Download 1 An Introduction to Microelectromechanical Systems(MEMS)

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Who am I?
An Introduction to
Microelectromechanical Systems(MEMS)
Bing-Feng Ju, Professor
Institute of Mechatronic Control Engineering,
College of Mechanical and Energy Engineering,
Zhejiang University
P.R.China, 310027
Email: [email protected]
Tel: 86-571-8795-1730
Fax: 86-571-8795-1941
Presented to
Graduate students at
College of Mechanical and Energy Engineering
Zhejiang University
February to May 2010
Education:
Ph.D. from Zhejiang University, 1999
MEng from Harbin Institute of Technology, 1996
BEng from Harbin Institute of Technology, 1994
(All degrees were in mechanical engineering; Ph.D. thesis in Precision Metrology)
Research and Teaching experiences:
2006.12-Present
College of Mechanical and Energy Engineering, Zhejiang University
Position: Professor (2007.12 Ph.D. Tutor Qualification)
2004.12-2007.04
Department of Nanomechanics, Tohoku University(東北大学), Japan
Position: Assistant Professor
2003.11-2004.11
Department of Nanomechanics, Tohoku University(東北大学), Japan
Position: JSPS Young Foreigner Scientist
2002.05-2003.11
DSO National Laboratories, Singapore
Position: Research Scientist
Adjunct Assistant Professor of National University of Singapore (NUS)
2000.05-2002.05
School of Mechanical & Aerospace Engineering,
Nanyang Technological University (NTU), Singapore
Position: Postdoctoral Research Fellow
Courses taught: BioMEMS, Precision & Nao Metrology
CONTENT
Self-introduction
1. Overview of MEMS and Microsystems
Working Principles of Microsystems
2. The Scaling Laws
Electromechanical Design of MEMS and Microsystems
3. Material for MEMS and Microsystems
Part 1: Silicon and silicon compounds
Part 2: Piezoelectric and polymers
4. Microfabrication Processes
Part 1: Photolithography, doping with ion implantation and diffusion
Part 2: Etching
Part 3: Depositions: physical, chemical and epitaxy
5. Micromanufacturing
Assembly, Packaging and Testing to Nanoscale Engineering
Part 1: Microassembly
Part 2: Packaging with surface and wire bonding
Part 3: Reliability and testing
6. Introduction to Nanoscale Engineering
Part 1: Overview of nanoscale engineering
Part 2: Material characterization and measurements
Textbooks:
1. MEMS and Microsystems: design and manufacture, by Tai-Ran Hsu, McGraw-Hill
Companies, Boston, 2002 (ISBN 0-07-239391-2)
中译本：徐泰然， 《 MEMS和微系统—设计与制造》 ，机械工业出版社，2004
2. Albert P. Pisano, An Introduction to Microelectromechanical Systems Engineering, Artech
House, 2000
3. Marc Madou, Fundamentals of Microfabrication, CRC Press, 2002
4. 庄达人，《VLSI制造技术》，高立图书有限公司，1996
Journals:
1. Journal of MEMS
http://www.ieee.org/pub_preview/mems_toc.html
2. Sensors Journal, IEEE
http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?puNumber=7361
3. Journal of Micromechanics and Microengineering
http://www.iop.org/Journals/jm
Covering microelectronics and vacuum microelectronics, this journal focuses on fundamental
work at the structural, devices and systems levels, including new developments in practical
applications.
4. Sensors and Actuators A: Physical
http://www.elsevier.com:80/inca/publications/store/5/0/4/1/0/3/
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MEMS-Related Newsletters:
• Micromachine Devices is a very thorough newsletter on MEMS and the MEMS industry. Contact
the editor Mr. Sid Marshall at:[email protected] for your free subscription.
•
R&D Magazine periodically contains articles on MEMS and related areas.
Alternative website: http://www.manufacturing.net/magazine/rd/index.htm
•
MST News based in Germany is a newsletter (available in English) which focuses on European
MEMS/MST activities. Also available from MST are "special reports" on US and Japanese
MEMS/MST activities.
•
Sensor Business Digest covers the sensor industry. Contact the editor Peter Adrian for
subscription information at: 415-345-7018.
•
Microtechnology News published by the Business Communications Company, Inc. (BCC) offers
an on-line sample issue. (http://www.vdivde-it.de/mst)
•
Nanotech Alert is a newsletter from John Wiley & Sons Technical Insights, covering the MEMS
and Nanotechnology industries. (http://www.wiley.com/technical_insights)
•
Sensors Magazine is a general magazine covering all aspects of the sensors industry.
(http://www.sensorsmag.com/)
Unit
10-18m-am:atto-meter
10-15m-fm:femto-meter
10-12m-pm:pico-meter
10-9m-nm:nano-meter
10-6m-µm:micro-meter
10-3m-mm:milli-meter
10-2m-cm:centi-meter
10-1m-dm: deci-meter
100m-m:meter
1
10 m-dam:deca-meter
102m-hm:hecto-meter
103m-km:kilo-meter
106m-Mm:mega-meter
109m-Gm:giga-meter
1012m-Tm:tera-meter
Lecture 1（Part I）
Overview of MEMS and Microsystems
WHAT IS MEMS?
MEMS = MicroElectroMechanical System
Any engineering system that performs electrical and mechanical functions
with components in micrometers is a MEMS. (1 µm = 1/10 of human hair)
Available MEMS products include:
● Microsensors (To sense and detect certain physical, chemical, biological
and optical quantity and convert it into electrical output
signal)
● Microactuators (to operate a device component, e.g., valves, pumps, electrical
and optical relays and switches; grippers, tweezers and tongs;
linear and rotary motors; micro gyroscopes, etc.)
● Read/write heads in computer storage systems.
● Inkjet printer heads.
● Microdevices components (palm-top reconnaissance aircrafts, toy cars, etc.)
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Inertia Sensor for Automobile “Air Bag” Deployment System
Micro inertia sensor (accelerometer) in place:
HOW SMALL ARE MEMS DEVICES?
They can be of the size of a rice grain, or smaller!
Three examples:
- Inertia sensors for airbag deployment systems
in automobiles
Sensor-on-a-chip:
(2 mm x 3 mmsmaller than a
rice grain)
- A microcar
- Robot musician
(Courtesy of Analog Devices, Inc)
Micro Cars
Robot musician
(Courtesy of Denso Research Laboratories, Denso Corporation, Aichi, Japan)
(Waseda University, Japan)
Rice grains
Over 100 micro-sensors and micro-actuators by MEMS technology
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Miniaturization
An irresistible trend in the New Century
Miniaturization of Digital Computers
- A remarkable case of miniaturization!
MEMS = a major milestone in
Miniaturization –
Size: 106 down
Power: 106 up
A leading technology for the 21st Century, and
A “Lap-top” Computer in 1996
The ENIAC Computer in 1946
108
Size:
down
Power: 108 up
an inevitable trend in industrial products and
systems development
The ENIAC computer
- 50 years later
A “Palm-top” Computer in 2003
This spectacular miniaturization took place in 50 years!!
Principal Driving Force for the 21st Century
Industrial Technology
There has been increasing strong market demand for:
Market Demand for Intelligent, Robusting, Smaller,
Multi-Functional Products - the evolution of cellular phones
Mobil phones 15 Years Ago:
“Intelligent,”
Current State-of-the Art:
Size reduction
“Robust,”
“Multi-functional,”
“Low-cost”
and
Palm-top Wireless PC
industrial products.
Transceive voice+ others
Miniaturization is the only viable solution to satisfy such
market demand
Transceive voice only
(Video-camera, e-mails, calendar,
and access to Internet; and a PC
with key board; GPS and multimedia
entertainment)
The only solution is to pack many miniature function components into the device
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Miniaturization Makes Engineering Sense !!!
• Small systems tend to move or stop more quickly due to low mechanical inertia.
It is thus ideal for precision movements and for rapid actuation.
• Miniaturized systems encounter less thermal distortion and mechanical vibration
due to low mass.
Enabling Technologies for Miniaturization
Microsystems Technology
• Miniaturized devices are particularly suited for biomedical and aerospace
applications due to their minute sizes and weight.
Initiated in 1947 with the invention of
transistors, but the term “Micromachining”
was coined in 1982
Miniature devices
(1 nm - 1 mm)
• Small systems have higher dimensional stability at high temperature due to
low thermal expansion.
• Smaller size of the systems means less space requirements.
This allows the packaging of more functional components in a single device.
A top-down approach
(MST)
(1 μm - 1 mm)*
A bottom-up approach
Inspired by Feynman in 1959, with active
R&D began in around 1995
There is a long way to building nanodevices!
Nanotechnology (NT)
(0.1 nm – 0. 1 μm)**
• Less material requirements mean low cost of production and transportation.
• Ready mass production in batches.
The Lucrative Revenue Prospects for
Miniaturized Industrial Products
Microsystems technology:
$43 billion - $132 billion* by Year 2005
( *High revenue projection is based on different definitions
used for MST products)
Nanotechnology:
$50 million in Year 2001
$26.5 billion in Year 2003
(if include products involving parts produced by nanotechnology)
$1 trillion by Year 2015 (US National Science Foundation)
An enormous opportunity for manufacturing industry!!
● There has been colossal amount of research funding to NT by
governments of industrialized countries around the world b/c
of this enormous potential.
* 1 μm = 10-6 m ≈ one-tenth of human hair
** 1 nm = 10-9 m ≈ span of 10 H2 atoms
Major Industrial Applications
1. Automotive Industry:
● Safety
● Engine and Power Trains
● Comfort and Convenience
● Vehicle Diagnostics and
Health Monitoring
2. Healthcare Industry:
● Diagnostics and Monitoring
● Testing
● Surgical Tools
● Drug Discovery and Delivery
3. Aerospace Industry:
● Instrumentations
● Safety
● Navigation and Control
● Micro Satellites
4. Information Technology Industry:
● Read/write Heads
● Inkjet Printer Heads
● Position Sensors
● Flat Panel Displays
5. Telecommunication Industry:
● Optical Switching for Fiber Optical
Couplings
● RF Switches
● Tunable Resonators, etc.
6. Industrial Products:
● Manufacturing Process Sensors
● Robotic Sensing
● Sensors for HVAC Systems
● Remote Sensing in Agriculture
● Environmental Monitoring
7. Consumer Products:
● Sporting Goods
● Smart Home Appliances
● Smart Toys and Games
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MST Global Markets for Established Product Types
Product Types
1996 Units
Revenue
2002 Units
Revenue
(millions)
($ million)
(million)
($ million)
MST Global Market for Emerging Products
Product Types
1996 Units
Revenue
2002 Units
Revenue
(millions)
($ millions)
(millions)
($ millions)
Hard disk drives
530
4500
1500
12000
Drug delivery systems
1
10
100
1000
Inkjet printer heads
100
4400
500
10000
Optical switches
1
50
40
1000
Heart pacemakers
0.5
1000
0.8
3700
Lab-on-chip (DNA)
0
0
100
1000
In vitro diagnostics
700
450
4000
2800
Magneto optical heads
0.01
1
100
500
4
1150
7
2000
Projection valves
0.1
10
1
300
115
600
309
1300
Coil-on-chip
20
10
600
100
Chemical sensors
100
300
400
800
Micro relays
0.1
50
100
Infrared imagers
0.01
220
0.4
800
Micromotors
0.1
5
2
80
24
240
90
430
Inclinometers
1
10
20
70
Gyroscopes
6
150
30
360
Injection nozzles
10
10
30
30
Magnetoresistive sensors
15
20
60
60
Anti-collision sensors
0.01
0.5
2
20
Electronic noses
Hearing aids
Pressure sensors
Accelerometers
Microspectrometers
TOTAL
0.006
3
0.15
40
1595
13033
6807
34290
0.001
0.1
0.05
5
33
107
1045
4205
TOTAL
$34 billion +
(Source: NEXUS 1998)
Source: NEXUS 1998
MEMS and Microsystems Devices and Products
Market Growth of MST Products
60
Micro Sensors:
$50 Billion
50
Revenue, $billion
40
30
Acoustic wave sensors
Biomedical and biosensors
Chemical sensors
Optical sensors
Pressure sensors
Stress sensors
Thermal sensors
Micro Actuators:
Grippers, tweezers and tongs
Motors - linear and rotary
Relays and switches
Valves and pumps
Optical equipment (switches, lenses &
mirrors, shutters, phase modulators, filters,
waveguide splitters, latching & fiber alignment
mechanisms)
RF MEMS (oscillators, varactors, switches)
20
Microsystems = sensors + actuators
+ signal transduction:
10
0
2000
2 001
200 2
2003
2 004
Yea r
20 05
● Airbag deployment systems
• Microfluidics, e.g. Capillary electrophoresis (CE)
• Drug delivery systems with micropumps and valves
Source: NEXUS
Source: Nexus=Network of Excellence in Multifunctional Microsystems of European Community
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MEMS as a Microsensor
MEMS as a Microactuator
Power
Supply
Power
Supply
Input
Signal
Micro
Sensing
Element
Output
Action
Transduction
Unit
Output
Signal
Micro
Actuating
Element
Transduction
Unit
Micro pressure sensors
Micromotor produced
by a LIGA Process
Components of Microsystems
Power
Supply
Typical Microsystems Products
Signal
Transduction &
Processing
Unit
Sensor
Actuator
Microsystem
Microsystems = sensors + actuators + signal transduction
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Inertia Sensor for “Air Bag” Deployment System
Inertia Sensor for Automobile “Air Bag” Deployment System
(Courtesy of Analog Devices, Inc.)
Micro inertia sensor (accelerometer) in place:
Sensor-on-a-chip:
(the size of a
rice grain)
(Courtesy of Analog Devices, Inc)
Unique Features of MEMS and Microsystems (1)
- A great challenge to engineers
•Components are in micrometers with complex geometry
using silicon, si-compounds and polymers:
Capillary Electrophoresis (CE) Network Systems for Biomedical Analysis
A simple capillary tubular network with cross-sectional area of 20-30 μm
is illustrated below:
Buffer
Reservoir,B
Analyte
Reservoir,A
Injection Channel
Analyte Waste
Reservoir,A’
A microgear-train by
Sandia National Laboratories
25 μm
Separation Channel
25 µm
“Plug”
Waste
Reservoir,B’
Silicon Substrate
Work on the principle of driving capillary fluid flow by applying electric voltages at the
terminals at the reservoirs. Fast separation of species in analyte sample for biomedical
Applications.
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Commercial MEMS and Microsystems Products
Micro Sensors:
Acoustic wave sensors
Biomedical and biosensors
Chemical sensors
Optical sensors
Pressure sensors
Stress sensors
Thermal sensors
Intelligent Microsystems - Micromechatronics systems
Package on a single “Chip”
Micro Actuators:
Grippers, tweezers and tongs
Motors - linear and rotary
Relays and switches
Valves and pumps
Optical equipment (switches, lenses &
mirrors, shutters, phase modulators,
filters, waveguide splitters, latching &
fiber alignment mechanisms)
Microsystems = sensors + actuators
+ signal transduction:
• Microfluidics, e.g. Capillary electrophoresis (CE)
• Micro accelerometers (inertia sensors)
INPUT:
Desired
Measurements
or
functions
Sensing and/or
actuating
element
Transduction
unit
MEMS
Signal
Conditioner
& Processor
OUTPUT:
Controller
Actuator
Measurements
or Actions
Signal
Processor
Comparator
Measurements
Evolution of IC Fabrication
Evolution of Microfabrication
Significant technological development towards miniaturization was
initiated with the invention of transistors by three Nobel Laureates, W.
Schockley, J. Bardeen and W.H. Brattain of Bell Laboratories in 1947.
● There is no machine tool with today’s technology can produce any device or MEMS
component of the size in the micrometer scale.
This crucial invention led to the development of the concept of
integrated circuits (IC) in 1955, and the production of the first IC three
years later by Jack Kilby of Texas Instruments.
● The complex geometry of these minute MEMS components can only be produced
by various physical-chemical processes – the microfabrication techniques originally
developed for producing integrated circuit (IC) components.
ICs have made possible for miniaturization of many devices and
engineering systems in the last 50 years.
The invention of transistors is thus regarded as the beginning of
the 3rd Industrial Revolution in human civilization.
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Natural Science:
Comparison of Microelectronics and Microsystems
Microelectronics
Physics, Chemistry
Biology
Microsystems (silicon based)
Primarily 2-dimensional structures
Stationary structures
Transmit electricity for specific electrical functions
IC die is protected from contacting media
Use single crystal silicon dies, silicon compounds,
ceramics and plastic materials
Fewer components to be assembled
Mature IC design methodologies
Complex patterns with high density of electrical
circuitry over substrates
Large number of electrical feed-through and leads
Industrial standards available
Mass production
Fabrication techniques are proven and well
documented
Manufacturing techniques are proven and well
documented
Packaging technology is relatively well established
Primarily involves electrical and chemical
engineering
Complex 3-dimensional structure
May involve moving components
Perform a great variety of specific biological, chemical,
electromechanical and optical functions
Delicate components are interfaced with working media
Use single crystal silicon dies and few other materials,
e.g. GaAs, quartz, polymers, ceramics and metals
Many more components to be assembled
Lack of engineering design methodology and standards
Simpler patterns over substrates with simpler electrical
circuitry
Fewer electrical feed-through and leads
No industrial standard to follow in design, material
selections, fabrication processes and packaging
Batch production, or on customer-need basis
Many microfabrication techniques are used for
production, but with no standard procedures
Distinct manufacturing techniques
Packaging technology is at the infant stage
Involves all disciplines of science and engineering
Quantum physics
Solid-state physics
Scaling laws
Electromechanical
-chemical Processes
Electrical Engineering
• Power supply.
• Electric systems
design in electrohydrodynamics.
• Signal transduction,
acquisition,conditioning and processing.
• Electric & integrated
circuit design.
• Electrostatic & EMI.
Material
Science
Mechanical Engineering
• Machine components design.
• Precision machine design.
• Mechanisms & linkages.
• Thermomechanicas:
solid & fluid mechanics, heat
transfer, fracture mechanics.
• Intelligent control.
• Micro process equipment
design and manufacturing.
• Packaging and assembly design.
Process Engineering
• Design & control of
micro fabrication
processes.
• Thin film technology.
Materials Engineering
• Materials for device
components & packaging.
• Materials for signal
transduction.
• Materials for fabrication
processes.
Industrial & Systems Engineering
• Process implementation.
• Production control.
• Micro packaging & assembly.
(Multidiscipline of MEMS.Slide presentation)HSU
Commercialization of MEMS and Microsystems
Major commercial success:
Pressure sensors and inertia sensors (accelerometers) with
worldwide market of:
• Airbag inertia sensors at 2 billion units per year.
• Manifold absolute pressure sensors at 40 million units per year.
• Disposable blood pressure sensors at 20 million units per year.
Recent Market Dynamics
Old MEMS
Pressure sensors
Accelerometers
Other MEMS
New MEMS
BioMEMS
IT MEMS for Telecommunication:
(OptoMEMS for fiber optical networks
RF MEMS for wireless)
Application of MEMS and Microsystems
in
Automotive Industry
52 million vehicles produced worldwide in 1996
There will be 65 million vehicle produced in 2005
Principal areas of application of MEMS and microsystems:
• Safety
• Engine and power train
• Comfort and convenience
● Vehicle diagnostics and health monitoring
● Telematics, e.g. GPS, etc.
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Silicon Capacitive Manifold Absolute Pressure Sensor
Principal Sensors
(7)
(6)(1)
(4)
(3)
(2)
(9)
(5)
(10)
(8)
(1) Manifold or Temperature manifold
absolute pressure sensor
(2) Exhaust gas differential
pressure sensor
(3) Fuel rail pressure sensor
(4) Barometric absolute pressure sensor
(5) Combustion sensor
(6) Gasoline direct injection pressure sensor
(7) Fuel tank evaporative fuel pressure sensor
(8) Engine oil sensor
(9) Transmission sensor
(10) Tire pressure sensor
Application of MEMS and Microsystems
in
Aerospace Industry
Application of MEMS and Microsystems
In Biomedical Industry
Disposable blood pressure transducers
Catheter tip pressure sensors
● Cockpit instrumentation.
● Wind tunnel instrumentation
● Microsattellites
● Command and control systems with MEMtronics
● Inertial guidance systems with microgyroscopes, accelerometers and fiber optic gyroscope.
● Attitude determination and control systems with micro sun and Earth sensors.
● Power systems with MEMtronic switches for active solar cell array reconfiguration, and
electric generators
● Propulsion systems with micro pressure sensors, chemical sensors for leak detection,
arrays
of single-shot thrustors, continuous microthrusters and pulsed microthrousters
● Thermal control systems with micro heat pipes, radiators and thermal switches
● Communications and radar systems with very high bandwidth, low-resistance radiofrequency switches, micromirrors and optics for laser communications, and micro variable
capacitors, inductors and oscillators.
● Sensors and actuators for safety - e.g. seat ejection
● Sensors for fuel efficiency and safety
Biosensors
Pace makers
Respirators
Lung capacity meters
Barometric correction instrumentation
Medical process monitoring
Kidney dialysis equipment
Micro bio-analytic systems: bio-chips, capillary electrophoresis, etc.
Drug delivery systems
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Application of MEMS and Microsystems
in
Consumer Products
Application of MEMS and Microsystems
in the
Telecommunication Industry
Scuba diving watches and computers
● Optical switching and fiber optic couplings
Bicycle computers
● RF relays and switches
Sensors for fitness gears
● Tunable resonators
Micro lenses:
Washers with water level controls
Micro switches:
Sport shoes with automatic cushioning control
Digital tire pressure gages
Vacuum cleaning with automatic adjustment of brush beaters
Smart toys, e.g., fish, dogs, etc.
Micro Optical Switches
Concluding Remarks
2-Dimensional
3-Dimensional
1. Miniaturization of machines and devices is an inevitable trend
in technological development in the new century.
2. There is a clear trend that microsystems technology will be further
scaled down to the nano level.
(1 nm = 10-3 μm = 10 shoulder-to-shoulder H2 atoms).
3. Despite the fact that many IC fabrication technologies can be
used to fabricate silicon-based MEMS components, microsystems
engineering requires the application of principles involving multidisciplines in science and engineering.
4. Team effort involving multi-discipline of science and engineering is
the key to success for any MEMS industry.
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In this lecture we will learn the working principles of many microsensors and
actuators in MEMS and microsystems.
Lecture 1（Part II）
Working Principles of
MEMS and Microsystems
● Minute sensors are expected to detect a variety of signals associated
with:
Accelerations (velocity and forces)
Pressure,
Chemical,
Optical,
Thermal (temperatures), humidity,
Biological substances,
etc.
Input samples may be: motion of a solid, pressurized liquids or gases,
biological and chemical samples.
● Due to the minute sizes, microactuators work on radically different
principles than the conventional electromagnetic means, such as
solenoids and ac/dc motors.
Instead, electrostatic, thermal, piezoelectric and shape-memory
alloys are extensively used in microactuations.
Working Principles for Microsensors
BioMEMS
Power
Supply
Input
Signal
Micro
Sensing
Element
Transduction
Unit
The term “BioMEMS” has been a popular terminology in the MEMS industry in
recent years due to the many breakthroughs in this emerging technology, which
many believe to be a viable lead to mitigate the sky-rocketing costs in health care
In many industrialized countries in which aging population is a common problem.
Output
Signal
BioMEMS include the following three major areas:
(1) Biosensors for identification and measurement of biological substances,
(2) Bioinstruments and surgical tools, and
(3) Bioanalytical systems for testing and diagnoses.
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Biomedical Sensors and Biosensors
Major Technical Issues in BioMEMS Production:
These sensors are extensively used in medical diagnosis, environmental protection,
drug discovery and delivery, etc.
(1) Functionality for the intended biomedical operations.
Biomedcial Sensors
(2) Adaptivity to existing instruments and equipment.
For the measurements of biological substances in the sample and also for medical
diagnosis purposes.
(3) Compatibility with biological systems of the patients.
(4) Controllability, mobility, and easy navigation for operations
such as those required in laparoscopy surgery.
(5) Functions of MEMS structures with high aspect ratio
(defined as the ratio of the dimensions in the depth of the
structure to the dimensions of the surface)
Note: Almost all bioMEMS products are subjected to the approval
for marketing by the FDA (Food and Drug Administration)
of the US government.
Example of a biomedical sensor:
Pt electrode
Power
supply
V
i
Microsensing element: a chemical that reacts with the sample.
Transduction unit: the product of whatever the chemical reactions between the
sample and the chemical in the sensing element will convert
itself into electrical signal (e.g. in millivolts, mV).
Output signal: The converted electrical signal usually in mV.
Biosensors
A sensor for measuring the glucose concentration of a patient.
H+
Input signal: Biological sample (typically in minute amount in µL or nL)
H+
Blood sample
Polyvinyl alcohol solution
H+
H+
H+
These sensors work on the principle of interactions between the
biomolecules in the sample and the analyte (usually in solution)
in the sensor.
Signal transduction is done by the sensing element as shown
below:
ANALYTE
Ag/AgCl Reference electrode
Working principle:
Biomolecule Layer
● The glucose in patient’s blood sample reacts with the O2 in the polyvinyl
alcohol solution and produces H2O2.
●The H2 in H2O2 migrates toward Pt film in a electrolysis process, and builds up
layers at that electrode.
Output
Signals
B
B
B B B
Sensor
B
B
Biomolecule
Supply
B
Chemical
Optical
Thermal
Resonant
Electrochemical
ISFET (Ion Sensitive
Field Effect Transducer)
●The difference of potential between the two electrodes due to the build-up of
H2 in the Pt electrode relates to the amount of glucose in the blood sample.
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Chemical Sensors
Chemical Sensors-Cont’d
Work on simple principles of chemical reactions between the sample, e.g. O2
and the sensing materials, e.g. a metal.
Signal transduction is the changing of the physical properties of the sensing
materials after the chemical reactions.
There are four (4) common types of chemical sensors:
(3) Chemimechanical sensors:
Work on certain materials (e.g. polymers) that change shapes when they
are exposed to chemicals. Measuring the change of the shape of the
sensing materials to determine the presence of the chemical.
(4) Metal oxide gas sensors:
Sensing materials: certain semiconducting materials, e.g. SnO2 change
their electrical resistance when exposed to certain chemicals.
(1) Chemiresistor sensors.
(2) Chemicapacitor sensors.
Chemically
Sensitive
Polyimide
Input current
or voltage
Input Voltage
Measurand Gas
Metal Insert
Output:
Change of Resistance
Metal Electrodes
Output:
Capacitance Change
Electric Contact
SnO2
SiO2
Silicon Substrate
Measurand Gas
Optical Sensors
Chemical Sensors-Cont’d
● These sensors are used to detect the intensity of lights.
Available metal oxide gas sensors:
Semiconducting Metals
● It works on the principle of energy conversion between the photons in
the incident light beams and the electrons in the sensing materials.
Catalyst Additives
Gas to be Detected
BaTiO3/CuO
La2O3, CaCO3
CO2
SnO2
Pt + Sb
CO
SnO2
Pt
Alcohols
SnO2
Sb2O3
H2, O2, H2S
SnO2
CuO
H2S
ZnO
V, Mo
Halogenated hydrocarbons
WO3
Pt
NH3
Fe2O3
Ti-doped + Au
CO
Ga2O3
Au
CO
MoO3
None
NO2, CO
In2O3
None
O3
● The following four (4) types of optical sensors are available:
Photon Energy
A is more
transparent to
photon energy in
incident light ⇒
than B.
R
Photon Energy
Semiconductor A
Junction
Semiconductor B
(a) Photovoltaic junction
(b) Photoconductive device
Bias
Voltage
Reverse _
Bias +
Voltage
ΔR
Photon Energy
Photon Energy
R
Vout
p-Material
n-Material
p
n
Leads
(c) Photodiodes
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Optical Sensors-Cont’d
Working Principle of Silicon Solar Photovoltaic (PV)
Photon Energy
p n p
Emitter
Junction (weak dielectric)
Collector
Base
p n p
Emitter
p-silicon (atoms with “holes” by unbalanced electrons)
Photons from Sun
Base
Electric field with 2 electrodes (a battery):
(d) Phototransistors
Silicon (Si) and Gallium arsenide (GaAs) are common sensing materials.
GaAs has higher electron mobility than Si- thus higher quantum efficiency.
Extra electrons:
-
-- -
+
+
-
+
-
+
- - - - +
+
- - - - - -- - - -
+
+
+
+
+
Current
Collector
Photon Energy
n-silicon (excessive electrons)
Migrating
Electrons
+
Other materials, e.g. Lithium (Li), Sodium (Na), Potassium (K) and
Rubidium (Rb) are used for this purpose.
Pressure Sensors
Pressure Sensors-Cont’d
● Micro pressure sensors are used to monitor and measure minute gas
pressure in environments or engineering systems, e.g. automobile intake
air pressure to the engine.
● The strains associated with the deformation of the diaphragm are
measured by tiny “piezoresistors” placed in “strategic locations” on
the diaphragm.
R1, R2, R3, R4 = Piezoresistors
● They are among the first MEMS devices ever developed and produced for
“real world” applications.
R4
Metal Pad
R1
● Micro pressure sensors work on the principle of mechanical bending of
thin silicon diaphragm by the contacting air or gas pressure.
Wire bond
Silicon Die
with
Diaphragm
Piezoresistors
+
Metal film
Dielectric layer
Cavity
Constraint
Base
Die
Attach
Pyrex Glass
Constraining
Base or Metal
Header
(b) Front side pressurized
Interconnect
Passage for
Pressurized
Medium
R3 (+ve)
Vin
R2(-ve)
Metal
Casing
R1(+ve)
a Vo
-
Silicone gel
Silicon
Diaphragm
Measurand
Fluid Inlet
(a) Back side pressurized
Metal Pad
Top view of silicon die
Measurand
Fluid Inlet
Cavity
R3
R2
● These tiny piezoresistors are made
from doped silicon. They work on
the same principle as “foil strain
gages” with much smaller sizes (in
µm) with much higher sensitivities
and resolutions.
b
R4(-ve)
Wheatstone bridge for signal
transduction
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Pressure Sensors-Cont’d
Pressure Sensors-Cont’d
● Other ways of transducing the deformation of the diaphragm to electronic
output signals are available, e.g.,
Metallic
Electrode
Silicon Cover
by capacitance changes
Metallic
Electrode
V
(for higher temperature applications)
Silicon Die
MEMS microphones work
on this principle.
Cavity
Constraint
Base
Measurand
Fluid Inlet
● Major problems in pressure sensors involve the
packaging and protection of the diaphragm from
the contacting air or gas pressure.
Diffused p-type
electrode
Vibrating beam:
(n-type Si wafer,40 μm wide
Silicon diaphragm
x 600 μm long x 6 μm thick)
1200 μm sq.x 100 μm thick
Silicon die
by resonant vibration
(400 μm thick)
(for higher resolutions)
Pressurized medium
Constraint base
Thermal Sensors
Thermal Sensors-Cont’d
● Thermal sensors are used to monitor or measure temperature in an
environment or an engineering systems.
● Common thermal sensors involve thermocouples and thermopiles.
Type
● Thermal sensors work on the principle of the electromotive forces (emf)
generated by heating the junction made by dissimilar materials (beads):
Metal Wire A
Heat
Metal Wire A
i
i
Bead
Cold
Junction
Metal Wire B
(a) A thermocouple
Heat
i
V Voltage Output
V
Voltage Output
i
Metal Wire B
(b) A dual junction thermocouple
The Seebeck coefficients for various thermocouples are:
Hot
Junction
E
J
K
Wire Materials
Chromel/constantan
Iron/constantan
Chromel/alumel
Seebeck Coefficient
(μV/oC)
Range (oC)
Range (mV)
58.70 at 0oC
-270 to 1000
-9.84 to 76.36
50.37 at
0oC
-210 to 1200
-8.10 to 69.54
39.48 at
0oC
-270 to 1372
-6.55 to 54.87
600oC
-50 to 1768
-0.24 to 18.70
R
Platinum (10%)-Rh/Pt
10.19 at
T
Copper/constantan
38.74 at 0oC
-270 to 400
-6.26 to 20.87
S
Pt (13%)-Rh/Pt
11.35 at 600oC
-50 to 1768
-0.23 to 21.11
The generated voltage (V) by a temperature rise at the bead (ΔT) is:
V = β ΔT
where β = Seebeck coefficient
Common thermocouples are of K and T types
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Thermal Sensors-Cont’d
Thermal Sensors-Cont’d
Thermopiles are made of connecting a series of thermocouples in parallel:
A micro thermal sensor:
3.6 mm
Thermocouples
3.6 mm
Hot Junction
Region, Th
32 Thermocouples
16 μm wide
● Response time is 50 ms.
Top view
ΔV
The induced voltage (ΔV) by the temperature change at the hot junction (ΔT) is:
Hot Junction
Region
20 μm
Thermocouples
with N = number of thermocouple pairs in the thermopile.
● dimension of thermopile is:
3.6 mm x 3.6 mm x 20 µm thick
● Typical output is 100 mV
Diaphragm: 1.6 mm dia
x 1.3 μm thick
Cold Junction
Region, Tc
ΔV = N β ΔT
Cold Junction
Region
Hot
Junction
Region
● 32 polysilicon-gold thermocouples
Silicon Rim
Support
Diaphragm
Elevation
Working Principles for Microactuators
Power
Supply
Actuation Using Thermal Forces
● Solids deform when they are subjected to a temperature change (∆T)
● A solid rod with a length L will deform in length by ∆L = α∆T, in which
Output
Action
Micro
Actuating
Element
α = coefficient of thermal expansion (CTE) – a material property.
Transduction
Unit
● When two materials with distinct CTE bond together and subject to a
temperature change, the compound material will change its geometry
as illustrated below with a compound beam:
Power supply:
Electrical current or voltage
Transduction unit: To covert the appropriate form of power supply
to the actuating element
Actuating element: A material or component that moves with power
supply.
Output action: Usually in a prescribed motion.
α1 > α2
α1
Heat
α2
● These compound beams are commonly used
as microswitches and relays
in MEMS products.
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Actuation Using Shape Memory Alloys (SMA)
Actuation Using Piezoelectric Crystals
● SMA are the materials that have a “memory” of their original geometry (shape)
at a typically elevated temperature of production.
● These alloys are deformed into desired geometry at typically room temperature.
● A certain crystals, e.g. quartz, exhibit an interesting behavior when subjected
to mechanical deformation or electric voltage.
● The deformed SMA structures at room temperature will return to their original
shapes when they are heated to the elevated temperature of their production.
● This behavior may be illustrated as follows:
● A micro switch actuated with SMA:
V
Shape Memory Alloy Strip
e.g. TiNi or Nitinolor
Induced Mechanical
Deformation
Applied Voltage, V
Mechanical
Forces
● Ti-Ni is a common SMA.
Resistance Heating Strip
Silicon Cantilever Beam
Constraint Base
Mechanical force induced
electric voltage
Electric voltage induced
mechanical deformation
● This peculiar behavior makes piezoelectric crystals ideal candidate for
micro actuation as illustrated in the following case:
Actuation Using Electrostatic Forces
Actuation Using Piezoelectric Crystals-Cont’d
● Electrostatic Force between Two Particles – The Coulomb’s Law:
Electrodes
V
Piezoelectric
Silicon Cantilever Beam
Constraint Base
r
e,
nc
s ta n F
i
D
o
cti
F
tra
At
on
lsi
pu
Re
A
(with charge q)
B
(with charge q’)
The attraction or repulsive force:
F =
1 qq '
4πε r 2
where ε = permittivity of the medium between the two particles
= 8.85 x 10-12 C2/N-m2 or 8.85 pF/m in vacuum (= εo)
r = Distance between the particles (m)
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Actuation Using Electrostatic Forces-Cont’d
● Electrostatic Force Normal to Two Electrically Charged Plates:
Actuation Using Electrostatic Forces-Cont’d
● Electrostatic Force Parallel to Two Misaligned Electrically Charged Plates:
Fd
Length, L
V
Gap, d
dth
Wi
C = εr εo
● The induced capacitance, C is:
,W
d
W
● Force in the “Width” direction:
1 εr εo L 2
V
2
d
Fw = −
● The induced normal force, Fd is:
Fd = −
1 ε r ε o WL 2
V
2
d2
FL
L
V
A
WL
= εr εo
d
d
Fw
● Force in the “Length” direction:
FL = −
in which εr = relative permittivity of the dielectric material between the two plates
(see Table 2.2 for values of εr for common dielectric materials).
1 εr εo W 2
V
2
d
Applications of Micro Actuations-Cont’d
Applications of Micro Actuations
Micromotors
W
W/3
Unlike traditional motors, the driving forces for micro motors is primarily the parallel
electrostatic forces between pairs of misaligned electrically charged plates
(electrodes), as will be demonstrated in the following two cases:
Moving set
electrodes:
Fixed set
electrodes:
Pitch:
w+w/3
A’
Step Movements
C’
B’
D’
Dielectric material
B
A
W
C
D
W
Linear stepping motors:
● Energize the set A-A’ will generate a force pulling A’ over A due to initial misalignment.
● Two sets of electrodes in the form of plates separated by dielectric material
(e.g. quartz film).
● One electrode set is fixed and the other may slide over with little friction.
● The two sets have slightly different pitch between electrodes
● Once A and A’ are aligned, the pair B and B’ become misaligned.
W
W/3
Moving set
electrodes:
Fixed set
electrodes:
Pitch:
w+w/3
A’
● It is now with C’ and C being misaligned.
Step Movements
C’
B’
● Energize the misaligned B-B’ will generate electrostatic force pulling B’ over B.
D’
● Energize C’ and C will produce another step movement of the moving set over the
stationary set.
Dielectric material
B
A
W
W
C
D
● Repeat the same procedure will cause continuous movements of the moving sets
● The step size of the motion = w/3, or the size of preset mismatch of the pitch
between the two electrode sets.
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Applications of Microactuations-Cont’d
Applications of Microactuations-Cont’d
Rotary stepping motors:
● Involve two sets of electrodes - one set for the rotor and the other for the stator.
● Dielectric material between rotor and stator is air.
● There is preset mismatch of pitches of the electrodes in the two sets.
● Working principle of this rotary motor is similar to that in linear motors.
A micro motor produced by Karlsruhe Nuclear Research Center, Germany:
Rotor
Stator
Micropumps
Microvalves
Electrostatically actuated micropump:
● A special microvalve designed by Jerman in 1990.
● Circular in geometry, with diaphragm of 2.5 mm in diameter x 10 μm thick.
● The valve is actuated by thermal force generated by heating rings.
● Heating ring is made of aluminum films 5 µm thick.
● The valve has a capacity of 300 cm3/min at a fluid pressure of 100 psig.
● Power consumption is 1.5 W.
Flexible Silicon Diaphragm
Gear for
transmitting
torque
Electric Resistance
Heating Rings
● An electrostatic actuated pump in 1992.
● The pump is of square geometry with 4 mm x 4mm x 25 μm thick.
● The gap between the diaphragm and the electrode is 4 µm.
● Pumping rate is 70 μL/min at 25 Hz.
Deformable
Silicon
Diaphragm
V
Electrode
INLET FLOW
Inlet
Check
Valve
Pumping Chamber
Silicon
Base
Outlet
Check
Valve
Constraint Base
FLOW OUTLET
Centerline
Low Pressure
Fluid Inlet
Constraint
Base
High Pressure
Fluid Outlet
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Micro Heat Pipes- a viable solution to cooling
in molecular electronics
Piezoelectrically actuated pump:
● An effective way to pump fluid through capillary tubes.
● Tube wall is flexible.
● Outside tube wall is coated with piezoelectric crystal film, e.g. ZnO
with aluminum interdigital transducers (IDTs).
● Radio-frequency voltage is applied to the IDTs, resulting in mechanical
squeezing in section of the tube (similar to the squeezing of toothpaste)
● Smooth flow with “uniform” velocity profile across the tube cross section.
Piezoelectric coating
with transducer
F
Flow
V
Flexible Tube
Wall
Conventional Heat Pipes
Heat Sink
Heat Source
Condensed
liquid
Wick
Vapor
Heat Source
Wick
Heat Sink
ink
Heat S
urce
Heat So
Micro Heat Pipe
Conde
ion
tic Sect
Adiaba
Sharp corners of microconduit
provide capillary driving pressure
for the return of condensed liquid
- no wicks is necessary
nser
rator
Evapo
Cross-Sections
Heat
Sink
LIQUID
Heat
Source
VAPOR
Elevation
Microaccelerometers
Micro Accelerometers-Cont’d
● Accelerometers are used to measure dynamic forces associated
with moving objects.
● These forces are related to the velocity and acceleration of the moving
objects.
● Traditionally an accelerometer is used to measure such forces.
● A typical accelerometer consists of a “proof mass” supported by a spring and
a “dashpot” for damping of the vibrating proof mass:
The accelerometer is
attached to the vibrating
solid body
Spring
k
Mass
M
Vibrating
Solid Body
Dashpot
with
damping
C
The accelerometer is
attached to the vibrating
solid body
● The instantaneous displacement of the mass
y(t) induced by the attached moving solid
body is measured and recorded with respect
to time, t.
● The associated velocity, V(t) and the acceleration
α(t) may be obtained by the following derivatives:
V (t ) =
dy (t )
dt
and
α (t ) =
Spring
k
Mass
M
Vibrating
Solid Body
Dashpot
with
damping
C
dy (t )
d 2 y (t )
=
dt
dt 2
● The associated dynamic force of induced by the moving solid is thus obtained
by using the Newton’s law, i.e. F(t) = M α(t), in which M = the mass of the
moving solid.
♦ In miniaturizing the accelerometers to the microscale, there is no room for the
coil spring and the dashpot for damping on the vibrating mass.
♦ Alternative substitutes for the coil spring, dashpot, and even the proof mass
need to be found.
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Microaccelerometers-Cont’d
Microaccelerometers-Cont’d
● There are two types microaccelerometers available.
(2) Balanced force microaccelerometer:
● This is the concept used in the “air-bag” deployment sensor in automobiles
(1) The cantilever beam accelerometer:
Silicon Cantilever
Beam
Casing
● In this design: Plate beam = proof mass;
Two end tethers = springs
Surrounding air = dashpot
Piezoresistor
Mass, M
Be
am
Constraint Base
Constraint Base
Stationary
electrodes
Moving electrode
Vibrating Base
Ac
c
Mo
ve
me
nt
ele
ra
tio
n
In this design: Cantilever beam = coil spring;
Surrounding viscous fluid = dashpot for damping of the proof mass
The movement of the proof mass is carried out by the attached piezoresistor.
● The movement of the proof mass is carried out by measuring the
change of capacitances between the pairs of electrodes.
Inertia Sensors – Unique Micromechatronics Devices
Working Principle of BalancedForce Accelerometers:
Balanced-Force Accelerometers:
MEMS Microphones
Applications:
● Beamforming microphone arrays for wind tunnels
● Beamforming microphone arrays for smart hearing aids
● Mobile telephones
● Notebook and palm-top computers
Acoustic Wave Input
(air pressure wave)
dB→ MPa
2 mm
3 mm
• The need for integrating microelectronics (ICs)
and moving microstructures – A great challenge!
Ac
ce
ler
a ti
on
Electrical signal output:
Diaphragm:
≈ 1µm thick
Air gap (≈2 µm)
Backplate (≈2 µm)
ΔC
Acoustic holes
Pressure equalization hole
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Microgyroscopes
- for precision motion control
A Microgyroscope Actuated by Electrostatic Forces
The Vectorial Representation of Coriolis Motion:
Ω
V
Fc
V
x
y
Fc
z
Ω
(b)
z
y
V
y
z
x
x
V
y
Fc
x
Proof
Mass
x-Spring
x
z
Ω
Fc
x
Resonator
for Linear Motion
Generation
x
(a)
y-Spring for
Force
Measurements
y
y
x
x-Position
Gyro Frame
z
Ω
x
y
y
z
y
y-Position
x
z
z
(c)
(d)
y
SUMMARY
● MEMS and microsystems consist of sensors, actuators, power supply
and signal transducers.
● Microsensors work on the principle of change of sensing material properties
in response to the substances to be sensed and detected.
● Actuating forces for MEMS and microsystems are radically different from
traditional electromagnetic forces.
● Microactuating forces include:
● Electrostatic forces – low in magnitudes, but fast responsransductioes
● Thermal forces – larger in magnitudes, but slow in response
● Piezoelectric forces – flexible in magnitudes, fast responses,
but with limited lasting power.
● Signal transduction and power supply are two major challenging factors in
the design of microsystems.
总结性的小问题
•
•
•
•
•
1. 微机电系统的英文全称（PPT第7页）
2. MEMS作为Sensor的的结构框图（PPT第24页）
3. MEMS作为Actuator的结构框图（PPT第25页）
4. Microsystem的结构框图（PPT第26页）
5. 从听课内容请举出任意一种MEMS器件的工作原
理（Actuator(linear motor, miropump)、
Sensor(Biosensor, Gas sensor, Pressure sensor)或
Microsystem）（PPT第55-93页）
• 5. 请你介绍两种以上你所知道的MEMS器件或系统
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