Slides of Group IV Photonics 2015 plenary talk, PDF

Transcription

Silicon Nanophotonic Packaging
Enabling large-scale deployment of photonics
through cost-efficient and scalable packaging
T. Barwicz, Y. Taira, T. W. Lichoulas, N. Boyer, H. Numata, Y. Martin, J.-W. Nah,
S. Takenobu, A. Janta-Polczynski, E. L. Kimbrell, R. Leidy, M. Khater, S. Kamlapurkar,
S. Engelmann, Y. A. Vlasov, P. Fortier
August, 2015
© 2015 IBM Corporation
Cost-Efficient Photonic Packaging
August, 2015
Cost can hinder the societal impact of a technology
Cost can define impact
Telecom fiber capacity
Tb/s
100
10
1
Gb/s
100
Tesla Motors, Tesla Roadster 2.5
First highway-capable electric vehicle
• $109k+  ~2400 sold (2008-2012)
• critical debut  limited Earth impact
10
1
1986
Adapted from Winzer, OPN 2015
1994
2002
2010
2018
• massive bandwidth
• cost prevents widespread applications
Cost is not just a commercial concern. It defines the accessibility of a technology.
Today’s challenge in optics: accessibility  reduce cost by 10-100X  major impact
2
Tymon Barwicz et al.,
August, 2015
Integration is changing the cost structure of optical devices
Cost structure of legacy devices
from discreet components
Discreet
components
Impact of photonic integration
 less components, assembly, testing
Assembly
Impact of silicon photonic
CMOS made Si fabrication
reliable and cheap
 large scale integration
 tiny cost
Testing
Cost
100G legacy
100G-LR4
Si Phot. 100G
lightwavestore.com
10G SONET transponder
•
•
3
Major cost reduction across the board with Si photonics.
Some cost elements remain unchanged  limiting factor.
August, 2015
Silicon photonics may be hampered by everything but the silicon
Silicon photonics device cost
Silicon chip(s)
Everything else
 assembly
 final test
 fiber connector(s)
 laser(s)
 etc.
Need to reduce the cost of
“everything else” for large
scale deployment
Leverage high-throughput microelectronic assembly lines for photonics packaging
Leverage costefficiency of
microelectronics in
package not just wafer
foxconn
datacon
4
August, 2015
What are we looking for in optical inputs and ouputs?
100GE agreements
400GE proposals
# of λs
λ spacing
Fiber count
LR4
4
4.5 nm
2
PSM4
1
N/A
CWDM4
4
CLR4
4
# of λs
λ spacing
Fiber count
LR8
8
4.5 nm
2
8
PSM4
1
N/A
8
20 nm
2
4x100G
4
20 nm
2
20 nm
2
8x50G
8
4.5 – 10 nm
2
For universal approach
Bandwidth  73 nm + wiggle room for fabrication/temperature tolerances
Number of fibers  ≤ 8 in core applications
 up to tens in peripheral applications (but not hundreds/chip)
Requirements 1.
2.
3.
4.
5
Low cost per optical port
Large bandwidth for CWDM
Scalability in port count (>8)
Scalability in manufacturing volume
August, 2015
Our solutions to low-cost and scalable photonic packaging
Parallelized fiber assembly
Standard MT fiber
interface
Compliant polymer interface
Standard MT fiber
interface
Polymer waveguides
in flexible ribbon
Cleaved
fiber array
InP die
Flip-chip
electrical connections
Flip-chip
Photonic die
InP laser array
Si
Direct flip-chip assembly of InP die
•
•
6
Both approaches fully compatible with high-throughput assembly lines.
Minimum number of parts and assembly steps for cost efficiency and scalability
August, 2015
Example of full package integration in high-throughput tools
flip chip
1. Laser(s) pick & place,
anneal and underfill
2. C4 flip-chip assembly and reflow
flip assembly
flip assembly
4. Coverplate, cure adhesive
3. Optical I/Os pick & place,
adhesive cure, C4 underfill
•
7
A few steps to a 1st level package for LGA or BGA surface mount technology (SMT)
August, 2015
Main challenges to leveraging high-throughput tools for photonics
1. Limited placement accuracy of ± 10 um
Self-alignment for 1-2 um accuracy
Polymer ribbon
Mode engineering for max tolerances
Connect at largest mode for tolerances
10 um
fiber mode
Photonic chip
Mode expansion
on wafer
Avoid small-mode fibers for cost and tolerances
2. Inflexible pick-and-place handling
Vacuum pick-tip handling
Pressure-sensing movement only vertical
Vacuum
picktip
Chip
assembly
Integrate polymer lid for fiber handling
8
August, 2015
Parallelized fiber assembly: details
InP die
Polymer lid
Fiber ribbon
V-groove
array
1
Cleaved ends
2
InP attach region
Flip-chip electrical interface
Standard MT
fiber interface
3
•
•
9
InP die
Photonic die
Low cost pick-and-place assembly in high-throughput tools (T.Barwicz et al. ECTC 2015)
Arbitrary number of fibers in 1D array, in-plane coupling for CWDM bandwidth.
August, 2015
Parallelized fiber assembly: automated assembly results
12 fiber array
Polymer lid
Short MT ferrule
Photonic die
Cross-section of an assembly, all 12 fibers seated.
Pick-tip
Fiber core
Adhesive
Polymer lid
…
100 um
Si
Fibers
butted
Side-view polished cross-section
Lid
Coupler in suspended
membrane
Fiber
Si
100 um
Adhesive
Sliding base
•
•
10
Sliding base enables fiber butting on coupler with pure vertical pick-tip movement.
Coupler in suspended membrane with undercut filled with adhesive at assembly.
August, 2015
Parallelized fiber assembly: fiber self-alignment in action
Pick tip
Polymer lid
Fiber
V-groove
Si photonic
chip
Pick tip
reflection
•
•
11
Can re-align fiber offsets of up to ~40 um.
Concept implemented in a common R&D flip-chip bonder
August, 2015
Metamaterial converter for coupling to cleaved standard fiber
Metamaterial converter
SiO2
SiO2
Si
Fiber coupler
Si
Undercut region
Tapered up
12
Venting
hole
Hybrid waveguide
Solid waveguide
SiO2
Non-linear taper
•
•
Si
S-band metamaterial converter
V-groove
Undercut
region
Butt-junction
Linear tapers
Coupler embedded in suspended oxide membrane for isolation to Si handle
First use of hybrid waveguide transition in Cheben et al., Optics Lett. 2010
August, 2015
Optical measurements of metamaterial converter performance
Loss to fiber (dB)
O-band converter response
-1
-1.3 dB
-2
TE
TM
1.26 1.28
Chip ID
1
2
3
4
5
Max in
-1.1 dB -1.2 dB -1.1 dB -2.4 dB -1.9 dB
polarization
0.8 dB
-3
1.31 um measurement with water immersion (n~1.31)
1.3 1.32 1.34 1.36
Wavelength (um)
Min in
-1.4 dB -1.5 dB -1.4 dB -2.6 dB -2.1 dB
polarization
Position on
random random random edge
wafer
edge
Measurement setup
Jig for pressing fibers into grooves
13
•
Manual assembly to V-grooves, no active
alignment (OFC’15, Th3F.3).
•
Spread on single wafer: -1.1 dB to -2.6 dB
•
V-groove variability expected to dominate spread
in this early production tools implementation
August, 2015
Montecarlo demonstrates manufacturability of fiber self-alignment.
V-groove related misalignment
Total statistical
misalignment
•
•
•
•
•
•
V-groove align to coupler
V-groove top open width and overetch
Anisotropic etch selectivity, depth
1
Total fiber core to waveguide misalignment
1.5
y misalignment (um)
y misalignment (um)
V-groove related misalignment (Montecarlo)
1.5
0.5
0
-0.5
-1
-1.5
-1.5 -1 -0.5 0 0.5 1
x misalignment (um)
V-groove uncertainty
Fiber diameter, non-circularity
Fiber core non-concentricity
1
0.5
0
-0.5
-1
-1.5
-1.5 -1 -0.5 0 0.5 1
x misalignment (um)
1.5
1.5
10,000 random error combinations plotted
with the marginal x and y distributions
•
•
14
Montecarlo analysis demonstrates manufacturability with 3σ misalignment < ±1.3 um
Details in T. Barwicz et al., ECTC 2015.
August, 2015
Compliant polymer interface: concept details
Ferrule
lid
Polymer
ribbon
Standard MT fiber interface
InP laser arrays
Flexible
region
Ferrule
Flip chip
Polymer
coupling region
InP attach region
•
•
15
InP die
Photonic die
Large number of optical ports per polymer interface, flexible for mechanical reliability
Low cost pick-and-place assembly in high-throughput tools
August, 2015
Compliant polymer interface: optical design for large bandwidth
•
•
16
Butt-coupling to fiber in standard MT interface
Adiabatic transformation in polymer ribbon and adiabatic coupling to Si
August, 2015
Compliant polymer interface: mechanical demonstration
Cross-sectional diagram of interface
Polymer ribbon
Si chip
Polymer waveguides
Si waveguides
Cross-sectional micrograph
Micrograph of polished ferrule facet
Ferrule lid
100 um
Polymer ribbon backing
Polymer waveguides
Ferrule
•
17
Polymer ribbon backing
Lamination glue
Polymer alignment ridge
SelfSelfalignment
alignment
structure
structure
UV adhesive
Si wafer
Si alignment groove
20 um
Self-alignment structures provide ± 1-2 um alignment despite ± 10 um placement accuracy
of high-throughput tools (T. Barwicz et al., ECTC 2014, Y. Taira et al. ECTC 2015)
August, 2015
Compliant polymer interface: self-alignment in action
Pick tip
Polymer
ribbon
Polymer
ridge
Si groove
Reflection
on Si chip
Si photonic
chip
18
August, 2015
Compliant polymer interface: optical demonstration
Typical spectral response
Polymer ribbon
Standard MTP
connector
Active
alignment
2
Automated assembly
19
Loss from fiber to silicon (dB)
1
-2
-2.5
TE
TM
OFC’15, Th3F.5
-3
-3.5
-4
-4.5
1.47
Polymer
transparency
Scattering at abrupt
chip-edge transition
1.49
1.51
1.53
Wavelength (um)
1.55
1.57
• Large bandwidth compatible with CWDM
• Unexpected polarization dependence at
long wavelengths
• Need design and assembly tweaks
August, 2015
Compliant polymer interface: scattering at abrupt junctions
(a)
(a) (b) (c)
(b)
adhesive
SiO2
0
-0.4
-0.8
TE design
TM design
Worst TE
Worst TM
-1.6
0
•
20
0.6
1.2
1.8
Adhesive height (um)
Si
Taper edge scattering
Taper edge loss (dB)
Chip edge loss (dB)
Chip edge scattering
-1.2
(c)
0
-0.4
-0.8
TE design
TM design
Worst TE
Worst TM
-1.2
-1.6
2.4
0
0.6
1.2
1.8
Adhesive height (um)
2.4
Scattering at chip edge and taper edge show the correct polarization
dependence and potential strength to explain excess loss (OFC’15, Th3F.5)
August, 2015
Compliant polymer interface: analysis of optical performance
Expected contribution
At design
point
Worst within
tolerances
Fiber-to-polymer coupling
0.2 dB
0.6 dB
Transition to wide polymer
waveguide
0.1 dB
0.2 dB
Polymer routing
0.3 dB
0.6 dB
Adiabatic coupling to Si
0.4 dB
1.1 dB
Total
1.0 dB
2.5 dB
Excess polymer loss
~0.5 dB
~0.5 dB
Scattering at abrupt junctions
~1.0 dB
~1.0 dB
Experimental range
~2.4 dB
to ~4.4 dB
•
21
Computational
tolerance analysis
(adapted from
IEEE Photon. J.,
6600818, 2014)
Rough preliminary
assertion
(OFC’15, Th3F.5)
Rough estimate of excess loss reconciles computational predictions with
experimental results  excess loss not fundamental and is being addressed
August, 2015
Direct flip-chip bonding of InP laser arrays in high-throughput tools.
Solder induced self-alignment
10 um
InP die with laser array
Photonic die or wafer
Pick and place, then anneal
Photonic die
Mode engineering for max tolerances
Field profile of “strip-loaded” coupler
BPSG
Mode size
on Si
Mode size
on InP
1 um
Connection at maximum delocalization
•
•
•
22
Si3N4
SOI metamaterial
Tighter alignment than in fibers as inherently smaller mode
Fully compatible with high-throughput assembly lines  no ball lenses, etc.
Solder surface tension pushes InP die at anneal on lithographically defined stops
August, 2015
Direct flip-chip bonding: example implementation in test vehicle
Top view micrograph of Si chip receiving structure
Waveguide
couplers
Standoff
Standoff and
lateral stop
Edge of
recess
Solder pads
200 um
Flipped micrograph of mockup laser die
Metal pads
•
23
Lateral stop
Lithographically defined stops on both Si and InP for lateral alignment
August, 2015
Experimental demonstrations of solder induced self-alignment
Cross-section of stops after assembly
Flipped laser
mock-up chip
Butting
Infrared view through assembly at anneal
Mock-up
laser pads
Lateral stop on
flipped chip
Photonic
pads
Tacking
fluid
Vertical and lateral stop
on photonic die
50 um
10 um
Photonic die/wafer
Cross-section of solder pads after assembly
Flipped laser mock-up chip
AgSn solder
Photonic die
•
•
24
10 um
Patterning limits accuracy at butting of lithographically defined stops.
Solder pads offset by design for sustained force at butting (J.-W. Nah et al, ECTC 2015)
August, 2015
Conclusion
Silicon photonics is changing the cost structure of optical devices
 Cost items that were of no particular interest before can be limiting now
Need disruptive advances in cost-efficiency and scalability of photonic packaging
 Leverage high-throughput microelectronic assembly lines for photonics
Identified main challenges
and their resolution
 tight alignment, fiber handling, etc.
Short MT ferrule
25
Photonic die
Photonic die
Ferrule
12 fiber array
Polymer lid
Demonstrated cost efficient and
scalable packaging
 working on bringing 3 solutions to
the photonics community
Polymer ribbon
Photonic die
August, 2015
Team and Acknowledgment
IBM Watson, NY USA
Design, fabrication, analysis
IBM Research - Tokyo
Ribbon-ferrule assembly
Outside partners
Ted Lichoulas
Eddie Kimbrell
Fiber stub fabrication
IBM - Burlington
Chip manufacturing
IBM Bromont – C2MI
Assembly, measurement
Shotaro Takenobu
Polymer ribbon fabrication
Masato Shiino
Custom ferrule fabrication
Follow our progress
Through our IBM project website  Google “Silicon nanophotonic packaging.”
26

Slides of Group IV Photonics 2015 plenary talk, PDF

Transcription

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