Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Plasmonics: Novel On-Chip InterconnectionsAbstract— We report antenna designs for surface plasmon polariton coupling to metal-insulator-metal waveguides. Theresulting plasmonic modes were tuned for maximum propagation length along the waveguide: for 1550 nm, we have observedmore than 40 micron propagation (along the length of the waveguide, +x direction) while for 532 nm this is below 10 micron.Our results lay the foundations for on-chip coupler-waveguide-photodetector interconnect technology.State-of-the-art on-chip and chip-to-chip technologies relyon copper interconnects. Ever increasing data transfer ratesand Moore’s Law dictate smaller devices packed into the samearea [1]. Besides, International Technology Roadmap forSemiconductor Industry reports project devices that processand transmit data faster. Interconnections, not chips, havebecome the limiting factor for the future of scaling. Copperinterconnects cannot meet the demanding data transfer raterequirements and have significant bandwidth limitations dueto RC time delays, resistive losses, and frequency dependentcross-talk at high modulation frequencies. In addition to theselimitations, electronic information transmission on a chip alsosuffer from impedance mismatch. On the device side, there isa high impedance and low capacitance, while transmissionlines have low impedance and high capacitance. Thismismatch limits the power transfer, even for the optimumcases [2-4].The incident light’s polarization significantly changes thecoupling efficiency. Because antennas couple SPP’s to thewaveguides in the near-field, the distance between the antennaand the waveguide was kept smaller than 50 nm. The antennashould not be connected to the waveguide either; otherwiseinterference of plasmonic modes reduces propagation length.Antenna and waveguide parameters were swept and the fieldprofiles were compared for metal layer thicknesses of 100,150 and 200 nm. The longest propagation length has beenachieved for 200 nm, while above 200 nm, the propagationlength is no longer enhanced by changing the thickness.Thinner arms (60nm) tend to propagate SPP’s over longerdistances. Reducing antenna gap enhanced local field betweenthe arms, but did not increase the propagation length.Surface plasmon polaritons (SPP) are collective electronoscillations along the interface of metal and a dielectric.Because of the fast decaying fields both inside the metal andthe dielectric, the mode field profile is highly confined alongthe interface. That is why; SPP’s can be a solution forachieving high integration densities, due to the smallattenuation lengths, i.e. 14 nm as our simulations show. SPP’sare proposed to be the data transfer medium for on-chipclocking and signaling. The proposed geometry fortransferring SPP’s is a metal-insulator-metal (MIM)waveguide structure where coupled SPP’s propagate along thetwo metal-insulator interfaces over long distances.In this work, we introduced a simple nanoantenna couplerand a metal-insulator-metal waveguide for demonstrating thepossibility of high density and reliable interconnects. Theinterconnect structure is as in Figure (a) and is placed on 500nm thick thermal oxide. Metallic nanoposts in front of thewaveguide behave as an antenna, increasing the coupling ofoptical field into the waveguide. The waveguide consists ofsilver cladding and silicon oxide core. The structure is excitedby plane waves from the left, propagating to the right. Thesimulations were repeated to optimize the structures over theantenna arm lengths and widths, gaps, metal layer thicknesses,and waveguide-to-antenna distances. The design wasoptimized for the longest propagation distance for thetelecommunication wavelength of free space = 1550 nm. Forefficient coupling, (i) arm length and the cladding width havebeen assumed to be equal, (ii) the arm gap and the core widthare taken as equal. Our simulations (not shown) indicated thatnot making these two assumptions significantly reducedcoupling efficiency.Figure: (a) Simulation volume, incident wave, nanoantenna and the waveguidestructure. (b) Top view of the interconnect. (c) E-field profile along the center of thewaveguide and the antenna (y=0 line), normalized with respect to incident field(d) E-field enhancement profile along the substrate and the interconnect interface,optimized for free space = 1550 nm (e) Normalized E-field intensity profile along thesubstrate and the interconnect interface, for free space = 780 nm.The propagation distances for = 532 nm, 780 nm,1550nm were 3, 9, about 50 μm, respectively. Metal’sabsorption progressively increases for shorter wavelengths.That is why; shorter wavelengths cannot propagate as long asin the 1550 nm case.The subwavelength nature of these interconnects enableshigh integration density. We are going to investigate thistechnique for noise immunity and broadband applications.This work was supported by TUBITAK 108E163, 109E044,EU FP7 PIOS.[1] Moore, G. E., Electronics, Vol. 38, No. 8, April 19, 1965[2] ITRS 2007 Edition,http://www.itrs.net/Links/2007ITRS/2007_Chapters/2007_Interconnect.pdf[3] Ali K. Okyay, PhD Thesis, Stanford University, September 2007[4] Gramotnev, Bozhevolnyi; Nature Photonics 4, 83 - 91 (2010)[5] L. Tang et. al., Nature Photonics 2, 226 - 229 (2008)6th Nanoscience and Nanotechnology Conference, zmir, 2010 625