Transcript Optical Switch Fabrics: What is their value, and When will

Optical MEMS:
Overview & MARS Modulator
Joseph Ford, James Walker, Keith Goossen
References:
“Silicon modulator based on mechanically-active antireflection layer with 1 Mbit/sec capability”
K. Goossen, J. Walker and S. Arney, IEEE Photonics Tech. Lett. 6, p.1119, 1994
"Micromechanical fiber-optic attenuator with 3 microsecond response"
J. Ford, J. Walker, D. Greywall and K. Goossen, IEEE J.of Lightwave Tech. 16(9), 1663-1670, September 1998
"Dynamic spectral power equalization using micro-opto-mechanics"
J. Ford and J. Walker, IEEE Photonics Technology Letters 10(10), 1440-1442, October 1998
"Micromechanical gain slope compensator for spectrally linear power equalization"
K. Goossen, J. Walker, D. Neilson, J. Ford, W. Knox, IEEE Photonics Tech. Lett.12(7), pp. 831-833, July 2000.
"Wavelength add/drop switching using tilting micromirrors"
J. Ford, V. Aksyuk, D. Bishop and J. Walker, IEEE J. of Lightwave Tech. 17(5), 904-911, May 1999.
"A tunable dispersion compensating MEMS all-pass filter"
Madsen, Walker, Ford. Goossen, Nielson, Lenz, IEEE Photonics Tech. Lett. 12(6), pp. 651-653, June 2000.
What are MEMS? Micro-Electro-Mechanical Systems
… manufactured using technology created for VLSI electronics
to build micron-scale devices “released” by selective etching
• Surface Micromachining
• LIGA (electroforming)
• Deep Reactive Ion Etching
…& electrically controlled by
• Electrostatic attraction
• Electromagnetic force
• Electrostriction
• Resistive heating
Photos courtesy
Sandia National Labs
Note: “MEMS” = passive silicon V-grooves
Mass commercial application: Acceleration Sensors
Elastic hinge
Spacer
Proof Mass
Force
Silicon substrate
Capacitive Accelerometer
Analog Devices' ADXL50 accelerometer
Surface micromachining capacitive sensor
2.5 x 2.5 mm die incl. electronic controls
Cost: $30 vs ~$300 bulk sensor (‘93)
Cut to $5/axis by 1998
Replaced by 3-axis ADXL150
“Every new car sold has micromachined sensors on-board. They
range from MAP (Manifold Absolute Pressure) engine sensors,
accelerometers for active suspension systems, automatic door locks,
and antilock braking and airbag systems. The field is also widening
considerably in other markets. Micromachined accelerometer sensors
are now being used in seismic recording, machine monitoring, and
diagnostic systems - or basically any application where gravity,
shock, and vibration are factors.”
http://www.analog.com/library/techArticles/mems/xlbckgdr4.html
Mass commercial application: Pressure Sensors
Pext
Membrane
Measure
RC time
Force
Pint
Spacer
Silicon substrate
Capacitive Pressure Sensor
Piezo-resistive pressure sensor
High-pressure gas sensor
(ceramic surface-mount)
NovaSensor’s piezo-resistive pressure sensors
Disposable medical sensor
Electrical actuation of active MEMS devices
magnetic layer
conductive layer
Force
Force
Apply
insulator
Voltage
substrate
conductive substrate
Apply
Current
Electrostatic attraction
Electromagnetic force
Apply Voltage
electrostrictive layer
patterned resistive layer
Force
substrate
Electrostriction
EM coil
Apply
Current
substrate
Resistive heating
Force
Surface Micromachining: Layer by layer addition
Starting from bare silicon wafer, deposit & pattern
multiple layers to form a (shippable) MEMS wafer
~ 10 mask steps
Completed MEMS wafer
Diced and released MEMS device
Release = isotropic chemical etch to remove oxides
Special techniques may be used to remove liquid
(e.g., critical point drying)
Assembly = mechanical manipulation of structures
(e.g., raising and latching a vertical mirror plate)
Various techniques used, some highly proprietary
From Cronos/JDSU MUMPS user guide at www.MEMSRUS.com
st Optical MEMS device
1
Texas Instruments Digital Light Projector
TM
& DLP PROJECTOR
Bulk MEMS Fabrication: Pattern & selective etch
Example: Bulk silicon DRIE: start with unpatterned wafer stack – a wafer-bonded SOI (silicon on insulat
(1) Pattern photoresist
(2) DRIE vertical etch
photoresist
wafer-bonded silicon
sacrificial silicon oxide
bulk silicon substrate
(4) Gold evaporation
(3) SiO2 isotropic etch
Narrow features released,
Wide features just undercut
Gold mirrors on top
and potentially sides
samlab
“Bulk Silicon” MEMS Devices
Single-axis tilt-mirror photo courtesy R. Conant, BSAC
Comb-drive switch photo courtesy IMT (Neuchatel)
MEMS reliability?
“MEMS Reliability: Infrastructure, Test Structures, Experiments and Failure Modes”
171 page report by D. M. Tanner et al, SAND2000-0091, January 2000.
Micromotor test device
40,000G impact test
Failure by rubbing contact
Comb-drive actuator
Flexural contact to gears
Ceramic package destroyed
MEMS survives (!)
Wear on silicon surface
Submicron particles generated
Conclusions:
(1) Properly designed MEMS devices are remarkably shock resistant
(2) Flexural failures due to fatigue were not apparent
(3) Rubbing wear (& resulting debris) was their primary failure mechanism
www.sandia.gov
Optical MEMS Devices
Classical vs Resonant
“Classical” optical MEMS
Sir Isaac Newton
(1642-1727)
…and his Corpuscular Theory of Light
Lucent’s “LambdaRouter” Device
1st-surface reflection
“Resonant” Optical MEMS
Christiaan
Huygens
Sir Isaac Newton
(1629-1695)
(1642-1727)
…
andhis
hisCorpuscular
1687 Wave Theory of Light
…and
Thomas Young
Silicon Light Machine’s Grating Light Valve
(1773-1829)
… and his 1801 theory of Interference
Interference / Diffraction
Resonant Optical MEMS
MEMS: Tunable Photonic Bandgap
Variable phase grating
~ 10 V drive
~ 200 nm actuation
~ 10 us response
Stanford’s grating light valve
Variable gap multilayer
5 - 30 V drive
~ 200 nm actuation
~ 10 us response
Lucent’s MARS modulator
Vd
The “MARS”
Resonant MEMS Modulator
Fabry-Perot etalon reflectivity
0.9
Incident
0.8
Initial gap
1.0
Operation
220 nm
Reflected
Transmitted
dd’
F sin2(pd/do)
Reflectivity = --------------------1+ F sin2(pd/do)
F = 4Rs/(1-Rs)2
Rs = top interface reflectivity = 30.6%
d = gap between plates
do = gap @ minimum reflectivity (l/2)
reflection
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.2 -0.1 0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
Gap reduction (microns)
Resonant optics = Sub-wavelength actuation
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
Fabry-Perot etalon spectral uniformity
1.00
1163
900
820
750 nm
nm
air gap
1163 nm
operation
Reflectivity
3lo/2
0.50
900 nm
lo/2
750 nm
820 nm
0.00
1.2
1.3
1.4
1.5 l
o
1.6
1.7
Wavelength (microns)
Resonant Optics = Wavelength dependence
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
The “MARS” resonant MEMS modulator
MARS (Membrane Anti-Reflection Switch) analog optical modulator
l/4 Silicon Nitride “drumhead” suspended over a Silicon substrate
input
reflect
l/4 SiNx
Vdrive
membrane edge
etch access holes
PSG
Silicon
0 < Vdrive < 30V
3l/4 < gap < l/2
PSG
transmit
150 mm
Goossen, Arney & Walker, IEEE Phot. Tech. Lett. 6, 1994
MARS dielectric multilayer structures
Dielectric Silicon Nitride
Conductive Polysilicon + Nitride
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
Lucent’s MARS “bulk” MEMS fabrication
Silicon Nitride
Double Polysilicon
etch via
to bottom poly
etch holes
for HF access
metal
deposition
HF release
Walker, Goossen & Arney, J. MEMS 5(1), 1996
MARS time & voltage response
Temporal Response
Voltage Response
measured
theory
Drive voltage (V)
500 um DPOL drum w/ 300 um window has 1.1 microsecond response
110 um SiNx drum w/ 30 um window has 85 nanosecond response
(used for 16 Mb/s digital data modulation)
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
Greywall, Busch & Walker, Sensors & Actuators A A72, 1999.
MARS Applications:
- Data modulator
- Variable attenuator
- Dynamic spectral equalizer
- Dispersion compensator
(see references or other presentations)