Table Of ContentMICROTECHNOLOGY AND MEMS
The photo shows a scanning electron micrograph of a shape memory microactuator. The
microactuator has been developed by Dr. Klaus Skrobanek and the author for control of the
defiection of a membrane. It consists of eight double beams, whose lateral shape has been
designed for optimum use of the shape memory effect upon bending actuation. Fabrication
has been done by laser cutting of a cold-rolled thin plate ofNiTi.
M. Kohl
Shape Memory
Microactuators
With 149 Figures
~ Springer
PD Dr. rer. nato habil. Manfred Kohl
Forschungszentrum Karlsruhe
Institut für Mikrostrukturtechnik
Postfach 3640
76021 Karlsruhe, Germany
E-mail: [email protected]
Se ries Editors:
Professor Dr. H. Baltes
ETH Zürich, Physical Electronics Laboratory
ETH Hoenggerberg, HPT-H6, 8093 Zürich, Switzerland
Professor Dr. Hiroyuki Fujita
University of Tokyo, Institute of Industrial Science
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
Professor Dr. Dorian Liepmann
University of California, Department of Bioengineering
466 Evans Hall, #1762, Berkeley, CA 94720-1762, USA
ISSN 1439-6599
ISBN 978-3-642-05837-0 ISBN 978-3-662-09875-2 (eBook)
DOI 10.1007/978-3-662-09875-2
Library of Congress Control Number: 2004'023'5
This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned,
specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction
on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof
is permitted only under the provisions of the German Copyright Law of September 9, '965, in its current
version, and permission for use must always be obtained from Springer-Verlag Berlin Heidelberg GmbH.
Violations are liable for prosecution under the German Copyright Law.
springeronline.com
© Springer-Verlag Berlin Heidelberg 2004
Originally published by Springer-Verlag Beflin Heidelbefg New York in 2004
Softcover reprint of the hardcover I st edition 2004
The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply,
even in the absence of a specific statement, that such names are exempt from the relevant protective laws and
regulations and therefore free for general use.
Typesetting by the author
Cover concept: eStudio Calamar Steinen
Cover production: design & production GmbH, Heidelberg
Printed on acid-free paper 10884414 57/3141/ba -5 4 3210
Contents
Preface ................................................................................................................. IX
Glossary of Notations ......................................................................................... XI
1 Introduction and Overview .............................................................................. l
2 Microactuators .................................................................................................. 5
2.1 Actuation Principles ................................................................................... 6
2.1.1 Electrostatic Principles .................................................................... 9
2.1.2 Magnetic Principles ......................................................................... 9
2.1.3 Fluidic Principles .......................................................................... 10
2.1.4 Inverse Piezoeffect.. ...................................................................... 11
2.1.5 Other Principles ............................................................................ 11
2.2 Microvalves ............................................................................................. 12
2.2.1 Electromagnetic Microvalves ........................................................ 12
2.2.2 Piezoelectric Microvalves ............................................................. 14
2.2.3 Electrostatic Microvalves .............................................................. 14
2.2.4 Thermopneumatic Microvalves .................................................... 14
2.2.5 Bimetal Microvalves ..................................................................... 16
2.3 Linear Actuators ...................................................................................... 17
2.3.1 Magnetic Linear Actuators ............................................................ 18
2.3.2 Electrostatic Linear Actuators ....................................................... 20
2.3.3 Piezoelectric Linear Actuators ...................................................... 22
2.4 Development Potential of SMA Microactuators ...................................... 23
3 Shape Memory Effects ................................................................................... 25
3.1 Overview .................................................................................................. 25
3.1.1 One-Way Effect ............................................................................ 27
3.1.2 Two-Way Effect. ........................................................................... 28
3.1.3 Pseudoelasticity ............................................................................. 28
3.2 Crystallographic Aspects of Martensitic Transformations ....................... 29
3.2.1 Microseopie Structural Changes ................................................... 29
3.2.2 Structural Changes in the Presence of Stress ................................ 32
3.2.3 Shape Memory .............................................................................. 34
3.2.4 Preconditions of Shape Memory ................................................... 34
3.2.5 Phenomenological Theory of Martensitic Transformations .......... 35
VI Contents
3.3 Thermodynamic Aspects of Martensitic Transformations ....................... 36
3.3.1 Gibbs Potentials ............................................................................ 36
3.3.2 Modeling ....................................................................................... 37
3.4 NiTi-Based Alloys ................................................................................... 45
3.4.1 Metallurgy ..................................................................................... 45
3.4.2 Phase Transformations .................................................................. 46
3.4.3 Mechanical Behavior .................................................................... 48
3.4.4 Temary Alloys On the Basis ofNiTi ............................................. 53
3.4.5 Thin Films ..................................................................................... 56
3.5 Development Trends ................................................................................ 59
4 Shape Memory Actuation .............................................................................. 62
4.1 Overview ................................................................................................. 62
4.2 Simulation ................................................................................................ 65
4.2.1 Three-Dimensional Mechanical Model for SMA Actuators ......... 66
4.2.2 FEM Formulation of Mechanical Model for SMA Actuators ....... 68
4.2.3 Simulation of Electrical Performance ........................................... 71
4.2.4 Simulation of Thermal Performance ............................................. 72
4.2.5 Coupled Multilevel Simulation ..................................................... 73
4.3 Design Optimization ................................................................................ 74
4.3.1 Mechanical Design Optimization .................................................. 76
4.3.2 Thermal Design Optimization ....................................................... 79
4.4 Conventional SMA Actuators .................................................................. 79
4.4.1 Overview ....................................................................................... 79
4.4.2 Design ........................................................................................... 82
4.4.3 Fabrication Technologies .............................................................. 83
4.5 SMA Microactuators ............................................................................... 84
4.5.1 Monolithic Integration of SMA Microactuators ........................... 85
4.5.2 Hybrid Integration of SMA Microactuators .................................. 92
4.6 Development Trends ................................................................................ 93
5 SMA Microvalves ........................................................................................... 96
5.1 Valve Concepts ........................................................................................ 96
5.1.1 Setup and Operation Principle ...................................................... 96
5.1.2 Design ........................................................................................... 98
5.1.3 Overview ..................................................................................... l0l
5.2 Material Properties ................................................................................. 101
5.2.1 Rolled SMA Thin Plates and Foils ............................................. 102
5.2.2 Sputtered SMA Thin Films ......................................................... 103
5.3 Normally Open SMA Microvalves ........................................................ l05
5.3.1 Valve Designs ............................................................................. 105
5.3.2 Valve Fabrication ........................................................................ 114
5.3.3 Performance Characteristics ....................................................... 122
5.3.4 Conclusions ................................................................................. 142
5.4 Normally Closed SMA Microvalves ..................................................... 146
5.4.1 Valve Design ............................................................................... 146
Contents VII
5.4.2 Valve Fabrication ........................................................................ 150
5.4.3 Stationary Valve Performance .................................................... 151
5.4.4 Dynamic Valve Performance ...................................................... 154
5.4.5 Conclusions ................................................................................. 158
5.5 Outlook .................................................................................................. 159
6 SMA Linear Actuators ................................................................................. 16l
6.1 Actuation Concepts ................................................................................ 161
6.1.1 Setup and Functionality .............................................................. 161
6.1.2 Design ......................................................................................... 163
6.1.3 Overview ..................................................................................... 166
6.2 Material Properties ................................................................................. 166
6.2.1 NiTiCu Thin Plates with One-Way Effect.. ................................ 166
6.3 SMA Linear Actuators with Passive Biasing Spring ............................. 167
6.3.1 Design and Fabrication ............................................................... 167
6.3.2 Performance Characteristics ........................................................ 171
6.3.3 Conclusions ................................................................................. 178
6.4 SMA Linear Actuators with Antagonism .............................................. 180
6.4.1 Design and Fabrication ............................................................... 180
6.4.2 Performance Characteristics ........................................................ 182
6.4.3 Conclusions ................................................................................. 188
6.5 Optical Microswitch .............................................................................. 189
6.5.1 Optical Microswitch with Movable Functional Element ............ 190
6.5.2 Optical Microswitch with Movable Optical Fiber ...................... 193
6.5.3 Conclusions ................................................................................. 198
6.6 Microgripper .......................................................................................... 199
6.6.1 Requirements of a Mechanical SMA Microgripper .................... 200
6.6.2 Design ......................................................................................... 202
6.6.3 Fabrication .................................................................................. 206
6.6.4 Performance Characteristics ........................................................ 207
6.6.5 Positioning .................................................................................. 212
6.6.6 Conclusions ................................................................................. 216
6.7 Outlook .................................................................................................. 217
7 Summary ....................................................................................................... 219
References .......................................................................................................... 223
Subject Index ..................................................................................................... 243
Preface
Shape memory alloys exhibit the fascinating property of shape recovery, which al
lows them to generate large work outputs particularly in small dimensions. Their
large potential for applications as "smart materials" is due to a number of addi
tional unique features like direct electrical control by small voltages, multifunc
tional performance, and biocompatibility. Upon miniaturization, intrinsic disad
vantages such as long time constants loose significance. Thus, shape memory
alloys are virtually predestined for applications in rnicrosystems technology,
which is presently rapidly evolving.
This book combines fundamental aspects of materials science and microme
chanics with selected design examples of demonstrators needed for a rnicrosys
tems engineer to develop shape memory rnicroactuators. While the fundamentals
are written in a textbook manner, the development of the demonstrators is de
scribed from the idea to the prototype in comprehensive breadth. For evaluation of
achieved specifications, the book also contains a review of comparable microac
tuator developments based on alternative actuation principles.
The purpose of this book is to disseminate recent progress and underlying fun
damentals of shape memory microactuators and to provide practicable approaches
for future developments of processes and products. The main intended audience
are engineers and engineering students from the materials, microsystems, and ap
plications communities. The reader not familiar with shape memory alloys will
find aB the information required for getting started. I hope that this book will help
to increase the awareness for this new field. Any comments or suggestions regard
ing this work are welcome.
The book originated from several research projects at Forschungszentrum
Karlsruhe and a lecture on rnicroactuators at the University of Karlsruhe. By and
by, a specific approach to designing, modeling and fabricating shape memory mi
croactuators has been developed based on monolithic components of micro
machined foils or thin films of shape memory alloys. Using this approach, several
prototypes of microvalves, linear actuators, and microgrippers have been devel
oped that serve as demonstrators in this book.
Various functional units may be realized in a monolithic shape memory com
ponent, which enables cost-effective fabrication by a single process step. The va
riety of structures and functions requires, however, a procedure to design opti
mized lateral shapes, which enable an optimum use of the shape memory effect.
For this purpose, mechanical and thermal optimization criteria are introduced and
their implementation is shown for the demonstrators.
Modeling realistic components requires either an approximate analytical or a
sufficiently meshed numerical representation of the governing equations. The use
of analytic models provides invaluable design insights. When dealing with an en-
X Preface
tire microactuator, the use of a macromodel capturing the essential physical be
havior appears most appropriate. In this book, analytic and numeric macromodels
are presented for design simulation and verification. As the electrical, thermal, and
mechanical properties of shape memory microactuators depend strongly on each
other, a finite element routine for coupled multilevel simulation is introduced to
achieve a quantitative description.
Shape memory microactuators may be fabricated by monolithic integration fol
lowing e.g. the procedure of surface micromachining in silicon technology or by
hybrid integration of shape memory microstructures fabricated separately from the
final microsystem. The book covers selected examples of both approaches. The
latter approach allows integration of shape memory microactuators in polymer
based microsystems, which are a main focus at Forschungszentrum Karlsruhe.
Hybrid integration also offers a larger flexibility with respect to the choice of
processes such as micromachining, heat treatment, etc. and related parameters.
Consequently, the demonstrators in this book have been fabricated by hybrid inte
gration.
I am indebted to Prof. V. Saile, Prof. H. Janocha, and Prof. K.H. Zum Gabr for
critically reading the manuscript, which was first written and published in German
as a professorial dissertation. Parts of the English translations have been done by
Mrs. Schröder from the translation bureau of Forschungszentrum Karlsruhe. The
presented developments of shape memory microactuators at Forschungszentrum
Karlsruhe rely on the support and input of many individuals. Special thanks go to
my colleague Dr. Berthold Krevet, an expert in finite element modeling, with
whom I spent many hours discussing various issues of engineering, physics, and
more. Berthold contributed significantly to the implementation of numeric mac
romodels for the demonstrators presented in this book and provided many helpful
comments. I would like to thank my colleague Siegfried Dürr for his competent
technical support. His input in solving technological problems of assembly and in
terconnection has been of immense help. I also thank my past and present students
for their contributions. Their excitement about their work and the good spirit in the
research group have been essential for the various achievements. The shape mem
ory microactuators have been fabricated from high quality SMA foils and thin
films provided from several sources. I am particularly thankful to Prof. Shuichi
Miyazaki, Dr. Eckhard Quandt, Dr. Bemhard Winzek, Prof. Toshiyuki Takagi,
and Kiyoshi Yamauchi for the very fruitful collaboration over many years. In ad
dition, Prof. David Allen, Dr. Andreas Schüßler, Dr. Wilhelm Pfleging, and Heino
Besser deserve my sincere thanks for their support in micromachining. Last but
not least, I would like to thank my wife Birgit for putting up with my preoccupa
tion and long working hours.
Karlsruhe, February 2004 Manfred Kohl
Glossary of Notations
This glossary lists the abbreviations and symbols used in the book, a brief defini
tion of their meaning, and typical units. Some symbols have different meanings in
separate contexts, matching common notation conventions.
Notation Description Units
a Lattice parameter m
a Radius of bridge in SMA microvalve m
aB Length of a bridge segment in SMA microvalve m
a A Parameter for the kinetic behavior of phase transformation K'
a M Parameter for the kinetic behavior of phase transformation K'
A Analog
A Ampere
A Austenite
A Area m 2
A, Austenite start transformation temperature K
A Austenite peak transformation temperature K
p
At Austenite finish transformation temperature K
Al Aluminium
At Atom
Au Gold
ASP Analog signal processing unit
b Lattice parameter m
b Width of a bridge segment in SMA microvalve m
s
bA Parameter for the kinetic behavior of phase transformation Pa-'
bM Parameter for the kinetic behavior of phase transformation Pa-'
B Magnetic field strength Tesla
B Operator of lattice deformation
C Lattice parameter m
