Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator

Rui Zhao; Haizhong Weng; Qing Wan

doi:10.1088/1674-4926/25120032

J. Semicond. > Just Accepted

Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator

Rui Zhao¹, Haizhong Weng^1, and Qing Wan^1,

+ Author Affiliations

Corresponding author: Haizhong Weng, haizhong-weng@ylab.ac.cn; Qing Wan, wanqing@nju.edu.cn

DOI: 10.1088/1674-4926/25120032CSTR: 32376.14.1674-4926.25120032

Abstract: Heterogeneously integrated lithium niobate (LN) electro-optic modulators have great potential for high-speed applications, but challenges remain in optimizing performance, particularly in terms of modulation efficiency, bandwidth, and the trade-offs. This work presents an optimized design for a silicon-nitride (Si₃N₄)-loaded modulator on a thin-film lithium niobate (TFLN) platform, consisting of 300 nm-thick LN film and 300 nm-thick Si₃N₄ optical waveguide. By systematically optimizing the dielectric layer thickness, electrode parameters, and achieving velocity and impedance matching, we demonstrate a modulator with a bandwidth exceeding 200 GHz. Our collaborative optimization scheme highlights the critical role of reducing the silicon oxide box layer thickness for velocity matching. We show that multiple structural configurations can achieve bandwidths greater than 120 GHz with V_π·L＜ 4 V·cm, providing feasibility in low-loss design and fabrication. These findings offer valuable design guidelines for high-performance electro-optic modulators suitable for data communications.

Key words: electro-optic modulator, silicon nitride, thin film lithium niobate, heterogeneous integration

References

[1]	Wang C, Zhang M, Chen X, et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature, 2018, 562(7725): 101 doi: 10.1038/s41586-018-0551-y
[2]	Desiatov B, Shams-Ansari A, Zhang M, et al. Ultra-low-loss integrated visible photonics using thin-film lithium niobate. Optica, 2019, 6(3): 380 doi: 10.1364/OPTICA.6.000380
[3]	Luke K, Kharel P, Reimer C, et al. Wafer-scale low-loss lithium niobate photonic integrated circuits. Opt Express, 2020, 28(17): 24452 doi: 10.1364/OE.401959
[4]	He M B, Xu M Y, Ren Y X, et al. High-performance hybrid silicon and lithium niobate Mach–Zehnder modulators for 100 Gbit s−1 and beyond. Nat Photonics, 2019, 13(5): 359 doi: 10.1038/s41566-019-0378-6
[5]	Weigel P O, Zhao J, Fang K, et al. Bonded thin film lithium niobate modulator on a silicon photonics platform exceeding 100 GHz 3-dB electrical modulation bandwidth. Opt Express, 2018, 26(18): 23728 doi: 10.1364/OE.26.023728
[6]	Valdez F, Mere V, Wang X X, et al. 110 GHz, 110 mW hybrid silicon-lithium niobate Mach-Zehnder modulator. Sci Rep, 2022, 12: 18611 doi: 10.1038/s41598-022-23403-6
[7]	Tan Y, Niu S P, Billet M, et al. Micro-transfer printed thin film lithium niobate (TFLN)-on-silicon ring modulator. ACS Photonics, 2024, 11(5): 1920 doi: 10.1021/acsphotonics.3c01869
[8]	Jin S L, Xu L T, Zhang H H, et al. LiNbO₃ thin-film modulators using silicon nitride surface ridge waveguides. IEEE Photonics Technol Lett, 2016, 28(7): 736 doi: 10.1109/LPT.2015.2507136
[9]	Ahmed A N R, Shi S Y, Mercante A, et al. High-efficiency lithium niobate modulator for K band operation. APL Photonics, 2020, 5(9): 091302 doi: 10.1063/5.0020040
[10]	Zhang P, Huang H J, Jiang Y H, et al. High-speed electro-optic modulator based on silicon nitride loaded lithium niobate on an insulator platform. Opt Lett, 2021, 46(23): 5986 doi: 10.1364/OL.446222
[11]	Qi Y F, Yue G C, Hao T, et al. Strong-confinement low-index-rib-loaded waveguide structure for etchless thin-film integrated photonics. Opto Electron Adv, 2025, 8(9): 250056 doi: 10.29026/oea.2025.250056
[12]	Valdez F, Mere V, Mookherjea S. 100 GHz bandwidth, 1 volt integrated electro-optic Mach–Zehnder modulator at near-IR wavelengths. Optica, 2023, 10(5): 578 doi: 10.1364/OPTICA.484549
[13]	Rahman A, Valdez F, Mere V, et al. High-performance hybrid lithium niobate electro-optic modulators integrated with low-loss silicon nitride waveguides on a wafer-scale silicon photonics platform. 2025: arXiv: 2504.00311. https://arxiv.org/abs/2504.00311
[14]	Shen J, Zhang Y, Zhang L, et al. Highly efficient slow-light Mach–Zehnder modulator achieving 0.21 V cm efficiency with bandwidth surpassing 110 GHz (laser photonics rev. 19(8)/2025). Laser Photonics Rev, 2025, 19(8): 2570031 doi: 10.1002/lpor.202570031
[15]	Ben Braham C, Belarouci A, Alonso-Ramos C, et al. Silicon-rich Silicon Nitride on Lithium Niobate thin film modulators with 100 GHz Electro-Optical bandwidth in the C-band. 2025 IEEE Silicon Photonics Conference (SiPhotonics), 2025: 1
[16]	Li Z Y, Chen Y, Zhang J M, et al. Hybrid silicon nitride/lithium niobate electro-optical modulator with wide optical bandwidth and high RF bandwidth based on ion-cut wafer-level bonding technology. 2025: Th1E. 1
[17]	Snigirev V, Riedhauser A, Lihachev G, et al. Ultrafast tunable lasers using lithium niobate integrated photonics. Nature, 2023, 615(7952): 411 doi: 10.1038/s41586-023-05724-2
[18]	Wu Y L, Shao S, Zhang H F, et al. Combining lithium-niobate and silicon-nitride integrated photonics in ultrafast tunable, low-noise lasers. Laser Photonics Rev, 2025: e02207
[19]	Ahmed A N R, Nelan S, Shi S Y, et al. Subvolt electro-optical modulator on thin-film lithium niobate and silicon nitride hybrid platform. Opt Lett, 2020, 45(5): 1112 doi: 10.1364/OL.381892
[20]	Nelan S P, Mercante A, Shi S Y, et al. Integrated lithium niobate intensity modulator on a silicon handle with slow-wave electrodes. IEEE Photonics Technol Lett, 2022, 34(18): 981 doi: 10.1109/LPT.2022.3197085
[21]	Badri S H, Kotlyar M V, Das R, et al. Compact modulators on silicon nitride waveguide platform via micro-transfer printing of thin-film lithium niobate. Sci Rep, 2025, 15: 11681 doi: 10.1038/s41598-025-95397-w
[22]	Chang L, Pfeiffer M H P, Volet N, et al. Heterogeneous integration of lithium niobate and silicon nitride waveguides for wafer-scale photonic integrated circuits on silicon. Opt Lett, 2017, 42(4): 803 doi: 10.1364/OL.42.000803
[23]	Churaev M, Wang R N, Riedhauser A, et al. A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform. 49th Eur Conf Opt Commun ECOC 2023, 2023, 2023: 1539
[24]	Cai J C, Kotz A, Larocque H, et al. Heterogeneously integrated lithium tantalate-on-silicon nitride modulators for high-speed communications. 2025: arXiv: 2508.06265. https://arxiv.org/abs/2508.06265
[25]	Weigel P O, Valdez F, Zhao J, et al. Design of high-bandwidth, low-voltage and low-loss hybrid lithium niobate electro-optic modulators. J Phys Photonics, 2021, 3(1): 012001 doi: 10.1088/2515-7647/abc17e
[26]	Han X, Jiang H, He J, et al. Breaking dense integration limits: Inverse-designed lithium niobate multimode photonic circuits. Nat Commun, 2026, 17: 1162 doi: 10.21203/rs.3.rs-7481144/v1
[27]	Xie Y Z, Li J Q, Zhang Y F, et al. Soliton frequency comb generation in CMOS-compatible silicon nitride microresonators. Photon Res, 2022, 10(5): 1290 doi: 10.1364/PRJ.454816

Fig. 1. (Color online) (a) Cross-section and the structural dimensions of the heterogeneously integrated Si₃N₄-LN modulator. Without considering the electrode structure: (b) Influence of W_rib and H_rib on η_LN at H_box = 1.5 μm and H_clad = 0 μm. (c) Influence of H_clad on η_LN at H_box = 1.5 μm. (d) Influence of H_clad on n_g at H_box = 1.5 μm. (e) Influence of H_box on α_int at H_clad = 0.3 μm.

DownLoad: Full-Size Img PowerPoint

Fig. 2. (Color online) Influence of G and H_clad on V_π·L (solid lines) and α_el considering the electrode structure. Red dashed contour denotes the range that satisfies the limits V_π·L ≤ 4 V·cm and α_el ≤ 0.1 dB/cm.

DownLoad: Full-Size Img PowerPoint

Fig. 3. (Color online) Influence of H_Au and W_sig on (a) n_RF and (b) Z₀ at G = 6 μm, H_clad = 0.3 μm, H_box = 1.5 μm. Influence of G and H_clad on (c) n_RF and (d) Z₀ at W_sig = 17 μm, H_Au = 0.5 μm, and H_box = 1.5 μm. Influence of H_box on (e) n_RF and (f) Z₀ .

DownLoad: Full-Size Img PowerPoint

Fig. 4. (Color online) Normalized influence factors of the modulator structure dimension on various optical and electrical parameters. Red and blue indicate positive and negative correlations, respectively, with depth representing strength of the correlation.

DownLoad: Full-Size Img PowerPoint

Fig. 5. (Color online) Z₀ and n_RF distributions at 100 GHz, with G∈[3 7] μm, W_sig∈[8, 20] μm, H_Au∈[0.5, 1.5] μm, under the following dielectric thickness variations.

DownLoad: Full-Size Img PowerPoint

Fig. 6. (Color online) Frequency dependence of (a) Z₀, (b) n_RF, (c) α_m, and (d) EO response for the selected eight subsets from the four quadrants.

DownLoad: Full-Size Img PowerPoint

Fig. 7. (Color online) (a) Three-dimensional schematic diagram of the modulation structure. (b) Enlarged view of the MMI region (upper) and the simulated optical field distribution. (c) Simulated transmission loss as a function of MMI length at 1550 nm. (d) Simulated transmission loss as a function of wavelength.

DownLoad: Full-Size Img PowerPoint

Table 1. Relationships linking the modulator's optical and electrical parameters to the upper and lower oxide layer thicknesses, and the electrode dimensions.

Paparameter	H_box	H_clad	G	H_Au	W_sig
n_g ↓	-	▲
α_int ↓	▲	-
α_el ↓	↑	↑	↑	-	-
V_π·L ↓	-	↓	▼	-	-
Z₀ ↓	↓	↓	↓	↑	▲
n_RF ↑	▼	↓	↑	↓	↑

DownLoad: CSV

Table 2. Dimensional parameter sets for each selected subset, along with their V_π·L and simulated 3-dB bandwidths.

Set	G (μm)	H_au (μm)	W_sig (μm)	H_clad (μm)	H_box (μm)	V_π·L (V·cm)	3-dB BW (GHz)
a1	5.7	0.5	15	0.3	1.5	3.9551	161
a2	5.6	0.5	14.5	0.3	1.5	3.8886	153
b1	5.7	0.5	16	0.3	2	3.9551	125
b2	5.6	0.5	15.5	0.3	2	3.8886	120
c1	6.6	0.5	15.5	0.1	1.5	3.9745	>200
c2	6.4	0.5	15	0.1	1.5	3.8485	>200
d1	6.6	0.5	17	0.1	2	3.9745	197
d2	6.5	0.5	16.5	0.1	2	3.9115	185

DownLoad: CSV

[1]	Wang C, Zhang M, Chen X, et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature, 2018, 562(7725): 101 doi: 10.1038/s41586-018-0551-y
[2]	Desiatov B, Shams-Ansari A, Zhang M, et al. Ultra-low-loss integrated visible photonics using thin-film lithium niobate. Optica, 2019, 6(3): 380 doi: 10.1364/OPTICA.6.000380
[3]	Luke K, Kharel P, Reimer C, et al. Wafer-scale low-loss lithium niobate photonic integrated circuits. Opt Express, 2020, 28(17): 24452 doi: 10.1364/OE.401959
[4]	He M B, Xu M Y, Ren Y X, et al. High-performance hybrid silicon and lithium niobate Mach–Zehnder modulators for 100 Gbit s−1 and beyond. Nat Photonics, 2019, 13(5): 359 doi: 10.1038/s41566-019-0378-6
[5]	Weigel P O, Zhao J, Fang K, et al. Bonded thin film lithium niobate modulator on a silicon photonics platform exceeding 100 GHz 3-dB electrical modulation bandwidth. Opt Express, 2018, 26(18): 23728 doi: 10.1364/OE.26.023728
[6]	Valdez F, Mere V, Wang X X, et al. 110 GHz, 110 mW hybrid silicon-lithium niobate Mach-Zehnder modulator. Sci Rep, 2022, 12: 18611 doi: 10.1038/s41598-022-23403-6
[7]	Tan Y, Niu S P, Billet M, et al. Micro-transfer printed thin film lithium niobate (TFLN)-on-silicon ring modulator. ACS Photonics, 2024, 11(5): 1920 doi: 10.1021/acsphotonics.3c01869
[8]	Jin S L, Xu L T, Zhang H H, et al. LiNbO₃ thin-film modulators using silicon nitride surface ridge waveguides. IEEE Photonics Technol Lett, 2016, 28(7): 736 doi: 10.1109/LPT.2015.2507136
[9]	Ahmed A N R, Shi S Y, Mercante A, et al. High-efficiency lithium niobate modulator for K band operation. APL Photonics, 2020, 5(9): 091302 doi: 10.1063/5.0020040
[10]	Zhang P, Huang H J, Jiang Y H, et al. High-speed electro-optic modulator based on silicon nitride loaded lithium niobate on an insulator platform. Opt Lett, 2021, 46(23): 5986 doi: 10.1364/OL.446222
[11]	Qi Y F, Yue G C, Hao T, et al. Strong-confinement low-index-rib-loaded waveguide structure for etchless thin-film integrated photonics. Opto Electron Adv, 2025, 8(9): 250056 doi: 10.29026/oea.2025.250056
[12]	Valdez F, Mere V, Mookherjea S. 100 GHz bandwidth, 1 volt integrated electro-optic Mach–Zehnder modulator at near-IR wavelengths. Optica, 2023, 10(5): 578 doi: 10.1364/OPTICA.484549
[13]	Rahman A, Valdez F, Mere V, et al. High-performance hybrid lithium niobate electro-optic modulators integrated with low-loss silicon nitride waveguides on a wafer-scale silicon photonics platform. 2025: arXiv: 2504.00311. https://arxiv.org/abs/2504.00311
[14]	Shen J, Zhang Y, Zhang L, et al. Highly efficient slow-light Mach–Zehnder modulator achieving 0.21 V cm efficiency with bandwidth surpassing 110 GHz (laser photonics rev. 19(8)/2025). Laser Photonics Rev, 2025, 19(8): 2570031 doi: 10.1002/lpor.202570031
[15]	Ben Braham C, Belarouci A, Alonso-Ramos C, et al. Silicon-rich Silicon Nitride on Lithium Niobate thin film modulators with 100 GHz Electro-Optical bandwidth in the C-band. 2025 IEEE Silicon Photonics Conference (SiPhotonics), 2025: 1
[16]	Li Z Y, Chen Y, Zhang J M, et al. Hybrid silicon nitride/lithium niobate electro-optical modulator with wide optical bandwidth and high RF bandwidth based on ion-cut wafer-level bonding technology. 2025: Th1E. 1
[17]	Snigirev V, Riedhauser A, Lihachev G, et al. Ultrafast tunable lasers using lithium niobate integrated photonics. Nature, 2023, 615(7952): 411 doi: 10.1038/s41586-023-05724-2
[18]	Wu Y L, Shao S, Zhang H F, et al. Combining lithium-niobate and silicon-nitride integrated photonics in ultrafast tunable, low-noise lasers. Laser Photonics Rev, 2025: e02207
[19]	Ahmed A N R, Nelan S, Shi S Y, et al. Subvolt electro-optical modulator on thin-film lithium niobate and silicon nitride hybrid platform. Opt Lett, 2020, 45(5): 1112 doi: 10.1364/OL.381892
[20]	Nelan S P, Mercante A, Shi S Y, et al. Integrated lithium niobate intensity modulator on a silicon handle with slow-wave electrodes. IEEE Photonics Technol Lett, 2022, 34(18): 981 doi: 10.1109/LPT.2022.3197085
[21]	Badri S H, Kotlyar M V, Das R, et al. Compact modulators on silicon nitride waveguide platform via micro-transfer printing of thin-film lithium niobate. Sci Rep, 2025, 15: 11681 doi: 10.1038/s41598-025-95397-w
[22]	Chang L, Pfeiffer M H P, Volet N, et al. Heterogeneous integration of lithium niobate and silicon nitride waveguides for wafer-scale photonic integrated circuits on silicon. Opt Lett, 2017, 42(4): 803 doi: 10.1364/OL.42.000803
[23]	Churaev M, Wang R N, Riedhauser A, et al. A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform. 49th Eur Conf Opt Commun ECOC 2023, 2023, 2023: 1539
[24]	Cai J C, Kotz A, Larocque H, et al. Heterogeneously integrated lithium tantalate-on-silicon nitride modulators for high-speed communications. 2025: arXiv: 2508.06265. https://arxiv.org/abs/2508.06265
[25]	Weigel P O, Valdez F, Zhao J, et al. Design of high-bandwidth, low-voltage and low-loss hybrid lithium niobate electro-optic modulators. J Phys Photonics, 2021, 3(1): 012001 doi: 10.1088/2515-7647/abc17e
[26]	Han X, Jiang H, He J, et al. Breaking dense integration limits: Inverse-designed lithium niobate multimode photonic circuits. Nat Commun, 2026, 17: 1162 doi: 10.21203/rs.3.rs-7481144/v1
[27]	Xie Y Z, Li J Q, Zhang Y F, et al. Soliton frequency comb generation in CMOS-compatible silicon nitride microresonators. Photon Res, 2022, 10(5): 1290 doi: 10.1364/PRJ.454816

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Received: 18 December 2025 Revised: 02 March 2026 Online: Accepted Manuscript: 27 March 2026

Article Navigation > Journal of Semiconductors > 2026 > Accepted Manuscript

Rui Zhao, Haizhong Weng, Qing Wan. Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/25120032 ****R Zhao, H Z Weng, and Q Wan, Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/25120032

Citation:

Rui Zhao, Haizhong Weng, Qing Wan. Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/25120032 ****

R Zhao, H Z Weng, and Q Wan, Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/25120032

Citation:

R Zhao, H Z Weng, and Q Wan, Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/25120032

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Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator

DOI: 10.1088/1674-4926/25120032

CSTR: 32376.14.1674-4926.25120032

Research Center for Heterogeneous Integration of Functional Materials and Devices, Yongjiang Laboratory, Ningbo, 315202, Zhejiang, China

More Information

Rui Zhao received the Master's degree from Beihang University in 2024. In June 2024, she joined the Yongjiang Laboratory. Her research interests include Lithium Niobate opto-electronic devices and heterogeneous integration
Haizhong Weng received the Ph.D. degree from the Institute of Semiconductors, Chinese Academy of Sciences, in 2018. Then he joined the Semiconductor Photonics Group at Trinity College Dublin as a research fellow. In January 2025, he joined the Yongjiang Laboratory. His research interests include Lithium Niobate opto-electronic devices, nonlinear photonics, microresonator optical frequency combs, and heterogeneous integration
Qing Wan received the Ph.D. degree from the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, in 2004. He has been a Professor at Nanjing University since 2013. Now he is the director of the Research Center for Heterogeneous Integration of Functional Materials and Devices, Yongjiang Laboratory. His research interests include neuromorphic transistors, oxide semiconductor devices, wafer bonding technique, large-size wafer grinding technique, opto-electronic, and MEMS devices
Corresponding author: haizhong-weng@ylab.ac.cn; wanqing@nju.edu.cn
Received Date: 2025-12-18
Revised Date: 2026-03-02

Available Online: 2026-03-27

Abstract

Abstract

Heterogeneously integrated lithium niobate (LN) electro-optic modulators have great potential for high-speed applications, but challenges remain in optimizing performance, particularly in terms of modulation efficiency, bandwidth, and the trade-offs. This work presents an optimized design for a silicon-nitride (Si₃N₄)-loaded modulator on a thin-film lithium niobate (TFLN) platform, consisting of 300 nm-thick LN film and 300 nm-thick Si₃N₄ optical waveguide. By systematically optimizing the dielectric layer thickness, electrode parameters, and achieving velocity and impedance matching, we demonstrate a modulator with a bandwidth exceeding 200 GHz. Our collaborative optimization scheme highlights the critical role of reducing the silicon oxide box layer thickness for velocity matching. We show that multiple structural configurations can achieve bandwidths greater than 120 GHz with V_π·L＜ 4 V·cm, providing feasibility in low-loss design and fabrication. These findings offer valuable design guidelines for high-performance electro-optic modulators suitable for data communications.
- electro-optic modulator,
- silicon nitride,
- thin film lithium niobate,
- heterogeneous integration

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