Feasibility of Plasmonic Circuits Merged with Silicon Integrated Circuits

Plasmonic signal transmission via nanoscale plasmonic waveguides is a new technique with the potential to increase the information transfer capacity in silicon integrated circuits (ICs). During propagation, surface plasmon polaritons (SPPs) exhibit characteristics of a lightwave whose transmission loss is mainly determined by the collective oscillation of electrons. Using this lightwave aspect of SPPs, information can be transmitted using plasmonic signals and optical transmission circuits and networks can be built at the micro/nanoscale. This size scale correlates well with that of electronic circuits comprising metal-oxide-semiconductor field-effect transistors (MOSFETs). In this article, the feasibility of on-chip interconnects and other circuits were discussed and confirmed on the basis of previously developed plasmonic components. The first example examined herein was a wavelength-division-multiplexing circuit comprising a multiplexer and demultiplexer (in 1310 and 1550 nm-wavelength bands), discussed based on the experimental results for each component. Multiplexed signals at the multiplexer were guided into a single-mode waveguide, divided at the demultiplexer and then passed to the electronic circuits. The transmitted plasmonic signals were converted to electric signals at the slits etched on the gate electrode, thereby driving the MOSFET without photodetectors, whereupon the MOSFET-amplified signals were outputted to the electronic circuits. The second example was coherent signal transmission via plasmonic circuits. The signal transmission was performed using micro/nanoscale plasmonic circuits in a manner similar to those of optical fiber transmission systems. These coherent signal transmissions via plasmonic signals were experimentally confirmed, being detected and converted to electric signals at the slits etched on the gate electrode of the MOSFET and then outputted therefrom. These experimental examples confirmed the feasibility of plasmonic circuits integrated with MOSFETs. In plasmonic circuits, signal transmission loss is generally high compared to that of electric and lightwave signals. Herein, it was numerically confirmed again that the plasmonic signal transmission losses were lower than those of electric signals transmitted in electric circuits for plasmonic circuits not exceeding an area of a few hundred square micrometers. The loss of lightwave signals (e.g., transmitted in silicon waveguides) was much lower than those of plasmonic signals. However, as the waveguide width approached the cut-off wavelength, the loss quickly increased to be greater than that of plasmonic signals. This work indicates that plasmonic circuits have an advantage in nanoscale circuits. The circuits presented herein are currently too primitive for actual silicon IC applications, but are adequate to indicate the feasibility of merging plasmonic circuits with silicon ICs.