Silicon nitride based plasmonic components for CMOS back-end-of-line integration

摘要: Silicon nitride waveguides provide low propagation loss but weak mode confinement due to the relatively small refractive index contrast between Si₃N₄ core and SiO2 cladding. On other hand, metal-insulator-metal (MIM) plasmonic offer strong large loss. In this work, MIM-like passive devices based on horizontal Cu-Si₃N₄-Cu or Cu-SiO₂-Si₃N₄-SiO₂-Cu structures are integrated in conventional waveguide circuits using standard CMOS backend processes, characterized around 1550-nm telecom wavelengths fiber-waveguide-fiber method. The Cu-Si₃N₄(~100 nm)-Cu exhibit ~0.78-dB/μm for straight waveguides, ~38% coupling efficiency with 1-μm-wide through a 2-μm-long taper coupler, ~0.2-dB bending sharp 90° bends, ~0.1-dB excess ultracompact 1 × 2 4 power splitters. Inserting ~10-nm SiO₂ layer Si3N4 Cu cover (i.e., Cu-SiO2(~10 nm)-Si₃N₄(~100 nm)-SiO2(~10 devices), improved ~0.37 dB/μm ~52% while degraded ~3.2 dB ~2.1 dB, respectively. These experimental results roughly consistent numerical simulation after taking influence of possible imperfect fabrication into account. Ultracompact ring resonators 1-μm radius demonstrated an extinction ratio ~18 quality factor ~84, close theoretical prediction.