Transcript ChongqingMEMS - Paul Ronney

MEMS: the state of the art
and future challenges
Paul Ronney
Dept. of Aerospace & Mechanical Engineering
Univ. of Southern California, Los Angeles, USA
Yiguang Ju
Department of Engineering Mechanics
Tsinghua University, Beijing, China
Outline
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Part 1: Introduction to MEMS
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What is MEMS?
Fabrication techniques
Applications
The market for MEMS
Opportunities for the future
What can the government do to help?
Part 2: Power MEMS as an example of MEMS
development
Dept. of Aerospace & Mechanical Engineering - University of Southern California
What is MEMS?
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Micro-Electro-Mechanical Systems (MEMS) is a
technology that:
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Leverages Integrated Circuit fabrication technology by adding
additional functions, for example
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Mechanical
Chemical
Biological
Optical
Mass-produces ultra-miniaturized components at low cost
Enables radical new micro-system applications, for example
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Pressure / acceleration sensors
Power production
Medical devices
Optical switches
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Advantages of MEMS
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Microscale fabrication techniques
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Bulk Micromachining
Deep reactive ion etching
Surface Micromachining
LIGA
Others
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EFAB
Micro EDM
3-D Lithography
Laser Micromachining
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Anisotropic Wet Etching of Silicon
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Deep Reactive Ion Etching
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Surface Micromachining
Dept. of Aerospace & Mechanical Engineering - University of Southern California
LIGA process
Dept. of Aerospace & Mechanical Engineering - University of Southern California
EFAB (Electrochemical FABrication) (NEW)
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Analogous to macroscale “rapid prototyping,” “solid freeform
fabrication” - enables fabrication of arbitrarily complex 3D
structures
Selective electroplating of structural and sacrificial metals
Developed at University of Southern California
Electrochemistry can also be used to deposit other types of
materials, e. g.
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Thermoelectric
Magnetic
Electrically insulating
Catalytic
Can use existing mechanical design software & modeling tools
No clean room required for device fabrication - much less
expensive than silicon-based techniques
Commercialization by MEMGen Inc., Torrance, CA, USA
Dept. of Aerospace & Mechanical Engineering - University of Southern California
EFAB key technology: “Instant Masking”
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Pre-fabricated masks serve as
reusable “printing plates”
Polymer mask patterned on anode
using conventional photolithography
Lithography for all layers done in
parallel, prior to, separate from
device fabrication, allowing:
Anode
Mask
1
Substrate / cathode
Low-cost, self-contained automated
machine
 Mask outsourcing - possible
collaboration with Chongqing
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2
Deposit
Electrolyte
3
Dept. of Aerospace & Mechanical Engineering - University of Southern California
EFAB process flow
Selectively deposited material
(usually sacrificial)
Blanket deposited 2nd
material (usually structural)
+
(a)
(b)
(c)
(d)
(e)
(f)
Dept. of Aerospace & Mechanical Engineering - University of Southern California
EFAB results
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12-layer chain, ≈ 290 m wide (world’s narrowest?)
Minimum feature size 20 µm
First-generation microcombustor built
90m
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Applications for MEMS
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Pressure transducers
Accelerometers
Gyroscopes
New areas
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Optical switches
Gas turbines
Nano-satellite systems
Drug delivery
Power MEMS
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Switches for fiber-optic networks
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Many possible
approaches, MEMS
and non-MEMS
3D: much higher
density of switches
than 2D, MEMS
fabrication required
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Space applications
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Advanced aircraft applications
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“Smart skin” - senses & reduces air
drag
Micro-mixing enhancement in
engines
Sensing in Gas turbine engine
Environment
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Flow
Vibration
Temperature
Strain
Pressure Sensors for Stall/Surge
Control
Fuel Valve Position Sensors
Chemical Sensors for Emissions
Monitoring
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Microfluidic system for bio-chemical sensing
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Drug delivery systems
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Micromachined needles
connected to individual
microvalves and supply
reservoirs
Each reservoir may
contain different
type/concentration of
drug
May be combined with
on-chip biosensor
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Drug delivery systems (2)
(a) Drug delivery
chamber
(b) Two
electrodes
(AgCl/Ag
electrode and
IsOx electrode)
for monitoring
pH
(c) Metal valves
Dept. of Aerospace & Mechanical Engineering - University of Southern California
MEMS Market (U. S. estimate)
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Conclusions (MEMS)
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Many potential MEMS applications - has been demonstrated
in USA
China can become a significant force in MEMS
development because of its existing infrastructure and its
large yet highly educated workforce
What can the government do to help?
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Difference between Japan and USA: USA time from research to
market is much shorter - why?
Support and stimulate joint collaborative research between
universities and companies
Attract different sources of funding to sustain research - government,
workshop registration fees, company staff training
Government provides funds to university for facilities that companies
can rent to test new ideas before buying their own facilities
DARPA funds applied research on MEMS but allow universities and
companies to retain intellectual property rights for non-government
applications
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Conclusions (MEMS)
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Expect 95 of 100 projects to fail (success of other 5 will
more than pay for 95 failures)
Balance between “traditional” MEMS areas and “radical”
new areas
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How to judge the future of MEMS technologies?
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Traditional Chinese successes in international markets based on
production cost advantages, especially lower labor costs
High technology successes in high value-added markets depend on
making use of skilled, educated, motivated Chinese workforce
High value added - unit cost of complete system is high
Enabling technology - can’t work without MEMS devices
Collaboration between industry and universities essential
Inter-disciplinary activity essential
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Microscale power generation (Power MEMS)
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USC effort supported by U. S. Defense Advanced Research
Projects Administration (DARPA)
Dept. of Aerospace & Mechanical Engineering - University of Southern California
The challenge of microcombustion
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Hydrocarbon fuels have numerous advantages over
batteries
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≈ 100 X higher energy density
Much higher power / weight & power / volume of engine
Inexpensive
Nearly infinite shelf life
More constant voltage, no memory effect, instant recharge
Environmentally superior to disposable batteries
… but converting fuel energy to electricity with a
small device has not yet proved practical despite
numerous applications
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Foot soldiers
Portable electronics - laptop computers, cell phones, …
Micro air and space vehicles
Dept. of Aerospace & Mechanical Engineering - University of Southern California
The challenge of microcombustion
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Most approaches use scaled-down macroscopic
combustion engines, but may have problems with
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Heat losses - flame quenching, unburned fuel & CO emissions
Heat gains before/during compression
Limited fuel choices – need knock-resistant fuels, etc.
Friction losses
Sealing, tolerances, manufacturing, assembly
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Smallest existing combustion engine
Cox Tee Dee .010
Weight:
0.49 oz.
Bore:
0.237” = 6.02 mm
Stroke: 0.226” = 5.74 mm
Displacement: 0.00997 cu in (0.163 cm3)
RPM:
30,000
Power ≈ 3 watts
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Some power MEMS concepts
Wankel rotary engine
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Free-piston
engine
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Some power MEMS concepts
Issues
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Micro gas turbine engine (MIT)
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Friction, heat losses
Very tight
manufacturing
tolerances
High production cost
Very high rotational
speed needed to
achieve compression
(speed of sound doesn’t
scale!)
Fuel: may always need
to run on hydrogen
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Some power MEMS concepts
Non-IC engine
concepts:
possible enabling
technologies, but
don’t address
complete system
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Our approach - microFIRE
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Integrated microscale power generation system
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Combustion
Heat transfer
Electrical power generation
Fabrication & assembly
“Swiss-roll” heat recirculating burner with toroidal 3-D geometry
Direct thermoelectric conversion of heat to electricity
Monolithic fabrication of the entire device with EFAB
Being developed by MEMGen, Inc.
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> $10 million venture capital funding in first year of existence
Dept. of Aerospace & Mechanical Engineering - University of Southern California
microFIRE approach (1) – Combustion
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“Swiss roll” heat recirculating burner minimizes heat losses
Combustion
volume
1600
1400
700
600
500
Products
Reactants
1600
1200
500
400
300 K
One-dimensional counterflow
combustor / heat exchanger
Two-dimensional “Swiss-roll” burner
Toroidal 3-D geometry - further
reduces losses - minimizes
external temperature on all surfaces
Dept. of Aerospace & Mechanical Engineering - University of Southern California
microFIRE approach (2) - Power generation
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Thermoelectric (TE) power generation elements embedded in wall
between hot (outgoing product) and cold (incoming reactant) streams
Hot side
Cold side
Load
Dept. of Aerospace & Mechanical Engineering - University of Southern California
microFIRE approach (3) - Fabrication
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EFAB (Electrochemical Fabrication)
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Enables fabrication of arbitrarily complex 3D structures
NASA Jet Propulsion Laboratory proprietary process for
electrochemical deposition of Bi2Te3 thermoelectric elements Process-compatible with EFAB, enabling monolithic
fabrication of entire device!
Targets
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Weight 500 mg
Volume 0.04 cc
Power 100 mW
Efficiency > 10%
100 m
Dept. of Aerospace & Mechanical Engineering - University of Southern California
microFIRE advantages
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Integrated combustor / heat exchanger / power generation
Heat losses / flame quenching problems minimized
External T (IR signature, touch-temperature hazards) minimized
Direct conversion, no moving parts!
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No friction losses
No tight manufacturing tolerances
Rugged, reliable, low maintenance
Quiet, stealthy, no vibration
Long life (no wear or fatigue-induced breakage)
Compact
Can use wide variety of conventional hydrocarbon fuels without
pre-processing
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Fabrication of macroscale test devices
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Development approach: build macroscale models, test, develop
numerical simulation capability, design microscale device
Soligen™ rapid prototyping process for 2-D and 3-D designs in
Al2O3 - SiO2 ceramic
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Mesoscale experiments
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Wire-EDM fabrication
Pt igniter wire / catalyst
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Combustion modes
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Combustion usually in “flameless” mode - no visible flame!
QuickTime™ and a
Video decompressor
are needed to see this picture.
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Quenching limits
Area-averaged V can be 30x stoichiometric burning velocity, even
with mixture 33% leaner than conventional lean limit & no insulation
 Lower limit can be reduced dramatically with catalytic Pt strips
…but it can also be increased dramatically
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No catalyst
Bulk Pt set #1
Bulk Ni
0.4 µm Pt plated on Cu
Bulk Pd
Bulk Pt set #2
Mole percent fuel at limit
4
Propane
3.5
3
2.5
2
Conventional
lean limit
1.5
1
10
100
Average inlet velocity (cm/s)
1000
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Numerical modeling
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FLUENT software package, 2D & 3D simulations
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Numerical modeling
High % fuel
Low % fuel
Reaction rates
Temperatures
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Conclusions (microFIRE)
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Combustion in microscale devices feasible even at low temperatures
compatible with thermoelectric elements, but will probably require
heat recirculation & catalytic assistance
Combustion behavior under such conditions quite different from
conventional flames
Expect similar findings in most other microscale systems performance cannot be predicted based only on macroscale results
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Challenges for Power MEMS
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microFIRE-specific
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Developing & calibrating gas-phase & surface chemistry sub-models
Modelling electrochemical processes - rely less on empirical testing
Catalyst preparation, degradation & restoration
Challenges for all micro-chemical/thermal/fluid systems
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Auxiliary components - valves, pumps, fuel tanks
System integration and packaging
Dept. of Aerospace & Mechanical Engineering - University of Southern California
Thanks to
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Chongqing Science & Technology Commission
Chongqing University
… and especially U. S. Defense Advanced
Research Projects Administration (DARPA)
Microsystems Technology Office !!!
Dept. of Aerospace & Mechanical Engineering - University of Southern California