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1HiLight Semiconductor Ltd
HiLight
CONFIDENTIAL
Don’t forget the electronics!Considerations for highly integrated silicon photonics devices
Photenex – Wednesday 11th OctoberSilicon Photonics Adoption in UK Industry
HiLightSemiconductor Ltd
Christian Rookes [email protected]
VP Marketing
2HiLight Semiconductor Ltd
HiLight
CONFIDENTIAL
HiLight Semiconductor Introduction
Founded 2012; Experienced Optical Team
VC backed, private company
Four previous successful IC company ‘exits’
>20 CMOS IC Designers
Southampton & Bristol Design Centres
Optical PMD Chipsets to 100Gbps+
Pure CMOS on 12” wafers
Now 55nm, 40nm and 28nm
Next 22nm/16nm
40M+ ICs shipped
3HiLight Semiconductor Ltd
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Optical ‘PMD’ Transceivers and ICs
Nx 25Gbps PMD examples 25GbE SFP28 LR
Integration in CMOS
100GbE QSFP28 SR4
PMD ICs:
Bare Die & Packaged Parts Transimpedance Amplifiers (TIAs) Limiting Amplifiers (LAs) Laser/VCSEL Drivers (DML) Modulator Drivers (EML) CDRs Integrated Combinations of above
4HiLight Semiconductor Ltd
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Optical Transceivers
ROSA = Receiver Optical Sub-AssemblyTOSA = Transmitter OSA
SFP+ QSFP+SFF (FTTH)
BOSA = Bi-Directional OSA
1.25/2.5G 1 – 10G 40G
LDD/VCSEL & L.A.(+ CDR)
Access
Telecom/Wireless/Datacom
Data CentreHiLight Product
QSFP28100G
SFP2825~28G
x1/x4 TIA+LA+CDRx1/x4 Tx Driver + CDR
‘Combo’ IC
TIA
‘Chip-On-Board’ IC
Optical Engines100G+
Bulk Optics Integrated Photonics
IntegratedPhotonics
200G400G800GTBD+
5HiLight Semiconductor Ltd
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Motivation? Cloud Scale Computing
Bandwidth demand == Increasing data rate Increase/Maintain Port Density & Lower Power
Leaf/ToR
Spine
48xSFP28 25G
32xQSFP28 100G
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Bulk Optics >> Integrated Photonics
Bulk Optics Bulk Optics used up to 100Gbps Well defined: Many Standards and
industry MSAs Many varied & manual processes
Known E/O and O/E interfaces 50Ω/100Ω Electrical interfaces Defined packaging technologies Electrical modelling available
Function blocks as separate elements
Integrated Photonics From 100Gbps + Target high automation Requires new tools, methods and
manufacturing processes
Re-define E/O and O/E interfaces? Optimise electrical interfaces? New approaches to packaging possible Measure & model electrical interfaces
Needs a holistic approach- Consider electronics from the start
7HiLight Semiconductor Ltd
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Why HiLight uses CMOS for PMD ICs
Advantages
Cost!
Power consumption
Capacity – 12” Wafers
Low noise TIAs- High sensitivity receivers
Digital integration- MCU, Memory, Control
Enables volume- Same process as high volume
consumer ICs
Low wafer/chip cost
Challenges
Experienced Analogue CMOS designers
NRE (mask set) costs
Layout:Schematic ratio
Requires volume
Tx drive capability- Lower voltages
- Smaller currents
8HiLight Semiconductor Ltd
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CONFIDENTIAL
HLx100G – 4x 25Gbps integrated CMOS chipset
100Gbps Integrated Receiver
4x TIA+LA+CDR
MMF and SMF
Low Power
100Gbps Integrated Transmitter
4x VCSEL+CDR
Low Power
Overview
Target < 1W total (Tx+Rx)
Rx 0.5dB x-talk (channel to channel)
TIA LA CDR
x4
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Photonic Integration
Hybrid Integration
Photonics separate from electronics
Choose best process technology for each functional element- Electronics – CMOS (≤28nm)- Optics - SiP (45~130nm)- Light Source (III-V)
Flexible & Scalable- Die sizes won’t be the same
Challenges for electro-optical interfaces- Bonding/Packaging
Full Integration
Photonics and electronics integrated on monolithic chip- But still need III-Vs! (Lasers)- SiGe for SiP, PDs & Electronics
Dedicated process- Selected for Photonics capability- Compromise elsewhere- Scalable/portable?
Electronics ‘shoe-horned’ into best process for photonics –compromises
Development time Vs Industry rate of change
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Electrical Interfacing with PMD ICs
Photo-detector <> TIA- Low capacitance vs active area; Wire-bond ‘peaking’
Modulator|Laser <> Driver IC- Bonds, microstrip >> direct wire-bonds/flip or bumped
Interface – Bond Wires, Flip Chip- Alternatives to wire-bonding or flip-bumping?
Driving Lasers – impedance matching- Impedance matching on-chip; previously off-chip- Wave-shaping to compensate for mismatch/bandwidth
Driving Modulators low power/low voltage- Modulator voltage drive; DML modulation current
X-talk/EMI (electrical)- Consider effects in photonics IC as well as electronic IC
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Example – 10G APDs
Was thought given to electrical interface? Was RF performance considered?
APD chip
Chip-on-Carrier
G-S-G;optimum pad sizes
G-S; Large anode padCathode on underside
Non symmetric;Large bond pads
Symmetric G-S-G
None of the above APD vendors provides a good electrical model!
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Example - GND provision on silicon µbench
Example of an integrated optical engine
No provision for RF GND between optics and Rx IC!
Integrated Photonicsmicrobench
Receiver ICHiLight HLR100G (4x 25G)
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Example – 25G VCSEL Model
Provided LIV data S-parameters
Not provided Electrical equivalent model E-O model (Rate equation)
Not considered RF metalisation Electrical variation
14HiLight Semiconductor Ltd
HiLight
CONFIDENTIAL
Holistic Approach Required
If the end goal is ‘optical transceivers on chips’…Lowest power, smallest form-factor, least cost
Then all aspects of transceiver design need to be considered whilst developing the photonics
Including electronics, interface, packaging
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Opportunities from holistic approach
Integrated control- Automatic control of Tx Extinction Ratio (in addition to mean power)- On-chip, highly accurate, temperature sensors- Performance monitoring (Bias, VDD)
Lower power- Reduce power in E/O and O/E interfaces- Reduce power required in photonics == reduce power in electronics- Reduce optical losses == reduce power in electronics
Performance- Reduce interface parasitics (Ls, Cs) == increased bandwidth- Improved receiver sensitivities- Increased transmission distances (EQ/EDC/Pre-Emphasis)
Manufacture & Cost- Scalable, highly automated- Built-in self test (BIST); Used widely in IC industry- High capacity, lower cost
16HiLight Semiconductor Ltd
HiLight
CONFIDENTIAL
Areas for Collaboration (wish list)
Low power transmitters (modulators / lasers)- Lower modulator voltages [≤ 1V] == low power (CMOS compatible)- More efficient lasers (DML) == less modulation current
• Impedances closely matched to output drive stages
Improved receivers (photodiodes)- Low capacitance == low TIA noise- High responsivity/gain
Reduced optical interfaces losses- Lower loss == Easier TIA & Driver design! == Lower Power
Improved electrical connections- Consider metalisation RF effects – symmetry and reduced parasitics- Beyond wire-bonding: Flip-chip/bumping alternatives
Photonics device modelling – electrical interface- Electrical characteristics of Photodiode, Laser, Modulator, VCSEL
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Summary
HiLight has significant experience developing highly integrated, high-speed PMD functions in pure CMOS- Low power, high performance- Low cost, high yield & capacity- Highly integrated functions
Silicon Photonics can benefit from CMOS IC/IP integration but need to consider the electronics capability whilst developing optics
Closer collaboration between Photonics and Electronics desirable
Holistic approach for optimised power, performance and cost