silicon photonics

Silicon Photonics Opportunity, Applicatoins & Recent ResultsDirector Photonics Technology Lab Intel Corporation Mario Paniccia, Intel Corporation CREOL April 1 2005 Agenda Opportunity for Silicon Photonics Copper vs optical Recent advances Intels SP Research Recent results – Intel’s Silicon Laser Summary *Third party marks and brands are the property of their respective respective owner 2 ELECTRONICS: Moore’s Law Scaling MIPS 10000 Processor Pentium® III Processor Pentium® II Processor Pentium® Pro Processor Pentium® 4 $/MIPS 100 1000 10 100 Pentium® Processor Intel486TM DX CPU Intel386TM DX Microprocessor Microprocessor 1 10 0.1 MIPS $/MIPS 0.01 1995 1997 1999 2001 1 1985 1987 1989 1991 1993 Integration & increased functionality Volume economics – faster, better, cheaper *Third party marks and brands are the property of their respective respective owner 3 The Opportunity of Silicon Photonics Take advantage of enormous ($ billions) CMOS infrastructure, process learning, and capacity – Available tools: litho requirements typically >90nm – Draft continued investment going forward Potential to integrate multiple optical devices Micromachining could provide smart packaging Potential to converge computing & communications Industry standard silicon manufacturing processes could enable integration, bring “volume economics” to optical. enable integration, bring to optical. To benefit from existing infrastructure optical wafers must run alongside product.. i.e CMOS fabrication compatible.. *Third party marks and brands are the property of their respective respective owner 4 Today's High Speed Interconnects Primarily Primarily Optical Copper Metro & Long Haul 0.1 – 80 km Chip to Chip 1 – 50 cm Billions Board to Board 50 – 100 cm Volumes Rack to Rack 1 to 100 m Millions Thousands Decreasing Distances→ Need to drive volume economics to drive optical closer to chip *Third party marks and brands are the property of their respective respective owner 5 Copper Approaching Limits Simulation of 20” channel transmitter w/ equalization 0 Channel Attenuation [dB] -10 -20 -30 -40 -50 0 10 18G Low Loss Ro4350 Standard FR4 20 30 40 Red Zone = Eye Closes 12G Data Rate [Gb/s] Copper scaling more challenging. Headroom getting squeezed. Howard Heck *Third party marks and brands are the property of their respective respective owner 6 Electrical to Optical Enterprise Distance: 0.1-10km 10G Silicon Photonics? 10G >= 40G Rack-Rack Distance: 1-100m OPTICAL 40G Optical Tech 3.125G Board-Board Distance: 50-100cm 3.125G 5-6G 10G Copper Tech 10G Chip-Chip Distance: 1-50cm ELECTRICAL 3.125G 5-6G Tra nsit ion Z on e 15-20G 20G 2005 *Third party marks and brands are the property of their respective respective owner 2010+ 7 Transition driven by cost The Photonic Dilemma Fiber has much more bandwidth than copper However, it is much more expensive….. *Third party marks and brands are the property of their respective respective owner 8 Photonics: The technology of emission, transmission, control and detection of light (photons) aka fiberoptics & opto-electronics Today: Most photonic devices made with exotic materials, expensive processing, complex packaging Silicon Photonics Vision: Research effort to develop photonic devices using silicon as base material and do this using standard, high volume silicon manufacturing techniques in existing fabs Benefit: Bring volume economics to optical communications *Third party marks and brands are the property of their respective respective owner 9 Agenda Opportunity for Silicon Photonics Copper vs optical Recent advances Intels SP Research Recent results – Intel’s Silicon Laser** Summary *Third party marks and brands are the property of their respective respective owner 10 Silicon Pro’s and Cons + + + + − − − − Transparent in 1.3-1.6 µm region CMOS fabrication compatibility Low cost High-index contrast – small footprint No electro-optic effect No detection in 1.3-1.6 µm region High index contrast – coupling Lacks efficient light emission Silicon will not win with passive devices.. Must produce active devices that add functionality *Third party marks and brands are the property of their respective respective owner 11 Silicon Photonics Breakthroughs Are Accelerating Raman Net Pulsed Gain 9/6: Intel 9/20: Cornell 9/29: UCLA 9/29: CUHK Raman λ Conversion UCLA SRS UCLA Si LEDs STM, Trento 30GHz SiGe Photodetector IBM Integrated APD+TIA UT Low Loss Strip MIT Inverted Taper NTT, Cornel Modeled GHz PIN Modulator Surrey, Naples GHz MOS Modulator Intel PBG WG <25dB/cm IBM PBG WG <7dB/cm IBM, FESTA, NTT CW Raman lasing Feb 05 2001 2002 2003 2004 Progress In Recent Years Is Accelerating still not there… *Third party marks and brands are the property of their respective respective owner 12 Agenda Opportunity for Silicon Photonics Copper vs optical Recent advances Intel’s SP Research Recent results – Intel’s Silicon Laser** Summary *Third party marks and brands are the property of their respective respective owner 13 Intel’s Silicon Photonics Research 1. Develop photonic building blocks in silicon 1) Light Source 2) Guide Light 3) Modulation Waveguides devices First Continuous Silicon Laser (Nature 2/17/05) 4) PhotoPhoto-detection 5) Low Cost Assembly Passive Align 6) Intelligence CMOS 1GHz (Nature ‘04) 4 Gb/s (‘05) SiGe Photodetectors Mirror First Prove that silicon is viable material for photonics *Third party marks and brands are the property of their respective respective owner 14 Packaging Approximate Optical Product Cost Breakdown Packaging 1/3 Device 1/3 Testing 1/3 In addition to device costs, packaging and testing costs must drop with to enable high volume photonics *Third party marks and brands are the property of their respective respective owner 15 Micromachining for Packaging U-Grooves Use standard pick and place technologies along with litho defined silicon micro-machining Tapers Mirror V-Grooves Laser Attach 45° Mirrors Facet Preparation 16 *Third party marks and brands are the property of their respective respective owner Intel’s Silicon Photonics Research 1. Develop photonic building blocks in silicon 2. Integrate increasing functionality directly onto silicon Integrated in Silicon Photodetectors Receiver Chip DEMUX Taper Driver Chip Passive Align Lasers MUX 17 *Third party marks and brands are the property of their respective respective owner Intel’s Silicon Photonics Research 1. Develop photonic building blocks in silicon 2. Integrate increasing functionality directly onto silicon 3. Long term explore monolithic integration ECL Modulator Filter Drivers Multiple Channels CMOS Circuitry TIA Passive Alignment TIA Photodetector *Third party marks and brands are the property of their respective respective owner 18 SILICON LASER What we announced on Feb 17th *Third party marks and brands are the property of their respective respective owner 19 The First Laser Developed by Ted Maiman, published in Nature, August 6, 1960. this ruby laser used a flash lamp as an optical pump Fully Reflective Mirror Flash Lamp Partially Reflective Mirror LASER BEAM RUBY CRYSTAL ROD *Third party marks and brands are the property of their respective respective owner 20 Raman: (Historical Note) Raman Effect or Raman Scattering: A phenomenon observed in the scattering of light as it passes through a transparent medium; the light undergoes a change in frequency and random alteration in phase due to a change in rotational or vibrational energy of the scattering molecules. • Discovered a material effect that is named after him •Nature published his paper on the effect on March 31, 1928 •He received the Nobel prize in 1930 for his discovery • The first laser using the Raman effect was built in 1962 • Today Raman based amplifiers are used throughout telecom • Most long distance phone calls will go through a Raman amplifier Typical Raman Amplifier *Third party marks and brands are the property of their respective respective owner 21 The Raman Effect Materials Silicon Indium Antimonide (III-V) Quartz Lithium Niobate (used for modulators) Diamond Glass Fiber (Raman lasers/amps) Raman gain coefficient (10-8m/MW) 0 5000 10000 15000 20000 Kilometers of fiber ... The Raman effect is 10,000 times stronger in silicon than in glass fiber This allows for significant gain in centimeters instead of kilometers Centimeters of silicon Fabrication of low-loss silicon waveguides is challenging *Third party marks and brands are the property of their respective respective owner 22 Raman Gain in Silicon Silicon Waveguide Pump in Pump out Pump/probe experiment Probe in Probe out 2.5 2.0 Raman Gain and WG loss vs. Input Pump Power 3.5 3 Raman Gain/WG Loss (dB) -0.2 -0.4 Gain-Loss (dB) -0.6 -0.8 -1 -1.2 -1.4 -1.6 0 200 400 Pump Power (mW) 600 Raman Gain WG Loss Loss w/o Pump Gain-Loss Raman gain (dB) (b) 1.5 1.0 0.5 0.0 2.5 2 1.5 1 0.5 0 200 400 600 800 1000 Input pump power(mW) 0 CW Gain Saturation due to TPA induced FCA *Third party marks and brands are the property of their respective respective owner 23 Two Photon Absorption In silicon, one infrared photon doesn't have the energy to free an electron e e e e e e e Free Electron e e SILICON WAVEGUIDE But, occasionally, two photons can knock an electron out of orbit. Free electrons absorb individual photons and cancel Raman gain *Third party marks and brands are the property of their respective respective owner 24 Overcoming TPA induced FCA − V + laser beam p-type silicon electrons n-type silicon Raman Gain Gain needed to make a laser oxide intrinsic silicon Gain limit due to Two Photon Absorption problem Pump power *Third party marks and brands are the property of their respective respective owner 25 Effective Carrier lifetime reduction SiO2 passivation Output power (mW) 500 Lifetime=16 ns Lifetime=6.8 ns Lifetime=3.2 ns Lifetime=1 ns Al contact Si rib waveguide Al contact 400 300 200 100 0 0 25 V 5V short open p-region H W h n-region Buried oxide Si substrate 200 400 600 800 1000 1200 Input power (mW) PIN Cross-section TPA coeff ~ 0.5 cm/GW, α 0.39 dB/cm, FCA cross sect 1.45e-17 cm^2 @ 1550 nm. The lifetime is used as a fitting parameter *Third party marks and brands are the property of their respective respective owner 26 CW gain vs. reverse bias voltage WG= ~1.5um by 1.5um NET GAIN NO NET GAIN Pump λ=1550 nm Signal λ=1686 nm 27 *Third party marks and brands are the property of their respective respective owner With gain can build Laser: Silicon Waveguide Cavity 16 mm Rf V bias n-region Rb Pump beam Laser output Dichroic coating SOI rib waveguide p-region Broad-band reflective coating 24%/71% 90% *Third party marks and brands are the property of their respective respective owner 28 2 mm Experimental setup Pump power monitor Pump at 1,550 nm 90/10 Tap coupler Optical spectrum analyzer 0 -10 -20 -30 -40 -50 -60 -70 -80 1684 1685 1686 1687 1688 1689 1690 1691 1692 Lensed Polarization fibre controller De-multiplexer Silicon waveguide LP filter Laser output at Dichroic 1,686 nm coating High reflection coating 90/10 Laser output power meter Tap coupler *Third party marks and brands are the property of their respective respective owner 29 Experimental Set up Test chip with 8 laser WG’s Laser chip *Third party marks and brands are the property of their respective respective owner 30 Typical Lasing Criteria •Threshold behavior: rapid growth in output power when gain > loss •Spectral linewidth narrowing: Coherent light emission *Third party marks and brands are the property of their respective respective owner 31 Threshold, Efficiency, and PIN effect 10.0 9.0 8.0 Laser output (mW) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 25V bias 5V bias 25V slope 5V slope 200 400 600 800 Coupled pump power (mW) Laser turns on at threshold, when gain per pass in cavity becomes greater than the loss. *Third party marks and brands are the property of their respective respective owner 32 Spontaneous emission vs. laser spectrum 2.50 2.50 Lasing Lasingsignal signal Spontaneous Spontaneous emmission emmission 2.00 2.00 Spectralpower power(a. (a.u.) u.) Spectral 1.50 1.50 1.00 1.00 Magnified 10^ 5x 0.50 0.50 0.00 0.00 1668.5 1668.5 1669 1669 1669.5 1669.5 1670 1670 1670.5 1670.5 Wavelength Wavelength (nm) (nm) When lasing, the spectrum becomes much more narrow and much higher in power. *Third party marks and brands are the property of their respective respective owner 33 Wavelength tuning (comparison) 0 -10 0 -10 pump 1552 nm 1554 nm 1556 nm 1558 nm Spactral power (dB) Spactral power (dB) -20 -30 -40 -50 -60 -70 -80 1680 1548 nm 1550 nm -20 -30 -40 -50 -60 -70 -80 1542 1548 nm 1550 nm 1552 nm 1554 nm 1556 nm 1558 nm 1685 1690 1695 1700 1547 1552 1557 1562 Laser wavelength (nm) Laser wavelength (nm) Silicon Raman laser *Third party marks and brands are the property of their respective respective owner Commercial ECDL 34 Potential Applications *Third party marks and brands are the property of their respective respective owner 35 Communications Applications PUMP LASER passively aligned waveguide coupler amplified data beam Si Raman Amplifier weak data beam 101110 101110 silicon waveguide (cm’s) laser cavity passively aligned PUMP LASER Si Multi-Channel Transmitter modulators MOD P MUX MOD MOD MOD N splitter Optical Fiber Si Raman Modulator integrated mirrors *Third party marks and brands are the property of their respective respective owner 36 Covering the Gaps • Different wavelengths require different types of lasers • Mid-Infrared very difficult for compact semiconductors • Raman Lasers could enable lasers at these wavelengths • Applications in sensing, analysis, medicine, and others 2.1µm Ho:YAG laser Compact Semi. Lasers PUMP LASER 2.9µm Er:YAG laser cascaded mirrors >2µm Could enable lasers for a variety of applications *Third party marks and brands are the property of their respective respective owner 37 Summary Long term true convergence opportunities are with silicon B/W will continue drive conversion of optical into interconnects Tremendous progress from research community Need to continue pushing & improving performance Research breakthrough with CW silicon laser Integration is next set of challenges In order to benefit Technologies must be CMOS fabrication compatible to benefit from HVM & infrastructure Silicon will not win with individual devices, but with integrated modules that bring increased total functionality & intelligence at a lower cost *Third party marks and brands are the property of their respective respective owner 38 BACKUP *Third party marks and brands are the property of their respective respective owner 39 Benefits of Integration Photonic Integration: Reduction in interfaces – lower loss Reduction in size Simpler assembly, testing, packaging Cost Optoelectronic Integration: Reduce parasitics, improved high-freq performance Further size, testing, packaging reductions ? Cost Integration is only useful if integrated device has benefit (functionality, cost, performance) over discrete devices *Third party marks and brands are the property of their respective respective owner 40 CMOS Integration Challenges – Film topology – Coupling to fiber – Contaminating the fab – Yield metrology – Thermal budgets – Heat dissipation – Complexity / yield Optoelectronic Integration To benefit from existing infrastructure optical wafers must run alongside product, introducing additional pragmatic challenges *Third party marks and brands are the property of their respective respective owner 41 Surface Topology: Litho vs DOF • Depth of focus (DOF) shrinks as litho improves • Many optical devices are much taller than transistors For 0.18µm and better, topology exceeds DOF New planarization techniques required for advanced litho DOF vs. Litho Technology (µm) 8µm Taper 0.25 0.5 µm 0.18 0.35µm 0.09 0.2µm Transistor on 90nm 0.9µm Rib 0.3µm Strip 0.1µm gate *Third party marks and brands are the property of their respective respective owner 42 Fiber Coupling Taper from (W x H): 10 x 8 µm to 2.5 x 2.3 µm Assume zero roughness Tip=0.5 Tip=1.0 Tip=2.0 10 Taper loss (dB) • Coupling from standard fiber to Si waveguides requires special structures (tapers, gratings, etc). • For wedge tapers, etch angle as well as the tip lithography impact loss. • Sidewall roughness is also a factor 1 1dB 0.1 80 82 84 86 88 2dB 90 Sidewall angle (degrees) Source: Intel Getting light from fibers into silicon waveguides will require couplers. For certain structures litho and etch parameters must be carefully controlled. *Third party marks and brands are the property of their respective respective owner 43 Yield Metrology • CMOS fabs monitor thousands of parameters across wafer in line • Tight control – e.g. CMOS gate width held to 10’s of angstroms • Significant per-wafer cost savings from screening out yield early • In-line wafer level optical probing is very immature • Most optical device testing is performed after wafer dicing To truly gain from HVM processing, automated & non-destructive techniques for probing optical devices at the wafer level must be developed *Third party marks and brands are the property of their respective respective owner 44 Opto-Electronic Integration (cont) Thermal: For optoelectronic integration , optical devices must tolerate heat generated by CMOS circuits. Simulated multi-core thermal map IO Pads Core Core Temp °C 80-85 75-80 70-75 65-70 60-65 Process compatibility: @ 10Gb/s CMOS IC’s need 90nm technology Silicon Photonic devices may only need ~.25um Other Logic Cache Core Core IO Pads Yield: Typical industry IC yields are high, but the process windows are extremely tight. Tweaks to enable opto-electronic integration may effect IC yield Trade off of yield and process compexity will determine if opto-electrical integration valuable *Third party marks and brands are the property of their respective respective owner 45 Animation Click in box while in slide show mode to start *Third party marks and brands are the property of their respective respective owner 46 Click outside animation box after animation Extending and Expanding Moore’s Law Sensors Mechanical Discrete SSI LSI VLSI Wireless E X P Biological A EXTENDING D Fluidics I N G Optical *Third party marks and brands are the property of their respective respective owner 47 Two Photon Absorption in Silicon Conduction band Pump λ=1.55µm Silicon band gap 1.1 eV Valence band Two photons can simultaneously hit an atom Combined energy enough to kick free an electron *Third party marks and brands are the property of their respective respective owner 48