High Performance, Low Cost PIN, APD Receivers in Fiber Optical Networks and FTTx Applications Hui Nie 4/23/2005 WOCC-2005
Receiver Applications � Back Bone Core Nodes LR and VLR I nterface Cards � Metro Transport Line Cards � Metro Access Line Cards ( ADM’s) Long-Haul Backbone Metropolitan Backbone Metropolitan � Transceivers Access � Transponders Enterprise � OXCs Access • FTTx Applications/Demands also heating up! WOCC-2005
Photodetectors and Optical Receivers � Introduction � Photodetectors Technologies � Overviews � PIN Photodiodes � Avalanche Photodiodes (APDs) � APD Design Trade-offs � Photoreceivers Technologies � Overviews � High Performance MSA Compliant Receivers & ROSAs � PIN, APD ROSA in FTTx Applications WOCC-2005
Photodiodes Technologies � Overview Transit Time Bandwidth RC Time Bandwidth Surface-Illuminated PINs � PINs Waveguide PINs Traveling-Wave PINs Etch-Regrowth Planar SACM APDs Buried-Mesa APDs w/ Regrowth Guard Ring � APDs Resonant-Cavity APD w/ Thin Multiplication Layer Wafer-Fused SHIP APD InGaAlAs/InAlAs Superlattice APD Waveguide APD WOCC-2005
Photoreceiver Sensitivities v.s. Bit-Rate -10 PIN OEIC PIN Hybrid EDFA Preamp Sensitivity @ BER=10 -9 (dBm) APD Hybrid -20 Quantum Limit -30 -40 -50 0.1 1 2.5 10 20 40 Bit Rate (Gbit/s) WOCC-2005
Receiver Systems & Applications (10Gb/s Systems) 0 10 Gb/s Receivers Sys. 0.3 dB/km -10 Dispersion Received Power (dBm) limit 0 PIN+Amp . . 2 5 d B -20 / k m APD+Amp. (+EDC) -30 0.4 dB/km 0.6 dB/km EDFA+PIN -40 1.5 µ m 1.3 µ m -50 0 20 40 60 80 100 120 140 Transmission Length (km) WOCC-2005
Industry Standard Top-illuminated Planar PIN Bonding pad Dielectric coating p+ Metal Contact SiNx Cap Layer Zn Diffused p+ InGaAs Absorption InP Buffer layer n - InP Substrate n++ AR coating WOCC-2005
High-Speed Surface-illuminated Mesa PINs InGaAs/InP Graded Double � Heterostructure p-i-n Metal Reflector Alloyed p-Metal Superlattice Interface Grading � Small Mesa Size <10 µ m 2 � i InGaAs < 0.2 µ m InGaAs Absorption Layer � Air-Bridged PMGI Undercut, Mushroom Mesa to � Metal n-Metal p InP Minimize Parasitic Capacitance QE <25%@1.3 µ m � Hard to Manufacture � n InP Integrated Bias Circuit (Bias Tee � and Matched Resistor) InP:Fe Substrate Possible Wafer-Fusion DBRs to � Enhance QE SiNx Coating Light Input WOCC-2005
Waveguide Photodetectors (WGPDs) Side-Illumination � Optimize Bandwidth and � QE Independently Multimode Ridge � Waveguide Micro-Lenses Fiber � Coupling, Small Spot Size External QE>70% � p+ InP Bandwidth>100GH p+ InGaAsP � i InGaAs -0.2 µ m Can be integrated OEIC � n+ InGaAsP n+ InP Photoreceiver polyimide WOCC-2005
Traveling-Wave Photodetectors (TWPDs) Electrical Waveguide � Concomitant with Optical Waveguide Match Between Electrical � Wave and Optical Wave (50 Ω ) Eliminate RC Time Tradeoff � 1 µ m Higher Saturation Power � Bandwidth=172 GHz, QE~40% � Small Geometry w=1 µ m � WOCC-2005
Multiplication Process Enhance Performance Multiplication region Distance p+ i n+ Electric field Injected electron Primary and Secondary electron E(k) + + + Time x Gain process will slow down Secondary hole transit-time! High Electrical Field near Figure of Merit: avalanche breakdown! Gain-Bandwidth Product WOCC-2005
APD Photocurrent & Gain vs. Temperature 1.E-04 13 12 11 10 1.E-05 9 8 Current, A Gain 7 6 1.E-06 5 4 3 2 1.E-07 1 0 10 20 30 40 50 60 70 Reverse Voltage, volt n40C n20C 0C 25C 50C 85C M_40C M_20C M0C M25C M50C M85C WOCC-2005
How does APD Enhance Rx Sensitivity? Receiver Sensitivity vs. APD Gain, TIA noise -24 Sen(120nA) Sen(250nA) Sen(350nA) -26 Receiver Sensitivty (dBm) Optimum-M Locus of Optimum APD gain -28 APD Noise < TIA Noise APD Noise > TIA Noise -30 -32 -34 -36 1 5 9 13 17 21 25 29 APD Gain WOCC-2005
Planar Separate Absorption, Multiplication (SAM) APD Structure P+ Diffusion p-metal Guard Ring SiNx layer n- InP cap layer n+ InP Multi. n- InGaAsP layer n- InGaAs abs. layer n+ InP Buffer n+ InP Sub. AR coating n-metal WOCC-2005
Planar SACM/SACGM APD n-Metal AR SiO 2 InGaAs/InP Two-step � MOCVD Planar Structure � p+ InP X j Etch and Regrowth Charge � and Multiplication Region X d n- InP Multiplication Diffusion controlled � t mesa n InP Charge t charge Multiplication Layer (single Grading Layer Diffusion or Well Etching- n InGaAs Diffusion) t InGaAs n- InGaAs Absorption Xd ~ 0.2-0.4 µ m � n- InP Buffer t Buffer GB product = 122 GHz � n+ InP Substrate Noise Ratio k ~0.45 � No Implant � WOCC-2005
Resonant-Cavity InGaAs/InAlAS SACM APD Resonant-Cavity Structure � High QE ~ 75% � Mesa Isolated � SACM Configuration � Thin InAlAs Multiplication � Region (200 nm) Lower Noise k ~ 0.18 � InGaAs Cap Ring Contact Bandwidth>20 GHz � h υ p+ InAlAs High Gain-Bandwidth � Dielectric DBR 50 nm InAlAs Spacer Product Metal Ring Probe Metal Contact 60 nm InGaAs Abs. Layer 50 nm InAlAs Spacer 150 nm p-InAlAs Charge Polyimide APD Active Region 200 nm InAlAs Multiplication n+ InAlAs/InGaAs DBR n+ InAlAs n+ InP Buffer Layer Semi-Insulating InP Substrate WOCC-2005
Wafer-Fused SHIP APD Silicon Heterointerface � Au/Zn Contact Photodetector (SHIP) PMGI Wafer-Fused Si � Multiplication Region Mesa Isolated (20-30 µ m) � p+ InGaAs Backside Illumination � n- InGaAs Bandwidth= 13 GHz � Bonding Interface GainxBandwidth= 315 � GHz p-type Implant n-type Si Substrate Reliability Issue � WOCC-2005
Buried Mesa APD with Regrown Guard-Ring Proton Regrown Mesa Etch and Regrowth Implant � p-InP Isolation Layer (Patented) Isolation No Diffused Junctions and � Multiple Implanted GRs P+-InP Regrowth p-InP Guard Ring � + Implanted Guard Ring n-InP Mulutplication Bandwidth< 4GHz for OC-48 � Applications (2.5 GHz) InGaAsP GB Product=37 GHz � i-InGaAs Sensitivity= -33 dBm � Excess Noise Factor=0.4 � n-InP WOCC-2005
Planar InGaAlAs/InAlAs MQW APD SI InP Substrate � Ti Implanted Guard-Ring Inverted Mesa Junction AR Coating � Ti Implanted Guard-Ring to � Decrease p-concentration of Field-Buffer Layer p+ InP SI-InP Substrate Dark Current Increase Due to P - InGaAs � Implantation p+ InP Field Buffer Zn Diffused SiN X Passivation � Region p+ Zn Diffusion Isolation � InGaAlAs/ InAlAs Contact Metal Deposition � Superlattice Flip-Chip Bonding � Cd=0.15pF, Cp=0.06pF p-contact n+ InAlAs Cap � R L =25 Ω to achieve � Sn Bump Bandwidth=15.2GHz Id=0.36 µ A@ M=10 � GB Product = 120GHz � WOCC-2005
Waveguide APD Multimode Waveguide Structure � Mesa Etch and SiNx Passivation � 20 µ m InAlAs/InAlGaAs MWQ � p-Metal Multiplication Layer ~0.25 µ m 6 µ m InGaAs Abs. Layer ~ 0.3 µ m � SiNx p+ InAlGaAs Top and Bottom InAlGaAs � InAlGaAs Cladding Layer ~ 0.8 µ m n-Metal InAlAs/InAlGaAs MQW Bandwidth= 20 GHz � GB Product= 160 GHz n+ InAlGaAs � Large Dark Current � 1 µ A @ 90% V B InP Substrate � Edge Coupled w/ Lensed Fiber (3 � µ m Spot Size) WOCC-2005
Real-World APD Device Specifications � Quantum Efficiency, Responsivity � Gain characteristics � Bandwidth @ M=10,12 when P IN is low (Sensitivity) � Bandwidth @ M< 4 when P IN is high (Overload) � Primary Dark Current � Excess Noise Factor � Capacitance � Breakdown Voltage WOCC-2005
Performance of APD comes with price! Trade-off 1: Bandwidth~ Responsivity � InGaAs Absorption Layer Thickness � Trade-off 2: RC Bandwidth ~ Transit Time Bandwidth � InGaAs, InP layer thickness � Device geometry � Trade-off 3: BW@ M~10 ~ BW@ M~3 � Multiplication layer doping � Diffusion junction depth control (Ehet control) � Trade-off 4: Breakdown Voltage ~ Thickness, Doping � InGaAs, InP layer thickness � Multiplication layer doping � WOCC-2005
APD Design- Balance between Trade-offs APD Bandwidth vs. Gain 10 3 dB Bandwidth (GHz) 1 1 10 100 Gain WOCC-2005
TriQuint APD Chips Over than 15 years of design and volume manufacturing APDs used � in commercial communication systems (AT&T Bell Labs -> Lucent -> Agere -> TriQuint -> CyOptics?) High quality, high yield and low cost MOCVD epi � Reliability proven with > 5000 hrs aging and >15 years of field use � High-speed automated wafer level electrical and optical probing � systems Receiver performance demonstrated with high performance APD � chips WOCC-2005
Failure Rates vs. Activation Energy Failure Rate vs. Ea 1000 P rojected Failure R ate, With >5000 hrs 100 MOCVD APD accelerated aging test, activation energy is FIT 10 extracted. 1 0.1 0.4 0.5 0.6 0.7 0.8 0.9 1 Activation Energy, eV With the estimated Ea of 0.96 eV, these devices have very small FIT (< 1 FIT). WOCC-2005
TriQuint Receiver Product Family � Traditional butterfly package receiver � MSA small-form-factor surface-mounted Receiver � Ceramic packaged ROSA � TO-can based ROSA WOCC-2005
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