氮化硅-铌酸锂异质集成高速光调制芯片关键技术研究

Lithium niobate based integrated photonics devices have great advantages in such as energy consumption, performance, device size and cost. However, it is hard to be fabricated by the traditional semiconductor technology, and the waveguide loss is a little high. Silicon nitride has similar transmission window and refractive index as lithium niobate, while its fabrication process is compatible with the CMOS technology and its transmission loss is low. In this project, we would realize a hetero-integration of lithium niobate on the phase modulation area of the silicon nitride chip, in order to take full advantage of the low loss silicon nitride waveguides and high nonlinear optical coefficients of lithium niobate. It is expected to overcome the film-stress-induced crack limitation of silicon nitride, which is caused by the planarization process based on chemical mechanical polishing. This project aims to develop a CMOS-compatible waveguide surface planarization technology by reactive-ion-etching, in order to realize the lithium niobate-silicon nitride heterogeneous integration by wafer bonding. After solving the mode field mismatch between silicon nitride and lithium niobate heterogeneous integrated waveguide by a spot-size converter, high-speed switches could be developed, which can realize electro-optical phase modulation and amplitude modulation. The realization of self-developed simple and efficient key hetero-integrated technologies of lithium niobate, can not only help to develop a low-loss, high-efficiency optical modulation device, but also be applied in other nonlinear optics field, which has important scientific significance and practical application prospects.

铌酸锂集成光电子器件在诸如能耗、性能、尺寸和成本等方面有优势，但基于传统半导体工艺实现困难，所制作的波导损耗较大。半导体CMOS工艺兼容的氮化硅材料，其透过窗口、折射率等与铌酸锂接近，传输损耗低。因而，本项目拟在氮化硅芯片上需进行光调制的区域，局部集成铌酸锂薄膜，实现用于信号传输的低损耗氮化硅波导与用于信号调制的氮化硅-铌酸锂异质集成波导的单片集成。首先研究基于等离子体刻蚀工艺的波导表面平坦化处理技术，通过晶圆键合方式实现氮化硅-铌酸锂异质集成，克服现有基于化学机械抛光进行表面平坦化处理时，氮化硅材料易由于膜应力变化而龟裂的瓶颈；再解决氮化硅波导与氮化硅-铌酸锂异质集成波导的模式场失配问题，设计高效的模斑转换器；最后完成高速的电光相位与振幅调制。研究铌酸锂异质集成关键技术，不仅可实现低损耗、高效率的集成光调制器件自主开发，也可用于其他非线性光学效应研究方向，具有重要科学意义与广袤实用前景。

随着大数据时代的到来，通信网络带宽和容量规模迅速增加，基于现有传统光信号处理器件，不仅带宽、速度遇到瓶颈，所消耗的能量也急剧增大，因而急需开发出超高速低能耗的新型集成光电子器件。其中，光调制器作为光信息处理、光谱测量、光存储等多个领域的核心器件，已发展出基于电光、声光、磁光等效应的多种器件。而电光调制器通过外加电场的变化调控输出光的振幅或相位，在能耗、速度、集成性等方面都有一定的优势，其研究最为广泛。铌酸锂集成光电子器件在诸如能耗、性能、尺寸和成本等方面有优势，但基于传统半导体工艺实现困难，所制作的波导损耗较大。对半导体CMOS工艺兼容的氮化硅材料，其透过窗口、折射率等与铌酸锂接近，传输损耗低。因而，本项目以基于异质集成氮化硅-铌酸锂波导平台的高速光调制芯片为主要研究内容，解决了氮化硅波导芯片表面平坦化瓶颈；研究了通过晶圆键合实现氮化硅波导基片上的铌酸锂薄膜异质集成的关键技术，并在此基础上实现了在绝缘体上铌酸锂材料平台的直接氮化硅生长，成功实现了氮化硅-铌酸锂异质集成波导的制备；进一步研究了宽带、高消光比的开关结构，实现了40dB高消光比的马赫-曾德干涉结构开关单元，并以此为基础，研制了偏振无关4×4矩阵光开关。此外，实现了多种三维自反馈型微腔滤波器件，并进一步探索了太赫兹波段的光调制器件。研究铌酸锂异质集成关键技术，不仅可实现低损耗、高效率的集成光调制器件自主开发，也可用于诸如量子调控等方向，具有重要的科学意义与广袤的实用前景。依托本课题的研究，在光学领域重要期刊Opt. Lett.、J. Lightwave. Technol.、Opt. Express等发表标注受本项目资助的论文15篇，其中SCI论文10篇；会议论文6篇，其中邀请报告3项；申请发明专利11项，其中授权4项；培养毕业研究生8名，其中获得国家奖学金、中国仪器仪表学会唐辉电子奖学金各1人次；作为第4参与人获得上海市自然科学二等奖1项。