Silicon photonics is poised to revolutionize data communications and served as the leading technological solution for applications like data center and long-haul communication. Big internet companies are forecasted to be the driving force pushing the silicon photonics to large volume production. By leveraging existing wafer foundry infrastructures, silicon photonics would benefit from economies of scale. To enable volume production for silicon photonics, foundries need to establish a systematic methodology of testing silicon photonics devices. Design of optical process control monitoring (PCM) test structure for silicon photonics and setup of fully automated optical test equipment are still at the research stage. The characterization of the fundamental silicon photonic building blocks and the challenge of wafer-level testing will be discussed in the presentation.

1. Challenges of Silicon Photonics Testing from A
Foundry’s Perspective
YAP Tiong Leh Johnny, Ph.D.
Senior Engineer
Product, Test and Failure Analysis

2. Acknowledgement
• Jeffrey LAM Eddy LO
• MAI Zhi Hong ZHU Lei
• MAN Guo Chang Alan LEK
• Natalie Feilchenfeld John Ferrario
• Kate McLean John Cartier
• Sahoo P B WU Bo
• Ian SEETOH THUM Sok Yee
• YU Ying PEK Seow Siong
Contributions from GLOBALFOUNDRIES Colleagues

3. Outline
• Introduction to Silicon Photonics (SiPh)
• SiPh Components/Devices
• Challenges of SiPh Testing in Foundries
• Summaries
Presentation Flow

4. Introduction of Silicon Photonics
• What is Silicon Photonics?
– Silicon Photonics is the application of
photonics systems that use silicon as an
optical medium[1]
• Why Silicon Photonics?
– Silicon Photonics offers the advantages of
CMOS process technology
– Potential Integration of CMOS Logic with
Optical Device
• Why Outsource To Foundries?
– Economies of Scale
– High Volume Production Experience
– Established Process Control
Definition and Benefit of Silicon Photonics
[1] https://en.wikipedia.org/wiki/Silicon_photonics
Optical Fiber Photodiode
Modulator LASER
4

5. Applications of Silicon Photonics
[1] http://www.submarinecablemap.com/#/ Last updated on March 26, 2016
[2] http://www.electronicsnews.com.au/features/what-bottleneck-silicon-photonics-technology-boost
[3] http://www.space-airbusds.com/en/equipment/mermig-project%E3%80%80bringing-silicon-photonics-to-space.html
[4] http://www.nist.gov/pml/div683/loc-080812.cfm
Transceivers
Lab on Chip
Gyro Cavity
Interconnect
[1]
[2]
[3]
[4]
Medical research/
sensor
Defense
Data Center
Long Haul Communication
5

6. Motivation/Driver for Photonics (Optical Interconnects)
• Big data is getting bigger by the second
– Driving the demand for expansion of Data Centers
• Transporting big data pushes the limits of copper interconnects,
demanding
– Lower Power Consumption
– Wider Bandwidth
– Higher Signal-to-Noise
Ratio [1]
Growth of Data Center
High Growth of Global
Data Center [2]
[1] D. A. B. Miller, Int. J. of Optoelectronics, vol. 11, pp. 155-168, 1997.
[2] DatacenterDynamics Global Industry Census 2011
6

7. Silicon Photonics Device Market TAM
CAGR 38%
SiPh market forecasted to have a turning point in
2018 with first large volume sales for data centre
[1] Silicon Photonics 2014 report, Yole Development, June 2014
[1]
7

8. Investment by Public Fundings
• China
– Major State Basic Research Development Program (973 projects) and
State High-Tech Development Plan (863 projects)
– Funding level per project ~10s of millions of Renminbi[1]
• European Commission
– Photonics Public-Private Partnership (PPP) invested ~ €700 million for
Horizon 2020 program[2]
• United State
– Invested $610 million to spur integrated photonics[3]
• $110M from the Department of Defence, $250M from the state of New York,
and rest from private contributions
More than $1B Invested Worldwide by Public Fundings!
[1] http://www.osa-opn.org/home/articles/volume_22/issue_9/features/integrated_photonics_research_in_china/
[2] http://www.photonics.com/Article.aspx?AID=58353
[3] http://www.gazettabyte.com/home/2015/9/10/us-invests-610-million-to-spur-integrated-photonics.html 8

9. Investment by Private Sector
Almost $1B Transactions for Photonics in Datacenter!
Lightwire (US) February 2010
Silicon CMOS
optoelectronics
interconnects / optical
transceivers.
US$271M Cisco (US)
To face with increasing traffic in
data centers / service providers
Luxtera AOC line
(US)
January 2011 AOC line US$20M Molex (US)
Luxtera may be changing
strategy to become an IP
licensing company. Molex had
AOC product line for 12-channel
AOCs with a product from
Furukawa/Fitel based on a
1060nm InGaAs VCSEL.
COGO Optronics
(CAN)
March 2013 InP modulators & lasers. Est. < $30M TeraXion (CAN)
To access 100Gb InP modulator
technology.
Cyoptics (US) April 2013
InP-based photonic
components.
US$400M Avago (US)
To strengthen products portfolio
for 40Gb & 100Gb data centers
applications.
Kotura(US) May 2013
Si photonics & VOAs for
data center.
$82M Mellanox (US)
To access 100Gb optical engine
for data centers.
IPTronics (US) June 2013
IC for parallel optical
interconnects (drivers).
$47M Mellanox (US)
To access products /
technologies for 100Gb optical
engine.
Caliopa(BE) September 2013
Si-based optical
transceivers for datacoms.
$20M Huawei (CHINA)
To develop European-based
R&D in Si photonics.
Company Date Product
Transaction
value
Acquirer Rationale for Transaction
[1] Silicon Photonics 2014 report, Yole Development, June 2014
[1]
9

10. Silicon Photonics Supply Chain
Suppliers Chip firms
Optical
interconnects
firms Servers End-users
Wafers
Manufacturing
equipment
Materials &
supplies
Design
Waferfab(CMOS&light
source)
Waferprobe:optical&
electricalsort
Assembly(2.5Dassembly,fiber/light
sourceattach,opticaltest,finaltest)
v
etc … etc … etc …
Today, end-users are driving the R&D for
optical data centers.
etc … etc … etc … etc …
[1] Silicon Photonics 2014 report, Yole Development, June 2014
[1]
10

11. Silicon Photonics Components/Device
Modulators
(Active)
Detectors
(Active)
Waveguides
(Passive)
Active
Devices
Modulator (Si-based PN diode )
Photo Detector (Ge-based PiN Diode)
Heater (Ti/TiN based)
Passive
devices
Si Channel Waveguide
Mux/DeMux
Edge Coupler
Top Grating coupler
[1] https://spie.org/membership/spie-professional-magazine/spie-professional-archives-and-special-content/spie-professional-
archives/archived-issues/2011july-archive/2011-july/----------july---------------------/si-x48944-ml
[2] https://www.kth.se/en/ees/omskolan/organisation/avdelningar/mst/research/optics/apodized-waveguide-to-fiber-surface-grating-
couplers-1.315473
[1]
Coupler
11
Mux/DeMux
(Passive)
Coupler Coupler
Waveguide Waveguide
Gratings
(Passive)
[2]
Edge Coupler
(Passive)
Coupler

12. Waveguide
Passive Component
SiO2
Silicon Substrate
BOX
Si
• Total Internal Reflection
– Propagating wave strikes medium boundary
at angle larger than critical angle
• Strong confinement can be formed within the
waveguide
– Large refractive index, n, differences between
Si (n=3.45) and SiO2 (n=1.45)
n1 < n2
12

13. Modulator
• Plasma Dispersion
– Most common method of achieving
modulation
– Changes free carriers
concentration  modulate the
refractive index
• MZI Shift The Relative Phase of Two
Propagating Waves
– Both waves interfere either
constructively or destructively
Active Component - Mach-Zehnder interferometer (MZI)
Continuous Light In Pulse Light Out
Splitter CombinerFixed Refractive
Index
Variable Refractive
Index
Incoming Electrical
Data Stream
13

14. Mux/DeMux
1. Waveguide (mixed λ channel)
2. Free Propagation Region (FPR)
3. Arrayed Waveguides with different length
 different phase shift at the exit
4. FPR  interference happened
5. Waveguides (separated λ channel)
• Light path from (1) to (5)demultiplexer
• Light path from (5) to (1)multiplexer
Passive Component
14
[1] https://en.wikipedia.org/wiki/arrayed waveguide grating
[2] Dai D. et al, Nanophotonics, vol. 3, pp. 283-311, 2014
The orange lines only illustrate the light path.
3
1(5) 5(1)
[2]
[1]

15. Photo Detector
• Silicon is naturally transparent in the 1300nm-
1550nm[1]
– Solution: Germanium-on-Silicon detectors
• Photodiode operation under reverse bias voltage
– In-coming photons create electron-hole pairs 
Photocurrent
Active Component - Photodiode
[1] F. Zhou et al. ISRN Optics vol 2012, ID 428690 (2012)
[2] K. Ang et al. IEEE topic in Q Electronics vol 16, pg 106-113 (2006)
[1]
Pulse Input Light with Data
Information
Reproduced Electrical
Data Stream
15
[2]

16. Challenges of Silicon Photonics (SiPh) Testing in Foundries
• How To Input/Output Light To The Silicon Photonics Chip?
• What To Measure On A Silicon Photonics Chip (Process Characterization)?
• How To Test Silicon Photonics Devices Automatically?
Importance of Optical Testing to Foundries
Silicon
wafer SiPh
1) SiPh wafer-
level fabrication
2) Dicing and
packaging
3) Assembly
PCM tests Wafer
sort tests
Foundry
$ $$ $$$$$
Final tests
16

17. How to Input/Output Light to the Silicon Photonics Chip?
• Two-order of magnitude difference in size between
the core of optical fiber and waveguide
• Direct coupling lead to >96% of insertion loss[1]
Challenges in Coupling
Silica Optical Fiber
Light In/Out
125µm 10µm
SOI Waveguide
0.2µm
0.5µm
Optical Fiber
Waveguide
Core
Cladding
Substrate
Waveguide
[1] CMDITR (Center on Materials and Devices for Information Technology Research) Science and Technology Center
[1]
17

18. Coupling Methods:
Modification to the End of Optical Waveguide
Edge Coupling
• Low coupling loss
• Wide bandwidth
Can only couple light upon dicing!!!
Grating Coupling
• Capability of wafer-level test
• Simplicity of fabrication
• Flexibility of interface positions
• Ease of alignment
HA = 5.5µm
HB = 0.5µm
L = 75µm
[1] A. Sure, Opt Exp, vol. 11, pp. 3555-3561, 2003.
[2] http://www.helios-project.eu/Media/Images/Image1
[1]
[2]
18
Foundries
Approach

19. Testing for Process Characterization
• The Objectives of Silicon Photonics (SiPh) Testing
– Monitor process
– Ensure basic characteristic of SiPh Devices
• Example of testing parameter
Parameter Unit Measurement Type
Photodiode Leakage (Dark Current) nA
Electrical Measurement
(Well Established)
Photodiode Breakdown V
Modulator Leakage nA
Modulator Junction Capacitor pF
Waveguide Propagation Loss dB Optical Measurement
(Under Development)Mux/DeMux Channel Uniformity dB
Modulator Attenuation dB
Optical-Electrical Measurement
(Under Development)
Modulator Phase-shift Efficiency V.cm
Modulator/Photodiode Bandwidth GHz
Photodiode Responsivity A/W
19
Challenges

20. SiPh Test Structure Layout
• Standardized test structure for fixed
probe/fiber positioning.
• Example of DUT:
a) Photodiode
b) Modulator
c) - i) Waveguide or Mux/DeMux
Optical Fiber
Electrical
Probe
Electrical Pads
20
Grating Coupler
Optical Fiber
Grating Coupler
DUT
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
[1]
[1] Edited from Y. Koji. Silicon Photonics II vol 119, chap 1, Springer (2010)

21. Example of Test Structure - Waveguide
• Cut-back Method
– Compared output intensity of waveguide with different length/width
• Propagation Loss
– Intrinsic Loss (carrier absorption)
– Extrinsic Loss (side-wall scattering)
Propagation Loss Measurement
[1] Edited from A. V. Velasco, Faculty of Physical Sciences, Universidad Complutense de Madrid (Spain)
[1]
Optical Grating Coupler
Input
Optical Grating Coupler
Output
Waveguide
21
Parameter
Challenges

22. How to Test Silicon Photonics Devices Automatically?
22
LASER
Controller
LASER
Polarization
Controller
Detector
Optical
Power Meter
Probe
Positioner
Optical
Fiber
Preferably
tunable LASER
Probe Positioner:
• 3-axis stage for course
movement
• Prefer to have peak search
algorithm for fine tuning
[1]
[1] http://www.actphast.eu/technology-platform/tp-5-silicon-based-photonic-integrated-circuits-pics-or-chips

23. How to Test Silicon Photonics Devices Automatically?
• Majority of test time spent on optical probe alignment
• Reduction of alignment time are needed
[1] B. Analui, IEEE Solid-State Circuit, vol. 41, pp. 2945-2955, 2006.
[2] Edited from JEM America Corp.
[1]
23
Fiber Optic
Grating Coupler
[2]

24. Challenges of Silicon Photonics Testing from A
Foundry’s Perspective
• Foundry’s mission
– Provide standardized and comprehensive testing at wafer-level
– Early screening to ensure meeting of process requirement
• Focus of SiPh Testing in Foundries
– Automation In Siph Chip Testing
• Fast, Focused, Low Cost Instrumentation
– Optical Structure Testing
• Improve test structure design to meet customer complex design requirement
– Wafer-level Testing
• Continuous research on grating coupler  improve coupling efficiency and
bandwidth
24

25. Thank you