The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

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Rationale and challenges for optical interconnects to electronic chips

Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (∼2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N , N ′-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection—related to the highest occupied and lowest unoccupied molecular orbitals—grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.

http://science.sciencemag.org/content/sci/296/5571/1293.full.pdf

Electrochemistry and Electrogenerated Chemiluminescence from Silicon Nanocrystal Quantum Dots

Laser ablation in liquids : Applications in the synthesis of nanocrystals

Deposition and element fractionation processes during atmospheric pressure laser sampling for analysis by ICP-MS

Metal-based reactive nanomaterials

Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si.

/pdf/hyperfine-structure-of-the-electron-spin-resonance-of-2x0ai4o2mc.pdf

Hyperfine structure of the electron spin resonance of phosphorus-doped Si nanocrystals.

Luminescent nanometer-sized silicon particles are fabricated by laser ablation of a silicon target in helium gas. The formation of products is found to be governed by the dynamics of the laser-ablated silicon particles in the gas. The products deposited on silicon substrates exhibit light emission with a peak at 1.6 eV in the air, while 2.1 eV after annealing for 20 min at 800°C in oxygen gas. Applying the laser ablation technique, we demonstrate a novel technique for fabricating silicon particles embedded in a silicon dioxide film. The particles also exhibit visible light emission.

https://iopscience.iop.org/article/10.1143/JJAP.35.4780/pdf

Light Emission from Nanometer-Sized Silicon Particles Fabricated by the Laser Ablation Method

We report the first observation of the vibrational Raman spectrum of hydrogen molecules ${\mathrm{H}}_{2}$ in crystalline silicon treated with hydrogen atoms at 400 \ifmmode^\circ\else\textdegree\fi{}C. The Raman spectrum of ${\mathrm{H}}_{2}$ in silicon observed at room temperature exhibits a frequency shift of around $4158{\mathrm{cm}}^{\ensuremath{-}1}$ and a very broad half-width of approximately $34{\mathrm{cm}}^{\ensuremath{-}1}$. An isotope shift was also detected at around $2990{\mathrm{cm}}^{\ensuremath{-}1}$ in silicon treated with deuterium atoms at 400 \ifmmode^\circ\else\textdegree\fi{}C. The frequency shifts of the observed lines are in close agreement with those reported for ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ in the gas, liquid, and solid phases.

/pdf/hydrogen-molecules-in-crystalline-silicon-treated-with-kjs7px9dkj.pdf

Hydrogen Molecules in Crystalline Silicon Treated with Atomic Hydrogen.

The dynamics of light‐emitting particles produced by the excimer laser ablation of the high Tc superconductor YBa2Cu3Oy has been investigated by means of space/time resolved optical measurements near the surface region with a space resolution of 100 μm and a time resolution of 0.1 ns. Two distinct components of ablated particles were observed: one with high average velocities over 5×106 cm/s and the other with slow velocities, depending on laser energy density. The position of the maximum emission intensity in the slower component moved away from the surface and was further delayed from the time of maximum laser intensity as the laser energy density increased. If the incident laser was tilted from the normal of the target surface, the spatial distribution of the luminous plume inclined toward the incident laser beam. These results suggest that the slower component consists of light‐emitting particles resulting from the fragmentation of clusters ejected from the surface.

/pdf/dynamics-of-laser-ablated-particles-from-high-tc-4sm3sy72n9.pdf

Dynamics of laser‐ablated particles from high Tc superconductor YBa2Cu3Oy

A gradual downshift and asymmetric broadening of the Si optical phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires (SiNWs) synthesized by laser ablation. This downshift and broadening can be interpreted by the phonon confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

/pdf/phonon-confinement-effect-of-silicon-nanowires-synthesized-3lt1iu0z83.pdf

Kouichi Murakami

Papers

Hyperfine structure of the electron spin resonance of phosphorus-doped Si nanocrystals.

Light Emission from Nanometer-Sized Silicon Particles Fabricated by the Laser Ablation Method

Hydrogen Molecules in Crystalline Silicon Treated with Atomic Hydrogen.

Dynamics of laser‐ablated particles from high Tc superconductor YBa2Cu3Oy

Phonon confinement effect of silicon nanowires synthesized by laser ablation