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

Silicon nitride waveguides provide low propagation loss but weak mode confinement due to the relatively small refractive index contrast between the Si3N4 core and the SiO2 cladding. On the other hand, metal-insulator-metal (MIM) plasmonic waveguides offer strong mode confinement but large propagation loss. In this work, MIM-like plasmonic waveguides and passive devices based on horizontal Cu-Si3N4-Cu or Cu-SiO2-Si3N4-SiO2-Cu structures are integrated in the conventional Si3N4 waveguide circuits using standard CMOS backend processes, and are characterized around 1550-nm telecom wavelengths using the conventional fiber-waveguide-fiber method. The Cu-Si3N4(similar to 100 nm)-Cu devices exhibit similar to 0.78-dB/mu m propagation loss for straight waveguides, similar to 38% coupling efficiency with the conventional 1-mu m-wide Si3N4 waveguide through a 2-mu m-long taper coupler, similar to 0.2-dB bending loss for sharp 90 degrees ends, and similar to 0.1-dB excess loss for ultracompact 1 x 2 and 1 x 4 power splitters. Inserting a similar to 10-nm SiO2 layer between the Si3N4 core and the Cu cover (i.e., the Cu-SiO2(similar to 10 nm)-Si3N4(similar to 100 nm)-SiO2(similar to 10 nm)-Cu devices), the propagation loss and the coupling efficiency are improved to similar to 0.37 dB/mu m and similar to 52% while the bending loss and the excess loss are degraded to similar to 3.2 dB and similar to 2.1 dB, respectively. These experimental results are roughly consistent with the numerical simulation results after taking the influence of possible imperfect fabrication into account. Ultracompact plasmonic ring resonators with 1-mu m radius are demonstrated with an extinction ratio of similar to 18 dB and a quality factor of similar to 84, close to the theoretical prediction. (C) 2013 Optical Society of America