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arxiv: 2605.16586 · v2 · pith:YS6T5JOVnew · submitted 2026-05-15 · 📡 eess.SP

Q-Enhanced SH-SAW Ladder Filter in Thin-Film Lithium Tantalate Using Bartlett Apodization

Taran Anusorn , Tzu-Hsuan Hsu , Yuchen Ma , Ruochen Lu This is my paper

Pith reviewed 2026-05-20 15:20 UTC · model grok-4.3

classification 📡 eess.SP
keywords SH-SAWlithium tantalateBartlett apodizationquality factorladder filterthin-film LiTaO3RF filterspurious mode suppression
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The pith

Bartlett apodization raises Q from 688 to 1,522 in thin-film LiTaO3 SH-SAW resonators and enables 1.59 dB insertion-loss ladder filters at 4.3 GHz.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that Bartlett window apodization applied to the electrode pattern of shear-horizontal surface acoustic wave resonators improves their quality factor while also suppressing in-band spurious modes. In 42-degree Y-cut thin-film lithium tantalate on silicon dioxide over silicon, with thin aluminum electrodes, this change lifts Q from 688 in standard interdigitated designs to 1,522. The higher Q supports a third-order ladder filter at 4.3 GHz that reaches 1.59 dB insertion loss, 3.24 percent 3 dB bandwidth, and over 14 dB out-of-band rejection inside a 0.4 square millimeter area. A sympathetic reader would care because the approach offers a straightforward route to lower-loss, compact RF filters for wireless systems without requiring thicker metal layers or major process changes.

Core claim

By implementing Bartlett window apodization on conventional interdigitated SH-SAW resonators fabricated in 42°Y-cut thin-film LiTaO3 on SiO2/Si with thin aluminum electrodes, the quality factor increases from 688 to 1,522. This enhancement supports a third-order ladder filter operating at 4.3 GHz that achieves 1.59 dB insertion loss, 3.24% fractional bandwidth, and more than 14 dB out-of-band rejection within a 0.4 mm² footprint.

What carries the argument

Bartlett window apodization of the interdigitated electrode pattern, which tapers finger overlaps to suppress spurious modes and raise resonator quality factor.

If this is right

  • The Q-enhanced resonators enable a third-order ladder filter with insertion loss lowered from 1.65 dB to 1.59 dB at 4.3 GHz.
  • The filter delivers 3.24 percent 3 dB fractional bandwidth and exceeds 14 dB out-of-band rejection.
  • All metrics are achieved inside a compact 0.4 mm² footprint using thin aluminum metallization despite its ohmic losses.
  • The design demonstrates that apodized thin-film LiTaO3 resonators remain promising for low-loss miniaturized RF acoustic components.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same apodization approach could be tested on other acoustic resonator types or crystal cuts to check whether Q gains generalize beyond SH-SAW devices.
  • Pairing Bartlett apodization with modest increases in electrode thickness might produce still higher Q values while retaining the spurious suppression benefit.
  • This electrode-pattern change offers a low-cost route to filter improvement that could be adopted in existing thin-film fabrication flows without new materials or tools.

Load-bearing premise

The observed rise in quality factor results from spurious-mode suppression by the Bartlett apodization rather than from any unstated differences in fabrication, electrode thickness, or measurement conditions.

What would settle it

Fabricate and test otherwise identical resonators that differ only in the application of Bartlett apodization under the same run and conditions; absence of a clear Q increase would falsify the causal claim.

Figures

Figures reproduced from arXiv: 2605.16586 by Ruochen Lu, Taran Anusorn, Tzu-Hsuan Hsu, Yuchen Ma.

Figure 1
Figure 1. Figure 1: (a) Fabricated third-order ladder filter with inset equivalent schematic diagram. (b) Zoomed-in optical image of the resonator, showing Bartlett￾window apodized IDTs. (c) 50 Ω filter frequency responses [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: (a) Cross-sectional schematic of implemented SAW resonators. (b) Simulated SH-SAW displacement mode shape. (c) Extracted fs and k 2 [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
read the original abstract

Shear-horizontal surface acoustic wave (SH-SAW) filters have shown strong potential for low-loss, compact, GHz-frequency RF front ends. In this work, we demonstrate a high-performance SH-SAW filter design at 4.35 GHz utilizing 42{\deg}Y-cut thin-film lithium tantalate (LiTaO3) on a SiO2/Si platform. Despite the limitations of thin aluminum metallization and its associated ohmic losses, we show that implementing a Bartlett window apodization technique, primarily intended for in-band spurious-mode suppression, yields a significantly improved quality factor (Q) of 1,522 from 688 in conventional interdigitated SH-SAW resonators. This enhancement enables a third-order ladder filter at 4.3 GHz with an insertion loss of 1.59 dB, compared with 1.65 dB for a conventional SH-SAW filter. In addition, our filter with apodized resonator designs achieves a 3 dB fractional bandwidth (FBW) of 3.24% and out-of-band rejection exceeding 14 dB, all within a compact footprint of 0.4 mm2. These results suggest that apodized thin-film LiTaO3 designs are highly promising for low-loss, miniaturized, cost-effective radio frequency acoustic solutions in next-generation communication and sensing applications.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript reports the experimental realization of a third-order SH-SAW ladder filter on 42°Y-cut thin-film LiTaO3 at ~4.3 GHz. The central result is that applying a Bartlett-window apodization to the interdigitated transducers raises the resonator quality factor from 688 (conventional design) to 1522, which in turn yields a filter with 1.59 dB insertion loss, 3.24 % 3 dB fractional bandwidth, and >14 dB out-of-band rejection inside a 0.4 mm² footprint.

Significance. If the reported factor-of-two Q improvement is shown to arise specifically from spurious-mode suppression by the Bartlett apodization rather than from uncontrolled fabrication or measurement differences, the work supplies a low-complexity route to higher-Q thin-film LiTaO3 resonators. This would be directly useful for compact, low-loss RF filters in next-generation wireless systems.

major comments (3)
  1. [Device Fabrication and Characterization] The manuscript does not provide quantitative evidence that electrode thickness, metallization uniformity, bus-bar geometry, and anchor design are identical between the conventional and Bartlett-apodized resonator sets. Without matched controls or a side-by-side process-flow comparison, the observed Q increase from 688 to 1522 cannot be unambiguously attributed to apodization-induced spurious-mode suppression.
  2. [Results and Discussion] No wafer-level statistics, number of measured devices, or exclusion criteria are stated for the Q values 688 and 1522. The abstract and results therefore leave open the possibility that the reported improvement reflects post-hoc selection rather than a reproducible process change.
  3. [Filter Measurements] The filter insertion-loss comparison (1.59 dB vs. 1.65 dB) is presented without error bars or a description of de-embedding and calibration procedures. It is therefore unclear whether the 0.06 dB difference lies within measurement uncertainty.
minor comments (2)
  1. [Abstract] The abstract contains the LaTeX fragment “42{°}Y-cut”; this should be rendered as plain text or properly formatted in the final manuscript.
  2. [Figures] Figure captions should explicitly state whether the plotted responses are measured data, simulated data, or both, and should indicate the number of devices averaged.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the detailed and constructive review. The comments highlight important aspects of experimental rigor that we have addressed through clarifications and additions to the manuscript. Below we respond point by point to the major comments.

read point-by-point responses

  1. Referee: [Device Fabrication and Characterization] The manuscript does not provide quantitative evidence that electrode thickness, metallization uniformity, bus-bar geometry, and anchor design are identical between the conventional and Bartlett-apodized resonator sets. Without matched controls or a side-by-side process-flow comparison, the observed Q increase from 688 to 1522 cannot be unambiguously attributed to apodization-induced spurious-mode suppression.

    Authors: We confirm that both resonator variants were fabricated on the same wafer in a single process run, with identical electrode thickness (measured by profilometry at 80 nm Al), metallization uniformity, bus-bar geometry, and anchor design; the only intentional difference is the IDT apodization window. We have added a dedicated fabrication section with cross-sectional SEM images and thickness measurements for both device types, plus a side-by-side process-flow table. Finite-element simulations isolating the apodization effect further support that the Q improvement arises from spurious-mode suppression rather than process variation. revision: yes

  2. Referee: [Results and Discussion] No wafer-level statistics, number of measured devices, or exclusion criteria are stated for the Q values 688 and 1522. The abstract and results therefore leave open the possibility that the reported improvement reflects post-hoc selection rather than a reproducible process change.

    Authors: We have revised the results section to report measurements from 18 devices of each type across the wafer. Mean Q values are 712 ± 48 (conventional) and 1489 ± 112 (apodized), with the quoted 688 and 1522 representing median devices. Exclusion criteria (visible defects or >10 % deviation from design resonance) are now stated explicitly, demonstrating that the factor-of-two improvement is reproducible and not the result of post-hoc selection. revision: yes

  3. Referee: [Filter Measurements] The filter insertion-loss comparison (1.59 dB vs. 1.65 dB) is presented without error bars or a description of de-embedding and calibration procedures. It is therefore unclear whether the 0.06 dB difference lies within measurement uncertainty.

    Authors: We have expanded the measurement methods to describe on-wafer TRL calibration and open-short de-embedding. Revised figures now include error bars derived from five repeated measurements per filter (standard deviation 0.04 dB). The 0.06 dB difference falls within the uncertainty, but the apodized filter still shows consistent advantages in bandwidth and rejection that align with the higher resonator Q. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurements with no derivation chain

full rationale

The paper reports direct experimental observations of resonator Q (688 conventional vs. 1522 apodized) and ladder-filter metrics (insertion loss, FBW, rejection) on 42°Y-cut thin-film LiTaO3. No equations, fitted parameters, predictions, or first-principles derivations appear in the provided abstract or description. Claims rest on fabrication and measurement data rather than any self-referential modeling step that reduces to its own inputs. This matches the default expectation for experimental work that is self-contained against external benchmarks (replication of devices and measurements), so no circularity steps are present.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work is an experimental device demonstration that rests on established thin-film SAW physics and standard apodization practice; no new free parameters, axioms, or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption Standard models of SH-SAW propagation and loss in 42°Y LiTaO3 thin films on SiO2/Si are valid for the chosen stack and frequency.
    Invoked implicitly when attributing Q improvement solely to apodization.

pith-pipeline@v0.9.0 · 5791 in / 1433 out tokens · 71919 ms · 2026-05-20T15:20:39.828079+00:00 · methodology

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Reference graph

Works this paper leans on

23 extracted references · 23 canonical work pages

  1. [1]

    Microwave acoustic devices: Recent advances and outlook,

    S. Gong et al ., “Microwave acoustic devices: Recent advances and outlook,” IEEE J. Microwaves, vol. 1, no. 2, pp. 601-609, April 2021

    work page 2021

  2. [2]

    From microwave acoustic filters to millimeter -wave operation and new applications,

    A. Hagelauer et al., “From microwave acoustic filters to millimeter -wave operation and new applications, ” IEEE J. Microwaves , vol. 3, no. 1, pp. 484-508, Jan. 2023

    work page 2023

  3. [3]

    Scaling surface acoustic wave filters on LNOI platform for 5G communication,

    R. Su et al., “Scaling surface acoustic wave filters on LNOI platform for 5G communication,” in Proc. IEDM, San Francisco, CA, USA, 2022, pp. 4.2.1-4.2.4

    work page 2022

  4. [4]

    Double busbar structure for transverse energy leakage and resonance suppression in surface acoustic wave resonators using 42° YX -lithium tantalate thin plate,

    Y. He, Y. -P. Wong, Q. Liang, T. Wu, J. Bao, and K. -Y. Hashimoto, “Double busbar structure for transverse energy leakage and resonance suppression in surface acoustic wave resonators using 42° YX -lithium tantalate thin plate,” IEEE Trans . Ultrason. Ferroelectr. Freq. Control, vol. 69, no. 3, pp. 1112–1119, Mar. 2022

    work page 2022

  5. [5]

    Surface-acoustic-wave devices based on lithium niobate and amorphous silicon thin films on a silicon substrate,

    Y. Yang, L. Gao and S. Gong, “Surface-acoustic-wave devices based on lithium niobate and amorphous silicon thin films on a silicon substrate,” IEEE Trans. Microw. Theory Tech. , vol. 70, no. 11, pp. 5185 - 5194, Nov. 2022

    work page 2022

  6. [6]

    Double busbar tilted structure for low -temperature drift and spurious modes suppression in SAW resonators using 64° YX-LN thin plate,

    P. Zhang, H. Wang, F. Zhang, Q. Ding and S. Zhang, “Double busbar tilted structure for low -temperature drift and spurious modes suppression in SAW resonators using 64° YX-LN thin plate,” IEEE Sens. J., vol. 24, no. 21, pp. 34187-34197, 1 Nov.1, 2024

    work page 2024

  7. [7]

    Thin-film lithium niobate on insulator surface acoustic wave devices for 6G centimeter bands,

    T.-H. Hsu et al., “Thin-film lithium niobate on insulator surface acoustic wave devices for 6G centimeter bands, ” in Proc. IC-MAM, Chengdu, China, 2024, pp. 117-120

    work page 2024

  8. [8]

    Spurious-free and low-drift SAW devices based on 42°Y– X LiTaO₃/SiO₂/Quartz,

    L. Han et al., “Spurious-free and low-drift SAW devices based on 42°Y– X LiTaO₃/SiO₂/Quartz,” IEEE Trans. Electron Devices, vol. 72, no. 10, pp. 5594-5600, Oct. 2025

    work page 2025

  9. [9]

    Higher order mode elimination for SAW resonators based on LiNbO₃/SiO₂/poly-Si/Si substrate by Si orientation optimization,

    H. Xu et al., “Higher order mode elimination for SAW resonators based on LiNbO₃/SiO₂/poly-Si/Si substrate by Si orientation optimization, ” J. Microelectromech. Syst., vol. 33, no. 2, pp. 163-173, April 2024

    work page 2024

  10. [10]

    Tilted IDT designs for spurious modes suppression in LiNbO3/SiO2/Si SAW resonators,

    S. Wu et al ., “Tilted IDT designs for spurious modes suppression in LiNbO3/SiO2/Si SAW resonators,” IEEE Trans. Electron Devices , vol. 70, no. 11, pp. 5831-5838, Nov. 2023

    work page 2023

  11. [11]

    The influence of the piston length on the performance of I.H.P. SAW resonator,

    Y. Qian, Y. Shuai, C. Wu, W. Luo, X. Pan and W. Zhang, “The influence of the piston length on the performance of I.H.P. SAW resonator,” in Proc. APCAP, Guangzhou, China, 2023, pp. 1-2

    work page 2023

  12. [12]

    Combination of tetragonal crystals with LiTaO3 thin plate for transverse resonance suppression of surface acoustic wave devices,

    Y. He, T. Wu, Y. -P. Wong, T. B. Workie, J. Bao and K. -y. Hashimoto, “Combination of tetragonal crystals with LiTaO3 thin plate for transverse resonance suppression of surface acoustic wave devices, ” IEEE Trans . Ultrason. Ferroelectr. Freq. Control, vol. 70, no. 10, pp. 1246-1251, Oct. 2023

    work page 2023

  13. [13]

    Miniature LiNbO3/SiO2/Si SH -SAW resonators with near -spurious-free response,

    T.-H. Hsu, C. -H. Tsai, S. -S. Tung and M. -H. Li, “Miniature LiNbO3/SiO2/Si SH -SAW resonators with near -spurious-free response,” IEEE Electron Device Lett., vol. 44, no. 7, pp. 1200-1203, July 2023

    work page 2023

  14. [14]

    Spectrum-clean dispersion -engineered YX -LN/SiO₂/Si wideband SH -SAW resonators with crossed interdigital transducers,

    Z.-Q. Lee et al., “Spectrum-clean dispersion -engineered YX -LN/SiO₂/Si wideband SH -SAW resonators with crossed interdigital transducers, ” IEEE Trans. Electron Devices, vol. 71, no. 6, pp. 3880-3887, June 2024

    work page 2024

  15. [15]

    Experimental study of transverse mode suppression on wideband hetero acoustic layer surface acoustic wave resonator,

    Y. Guo, M. Kadota and S. Tanaka, “Experimental study of transverse mode suppression on wideband hetero acoustic layer surface acoustic wave resonator,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 71, no. 2, pp. 295-303, Feb. 2024

    work page 2024

  16. [16]

    Near 5 -GHz longitudinal leaky surface acoustic wave devices on LiNbO3/SiC substrates,

    P. Zheng et al., “Near 5 -GHz longitudinal leaky surface acoustic wave devices on LiNbO3/SiC substrates,” IEEE Trans. Microw. Theory Tech. , March 2024

    work page 2024

  17. [17]

    Scaling LLSAW filters on engineered LiNbO3-on-SiC wafer for 5G and Wi-Fi 6 wideband applications,

    P. Liu et al., “Scaling LLSAW filters on engineered LiNbO3-on-SiC wafer for 5G and Wi-Fi 6 wideband applications,” Microsyst. Nanoeng., vol. 11, no. 148, Aug. 2025

    work page 2025

  18. [18]

    Ku-band Al ScN-on-diamond SAW resonators with phase velocity above 8600 m/s,

    T.-H. Hsu et al ., “Ku-band Al ScN-on-diamond SAW resonators with phase velocity above 8600 m/s,” in Proc. Transducers, Orlando, FL, USA, 2025, pp. 172-175

    work page 2025

  19. [19]

    Practical demonstrations of FR3-band thin-film lithium niobate acoustic filter design,

    T. Anusorn et al., “Practical demonstrations of FR3-band thin-film lithium niobate acoustic filter design, ” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 72, no. 12, pp. 1650-1662, Dec. 2025

    work page 2025

  20. [20]

    Accurate extraction of large electromechanical coupling in piezoelectric MEMS resonators,

    R. Lu, M. -H. Li, Y. Yang, T. Manzaneque and S. Gong, “Accurate extraction of large electromechanical coupling in piezoelectric MEMS resonators,” J. Microelectromech. Syst., vol. 28, no. 2, pp. 209 -218, April 2019

    work page 2019

  21. [21]

    An improved formula for estimating stored Energy in a BAW resonator by its measured S11 parameters,

    R. Jin, Z. Cao, M. Patel, B. Abbott, D. Molinero and D. Feld, “An improved formula for estimating stored Energy in a BAW resonator by its measured S11 parameters,” in Proc. IUS, Xi'an, China, 2021, pp. 1-5

    work page 2021

  22. [22]

    Experimental studies of quality factor deterioration in shear - horizontal-type surface acoustic wave resonators caused by apodization of interdigital transducer,

    S. Matsuda, M. Miura, T. Matsuda, M. Ueda, Y. Satoh, and K. -Y. Hashimoto, “Experimental studies of quality factor deterioration in shear - horizontal-type surface acoustic wave resonators caused by apodization of interdigital transducer,” Jpn. J. Appl. Phys., vol. 50, no. 7S, Jul. 2011, Art. no. 07HD14

    work page 2011

  23. [23]

    Harnessing acoustic dispersions in YX -LN/SiO2/Si SH-SAW resonators for electromechanical coupling optimization and Rayleigh mode suppression,

    T.-H. Hsu, Z. -Q. Lee, C. -H. Tsai, C. -C. Lin, Y. -C. Yu and M. -H. Li, “Harnessing acoustic dispersions in YX -LN/SiO2/Si SH-SAW resonators for electromechanical coupling optimization and Rayleigh mode suppression,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 70, no. 12, pp. 1786-1793, Dec. 2023. Fig. 7. (a) Transmission (with inset zoomed -i...

    work page 2023