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CfAO AO Short Course MEMS Overviewcfao.ucolick.org/Aosummer/2007/Pdfs/MEMS_Overview_Kubby.pdfWater...
Transcript of CfAO AO Short Course MEMS Overviewcfao.ucolick.org/Aosummer/2007/Pdfs/MEMS_Overview_Kubby.pdfWater...
MEMS Devices
Joel [email protected]
Outline1) 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
© 2002 by CRC Press LLC
Micro-Electro-
Mechanical Systems
(MEMS)
Scaling
Length 1/r (meters-1)• 1 meter 1• 1 mm 1,000• 1 μm 1,000,000• 1 nm 1,000,000,000
Surface to volume ratio varies as 1/r:
Surface to Volume Ratio
24 rπ 3
34 rπ
Surface area of a sphere Volume of a sphere
rrr 3
34
43
2=
ππ
Surface to volume ratio of a sphere
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
Bishnu Gogci, Sensors Product Division, Motorola
Tronics
NMRC
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
Pister K S J, Judy M W, Burgett S R and Fearing R S 1992 Microfabricated hinges Sensors Actuators A 33 249–56
Hinged microstructures
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
2007
2002
Share of MEMS Revenues by Device, 2002 vs. 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 andDavis J R Jr 1967 The resonant gate transistor IEEE Trans. Electron Devices 14 117
First polysilicon surface micromachinedMEMS device integrated with circuits
Howe R T and Muller R S 1986 Resonant-microbridge vapor sensor IEEE Trans. Electron Devices 33 499–506
Surface Micromachined Motor
Fan L-S, Tai Y-C and Muller R S 1988 Integratedmoveable 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 ApplicationsInertial Sensors
Bulk Micromachined Accelerometer
P J French and P M Sarroz, J. Micromech. Microeng. 8 (1998) 45–53
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
Ford Microelectronics ISAAC two-chip automotive airbag accelerometer
Automotive Airbag Accelerometer
• Monolithically integrated accelerometer
• Electronics occupy the majority of the 3 mm2 chip area
• 2-axis deviceIn 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• 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
Your kid on MEMS
Overview of MEMS ApplicationsPressure 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 PressureSensor, Lucas NovaSensor, 1055 Mission Court, Fremont,CA 94539, USA, http://www.novasensor.com/
Manifold Absolute Pressure (MAP)
• 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
Bosch engine control manifold absolute pressure (MAP) sensor
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 ApplicationsOptical MEMS
Cantilever VCSEL
A Large Aperture Fabry-Perot Tunable Filter Based On Micro Opto Electromechanical
Systems Technology
Photo: NASA
Lens dd DetectorActuator
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 siliconPhD Thesis Delft University of Technology
Pill Camera
Distal esophagus with edema and erythema. Geographic ulceration suggestive of Barret'sEsophagus.
Overview of MEMS Applications
RF MEMS
1 GHz NEMS Resonator
SOIresonator
Senseelectrode
Driveelectrode
SOISi double-ended tuning fork• tine width = 35nm• length = 500 nm• thickness = 50 nm
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
Micromachined Polymerase Chain Reaction (PCR) chamber
Northrup M A, Ching M T, White R M and Lawton R T 1993DNA amplification with a microfabricated reactionchamber Int. Conf. on Solid-State Sensors and Actuators,Transducers ’93 (Yokohama, 1993) pp 924–6
DNA Amplification
1) Denature @ 95°C
2) Anneal (primer) @ 65°C
3) Extend nucleotides @ 72°C
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 MillipedeArray of AFM tips write and read bits:
potential for low and adaptive power
IBM MillipedeCurrent: 517 Gb/sq. in.
Goal: Tb/sq. in
MEMS Actuation Mechanisms
MEMS Actuation Mechanisms
• Electrostatic Coulomb's Law (q1q2/r2) • Piezoelectric Polarization↔Stress• Thermal Thermal Expansion• Magnetic Lorentz Force (qVxB)• Pneumatic Boyle’s Law (p1V1=p2V2)• Phase change Liquid↔gas, solid↔gas
Electrostatic Actuation
• Lower plate is fixed, upper plate can move
• Attractive force between the plates is balanced by restoring force of the spring
Fixed plate
Moveable plate
Electrostatic Force
zCVF
CVzF
CVCVzF
ΔΔ
−=
Δ−=Δ
Δ=Δ+Δ
2
2
22
21
21
21
Mechanical Work
Electrical Work (Battery)
Change in the Total Energy Stored in Capacitor
Electrostatic Force
( )
( )
2
20
20
0
)(2 zgAV
F
zgA
dzdC
zgA
C
e−
=
−
−=
−=
ε
ε
ε
Force Balance Fm = Fe
em Fzg
AVkzF =
−== 2
20
)(2ε
2/1
0
2)(2⎥⎥⎦
⎤
⎢⎢⎣
⎡ −=
AzgkzV
ε
Solve for V as a function of z;
http://bifano.bu.edu/tgbifano/Web/EK130/PDF/EK130Lect4.pdf
2
20
)(2 zgAV
kz−
=ε
z
Force Balance Fm = Fe
Force ImbalanceNo equilibrium above critical voltage, electrostatic force is always larger
http://bifano.bu.edu/tgbifano/Web/EK130/PDF/EK130Lect4.pdf
2
20
)(2 zgAV
kz−
<ε
z
Pull-In
z/g
3gz inpull =−
A
kgVpi
0
3
27
8
ε=
Stable region
2/1
0
2)(2⎥⎥⎦
⎤
⎢⎢⎣
⎡ −=
AzgkzV
ε
gkA
gV
20ε
MEMS Deformable Mirrors for Adaptive Optics
California Extremely Large Telescope (CELT, http://celt.ucolick.org/)
California Extremely Large Telescope (CELT)
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
PolyMUMPS III
SUMMiT V
SUMMiT VII
1998
Additional structural level
Additional interconnect level
1992 2004
PolyMUMPS III
SUMMiT V
SUMMiT VII
1998
Additional structural level
Additional interconnect level
1992 2004
Process development has required 3 years/layer
Terminology
Continuous face-plate
Segmented mirrors
Electrostatically actuated diaphragm
Attachment post
Membrane mirror
Continuous mirror
Segmented mirrors (piston)
Terminology
Stroke– The DM must “match” the wavefront error
δ
Would like stroke ≈ 10 μm
z/g
3gz inpull =−
A
kgVpi
0
3
27
8
ε=
Stable region
2/1
0
2)(2⎥⎥⎦
⎤
⎢⎢⎣
⎡ −=
AzgkzV
ε
gkA
gV
20ε
z/g
3gz inpull =−
A
kgVpi
0
3
27
8
ε=
Stable region
2/1
0
2)(2⎥⎥⎦
⎤
⎢⎢⎣
⎡ −=
AzgkzV
ε
gkA
gV
20ε
z
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 sheetNanolaminate 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
Membrane mirror
Continuous 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 2
Figure 1
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 ResourcesOnline 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 ResourcesJournals
• 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 ResourcesConferences
• 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