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arxiv: 2604.06426 · v2 · submitted 2026-04-07 · 📡 eess.SY · cs.SY

Spurious-Free Lithium Niobate Bulk Acoustic Wave Resonator with Grounded-Ring Electrode

Vakhtang Chulukhadze , Kristi Nguyen , Eric Stolt , Kilian Shambaugh , Weston Braun , Tzu-Hsuan Hsu , Osama Jameel , Juan Rivas-Davila
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Ruochen Lu
This is my paper

Pith reviewed 2026-05-10 18:32 UTC · model grok-4.3

classification 📡 eess.SY cs.SY
keywords lithium niobatebulk acoustic wave resonatorspurious modesgrounded ring electrodeelectromechanical couplingthickness extensional modepiezoelectric power conversion
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The pith

A grounded-ring electrode modifies boundary conditions in lithium niobate BAW resonators to produce piston-like motion that suppresses lateral spurious modes.

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

The paper shows that adding a grounded ring around the electrode of a thickness-extensional lithium niobate bulk acoustic wave resonator changes how acoustic waves reflect at the edges. This change creates uniform vertical motion instead of complex side-to-side patterns, removing unwanted resonances inside the frequency band where the device behaves inductively. The result is a resonator that keeps high electromechanical coupling while staying free of spurious modes, which matters for using these compact devices in power conversion circuits that need wide bandwidth and low loss. Measurements at 10.14 MHz confirm 29.6 percent coupling, quality factors up to 5230, and a figure of merit of 1548, backed by both simulation and laser vibrometry.

Core claim

The authors establish that the grounded-ring electrode architecture modifies the effective acoustic boundary conditions of a single-crystal lithium niobate thickness-extensional BAW resonator. This produces a piston-like modal response that suppresses lateral spurious modes across the entire inductive band. The demonstrated device reaches 10.14 MHz with 29.6 percent electromechanical coupling, a maximum in-band Bode quality factor of 5230, and a figure of merit of 1548.

What carries the argument

The grounded-ring electrode, which alters acoustic boundary conditions to enforce piston-like motion and suppress lateral modes.

If this is right

  • The resonator maintains high coupling and quality factor over a wide inductive bandwidth suitable for power conversion.
  • The design removes the usual trade-off between strong electromechanical coupling and spurious resonances.
  • The grounded-ring approach supplies a repeatable method for building spurious-free thickness-extensional resonators.

Where Pith is reading between the lines

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

  • The same boundary-condition change could be tested in other piezoelectric films or at higher frequencies to expand the usable range.
  • Combining this resonator with switched-capacitor circuits might eliminate the need for magnetic inductors in compact converters.
  • Fabrication tolerances on ring width and alignment would need checking to confirm the suppression remains reliable in volume production.

Load-bearing premise

The piston-like response and spurious-mode suppression must hold uniformly across the full inductive bandwidth without introducing new loss mechanisms or fabrication sensitivities.

What would settle it

Detection of lateral spurious peaks in the measured electrical response or LDV displacement maps anywhere inside the inductive band would show the suppression does not occur as described.

Figures

Figures reproduced from arXiv: 2604.06426 by Eric Stolt, Juan Rivas-Davila, Kilian Shambaugh, Kristi Nguyen, Osama Jameel, Ruochen Lu, Tzu-Hsuan Hsu, Vakhtang Chulukhadze, Weston Braun.

Figure 1
Figure 1. Figure 1: (a) BVD circuit model of piezoelectric resonator integrated into a power converter. (b) Idealized voltage and current waveforms for 40 V input, 30 V output [13]. itation, yielding a high-performance, spurious-free acoustic resonator for piezoelectric power conversion. A piezoelectric power converting circuit can be modeled as a resonator connected to various switch configurations (S1, S2, S3, S4) and direc… view at source ↗
Figure 2
Figure 2. Figure 2: Coupling coefficients as a function of rotation from the crystal Y-axis, for TS mode (k 2 M_35) and TE mode (k 2 M_33). 36Y-cut LN combines high k 2 M_33 with low parasitic k 2 M_35. k 2 comparable to PZT, but exhibits a significantly lower εr and superior linearity. These characteristics enable compact and efficient operation in high-frequency and high-power regimes. This contrast is reflected in Table I … view at source ↗
Figure 3
Figure 3. Figure 3: Illustration of cross-section and top view of the proposed resonator design with a grounded ring, with parameters tabulated. All electrodes are 300 nm thick, significantly thinner than LN. studies have examined many of their modal profiles and key design parameters to assess their suitability for power conversion. While radial-mode LN devices are promising for kHz operation, TS and TE modes are the primary… view at source ↗
Figure 5
Figure 5. Figure 5: Optical image of fabricated LN resonator mounted on a PCB. The inset image shows a magnified view of the ring and gap regions. and the circular reference is a fully metalized disk with a 7 mm radius [ [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
Figure 4
Figure 4. Figure 4: Simulated impedance and resistance for (a) rectangular, (b) circular, and (c) grounded-ring TE resonators. Inset images show 3D mode shapes and electrode configurations. function of the rotational angle θ in ZXZ Euler angle rotation (0, 90 - θ, 0), as shown in [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 7
Figure 7. Figure 7: Measured Bode Q from (a) a conventional rectangular device, (b) a conventional circular device, (c) the proposed grounded-ring design. The results highlight high QBode achieved within the spurious-free band of the grounded-ring device. highlighting the compactness of the proposed solution relative to its EM counterparts. B. Electrical Measurements The fabricated device was measured using a vector net￾work … view at source ↗
Figure 8
Figure 8. Figure 8: Zoomed in measured resistance curves and an ideal spurious￾free case obtained with the BVD model for (a) a conventional rectangular device, (b) a conventional circular device, and (c) the proposed grounded-ring structure. The grounded-ring resonator shows the least deviation from the ideal case. the proposed structure exhibits a high resonance frequency and a spurious-free response over a wide frequency ra… view at source ↗
Figure 9
Figure 9. Figure 9: LDV characterization of the rectangular reference TE-mode LN BAW resonator (without a grounded ring). (a)-(f) Measured vz deflection profiles (colorbar: vz magnitude in mm/s, blue = minimum, red = maximum) at the six frequencies labeled 1-6. (g) vz amplitude (blue, left axis) overlaid with the measured electrical resistance (red, right axis), showing a high density of in-band spurious modes across the indu… view at source ↗
Figure 10
Figure 10. Figure 10: LDV characterization of the circular reference TE-mode LN BAW resonator (without a grounded ring). (a)-(f) Measured vz deflection profiles (colorbar: vz magnitude in mm/s, blue = minimum, red = maximum) at the six frequencies labeled 1-6. (g) vz amplitude (blue, left axis) overlaid with the measured electrical resistance (red, right axis), showing in-band spurious modes. ing waves across the entire induct… view at source ↗
Figure 11
Figure 11. Figure 11: LDV characterization of the proposed grounded-ring TE-mode LN BAW resonator. (a)-(f) Measured vz deflection profiles (colorbar: vz magnitude in mm/s, blue = minimum, red = maximum) at the six frequencies labeled 1-6. (g) vz amplitude (blue, left axis) overlaid with the measured electrical resistance (red, right axis), demonstrating spurious mode suppression across the inductive band. mode immediately prio… view at source ↗
Figure 12
Figure 12. Figure 12: Comparison of measured resonant mode-shapes between the circular reference and grounded-ring designs, demonstrating a TE￾mode resonance in the conventional structure, while the grounded-ring device shows a uniform piston-like vz profile. A. Piston Mode Operation The LDV measurements in Figs. 10 and 11 provide direct experimental validation of the effect of the narrow gap and clarify the underlying operati… view at source ↗
Figure 13
Figure 13. Figure 13: Simulated impedance and resistance profiles from 2D cross￾sectional FEA for (a) zero ux at the lateral boundaries, leading to a pure piston mode. (b) Zero ux at the midplane, exciting a piston-like mode. (c) A free boundary condition at the device edge, leading to the TE mode [PITH_FULL_IMAGE:figures/full_fig_p010_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Dispersion analysis of the proposed structure. The obtained solutions are color-coded as blue for solutions in electrically open LN and red for solutions in electrically short LN. Line brightness corresponds to the admittance magnitude obtained from the periodic boundary condition sweep: brighter regions indicate stronger resonant responses. exhibits type-2 dispersion, in which the longitudinal wave veloc… view at source ↗
Figure 15
Figure 15. Figure 15: Simulated (a) displacement, (b) out-of-plane stress, (c) out￾of-plane displacement, (d) shear stress, and (e) in-plane displacement of the reference (left) and grounded-ring (right) resonators, highlighting the piston-like mode and distinct shear-stress and lateral-displacement profiles in the grounded-ring design. To understand acoustic resonator behavior in the relevant low-impedance region for piezoele… view at source ↗
Figure 16
Figure 16. Figure 16: (a) Cut-line locations for data extraction; a reference device without the grounded ring is used for comparison. (b) Txz along A-A’, showing opposing-polarity antinodes at the gap interfaces. (c) Zoomed Txz profile within the gap, highlighting antinodes excited at both the active area/gap and the gap/ring interface with opposing polarities traveling in opposite directions. (d) Lateral displacement along B… view at source ↗
Figure 17
Figure 17. Figure 17: Simulated impedance and resistance curves for the grounded￾ring resonator with parameters seen in [PITH_FULL_IMAGE:figures/full_fig_p012_17.png] view at source ↗
read the original abstract

High-performance piezoelectric resonators are promising energy storage elements for piezoelectric power conversion due to their compact footprint and low loss at frequencies where conventional magnetic components become bulky and inefficient. However, their practical use is often limited by the trade-off between a high electromechanical coupling coefficient (k^2) for wide-band operation and the emergence of spurious acoustic modes that limit the resonators' inductive bandwidth. This work reports a spurious-free thickness-extensional (TE)-mode bulk acoustic wave (BAW) resonator in single-crystal lithium niobate (LN) based on a grounded-ring electrode architecture. The proposed structure is analyzed through simulation and experimentally validated using electrical characterization and laser Doppler vibrometry (LDV). The results show that the grounded ring modifies the effective boundary conditions of the acoustic device, enabling a piston-like modal response that suppresses lateral spurious modes across the inductive band. The demonstrated device operates at 10.14 MHz and achieves an electromechanical coupling coefficient of 29.6%, a maximum in-band Bode quality factor (Q_Bode) of 5230, and a figure of merit (FoM, Q*k^2) of 1548. These results establish the grounded-ring TE-mode LN BAW resonator as a practical platform for piezoelectric power conversion and a broader design approach for realizing high-performance spurious-free acoustic resonators.

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

2 major / 2 minor

Summary. The manuscript presents a grounded-ring electrode architecture for single-crystal lithium niobate thickness-extensional bulk acoustic wave resonators that modifies acoustic boundary conditions to produce a piston-like displacement profile. Finite-element simulations, electrical impedance measurements, and laser Doppler vibrometry are used to demonstrate suppression of lateral spurious modes, yielding a device at 10.14 MHz with k² = 29.6 %, peak in-band Q_Bode = 5230, and FoM = Q·k² = 1548. The work positions the design as a practical solution for spurious-free operation in piezoelectric power-conversion applications.

Significance. If the broadband mode suppression holds, the result is significant because it directly addresses the long-standing trade-off between high electromechanical coupling and the appearance of unwanted lateral modes that shrink the usable inductive bandwidth. The combination of measured high Q, high k², and multi-method experimental confirmation (electrical + LDV) provides a concrete, high-FoM platform that could enable compact piezoelectric converters where magnetic components are size-limited. The grounded-ring boundary-condition approach may also generalize to other piezoelectric materials and resonator geometries.

major comments (2)
  1. [§IV] §IV (Experimental Validation) and Fig. 7: LDV mode-shape data and electrical spectra are shown at the design frequency and a single operating point; the claim that lateral modes remain suppressed throughout the full inductive interval (fs to fp) therefore rests on an untested extrapolation. Additional LDV or impedance data at several frequencies inside the band are required to confirm that no weak lateral or interface modes reappear.
  2. [§III.B] §III.B (Simulation) and §V (Discussion): The piston-like response is asserted to be frequency-independent, yet the finite-element results appear to be reported only near the target resonance. A frequency sweep of the displacement uniformity metric (or equivalent) across the inductive band would directly test whether the grounded-ring boundary condition eliminates all standing-wave solutions inside the operating window.
minor comments (2)
  1. The manuscript does not report error bars or repeatability statistics on the extracted k², Q_Bode, and FoM values; inclusion of these would strengthen the quantitative claims.
  2. Figure captions for the LDV and impedance plots should explicitly state the frequency at which each image or trace was acquired and whether the data are representative of the entire inductive band.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive review. The comments correctly identify that our current presentation of mode-shape data and simulations is limited to the design frequency, and we agree that additional frequency-dependent validation will strengthen the claims of broadband spurious-mode suppression. We address each major comment below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: §IV (Experimental Validation) and Fig. 7: LDV mode-shape data and electrical spectra are shown at the design frequency and a single operating point; the claim that lateral modes remain suppressed throughout the full inductive interval (fs to fp) therefore rests on an untested extrapolation. Additional LDV or impedance data at several frequencies inside the band are required to confirm that no weak lateral or interface modes reappear.

    Authors: We acknowledge that the LDV data in Fig. 7 is shown at the resonance frequency. The electrical impedance spectrum (Fig. 6) already shows a clean response with no visible spurious modes from fs to fp, supporting the suppression claim. To directly address the concern, we will add LDV displacement maps at three additional frequencies within the inductive band (near fs, mid-band, and near fp) in the revised manuscript. revision: yes

  2. Referee: §III.B (Simulation) and §V (Discussion): The piston-like response is asserted to be frequency-independent, yet the finite-element results appear to be reported only near the target resonance. A frequency sweep of the displacement uniformity metric (or equivalent) across the inductive band would directly test whether the grounded-ring boundary condition eliminates all standing-wave solutions inside the operating window.

    Authors: The grounded-ring boundary condition is designed to be broadband, but we agree that the simulation results are presented only at the target frequency. In the revised manuscript we will include a frequency sweep of the displacement uniformity metric (defined as the ratio of center-to-edge displacement amplitude) across the full inductive band to explicitly demonstrate the absence of standing-wave solutions. revision: yes

Circularity Check

0 steps flagged

No circularity; results from direct fabrication, simulation, and measurement

full rationale

The paper presents a fabricated LN BAW resonator with grounded-ring electrode, supported by FEM simulation and validated via electrical spectra and LDV mode imaging. The piston-like response and lateral-mode suppression are reported as observed outcomes from these independent methods rather than any closed mathematical derivation. All key metrics (resonance frequency, k^2 = 29.6%, Q_Bode = 5230, FoM = 1548) are stated as measured quantities on physical devices. No equations, fitted parameters, or self-citations are invoked in a load-bearing way that would make the central claim equivalent to its inputs by construction. The work is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on standard linear piezoelectric constitutive relations and acoustic boundary-condition modeling; no new free parameters or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption Linear piezoelectric constitutive equations and isotropic boundary conditions apply to the LN plate
    Invoked implicitly for both simulation and interpretation of piston-mode behavior.

pith-pipeline@v0.9.0 · 5578 in / 1127 out tokens · 44704 ms · 2026-05-10T18:32:21.768266+00:00 · methodology

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Reference graph

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