PHOTONICS RESEARCH GROUP 1 PHOTONICS RESEARCH GROUP Silicon Photonics: silicon nitride versus silicon-on-insulator Roel Baets , Ananth Z. Subramanian, Stéphane Clemmen, Bart Kuyken, Eva Ryckeboer, Peter Bienstman, Nicolas Le Thomas, Günther Roelkens, Dries Van Thourhout, Philippe Helin*, Simone Severi*, Xavier Rottenberg* Ghent University – imec * imec
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Silicon Photonics: silicon nitride versus silicon-on … Silicon-on-Insulator versus silicon nitride Silicon nitride fabrication platforms Silicon nitride on-chip spectrometers Application
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PHOTONICS RESEARCH GROUP 1
PHOTONICS RESEARCH GROUP
Silicon Photonics: silicon nitride versus silicon-on-insulator
Roel Baets, Ananth Z. Subramanian, Stéphane Clemmen, Bart Kuyken, Eva Ryckeboer, Peter Bienstman, Nicolas Le Thomas, Günther Roelkens, Dries Van Thourhout, Philippe Helin*, Simone Severi*, Xavier Rottenberg*
Ghent University – imec* imec
PHOTONICS RESEARCH GROUP 2
What is silicon photonics?
The implementation of high density photonic integrated circuits by means of CMOS process technology in a CMOS fab
Enabling complex optical functionality on a compact chipat low cost
PHOTONICS RESEARCH GROUP 3
CMOS technology economics
CMOS fab huge cost G$
Fabrication run (25 wafers) large cost 100K$ - M$
Fabrication run (MPW-mode) moderate cost 10-100K$/user
Chip (large volume) very low cost 1-100$
Chip (moderate volume) very low cost 1-100$
Chip (low volume) low cost 5-500$Assuming the process flow is based on the standard tool set of the CMOS fab.
And assuming the fab is fully loaded.
PHOTONICS RESEARCH GROUP 4
Outline
Silicon-on-Insulator versus silicon nitride
Silicon nitride fabrication platforms
Silicon nitride on-chip spectrometers
Application example
PHOTONICS RESEARCH GROUP 5
Why silicon-on-insulator photonics
High index contrast very compact PICs
CMOS technology nm-precision, high yield, existing fabs, low cost in volume
High performance passive devices
High bitrate Ge photodetectors
High bitrate modulators
Wafer-level automated testing
Hierarchical set of design tools
Light source integration (hybrid/monolithic?)
Integration with electronics (hybrid/monolithic?)
n1(=3.5)>n2(=1.45)
PHOTONICS RESEARCH GROUP 6
Limitations of silicon-on-insulator PICs
Spectral transparency: shortest
Spectral transparency: longest
Optical power limitation (1.3/1.5µm)
Distributed backscatter
Optical pathlength error
T-sensitivity of pathlength
Layer stack flexibility
Integration with CMOS electronics
1.1 µm
4 µm
10’s of mW
%’s per cm
0.1% - level
0.01%/K
Limited
Challenging
Silicon bandgap
SiO2 absorption
Two-photon absorption
nm-level sidewall roughness + HIC
nm-level width inaccuracy + HIC
Thermo-optic coeff. silicon
SOI-wafers made by bonding
Technical or economic mismatch
PHOTONICS RESEARCH GROUP 7
High index contrast of SOI: distributed scattering
PHOTONICS RESEARCH GROUP 8
Optical power limitation
Jalali et al, OPN 2009
PHOTONICS RESEARCH GROUP 9
Crosstalk in SOI based AWG’s
S. Pathak et al, IEEE Photonics Journal 2014
Typical crosstalk values in SOI-based AWG: 20-25 dB
This example: 27 dB (for 8-channel AWG)
PHOTONICS RESEARCH GROUP 10
Silicon photonics: dealing with the limitations
Si
SiO2
[2um box]
Si3N4
SiO2
without leaving the CMOS fab
Silicon: n=3.5Silicon oxide: n=1.45Very high index contrast
Silicon nitride: n=2Silicon oxide: n=1.45Moderately high index contrast
PHOTONICS RESEARCH GROUP 11
Limitations of silicon-on-insulator PICs
Spectral transparency: shortest
Spectral transparency: longest
Optical power limitation (1.3/1.5µm)
Distributed backscatter
Optical pathlength error
T-sensitivity of pathlength
Layer stack flexibility
Integration with CMOS electronics
1.1 µm
4 µm
10’s of mW
%’s per cm
0.1% - level
0.01%/K
Limited
Challenging
Silicon bandgap
SiO2 absorption
Two-photon absorption
nm-level sidewall roughness + HIC
nm-level width inaccuracy + HIC
Thermo-optic coeff. silicon
SOI-wafers made by bonding
Technical or economic mismatch
0.4 µm
x10
÷10
÷10
÷10
excellent
doable
SiN PICs
PHOTONICS RESEARCH GROUP 12
Layer stack flexibility
Metal or DBR reflector underneath silicon nitride
Quantum dot integration within silicon nitride layer
Photonic ICs with two photonic layers
13
Focusing Grating Coupler with AlCu/TiN bottom reflector
Unclad section to be filled with sensing solution
Light coupling section Distribution
Network
- Grating Coupler with metal back-reflector for in-coupling
- Waveguides with optimized evanescent field overlap
- Power splitters (MMI) for light distribution network
Si
SiO2
SiO2SiO2
SiN
14
Focusing Grating Coupler with AlCu/TiN bottom reflector