Silicon Photonics: an Industrial Perspective

Transcription

1 Silicon Photonics: an Industrial Perspective Antonio Fincato Advanced Programs R&D, Cornaredo, Italy

2 OUTLINE 2 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion

3 OUTLINE 3 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion

4 Silicon Photonics Main Application Areas 4 High Performance Computer Data Center Access Network RF Cable Typical Losses of Electrical Transmission 15GHz 1dB/m Typical Losses of Optical Transmission 1310nm SM Fiber 0.5 db/km Backplane 3 db/cm Si waveguide db/cm Board 1 db/cm SiN waveguide 0.1dB/cm Intrachip 1 db/mm SiO 2 waveguide < 0.1 db/cm

5 The Zettabyte Era 5 By the end of 2016, global IP traffic will reach 1.1 ZB per year, or 88.7 EB per month By 2020 global IP traffic will reach 2.3 ZB per year, or 194 EB per month Overall, IP traffic will grow at a compound annual growth rate (CAGR) of 22% from 2015 to 2020 The Zettabyte Era: Trends and Analysis, July White Paper - CISCO

6 Global Data Center IP Traffic: Three-Fold Increase by Annual global data center IP traffic will reach 10.4 ZB (863 EB per month) by the end of 2019, up from 3.4 ZB per year (287 EB per month) in Zettabyte per Year Global data center IP traffic will grow 3- fold over the next 5 years. Overall, data center IP traffic will grow at a compound annual growth rate (CAGR) of 25% from 2014 to By 2019, 86% of workloads will be processed by cloud data centers; 14% will be processed by traditional data centers. Cisco Global Cloud Index: Forecast and Methodology, White Paper - CISCO

7 Supercomputing Power Growth 7 Exponential growth of supercomputing power as recorded by the TOP500 list TOP 500

8 International Standard Requests 8 Speed will increase Size and power will decrease

9 OUTLINE 9 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion Total internal reflection is a special optical condition in which optical rays cannot escape the material in which they are traveling. John Tyndall

10 Optical Properties of Silicon in Near IR (1) 10 Momentum not conserved Indirect Bandgap No laser source Centro-Symmetric Crystal No Electrooptic effect

11 Absorption coefficient (cm -1 ) Optical Properties of Silicon in Near IR (2) 11 Silicon Absorption Coefficient Transparency Photodetectors VISIBLE Wavelength (nm) Wavelength (nm)

12 Electronic-Photonic Monolitic Integration (1) 12 CMOS 130nm CMOS 90nm DRAM Luxtera, ISSCC 2006 IBM, IEDM 2012 Samsung, OFC 2013 BOX SOI nm BUT Photonics PD-SOI or SOI-FinFET UTBB-FDSOI Bulk SOI 130nm,90nm,45nm <100nm 28nm,14nm,10nm <10nm 55nm, 28nm,20nm 22,14,10 nm FinFET 1 µm 0.1 µm 0.02 µm

13 Electronic-Photonic Monolitic Integration (2) 13 Local Photonics Substrate creation Integrate CMOS on Photonics Substrate Photonics Electronics Photonics Electronics Samsung, OFC 2013,GFP2013 Micron, VLSI tech IHP, GFP 2013 Luxtera, ISSCC 2006, IBM, IEDM 2012 Need a re-development of the CMOS technology Cost issues, especially with Advanced Technologies (55nm and below)

14 3D Integration Strategy of ST 14 Opto-Electronic System = Photonic IC + Electronic IC Photonic IC Cu pillar Opto-Electronic IC Independent evolution for optimization of technology platform (process flow & design environment) Opto-Electronic System Electronic IC: CMOS or BiCMOS Cu pillar

15 EIC PIC 3D integration: F2F Assembly 15 EIC PIC EIC 40µm PIC

16 OUTLINE 16 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion

17 l=1310nm & 1490nm PIC25G Silicon Photonics Technology Platform 17 Joint Development started 2012 l Type Function Multimode waveguide Single Mode waveguide Curved waveguide Tapered waveguide 90 C Bend (R=40µm) Optical Passives Directional coupler Split ratio 1 99% Y-junction: Splitter Fiber (8 ) Single Polarization Grating Coupler (TX-out) Laser (13.2 ) Single Polarization Grating Coupler (TX-in) Dual Polarization Grating Coupler (RX-in) WG termination High Speed Amplitude Modulator Vcc=1.8V-2.5V Optical Modulators Phase Modulator Vcc = 2.5V Photodiode High Speed PiN PD - Vcc= V

18 ST Silicon Photonics Platform: PIC25G 18 Single Mode Waveguide cross-section F.Boeuf et al., Electron Devices Meeting (IEDM), 2013 IEEE International, 9-11 Dec Back End of Layer stack cross section

19 300mm Process Integration 19 Existing Tools 300mm Photonics Tool Set Portfolio 300mm PHOTONICS Technological Platform 193 i 193 nm Litho SiGe & Ge epitaxies Ni,Co,Pt silicide Etch Low T Dep High volume Sub-90nm CMOS node tools 193nm/193i photolithography Improved Process control

20 Silicon Photonics pros and cons 20 Key driving force Fabrication based on CMOS technology High volume production Low cost [ $/Gbps ] Small size [ mm 3 /Gbps ] Scalability Speed Channel number Wavelength number Number of functions Different kind of modulation Drawbacks: Silicon is an indirect bandgap material Very inefficient light emitter Si Photodetectors not available at 1310nm and 1550nm Telecom wavelength Light modulation or amplification not possible using direct properties of Silicon BUT It is possible to overcome those difficulties by means of: Monolithic or Hybrid Integration of different materials Dedicated architectures Made possible by CMOS technology

21 OUTLINE 21 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion Photodiode PhaseModulator SPGC PSGC DC WG

22 Fiber coupling 22 Single-mode Fiber Optical Core Silicon waveguide Mode mismatch: Size 10mm vs 400nm Spot-size converter Polarization problem: Only TE mode is propagated in Si-waveguide Polarization splitter AND polarization rotator 10mm

23 Grating Coupler 23 Single Polarization Grating Coupler (SPGC) TE mode Emitted radiadion Polarization- Splitting Grating Coupler (PSGC) F.Boeuf et al., Electron Devices Meeting (IEDM), 2013 IEEE International, 9-11 Dec. 2013

24 Carrier Depletion 24 Real refractive index and absorption coefficient of the doped Si regions due to the free-carrier dispersion (R. A. Soref and B. R. Bennett ): n n n e e h h N N P P 0.8 Lightly doped p- and n- regions are realized in the waveguide to form a p n diode. The depletion area of the diode becomes larger with increasing reverse bias voltage. where: Δn e is the refractive index change due to electron concentration change Δn h is the refractive index change due to hole concentration change ΔN is the electron concentration change in cm -3 ΔP is the hole concentration change in cm -3 Δ e (in cm -1 ) is the absorption coefficient variations due to ΔN Δ h (in cm -1 ) is the absorption coefficient variation due to ΔP losses of 0.1 db/cm require ΔN < 2.7x10 15 cm 3 or ΔP < 3.8x10 15 cm 3 material

25 Carrier Depletion Based High-Speed Phase Modulator 25 M2 M1 Single mode waveguide p n Cut-off frequency measurement Insertion loss vs Phase Shift vs Voltage

26 Mach-Zehnder Interferometer Modulator Pcross Pbar 26 L n P L n P g bar g cross sin cos l l

27 Germanium Photodetector 27 TEM Cross Section Top view Ge PiN diode I-V curve(λ=1310nm) Ge PD 3dB Modulation Bandwidth

28 3D Integrated Silicon-Photonics Transmitter 28 EIC PIC 3D assembly and stand-alone EIC 28Gbps PRBS31 MZM eye diagrams: measurements at quadrature point Travelling-wave push-pull modulator architecture Enrico Temporiti et al., ISSCC Gbps PRBS31 MZM eye diagrams: measurements vs simulations

29 Meas. Control Optical / RF / DC Meas. Full Auto Prober. 300mm Photonics Testing 29 Test Interface Enable full auto characterization at wafer /lot scale (300mm) of: All Optical passive devices (Waveguide / coupler / MZI ) Electro Optical devices: (photodiode / modulator ) Modulation Bandwidth up to 67GHz BER & Eye Diagram up to 28Gbs/s Auto alignement of the fiber array on the grating coupler & fine positioning with piezoelectric actuators X Optical power Y Test Interface: DC/RF Probes Optical head with a 16-channel Fiber Array mounted on 6 axis micro positioner Use of a capacitive sensor to fine adjust distance from wafer top

30 OUTLINE 30 Introduction Silicon Photonics Concept 300mm (12 ) Photonic Process Main Silicon Photonics Devices Future Evolution Conclusion

31 Hybrid integration 31 Photonics SoC (System on Chip) able to perform several optical and electrical functions through hybrid integration Based on Si technology, using 1 or more Si-photonics layers on SOI Using 3D layers of different materials: III-V for laser and/or electro-absorption modulator SiN (or other MidEx materials) for WDM, coupling or sensing Ge or SiGe for far IR applications Integration can rely on local epitaxy, wafer bonding or backside processing Electrical connections are based on CMOS-like BEOL 3D assembly using TSV and Cu-Pillar

32 Conclusions 32 After 25 years of research Silicon Photonics has now reached an industrial maturity for mass production Data-center market will be the main driver for the next 5 years Scalability, cost reduction and downsizing are key factors making Silicon Photonics the only technology allowing to address the requirements of future products for high speed communications 3D face-to-face assembly of PIC and EIC allows maximum flexibility of both photonic and electronic processes Photonics on Silicon substrate has the potential to increase his capabilities thanks to the numerous integration opportunities of different materials