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
Surface Micromachining
LIGA (electroforming)
Deep Reactive Ion Etching
Electrostatic attraction
Electromagnetic force
Electrostriction
Resistive heating
Photos courtesy
Sandia National Labs
… manufactured using technology created for VLSI electronics
to build micron-scale devices,released” by selective etching
…& electrically controlled by
Note:,MEMS” = passive silicon V-grooves
Mass commercial application,Acceleration Sensors
http://www.analog.com/library/techArticles/mems/xlbckgdr4.html
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.”
Capacitive Accelerometer
Silicon substrate
Elastic hinge Proof Mass
Spacer Force
Mass commercial application,Pressure Sensors
Capacitive Pressure Sensor
Silicon substrate
Pint
Pext
Spacer
Membrane
Force
Measure
RC time
NovaSensor?s piezo-resistive pressure sensors Disposable medical sensor
High-pressure gas sensor
(ceramic surface-mount)
Piezo-resistive pressure sensor
substrate
magnetic layer
EM coil
conductive substrate
conductive layer
insulator
substrate
patterned resistive layer
substrate
electrostrictive layer
Force
Force
Force
Force
Apply
Current
Apply
Voltage
Electrical actuation of active MEMS devices
Electrostatic attraction
Resistive heatingElectrostriction
Electromagnetic force
Apply
Current
Apply Voltage
Surface Micromachining,Layer by layer addition
Starting from bare silicon wafer,deposit & pattern
multiple layers to form a (shippable) MEMS wafer
From Cronos/JDSU MUMPS user guide at www.MEMSRUS.com
Assembly = mechanical manipulation of structures
(e.g.,raising and latching a vertical mirror plate)
Various techniques used,some highly proprietary
Release = isotropic chemical etch to remove oxides
Special techniques may be used to remove liquid
(e.g.,critical point drying)
Diced and released MEMS device
Completed MEMS wafer
~ 10 mask steps
Texas Instruments Digital Light Projector
& DLP PROJECTORTM
1st Optical MEMS device
Bulk MEMS Fabrication,Pattern & selective etch
(2) DRIE vertical etch
samlab
bulk silicon substrate
Example,Bulk silicon DRIE,start with unpatterned wafer stack – a wafer-bonded SOI (silicon on insulator)
wafer-bonded silicon
sacrificial silicon oxide
(1) Pattern photoresist
photoresist
(4) Gold evaporation
Gold mirrors on top
and potentially sides
(3) SiO2 isotropic etch
Narrow features released,
Wide features just undercut
“Bulk Silicon” MEMS Devices
Comb-drive switch photo courtesy IMT (Neuchatel)Single-axis tilt-mirror photo courtesy R,Conant,BSAC
MEMS reliability?
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
40,000G impact test
Ceramic package destroyed
MEMS survives (!)
Micromotor test device
Comb-drive actuator
Flexural contact to gears
Failure by rubbing contact
Wear on silicon surface
Submicron particles generated
“MEMS Reliability,Infrastructure,Test Structures,Experiments and Failure Modes”
171 page report by D,M,Tanner et al,SAND2000-0091,January 2000.
www.sandia.gov
Optical MEMS Devices
Classical vs Resonant
Lucent’s,LambdaRouter” DeviceSir Isaac Newton(1642-1727)
…and his Corpuscular Theory of Light
“Classical” optical MEMS
1st-surface reflection
Sir Isaac Newton
(1642-1727)
…and his Corpuscular Theory of Light
Silicon Light Machine’s Grating Light Valve
“Resonant” Optical MEMS
Interference / Diffraction
Thomas Young
(1773-1829)
… and his 1801 theory of Interference
Christi an Huyge s
(1629-1695)
… and his 1687 Wave The r f i
Resonant Optical MEMS,Tunable Photonic Bandgap
Variable gap multilayer
5 - 30 V drive
~ 200 nm actuation
~ 10 us response
Lucent’s MARS modulator
Variable phase grating
~ 10 V drive
~ 200 nm actuation
~ 10 us response
Stanford’s grating light valve
Vd
The,MARS”
Resonant MEMS Modulator
Fabry-Perot etalon reflectivity
Reflectivity = ---------------------F sin
2(pd/do)
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)
Resonant optics = Sub-wavelength actuation
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
-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)
re
fle
ct
ion
d
Incident
Reflected Transmitted
Operation
220 nmInitia
l g
ap
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
d?
1163 nm
Wavelength (microns)
0.00
0.50
1.00
1.2 1.3 1.4 1.5 1.6 1.7
Re
fle
ct
ivi
ty
air gap
lo
3lo/2
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
1163 nm
900 nm
900 nm
820 nm
82
750 nmlo/2
75
op
er
ati
on
Fabry-Perot etalon spectral uniformity
Resonant Optics = Wavelength dependence
The,MARS” resonant MEMS modulator
MARS (Membrane Anti-Reflection Switch) analog optical modulator
l/4 Silicon Nitride,drumhead” suspended over a Silicon substrate
150 mm
etch access holes
membrane edge
PSG
0 < Vdrive < 30V
3l/4 < gap < l/2
input
l/4 SiNx
Silicon
PSG
reflect
transmit
Vdrive
Goossen,Arney & Walker,IEEE Phot,Tech,Lett,6,1994
MARS dielectric multilayer structures
Dielectric Silicon Nitride
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
Conductive Polysilicon + Nitride
Lucent’s MARS,bulk” MEMS fabrication
Walker,Goossen & Arney,J,MEMS 5(1),1996
etch holes
for HF access
metal
deposition
HF release
Silicon Nitride Double Polysilicon
etch via
to bottom poly
MARS time & voltage response
Temporal Response
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
Greywall,Busch & Walker,Sensors & Actuators A A72,1999.
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)
Voltage Response
theory
measured
Drive voltage (V)
MARS Applications:
- Data modulator
- Variable attenuator
- Dynamic spectral equalizer
- Dispersion compensator
(see references or other presentations)
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
Surface Micromachining
LIGA (electroforming)
Deep Reactive Ion Etching
Electrostatic attraction
Electromagnetic force
Electrostriction
Resistive heating
Photos courtesy
Sandia National Labs
… manufactured using technology created for VLSI electronics
to build micron-scale devices,released” by selective etching
…& electrically controlled by
Note:,MEMS” = passive silicon V-grooves
Mass commercial application,Acceleration Sensors
http://www.analog.com/library/techArticles/mems/xlbckgdr4.html
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.”
Capacitive Accelerometer
Silicon substrate
Elastic hinge Proof Mass
Spacer Force
Mass commercial application,Pressure Sensors
Capacitive Pressure Sensor
Silicon substrate
Pint
Pext
Spacer
Membrane
Force
Measure
RC time
NovaSensor?s piezo-resistive pressure sensors Disposable medical sensor
High-pressure gas sensor
(ceramic surface-mount)
Piezo-resistive pressure sensor
substrate
magnetic layer
EM coil
conductive substrate
conductive layer
insulator
substrate
patterned resistive layer
substrate
electrostrictive layer
Force
Force
Force
Force
Apply
Current
Apply
Voltage
Electrical actuation of active MEMS devices
Electrostatic attraction
Resistive heatingElectrostriction
Electromagnetic force
Apply
Current
Apply Voltage
Surface Micromachining,Layer by layer addition
Starting from bare silicon wafer,deposit & pattern
multiple layers to form a (shippable) MEMS wafer
From Cronos/JDSU MUMPS user guide at www.MEMSRUS.com
Assembly = mechanical manipulation of structures
(e.g.,raising and latching a vertical mirror plate)
Various techniques used,some highly proprietary
Release = isotropic chemical etch to remove oxides
Special techniques may be used to remove liquid
(e.g.,critical point drying)
Diced and released MEMS device
Completed MEMS wafer
~ 10 mask steps
Texas Instruments Digital Light Projector
& DLP PROJECTORTM
1st Optical MEMS device
Bulk MEMS Fabrication,Pattern & selective etch
(2) DRIE vertical etch
samlab
bulk silicon substrate
Example,Bulk silicon DRIE,start with unpatterned wafer stack – a wafer-bonded SOI (silicon on insulator)
wafer-bonded silicon
sacrificial silicon oxide
(1) Pattern photoresist
photoresist
(4) Gold evaporation
Gold mirrors on top
and potentially sides
(3) SiO2 isotropic etch
Narrow features released,
Wide features just undercut
“Bulk Silicon” MEMS Devices
Comb-drive switch photo courtesy IMT (Neuchatel)Single-axis tilt-mirror photo courtesy R,Conant,BSAC
MEMS reliability?
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
40,000G impact test
Ceramic package destroyed
MEMS survives (!)
Micromotor test device
Comb-drive actuator
Flexural contact to gears
Failure by rubbing contact
Wear on silicon surface
Submicron particles generated
“MEMS Reliability,Infrastructure,Test Structures,Experiments and Failure Modes”
171 page report by D,M,Tanner et al,SAND2000-0091,January 2000.
www.sandia.gov
Optical MEMS Devices
Classical vs Resonant
Lucent’s,LambdaRouter” DeviceSir Isaac Newton(1642-1727)
…and his Corpuscular Theory of Light
“Classical” optical MEMS
1st-surface reflection
Sir Isaac Newton
(1642-1727)
…and his Corpuscular Theory of Light
Silicon Light Machine’s Grating Light Valve
“Resonant” Optical MEMS
Interference / Diffraction
Thomas Young
(1773-1829)
… and his 1801 theory of Interference
Christi an Huyge s
(1629-1695)
… and his 1687 Wave The r f i
Resonant Optical MEMS,Tunable Photonic Bandgap
Variable gap multilayer
5 - 30 V drive
~ 200 nm actuation
~ 10 us response
Lucent’s MARS modulator
Variable phase grating
~ 10 V drive
~ 200 nm actuation
~ 10 us response
Stanford’s grating light valve
Vd
The,MARS”
Resonant MEMS Modulator
Fabry-Perot etalon reflectivity
Reflectivity = ---------------------F sin
2(pd/do)
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)
Resonant optics = Sub-wavelength actuation
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
-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)
re
fle
ct
ion
d
Incident
Reflected Transmitted
Operation
220 nmInitia
l g
ap
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
d?
1163 nm
Wavelength (microns)
0.00
0.50
1.00
1.2 1.3 1.4 1.5 1.6 1.7
Re
fle
ct
ivi
ty
air gap
lo
3lo/2
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
1163 nm
900 nm
900 nm
820 nm
82
750 nmlo/2
75
op
er
ati
on
Fabry-Perot etalon spectral uniformity
Resonant Optics = Wavelength dependence
The,MARS” resonant MEMS modulator
MARS (Membrane Anti-Reflection Switch) analog optical modulator
l/4 Silicon Nitride,drumhead” suspended over a Silicon substrate
150 mm
etch access holes
membrane edge
PSG
0 < Vdrive < 30V
3l/4 < gap < l/2
input
l/4 SiNx
Silicon
PSG
reflect
transmit
Vdrive
Goossen,Arney & Walker,IEEE Phot,Tech,Lett,6,1994
MARS dielectric multilayer structures
Dielectric Silicon Nitride
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
Conductive Polysilicon + Nitride
Lucent’s MARS,bulk” MEMS fabrication
Walker,Goossen & Arney,J,MEMS 5(1),1996
etch holes
for HF access
metal
deposition
HF release
Silicon Nitride Double Polysilicon
etch via
to bottom poly
MARS time & voltage response
Temporal Response
Ford,Walker,Greywall & Goossen,IEEE J,Lightwave Tech,16,1998
Greywall,Busch & Walker,Sensors & Actuators A A72,1999.
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)
Voltage Response
theory
measured
Drive voltage (V)
MARS Applications:
- Data modulator
- Variable attenuator
- Dynamic spectral equalizer
- Dispersion compensator
(see references or other presentations)
