1. Handbook of Silicon Based MEMS Materials and Technologies

2. Micro & Nano TechnologiesSeries Editor: Jeremy RamsdenProfessor of NanotechnologyMicrosystems and Nanotechnology Centre, Department of MaterialsCranfield University, United KingdomThe aim of this book series is to disseminate the latest developments in small scale technologies with a particular emphasis on accessible and practical content. These books will appeal to engineers from industry, academic and government sectors.9780815515944 Veikko Lindroos, Markku Tilli, Ari Lehto and Teruaki Motooka, Handbook of Silicon Based MEMS Materials and Technologies (2010) 9780815515838 Waqar Ahmed and M.J. Jackson, Emerging Nanotechnologies for Manufacturing (2009) 9780080964546 Richard Leach, Fundamental Principles of Engineering Nanometrology (2009) 9780815520238 Jeremy Ramsden, Applied Nanotechnology (2009) 9780815515869 Matthew Hull and Diana Bowman, Risk Governance of Nanotechnology (2009) 9780815515432 Nam-Trung Nguyen, Micromixers (2008) 9780815515449 Jean Berthier, Microdrops and Digital Microfluidics (2008) 9780815515777 Behraad Bahreyni, Fabrication and Design of Resonant Microdevices (2008) 9780815515739 Francois Leonard, The Physics of Carbon Nanotube Devices (2009) 9780815515784 Mamadou Diallo, Jeremiah Duncan, Nora Savage, Anita Street and Richard Sustich, Nanotechnology Applications for Clean Water (2009) 9780815515876 Rolf Wthrich, Micromachining Using Electrochemical Discharge Phenomenon (2009) 9780815515791 Matthias Worgull, Hot Embossing (2009) 3. Handbook of Silicon Based MEMS Materials and TechnologiesVeikko Lindroos,Markku Tilli ,Ari Lehto andTeruaki MotookaWilliamAndrewApplied Science Publishers 4. William Andrew is an imprint of Elsevier The Boulevard, Langford Lane, Oxford OX5 1GB, UK 30 Corporate Road, Burlington, MA 01803First edition 2010Copyright 2010 Published by Elsevier Inc. All rights reservedNo part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publishers permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions .This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).NoticesKnowledge and best practice in this fi eld are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.Practitioners and researchers must always rely on this own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.British Library Cataloguing in Publication Data A catalogue record for this book is available from the British LibraryLibrary of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of CongressISBN : 978-0-8155-1594-4For information on all Elsevier publications visit our website at www.elsevierdirect.comTypeset by MPS Limited, a Macmillan Company, Chennai, India www.macmillansolutions.comPrinted and bound in United States of America 10 11 12 11 10 9 8 7 6 5 4 3 2 1 5. PrefaceIn summer 2006 we were approached by William Andrew Publishing about producing a MEMS related handbook. As the general guideline from the publisher was to keep in mind that they are particularly seeking book content geared towards practical applications rather than theory.During the summer of 2006 we matured our understanding of the state-of-art as well as the further development and needs of MEMS materials and technologies. As a result of such a maturation process, we understood that there are currently many handbooks and textbooks covering MEMS components, but their focus is more in the device physics and design rather than in materials and manufacturing processes. Also, it has been experienced in practice, that there is a need for a book covering starting materials as well as the most important process steps in bulk micromachining fulfi lling the needs of a device design engineer as well as process or development engineer working in manufacturing processes. Although many comprehensive textbooks cover, for instance, silicon from many aspects, they are not worn out in the hands of MEMS engineers, as they are too specialized. That is why a special emphasis was put on silicon, the most important starting material used in MEMS devices, different varieties of silicon wafer types used in MEMS process, material properties and measurement techniques as well as analytical methods used in the silicon materials characterization. The aim is not to go too deep into the scientifi c details but, instead, to give a broader overview tailored for the needs of the MEMS industry. Also, in a similar manner, important selected process steps in MEMS manufacturing are treated to give an overview of the most recent progress.The MEMS industry is now at a turning point; MEMS industry has been so far mainly driven by automotive and industrial applications now the industry driver will be consumer electronics, more precisely portable electronics: mobile phones, MP3 players, digital cameras, camcorders, etc. The growth of the MEMS industry is forecast to be close to 20% annually, and there will be new entrants in the industry, who need to get basic understanding of the MEMS materials and processes. Consumer electronics applications are also very cost sensitive. Therefore, it is essentially important to minimize the overall device costs and to understand the whole supply chain. By applying proper material selection it makes possible to infl uence on the MEMS device processing costs. In order to fully understand the present state-of-the-art and, in particular, the future trends of MEMS technology and industry, the Editors appreciate this opportunity to include the invited introductory overview contribution Impact of Silicon MEMS 30 Years After by Dr. Tapani Ryh nen from Nokia Nanoscience Centre at the University of Cambridge.Based on the above motivation of the present state as well as the further development and needs, we have prepared the present Handbook of Silicon Based MEMS Materials and Technologies . The book consists of fi ve parts:Part I Silicon as MEMS materialPart II Modeling in MEMS Part III Measuring MEMS Part IV Micromachining technologies in MEMSPart V Encapsulation of MEMS componentsThese fi ve parts are consisting of altogether 42 chapters written by 73 world class MEMS contributors from 12 countries from Europe, North America and Asia. In addition to the general Editors of the book there were also invited and nominated additional Part Editors for each part of the book; i.e., Markku Tilli for Part I, Teruaki Motooka and Risto Nieminen for Part II, Veli- Matti Airaksinen for Part III, Helmut Seidel for Part IV and Ari Lehto and Heikki Kuisma for Part V.During the actual course of the writing process of the book, there were arranged, in addition to the regular editorial meetings, also MEMS book author meetings, once or twice annually, in order to maintain the common scope and objective for a uniform compilation of the book.Finally , the Editors would like to express their great appreciation to all of their fellow contributors for this unique window of opportunity to work with them, resulting in a comprehensive MEMS handbook, which illustrates a global cutting edge knowledge and expertise within the most vigorously growing industry today. Furthermore, the Editors are grateful for the appropriate and constructive co-operation with the publishers, i.e. William Andrew (WA) and Elsevier, since its acquisition ix 6. Prefaceof WA in January 2009. Our particular thanks go to Dr. Nigel Hollingworth of WA as well as to Matthew Deans, Melanie Benson and Renata Corbani of Elsevier for their valuable co-operation during the course of the work. Finally, the Editors are grateful to the Helsinki University of Technology, which will be a member of the new Aalto University to be established at the beginning of the year 2010, for providing various premises, such as secretarial and computational services, for the needs of the editorial work.x 7. List of ContributorsTimo AaltoVTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, FinlandVeli -Matti AiraksinenHelsinki University of Technology, P.O. Box 3500, FI02015 TKK, FinlandMarco AmiottiSAES Getters S.p.A., Viale Italia 77, 20010 Lainate (Milan), ItalyOlli AnttilaSilfex Incorporated - A Division of Lam Research Corporation, 950 South Franklin Street, Eaton, Ohio 45320, USAPaul A. AnzaloneFEI Company, P.O. Box 332, Merrimack, NH 03054, USAAbhinav BhushanUniversity of California, Department of Mechanical and Aeronautical Engineering - College of Engineering -Bainer Hall -One Shields Avenue-Davis, CA 95616, USAAntonio BonucciSAES Getters S.p.A., Viale Italia 77, 20010 Lainate (Milan), ItalyJakub BruzdzinskiThe Nordic Hysitron Laboratory, Helsinki University of Technology, P.O. Box 6200, 02015 TKK, FinlandRobert CandlerUCLA Department of Electrical Engineering, Department of Electrical Engineering, 6731-H Boelter Hall, Los Angeles, CA, 90095, USAKuo -Shen ChenNational Cheng-Kung University, Tainan, Department of Mechanical Engineering, National Cheng-Kung University, 1 University Rd., Taiwan, 70101, R.O.C.Andrea ConteSAES Getters S.p.A., Viale Italia 77, 20010 Lainate (Milan), ItalyCristina DavisUniversity of California, Department of Mechanical and Aeronautical Engineering - College of Engineering - Bainer Hall -One Shields Avenue - Davis, CA 95616, USAViorel DragoiEV Group, E. Thallner GmbH, DI Erich Thallner Strasse 1, A-4782 St. Florian/Inn, AustriaSimo Er nenVTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, FinlandSami FranssilaHelsinki University of Technology, P.O. Box 3500, FI-02015 TKK, FinlandAlois FriedbergerEADS Innovation Works, IW-SI, 81663 Munich, GermanyMaria GanchenkovaHelsinki University of Technology, P.O. Box 1100, FI-02015 TKK, FinlandLucille GiannuzziFEI Company, Hillsboro, OR 97124, USAMiguel Gos lvezDept . Micro Nanosystems Engineering, Nagoya University, 464-8603 Nagoya, JapanJakub GroniczThe Nordic Hysitron Laboratory, Helsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandAtte HaapalinnaOkmetic Oyj, P.O. Box 44, FI-01301 Vantaa, FinlandEero HaimiHelsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandKimmo HenttinenOkmetic Oyj, P.O. Box 44, FI-01301 Vantaa, Finlandxi 8. List of ContributorsDavid HorsleyUniversity of California, Davis, Department of Mechanical and Aeronautical Engineering, University of California, Davis, One Shields Ave., Davis, CA 95616, USAAkihisa InoueTohoku University, Institute for Materials Research, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, JapanHenrik JakobsenInstitute for Microsystem Technnology, Faculty of Technology and Engineering, Vestfold University College, P.O. Box 2243, N-3103 TnsbergKerstin JonssonNanoSpace AB, Uppsala Science Park, SE-751 83, Uppsala, SWEDENDirk K hlerAdvanced Electronic Packaging, Fraunhofer Institut f r Siliziumtechnologie, Fraunhofer Str. 1, D-25524, Itzehoe, GermanyHannu KattelusVTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, FinlandRoy KnechtelX -FAB Semiconductor Foundries AG, Haarbergstra e 67, D-99097 Erfurt, GermanyKathrin KneseRobert Bosch GmbH, Automotive Electronics (AE/ EST2), Postfach 13 42, 72703 Reutlingen, GermanyKai KolariVTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, FinlandMika KoskenvuoriOkmetic Oyj, P.O. Box 44, FI-01301 Vantaa, FinlandHeikki KuismaVTI Technologies Oy, P.O. Box 27, FI-01621 Vantaa, FinlandAdriana LapadatuSensoNor Technologies AS, P.O. Box 196, N-3192 Horten, NorwayFranz LaermerRobert Bosch GmbH, Corporate Sector Research and Advance Engineering, Microsystems (CR/PJ-TOP54), Postfach 10 60 50 , 70049 Stuttgart, GermanyBrandon Van LeerFEI Company, Hillsboro, OR 97124, USAAri LehtoHelsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandChristina LeinenbachRobert Bosch GmbH, P.O.Box 10 60 50, 70049 Stuttgart, GermanyPaul LindnerEV Group, E. Thallner GmbH, DI Erich Thallner Strasse 1, A-4782 St.Florian am Inn, AustriaVeikko LindroosHelsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandGiorgio LongoniSAES Getters S.p.A., Viale Italia 77, 20010 Lainate (Milan), ItalyJari M kinenOkmetic OyjP .O. Box 44, FI-01301 Vantaa, FinlandPeter MerzMEMS Department, Fraunhofer Institut f r Siliziumtechnologie, Fraunhoferstrasse 1, D-25524, Itzehoe, GermanyDouglas J. MeyerAZonic Solar, Mesa, AZ, USA 2753 East El Moro Ave, Mesa, AZ 85204, USAMarco MorajaSAES Getters S.p.A., Viale Italia 77, 20010 Lainate (Milan), ItalyTeruaki MotookaDept . of Materials Science & Engineering Kyushu University, Motooka 744, Fukuoka 819-0395, JapanGerhard M llerEADS Innovation Works, IW-SI Sensors, Electronics & Systems Integration, 81663 Munich, GermanyShijo NagaoThe Nordic Hysitron Laboratory, Helsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandRisto NieminenHelsinki University of Technology, P.O. Box 1100, FI-02015 TKK, Finlandxii 9. List of ContributorsRoman NowakThe Nordic Hysitron Laboratory, Helsinki University of Technology, P.O. Box 6200,FI- 02015 TKK, FinlandJuuso OlkkonenVTT Technical Research Centre of Finland, P.O.Box 1000, FI-02044 VTT, FinlandKuang -Shun OuDepartment of Mechanical Engineering, National Cheng-Kung University, 1 University Rd., Taiwan, 70101, R.O.C.Jari PaloheimoOkmetic Oyj, P.O. Box 44, FI-01301 Vantaa, FinlandRiikka PuurunenVTT Technical Research Centre of Finland, Tietotie 3, Espoo, FinlandWolfgang ReinertAdvanced Electronic Packaging, Fraunhofer Institut f r Siliziumtechnologie, Fraunhofer Str. 1, D-25524, Itzehoe, GermanySteve ReyntjensFEI Company, PO Box 80066, 5600 KA Eindhoven, The NetherlandsTapani Ryh nenNokia Research Centre, Eurolab, c/o Nanoscience Centre, University of Cambridge, 11 J J Thomson Avenue, Madingley Road, Cambridge, CB3 0FF, UKLauri SainiemiHelsinki University of Technology, P.O. Box 3500, FI-02015 TKK, FinlandHele SavinHelsinki University of Technology, Espoo, P.O. Box 3500, FI-02015 TKK, FinlandHelmut SeidelUniversit t des Saarlandes, Lehrstuhl f r Mikromechanik, Mikrofl uidik/Mikroaktorik, Postfach 15 11 50, D-66041 Saarbr cken, GermanyParmanand SharmaTohoku University, Institute for Materials Research, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, JapanScott SullivanDisco Hi-Tec America, Inc., 3269 Scott Blvd. Santa Clara, CA 95054-3011, U.S.A.Tommi SuniVTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, FinlandTuomo SuntolaPicosun Oy, Tietotie 3, FI-02150 Espoo, FinlandMarkku TilliOkmetic Oyj, P.O. Box 44, FI-01301 Vantaa, FinlandIlkka TittonenHelsinki University of Technology, P.O. Box 3500, FI-02015 TKK, FinlandSanteri TuomikoskiVTI Technologies Oy, P.O. Box 27, 01621 Vantaa, Finland rjan VallinUppsala University, The ngstr m Laboratory, Solid State Electronics, Box 534, SE 75121 Uppsala, SwedenTimo VeijolaHelsinki University of Technology, P.O. Box 3000, FI-02015 TKK, FinlandEeva ViinikkaCulminatum Innovation, Tekniikantie 12, FI-02150 Espoo, FinlandOliver WilhelmiFEI Company, PO Box 80066, 5600 KA Eindhoven, The NetherlandsPiotr ZachariaszThe Nordic Hysitron Laboratory, Helsinki University of Technology, P.O. Box 6200, FI-02015 TKK, FinlandIrena ZubelFaculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Polandxiii 10. xvexpressions of new user interface concepts based oncapabilities to sense, compute and create an action inreal time. However, this pervasive capability of sensing,computing and communication means a complete newera of mobile devices and related digital services.This book is a demonstration of the maturity of thesilicon MEMS technologies. The silicon micromechanics,measurement electronics and the packaging technologieshave all been developed to a level where very large vol-umemanufacturing is possible. We are ready to take thenext leap towards the future devices and digital services.Towards Mass Volumes of MEMSDevicesEarly VisionsWhen Kurt E. Petersen wrote his famous review [1] of sili-conmicromechanics in 1982, there existed already eightcompanies working in the field. He covered nearly twohundred essential references in his paper. Above all thevision of the applications and opportunities was alreadywell understood. Petersen discussed a very broad set ofpotential applications with commercial significance, suchas, accelerometers, pressure transducers, torsional mir-rors,resonant gate transistors, light modulators, resonatingbeam arrays, inkjet printer heads, and microelectrome-chanicalswitches. The research community was alreadyformed: for example, the IEEE Transducers confer-encewas organized already in 1969, and the Sensors andActuators journal was established in 1980. The first largevolume application of MEMS was only some years away.IntroductionSilicon deforms elastically and is a very robust mechanicalmaterial. Silicon has small thermal expansion, high speed ofsound and very low intrinsic mechanical losses. There existvarious methods for both isotropic and anisotropic etch-ingof silicon. The well controlled anisotropic etching ofsilicon especially has enabled the fabrication of microscalemechanical structures and devices. When these mechani-calcharacteristics and the micromachining are combinedwith the mass scale manufacturing solutions from the ICindustry, we have a platform for producing micromechani-calsensors and actuators in huge volumes at low cost.First mechanical characterization and experiments inchemical wet etching of silicon were already carried outin the 1950s; and the industrial scale MEMS was bornin the late 1970s.Today the various devices and even smaller objects ofour physical world are becoming extensively connectedto the digital information networks. We can say that thephysical and digital worlds are merging. Smaller andsmaller physical objects can be indexed by RF ID tagsand other electrical labels. Small processors and com-municationcapabilities can be integrated into a varietyof small physical objects. The microelectromechanicalcomponents and systems (MEMS) developed over thepast 30 years form the technology platform that enablessensing and even actuation in these small devices.Here the development of MEMS technologies is pre-sentedfrom the perspective of the mobile communica-tionindustryfrom the rise of automotive applicationsof MEMS sensors to the expansion of MEMS compo-nentsinto consumer products. We have seen the firstImpact of Silicon MEMS30Years AfterTapani RyhnenNokia Research Centre, Cambridge, UKOverview 11. OverviewxviMost of the concepts of micromechanical devices andfabrication technologies go back in time to the 1960s andthe early 1970s. The mechanical characteristics of sin-glecrystalline silicon, the anisotropic etching of siliconby potassium hydroxide (KOH) and several concepts ofmicromechanical devices were studied [26]. An interest-ingexample of early device concepts is shown in Fig. 1.W.E. Newell and his coworkers [7, 8] published a reso-nantgate transistor based on a micromechanical resona-tormade of electroplated gold in 1967.Integration of micromechanical structures, such asresonators, was a natural continuum from the pre-siliconelectronics to the early concepts of silicon integrateddevices. The first commercial application by HewlettPackard used a MEMS cantilever based frequencydetector in frequency synthesizers in 1980 [9]. In spiteof these early concepts, the development of practicalcommercial applications based on MEMS resonators hastaken nearly 30 years, even today very few commercialdevices exist besides the scientific instruments, such as,the resonating cantilevers of the atomic force micro-scopes[10, 11] and the biosensors [12].The capability to create large arrays of similar com-ponentswith precise dimensions enabled new deviceconcepts. Furthermore, the possibility to benefit fromthe fabrication capabilities that were scaling up in theIC industry created the starting point towards the com-mercialapplications of MEMS.Ink Jet Printer Nozzles Create theIndustryThis capability to manufacture precise componentsand arrays of micromachined structures practicallyenabled the ink jet printers during the 1980s. IBMdemonstrated [13, 14] the value of silicon microma-chiningto achieve the necessary printing precision withthe integrated methods to control and manage the inksin the same micromachined device. The first mass vol-umeapplication of silicon MEMS was created, and theink jet printers became the main stream of printing inthe growing information technology market.The electrostatic control of ink jets [15] for print-ingpurposes was studied in the beginning of the 1970s.The capability to etch the ink jet nozzles into the siliconwafer using anisotropic KOH wet etching and to inte-gratethe control electrodes into the same device usingthin film and semiconductor processes enabled the suf-ficientminiaturization to improve the quality of ink jetprinting to the level where the commercial solutionswere possible.Still today the ink jet printer application forms onethird of the total MEMS market. Today the printingis expanding as a paradigm to electronics manufactur-ing[16]. Reel-to-reel manufacturing solutions based oneither inorganic or organic inks will be one of the futuresolutions for manufacturing low cost electronics.Automotive Applications Drive theReliability and the QualityThe automotive applications of pressure and motionsensors practically created the MEMS industry. Themanifold air pressure (MAP) sensor introduced by Fordin the mid seventies was the first micromechanical sen-sorin mass volumes. The accelerometers [1719] wereintroduced to replace mechanical switches in airbaglaunchers, and later they enabled sophisticated chassiscontrol systems.Fig 1 l Resonant gate transistor published in 1968 by William E. Newell and his coworkers [8]. 12. OverviewxviiThe automotive industry already in the 1980s wascharacterized by advanced project management andquality control that included all the module manufac-turersand subcontractors. The duration of productdevelopment projects was long and required a com-mitmentfor several years. The MEMS developers soonlearned to apply these strict rules of project and qualitymanagement. The high requirements for reliability cre-atedlong development projects with careful testing andverification phases.The automotive applications also created the require-mentsfor the sensor electronics, such as voltage lev-elsand system interfaces, and for the sensor modulepackaging. Robust system-on-package solutions werecreated. Operating temperatures and shock tolerancewere extremely demanding. In addition, the frequencydependence of the sensors in chassis control and airbaglaunchers required very careful control of intrinsic gasdamping and structural parameters.The motion sensors in automotive applications weresoon divided into two categories: the high performance35 g sensors for measurement of the motion of thechassis of the vehicle and the low cost 50200 g sensorsfor the airbag launchers. This created the distinct pathsfor the development of the manufacturing solutions.Leaps Towards a GenericManufacturing PlatformThe two paradigms of micromachining develop almostin parallel. In the beginning the anisotropic etching ofbulk silicon to form microstructures into the siliconwafer was a more efficient strategy [20]. The bulkmicromachining benefits from the optimal mechanicalcharacteristics of the single crystalline silicon. The dop-ingof the silicon wafers and the optimization of theircharacteristics for chemical etching required specificdevelopment by the wafer manufacturers.Even the simplest MEMS devices require insulat-inglayers. The successful practical method [18, 20]was to use a sandwich of silicon and borosilicate glasswafers. The wafers were bonded together by a so calledanodic bonding process. However, the difference in thethermal expansion of the glass and silicon wafers was aproblem causing strong temperature dependence andeven warping or buckling of the micromechanical struc-tures.The solution was to use only very thin insulatingglass layers between silicon wafers [19] . Later the glassmanufacturers, such as, Corning and Hoya, introducedglass wafers with thermal expansion characteristics thatmatched the silicon.Bulk micromachining enabled several different prod-ucts[20]: pressure sensors, accelerometers, lab-on-chipdevices, etc. As the bulk micromachining provided aninherent wafer level packaging of the micromechanicalstructures, the very accurate control of the gas dampingof accelerometers or the reference pressure of the abso-lutepressure sensors was feasible.The other paradigm was to grow a polysilicon thinfilm on top of a sacrificial silicon dioxide layer [21, 22].The polysilicon film was anchored to the underlying sili-conwafer and patterned to form the particular mechan-icalstructure, e.g., the proof mass and the capacitorstructures of an accelerometer. When the sacrificial sili-conoxide layer was removed, the mechanical structurewas released to move.The promise of the polysilicon surface micromachin-ingwas in the integration of mechanical structures withCMOS electronics. The approach was very successful inthe development of accelerometers for the airbag appli-cationthat was not as demanding on the accelerationresolution. The thickness of the polysilicon layer deter-minesthe proof mass of the accelerometer, and theintrinsic acceleration resolution is inversely proportionalto the square root of the proof mass. Thus the smallermass of the polysilicon structures became a limiting fac-torfor the application that required high accelerationresolution.The control of the intrinsic stress of the polysiliconmembranes was challenging and made the release of themicromechanical structures difficult. The deposition ofa thick polysilicon layer was eventually developed [22].After solving the challenge of wafer level encapsulation,the polysilicon surface micromachining provided smallerdimensions at lower cost, possibility for monolithic inte-grationwith CMOS devices and allowed more complexmechanical structures.In the mid 1990s two disruptive technologiesappeared. The deep reactive ion etching (DRIE) ofsilicon using an inductively coupled plasma source, theBosch process [23], made it possible to etch deep highaspect ratio trenches into silicon. Secondly, the develop-mentof silicon on insulator (SOI) wafers enabled highquality relatively thick monocrystalline silicon layers formicromechanical structures [24]. These technologiesbrought together the advantages of the bulk and surfacemicromachining. Through these innovative processesthe MEMS technologies are becoming a true generictechnology and manufacturing platform.The CMOS electronics integration with MEMSdevices has been an intensive topic of research anddevelopment (see Review in [25]). Both pre- and post-CMOS integration have been used. The key challengehas been the different pace in the development ofMEMS and CMOS processes. In addition, the cost ofthe area on a CMOS wafer is getting increasingly moreexpensive; the CMOS components get smaller but theminiaturization of the MEMS devices is constrained bythe sensor resolution and the necessary physical size. 13. OverviewxviiiMost of the manufacturers have adopted a system-in-packagestrategy to overcome the integration challenge.Silicon on insulator (SOI) wafers has also opened apath towards embedding mechanical structures dur-ingthe wafer manufacturing [26]. This can be a majorchange in the value chain of the MEMS manufactur-ing.The primary mechanical structures can be embed-dedinto the SOI wafer by the wafer manufacturer. Thedevice manufacturer can integrate the CMOS circuitson the wafer and finally release the mechanical struc-turesby the DRIE process.The capabilities for large scale manufacturing andfoundries capable of producing components in scalablevolumes exist today.Towards Every PocketNew TrendsAt the end of the 1990s the micromechanical pressuresensors and accelerometers existed in relatively largevolumes for the automotive industry. The sensor ele-ments,signal conditioning electronics and the packagingwere developed according to the automotive system andenvironmental requirements. When consumer electron-icsand mobile phone manufacturers became interestedin sensors and other MEMS devices suitable for theirproducts, immediately they faced some challenges:n The interface electronics with sufficiently low powerconsumption and low supply voltage level did not exist.n Even though a large variety of packaging standardsexisted, the miniaturization had not addressed thecritical requirement of thinness.n Strict requirements for sensor performance and reli-abilityincreased the cost, and the testing and verifica-tionduring both product development and productionwere very expensive procedures.n Manufacturing volumes were not yet sufficient forconsumer applications, and the lack of long-termcommitment from the consumer industry did notsupport the investments to scale up the productioncapabilities.n Industry dynamics of consumer products and mobilephones were disruptive to the operations of the sensormanufacturers: emphasizing faster ramp-ups, shortercommitments, speed of innovation, and extreme costconsciousness.Figure 2 illustrates the major shifts in the MEMSindustry. The consumer products created a demand oflower cost MEMS devices with more relaxed require-mentson performance. Especially, measurement elec-tronicsand packaging required rethinking. Figure 3illustrates an example of the miniaturization of acceler-ometermodules for consumer products, for the gamecontrollers and the mobile phones [37, 38]. In the early2000s the ground was very fruitful for new innovation,and the global MEMS industry was very optimisticabout these new application areas.Figure 4 shows a recent estimate of the growth of theMEMS component volumes [39]. Even the total unit vol-umeof MEMS components is expected to nearly tripleduring the coming five years, the total annual growth ofthe revenue is clearly smaller with roughly 14% CAGR.Most of the growth is expected to come from the con-sumerapplications of inertial sensors, silicon microphonesand RF MEMS. In addition, the significant growth ofmicrofluidics systems in medical applications, such as,Fig 2 l MEMS devices are moving towards consumer products and will enable the embedding of intelligence into human environments,i.e., the ambient intelligence. 14. OverviewxixFig 3 l Miniaturization of packaged MEMS accelerometers by ST Microelectronics [38].Fig 4 l The estimated MEMS market trend by the Yole Dveloppement [39]. 15. Overviewxxthe drug delivery, may happen during the coming fiveyears. The price erosion of the MEMS components canactually be even more dramatic due to the extreme costcompetition in consumer products and mobile phones.Eventually, the new cost structure of MEMS devices willaffect the automotive sensor market as well.What are these consumer applications that motivatethe annual implementation of half a billion accelerome-ters,over one billion RF MEMS components and nearlytwo billion silicon microphones?Consumer ProductsFrom Wristwatch to Wearable ElectronicsAs the wristwatch is one of the miracles of miniaturiza-tionin the early 20th century, it is not surprising thatsensors measuring the motional and physiological stateof a person and the environmental conditions became apart of the wearable wrist devices. These wrist top com-putersbecame a driver for the integration of MEMSdevices into consumer applications, such as sports, out-doorsand wellness. The heart rate monitor, altimeterand the electrical compass with integrated accelerom-eterto compensate the inclination create benefits toany active persons exercising, skiing or trekking in thewilderness. Even this consumer segment is relativelylimited, the applications defined the requirements ofbattery powered wearable devices: small package andvery power efficient operation.The wrist devices created a starting point for wear-ableelectronics applications [40, 41] where the sensors,processors and the user interface are embedded intowearable devices or clothes. The concepts can be usedfor following the daily activity of a person, measuringphysiological parameters, detecting the physical contextand location of a person or for observing the environ-mentalconditions.Wearable electronics creates a new platform for dig-italservices when the measured information is connectedvia Internet to communities of people that benefit fromsharing their own data with other members [42]. Themeasured data from the individuals can be aggregatedinto meaningful shared information and knowledge. Forexample, sharing of sports, fitness or wellness data witha reference group enables a person to compare their ownperformance with the reference group.The measurement of human scale motion by acceler-ometersand angular rate sensors can be used to extractand recognize relatively complex patterns of humanscale motion, such as, walking, running, climbing stairs.Figure 1.5 shows an example of a wearable pilot devicedeveloped by Nokia in 2003. The device was capableof detecting motion patterns and recording the dailyactivity of a person. Even more complex motion pat-terns,e.g., playing golf or exercising yoga, can be rec-ognized,recorded and used to help the person to learn,repeat and to correct these complex motion patterns.Professional training methods thus become possiblefor any serious amateur sportsman, and eventually, thesports and gaming will merge into various interestingcombinations of physical and virtual realities.Cameras and ProjectorsThe data projectors and projection displays became anew driver of MEMS development after the inventionof micromirror devices at the end of the 1980s. TheDLP technology by Texas Instruments was ahead ofits time in complexity when it was first introduced in1993 [43, 44]. Based on digitally controllable aluminummicromirrors, the DLP chip enabled the miniaturiza-tionof video projectors when the personal computersbecame the primary tool for creating presentations.The miniaturization of data projectors has made themportable. The further miniaturization depends primarilyon the power consumption and efficiency of the lightsource and the thermal management of the device. Inaddition to LED projectors also the laser sources, evenRGB laser sources [45], are appearing. The micromirrorbased reflection devices will, however, meet a lot of com-petitionfrom other technologies, such as, holographicdisplays that can be much more power efficient [46].Image stabilization became an essential feature ofSLR cameras and their optics. Miniaturized Quartzgyroscopes are used to measure the camera movementin order to control the mechanical actuators compen-satingthe movement. The silicon angular rate sensorsFig 5 l Nokia Fitness Monitor pilot product that measures andrecognizes various motion patterns. 16. Overviewxxiare becoming an alternative for piezoelectric devicesin image stabilization. Digital photography may opennew applications for sensors. Automatic rotation of theimage requires a mechanical sensor. Advanced imagestabilization and more complex algorithms to improvethe quality of still and video images are beneficial alsofor people who are not especially experienced in pho-tography.However, many of these operations can beperformed by pure image processing.The automatic generation of metadata for digitalimages [47, 48] will be primarily based on date, timeand location. However, additional sensor informationcan be used for more complete sets of metadata; lightcondition, barometric pressure, humidity, temperature,direction, inclination are valuable information in themetadata for the further use and processing of images.Based on the metadata the sharing and searching of theimages will become possible in a global scale in variousInternet services [49].GamingThe future of user interface and human machine inter-actionmay already be visible in computer games andgame controllers. Ideas for using sensors and haptics inthe user interfaces of gaming devices has been devel-opedby several research groups during the last tenyears [50].Figure 6 presents this kind of prototype device devel-opedand published by Nokia Research Center in 2004.The detection of movements and gestures can be used tocreate an immersive gaming experience; a combination ofa near-eye display, advanced audio functionality, gestureand body movement detection and a haptic feedbackinterface are ways to create virtual reality games or toaugment the physical reality by virtual features [51].Nintendo created a commercial breakthrough withtheir Bluetooth game control Wii Remote that extensivelyintroduced the motion and gesture control to computergames. The game controller uses a 3D accelerometer fortracking the motion patterns. Game controllers togetherwith an excellent set of games and a very good marketingcampaign made the product a real success story in 2007.Nintendo Wii is a viable demonstration of multimodaluser interface for augmented or virtual reality conceptsand eventually also for remote communication.Medical Applications of MEMS DevicesThe health care services are globally challenged bythe increasing population in the developing countriesand the ageing population in the developed countries,including China [52, 53]. Other global phenomena,such as, obesity, require new solutions and rethinkingof the preventive health care strategy. Furthermore,the Internet connectivity enables the access to personalhealth information and remote services.The health care services are moving closer to the con-sumers.Networked professionals are capable of provid-ingmore demanding treatments. The health data of anindividual can be managed more efficiently and accessedby an authorized institution or a health care profes-sional.The personal health data can be managed in adistributed manner but also accessed by the individualanywhere, anytime. Based on this more easily accessiblehealth data, the health care services can be tailored tofit to the medical history of the patient.Furthermore, the medical treatments can be movedto more convenient and less costly settings. A smallerpoint-of-care can be responsible for diagnostics andtreatments that require an extremely sophisticatedenvironment today. In practice, this means remotehealth care services in developed countries; for exam-ple,capabilities to provide a service for chronic patientsor elderly persons at home. In the developing countries,the improvement of health care in the rural areas can bebased on similar solutions. Nurses and doctors in rural,remote locations can benefit from the connectivity tolarge hospitals and their information and diagnosticscapabilities.The key driver for this kind of change is the needto find very low cost solutions for health care usingnew diagnostic tools, remote connectivity and capa-bilitiesto efficiently manage the personal health data.Miniaturized diagnostics based on MEMS devices willpotentially influence both the future diagnostics and thetreatments.Today the most important MEMS devices in medi-calapplications are the microfluidics systems, pressureFig 6 l 3D accelerometer and 2D angular rate sensor-basedgame controllers created by Nokia Research Center in 2004. 17. Overviewxxiisensors for blood pressure monitoring and the acceler-ometersfor cardiac pacemakers. The largest potentialfor new applications and business growth is related tomicrofluidics used in diagnostics and drug delivery.The micromachined structures have made it possibleto handle very small samples of liquids in a reliable way.Furthermore, the MEMS miniaturization creates a possi-bilityto use simultaneous parallel measurements in thesame system. These highly integrated lab-on-chip solu-tions[54, 55] change the nature of the in vitro diagnos-ticdevices. Multichannel integrated biosensors, advancedsample handling and new sensitive transducers will ena-blepoint-of-care devices that are capable of, e.g., cancerdiagnostics or any other analysis of the genomes [56].The continuous monitoring of physiological param-etersof a patient opens opportunities for more precisediagnostics. In addition to monitoring of heart rate,ECG and blood figures the possibility to monitor andregister the daily activity and context of the patientduring these measurements gives more information thatmay have a correlation to the physiological data and thatcan help in the diagnostics. The continuous monitoringand the possible remote connectivity will open a newsegment of wearable health care products.The MEMS devices are already used in the in vivodevices: the cardiac pacemakers use accelerometers todetect the activity of the patient in controlling the pace-makerrhythm [57, 58]. This application is a marvelousexample of the reliability of the MEMS sensors. Thenext very potential application will be the implantableMEMS drug delivery systems [59]. The possibilities tointegrate timing, sensors and microfluidics actuatorsinto an implantable device will revolutionize the treat-mentof several chronic diseases, such as, diabetes.Mobile Phones and MobileMultimedia ComputersThe mobile phones have converted to smart phones ormobile multimedia computers. These mobile devicesare continuously gaining more dominance. These mobilemultimedia devices outnumber personal computers bya factor of five. In some growth markets, such as Chinaand India, the ratio is even higher-close to 10:1. Thismeans concretely over three billion mobile subscribersand over one billion wireless broadband subscribers. By2010 it is expected that up to 90% of the global popula-tionwill have mobile coverage. This creates an immenseplatform to build digital services that are based onremote connectivity.The mobile phones have become digital cameras, musicplayers, internet browsers, mobile TVs in addition tobeing communication devices that people carry with themalways and everywhere. The mobile phones integrate alot of functionality from consumer appliances and per-sonalcomputers into a small integrated device. Figure 7presents potential new arising trends in the mobile com-municationindustry. Currently, the industry is shiftingtowards Internet-based mobile services. This is a clearconsequence of new Internet-based business modelsand the ongoing convergence of mobile communication,information technologies and consumer electronics.The studies and trials of MEMS components in mobiledevices started at the end of the 1990s in the laboratoriesof both the mobile devices and MEMS component manu-facturers.The MEMS provided possible solutions for RFintegration, local oscillators, sensors, microphones, displays,power solutions, etc. The most potential applications ofFig 7 l Mobile industry in shift towards services and ambient intelligence. 18. OverviewxxiiiMEMS in mobile devices are related to the RF imple-mentation,sensors and the audio functionality. On theother hand, practically all the consumer electronicsfunctionalities can be integrated into mobile multimediacomputers or at least used in their accessories.The rapidly growing volumes of mobile phones cre-atedexpectations of large volumes of MEMS devices.However, after roughly ten years of development theimpact is still rather modest. Why?RF MEMSThe radio and the antenna implementations in mobiledevices are continuously getting more complex. Thenumber of supported radio standards has increased, mak-ingthe design of the radio chip sets and the antenna solu-tionsmore challenging. The promise of MEMS deviceshas been related to tunable RF components that reducethe number of discrete elements in the radio front end.MEMS RF switches, tunable MEMS capacitors andMEMS resonator-based devices, such as, delay lines andfilters, have been the focus of extensive developmentboth in the university and industry laboratories [2730].The development of reliable RF MEMS deviceshas, however, taken much longer than expected in thebeginning. There are some fundamental dimensionalconstraints that make the integration of RF MEMScomponents to mobile devices challenging:n The conductivity of even highly doped bulk silicon orpolysilicon is not sufficient for a high enough qualityfactor for capacitors, inductors or switches in the fre-quencyrange of 15 GHz.Thus the use of metal filmbased micromechanical structures is required, leadingto several other challenges.n The temperature dependence in devices that consist ofmultiple materials is very difficult to control and reduce.Even practical solutions have been found [35,36].n Low cost system-in-package integration of RF ICs, pas-sivecomponents and MEMS devices is challenging.n Voltage levels required to actuate RF MEMS devicesare typically much higher than the supply voltage lev-elsof modern ICs.n Oscillators based on MEMS resonators at 10 MHzfrequency range with low losses (Q~200000) andvery good phase noise (155dBm/ Hz ) have beendeveloped [31, 32]. However, the thermal stability ofthe devices is still a challenge.n MEMS resonators are limited to roughly 10 MHz fre-quency.At higher frequencies, e.g., in 15 GHz range,the fabrication tolerance of narrow electrode gaps,very high control voltages and the lower Q values ofresonators limit the development of practical devices.Recently, the development of piezoelectric actuatorsfor MEMS resonators has improved the efficiency ofelectrical coupling [33,34].The complexity of the value chain has also made thedevelopment slower: the MEMS devices, RF ICs and RFmodules have been manufactured in many cases by differ-entmanufacturers, according to the specifications of thesystem integrators. Both technical and commercial chal-lengesin creating integrated solutions have existed. Recentdevelopment is clearly bringing the technologies together.The radio communication is gradually developingtowards concepts that are generally known as the cogni-tiveradio [60, 61]. The concept is based on the capabilityof the radio system to sense the available radio resourcesand the context of the user, assess the situation, dynami-callyplan and take the actions to allocate radio resources,and finally learn about them. The requirements for theradio front-end implementation are very demanding: theradio spectrum analysis over a broad frequency range andthe fast adaptation to the optimal radio band. The powerefficient tunable antennas, filters and impedance match-ingcircuits are the fundamental enablers of the futureintelligent radios. The technology for the cognitive radiodoes not exist today; the RF MEMS components mayenable some of these required capabilities.Sensors and ActuatorsThe sensor functionality is clearly becoming a part ofconsumer products. However, there still exists a chal-lengein integrating new functionality in devices that aresold in huge volumes. The products are extremely costsensitive, and the functionality needs to be meaningfulfor most of the end users. What are these new functionsenabled by MEMS sensors?Furthermore, the mobile phone market is drivenglobally by mobile network operators. What are thebenefits and the revenue opportunities for the telecom-municationoperators of the sensor functionality? Sofar applications that would motivate a very large scaleintegration of sensors into mobile devices have simplynot existed. The additional cost related to the sensorsFig 8 l Tunable metal film capacitor design by Nokia ResearchCenter and fabricated by Philips Research. 19. Overviewxxivand their application software has slowed down thedevelopment.The number of possible sensor applications in mobiledevices is huge. Table 1 summarizes some possible mobiledevice applications and their requirements for the sensorsystem. Even if it is possible to list a large number of usecases and applications, the key challenge is how to makethe functionality so generic that it enables this multitudeof applications for various consumers.Recently, Nokia has introduced three axis accelerom-etersin the high end mobile multimedia computers, suchas, the models N82 and N95. The application program-minginterface (API) to the sensors has been publishedfor third parties. Nokia has also produced a multitude ofbeta applications for fitness and sports [62]. The threeaxis accelerometer-based motion detection and the GPSbased location have been the key data sources. AppleiPhone, LG, Nokia, and Samsung have also used accel-erometersfor controlling the user interface. Recently,Apples novel Appstore business model has enableddevelopment of various accelerometer applications formobile devices by the software development community.The three axis accelerometer is the key sensor formobile devices. It enables several possible functions: harddisk protection, gesture recognition, user interface control,activity monitoring, etc. The functionality is generic, andthe motion data can create a basis for several applications.The awareness of the context means to be able to rec-ognisethe status of the environment, the user, the deviceitself and of the network. The context awareness is thegeneric functionality that enables the future intelligentsensing, computing and communication devices. Thecontext awareness is based on merging information andmeasurements from several different sources. From theembedded sensors it is possible to get, e.g., the activity, thelocation, the physiological state of the user and the envi-ronmentalconditions, such as, temperature, illuminationand humidity. Based on this primary sensor data the higherlevel abstraction of the context of the user can be created.Based on the context information it is possible tobuild the applications for sports, gaming, gesture-baseddevice control, user interface control and adaptation,automatic generation of image metadata, more sophis-ticatedimaging algorithms, etc. Various sensor applica-tionscan be created using a generic software library thatconsists of routines to compute the various abstractionlevels of context.Silicon MicrophoneEven the introduction of silicon MEMS microphones[63, 64] into mobile devices has happened much slowerthan anticipated, the silicon MEMS microphones haveclear benefits in comparison to, e.g., electret condensermicrophones. The silicon microphones are smaller. Theyare surface mountable through a standard reflow assem-blyprocess. It is easier to protect them against EM andRF interferences. They own better linearity and smallerdevice-to-device variances in their design parameters.Furthermore, their dependence on temperature andhumidity is lower.These benefits are clear in the mobile device applica-tions.However, replacement of an existing technologyalways takes a long time. The existing technologies havetheir cost advantages, operational supplier chains, theassembly of existing components has been verified in largevolumes, and typically their characteristics fulfill most ofthe application requirements. In order to be successful anynew technology needs to bring some unique advantage thatmakes a difference to the end user of the product.Table 1 Sensors and sensor applications in mobile devicesSensor Sports Gaming Gestures UI Metadata ImagingAccelerometer (3 axis) M M M M I NAngular rate sensor I N I I MMagnetometer M N NGPS I N MBarometric pressure M NTemperature I N IHumidity N N N(M Must. I Important. N Nice to have.) 20. OverviewxxvIn the case of silicon MEMS microphones the addedvalue became primarily not from the tangible added value tothe end user in the first place. The benefits were related ton the manufacturing solutions, and the possibility to usethe reflow processn simpler testing procedures in productionn easier implementation into device mechanicsThe capability to integrate the silicon MEMS micro-phonemore easily with the CMOS electronics makesa real difference. A compact digital microphone mod-uleand even a single chip implementation are recentlyshown to be feasible by Akustica and other manufactur-ers.Even the cost of such a highly integrated device canbe a challenge in consumer electronics, the integrateddigital microphones enable multimicrophone arrays thatcan be used for spacial filtering and directional control.The active noise cancellation algorithms are based onmultiple microphones. The digital microphones can befreely placed far from each other, owing to the digitaloutput signals that are resistant to interferences.As the natural language is becoming a more importantway to interact with digital devices, applications andservices, these novel features and intelligences in theoverall audio system are drivers for high quality MEMSmicrophones with integrated mixed signal electronics.Towards Modular Architectures in ConsumerProductsThe requirements for the MEMS-based technologies in theconsumer electronics can be contradictory. There is a cleartendency towards modularity; the new functionality shouldbe easy to implement in the devices. On the other hand,the large volumes create severe cost constraints. MEMSproducts with different levels of integration and complex-ityare needed, e.g., sensors varying from simple indicatorsto integrated complex intelligent wireless sensors.Figure 9a presents a possible configuration of an intel-ligentsensor module for a consumer product. The typicalfeatures of such an implementation [65] are that the sen-sorsand their primary signal conditioning circuitry are inte-gratedinto the same module. However, the system of Fig. 9has several other interesting features. An integrated lowpower DSP core and a specific hardware accelerator areused for sensor signal processing. The feedback to the actu-atorscontrolled by the sensor signals is computed locally tominimise the control loop delay. The efficient power man-agementcircuitry is used to control the various sleep andactive states of the device. The regulation of MEMS con-trolvoltages and the system clock are integrated into thesystem. Optionally, a general purpose signal processor canbe added for more complex computational tasks, such as,the asynchronous communication with the host processor.The driver for such a high level of integration is theautonomous, energy efficient sensing and signal process-ing.In many cases, continuous measurements are needed.The modular implementation and careful design of theinternal power management of the sensor module areessential. Various wake-up mechanisms, e.g., based ona defined signal threshold or an interrupt from the hostprocessor, can be used. Only the minimal necessary func-tionalityof the system is powered at any time.Fig 9 l Architecture of an autonomous smart sensor module. (a) Sensor module that can be integrated via asynchronous digitalcommunication interface. (b) Wireless autonomous device with its own energy sources and storage. 21. OverviewxxviThe high signal abstraction level in the system inter-faceof the module enables easier integration to the endproduct. The processing and recording of sensor signalsand the recognition of the motion patterns or the con-textcan be performed by the energy optimized sensormodule. These high abstraction states or their recordedtime sequences can be requested by the host processorapplications. In general, this kind of service orientedarchitectures (SOAs) are becoming more common inthe distributed information technologies [66] but canalso be applied to embedded devices [67].The modular implementation opens a new opportu-nityfor MEMS devices. The low cost and miniaturizedintegration of a system clock into the module, as illus-tratedin Fig. 9, is a challenge using a separate Quartzcrystal. The MEMS reference oscillators based on sili-conresonators are a very potential solution. Currently,the quality of the MEMS-based reference oscillators inthe 10 MHz range are becoming feasible.The same type of modular architecture can be appliedto other electronics modules: mass storage, projectiondisplay, radio modem, etc. The modular implementa-tionwill open new possibilities for adding functionalityto consumer products. There are several initiatives todefine the low power scalable digital interfaces, such as,the USB and the MIPI consortia [68, 69].Ubiquitous Sensing, Computingand CommunicationMerged Physical and Digital WorldsThe capability to add an index and a digital identity tosmaller physical items, such as sales packages and con-sumergoods, will enable more efficient logistics andquality control from manufacturers to retailers. Thesecommercial solutions will create an information platformthat also enables the consumers to get deeper knowledgeof their purchased goods. We are talking about the firststeps towards the Internet of Things that is a concept ofconnecting different physical objects to the informationnetworks [70]. These concepts extend towards possibili-tiesto have an Internet address or an URL embedded inthe physical objects and thus a possibility to link theminto the information networks.The next possible phase of this development hasmany names [7174]: Ambient Intelligence, PervasiveComputing, Ubiquitous Computing (see Fig. 7). Thenetworkeddevices embedded in our physical environ-mentprovide sensing, computing and communicationservices that can be accessed locally. When this local-izedinformation is connected to the global informationnetworks that are capable of data aggregation, we willlive in a responsive environment that knows our pref-erenceand adapts to serve our particular needs. Themicrosystems of sensors, processors and radios areessential enablers of these intelligent environments.The safety and comfort have been the key drivers ofautomotive sensor applications. The adaptive and intel-ligentuser interface is the driver of consumer applica-tions.The key drivers for the Internet of Things andthe Ambient Intelligence will be related to the next bigchallenges of human societies. The challenge of energyproduction, the scarce natural resources and the age-ingglobal population are creating a need to optimizethe human economical processes. The increasing urbanpopulation creates more severe issues with the securityand safety of persons and their properties. The environ-mentalchallenges of pollution and changes in naturalecosystems will require increasing human care.Wireless Sensing and Sensor NetworksThe wireless sensor networks [7578] are enablers forthe Internet of Things and the future ambient intelli-gence.The sensor networks can be used for optimizingthe logistics and transport; the possibilities to localizeand to measure the condition of transported goods canbe used to optimize logistics cost and energy consump-tion.The safety and security can be increased by moreefficient sensor networks.The wireless sensor networks will enable more precisemeasurements and denser grids for monitoring of ourchemical environment and the atmospheric, hydrologicaland seismic processes. The building automation and themonitoring of the structural integrity will improve theenergy efficiency, the safety of the urban infrastructuresand the comfort of living. The solutions for assisted livingof elderly or handicapped people can be based on sensornetworks embedded in their home environment.The intelligence and computing in a wireless sensornetwork can be distributed in various ways [78, 79].In an optimised wireless sensor network, some level ofdata aggregation is typically calculated in each node inorder to reduce the energy consumption related to thecommunication. In addition, the distance of the sensornodes is optimized with respect to the necessary trans-missionpower. The very lower power operation of asensor network requires some complexity in the com-municationprotocols and thus signal processing capa-bilities.A multitude of possible wireless protocols havebeen developed for sensors and sensor networks.Table 2 summarizes the key figures of merit of themost important initiatives of wireless sensor radios, theBluetooth, Zigbee and the Near Field Communication 22. Overviewxxvii(NFC) standards. These standards have not been devel-opedand optimized for actual multi-hop sensor networkapplications. The basic concept of these radios is relatedto connecting various sensors into a host device, such as,a mobile phone, that can be a gateway into the informa-tionnetworks [80, 81].A wireless sensor consists typically of a radio, a micro-processor,a small memory, and an energy source in onesingle robust package. Figure 1.9b presents a possible archi-tectureof wireless sensor that has specific requirementsrelated to the radio communication and autonomousoperation: extremely low power consumption enablingenergy autonomy, capability to wake-up the system by anexternal sensor signal or an external radio (i.e., a wake-upradio [86]), and an efficient control of the measurementand signal processing duty cycles. Furthermore, the wire-lesssensor nodes need to be easy to deploy, self-configur-ing,extremely robust and fault tolerant.The challenges in developing the energy solutionsfor the ambient intelligent systems requires new think-ingand new technologies. Today business models arestill missing, and various societal issues, such as, privacyand security in these novel networks, need to be solvedbefore any broad deployment.Mobile Phone as a SensorAs discussed before, soon 90% of the global human pop-ulationwill have mobile coverage. In some years thesedevices have become also sensors and computers thatare inherently connected to the global information net-work.The mobile devices can have several roles in thecontext of ambient intelligence and sensor networks.The mobile device is already today a user interfacetowards the global Internet based services and digitalcontent, and the user interfaces of the mobile deviceswill have improved capabilities for this multimodalinformation. Secondly, based on the efficient radio solu-tions(see Table 2) the mobile devices are also becominga user interface to access the sensors and other devicesin the local environments. Figure 10 presents the para-digmof a mobile device as a trusted personal user inter-facetowards the local and global information.However, the most important new capability is touse the mobile device as a gateway between the localnetworked environment and the global informationnetworks. The mobile devices all over the world cansimultaneously collect information and feed it into com-putingservices that can aggregate the information intomeaningful form for the end users. Powerful data min-ingand search algorithms [87] can be used to extractlocal information, local history and predictions. Possibleexamples are pollution and traffic monitoring where theinformation of individual devices can be aggregated intomaps and future projections that are meaningful forthe people joining to these services. The mobile solu-tionsfor remote health care and continuous monitor-ingof patients are another clear example of this kindof application. The privacy of the individuals connectedto these services is an essential feature of the networkoperation and the infrastructure.The mobile device itself can be a sensor node of asensor network. The multiple integrated sensors andtheir context and location awareness create as such theinformation that is meaningful to be aggregated intoknowledge. The information that can be retrieved fromthe behavior and the preferences of the consumers isalways valuable for service providers. The questionsare, with whom the consumers are willing to share theirpreferences and what do they win by doing so? Andwhat will be the future business models?Table 2 Comparison of the most important existing sensor radiosFigure of merit Bluetooth [82] Bluetooth LE [83] Zigbee [84] NFC (RFID) [85]Range 10 m 10 m 50 m 5 cmPower Ref index 1 0.1-0.5 0.6 4 reader/0 tagData rate 1 Mbps 1 Mbps 0.25 Mbps 0.4 MbpsPairing speed Slow Fast Fast InherentSecurity Authentication Access approval n/a n/aSilicon size Medium Tiny Small Very smallTyp use case Accessories Sensors Automation Identification 23. OverviewxxviiiFuture of MEMS TechnologiesIs Silicon Enough?Silicon is a nearly perfect mechanical material and ena-blesthe micromachining of very precise structures. Thereare also some limitations related to the cost and the ulti-matematerial properties. In microfluidics and opticalapplications, e.g., in diffractive optics, the use of polymersubstrates and structures is much more inexpensive inlarge volumes. The sophisticated technologies for rep-licatingthe microstructures into polymer surfaces havebeen developed [8891]. The basic idea of the processis to fabricate the primary mechanical structure into thesurface of the silicon wafer, deposit a metal film on top ofthe silicon structure and electroplate a thick metal layer(for example, a nickel layer). When the thick metal layeris removed from the surface of the silicon wafer, we havea mold to replicate the structure on a polymer surface,for example, using injection molding or hot embossing.In RF applications the conductivity of even the veryhighly doped silicon or polysilicon is not sufficient fora high enough quality factor for tunable RF capacitors,switches or inductors. The use of metal films has beena way to increase performance of the micromechanicalcomponents. The use of free standing metal thin filmsfor tunable or switchable structures is shown to bepossible. The behavior of metal thin films differs frombulk metals; for example, inelastic deformations aresmaller [92, 93].The novel nanomaterials will create a possible impactin the future MEMS. The use of carbon nanotubes aspiezoelectric transducers has been demonstrated withgood results [9499]. The use of bottom up grown sili-connanowires for resonators has been studied [100-102]. Nanotechnologies will create new materialsolutions for MEMS, and possibly some new nanoscalemechanical structures, so called NEMS structures, willbecome commercially feasible some day.Figure 11 illustrates a concept of a future consumerdevice based on polymer electronics [103], stretchableelectronics [104] and new functional surface materials[105, 106]. The key attributes of such a future deviceare transformability, compliancy in terms of controlla-bleflexibility and stretchability, extreme thinness andtransparency. The integration of functionality will bebased on reel-to-real assembly [107] and printing ofinterconnects [16] together with many active and pas-siveprinted components [108, 109]. This kind of deviceis still very far in the future but the first steps towardsthe novel integration solutions will be taken within thecoming years based on printed electronics. What are theimplications to the MEMS module packaging?Platform for Nanoscienceand NanotechnologiesThe MEMS has also created capabilities for the probingand manipulation of matter in the nanoscale. The atomicforce microscopy based on micromechanical cantileversand tips is one of the key methods for scanning, imagingand measuring nanoscale objects. The micromechani-calprobes can be used for accessing nanoscale systemsand their dynamical properties. The micromechanicalsystems will play a significant role in developing thenanoscale electronics, functional nanomaterials and sur-facestructures.Fig 10 l Mobile phone as a gateway between local intelligent environment and global digital services and content. 24. OverviewxxixThe explosion of digital content in terms of images,music and videos creates an increasing need for highdensity, low power and intelligent mass storage systems.The magnetic hard disks will not scale to the memorydensities that would fulfill these requirements.The micromechanical cantilever array has already beendeveloped for nanoscale mass storage concept. Severalcompanies, such as, IBM, HP, ST Microelectronics andSeagate, have been working for a concept called probestorage [110, 111]. The concept is based on reading,writing and erasing information on the surface of a poly-merfilm, metal film or a magnetic film using a microelec-tromechanicalcantilever and a micromachined tip.The IBM Millipede [112] has a capability to read,write and erase dots on the surface of the polymer filmwith the pit resolution of 20 nm. The micromachinedsystem is relatively complex with the array of cantilev-ersand the actuators to move the plate hosting the pol-ymerfilm. However, the manufacturing of the MEMSsystem is feasible today; the challenge of the probememory technologies is the stability of the nanostruc-turesused for the memory.ConclusionsAfter over 30 years of development the silicon micro-mechanicshas become a major established industry ofits own. The applications in ink jet printer nozzles andautomotive sensors had the sufficient momentum todevelop technologies that are now applicable to con-sumerproducts in large volumes. The requirements ofthe consumer products have pushed the manufactur-ersto invent solutions for extreme miniaturization ofMEMS devices and their packages. Very low power andlow voltage sensor electronics exist as well.The driver for automotive sensors was the safety andcomfort of the vehicles. The consumer electronics createdsensor applications related to the more sophisticated inter-actionbetween the human and the different intelligentdevices. The replacement of existing technologies withpurely technical arguments never creates an immediatemarket pull. The integration of new functionality in costoptimized consumer products depends on the real valueand novelty to the end user. Understanding of the completebusiness case and the added value related to all the stake-holdersis essential for MEMS component manufacturers.The business models of the consumer electronics arechanging as the strong bundling of devices with servicesand content is becoming a necessity. The new businessmodels will require increasingly fast response time to bringnew products to the market. Modular solutions to imple-mentnew functionality, such as, tunable RF componentsfor the cognitive radio, low cost integrated reference oscil-latorsfor modular electronics, three axis accelerometersfor motion pattern recognition and digital silicon micro-phonesfor advanced audio systems, are surely needed.The ramping up and down of the production will need tohappen very fast because the volumes of particular endproducts are going to be very difficult to estimate.The global challengesscarce energy and other natu-ralresources, environmental and heath care challenges,growing urban populationwill require more efficientsustainable economics and new ways to guarantee thesafety, security and well being of people globally. Sensornetworks and ambient intelligence will be enablers of ourfuture sustainable way of living, and the microelectro-mechanicalsystems together with arising nanotechnolo-giesare important to make this global implementation ofsensing, computing and communication possible.AcknowledgementsWe would like to acknowledge the numerous col-leaguesat Nokia Research Center, especially, VladimirErmolov, Kari Hjelt, Antti Lappetelinen, JukkaSalminen and Henry Tirri, with whom I have workedFig 11 l A transformable and wearable device, based onstretchable electronics. Industrial design by Jaakko Saunamki,Nokia [113]. 25. Overviewxxxtowards microsystems, sensors and their applications inthe mobile industry. In addition, I want to express mygratitude to Heikki Kuisma, Markku Tilli and BenedettoVigna for sharing their deep insights of the MEMSindustry.This chapter is not meant to be a thorough review.We are aware of the very extensive research in variousMEMS technologies and their applications. 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Drig, W. Hberle,M. Lutwyche, H. Rothuizen, R.Stutz, R. Widmer, G. Binnig,Ultrahigh density, high-data-rateNEMS-based AFM data storagesystem, J. Microelectron. Eng. 46(1999) 1117.113. T. Ryhnen, M. Uusitalo, O. Ikkala,A. Krkkainen, Nanotechnologies forFuture Mobile Devices, CambridgeUniversity Press, 2010. 28. Chapter OneProperties of Silicon1.1 Properties of SiliconSilicon is an abundant element found in the Earths crust in various compounds. Semiconductor and MEMS applications use more than 20000 tons/year (2008) of high-purity silicon. Today most of the silicon used is either N- or P-type, doped with antimony, arsenic, phosphorus (N-type) or boron (P-type); the dopant concentration ranges between 1013 and 1020 dopant atoms/cm3 Si. Intrinsic (no intentional doping) or very slightly doped high resistivity silicon above 1 k cm is used in small amounts. Statistics pertaining to silicon can be found, for example, in the US Geological Survey 2006 Minerals Yearbook [1].Quartz , or silicon dioxide, is the most common starting raw material for purifi ed silicon for semiconductor and sensor applications, and the Siemens process is the most commonly used in semiconductor-grade silicon production. In the classical Siemens process, metallurgical- grade silicon, made first in an electric arc furnace by reducing quartz with coke, is turned to silicon-hydrogenchloride compounds in fl uidized bed reactors and those compounds are converted to TCS (trichlorosilane, or SiHCl3). TCS is purified by distillation, during which concentrations of impurity compounds having either a lower or higher temperature of volatility than TCS(38.4 C) are reduced. Purifi ed TCS is fed together with hydrogen into a reactor. In the reactor TCS is decomposing onto hot silicon fi laments forming a pure poly- silicon rod. This rod is then used as a raw material for crystal growth, either in rod form or in crushed pieces. There are alternative, newer techniques for purifying silicon; one variant is similar to the Siemens processMarkku Tilli and Atte Haapalinna Okmetic Oyj, Vantaa, Finland 1but uses silane (SiH4) as a precursor. In some processes, heated silicon fi laments are replaced by silicon particles fl oating in fl uidized bed reactors; these processes yield granular polysilicon.The result of the purifi cation process is high-purity silicon containing very small amounts of foreign dissolved atoms. If the single crystals are manufactured by a Czochralski (CZ) technique, which is most commonly used ( 90% of the crystals), the impurity level increases, as the growth is made from a quartz crucible having some impurities. The result is, however, still acceptable. Typically, most of the contamination of the silicon takes place during actual device manufacturing. Of impurities, metals are generally harmful, with rare exceptions, and their concentration should be as low as possible, typically1012 at/cm3 Si. Oxygen coming from the CZ-crystal growth step as an impurity has a dual role: it has benefi cial effects (strengthening of the silicon la