光子集成是当今科技界的热门课题，提高集成度最为重要。SOI(Silicon- on-insulator)等材料在光子集成中显现出重要的地位，然而其损耗偏大，对集成度产生影响。因此，寻求新的波导材料极为重要。在这种要求下，Si3N4应运而生，成为人们研究的热点。Si3N4结构稳定，禁带宽度宽，Eg~5.1 eV，对紫外到红外整个波段是透明的。在这一光波段中的损耗低达0.045±0.04 dB/m，比SOI波导低3—4个数量级。Si3N4在1550 nm处的折射率~2，能够同Si和SiO2一起构成高性能的介质波导结构，因此是很好的波导材料。Si3N4的热膨胀系数~2.35×10-6 /℃，比Si小许多，在Si上生长Si3N4会产生较大的拉应力，因此容易产生龟裂，生长大面积薄膜或者较厚的Si3N4都十分困难。采用LPCVD或PECVD方法可以在低折射率的SiO2上淀积Si3N4薄膜，形成Si3N4—SiO2波导结构，减小了波导尺寸，提高了集成度。文章综述新型波导材料Si3N4的研究进展，并对其应用进行描述与展望。
Photonic integration is one of the most important issues in scientific research. Silicon-on-insulator (SOI) and other materials play an important role in photonic integration, but their losses are large and affect the integration, so it is very important to find new waveguide materials. As a consequence, Si3N4 came into being and is now a hot area of research. Its crystal structure is stable, with a wide energy band of Eg~5.1 eV, so it is transparent in the whole optical range from ultraviolet to infrared. Also, its optical loss in this range is very low, α~0.045±0.04 dB/m, which is lower than that of SOI waveguides by 3—4 orders of magnitude. Its refractive index at 1550 nm is ~2, so combined with Si and SiO2, high-performance dielectric waveguide structures can be designed. Its thermal expansion coefficient is ~2.35×10-6/℃, smaller than that of Si, so its growth on Si will introduce a larger tensile stress and may produce cracks. Thus, growing thick films of large area is very difficult. By using low-pressure or plasma-enhanced chemical vapor deposition, Si3N4 films can be deposited on low refractive index SiO2 to form Si3N4-SiO2 waveguides, which are smaller in size and allow better integration. Current research progress in this field is reviewed, and future application prospects are reviewed.
- 刘耀东，李志华，余金中. 光子集成用的新型波导材料Si3N4[J]. 物理, 2019, 48(2): 82-87.
- LIU Yao-Dong，LI Zhi-Hua，YU Jin-Zhong. New waveguide material Si3N4 for photonic integration[J]. Physics, 2019, 48(2): 82-87.