MEMS Devices - Center for Adaptive Optics

MEMS Devices
Joel Kubby
jkubby@soe.ucsc.edu
Outline
1) MEMS overview
–
–
–
–
–
Fabrication processes
Why micro-machine?
MEMS markets
Overview of MEMS applications
Actuation mechanisms
2) MEMS deformable mirrors for adaptive optics
– Challenges
– Sampling of current MEMS AO projects
– Conclusions
MEMS Overview
What are MEMS?
• Micro
- Small size, microfabricated structures
• Electro
- Electrical signal /control
( In / Out )
• Mechanical - Mechanical functionality
( In / Out )
• Systems
- Structures, Devices, Systems
- Control
Multidisciplinary
Scaling
Log Plot
MicroElectroMechanical
Systems
(MEMS)
© 2002 by CRC
Press LLC
Scaling
Surface to volume ratio
varies as 1/r:
•
•
•
•
Length
1/r (meters-1)
1 meter
1 mm
1 μm
1 nm
1
1,000
1,000,000
1,000,000,000
Surface to Volume Ratio
Surface area of a sphere
4πr
Volume of a sphere
4 3
πr
3
2
Surface to volume ratio of a sphere
4πr
2
4 3
πr
3
=3
r
Water Bug
The weight of the water bug scales as the volume, or S3,
while the force used to support the bug scales as the
surface tension (S1) times the distance around the bug’s
foot (S1), and the force on the bug’s foot scales as
S1×S1=S2
When the scale size, S, decreases, the weight decreases
more rapidly than the surface tension forces. Changing from
a 2-m-sized man to a 2-mm-sized bug decreases the weight
by a factor of a billion, while the surface tension force
decreases by only a factor of a million. Hence, the bug can
walk on water.
Water Bug
Water Bug
Water Bug
Gravitational Potential Energy
Gravitational potential energy mgh scales as S4. If
the dimensions of a system are scaled from meters
(human size) to 1 mm (ant size), the gravitational
potential energy scales as:
(1/1000)4 = 1/1,000,000,000,000
The potential energy decreases by a factor of a
trillion. This is why an ant can walk away from a
fall that is 10 times it’s height, and we do not!
Gravitational Potential Energy
NASA says tiny nematode worms that were aboard the
space shuttle Columbia when it exploded were recovered
alive in Texas.
When Columbia broke up the morning of Feb. 1, 2003, the
nematode canisters plunged from the orbiter at speeds up
to 650 mph and hit the ground with an impact 2,295 times
the force of Earth's gravity.
History of MEMS Technology
•
Richard Feynman "There's Plenty of Room at the Bottom” in 1959
– Presentation given December 26,1959 at California Institute of
Technology
•
Westinghouse creates the "Resonant Gate FET" in 1969
– Mechanical curiosity based on new microelectronics fabrication
techniques
•
•
Bulk-etched silicon wafers used as pressure sensors in 1970’s
Kurt Petersen published “Silicon as a Structural Material” in 1982
– Reference for material properties and etching data for silicon
•
Early experiments in surface-micromachined polysilicon in 1980’s
– First electrostatic comb drive actuators used for micro-positioning disc
drive heads, electrostatic micro-motors
•
Micromachining leverages microelectronics industry in late 1980’s
– Widespread experimentation and documentation increases public
interest
•
Telecom bubble spurs investment in optical MEMS in late 90’s
– Start-up MEMS companies were acquired for $1B!
– Bubble burst in the early ’00’s
MEMS Patents Per Annum
Steven Walker, Dave Nagel, NRL
Fabrication Processes
MEMS Fabrication Flow
Basic Process Flow in
Micromachining
Nadim Maluf, An introduction to
Microelectromechanical Systems Engineering
MEMS Fabrication Processes
Tronics
NMRC
Bishnu Gogci, Sensors Product Division, Motorola
Bulk Micromachining
Bulk Micromachining:
Crystallography
Hiroshi Toshiyoshi, UCLA
Bulk Micromachining: Etch Rates
• Typically, anisotropic etch
rates are: (100) > (110) >
(111)
• (111) crystallographic
planes have the slowest
etch rate
• Etch pit geometry defined
by the bounding (111)
crystallographic planes
• Pyramidal sidewalls are
sloped at 54.7 degrees
(100) Surface
Bulk Micromachining
Surface Micromachining
Surface Micromachining
Surface Micromachining
MUMPS
Hinged microstructures
Pister K S J, Judy M W, Burgett S R and Fearing R S 1992
Microfabricated hinges Sensors Actuators A 33 249–56
Sandia SUMMIT
Why Micromachine?
Smaller, faster, better, cheaper
•
•
•
•
•
•
•
•
•
Minimize energy and materials use in manufacturing
Redundancy and arrays
Integration with electronics
Reduction of power budget
Faster devices
Increased selectivity and sensitivity
Cost/performance advantages
Improved reproducibility (batch fabrication)
Minimally invasive (e.g. pill camera)
MEMS Markets
Total MEMS Revenue 2002-2007
Source: In-Stat/MDR, 7/03
Share of MEMS Revenues by Device, 2002
vs. 2007
2002
2007
Source: In-Stat/MDR, 7/03
Overview of MEMS
Applications
Historical
Resonant Gate Transistor
Resonant gate transistor
Nathanson H C, Newell W E, Wickstrom R A and
Davis J R Jr 1967 The resonant gate transistor
IEEE Trans. Electron Devices 14 117
First polysilicon surface micromachined
MEMS device integrated with circuits
Howe R T and Muller R S 1986 Resonantmicrobridge vapor sensor IEEE Trans. Electron
Devices 33 499–506
Surface Micromachined Motor
Fan L-S, Tai Y-C and Muller R S 1988 Integrated
moveable micromechanical structures for
sensors and actuators IEEE Trans. Electron
Devices ED-35 724–30
Rotary Electrostatic Micromotor
Fan Long-Shen, Tai Yu-Chong and
Muller R S 1989 IC-processed
electrostatic micromotors Sensors
Actuators 20 41–7
Entertainment for Dust Mites
Overview of MEMS
Applications
Inertial Sensors
Bulk Micromachined Accelerometer
P J French and P M Sarroz, J. Micromech.
Microeng. 8 (1998) 45–53
Automotive Airbag Accelerometer
Ford
Microelectronics
ISAAC two-chip
automotive airbag
accelerometer
• Sensor chip is on the
right
• Signal processing and
control IC is on the left
• The accelerometer
structure is a suspended
crystal silicon mass over
a fixed metal electrode
that provides a capacitive
output as a function of
acceleration
Automotive Airbag Accelerometer
• Monolithically
integrated
accelerometer
• Electronics occupy
the majority of the 3
mm2 chip area
• 2-axis device
In the Analog
Devices ADXL 50
accelerometer
Vibrating Wheel Gyro
• A wheel is driven to
vibrate about its axis
of symmetry
• Rotation about either
in-plane axis results
in the wheel’s tilting
• Tilting of the wheel
can be detected with
capacitive electrodes
under the wheel
Virtual Reality (VR) Systems
•
•
•
•
Your kid on MEMS
A VR systems’ utility is
intimately connected to how
convincingly it can recreate life
Accelerometers and angular
rate sensors are required to
achieve credibility
Accelerometer data are
converted into positional
information via double
integration
Angular rate sensors
determine rotational position
by integrating the angular rate
Overview of MEMS
Applications
Pressure Sensors
Bulk Micromachined Pressure
Sensor
P J French and P M Sarroz, J. Micromech.
Microeng. 8 (1998) 45–53
Blood Pressure Sensors
Micromachined pressure sensor dice with the smallest having
dimensions 175 × 700 × 1000 µm3
Data Sheet: NPC–107 Series Disposable Medical Pressure
Sensor, Lucas NovaSensor, 1055 Mission Court, Fremont,
CA 94539, USA, http://www.novasensor.com/
Manifold Absolute Pressure (MAP)
Bosch engine
control manifold
absolute pressure
(MAP) sensor
• The manifold absolute
pressure (MAP)
sensor is used in
automobile fuel
injection systems
• By measuring the
manifold pressure,
the amount of fuel
being injected into the
engine cylinders can
be calculated
52 Million Vehicles Means a Lot of
Sensors!
• Crash Sensing for
Airbag Control
• Vehicle Dynamic
Control
• Rollover Detection
• Antitheft Systems
• Electronic Parking
Brake Systems
• Vehicle Navigation
Systems
Overview of MEMS
Applications
Optical MEMS
Cantilever VCSEL
A Large Aperture Fabry-Perot Tunable Filter
Based On Micro Opto Electromechanical
Systems Technology
Lens
d
Actuator
Detector
Photo:
NASA
J. A. Palmer, M. A. Greenhouse, D. B. Mott, W. T. Hsieh, W. D. Powell, E. A. Akpan,
R. B. Barclay, NASA Goddard Space Flight Center Greenbelt, MD 20771, U. S. A.
A Large Aperture Fabry-Perot Tunable Filter
Based On Micro Opto Electromechanical
Systems Technology
Micromachined Tunable Fabry-Perot Filters for Infrared Astronomy
NASA, Goddard Space Flight Center, Greenbelt, MD
Adaptive Optics
Vdovin G 1996 Adaptive mirror micromachined in silicon
PhD Thesis Delft University of Technology
Pill Camera
Distal esophagus with edema and erythema.
Geographic ulceration suggestive of Barret's
Esophagus.
Overview of MEMS
Applications
RF MEMS
1 GHz NEMS Resonator
SOI
Drive
electrode
SOI
resonator
Si double-ended tuning fork
• tine width = 35nm
• length = 500 nm
• thickness = 50 nm
Sense
electrode
L. Chang, S. Bhave, T.-J. King, and R. T.
Howe UC Berkeley (unpublished)
RF MEMS
Overview of MEMS
Applications
Fluidic MEMS
Fluidic MEMS
Yael Hanein
Bio MEMS
DNA Amplification
Micromachined Polymerase
Chain Reaction (PCR) chamber
1) Denature @ 95°C
2) Anneal (primer) @ 65°C
3) Extend nucleotides @ 72°C
Northrup M A, Ching M T, White R M and Lawton R T 1993
DNA amplification with a microfabricated reaction
chamber Int. Conf. on Solid-State Sensors and Actuators,
Transducers ’93 (Yokohama, 1993) pp 924–6
Bio MEMS
Microfabricated silicon neural probe
arrays
Kewley D T, Hills M D, Borkholder D A, Opris I E,
Maluf N I, Storment C W, Bower J M and Kovacs G T
A, 1997 Plasma-etched neural probes Sensors
Actuators A 58 27–35
Overview of MEMS
Applications
Memory
Memory
35 Xenon atoms
MEMS Memory: IBM’s Millipede
Array of AFM tips write and read bits:
potential for low and adaptive power
IBM Millipede
Current: 517 Gb/sq. in.
Goal: Tb/sq. in
MEMS Actuation Mechanisms
MEMS Actuation Mechanisms
•
•
•
•
•
•
Electrostatic
Piezoelectric
Thermal
Magnetic
Pneumatic
Phase change
Coulomb's Law (q1q2/r2)
Polarization↔Stress
Thermal Expansion
Lorentz Force (qVxB)
Boyle’s Law (p1V1=p2V2)
Liquid↔gas, solid↔gas
Electrostatic Actuation
Moveable
plate
Fixed plate
• Lower plate is fixed, upper plate can move
• Attractive force between the plates is balanced by
restoring force of the spring
Electrostatic Force
Mechanical
Electrical
Work
Work (Battery)
Change in the Total Energy
Stored in Capacitor
1 2
FΔz + V ΔC = V ΔC
2
1 2
FΔz = − V ΔC
2
1 2 ΔC
F =− V
2
Δz
2
Electrostatic Force
C=
ε0 A
(g − z )
−ε0A
dC
=
dz (g − z )2
Fe =
ε 0 AV 2
2( g − z ) 2
Force Balance Fm = Fe
Fm = kz =
ε 0 AV
2
2( g − z )
2
= Fe
Solve for V as a function of z;
⎡ 2kz ( g − z ) 2 ⎤
V =⎢
⎥
ε0 A
⎢⎣
⎥⎦
1/ 2
Force Balance Fm = Fe
kz =
ε 0 AV
2
2( g − z ) 2
z
http://bifano.bu.edu/tgbifano/Web/EK130/PDF/EK130Lect4.pdf
Force Imbalance
No equilibrium above critical voltage, electrostatic force is always larger
kz <
ε 0 AV 2
2( g − z )
2
z
http://bifano.bu.edu/tgbifano/Web/EK130/PDF/EK130Lect4.pdf
Pull-In
⎡ 2kz ( g − z )
V =⎢
ε0 A
⎢⎣
z/g
z pull −in
g
=
3
2
⎤
⎥
⎥⎦
1/ 2
Vpi =
Stable region
V
g
8 kg
3
27ε0A
Aε 0
2 gk
MEMS Deformable Mirrors for
Adaptive Optics
California Extremely Large
Telescope (CELT)
California Extremely Large Telescope (CELT, http://celt.ucolick.org/)
California Extremely Large
Telescope (CELT)
Jerry Nelson, Don Gavel 2004 August 19 MEMS workshop UCSC
Current AO Technology
Piezoelectric Actuators
Xinetics
146mm clear aperture
349 actuators on 7 mm spacing
Cost-Performance
MEMS AO Challenges
•
Mirror flatness
– Stress related deformations due to thin film characteristics
– Topography due to print through from conformal depositions
•
Mirror reflectivity
– Silicon is not a good optical reflector in the visible or IR
– Thin film coatings to increase reflectivity can lead to stress related
deformations
•
Stroke
– Current requirements of 10 μm of mirror stroke exceeds today’s
sacrificial thin film thicknesses
•
Yield
– Mirror yield requirements are very high for astronomical applications
– Yield becomes more challenging with larger mirror arrays (100x100)
•
•
Wirebonding/microlectronic integration
Cost
– AO is not a high volume application
– Is there a standard process that can be leveraged?
History of process development for
surface micromachining
SUMMiT VII
Additional
structural
level
SUMMiT V
PolyMUMPS III
Additional
interconnect
level
1992
1998
2004
Process development has required 3 years/layer
Terminology
Electrostatically
actuated
diaphragm
Attachment
post
Continuous face-plate
Continuous mirror
Segmented mirrors
Segmented mirrors (piston)
Membrane
mirror
Terminology
Stroke
– The DM must “match” the wavefront error
⎡ 2kz ( g − z ) 2 ⎤
V =⎢
⎥
A
ε
0
⎣⎢
⎦⎥
z/g
z pull −in
δz
g
=
3
1/ 2
Vpi =
Stable region
V
g
Would like stroke ≈ 10 μm
8 kg
3
27ε0A
Aε 0
2 gk
Terminology
Actuator spacing
– Sets the highest spatial frequency controlled
d
d
Terminology
Woofer-Tweeter
– Woofer gives large stroke at low spatial
frequency
– Tweeter gives high spatial frequency with low
stroke
Terminology
Nanolaminate face sheet
Nanolaminate materials are engineered at the
atomic level to provide optimal strength,
stiffness, and surface properties for lightweight
optics
Photo of 25 cm diameter, 110 um thick
nanolaminate mirror consisting of
alternating 600 Å thick copper layers and
80 Å thick copper/zirconium amorphous
intermetallic layers with a surface finish of
10 Å. LLNL
Boston Micromachines/Boston
University
Boston Micromachines
Electrostatically
actuated
diaphragm
Attachment
post
Continuous mirror
Membrane
mirror
Boston Micromachines
Boston Micromachines
Boston Micromachines
Boston Micromachines
Boston Micromachines
Iris AO
Iris AO MEMS Segmented DM
Iris AO MEMS Segmented DM
Iris AO MEMS Segmented DM
Iris AO MEMS Segmented DM
Iris AO MEMS Segmented DM
Scalable Assembly: 367 Segment Demo
Iris AO MEMS Segmented DM
2nd Generation assembled mirrors
Iris AO MEMS Segmented DM
2nd Generation assembled mirrors
Intellite/Stanford
Intellite/Stanford
Intellite/Stanford
Intellite/Stanford
Imagine Optic
Imagine Optic
Imagine Optic
Imagine Optic
Stanford/LLNL/UC Davis
Vertical Comb Drive
Vertical Comb Drive
UCSC
EE215 MEMS Design
•
•
•
•
Airheads
Buckle
Rokkakei
JEXA
Figure 1
Figure 2
eFab
Why eFab?
• Existing process that does not require
process development
• Unlimited number of layers with user
specified thickness
• Thick sacrificial layers for large stroke
actuators
• Tall structures (up to 1 mm)
• Metal surface for mirrors, potential for
integrated faceplate
• Low temperature process, potential for
microelectronic integration
eFab
eFab
Parallel Plate Actuator
Comb-Drive Actuator
eFab
Parallel Plate Actuator
Comb-Drive Actuator
HT-Micro
• X-ray Lithography based LIGA-like process
• Thicknesses of molds or photoresists:
– 50μm to 1mm
• Parts can be bonded together after fabrication
Bautista Fernandez
HT-Micro
Bautista Fernandez
HT-Micro
Bautista Fernandez
Conclusions
• MEMS technology can be used to decrease the
cost and improve the performance of AO
systems
– Smaller, faster, cheaper, better
• AO is a niche market with lower volumes
compared to other MEMS solutions
– Will never reach volumes of millions
– Less benefit from the economies of scale for batch
fabrication
• Try to use existing fabrication processes
– Process development is slow (years) and expensive
($M’s)
That’s All Folks!
Information Resources
Online Resources
•
•
•
•
•
•
•
•
•
•
•
•
•
BSAC http://www-bsac.eecs.berkeley.edu/
DARPA MTO http://www.darpa.mil/mto/
IEEE Explore http://ieeexplore.ieee.org/Xplore/DynWel.jsp
Introduction to Microengineering
http://www.dbanks.demon.co.uk/ueng/
MEMS Clearinghouse http://www.memsnet.org/
MEMS Exchange http://www.mems-exchange.org/
MEMS Industry Group http://www.memsindustrygroup.org/
MOSIS http://www.mosis.org/
MUMPS http://www.memscap.com/memsrus/crmumps.html
Stanford Center for Integrated Systems http://www-cis.stanford.edu/
USPTO http://www.uspto.gov/
Trimmer http://www.trimmer.net/
Yole Development http://www.yole.fr/pagesAn/accueil.asp
Information Resources
•
•
•
•
•
•
•
Journals
Journal of Micromechanical Systems (JMEMS)
Journal of Micromechanics and
Microengineering (JMM)
Micromachine Devices
Micronews (Yole Development)
MST News
Sensors and Actuators (A, B & C)
Sensors Magazine
Information Resources
•
•
•
•
•
Conferences
International Conference on Solid-State Sensors
and Actuators (Transducers), held on odd years
International Society for Optical Engineering
(SPIE)
MicroElectroMechanical Systems Workshop
(MEMS), IEEE
Micro-Total-Analysis Systems (μTAS)
Solid-State Sensor and Actuator Workshop
(Hilton Head), held on even years
Pull-In Voltage
Fe = (εoA/2(g-z)2)V2 = Fm = kz
V2 = 2kz(g-z)2/(εoA)
V = [2kz(g-z)2/(εoA)]1/2 = ξ[z(g-z)2]1/2
where ξ = [2k/εoA]1/2
dV/dz = (ξ/2) [z(g-z)2]-1/2[(g-z)2-2z(g-z)] = 0 for maximum
(g-z)2-2z(g-z) = 0 → z = g/3 at pull-in
VPI = ξ[(g/3)(g-g/3)2]1/2 = [2k/εoA]1/2[4g3/27]1/2 = [8kg3/27ε0 A]1/2