© 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