs and provide design guidance for jointly optimizing k2 and Q.
Versions
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BibTeX
@misc{kim2026inplane,
title = {{In-Plane Q Anisotropy of Higher-Order XBARs in 128°Y-Cut Lithium Niobate}},
author = {Byeongjin Kim and Ian Anderson and Ruochen Lu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.16177},
eprint = {2606.16177},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.16177},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - In-Plane Q Anisotropy of Higher-Order XBARs in 128°Y-Cut Lithium Niobate
AU - Byeongjin Kim
AU - Ian Anderson
AU - Ruochen Lu
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2606.16177
UR - https://arxiv.org/abs/2606.16177
AB - 128^∘Y-cut lithium niobate (LN) laterally field-excited higher-order antisymmetric bulk acoustic resonators (XBARs) have attracted interest for high-frequency acoustic devices thanks to their high electromechanical coupling coefficient (k^2), high quality factor (Q) from low metal coverage ratio, and thickness-defined resonant frequency. So far, the in-plane orientation of these resonators is commonly chosen to maximize k^2, thereby maximizing bandwidth. More recently, in-plane-rotated XBARs in 128^∘Y-cut LN have been built to provide greater design flexibility in filter synthesis. However, the in-plane anisotropy of Q has been far less explored. This leaves an important gap in understanding whether the propagation direction that determines k^2 also affects Q. In this work, we investigate the anisotropic Q of higher-order antisymmetric modes (namely, A_3, A_5, and A_7) in 500-nm-thick 128^∘Y-cut LN on Si. By characterizing resonator performance in various in-plane orientations, we observe that both Bode Q and Q_3dB, f_p show minimum values at 90^∘ to the material x-axis and maximum values around 0^∘, following a trend similar to k^2. The A_3, A_5, and A_7 modes around 10.4, 17, and 24 GHz exhibit averaged Bode Q/Q_3dB, f_p values of 735/556, 204/149, and 59/37, respectively. At 90^∘, the average Bode Q values are reduced to 66, 9, and 12. Finite element analysis (FEA) results suggest that the orientation-dependent degradation of Q near 90^∘ is associated with stronger transverse displacement near the inactive and anchor regions, resulting in enhanced energy leakage. These results reveal an orientation-dependent loss pathway in 128^∘Y-cut LN XBARs and provide design guidance for jointly optimizing k^2 and Q.
ER -