Technology Developments Towars Silicon Photonics Integration

Transcription

1 Technology Developments Towars Silicon Photonics Integration Marco Romagnoli Advanced Technologies for Integrated Photonics, CNIT Venezia - November 23 th, 2012

2 Medium short reach interconnection Example: connection of high-speed electronics on a line card or link equipment such as Ethernet switches in the data center. 12x10 Gb/s Avago Micropod

3 Advanced Technologies for Integrated Photonics Integrated Si Photonics Large volumes applications Low consumption Small footprint Full integration! Presently laser integration cost exceeds chip cost and laser efficiency is too low. Need for monolithic integrated laser!

4 Advanced Technologies for Integrated Photonics Si Photonics Applications 100 Gb/s based I/O and links (PAM or WDM) - transport network - metro network - data center interconnections (intra and inter) - backhaul - multichip modules - intrachip Wireless network (base station remotization) Switching

5 Medium/short reach interconnection technologies InP/SiO2 PIC, hybrid mounted electronics (ASIC or discrete), wire bonding SOI wafer, laser mounted on chip, external electronics, wire bonding,. SOI wafer, laser mounted on chip, integrated electronics. SOI wafer, electronic integration, laser integration. (Full integration + energy efficient design) Comment: The Future of Silicon Photonics: Not So Fast? Insights From 100G Ethernet LAN Transceivers E. Fuchs, R. Kirchain, S. Liu. JLT 29, (2011) Contrary to popular belief, we demonstrate that InP platforms can, depending on the yields achieved in each technology, have equal to or lower production costs than silicon for all expected production volumes. Silicon photonics does hold great potential to be cost competitive in markets with annual sales volumes above , including servers, computing, and mobile devices.

6 Medium/short reach interconnection technologies

7 Medium/short reach interconnection technologies Si waveguides 32 x 10Gb/s Si-Ge monolithic receiver Ge PD

8 Medium/short reach interconnection technologies Photonic chip

9 Medium/short reach interconnection technologies 3D integration of SOI technology for the photonic layers with Si CMOS technology for the circuit layers. Integration in a 65nm node/12 fab based on wf/wf or wf/die bonding and low capacitance TSV technology. Bond Pads Si Logic Layer Si TSV TSV Thermal Compression Bonding SOI Photonics Layer PD Mod Si waveguide Substrate

10 Medium/short reach interconnection technologies Integrated Laser Source Hybrid mounting III-V Laser: conventional solution. It can be butt coupled or coupled through grating coupler. Coupling loss 1 3dB, TEC, Packaging, assembly. Cost and large consumption. Uncooled solution could help. Bonded III-V Laser: remarkable solution with a certain maturity. CMOS manufacturing to be demonstrated. Low T operation. Good performances. Integration with electronics to be demonstrated. Ge Laser: early stage. Monolithic integration. Potential good performance in power and threshold. 200 nm gain BW. Best at high T ( C).

11 Advanced Technologies for Integrated Photonics basic research: Ge laser ev ev Ge Laser (a) E (b) E (c) E Γ L Γ L Γ L electrons k <111> k <111> <111> k bulk Ge tensile strained i-ge tensile strained n + Ge Ge is pseudo-direct gap. Energy difference between L and G valley only 134meV Tensile strain reduces energy difference % tensile strain due to thermal expansion coefficient difference Liu et al., Opt. Express 15, (2007) n-type doping fills L-valley. Thermal excitation leads to electron scattering into to Γ valley

12 From Optical Pumping to Electrical Pumping Heavy doping in n + and p + Si electrodes for electrical pumping increases modal optical loss Modal losses of 100 cm -1 to 1000 cm -1 depending on Ge waveguide thickness Increase P-doping level for larger material gain in Ge Limited incorporation of P in Ge during growth High P diffusivity limits process temperature 12

13 Ge Laser Design phosphorous concentration (cm -3 ) as grown RTA 600 o C 1min RTA 700 o C 1min depth (nm) 0.01 Delta doping of P to form dopant reservoir for indiffusion. Annealing step to increase doping level in active laser region. CMP to remove dopant reservoir after diffusion step. 13

14 Intensity (a.u.) Sharp Line Emission from Ge Fabry-Perot Laser Intensity (a.u.) ka/cm ka/cm Wavelength (nm) Wavelength (nm) RT measurements Cavity length: 333μm Waveguide height: 100nm Current injection: pulses with 50μs widths at 800Hz Detector spectral resolution: 1.2nm Broad direct bandgap emission observable below threshold only with long sampling times. Laser lines below 1.2nm linewidth. 14

15 Advanced Technologies for Integrated Photonics basic research: Ge laser An electrically pumped germanium laser, Opt. Expr Electroluminescence Laser emission FP Laser Comparison 230 nm Wavelength (nm) 1576nm 1622nm 1656nm

16 Power emission (mw) L- I curve of Ge Fabry-Perot Laser 1,2 1 0,8 0,6 RT measurements Device length: 270μm. Current injection: pulses with 40μs at 1000Hz. 0,4 0, Current density (ka/cm 2 ) Clear threshold behavior at 270kA/cm 2 current density. Output power of > 1mW observed. 16

17 Gain Clamping Conditions for Ge F-P Laser Net material gain (cm -1 ) nm Ge thickness High injection level cm nm Ge thickness Low injection level cm Modal loss (cm -1 ) Wavelength (nm) 17

18 Conclusions Silicon Photonics is promising for short reach, low cost, large volume productions. Cost of Si photonics depends on the level of integration. Photonics and electronics monolithic integration is required both for low cost and consumption efficiency Electrically pumped lasing from monolithic integrated Ge laser is demonstrated Wide gain spectrum of roughly 200nm due to gain clamping observed. Output power > 1mW observed. 18

19 Jurgen Michel, Rodolfo E. Camacho-Aguilera, Yan Cai, Neil Patel, Jonathan T. Bessette, Marco Romagnoli, Lionel C. Kimerling Supported by the Fully Laser Integrated Photonics (FLIP) program under APIC and sponsored by the Naval Air Warfare Center - Aircraft Division (NAWC-AD) under OTA N

20 thank you!

21 Band Structure Engineering for Direct Bandgap Ge Ge Si Ge Si High T Room T Heavy n-type doping + moderate tensile strain direct bandgap cm -1 n-type doping 0.2%~0.25% tensile strain