© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 1 of 20
A 1.23pJ/b 2.5Gb/s Monolithically Integrated
Optical Carrier-Injection Ring Modulator and All-
Digital Driver Circuit in Commercial 45nm SOI
Benjamin R. Moss1, Chen Sun1, Michael Georgas1, Jeff Shainline2,
Jason S. Orcutt1, Jonathan C. Leu1, Mark Wade2, Yu-Hsin Chen1,
Kareem Nammari2, Xiaoxi Wang1, Hanqing Li1, Rajeev Ram1,
Milos Popovic2, Vladimir Stojanovic1
1Massachusetts Institute of Technology, Cambridge, MA, 2University of Colorado, Boulder, CO
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 2 of 20
Motivation
Difficult for electrical I/O to simultaneously improve
energy-efficiency and bandwidth density
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20 25
Chip2Chip Backplane
En
erg
y-c
ost
[pJ/b
]
Data-rate [Gb/s]
Best electrical links
Loss ~10dB
Loss ~20-25dB
I/O
Source: ISSCC
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 3 of 20
• WDM improves bandwidth density
– 0.5 to 1Tb/s per waveguide (16-32 wavelengths)
• Monolithic integration improves energy-efficiency
– 100fJ/b to 1pJ/b
System Concept
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 4 of 20
Monolithic Photonics Platform
• 45nm IBM SOI
• No process changes
• Monolithic integration
• Substrate removed
Source: Orcutt, Optics Express 2012
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 5 of 20
Ring Modulator Device
• Strip-loaded (rib) waveguide
• Poly-Si over Body-Si
• Lateral PIN diode
• Carrier-injection operation
=
Optical In
Optical
Through
PIN
Device Cross-Section Source: Orcutt, Optics Express 2012
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 6 of 20
Modulator Device Operation
Laser
Optical Zero Unbiased
Transmission
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 7 of 20
Modulator Device Operation
Laser
Optical Zero Unbiased
Transmission
Optical -3dB
Bandwidth is
45 GHz
Max
Extinction:
-13dB
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 8 of 20
Modulator Device Operation
Laser
Optical Zero Unbiased
Transmission
Optical One Carrier Injected
Transmission
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 9 of 20
Modulator Device Operation
Laser
Optical Zero Unbiased
Transmission
Optical One Carrier Injected
Transmission
Extinction Ratio
Insertion Loss
Resonance Shift
(Energy Cost)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 10 of 20
Modulator Device Properties
Electrical bandwidth:
200MHz
Source: Orcutt, Optics Express 2012
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 11 of 20
Effect of Signal Conditioning T
rad
itio
na
l T
his
Wo
rk
Driver
Str
ength
D
river
Str
ength
Novel 0-bit Forward-Bias
Precharge
Rise: 1.42 ns
Fall: 0.24 ns
(20% to 80%)
Rise: 0.29 ns
Fall: 0.24 ns
(20% to 80%)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 12 of 20
All-Digital Driver
(Active Low)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 13 of 20
Driver Operation – Strong injection
(Active Low)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 14 of 20
Driver Operation – Weak injection
(Active Low)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 15 of 20
Driver Operation – Depletion
(Active Low)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 16 of 20
Driver Operation – Accumulation
(Active Low)
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 17 of 20
Final Drive Heads
• Split-supply operation
• HVDD up to 1.5V
(can use I/O supply)
• Digitally configurable
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 18 of 20
2.5Gb/s, 1550nm, 1.23pJ/b
Eye Opening Comparison
600Mb/s, 1550nm, 4.2pJ/b
Signal conditioning improves speed and
energy-efficiency by 4x
Before This Work
Source: Orcutt, Optics Express 2012
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 19 of 20
Energy Cost and Extinction Ratio
Driver cost:
130fJ/bit
Measured at fixed
Insertion Loss of 3dB
Modulator on-current
dominates energy cost
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 20 of 20
Summary
• Monolithic integration mitigates 3D
integration overheads
• Flexible, all-digital driver circuit
• Signal conditioning allows 4x speed and
energy-efficiency improvement above
intrinsic device bandwidth
• Fastest and lowest energy electro-optical
modulation demonstrated in 45nm CMOS
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 21 of 20
Backup Slides
21
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 22 of 20
Electro-Optical Test Setup
IR Camera
Laser
DUT
FPGA
HS Clock In
Microscope
Die Surface
Optical Fibers
Fiber
Positioners
USB
© 2013 IEEE © 2013 IEEE IEEE International Solid-State Circuits Conference
7.6: A 1.23pJ/b 2.5Gb/s Monolithically Integrated Optical Carrier-Injection Ring Modulator and All-Digital Driver Circuit in Commercial 45nm SOI 23 of 20
Need to Optimize Carefully
• Laser energy increases with data-rate
• Limited Rx sensitivity
• Modulation more expensive -> lower
extinction ratio
• Tuning costs decrease with datarate
• Moderate data rates most energy-efficient
Georgas CICC 2011