LSI on-chip optical interconnections are discussed from the viewpoint of a comparison between optical and electrical interconnections. Based on a practical prediction of our optical device development, optical interconnects will have an advantage over electrical interconnects within a chip that has an interconnect lengthless than about 10mm at the hp32-22nm technology node. Fundamental optical devices and components used in interconnections have also been introduced that are small enough to be placed on top of a Si LSI and that can be fabricated using methodsc ompatible with CMOS processes. A SiON waveguide showed a low propagation loss around 0 .3dB/cm at a wavelength of 850nm, and excellent branching characteristics were achieved for MMI (multimode interference) branch structures. A Si nano-photodiodse howed highly enhanced speed and efficiency with a surface plasmon antenna. By combining our Si nano-photonic devices with the advanced TIA-less optical clock distribution circuits, clock distribution above 10GHz can be achieved with a small footprint on an LSI chip.
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