[论文解读] Lithium tantalate electro-optical photonic integrated circuits for high volume manufacturing

Chengli Wang, Zihan Li+12 more|arXiv (Cornell University)|Jun 28, 2023

Photonic and Optical Devices被引用 5

一句话总结

该论文展示了一种基于钽酸锂（LiTaO₃）的可扩展、低成本制造平台，用于高性能电光光子集成电路（PICs），利用现有5G/6G声学滤波器的工业基础设施。作者实现了低传输损耗（5.6 dB/m）、VπL产品为4.2 V·cm，并在O至L波段实现宽带操作，首次在X切钽酸锂中实现孤子微梳生成（重复频率30.1 GHz），适用于高速通信和量子光子学应用。

ABSTRACT

Photonic integrated circuits based on Lithium Niobate have demonstrated the vast capabilities afforded by material with a high Pockels coefficient, allowing linear and high-speed modulators operating at CMOS voltage levels for applications ranging from data-center communications and photonic accelerators for AI. However despite major progress, the industrial adoption of this technology is compounded by the high cost per wafer. Here we overcome this challenge and demonstrate a photonic platform that satisfies the dichotomy of allowing scalable manufacturing at low cost, while at the same time exhibiting equal, and superior properties to those of Lithium Niobate. We demonstrate that it is possible to manufacture low loss photonic integrated circuits using Lithium Tantalate, a material that is already commercially adopted for acoustic filters in 5G and 6G. We show that LiTaO3 posses equally attractive optical properties and can be etched with high precision and negligible residues using DUV lithography, diamond like carbon (DLC) as a hard mask and alkaline wet etching. Using this approach we demonstrate microresonators with an intrinsic cavity linewidth of 26.8 MHz, corresponding to a linear loss of 5.6 dB/m and demonstrate a Mach Zehnder modulator with Vpi L = 4.2 V cm half-wave voltage length product. In comparison to Lithium Niobate, the photonic integrated circuits based on LiTaO3 exhibit a much lower birefringence, allowing high-density circuits and broadband operation over all telecommunication bands (O to L band), exhibit higher photorefractive damage threshold, and lower microwave loss tangent. Moreover, we show that the platform supports generation of soliton microcombs in X-Cut LiTaO3 racetrack microresonator with electronically detectable repetition rate, i.e. 30.1 GHz.

研究动机与目标

• 通过采用已在5G/6G滤波器中大规模生产的钽酸锂（LiTaO₃）材料，克服基于铌酸锂（LiNbO₃）的光子集成电路（PICs）成本高和晶圆尺寸受限的问题。
• 利用现有工业基础设施和晶圆级工艺，实现高性能电光PICs的可扩展、低成本制造。
• 与LiNbO₃相比，实现LiTaO₃基PICs中更低的传播损耗、更低的双折射率、更高的光致折变损伤阈值以及更低的微波损耗正切。
• 在O至L通信波段（1260–1620 nm）实现宽带操作，且因双折射率降低而有效抑制模式混合。
• 首次在X切LiTaO₃中实现孤子微梳生成，支持微波光子学和量子技术应用。

提出的方法

• 采用智能剥离工艺，在150 mm和200 mm基板平台上制造钽酸锂绝缘体（LTOI）晶圆。
• 使用类金刚石碳（DLC）作为硬掩模，结合深紫外（DUV）光刻技术，实现LiTaO₃波导的高精度图案化。
• 采用碱性湿法刻蚀工艺，实现无残留侧壁，最大限度降低波导中的传播损耗。
• 制造厚实、高质量的金属电极，用于行波调制器，实现低VπL产品操作。
• 采用完整的晶圆级工艺流程，集成基板键合、图案化、刻蚀和电极沉积。
• 利用矢量网络分析仪和微梳产生的微波拍频信号的光电探测，表征光学与微波性能。

Figure 1: Lithium-tantalate-on-insulator (LTOI) substrates and optical waveguides. (a) Crystallographic unit cell of $\mathrm{LiTaO}_{3}$ . (b) Colorized SEM of LTOI ring resonator. (c) Colorized scanning electron micrograph (SEM) of etched LTOI (blue) waveguide and sidewall. (d) Colorized SEM cross

实验结果

研究问题

• RQ1 能否利用现有大批量制造基础设施，在钽酸锂（LiTaO₃）上实现低损耗、高性能的电光光子集成电路？
• RQ2 LiTaO₃在可扩展PIC应用中，其电光与光学性能是否与铌酸锂（LiNbO₃）相当或更优？
• RQ3 能否在X切LiTaO₃中实现孤子微梳生成？其产生的微波拍频信号的相位噪声性能如何？
• RQ4 LiTaO₃的低双折射率在多大程度上实现了O至L波段（1260–1620 nm）的宽带、单模操作？
• RQ5 LiTaO₃的低介电损耗正切是否能够支持超导量子处理器的高保真度量子转换？

主要发现

• 作者通过精确的DUV光刻与DLC硬掩模结合的碱性湿法刻蚀，实现了LiTaO₃波导中5.6 dB/m的传播损耗。
• 实现了VπL产品为4.2 V·cm的马赫-曾德尔调制器，表明其具有高电光效率，适用于CMOS兼容操作。
• 微腔的本征线宽为26.8 MHz，对应品质因数约为1.1×10⁶，表明光学损耗极低。
• 在X切LiTaO₃跑道形微腔中成功实现孤子微梳生成，重复频率为30.1 GHz，支持直接电子检测。
• 微波拍频信号的相位噪声为−86 dBc/Hz（10 kHz偏移）和−114 dBc/Hz（1 MHz偏移），优于此前在Si₃N₄和Z切LiNbO₃中的结果。
• 由于双折射率抑制和模式混合减少，该平台可在整个O至L波段（1260–1620 nm）实现宽带、单模操作。

Figure 2: Optical characterization of $\mathrm{LiTaO}_{3}$ photonic integrated circuits. (a) Wafer-scale map of mean intrinsic loss $\kappa_{0}/2\pi$ for similar resonators fabricated using DUV stepper lithography. (b) Normalized resonance transmission spectrum of optical racetrack microresonator at