MEMS Overview Kubby

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



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.


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


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


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






Iris AO

Iris AO MEMS Segmented DM





Scalable Assembly: 367 Segment Demo


2nd Generation assembled mirrors


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

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MEMS Overview Kubby