Download - Micro and Smart Systems
-
8/11/2019 Micro and Smart Systems
1/497
-
8/11/2019 Micro and Smart Systems
2/497
-
8/11/2019 Micro and Smart Systems
3/497
Micro and Smart Systems
-
8/11/2019 Micro and Smart Systems
4/497
-
8/11/2019 Micro and Smart Systems
5/497
Micro and Smart SystemsTechnology and Modeling
G.K. ANANTHASURESH
K.J. VINOY
S. GOPALAKRISHNAN
K.N. BHAT
V.K. AATRE
Indian Institute of Science
Bangalore INDIA
-
8/11/2019 Micro and Smart Systems
6/497
VP AND EXECUTIVE PUBLISHE R Don Fowley
ASSISTANT PUBLISHER Daniel Sayr e
SENIOR EDITORIAL ASSISTANT Katie Singleton
EXECUTI VE MARKETING MANAGER Christopher Ruel
MARKETI NG ASSISTANT Ashley Tomeck
SENIOR PRODUCTION MANAGER Janis Soo
ASSISTANT PRODUCTION EDITOR Elaine S. Chew
EXECUTI VE MEDIA EDITOR Tom Kulesa
MEDIA EDITOR Wendy Ashenberg
MEDIA SPECIALIST Jennif er Mullin
COVER DESIGNER Wendy Lai
COVER I MAGE Sambuddha Khan
T h i s b o o k w a s s e t i n T i m e s b y T h o m s o n D i g i t a l , N o i d a , I n d i a a n d p r i n t e d a n d b o u n d b y C o u r i e r W e s t f o r d , I n c .
T h e c o v e r w a s p r i n t e d b y C o u r i e r W e s t f o r d , I n c .
T h i s b o o k i s p r i n t e d o n a c i d f r e e p a p e r . 1
F o u n d e d i n 1 8 0 7 , J o h n W i l e y & S o n s , I n c . h a s b e e n a v a l u e d s o u r c e o f k n o w l e d g e a n d u n d e r s t a n d i n g f o r m o r e t h a n2 0 0 y e a r s , h e l p i n g p e o p l e a r o u n d t h e w o r l d m e e t t h e i r n e e d s a n d f u l fi l l t h e i r a s p i r a t i o n s . O u r c o m p a n y i s b u i l t o n a
f ounda t i on of pr i nc i pl e s t ha t i nc l ude r e s pons i bi l i t y t o t he c om m uni t i e s w e s e r ve a nd w he r e w e l i ve a nd w or k. I n
2008, w e l a unc he d a C or por a t e C i t i z e ns hi p I ni t i a t i ve , a gl oba l e f f or t t o a ddr e s s t he e nvi r onm e nt a l , s oc i a l ,
e c onom i c , a nd e t hi c a l c ha l l e nge s w e f a c e i n our bus i ne s s . A m ong t he i s s ue s w e a r e a ddr e s s i ng a r e c a r bon i m pa c t ,
pa pe r s pe c i fi c a t i ons a nd pr oc ur e m e nt , e t hi c a l c onduc t w i t hi n our bus i ne s s a nd a m ong our ve ndor s , a nd c om m uni t y
a nd c har i t a bl e s upport . F or m or e i nf orm a t ion, pl ea s e vi s it our w e bs i t e: www.wiley.com/go/citizenship.
Copyright # 2 0 1 2 , J o h n W i l e y & S o n s , I n c . A l l r i g h t s r e s e r v e d . N o p a r t o f t h i s p u b l i c a t i o n m a y b e r e p r o d u c e d ,
s t o r e d i n a r e t r i e v a l s y s t e m o r t r a n s m i t t e d i n a n y f o r m o r b y a n y m e a n s , e l e c t r o n i c , m e c h a n i c a l , p h o t o c o p y i n g ,
r e c o r d i n g , s c a n n i n g o r o t h e r w i s e , e x c e p t a s p e r m i t t e d u n d e r S e c t i o n s 1 0 7 o r 1 0 8 o f t h e 1 9 7 6 U n i t e d S t a t e s
C o p y r i g h t A c t , w i t h o u t e i t h e r t h e p r i o r w r i t t e n p e r m i s s i o n o f t h e P u b l i s h e r , o r a u t h o r i z a t i o n t h r o u g h p a y m e n t o f t h e a p p r o p r i a t e p e r - c o p y f e e t o t h e C o p y r i g h t C l e a r a n c e C e n t e r , I n c . 2 2 2 R o s e w o o d D r i v e , D a n v e r s , M A 0 1 9 2 3 ,
website www.copyright.com . R e que st s t o t he P ubl i she r f or pe r mi s s i on s houl d be a ddr e ss e d t o t he P e r m i ss i ons
D e p a r t m e n t , J o h n W i l e y & S o n s , I n c . , 1 1 1 R i v e r S t r e e t , H o b o k e n , N J 0 7 0 3 0 - 5 7 7 4 , ( 2 0 1 ) 7 4 8 - 6 0 1 1 , f a x ( 2 0 1 ) 7 4 8 -
6008, website http://www.wiley.com/go/permissions.
E v a l u a t i o n c o p i e s a r e p r o v i d e d t o q u a l i fi e d a c a d e m i c s a n d p r o f e s s i o n a l s f o r r e v i e w p u r p o s e s o n l y , f o r u s e i n t h e i r
c o u r s e s d u r i n g t h e n e x t a c a d e m i c y e a r . T h e s e c o p i e s a r e l i c e n s e d a n d m a y n o t b e s o l d o r t r a n s f e r r e d t o a t h i r d
p a r t y . U p o n c o m p l e t i o n o f t h e r e v i e w p e r i o d , p l e a s e r e t u r n t h e e v a l u a t i o n c o p y t o W i l e y . R e t u r n i n s t r u c t i o n s a n d
a f re e o f c ha r ge r et u rn m a il in g la b el a re a va il ab l e a t www.wiley.com/go/returnlabel . I f you ha ve c hos e n to a dopt
t h i s t e x t b o o k f o r u s e i n y o u r c o u r s e , p l e a s e a c c e p t t h i s b o o k a s y o u r c o m p l i m e n t a r y d e s k c o p y . O u t s i d e o f t h e
U ni t e d S t a t e s , pl e a s e c ont a c t your l oc a l s a l e s r e pr e s e nt a t i ve .
Library of Congress Cataloging-in-Publication Data
M ic ro a nd s ma rt s ys te ms / G .K . A n a nt ha su re sh . . . [ et a l. ].
p . c m .
I nc l ude s bi bl i ogr a phi c a l r e f e r e nc e s a nd i nde x.
I S B N 978- 0- 470- 91939- 2 ( a c i d- f r e e pa pe r )
1 . M i cr o el e ct r om e ch a n ic a l s ys t em s D e si g n a nd c o n st r u ct i on . 2 . I n te l li g en t c o nt r ol s y s te m s D es i gn a n d
c o ns tr u ct io n . I . A na nt ha su re sh , G. K .
T K 7875. M 524 2012
621.381dc23
2011029301
P r i n t e d i n t h e U n i t e d S t a t e s o f A m e r i c a
10 9 8 7 6 5 4 3 2 1
http://www.wiley.com/go/citizenshiphttp://www.copyright.com/http://www.wiley.com/go/permissionshttp://www.wiley.com/go/returnlabelhttp://www.wiley.com/go/returnlabelhttp://www.wiley.com/go/returnlabelhttp://www.wiley.com/go/permissionshttp://www.copyright.com/http://www.wiley.com/go/citizenship -
8/11/2019 Micro and Smart Systems
7/497
Dedicated to
The Institute of Smart Structures and Systems (ISSS)without whose initiative and support this book would not have materialized
-
8/11/2019 Micro and Smart Systems
8/497
-
8/11/2019 Micro and Smart Systems
9/497
cPrefaceIf we trace the history of electronics technology over the last six decades, we see that the
discovery of the transistor and the development of the integrated circuit (IC) are the key
milestones. However, it is miniaturization and the ensuing very-large-scale-integration
(VLSI) technologies that really created the electronics and computer revolutions. It is only
more recently, within the last couple of decades, that the technology of miniaturization has
been extended to mechanical devices and systems; we now have the microelectromechan-
ical system (MEMS) revolution. Complemented by the advances in smart materials, this
has led to highly application-oriented microsystems and smart systems.
A microsystem is a system that integrates, on a chip or in a package, one or more of
many microdevices: sensors, actuators, electronics, computation, communication, control,power generation, chemical processing, biological reactions, etc. It is now clear that the
functionality of such an integrated system will not only be far superior to any other
engineered system that we know at the macroscale but will also be able to achieve things
well beyond what macroscale integrated systems can do. Smart microelectromechanical
systems are collections of microsensors and actuators that can sense their environment and
can respond intelligently to changes in that environment by using microcircuit controls.
Such microsystems include, in addition to the conventional microelectronics, packaging,
integrated antenna structures for command signals, and microelectromechanical structures
for desired sensing and actuating functions.
However, micromachined actuators may not be powerful enough to respond to the
environment. Using macroscale actuators would defeat the purpose of miniaturization,
cost-effective batch-processing, etc. Hence, there is a need to integrate smart material-
based actuators with microsystems. This trend is currently being witnessed as this field
moves beyond microsensors, which have been the main emphasis in microsystems so far.
Microsystems and smart system technologies have immense application potential in
many fields, and in the coming decades, scientists and engineers will be required to design
and develop such systems for a variety of applications. It is essential, then, that graduating
engineers be exposed to the underlying science and technology of microsystems and smart
systems. There are numerous books that cover both microsystems and smart systems
separately and a few that cover both. Many of them are suitable for practicing professionals
or for advanced-level courses. However, they assume certain fundamentals in various topicsof this multidisciplinary field and thus serve the function of a reference book rather than a
primary textbook. Many do not emphasize modeling at the fundamental level necessary to be
useful at the undergraduate level or for self-study by a reader with background in other
disciplines.
This book essentially deals with the basics of microsystem technology and is intended
principally as a textbook at the undergraduate level; it can also be used as a background
book at the postgraduate level. The book provides an introduction to smart materials and
systems. We have tried to present the material without assuming much prior disciplinary
background. The aim of this book is to present adequate modeling details so that readers
can appreciate the analysis involved in microsystems (and to some extent, smart systems),
thereby giving them an in-depth understanding about simulation and design. Therefore, the
book will also be useful to practicing researchers in all branches of science and engineering
vii
-
8/11/2019 Micro and Smart Systems
10/497
who are interested in applications where they can use this technology. The book presents
adequate details on modeling of microsystems and also addresses their fabrication and
integration. The engineering of practical applications of microsystems provides areas for
multidisciplinary research, already laden with myriad technological issues, and books
presently available do not address many of these aspects in sufficient depth. We believe
that this book gives a unified treatment of the necessary concepts under a single title.Anticipating the need for such a technology, the Institute of Smart Structures and
Systems (ISSS), an organization dedicated to promoting smart materials and micro-
systems, was established. This Institute was instrumental not only in mounting a national
program and triggering R&D activities in this field in India, but also in creating the
required human resources through training courses and workshops. Furthermore, ISSS also
initiated a dialogue with Visvesveraya Technological University (VTU), Belgaum,
Karnataka, a conglomerate of over 170 Karnataka engineering colleges, to introduce
an undergraduate-level course in microsystems and MEMS and to set in motion the
creation of a potential syllabus for this course. The culmination of this dialogue is the
present book. The material for this book has been taken from several advanced workshops
and short courses conducted by the authors over last few years for faculty and students of
VTU. A preliminary version of book was used at VTU colleges, where a course on
microsystems was first introduced in 2009, and very helpful feedback was received from
teachers of this course, who patiently used the draft to teach about 500 students at various
colleges. In a sense this book has been class- and student-tested and is a substantially
enhanced version of the original draft.
This book has ten chapters covering various topics in microsystems and smart systems
including sensors and actuators, microfabrication, modeling, finite-element analysis,
modeling and analysis of coupled systems (of great importance in microsystems),
electronics and control for microsystems, integration and packaging, and scaling effects
in microsystems. The book also includes case studies on a few microsensor systems toillustrate the applications aspects.
In the authors opinion, the material of the book can be covered in a standard
undergraduate one-semester course. The content of Chapters 5 and 6 may be considered
optional. The entire book can be covered in a single-semester postgraduate course or a
two-semester undergraduate course supplemented by a design and case-study oriented
laboratory.
viii c Preface
-
8/11/2019 Micro and Smart Systems
11/497
cAcknowledgmentsAny project like writing a book depends on the help, advice, and consent of a large number
of people. The authors have received such help from many people and it is a pleasure to
acknowledge all of them. The trigger for the book was provided by the initiative taken by
the Institute of Smart Structures and Systems. The authors acknowledge their indebtedness
to ISSS and its presidents, and indeed dedicate the book to ISSS. The authors would like to
specially thank Prof. S. Mohan of Indian Institute of Science and Dr. A.R. Upadhya,
Director, National Aerospace Laboratories, for their support and encouragement.
While ISSS initiated the writing of the book, it was the support and enthusiasm of the
Visvesvaraya Technological University (VTU) that sustained its writing. The authors
gratefully acknowledge this support, especially from the former vice-chancellors, Prof. K.Balaveer Reddy and Prof. H.P. Khincha.
A number of VTU faculty and students who attended the workshops based on the
preliminary versions of the book provided the all-important feedback necessary to finalize
the book. While thanking them all, the authors would like to mention in particular Prof.
Premila Manohar (MSR Institute of Technology, Bangalore) and Prof. K. Venkatesh
(presently at Jain University, Bangalore). In addition, the significant contributions of Prof.
N.G. Kurahatti (presently at East Point College of Engineering and Technology,
Bangalore), who compiled part of the contents of Chapter 3 during the initial stages of
manuscript preparation, are gratefully acknowledged. The writing of the book would not
have been possible without the work put in by several of our post-graduate students.
Contributions of P.V, Aman, Santosh Bhargav, A.V. Harikrishnan, Shyamsananth
Madhavan, Ipe Mathew, Rizuwana Parveen, Pakeeruraju Podugu, and Jayaprakash Reddy,
who collected much of the information presented in Chapter 2, are gratefully appreciated.
Also acknowledged for their help are: Subhajit Banerjee, Varun Bollapragada, Vivek
Jayabalan, Shymasananth Madhavan, Fatih Mert Ozkeskin, Krishna Pavan, Sudhanshu
Shekhar, and Puneet Singh who ran simulations and provided material for Chapter 10.
Assistance given by M. S. Deepika and R. Manoj Kumar in creating some of the
illustrations is also gratefully acknowledged. The authors thank all their students who
read the early manuscripts of this book and provided useful feedback. The credit for the
cover image goes to Sambuddha Khan. The image shows a part of the bulk-micromachined
accelerometer with a mechanical amplifier developed by him as part of his PhDdissertation.
ix
-
8/11/2019 Micro and Smart Systems
12/497
-
8/11/2019 Micro and Smart Systems
13/497
cA N o t e t o t h e R e a d e rMost chapters include worked-out examples, problems given within the text, and end-of-
the-chapter exercises.
Some chapters also include exploratory questions marked as Your Turn. They urge
the reader to think beyond the scope of the book. They are intended to stimulate the interest
of the reader.
Acronyms and notation used in the book are included in separate lists at the beginning
of the book. Additionally, a glossary of important terms appears at the end of the book.
An Appendix that appears at the end of the book provides supplementary material for
the convenience of the reader.
Typographical oversights, technical mistakes, or any other discrepancies may pleasebe broughtto the attentionof the authors by sendinge-mail to: [email protected].
xi
-
8/11/2019 Micro and Smart Systems
14/497
-
8/11/2019 Micro and Smart Systems
15/497
cAcronymsmBGA Microball-grid array
mCP Microcontact printing
mTM Microtransfer molding
mTAS Micro-total analysis system
1D One-dimensional
2D Two-dimensional
3D Three-dimensional
ADC or A/D Analog-to-digital converterAFM Atomic force microscopy
APCVD Atmospheric pressure chemical vapor
deposition
ASIC Application-specific integrated circuits
ASIC Application-specific-integrated circuit
BEM Boundary element method
BGA Ball-grid array
BiCMOS Bipolar CMOS
bio-MEMS bio-microelectromechanical systems
BJT Bipolar junction transistor
BSG Borosilicate glass
BST Barium strontium titanate
BW Bandwidth
CMOS Complementary metal-oxide-
semiconductor
CMP Chemicalmechanical planarization
CMRR Common-mode rejection ratio
COC Cyclic olefin copolymer
COF Chip-on-flex
CPD Critical point drying
CRT Cathode ray tube
CTE Coefficient of thermal expansion
CVD Chemical vapor deposition
DAC or D/A Digital-to-analog converter
DFT Discrete Fourier transform
DLC Diamond-like carbon
DLP Digital light processor
DMD Digital Mirror Device
DoD Drop-on-demand
DOF Degree of freedom
DRIE Deep reactive-ion etching
DSP Digital signal processing
EDP Ethylene diamine pyrocatechol
EDM Electrical discharge machining
EEPROM Erasable programmable read-onlymemory
EGS Electronic grade silicon
EMI Electromagnetic interference
ER Electrorheological
ETC Electro-thermal-compliant
ER Electro rheological
FBG Fiber Bragg grating
FCC Face-centered cubic
FCP Few-chip package
FDM Finite difference method
FE Finite element
FEA Finite element analysis
FEM Finite element method
FFT Fast Fourier transform
FPI Fabry Perot interferometer
HDTV High-definition television
HF HydrofluoricHVAC Heat, ventilation, and air-conditioning
I/O Input/output
IBE Ion beam etching
IC Integrated circuit
ICP Intracranial pressure
IF Intermediate frequency
IR Infrared
ISR Interrupt service routine
LCD Liquid crystal display
LED Light-emitting diode
xiii
-
8/11/2019 Micro and Smart Systems
16/497
LIGA Lithographie Galvanoformung
& Abformung
LPCVD Low-pressure chemical vapor deposition
LPF Low-pass filter
LSB Least significant bit
LTCC Low-temperature cofired ceramics
LVDT Linear variable differential transformer
MAP Manifold-absolute pressure
MBE Molecular beam epitaxy
MCM Multichip module
MCM-D Multichip module deposited
MEMS Microelectromechanical systems
MGS Metallurgical grade silicon
Micro-EDM Microelectrical discharge machining
MMF Magneto motive force
MMIC Monolithic microwave integrated circuits
MOCVD Metal-organic chemical vapor
deposition
MOEMS Micro-opto-electromechanical systems
MOS Metal-oxide-semiconductor
MOSFET Metal oxide semiconductor field-effect
transistor
MR Magnetorheological
MS Metal semiconductor
nMOS n-channel MOSFETs
pMOS p-channel MOSFET
ODE Ordinary differential equation
Op-amp Operational amplifier
PCB Printed circuit board
PCR polymerase chain reaction
PDE Partial differential equationPBGA Plastic-ball-grid array
PDMS Polydimethylsiloxane
PECVD Plasma-enhanced chemical vapor
deposition
PFC Piezofiber composite
PHET Photovoltaic electrochemical etch-stop
technique
PID Proportional-integral-derivative
PLC Programmable logic controller
PLL Phase-locked loop
PMMA Polymethyl methacrylate
pMOS p-channel MOSFETs
PMPE Principle of minimum
potential energy
PSG Phosphosilicate glass
PTFE Polytetra-fluoroethylene
PVC Polyvinyl chloride
PVD Physical vapor deposition
PVDF Polyvinylidene fluoride
PVW Principle of virtual work
PZT Lead zirconate titanate
R&D Research and development
RF Radio frequency
RIE Reactive-ion etching
RTA Rapid thermal annealing
SAC Successive-approximation converter
SAW Surface acoustic wave
SCS Single-crystal silicon
SEM Scanning electron microscope
SFB Silicon fusion bonding
SFEM Spectral FEM
SI unit International standard unitSIP System-on-a-chip
SISO Single-inputsingle-output
SMA Shape-memory-alloy
SNR Signal-to-noise ratio
SOI Silicon-on-insulator
SOP System-on-a-package
sPROMs Structurally programmable microfluidic
system
SuMMiT Santia ultra multi-layer microfabricationtechnology
TCR Temperature coefficient of resistivity
UV Ultraviolet
VCO Voltage-controlled oscillator
VED Vacuum electron devices
VLSI Very large-scale integration
VPE Vapor phase epitaxy
WRT Weighted residual technique
XFEM Extended FEM
xiv c Acronyms
-
8/11/2019 Micro and Smart Systems
17/497
cNotat ionThere are 26 letters in the English alphabet and 24 in the Greek alphabet. Using both lower
and upper case, we have 100 symbols to denote various quantities. Traditionally, every
discipline reserves certain symbols for certain quantities. When we mix disciplines, as
happens in interdisciplinary subjects, there are bound to be clashes: the same symbol is
used for different quantities in different disciplines (e.g., Rfor reaction force in mechanics
and resistance in electronics). We have made an effort to minimize the overlap of such
quantities when they are used in the same chapter. As a result, we use nontraditional
symbols for certain quantities. For example, Yis used for Youngs modulus instead ofE
sinceEis used for the magnitude of the electric field, because they both appear in the same
chapter.Occasionally, we also use subscripts to relate a certain symbol to a discipline (e.g.,kth
for thermal conductivity). Boldface symbols are used for vectors (e.g., E for the electric
field vector).
The symbols in the list below are arranged in this order: upper-case English, lower-
case English, upper-case Greek, and lower-case Greek, all in alphabetical order. For each
symbol, boldface symbols appear first and symbols with subscripts or superscripts appear
afterwards. If the same symbol is used in two different disciplines, the descriptions are
separated by OR; if the same symbol is used within the same discipline, or is used.
A Cross-sectional area of a bar or beam ORarea of a parallel-plate capacitor or a proof
mass
B Magnetic flux density vector
A0 Difference mode gain
AC Common mode gain
Bo Bond number
C Capacitance OR a constant
Cox Gate oxide capacitance per unit area
D Coil diameter of a helical spring OR
magnitude of the electric displacement
vector OR diffusion constant
Dn Normal component of the electric
displacement vector
DE Dissipated energy
E Electric field vector
En Normal component of the electric field
ESE Electrostatic energy
ESEc Electrostatic complementary energy
F Force; occasionally, also the transverse force
on a beam or a point force on a body
Fe Electrostatic forceFd Damping force
G Gauge factorH Magnetic field
I Inertia in general or area of moment of
inertia of a beam OR electric current
Ic0 Reverse saturation current
Kd Derivative controller gain
KP Proportional controller gain
KI Integral controller gain
J Polar moment of inertia OR the magnitude
of the electric current density
K Bulk modulus of a material
KB Boltzmann constant
Kn Knudsen number
KE Kinetic energy
L Length or size OR inductance OR
Lagrangian
M Magnetization
M Bending moment in a beam or a column OR
mass of the proof mass
MSEc Magnetostatic coenergy
n Number of turns
NA Acceptor dopant concentrationND Donor dopant concentration
xv
-
8/11/2019 Micro and Smart Systems
18/497
No
Intrinsic concentration
P Axial force in a bar or a beam or a point force
on a body OR magnitude of an electric
polarization vector
PE Potential energy
Q Electric chargeR Reaction force OR electrical resistance
Re Reynolds number
S Sensitivity
SE Strain energy
SEc Complementary strain energy
T Torque OR temperature
U Velocity vector
V Volume OR vertical shear force OR voltage
W Work
Vth Threshold voltage
Vbi Built in potential
Y Youngs modulus, a material property usually
denoted byain mechanics; we useabecausea
is used for the magnitude of the electric field
and for acceleration
n Unit vector usually normal to a surface and
directed outward
a Acceleration
b Width of a beam or damping coefficient
dl A differential vector tangential to a path at a
pointds A differential vector normal to a surface
dV Differential volume
g Acceleration due to gravity OR gap in parallel-
plate capacitor
g0 Initial gap in parallel-plate capacitor
h Convective heat transfer coefficient
i Electric current
k Spring constant or stiffness in general
kB Boltsmann constant
ke Electrical conductivity
kth Thermal conductivityl Length
p Perimeter OR pressure
q Distributed transverse load OR electric charge
qe
Charge of electron
r Position or distance vector
r Unit vector in the direction of a position or
distance vector
se Strain energy per unit volume
t Surface force on an elastic body (also called
traction)
te Electrostatic force on a conductor
t Time OR thickness OR force (traction) on a
surface
u Displacement in general or onlyx-displacementin 2D or 3D objects
v y-displacement in 2D or 3D objects
w Width OR transverse displacement of a beam or
z-displacement in a 3D object
D Deflection OR an increment in a quantity (if
followed by another symbol)
a Coefficient of thermal expansion OR a constant
of proportionality
xe Electrical susceptibility
d Deflection OR an increment in a quantity (if
followed by another symbol)
2 Normal strain
e Permittivity
e0 Permittivity of free space
er Relative permittivity
h Viscosity
f Twist OR electric potential
g Shear strain OR surface tension
k Torsional spring constant
l Wave length
m Permeabilitymn
electron mobility
m0 Permeability of free space
n Poisson ratio
u Slope of a bent beam
r Radius of curvature of a straight beam that is
bent
re Electrical resistivity
rm Mass density
se Maxwells stress tensor
s Normal stress
t Shear stress or time constantv Frequency of applied stimulus (force, voltage,
etc.)
vn Natural frequency (also called resonance
frequency)
cL Line charge density
cs Surface charge density
cv Volumetric charge density
xvi c Notation
-
8/11/2019 Micro and Smart Systems
19/497
cContentsPreface viiAcknowledgments ixA Note to the Reader xiAcronyms xiiiNotation xv
c CHAPTER 1
Introduction 11.1. Why Miniaturization? 2
1.2. Microsystems Versus MEMS 4
1.3. Why Microfabrication? 5
1.4. Smart Materials, Structures and Systems 7
1.5. Integrated Microsystems 9
1.5.1. Micromechanical Structures 10
1.5.2. Microsensors 11
1.5.3. Microactuators 12
1.6. Applications of Smart Materials and
Microsystems 131.7. Summary 15
c CHAPTER 2
Micro Sensors, Actuators, Systems andSmart Materials: An Overview 172.1. Silicon Capacitive Accelerometer 18
2.1.1. Overview 18
2.1.2. Advantages of Silicon Capacitive
Accelerometers 19
2.1.3. Typical Applications 192.1.4. An Example Prototype 19
2.1.5. Materials Used 19
2.1.6. Fabrication Process 19
2.1.7. Key Definitions 20
2.1.8. Principle of Operation 21
2.2. Piezoresistive Pressure Sensor 22
2.2.1. Overview 22
2.2.2. Advantages of Piezoresistive Pressure
Sensors 22
2.2.3. Typical Applications 22
2.2.4. An Example Commercial Product 23
2.2.5. Materials Used 23
2.2.6. Fabrication Process 23
2.2.7. Key Definitions 23
2.2.8. Principle of Operation 23
2.3. Conductometric Gas Sensor 24
2.3.1. Overview 24
2.3.2. Typical Applications 25
2.3.3. An Example Product Line 25
2.3.4. Materials Used 25
2.3.5. Fabrication Process 25
2.3.6. Key Definitions 26
2.3.7. Principle of Operation 26
2.4. Fiber-Optic Sensors 26
2.4.1. Overview 26
2.4.2. Advantages of Fiber-Optic Sensors 27
2.4.3. An Example Prototype 27
2.4.4. Materials Used 27
2.4.5. Fabrication Process 27
2.4.6. Key Definitions 28
2.4.7. Principle of Operation 282.5. Electrostatic Comb-Drive 29
2.5.1. Overview 29
2.5.2. An Example Prototype 30
2.5.3. Materials Used 31
2.5.4. Fabrication Process 31
2.5.5. Key Definitions 31
2.5.6. Principle of Operation 31
2.6. Magnetic Microrelay 32
2.6.1. Overview 32
2.6.2. An Example Prototype 33
2.6.3. Materials Used 332.6.4. Fabrication Process 33
2.6.5. Key Definitions 33
2.6.6. Principle of Operation 33
2.7. Microsystems at Radio Frequencies 34
2.7.1. Overview 34
2.7.2. Advantages of RF MEMS 34
2.7.3. Typical Applications 35
2.7.4. An Example Prototype 35
2.7.5. Materials Used 36
2.7.6. Fabrication Process 362.7.7. Key Definitions 36
2.7.8. Principle of Operation 37
xvii
-
8/11/2019 Micro and Smart Systems
20/497
2.8. Portable Blood Analyzer 37
2.8.1. Overview 37
2.8.2. Advantages of Portable Blood
Analyzer 39
2.8.3. Materials Used 39
2.8.4. Fabrication Process 392.8.5. Key Definitions 39
2.8.6. Principle of Operation 39
2.9. Piezoelectric Inkjet Print Head 40
2.9.1. Overview 40
2.9.2. An Example Product 40
2.9.3. Materials Used 41
2.9.4. Fabrication Process 41
2.9.5. Key Definitions 41
2.9.6. Principle of Operation 41
2.10. Micromirror Array for Video Projection 42
2.10.1. Overview 42
2.10.2. An Example Product 43
2.10.3. Materials Used 43
2.10.4. Fabrication Process 44
2.10.5. Key Definitions 44
2.10.6. Principle of Operation 44
2.11. Micro-PCR Systems 45
2.11.1. Overview 45
2.11.2. Advantages of Micro-PCR
Systems 45
2.11.3. Typical Applications 462.11.4. An Example Prototype 46
2.11.5. Materials Used 46
2.11.6. Fabrication Process 46
2.11.7. Key Definitions 47
2.11.8. Principle of Operation 47
2.12. Smart Materials and Systems 48
2.12.1. Thermoresponsive Materials 49
2.12.2. Piezoelectic Materials 50
2.12.3. Electrostrictive/Magnetostrictive
Materials 50
2.12.4. Rheological Materials 512.12.5. Electrochromic Materials 51
2.12.6. Biomimetic Materials 51
2.12.7. Smart Gels 51
2.13. Summary 52
c CHAPTER 3
Micromachining Technologies 553.1. Silicon as a Material for Micromachining 56
3.1.1. Crystal Structure of Silicon 563.1.2. Silicon Wafer Preparation 59
3.2. Thin-film Deposition 60
3.2.1. Evaporation 60
3.2.2. Sputtering 61
3.2.3. Chemical Vapor Deposition 62
3.2.4. Epitaxial Growth of Silicon 64
3.2.5. Thermal Oxidation for Silicon
Dioxide 653.3. Lithography 65
3.3.1. Photolithography 66
3.3.2. Lift-Off Technique 68
3.4. Doping the Silicon Wafer: Diffusion and Ion
Implantation of Dopants 69
3.4.1. Doping by Diffusion 70
3.4.2. Doping by Ion Implantation 72
3.5. Etching 75
3.5.1. Isotropic Etching 75
3.5.2. Anisotropic Etching 76
3.5.3. Etch Stops 81
3.6. Dry Etching 82
3.6.1. Dry Etching Based on Physical
Removal (Sputter Etching) 84
3.6.2. Dry Etching Based on Chemical
Reaction (Plasma Etching) 84
3.6.3. Reactive Ion Etching 85
3.6.4. Deep Reactive Ion Etching (DRIE) 87
3.7. Silicon Micromachining 89
3.7.1. Bulk Micromachining 91
3.7.2. Surface Micromachining 923.8. Specialized Materials for Microsystems 97
3.8.1. Polymers 97
3.8.2. Ceramic Materials 98
3.9. Advanced Microfabrication Processes 99
3.9.1. Wafer Bonding Techniques 99
3.9.2. Dissolved Wafer Process 101
3.9.3. Special Microfabrication
Techniques 102
3.10. Summary 106
c CHAPTER 4
Mechanics of Slender Solids inMicrosystems 111
4.1. The Simplest Deformable Element: A
Bar 112
4.2. Transversely Deformable Element: A
Beam 115
4.3. Energy Methods for Elastic Bodies 124
4.4. Examples and Problems 127
4.5. Heterogeneous Layered Beams 1324.6. Bimorph Effect 135
4.7. Residual Stresses and Stress Gradients 136
xviii c Contents
-
8/11/2019 Micro and Smart Systems
21/497
4.7.1. Effect of Residual Stress 137
4.7.2. Effect of the Residual Stress
Gradient 140
4.8. Poisson Effect and the Anticlastic Curvature
of Beams 141
4.9. Torsion of Beams and Shear Stresses 1444.10. Dealing with Large Displacements 151
4.11. In-Plane Stresses 153
4.12. Dynamics 159
4.12.1. A Micromachined Gyroscope:
Two-Degree-of-Freedom Dynamic
Model for a Single Mass 160
4.12.2. A Micromechanical Filter:
Two-Degree-of-Freedom Dynamic
Model with Two Masses 166
4.12.3. Dynamics of Continuous Elastic
Systems 171
4.12.4. A Note on the Lumped Modeling of
Inertia and Damping 172
4.13. Summary 173
c CHAPTER 5
The Finite Element Method 1775.1. Need for Numerical Methods for Solution of
Equations 177
5.1.1. Numerical Methods for Solution ofDifferential Equations 178
5.1.2. What is the Finite Element Method?
179
5.2. Variational Principles 182
5.2.1. Work and Complementary Work 182
5.2.2. Strain Energy and Kinetic
Energy 184
5.2.3. Weighted Residual Technique 185
5.2.4. Variational Symbol 190
5.3. Weak Form of the Governing Differential
Equation 1915.4. Finite Element Method 192
5.4.1. Shape Functions 193
5.4.2. Derivation of the Finite Element
Equation 199
5.4.3. Isoparametric Formulation and
Numerical Integration 204
5.4.4. One-Dimensional Isoparametric Rod
Element 204
5.4.5. One-Dimensional Beam Element
Formulation 2075.4.6. Two-Dimensional Plane Isoparametric
Element Formulation 209
5.4.7. Numerical Integration and Gauss
Quadrature 210
5.5. Numerical Examples 212
5.5.1. Example 1: Analysis of a Stepped Bar
(Rod) 212
5.5.2. Example 2: Analysis of a Fixed RodSubjected to Support Movement 214
5.5.3. Example 3: A Spring-Supported Beam
Structure 215
5.6. Finite Element Formulation for
Time-Dependent Problems 217
5.6.1. Mass and Damping Matrix
Formulation 218
5.6.2. Free Vibration Analysis 223
5.6.3. Free Vibration Analysis of a Fixed
Rod 225
5.6.4. Free-Vibration Analysis of Proof-
Mass Accelerometer 229
5.6.5. Forced Vibration Analysis 230
5.6.6. Normal Mode Method 231
5.7. Finite Element Model for Structures with
Piezoelectric Sensors and Actuators 233
5.8. Analysis of a Piezoelectric Bimorph
Cantilever Beam 235
5.8.1. Exact Solution 236
5.8.2. Finite Element Solution 238
5.9. Summary 239
c CHAPTER 6
Modeling of Coupled ElectromechanicalSystems 245
6.1. Electrostatics 246
6.1.1. Multiple Point Charges 247
6.1.2. Electric Potential 248
6.1.3. Electric Field and Potential Due to
Continuous Charge 252
6.1.4. Conductors and Dielectrics 2536.1.5. Gausss Law 254
6.1.6. Charge Distribution on the
Conductors Surfaces 257
6.1.7. Electrostatic Forces on the
Conductors 258
6.2. Coupled Electromechanics: Statics 259
6.2.1. An Alternative Method for Solving the
Coupled Problem 264
6.2.2. Spring-Restrained Parallel-Plate
Capacitor 2676.3. Coupled Electromechanics: Stability and
Pull-In Phenomenon 276
Contents b xix
-
8/11/2019 Micro and Smart Systems
22/497
6.3.1. Computing the Pull-In and Pull-Up
Voltages for Full Models 282
6.4. Coupled Electromechanics: Dynamics 283
6.4.1. Dynamics of the Simplest Lumped
Electromechanical Model 285
6.4.2. Estimating the Lumped Inertia of anElastic System 287
6.4.3. Estimating the Lumped Damping
Coefficient for the In-Plane
Accelerometer 290
6.5. Squeezed Film Effects in
Electromechanics 294
6.6. Electro-Thermal-Mechanics 295
6.6.1. Lumped Modeling of the Coupled
Electro-Thermal-Compliant
Actuators 297
6.6.2. General Modeling of the Coupled ETC
Actuators 304
6.7. Coupled Electromagnet-Elastic Problem 306
6.8. Summary 308
c CHAPTER 7
Electronics Circuits and Control for Microand Smart Systems 313
7.1. Semiconductor Devices 314
7.1.1. The Semiconductor Diode 3147.1.2. The Bipolar Junction Transistor 317
7.1.3. MOSFET 320
7.1.4. CMOS Circuits 323
7.2. Electronics Amplifiers 325
7.2.1. Operational Amplifiers 325
7.2.2. Basic Op-Amp Circuits 327
7.3. Signal Conditioning Circuits 330
7.3.1. Difference Amplifier 331
7.3.2. Instrumentation Amplifier as a
Differential Voltage Amplifier 332
7.3.3. Wheatstone Bridge for Measurementof Change in Resistance 334
7.3.4. Phase-Locked Loop 336
7.3.5. Analog-to-Digital Converter 337
7.4. Practical Signal conditioning Circuits for
Microsystems 341
7.4.1. Differential Charge
Measurement 341
7.4.2. Switched-Capacitor Circuits for
Capacitance Measurement 343
7.4.3. Circuits for Measuring FrequencyShift 343
7.5. Introduction to Control Theory 344
7.5.1. Simplified Mathematical
Description 344
7.5.2. Representation of Control
Systems 345
7.5.3. State-Space Modeling 346
7.5.4. Stability of Control Systems 3517.6. Implementation of Controllers 354
7.6.1. Design Methodology 354
7.6.2. Circuit Implementation 356
7.6.3. Digital Controllers 357
7.7. Summary 360
c CHAPTER 8
Integration of Micro and SmartSystems 363
8.1. Integration of Microsystems andMicroelectronics 364
8.1.1. CMOS First 364
8.1.2. MEMS First 365
8.1.3. Other Approaches of Integration 365
8.2. Microsystems Packaging 366
8.2.1. Objectives of Packaging 366
8.2.2. Special Issues in Microsystem
Packaging 367
8.2.3. Types of Microsystem Packages 369
8.2.4. Packaging Technologies 3708.2.5. Reliability and Key Failure
Mechanisms 374
8.3. Case Studies of Integrated
Microsystems 375
8.3.1. Pressure Sensor 376
8.3.2. Micromachined Accelerometer 388
8.4. Case Study of a Smart Structure in Vibration
Control 401
8.4.1. PZT Transducers 402
8.4.2. Vibrations in Beams 403
8.5. Summary 404
c CHAPTER 9
Scaling Effects in Microsystems 4099.1. Scaling in the Mechanical Domain 410
9.2. Scaling in the Electrostatic Domain 413
9.3. Scaling in the Magnetic Domain 414
9.4. Scaling in the Thermal Domain 415
9.5. Scaling in Diffusion 417
9.6. Scaling in Fluids 4189.7. Scaling Effects in the Optical Domain 420
9.8. Scaling in Biochemical Phenomena 422
xx c Contents
-
8/11/2019 Micro and Smart Systems
23/497
9.9. Scaling in Design and Simulation 423
9.10. Summary 426
c CHAPTER 10
Simulation of Microsystems Using FEA
Software 42910.1. Background 429
10.2. Force-Deflection of a Tapering Helical Spring
Using ABAQUS 430
10.3. Natural Frequencies of an Accelerometer in
ANSYS 432
10.4. Deflection of an Electro-Thermal-Compliant
(ETC) Microactuator in COMSOL
MultiPhysics 436
10.5. Lumped Stiffness Constant of a Comb-Drive
Suspension in NISA 438
10.6. Piezoelectric Bimorph Beam in a
Customized FEA Program 440
10.7. Resonant Micro-Accelerometer in
ABAQUS 442
10.8. Pull-In Voltage of an RF-MEMS Switch in
IntelliSuite 44410.9. A Capacitive Pressure Sensor in
Coventorware 447
10.10. Summary 449
Appendix 451Glossary 459Index 463About the Authors 473
Contents b xxi
-
8/11/2019 Micro and Smart Systems
24/497
-
8/11/2019 Micro and Smart Systems
25/497
cCHAPTER 1I n t r o d u c t i o n
L E A R N I N G O B J E C T I V E S
After completing this chapter, you will be able to:
c Get an overview of microsystems and smart systems.c Understand the need for miniaturization.
c Understand the role of microfabrication.
c Learn about smart materials and systems.
c Learn about typical applications of microsystems and smart systems.
M yt ho lo gy a nd f ol k t al es i n a ll c ul tu re s h av e f as ci na t in g s to ri e s i nv ol vi n g m ag i c a nd
m i n i a t u r i z a t i o n . A l i B a b a , i n a s t o r y i n1001 Arabian Nights, h a d t o s a y Open Sesame to
m ak e t he c av e d oo r o pe n b y i ts el f. W e n ow h av e a ut o ma ti c d oo rs i n s up er ma r ke ts t ha t o pe na s y o u m o v e t o w a r d t h e m w i t h o u t e v e n u t t e r i n g a w o r d . J o n a t h a n S w i f t s fi c t i t i o u s B r i t i s h
h e r o , L e m u e l G u l l i v e r , t r a v e l e d t o t h e i s l a n d o f L i l l i p u t a n d w a s a m a z e d a t t h e m i n i a t u r e
w o r l d h e s a w t h e r e . G u l l i v e r w o u l d p r o b a b l y b e e q u a l l y a m a z e d i f h e w e r e w a s h e d a s h o r e
i n t o t h e 2 1st- c en t ur y w or l d b e ca u se w e n o w h a ve f a bu l ou s m i ni a tu r e m a rv e ls u n dr e am t
o f i n S wi ft s t im e . M ag i c a nd m in ia t ur iz at io n a re r ea li t ie s t od ay . A rt hu r C . C la rk e, a
f am ou s s ci en ce fi ct i on w ri te r, o nc e s ai d t ha t a s uf fic i en tl y a dv an ce d t ec hn ol og y i s
i n di s ti n gu i sh a bl e f r om m a gi c . W h at m a ke s t h is m a gi c a r e al i ty ? T h e a n sw e r l i e s i n e x ot i c
a n d s m ar t m a te r ia l s, s e ns o rs a n d a c tu a to r s, c o nt r ol a n d m i ni a t ur i za t io n . S m ar t ne s s a n d
s m a l l n e s s g o h a n d i n h a n d . S m a r t s y s t e m s a r e i n c r e a s i n g l y b e c o m i n g s m a l l e r , l e a d i n g t o a
m a g i c a l r e a l i t y . S m a l l s y s t e m s a r e i n c r e a s i n g l y b e c o m i n g s m a r t e r b y i n t e g r a t i n g s e n s i n g ,
a c t ua t io n , c o mp u ta t io n , c o mm u ni c at i on , p o we r g e ne r at i on , c o nt r ol , a n d m o re . L i ke t h e
I n d i a n m y t h o l o g i c a l i n c a r n a t i o n V a m a n a , d e s c r i b e d a s b e i n g s m a l l a n d s m a r t , y e t a b l e t o
c ov er t he E ar th , s ky , a nd t he w or ld b en ea t h i n t hr ee f oo ts te ps , t he c om bi na t io n o f s ma ll ne ss
a nd s ma rt ne ss h as l im it le ss p os si bi l it ie s. T hi s b oo k i s a bo ut m ic ro sy st em s a nd s ma rt
s ys te ms , n ot a bo ut m ag ic . A s N ob el L au re at e p hy si c is t R ic ha rd F ey nm an n ot ed i n h is
l e c t u r e s , t h e l a w s o f s c i e n c e a s w e k n o w t h e m t o d a y d o n o t p r e c l u d e m i n i a t u r i z a t i o n , a n d
t h e r e i s s u f fi c i e n t r o o m a t t h e b o t t o m [ 1 , 2 ] . I t i s o n l y a q u e s t i o n o f d e v e l o p i n g t h e r e q u i s i t e
t e c h n o l o g i e s a n d p u t t i n g t h e m t o g e t h e r t o m a k e i t a l l h a p p e n . L e t u s b e g i n w i t h t h e n e e d
f o r m i n i a tu r i z at i o n .
1
-
8/11/2019 Micro and Smart Systems
26/497
c 1.1 WHY MINIATURIZATION?
A m i c r o s y s t e m i s a s y s t e m t h a t i n t e g r a t e s , o n a c h i p o r i n a p a c k a g e , o n e o r m o r e o f m a n y
t h in g s: s e ns o rs , a c tu a to r s, e l ec t r on i cs , c o mp u ta t io n , c o mm u ni c at i on , c o nt r ol , p o we rg e n e r a t i o n , c h e m i c a l p r o c e s s i n g , b i o l o g i c a l r e a c t i o n s , a n d m o r e . Y o u m a y fi n d i t i n t e r e s t -
i n g t h a t t h i s d e fi n i t i o n d o e s n o t e x p l i c i t l y m e n t i o n s i z e o t h e r t h a n a l l u d i n g t o a c h i p o r a
p a c k a g e d s y s t e m c o n s i s t i n g o f c h i p s a n d o t h e r a c c e s s o r i e s . M i n i a t u r i z a t i o n i s e s s e n t i a l i na c hi e vi n g t h is l e ve l o f i n te g ra t io n o f a d i sp a ra t e a r ra y o f c o mp o ne n ts .
T h e r e i s n o d o u b t t h a t t h e f u n c t i o n a l i t y o f s u c h a n i n t e g r a t e d s y s t e m w i l l n o t o n l y b e
f a r s u p e r i o r t o a n y o t h e r e n g i n e e r e d s y s t e m t h a t w e k n o w a t t h e m a c r o s c a l e b u t w i l l a l s o
a c h i e v e t h i n g s b e y o n d t h o s e a c h i e v a b l e b y m a c r o s y s t e m s . T h i n k o f a b i g s h i p , a n a i r c r a f t ,
o r a p ow er p la n t: t he y a ll s er ve o ne p ri ma r y p ur po se . B ut a c hi p t ha t i nt eg ra te s s ev er al
c o m po n e n t s, a s a l r e a dy m e n t i on e d ,can serve multiple functions. T hi s i s o ne r ea so n f or
m i ni a tu r iz a t io n . T h is d o es n o t i m p l y t h at w e c a nn o t i n te g ra t e m a ny t h in g s a t t h e m a cr o
s ca le ; i t i s a q ue st io n o f e co no my a nd t o s om e e xt en t f un ct io na li ty . M ic ro sy st em s
t e ch n ol o gy , b y f o ll o wi n g t h e l a rg e l y s u cc e ss f ul p a ra d ig m o f m i cr o el e ct r on i cs , r e ma i ns
economical due to the batch production o f m i cr o fa b ri c at i on p r oc e ss e s. Y o u c a n m a kep l e n t y o f t h i n g s o n o n e s i n g l e s i l i c o n w a f e r , a n d t h u s , t h e c o s t p e r i n d i v i d u a l t h i n g c o m e s
d o wn d r as t i ca l ly . T h is i s a n ot h er r e as o n f o r m i ni a tu r iz a t io n . N o th i ng w o ul d b e tt e r i l l us t ra t e
t hi s t ha n a dv an ce s i n c om pu te r t ec hn ol og y. C om pu ti ng s ys te ms o f t od ay a re m uc h
m o re p o we r fu l , h a ve m a ny m o re f e at u re s , a r e f a r l e ss p o we r -c o ns u mi n g a n d, o f c o ur s e,
a re s ig ni fic an tl y c he ap er t ha n t ho se a va il a bl e 2 0 o r 3 0 y ea rs a go . M in i at ur iz at i on a nd
i n te g ra t io n a p pr o ac h es h a ve p l ay e d a s i gn i fic a nt r o le i n a c hi e vi n g t h es e ( s ee F i gu r e 1 . 1) .
C om mo n o bj ec ts i n v ar io us s iz e s ca le s a re c om pa re d i n F ig ur e 1 .2 . I n a l ig ht e r v ei n, a
p o p u l a r a c r o n y m f o r t h e m i c r o s y s t e m s t e c h n o l o g y i s s p e l l e d MDM $ : i t r e a d s m i l l i o n s o f
e ur os a nd m il li on s o f d ol la rs ! T he m ar ke t s ha re o f microelectromechanical systems
( ME MS ) h as e xc ee de d t he m il li on -d ol la r m ar k s om e t im e b ac k a nd i s w el l p oi se d t o
c r o ss t h e b i l l i on - d ol l a r m a r k.E n e r g y h a s a l w a y s b e e n a p r e c i o u s c o m m o d i t y . T o d a y i t i s i n c r e a s i n g l y s o b e c a u s e o f
e v e r - i n c r e a s i n g d e m a n d c o u p l e d w i t h r a p i d l y d e p l e t i n g e n e r g y r e s o u r c e s . W i t h t h e h u m a n
p ro pe ns it y f or e le c tr on ic g ad ge ts , t he r eq ui re m en ts f or b at te ri es a re a ls o o n t he r is e,
t r i g g e r i n g r e s e a r c h e f f o r t s o n h i g h - e n e r g y m i n i a t u r e b a t t e r i e s . A n d t h e s m a l l e r t h e g a d g e t s
( a n d c o n s t i t u e n t d e v i c e s ) , t h elower theenergy requirements, t h u s a d d i n g a f u r t h e r r e a s o n
f o r m i n i at u r i z in g d e v i ce s a n d s y s te m s .
T h er e a r e, o f c o ur s e, m o re t e ch n ic a l r e as on s f o r m i ni a t ur i za t io n .Some phenomena
favor miniaturization. T a k e o p t i c s , f o r e x a m p l e . I f w e h a v e a m i c r o m e c h a n i c a l d e v i c e t h a t
Figure 1.1 M i n i a t u r i z a t i o n o f c o m p u t e r h a r d w a r e t e c h n o l o g y .
2 c 1 Introduction
-
8/11/2019 Micro and Smart Systems
27/497
c a n m o v e a m i cr o n- s iz e d c o m p on e nt a n d c o n t ro l i t s m o v e me n t t o a f r ac t io n o f a m i cr o n
( t h e r a n g e o f l i g h t w a v e l e n g t h v i s i b l e t o h u m a n s ) , t h i s o p e n s u p n u m e r o u s n e w p o s s i b i l i t -
i e s . T h e r e a r e a l r e a d y c o m m e r c i a l p r o d u c t s t h a t u s e o p t i c a l m i c r o s y s t e m s , a l s o k n o w n a s
m i c r o -o p t o- e l e c tr o m e c ha n i c al s y s t em s ( M OE M S ) .
T h in k o f t h e b i ol o gi c al c e ll s t h at a r e t h e b a si c b u il d in g b l oc k s o f l i vi n g o r g a ni s ms .T h e y a r e t h e w o r k s h o p s w h e r e a m a z i n g m a n u f a c t u r i n g , a s s e m b l i e s a n d d i s a s s e m b l i e s t a k e
p l a c e m o s t e f fi c i e n t l y . T h e s e c e l l s t o o h a v e f e a t u r e s , t h a t i s , s i z e , m o t i o n , a n d f o r c e s , t h a t
Atoms
Molecules
NanostructuresViruses
Smallestmicroelectronic
features
BacteriaBiological cellsDust particles
Diameter of human hairMicrosystem devices
Optical fibers
Packaged ICsPackaged MEMS
Lab-on-a-chip
Plain old machinesHumansAnimalsPlants
Planes, trains, automobiles
1 nm
0.1 m
10 m
1 mm
100 mm
10 nm
1 m
100 m
10 mm
1 m
10 m
Figure 1.2 I l l u s t r a t i o n o f o b j e c t s a t v a r i o u s s i z e s c a l e s .
1.1 Why Miniaturization? b 3
-
8/11/2019 Micro and Smart Systems
28/497
a re c om pa ra bl e t o t ho se o f m ic ro me ch an ic al s tr uc tu re s. S o, t he re i s a s ub fie ld w it hi n
m i c ro s ys t e ms k n ow n a s b io - m ic r o el e c t ro m ec h a ni c a l s y st e m s ( b i o- M EM S ). F u r th e r -
m o re , t h e re a r e r e a so n s f o r m i n ia t u ri z i ng c h e mi c a l p r oc e s si n g . C o nt r o ll i n g p r o ce s s c o n di -
t io ns o ve r a s ma ll v ol um e i s m uc h e as ie r t ha n o ve r a l ar ge v ol um e. H en ce , t he efficiency of a
chemical reaction is greater i n m i n i a t u r i z e d s y s t e m s . I t i s c l e a r f r o m t h i s p e r s p e c t i v e w h y
l i v in g o r g an i s ms a r e c o m pa r t me n t al i z e d i n t o m i c ro n - si z e d u n i ts t he c e l ls .M in ia tu r iz at io n c an r es ul t i n f as te r d ev i ce s w it h improved thermal management.
E n e r g y a n d m a t e r i a l s r e q u i r e m e n t d u r i n g f a b r i c a t i o n c a n b e r e d u c e d s i g n i fi c a n t l y , t h e r e b yr e s ul t i n g i n cost/performance advantages. A rr ay s o f d ev ic es a re p os si bl e w it hi n a s ma ll
s p ac e . T h is h a s t h e p o te n ti a l f o r i m pr o ve d r e du n da n cy . A n ot h er i m po r ta n t a d va n ta g e o f
m in ia tu ri z at io n i s t he p os si b il it y o f i nt eg ra ti on o f m ec ha ni ca l a nd fl ui di c p ar ts w it h
e l e c tr o n i c s, t h e r eb y s i m p li f y i n g s y s t e m s a n d r e d u c in g p o w e r r e q u i r e m e nt s . M i c r of a b ri -
c a t i o n e m p l o y e d f o r r e a l i z i n g s u c h d e v i c e s h a s improved reproducibility, a n d d e v i c e s t h u s
p r od u ce d h a ve increased selectivity and sensitivity, wider dynamic range, improved
accuracy and reliability.
I n t e g r a t e d m i c r o s y s t e m s a r e a c o l l e c t i o n o f m i c r o s e n s o r s a n d a c t u a t o r s t h a t c a n s e n s e
t he ir e nv i ro nm en t a nd r ea ct t o c ha ng es i n t ha t e nv ir on me nt b y u se o f a m ic ro ci rc ui t c on tr ol .S u c h m i c r o s y st e m s i n c l ud e , i n a d d i ti o n t o t h e c o n ve n t i o na l m i c r o el e c t r on i c s p a c k ag i n g ,
i n t e gr a t e d a n t e nn a s t r uc t u r e s f o r c o m m an d s i g n al s , a n d m i c r oe l e c t ro m e c ha n i c a l c o n fig u -
r a t i o n s f o r d e s i r e d s e n s i n g a n d a c t u a t i n g f u n c t i o n s . T h e s y s t e m m a y a l s o n e e d m i c r o p o w e r
s u pp l y, m i cr o re l ay , a n d m i cr o si g na l p r oc e ss i ng u n it s . S uc h s y st e ms w i th m i cr o co m po -
n e n t s a r e f a s t e r , m o r e r e l i a b l e , m o r e a c c u r a t e , c h e a p e r , a n d c a p a b l e o f i n c o r p o r a t i n g m o r e
c o mp l ex a n d v e rs a ti l e f u nc t i on s t h an s y st e m s u s ed t o da y .
A m i ni a tu r iz e d l o w- p ow e r t r an s ce i ve r i s a n e x ce l le n t e x am p le o f a m i cr o sy s te mt ec hn ol og y. F ig ur e 1 .3 (a ) s ho ws a s im pl ifi ed b lo ck d ia gr am o f a t ra ns ce iv er a nd a
b o a rd - l e ve l i m p le m e n ta t i o n o f t h e s a m e c o n s i s ti n g o f s e v er a l c h i ps t h a t a r e b a s ic a l l y
c o mp o ne n ts w i th h i gh q u al i ty - fa c to r s s uc h a s r a di o f r eq u en c y ( R F) fi l te r s, s ur f ac ea c ou st i c w a ve ( SA W ) i n te r me d ia t e- f re q ue n cy ( I F) fi l te r s, c r ys t al o sc i ll a to rs , a n d
t r a n s i s t o r c i r c u i t s [ 3 ] . A p o s s i b l e s i n g l e - c h i p i m p l e m e n t a t i o n o f t h i s t r a n s c e i v e r u s i n g
m i c r o s y s t e m s t e c h n o l o g y i s s h o w n i n F i g . 1 . 3 ( b ) . T h i s e n a b l e s m i n i a t u r i z a t i o n a s w e l l
a s l o w p o w er c o n su m p ti o n .
c 1.2 MICROSYSTEMS VERSUS MEMS
W e h a ve p r es e nt e d s e ve r al r e as o ns f o r m i ni a tu r iz a ti o n f r om d i ff e re n t p o in t s o f v i ew . L e t u s
n o w e x a m i ne h o w m i cr o sy s te m s t e ch n ol o gy c a me i n to e x is t en c e . I n t h e l a te 1 9 60 s a n d
e a r l y 1 9 7 0 s , n o t l o n g a f t e r t h e e m e r g e n c e o f t h e i n t e g r a t e d c h i p , r e s e a r c h e r s a n d i n v e n t o r si n a c a d e m i a a n d i n d u s t r y b e g a n t o e x p e r i m e n t w i t h m i c r o f a b r i c a t i o n p r o c e s s e s b y m a k i n g
m o v ab l e m e c h an i c a l e l e m e nt s . A c c e l er o m et e r s , m i c r om i r r o rs , g a s -c h r o ma t o g r ap h y i n s t ru -m e n t s , e t c . , w e r e m i n i a t u r i z e d d u r i n g t h i s p e r i o d . S i l i c o n w a s t h e m a t e r i a l o f c h o i c e a t t h a t
t i m e . A s e m i na l p a p e r b y P e t e r se n [ 4 ] s u m m a r i ze s t h e s e d e v e l o pm e n t s. I n c r ea s e d a t t e n t i o n
t o t h e m i cr o sy s te m s fi e ld c a me i n l a te 1 9 80 s w h en a m i cr o ma c hi n ed e l ec t ro s ta t i c m o to r
w as m ad e a t t he U ni ve rs it y o f C al if or ni a, B er ke l ey a nd M as sa ch us et ts I ns ti tu te o f
T e ch n ol o gy , C a mb r id g e. T h is m o vi n g m i cr o me c ha n ic a l e n ti t y f a sc i na t e d e v er y on e a n d
s h o w e d t h e w a y f o r w a r d f o r m a n y o t h e r d e v e l o p m e n t s . T h e a c r o n y m M E M S w a s c o i n e d
d u ri n g t h at p e ri o d. H o we v er , t h is a c ro n ym i s i n ad e qu a te t o da y b e ca u se o f t h e n u me r ou s
d is ci pl i ne s b ey on d j us t m ec ha ni ca l a nd e le ct ri c al t ha t h av e j oi ne d t he l ea gu e. A m or es u it a bl e t e r m i s mi c ro s ys t em s ; h e nc e t h e t i tl e f o r t h is b o ok .
4 c 1 Introduction
-
8/11/2019 Micro and Smart Systems
29/497
c 1.3 WHY MICROFABRICATION?
M i c r o s y s t e m s t e c h n o l o g y e m e r g e d a s a n e w d i s c i p l i n e b a s e d o n t h e a d v a n c e s i n i n t e g r a t e dc i r c ui t ( I C ) f a b r i c a ti o n p r o c es s e s, b y w h i c h s e n s o rs , a c t u at o r s a n d c o n t ro l f u n ct i o n s w e r e
c o- fa br ic at ed i n s il ic on . T he c on ce pt s a nd f ea si bi l it y o f m or e c om pl e x m ic ro sy st em sd e vi c e s h a ve b e en p r op o se d a n d d e mo n st r at e d f o r a p pl i ca t io n s i n s u ch v a ri e d fi e ld s a s
m i c r o flu i d i cs , a e r os p a c e , a u t o mo b i l e, b i o m ed i c a l , c h e m ic a l a n a l ys i s , w i r el e s s c o m m un i -
c a t io n s, d a ta s t or a ge , a n d o p ti c s.
I n m i c r o s y s t e m s , m i n i a t u r i z a t i o n i s a c h i e v e d b y a f a b r i c a t i o n a p p r o a c h s i m i l a r t o t h a t
f o l l o w e d i n I C s , c o m m o n l y k n o w n a s micromachining. A s i n I C s , m u c h o f t h e p r o c e s s i n g
i s d o ne b y c h em i ca l p r oc e ss i ng r a th e r t h an m e ch a ni c al m o di fi ca t io n s. H e nc e ,machiningh er e d oe s n ot r ef er t o c on ve nt io na l a pp ro ac he s ( su c h a s d ri l li ng , m il li ng , e tc .) u se d i n
r e al i z in g m a cr o me c h an i ca l p a rt s , a l th o ug h t h e o b je c ti v e i s t o r e al i z e s u ch p a rt s . A s w i th
s e m i c o n d u c t o r p r o c e s s i n g i n I C f a b r i c a t i o n , m i c r o m a c h i n i n g h a s b e c o m e t h e f u n d a m e n t a l
t e c hn o lo g y f o r t h e f a br i ca t io n o f m i cr o sy s te m s d e vi c es a n d, i n p a rt i cu l a r, m i ni a tu r iz e ds e ns o rs a n d a c t ua t or s . S i li c on m i cr o ma c hi n i ng , t h e m o st m a tu r e o f t h e m i cr o ma c hi n i ng
(a)
Surfaceacoustic
wave(SAW)
RF filter LNA
VCOVCO
BPF
Mixer Mixer
IF Amp.Basebandprocessing
circuits
IF filter
Off oron-boardantenna
Crystaloscillator
Off-chip
Ceramicor boardlevel MIC
(b)
RF filter LNA
Micromachinedfilters
Micromachinedfilter
Micromachined
antennas
Micromachinedresonator
VCOVCO
BPF
Mixer Mixer
IF Amp.Basebandprocessing
circuits
IF filter
Crystaloscillator
Figure 1.3 I n t e g r a t e d r a d i o f r e q u e n c y t r a n s c e i v e r s : a t y p i c a l a p p l i c a t i o n o f m i c r o s y s t e m s [ 3 ] . ( a) C u r r e n t a p p r o a c h e s
( s h a d e d r e m a r k s i n d i c a t e c o m p o n e n t s o u t s i d e t h e e l e c t r o n i c s d i e ) . (b) I n t e g r a t e d M E M S - b a s e d R F r e c e i v e r o n a s i n g l e
c h i p . L N A , l o w n o i s e a m p l i fi e r ; R F , r a d i o f r e q u e n c y ; V C O , v o l t a g e - c o n t r o l l e d o s c i l l a t o r ; I F , i n t e r m e d i a t e f r e q u e n c y ;
B P F , b a n d p a s s fi l t e r .
1.3 Why Microfabrication? b 5
-
8/11/2019 Micro and Smart Systems
30/497
t e ch n ol o gi e s, a l lo ws t h e f a br i ca t io n o f m i cr o sy s te m s t h at h a ve d i me n si o ns i n t h e s u b-
m i ll i me t e r t o m i cr o n r a ng e . I t r e fe r s t o f a sh i on i ng m i cr o sc o pi c m e ch a ni c al p a rt s o u t o f a
s il ic on s ub st ra t e o r o n a s il i co n s ub st ra te t o m ak e t hr ee -d im en si on al ( 3D ) s tr uc tu re s,
t h er e by c r ea t in g a n e w p a ra d i gm i n t h e d e si g n o f m i ni a tu r iz e d s y st e m s. B y e m pl o yi n g
m a te r ia l s s u ch a s c r ys t al l in e s i li c on , p o ly c ry s ta l li n e s i li c on , s i li c on n i tr i de , e t c. , a v a ri e ty o f
m e ch a ni c al m i cr o st r uc t ur e s i n cl u di n g b e am s , d i ap h ra g ms , g r oo v es , o r ifi c es , s p ri n gs ,g e ar s , s u sp e ns i on s , a n d a g r ea t d i ve r si t y o f o t he r c o mp l ex m e c ha n ic a l s t ru c tu r es h a ve
b e e n c o n ce i v e d , i m p l em e n t e d, a n d c o m m e rc i a l l y d e m o ns t r a te d .S il ic on m ic ro ma ch in i ng h as b ee n t he k ey f ac to r i n t he f as t p ro gr es s o f m ic ro sy st em s i n
t he l as t d ec ad e o f t he 2 0t h c en tu ry . T hi s i s t he f as hi on in g o f m ic ro sc op ic m ec ha ni c al
p ar ts o ut o f s il i co n s ub st ra te s a nd
m o re r e ce n tl y o t he r m a te r ia l s. T h is
t e ch n iq u e i s u se d t o f a br i c at e s u ch
f ea tu re s a s c la mp ed b ea ms , m em -
b ra ne s, c an ti le ve r s, g ro ov e s, o ri -
fi ce s, s pr in gs , g ea rs , c ha mb er s,
e tc ., t ha t c an t he n b e s ui t ab ly c om -b i n e d t o c r e a t e a v a r i e t y o f s e n s o r s .
Bulk micromachining, which in-
vo lve s c ar vi ng o ut t he r eq ui re d
s t ru c tu r e b y e t ch i ng o u t t h e s i li c on
s ub st ra te , i s t he c om mo nl y u se d
m et ho d. F or i ns ta nc e, a t hi n d ia -
p hr ag m o f p re ci se t hi c kn es s i n t hef e w- m ic r on r a ng e s u it a bl e f o r i n te -
g ra ti ng s en si ng e le me nt s i s v er y
o ft en r ea li z ed w it h t hi s a pp ro ac h.F i g u r e 1 . 4 s h o w s t h e s c a n n i n g e l e c -
t ro n m ic ro sc op e ( SE M) i ma ge o f a c an t il ev er b ea m o f S iO2 f a br i c at e d b y b u lk m i cr o -
m a ch i ni n g ( w et c h em i ca l e t ch i ng ) o f s i li c on . T h e d i me n si o ns o f t h is c a nt i l ev e r b e am a r e
length65mm , w i dt h15mm , a n d t h ic k ne s s 0.52mm (1mm 106 m).
Surface micromachining i s a n a lt er na te m ic ro ma ch in in g a pp ro ac h. I t i s b as ed o np a t t e r n i n g l a y e r s d e p o s i t e d o n t h e s u r f a c e o f s i l i c o n o r a n y o t h e r s u b s t r a t e . T h i s a p p r o a c h
o ff er s t he a tt ra c ti ve p os si bi l it y o f i nt eg ra ti ng t he m ic ro ma ch in ed d ev ic e w it h m ic ro -
e l ec t ro n ic s p a tt e r ne d a n d a s se m bl e d o n t h e s a m e w a fe r . I n a d di t io n , t h e t h ic k ne s s o f t h e
s t r u c t u r a l l a y e r i n t h i s c a s e i s p r e c i s e l y d e t e r m i n e d b y t h e t h i c k n e s s o f t h e d e p o s i t e d l a y e r
a n d h e nc e c a n b e c o nt r ol l ed t o s u bm i cr o n t h ic k ne s s l e ve l s.
F i g u r e 1 . 5 s h o w s a s c h e m a t i c o f a p o l y c r y s t a l l i n e s i l i c o n r e s o n a t i n g b e a m t h a t c a n b em a d e b y t h e s u r f a c e m i c r o m a c h i n i n g t e c h n i q u e . N o t e t h a t t h e r e s o n a t o r b e a m i s a n c h o r e d
a t i t s e n d s a n d t h a t a g a p o f d 0.1mm e x i s t sb e t w e e n t h e r e s o n a t o r a n d t h e r i g i d b e a m l a i d
p e rp e nd i cu l ar t o i t . A s a r e su l t, t h e r e so n at o r
v ibr at es a t t he f re que ncy of t he a c si gna l
a pp li ed t o i t w it h r es pe ct t o t he r ig id b ea m
a nd a c ur re nt fl ow s d ue t o t he c ap ac it an ce
v a r i a t i o n w i t h t i m e . T h i s c u r r e n t p e a k s w h e n
t he f re qu en c y o f t he i np ut s ig na l m at ch e s w it h
t he m ec ha ni ca l r es on an ce f re qu en cy o f t hev ib ra ti ng b ea m. T hu s t he r es on at or c an b e
u se d a s a fi lt er .
Figure 1.4 S E M i m a g e o f S i O2 microcantilever beam
p r e p a r e d b y b u l k m i c r o m a c h i n i n g ( w e t c h e m i c a l
e t c h i n g ) o f s i l i c o n .
Anchor Resonator
Rigid beamElectrodes
Figure 1.5 S c h e m a t i c o f a r e s o n a t o r b e a m [ 4 ] .
6 c 1 Introduction
-
8/11/2019 Micro and Smart Systems
31/497
U n ti l a b o ut t h e 1 9 90 s , m o st m i c ro s ys t em s d e v ic e s w i th v a r io u s s e ns i ng o r a c tu a t in g
mechanismswerefabricatedusingsiliconbulkmicromachining,surfacemicromachining,and
micromolding processes. More recently, 3D microfabrication processes incorporating other
materials(suchaspolymers)havebeenintroducedinmicrosystemstomeetspecificapplication
requirements (e.g. biomedical devices and microfluidics).
I t i s i n t e r e s t i n g t o n o t e t h a t a l m o s t a l l t h e m i c r o s y s t e m s d e v i c e s e m p l o y o n e o r m o r eo f t h e t h re e b a si c s t ru c tu r es n a m el y , a d i ap h ra g m, a m i cr o br i dg e , o r a b e am th a t a r e
r ea li z ed u si ng m ic ro ma ch in in g o f s il ic on i n m os t c as es a nd o th er m at er i al s i nc lu di ngp ol ym e rs , m et al s, a nd c er am ic s. T he se t hr ee s tr uc tu re s p ro vi d e f ea si bl e d es ig ns f or
m ic ro se ns or s a nd a ct ua to rs t ha t e ve nt u al ly p er fo rm t he d es ir ed t as k i n m an y s ma rt
s t ru c tu r es . T h e m a in i s su e s w i th r e sp e ct t o i m pl e me n ti n g t h es e s t ru c tu r es a r e t h e c h oi c e
o f m a te r ia l s a n d t h e m i cr o ma c hi n in g t e ch n ol o gi e s u s ed t o f a br i c at e t h es e d e vi c e s.
c 1.4 SMART MATERIALS, STRUCTURES AND SYSTEMS
T he a re a o f s ma r t m at er ia l s ys te ms h as e vo lv ed f ro m t he u ne nd in g q ue st o f m an ki nd t o
m im ic s ys te ms o f n at ur al o ri gi n. T he o bj e ct iv e o f s uc h i ni ti at iv es i s t o d ev el o p t ec hn ol og ie s
t o p r o du c e n o n bi o l og i c a l s y s t e m s t h a t a c h ie v e
o p ti m um f u nc t io na l it y a s o b se r ve d i n n at u ra l
b i ol og i ca l s y st e ms a n d e mu l at e t h ei r a d ap t iv e
c a p a bi l i ti e s b y a n i n t e gr a t ed d e si g n a p pr o a ch .I n t h e p r e s en t c o nt e xt , a s ma r t m a te ri a l i s o n e
w h o se e l e ct r i ca l , m e c ha n ic a l , o r a c o us t i c p r o -
p e r t ie s o r w h os e s t r uc t u re , c o m po s it i o n, o r f u n c-
t i on s c h an g e i n a s p ec i fie d m a nn e r i n r es p on se t o
s o m e s t i m u l u s f r o m t h e e n v i r o n m e n t . I n a s i m i -
l a r w a y , o n e m a y e n v i s a g e s m a r t s t r u c t u r e s t h a tr e qu ir e t he a d di ti o n o f p r op e rl y d e si g ne d s e n-
s o r s, a c t ua t or s , a n d c o n tr o ll e r s t o a n o t h er w i se d um b s t r uc t u re ( s e e s c he m a ti c i n F i g ur e 1 . 6 ).
A s s m ar t m a te r ia l s s y st e ms s h ou l d m i mi c
n at ur al ly o cc ur ri n g s ys te ms , t he g en er a l r e-
q u i r e me n t s e x p e c te d f r o m t h e s e n o n bi o l o g ic a l
s y s t em s i n c l ud e :
1. F u l l i n te g ra t io n o f a l l f u nc t io n s o f t h e s y st e m.
2. C o n t i nu o u s h e a l t h a n d i n t e gr i t y m o n it o r i ng .3. D a m a g e d e t e ct i o n a n d s e l f -r e c o v er y .
4. I n t e l l i g e nt o p e r at i o n a l m a n a ge m e n t .
5. H i g h d e g re e s o f s e c u ri t y , r e l i ab i l i t y , e f fi c i e n c y a n d s u s t ai n a b il i t y .
A s o ne c an n ot e, t he m at er i al s i nv ol ve d i n i mp le me nt in g t hi s t ec hn ol o gy a re n ot
n e c e s s a r i l y n o v e l . Y e t t h e t e c h n o l o g y h a s b e e n a c c e l e r a t i n g a t a t r e m e n d o u s p a c e i n r e c e n t
y e ar s a n d h a s i n de e d b e en i n sp i re d b y s e ve r al i n no v at i ve c o nc e pt s .
A s m en ti on ed e ar li er , t he s tr uc tu ra l , p hy si ca l, o r f un ct io na l p ro pe rt ie s o f s ma rt
m at er ia ls r es po nd t o s om e s ti mu lu s f ro m t he e nv ir on m en t a nd t hi s r es po ns e s ho ul d b e
r ep et it iv e i n t he s en se t ha t t he s am e c ha ng e i n t he e nv i ro nm en t m us t p ro du ce t he s am er e s p o n s e . W e k n o w t h a t e v e n w i t h o u t d e s i g n , m o s t m a t e r i a l s d o r e s p o n d t o t h e i r e n v i r o n -
m en t. F or e xa mp le , n ot e t he c ha ng e i n d im en si on s o f m os t m at er ia l s w he n h ea te d o r
Structure
Sensor Actuator
Controlunit
Figure 1.6 B u i l d i n g b l o c k s o f a t y p i c a l
s m a r t s y s t e m .
1.4 Smart Materials, Structures and Systems b 7
-
8/11/2019 Micro and Smart Systems
32/497
c o o l e d . H o w e v e r , w h a t d i s t i n g u i s h e s a s m a r t m a t e r i a l f r o m t h e r e s t i s t h a t w e design the
m a t e r i a l s o t h a t s u c h c h a n g e s o c c u r i n a s p e c i fi c m a n n e r f o r s o m e d e fi n e d o b j e c t i v e t o b e
a cc om pl is he d. H en ce , t he m ai n f ea tu re t ha t d is ti ng ui sh es s ma rt m at er ia l s i s t ha t t he y
respondsignificantly t o s o me e x te r na l s t im u li t o w hi c h m o st m a te r ia l s a r e u n re s po n si v e.
F u r t h e r m o r e , o n e w o u l d l i k e t o e n h a n c e s u c h a r e s p o n s e b y a t l e a s t o n e o r t w o o r d e r s o f
m a g ni t u d e o v e r o t h e r m a t e r i a l s.B ot h a ct i ve a n d p a ss iv e a p pr oa c he s h a ve b e en a t te mp t ed i n t hi s c o nt e xt . T h is d i st i nc t io n
i s b a se d o n t he r e qu ir e me n t t o g e ne ra t e p o we r r e qu ir e d t o p e rf o rm r e sp on s es . H en c e, a na ct i ve s ys t em h as a n i n bu i lt p o we r s o ur c e. T y pi ca l ly , a c ti v e s e ns or s a n d a ct u at or s h a ve b e en
f av o re d i n d e si gn i ng s ma r t s tr u ct u re s. H ow ev e r, i n r e ce nt y e ar s t h e c on c ep t o f p a ss iv e
s m a r t n e s s h a s c o m e t o t h e f o r e . P a s s i v e s m a r t n e s s c a n b e p e r v a s i v e a n d e v e n c o n t i n u o u s i n
t he s t ru c tu r e. S uc h s t ru c tu re s d o n o t n e ed e x te r na l i n te r ve nt i on f or t h ei r o p er a ti on . I n
a d d i t i o n , t h e r e i s n o r e q u i r e m e n t f o r a p o w e r s o u r c e . T h i s i s p a r t i c u l a r l y r e l e v a n t i n l a r g e -
s ca l e c i vi l e n gi ne e ri n g s tr uc t ur es . P a ss i ve s ma r tn e ss c a n b e d e ri ve d f ro m t h e u n iq u e i n tr in si c
p r o p e r t i e s o f t h e m a t e r i a l u s e d t o b u i l d s u c h s t r u c t u r e s . O n e c o m m o n e x a m p l e i s t h e s h a p e -
m e m o r y - a l l o y ( S M A ) m a t e r i a l e m b e d d e d i n a e r o s p a c e c o m p o s i t e s , d e s i g n e d s o t h a t c r a c k s
d o n o t p r op a ga t e. S u ch s m ar t m at e ri a ls a r e d i sc us se d b ri e fly i n C ha p te r 2 .B e si d e s sm a rt s y st e m o r sm a rt m a te r ia l , a n ot h er w i de l y u s ed t e rm i s smart
structure. O n e d i s t i nc t iv e f e at u re o f s m ar t s t ru c tu r es i s t h at a c tu a to r s a n d s e ns o rs c a n b e
e m be d de d a t d i sc r et e l o ca t io n s i n si d e t h e s t ru c tu r e w i th o ut a f fe c ti n g t h e s t ru c tu r al i n te g ri t y
o f t he m ai n s tr uc tu re . A n e xa mp le i s t he e mb ed de d s ma rt s tr uc tu re i n a l am in at ed
c o mp o si t e s t ru c tu r e. F u rt h er m or e , i n m a ny a p pl i ca t io n s, t h e b e ha v io r o f t h e e n ti r e s t ru c tu r e
i ts el f i s c ou pl ed w it h t he s ur ro un di ng m ed iu m. T he se f ac to rs n ec es si ta te a c ou pl e d
m o de l in g a p pr o ac h i n a n al y zi n g s uc h s m ar t s t ru c tu r es . T h e f u nc t i on a n d d e sc r ip t io n o f v ar io us c om po ne nt s o f t he s ma rt s ys te m i n T ab l e 1 .1 a re s um ma ri ze d i n T ab le 1 .1 [ 5] .
C i vi l e n gi n ee ri n g s y st e ms s uc h a s b u il di n g f ra m es , t ru s se s , o r b ri d ge s c o mp r is e a
c om p le x n e tw or k o f t r us s, b e am , c o lu m n, p la t e, a n d s h el l e l em en t s. M o ni t or i ng t he s tr u ct u ra lh ea lt h o f b ri dg e s tr uc tu re s f or d if fe re nt m ov in g l oa ds i s a n a re a o f g re at i mp or ta nc e i n
i nc r ea s in g t h e s t ru ct u ra l i nt e gr i ty o f i n fr a st ru c tu re s a n d h as b e en p u rs ue d i n m an y c o un tr i es .
D a m p i n g o f e a r t h q u a k e m o t i o n s i n s t r u c t u r e s i s y e t a n o t h e r a r e a t h a t h a s b e e n t a k e n u p f o r
a ct i ve r e se a rc h i n m an y s ei s mi c al l y a c ti ve c o un tr i es . S ma r t d ev i ce s d e ri v ed f ro m s ma rt
m at e ri a ls a r e e x te n si ve l y u s ed f o r s uc h a p pl i ca t io n s. A b r id g e w ho s e s t ru c tu ra l h e al t h c a n b em on i to r ed i s s h ow n i n F i gu r e 1 . 7. I n s u ch a b ri d ge , fi b er o pt i c s en s or s a r e u s ed a s s e ns in g
d ev i ce s, w he re a s l e ad z i rc o na t e t i ta n at e ( P ZT ) o r T e rf e no l- D a c tu at o rs a r e n o rm al l y u s ed f or
p e rf o r mi n g a c t ua t i on s s u ch a s v i b ra t i on i s o la t i on a n d c o n tr o l.
Table 1.1 Purpose of various components of a smart system
Unit
Equivalent in
Biological Systems Purpose Description
Sensor Tactile sen sing Data acquisition Collect required raw data needed for appropriate
s e n s i n g a n d m o n i t o r i n g
Data bus 1 Sensory nerves Data tran smission Forward raw data to local and/or central command
a n d c o n t r o l u n i t s
Control system Brain Command and
c o n t r o l u n i t
M a n a g e a n d c o n t r o l t h e w h o l e s y s t e m b y a n a l y z i n g
d a t a , r e a c h i n g t h e a p p r o p r i a t e c o n c l u s i o n s , a n d
d e t e r m i n i n g t h e a c t i o n s r e q u i r e d
Data bus 2 Moto r n erves Data instruction s Transmit decisions and asso ciated instructions tom e m b e r s o f s t r u c t u r e
Actuator Muscles Action d ev ices Take action by triggering controlling devices/u nits
8 c 1 Introduction
-
8/11/2019 Micro and Smart Systems
33/497
T h e b e n e fi c i a r i e s a n d s u p p o r t e r s o f t h e s m a r t s y s t e m s t e c h n o l o g y h a v e b e e n m i l i t a r y
a n d a e ro s pa c e i n du s tr i e s. S o me o f t h e p r oo f -o f -c o nc e pt p r og r am s h a ve a d dr e ss e d s t ru c -
t u ra l h e al t h m o ni t or i ng , v i br a ti o n s u pp r es s io n , s h ap e c o nt r ol , a n d m u lt i fu n ct i on a l s t ru c -
t u ra l c o nc e pt s f o r s p ac e cr a ft s , l a un c h v e hi c le s , a i rc r af t s a n d r o to r cr a ft s . T h e s t ru c tu r es b u il t
s o f a r h a v e f o c u se d o n d e m o ns t r a ti n g p o t e nt i a l s y s te m - l e ve l p e r f or m a n c e i m p r o v e m en t s
u s in g s m ar t t e ch n ol o gi e s i n r e al i st i c a e ro s pa c e s y st e ms . C i vi l e n gi n ee r in g s t ru c tu r es
i nc lu di n g b ri dg es , r un wa ys a nd b ui l di ng s t ha t i nc or po ra te t hi s t ec hn ol og y h av e a ls ob e en d e mo n st r at e d. S m ar t s y st e m d e si g n e n vi s ag e s t h e i n te g ra t io n o f t h e c o nv e nt i on a l
fi e l d s o f m e c h an i c a l e n g i n ee r i n g, e l e c t ri c a l e n g i n ee r i n g, a n d c o m pu t e r s c i e nc e / i n fo r m a -
t i on t ec hn ol o gy a t t he d es ig n s ta ge o f a p ro du ct o r a s ys te m.
A s d i s c u s s e d e a r l i e r , s m a r t s y s t e m s s h o u l d r e s p o n d t o i n t e r n a l ( i n t r i n s i c ) a n d e n v i r o n -
m e nt a l ( e xt r i ns i c) s t im u li . T o t h i s e n d , t h ey s h o u ld h a v e s e ns o rs a n d a c tu a to r s e m be d de d i n
t h em . S o me o f t h es e d e vi c es c o mm o nl y e n co u nt e re d i n t h e c o nt e xt o f s m ar t s ys t em s a r e
l i st e d i n T ab le 1 .2 .
c 1.5 INTEGRATED MICROSYSTEMS
I n te g ra t ed m i cr o sy s te m s c a n b e c l as si fi ed i n to t h re e m a jo r g r ou p s a s f o ll o ws :
1. Micromechanical structures: T h e s e a r e n o n - m o v i n g s t r u c t u r e s , s u c h a s m i c r o b e -
a m s a n d m i c r oc h a n ne l s .
Figure 1.7 T h e h i s t o r i c G o l d e n B r i d g e b u i l t i n 1 8 8 1 t o c o n n e c t A n k l e s h w a r a n d B h a r u c h i n G u j a r a t ,
I n d i a . T h e i n s e t s h o w s t h e d e t a i l s o f o n e - t i m e s t r u c t u r a l h e a l t h m o n i t o r i n g o f a s e c t i o n o f t h e b r i d g e .
I t h a d 6 6 fi b e r o p t i c s t r a i n g a u g e s a n d m i c r o m a c h i n e d a c c e l e r o m e t e r s . C o u r t e s y : I n s t r u m e n t a t i o n
Scientific Technologies Pvt. Ltd., Bangalore, www.inscitechnologies.com.
Table 1.2 Some sensors and actuators used in smart systems
Device Physical Quantity Example Successful Technologies
Sensor Acceleration Accelerometer PZT , Microfabrication
Angular rate Gyroscope Fiber o ptic, Micro fabricatio n
Position Linear variab le d ifferential
transformer (LVDT)
Electromagnetic
Tran sd ucer Crack detection Ultrasonic transducer PZT
Actuator Movement Thermal Shape memory alloy
1.5 Integrated Microsystems b 9
http://www.inscitechnologies.com/http://www.inscitechnologies.com/http://www.inscitechnologies.com/ -
8/11/2019 Micro and Smart Systems
34/497
2. Microsensors: T h e s e r e s p o n d t o p h y s i c a l a n d c h e m i c a l s i g n a l s ( s u c h a s p r e s s u r e ,
a c ce l er a ti o n, p H, g l uc o se l e ve l , e t c. ) a n d c o nv e rt t h em t o e l ec t ri c al s i gn a ls .
3. Microactuators: T h e se c o nv e rt e l ec t ri c al o r m a gn e ti c i n pu t t o m e ch a ni c a l f o rm so f e n er g y ( e .g . r e so n at i ng b e am s , s wi t c he s , a n d m i cr o pu m ps ) .
Microsystems i n te g ra t e s e ns o rs , a c tu a t or s a n d e l ec t ro n ic s t o p r ov i de s o me u s ef u l
f un ct io n. T he A DX L5 0, w hi ch w as r el ea se d i n 1 99 1 a nd w as A na lo g D ev ic es fi rs t
c o m m e r c i a l d e v i c e , i s a n e x c e l l e n t e x a m p l e o f s u c h a m i c r o s y s t e m . T h e b l o c k d i a g r a m o f
t hi s s ys te m i s s ho wn i n F ig ur e 1 .8 [ 6] . T hi s m ic ro sy st em i s b as ed o n a s ur fa ce m ic ro -
m ac hi ni ng t ec hn ol og y w it h s en si ng e le ct ro ni cs i nt eg ra te d o n t he s am e c hi p a s t he
a cc el e ro me te r. H er e, t he a cc el er om et e r i s a s en so r t ha t r es po nd s t o t he a cc el er at io n o r
d e ce l er a ti o n a n d g i ve s a n o u tp u t v o lt a ge t o t h e c o nt r ol c i rc u it , w h ic h i n t u rn t r ig g er s a n
a c t u a t o r t o d e p l o y t h e a i r b a g d u r i n g a c r a s h , s o t h a t t h e p e r s o n s s e a t e d i n t h e f r o n t s e a t a r ep r ot e ct e d f r om c r as h in g i n to t h e f r on t w i nd s hi e l d o r t h e d a sh b oa r d.
1.5.1 Micromechanical Structures
M ic ro ma c hi ni ng i s u se d c om me r ci al ly t o p ro du ce c ha nn el s f or m ic ro flu id ic d ev ic es
a nd a ls o t o f ab ri ca te s ys te ms r ef er re d t o a s l ab s o n a c hi p f or c he mi al a na ly si s a nd
a n a l y s i s o f b i o m e d i c a l m a t e r i a l s [ 7 ] . U s u a l l y s u c h c h a n n e l s a r e m a d e o n p l a s t i c s o r g l a s s
s ub st ra t es . F ig ur e 1 .9 ( a) s ho ws o ne s uc h d ev ic e r ep or te d i n t he l it er at ur e [ 8] . M ic ro -
m a ch i ni n g i s a l so u s ed t o m a ke a v a ri e t y o f m e ch a ni c al s t ru c tu r es . F i gu r e 1 . 9 ( b ) s h o ws a n
S E M i m a g e o f a s i li c on n a no t i p f a br i ca t e d [ 9 ] u s in g a bu l k m i cr o ma c hi n in g p r oc e ss .
S u c h m i c r o t i p s fi n d a p p l i c a t i o n s i n a t o m i c f o r c e m i c r o s c o p y ( A F M ) t e c h n o l o g y a n d fi e l de m is s io n a r ra y f o r f u tu r is t i c v a cu u m e l ec t r on d e vi c es c a pa b l e o f o p er a t io n i n t e ra h er t z
f r e qu e n c y r a n g e [ 1 0 ] .
Outputvoltage
PreampBufferDemodulatorand low-pass
filter
Square waveoscillator
Feedback voltage
Anchor
Polysilicon proofmass and moving
electrodes
Fixed polysiliconcapacitor plates
Suspensionsystem
Figure 1.8 A s c h e m a t i c d i a g r a m o f A D X L 5 0 a c c e l e r o m e t e r .
10 c 1 Introduction
-
8/11/2019 Micro and Smart Systems
35/497
1.5.2 MicrosensorsS e v e r a l m i c r o m a c h i n e d s e n s o r s h a v e e v o l v e d o v e r t h e l a s t t w o d e c a d e s . A m o n g t h e m t h e
p r e s s u r e s e n s o r s o c c u p y a l m o s t 6 0 % o f t h e m a r k e t . A s c h e m a t i c i s o m e t r i c c u t - a w a y v i e w
o f a p i ez o re s is t iv e p r e s su r e s e n so r d i e i s s h o w n i n F i g. 1 . 10 ( a ). H e re , w e c a n s e e t h e f o ur
Figure 1.9 Miniature mechanicals t r u c t u r e s s h o w i n g ( a ) p o l y m e r
m e s o p u m p ; ( b ) s i l i c o n n a n o t i p
f a b r i c a t e d u s i n g b u l k
micromachining.(a) (b)
Figure 1.10 Schematic diagrams
o f m i c r o s e n s o r s : ( a ) c u t - a w a y
v i e w o f a p i e z o r e s i s t i v e p r e s s u r es e n s o r; ( b ) c a p a c it i v e -s e n s in g
accelerometer.
(a)
Piezoresistor
Pad
Diaphragm
Pressure port
Glass
Glass
(b)
Fixed electrode
Fixed electrode
Seismic massSi
1.5 Integrated Microsystems b 11
-
8/11/2019 Micro and Smart Systems
36/497
p r es su r e- s en s it i ve r e si s to r s ( p ie z or e si s to r s) i n te g ra t e d o n a m i cr o ma c hi n ed s i li c on d i a-
p h ra g m. M i cr o ma c h in e d a c ce l er o me t er i s y e t a n ot h er d e vi c e w hi c h h a s r e ce i v ed c o ns i d-
e r a b le a t t e nt i o n f r o m t h e a e r o s p a c e, a u t o mo b i l e , a n d b i o m ed i c a l i n d u s t r ie s . F i g u r e 1 . 1 0 ( b )
s h o w s a s c h e m a t i c c r o s s - s e c t i o n a l v i e w o f o n e s u c h d e v i c e . T h e s e i s m i c m a s s r e s p o n d s t o
a cc el e ra ti on a nd d efl ec t s, t hu s b ri ng in g a bo ut a c ha ng e i n t he c ap ac i ta nc e b et we en t he m as s
a nd t he fi xe d e le ct r od es . T he c ha ng e i n c ap ac i ta nc e i s a m ea su re o f t he d is pl ac em en t,w hi c h i n t u rn d e pe n ds u p on t h e a c ce l e ra t io n .
1.5.3 Microactuators
O v e r t h e l a s t f e w y e a r s , m i c r o m a c h i n e d a c t