Modeling, design and realization of microfluidic components

247 Pages·2000·8.8 MB·English

by  Rijk Edwin Oosterboek

MODELING, DESIGN AND REALIZATION
OF
MICROFLUIDIC COMPONENTS
Edwin Oosterbroek
The research described in this thesis was carried out at the Micromechanical Transducers
Group of the MESA Research Institute at the University of Twente, Enschede, The
Netherlands. The project was financially supported by the OSF funds “Micro total analysis
systems (µTAS), societal impact and fundamental micromechanical, optical and chemical
aspects” of the University of Twente.
Promotiecommissie:
Voorzitter
Prof.dr. H. Wallinga Universiteit Twente
Secretaris
Prof.dr. H. Wallinga Universiteit Twente
Promotoren
Prof.dr.ir. A. van den Berg Universiteit Twente
Prof.dr. M.C. Elwenspoek Universiteit Twente
Leden
Prof.dr.ir. J.A.M. Kuipers Universiteit Twente
Prof.dr.ir. H. Tijdeman Universiteit Twente
Prof.dr. P.J. French Technische Universiteit Delft
Prof. G. Stemme The Royal Institute of Technology, Stockholm
Prof. R. Zengerle Albert-Ludwigs Universität, Freiburg
CIP-GEGEVENS KONINKLIJKE BIBLIOTHEEK, DEN HAAG
Oosterbroek, Rijk Edwin
Modeling, design and realization of microfluidic components / Rijk Edwin Oosterbroek
[S.I. : s.n.]
Ph.D. thesis University of Twente, Enschede, The Netherlands
ISBN 90-36513464
Subject headings: µTAS / microsystem technology / flowsensors / microvalves / modeling
Copyright © 1999 by R.E. Oosterbroek, Enschede, The Netherlands
MODELING, DESIGN AND REALIZATION
OF
MICROFLUIDIC COMPONENTS
PROEFSCHRIFT
ter verkrijging van
de graad van doctor aan de Universiteit Twente,
op gezag van de rector magnificus,
prof.dr. F.A. van Vught,
volgens besluit van het College voor Promoties
in het openbaar te verdedigen
op vrijdag 12 november 1999 te 16.45 uur.
door
Rijk Edwin Oosterbroek
geboren op 28 januari 1970
te Borne
Dit proefschrift is goedgekeurd door de promotoren:
Prof.dr.ir. A. van den Berg
Prof.dr. M.C. Elwenspoek
CONTENTS
1 INTRODUCTION..................................................................................................................1
1.1 Title explanation.............................................................................................................1
1.2 Microsystem research.....................................................................................................2
1.3 Project description..........................................................................................................3
1.4 Outline............................................................................................................................3
2 HISTORY AND LITERATURE SURVEY OF MST AND µTAS.......................................7
2.1 Classification of microsystems technology....................................................................7
2.2 Microsystem technology history....................................................................................9
2.3 Classification of µTAS.................................................................................................11
2.4 History of micro chemical analysis systems.................................................................13
2.5 Designing and modeling of microsystems....................................................................14
2.6 Device and system simulation tools.............................................................................18
2.7 Trends and prospects of MST and µTAS.....................................................................21
3 MICRO FLUID DYNAMICS..............................................................................................31
3.1 Introduction..................................................................................................................31
3.2 Quantitative down-scaling effects................................................................................32
3.3 Fluid dynamics.............................................................................................................36
3.4 Surface effects in micro-flows......................................................................................38
3.4.1 Introduction...........................................................................................................38
3.4.2 Surface energy......................................................................................................38
3.4.3 Double layers........................................................................................................40
3.5 Hydraulic channel resistance in stationary flows.........................................................43
3.5.1 Introduction...........................................................................................................43
3.5.2 Numerical solutions of the Laplace equation........................................................43
3.5.3 Exact analytical solutions.....................................................................................46
3.5.4 The virtual work principle....................................................................................47
3.5.5 Channel resistance................................................................................................56
3.6 Conclusions:.................................................................................................................60
4 THE PRESSURE / FLOW SENSOR, A CASE STUDY....................................................65
4.1 Introduction..................................................................................................................65
4.2 The flow sensing principle...........................................................................................67
4.3 Fabrication....................................................................................................................68
4.4 Modeling of the stationary sensor behavior.................................................................72
4.4.1 Membrane deflection............................................................................................72
4.4.2 Electric pressure-sensor capacitance.....................................................................74
4.4.3 The hydraulic resistance.......................................................................................75
4.5 Modeling of the quasi-dynamic sensor behavior..........................................................78
4.6 Accuracy and stability..................................................................................................82
4.7 Viscosity versus inertance induced dissipation............................................................84
4.8 Conclusions and discussion..........................................................................................85
5 MICROVALVES.................................................................................................................89
5.1 Introduction..................................................................................................................89
5.2 Valve types...................................................................................................................91
5.2.1 Passive valves.......................................................................................................91
5.2.2 Active valves.........................................................................................................92
5.3 The bossed valve..........................................................................................................94
5.3.1 Introduction...........................................................................................................94
5.3.2 Surface micromachined bossed valves.................................................................94
5.3.3 Bulk micromachined bossed valves......................................................................97
5.3.4 Selective fusion bonding.....................................................................................100
5.4 The membrane valve..................................................................................................103
5.4.1 Introduction.........................................................................................................103
5.4.2 Membrane check / pressure actuated normally open valves...............................104
5.4.3 Pressure actuated normally closed valves...........................................................105
5.5 The duckbill check valve............................................................................................107
5.5.1 Principle..............................................................................................................107
5.5.2 Design and fabrication of thin <111> oriented membranes................................108
5.5.3 Membrane tapering.............................................................................................111
5.5.4 Applications........................................................................................................113
5.5.5 Selective anodic bonding....................................................................................114
5.6 Micromachining possibilities in <111> oriented silicon............................................115
5.6.1 Introduction.........................................................................................................115
5.6.2 Crystallographic orientations in <111> wafers...................................................115
5.6.3 Pre-etching without wall coating........................................................................117
5.6.4 Pre-etching with wall coating.............................................................................118
5.7 Conclusions................................................................................................................121
6 FLOW-STRUCTURE COUPLING...................................................................................135
6.1 Introduction................................................................................................................135
6.2 Flow-structure interaction in check valves.................................................................136
6.3 Numerical implementation.........................................................................................139
6.3.1 Introduction.........................................................................................................139
6.3.2 Bi-directional coupled solving............................................................................140
6.4 Domain de-coupling...................................................................................................148
6.5 Stability.......................................................................................................................148
6.6 Conclusions................................................................................................................152
7 VALVE CHARACTERIZATION.....................................................................................155
7.1 Introduction................................................................................................................155
7.2 Characterization setup................................................................................................156
7.3 The bossed valve........................................................................................................158
7.3.1 Structural mechanics...........................................................................................158
7.3.2 Flow-structure coupling......................................................................................166
7.4 The membrane valve..................................................................................................171
7.4.1 Membrane check / pressure actuated normally open valve................................171
7.4.2 The pressure actuated normally closed valve.....................................................178
7.5 The duckbill valve......................................................................................................183
7.5.1 Membrane analysis.............................................................................................183
7.5.2 Flow-structure coupling......................................................................................189
7.6 Conclusions................................................................................................................193
8 CONCLUSIONS & OUTLOOK.......................................................................................197
8.1 Overview....................................................................................................................197
8.2 Outlook.......................................................................................................................199
A BOSSED VALVE FABRICATION PROCESS DESCRIPTION.....................................203
B DUCKBILL VALVE FABRICATION PROCESS DESCRIPTION................................217
SUMMARY............................................................................................................................227
SAMENVATTING.................................................................................................................229
BIBLIOGRAPHY...................................................................................................................231
DANKWOORD......................................................................................................................235
BIOGRAPHY..........................................................................................................................238
LEVENSLOOP.......................................................................................................................239

1
1
1
IINNTTRROODDUUCCTTIIOONN
The first chapter gives an impression of the fascinating
world of micromechanics and the relevance of the
achievements of microsystem research for “daily life” and
the future. Specific attention is paid to position of the work,
described in this thesis, in the framework of the research
done within the MESA+ Research Institute and more
specific within the µTAS orientation. Thereafter, the aims of
the project are discussed and a brief overview is given of the
subject-matter of the following chapters in this thesis.
1.1 Title explanation
The thesis title “Modeling, design and realization of microfluidics components” refers to the
described activities performed in the microfluidic research area. Microfluidics is a rather
new term for describing the world of controlling and using small fluid flows with use of
microsystem components. The word originates from the term “fluidics” used in the “macro
world”. It is a contraction of the words “fluid” and “logics” and used to indicate the research
area that deals with fluid control to make logic Boolean switches [14,4,20]. With use of the
Coanda effect valve-less bi- or mono-stable switches are made to construct for example
AND and OR switches. Microfluidics however covers a broader area including all types of
passive and active valves, micro flow and pressure sources as well as flow and pressure
sensors [16,11,32,6] made with micromachining techniques.
In this thesis a few components within the microfluidics area will be scrutinized. From
these components the design trajectories will be followed, starting with the theoretical
2 Chapter 1
description followed by the modeling and fabrication stage and finishing with performing
measurement results.
1.2 Microsystem research
The fascinating and fast growing world of microsystem technology plays more often an
important role in daily life. Simply said, microsystem technology covers the area of small,
microns sized systems and devices. A more detailed discussion about the definition of
microsystem technology is found in chapter 2. Examples of microdevices that are very
successful nowadays are among others the inkjet nozzles [3], airbag (acceleration) sensors
[22], pressure sensors [8,19] in for example car engines and magnetic recording heads for
computer harddisks [15,30,18]. The research area started some 30 years ago, arisen from the
electronic semiconductor development. This history has influenced the development of
micromechanics substantially. Microsystems allow for example high level integration with
electronic integrated circuitry and large reduction of costs by mass fabrication processing.
Integration with electronic circuits allows for the extension of the nowadays highly
developed microprocessors with sensors and actuators [29]. In this way electronic circuitry
will get “sense-organs” and “hands”. On the other hand, dimension reduction not only allows
the fabrication of smaller systems but also can improve signal quality as well as sensitivity
and facilitates exploiting physical and chemical effects that become dominant and usable
when downscaling occurs [12,13].
For chemical analysis systems this means that for classical analysis methods, the
needed time can be speeded-up, less sample material and reagents are needed and better
quality reaction products can be obtained [26]. In chapter 2 the benefits of downscaling will
be discussed in more detail as well as the fast growing area of µTAS which stands for Micro
Total Analysis Systems [26]. µTAS covers the research of miniaturized chemical analysis
systems and the microfluidics components needed to complete such systems. The last years
the development of microfluidic components is strongly influenced by the successes of the
µTAS analysis research and the fast growth of companies active in this business [24].
Miniaturization has caused a revolution in information gathering in biochemistry. The lab-
on-a-chip approach makes massive parallel DNA analysis and PCR techniques available,
resulting in a substantial analysis time reduction at limited costs [10,1,21,2,9].
Besides these benefits and successes of microsystem technology a big drawback,
which makes the used techniques less accessible for companies and research institutes, is the
need of expensive conditioned cleanroom facilities and sophisticated cleanroom equipment
such as deposition and etching machines. In order to be able to obtain a good process
control, much specific knowledge about these processes is needed, which is often closely