Micro Electronic and Mechanical Systems Micro Electronic and Mechanical Systems Edited by Kenichi Takahata I-Tech IV Published by In-Teh In-Teh Olajnica 19/2, 32000 Vukovar, Croatia Abstracting and non-profit use of the material is permitted with credit to the source Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher No responsibility is accepted for the accuracy of information contained in the published articles Publisher assumes no responsibility liability for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained inside After this work has been published by the In-Teh, authors have the right to republish it, in whole or part, in any publication of which they are an author or editor, and the make other personal use of the work © 2009 In-teh www.in-teh.org Additional copies can be obtained from: publication@intechweb.org First published December 2009 Printed in India Technical Editor: Teodora Smiljanic Micro Electronic and Mechanical Systems, Edited by Kenichi Takahata p cm ISBN 978-953-307-027-8 Preface The miniaturization and performance improvement in semiconductor devices and integrated circuits (ICs) are expected to continue through leveraging of nanotechnologies and nanomaterials This evolution should accelerate the System-on-a-Chip (SoC) trend, i.e., singlechip integration of multifunctional, mixed-signal electronic components, toward realizing embedded nanoelectronic systems In parallel with advances in electronics, we are witnessing the rise of micro-electro-mechanical systems (MEMS), with rapidly growing commercial opportunities and markets extending to a broader range of industrial sectors on a global scale The emergence of MEMS is primarily attributed to the establishment of sophisticated IC manufacturing techniques and processes that served as a foundation for realizing many innovative silicon-based micromachining technologies Advances in this area have brought about a revolution in mechanical engineering, enabling the miniaturization and system-level integration of mechanical structures and devices with ICs on a chip for MEMS fabrication With miniaturized sensors and actuators, MEMS provide us with the ability to interact with micro-scale environments with non-electrical/-electronic parameters, found in the mechanical, optical, chemical, biological, and other domains This exceptional ability has led to their application in fields ranging from implantable medical sensors to video game controllers There is no doubt that continued development of MEMS and microsystems with electromechanical functionalities will extend their contribution to society, in parallel with the evolution of IC technologies This book discusses key aspects of these technology areas, organized in twenty-seven chapters that present the latest research developments in micro electronic and mechanical systems The book addresses a wide range of fundamental and practical issues related to MEMS, advanced metal-oxide-semiconductor (MOS) and complementary MOS (CMOS) devices, SoC technology, integrated circuit testing and verification, and other important topics in the field Several chapters cover state-of-the-art microfabrication techniques and materials as enabling technologies for the microsystems Reliability issues concerning both electronic and mechanical aspects of these devices and systems are also addressed in various chapters This book is the result of contributions from many researchers worldwide I would like to thank the authors for their kind cooperation and efforts to provide their most up-to-date research results A special thanks goes to the IN-TECH team for their dedicated work in making this book possible November 2009 Editor Kenichi Takahata Canada Research Chair University of British Columbia, Vancouver, Canada Contents Preface Membrane Micro Emboss (MeME) Process for 3-D Membrane Microdevice V 001 Masashi Ikeuchi and Koji Ikuta A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications 015 Chris Gould and Noel Shammas Micro Power Generation from Micro Fuel Cell Combined with Micro Methanol Reformer 025 Taegyu Kim Non-contact Measurement of Thickness Uniformity of Chemically Etched Si Membranes by Fiber-Optic Low-Coherence Interferometry 051 Zoran Djinovic, Milos Tomic, Lazo Manojlovic, Zarko Lazic and Milce Smiljanic Nanomembrane: A New MEMS/NEMS Building Block 061 Jovan Matovic and Zoran Jakšić Nanomembrane-Enabled MEMS Sensors: Case of Plasmonic Devices for Chemical and Biological Sensing 085 Zoran Jakšić and Jovan Matovic Specific Serum-free Conditions can Differentiate Mouse Embryonic Stem Cells into Osteochondrogenic and Myogenic Progenitors 107 Hidetoshi Sakurai, Yuta Inami, Naomi Nishio, Sachiko Ito, Toru Yosikai, Haruhiko Suzuki and Ken-Ichi Isobe Micromanipulation with Haptic Interface 113 Shahzad Khan, Hans H Langen and Asif Sabanovic Fabrication of High Aspect Ratio Microcoils for Electromagnetic Actuators Daiji Noda, Masaru Setomoto and Tadashi Hattori 125 VIII 10 Micro-Electro-Discharge Machining Technologies for MEMS 143 Kenichi Takahata 11 Mechanical Properties of MEMS Materials 165 Zdravko Stanimirović and Ivanka Stanimirović 12 Reliability of MEMS 177 Ivanka Stanimirović and Zdravko Stanimirović 13 Numerical Simulation of Plasma-Chemical Processing Semiconductors 185 Yurii N Grigoryev and Aleksey G Gorobchuk 14 Experimental Studies on Doped and Co-Doped ZnO Thin Films Prepared by RF Diode Sputtering 211 Krasimira Shtereva, Vladimir Tvarozek, Pavel Sutta, Jaroslav Kovac and Ivan Novotny 15 Self-Aligned π-Shaped Source/Drain Ultrathin SOI MOSFETs 235 Yi-Chuen Eng and Jyi-Tsong Lin 16 Accurate LDMOS Model Extraction using DC, CV and Small Signal S Parameters Measurements for Reliability Issues 245 Mouna Chetibi-Riah, Mohamed Masmoudi, Hichame Maanane, Jérôme Marcon, Karine Mourgues, Mohamed Ketata and Philippe Eudeline 17 Comparative Analysis of High Frequency Characteristics of DDR and DAR IMPATT Diodes 267 Alexander Zemliak 18 Ohmic Contacts for High Power and High Temperature Microelectronics 293 Lilyana Kolaklieva and Roumen Kakanakov 19 Implications of Negative Bias Temperature Instability in Power MOS Transistors 319 Danijel Danković, Ivica Manić, Snežana Djorić-Veljković, Vojkan Davidović, Snežana Golubović and Ninoslav Stojadinović 20 Radiation Hardness of Semiconductor Programmable Memories and Over-voltage Protection Components 343 Boris Lončar, Miloš Vujisić, Koviljka Stanković and Predrag Osmokrović 21 ANN Application to Modelling of the D/A and A/D Interface for Mixedmode Behavioural Simulation Miona Andrejević Stošović and Vančo Litovski 369 IX 22 Electronic Circuits Diagnosis using Artificial Neural Networks 385 Miona Andrejević Stošović and Vančo Litovski 23 Integration Verification in System on Chips Using Formal Techniques 405 Subir K Roy 24 Test Generation based on CLP 431 Giuseppe Di Guglielmo, Franco Fummi, Cristina Marconcini and Graziano Pravadelli 25 New Concepts of Asynchronous Circuits Worst-case Delay and Yield Estimation 455 Miljana Milić and Vančo Litovski 26 Neuron Network Applied to Video Encoder 477 Branko Markoski, Jovan etrajčić, Jasna Mihailović, Branko Petrevski, Miroslava Petrevski, Borislav Obradović, Zoran Milošević, Zdravko Ivanković, Dobrivoje Martinov and Dušanka Tesanović 27 Single Photon Eigen-Problem with Complex Internal Dynamics Nenad V Delić, Jovan P Šetrajčić, Dragoljub Lj Mirjanić, Zdravko Ivanković, Dobrivoje Martinov, Snežana Jokić, Ivana Petrevska–Đukić, Dušanka Tešanović and Svetlana Pelemiš 493 Membrane Micro Emboss (MeME) Process for 3-D Membrane Microdevice 11 The hysteresis of the P-θ curve is apparently caused by the buckling behavior of the folded chambers and air trapped in the microtube (Fig 11b) The buckling behavior can be improved by modifying the folding angle and pattern of the chambers, and the trapping of air in the system can be prevented by assembling the catheter in vacuo Most importantly, little increase in the diameter of the bellows was observed during bending due to the microchannels inserted between the microchambers This leads to a safer and smoother insertion of the catheter at bifurcations For in vitro demonstration of the active catheter, a small blood vessel model made of silicone was fabricated using the lost-wax method The model consists of narrow blood vessels of φ ~ mm into which conventional active catheters could not be inserted The pressure-driven microactive catheter was actuated and inserted into the narrow vessels (Fig 12a) At the bifurcation, the catheter was bent slightly to the left from the straight position (Fig 12b,c) by supplying saline water from the syringe, turned to the desired direction, and then successfully introduced into the target aneurysm (Fig.12d) (a) (b) tip of the catheter vessel wall target aneurysm (c) (d) Fig 12 Video frames showing insertion of the catheter into a 3-D vascular model 4.4 Summary In this section, the pressure-driven microactive catheter was proposed and its development by the MeME-X process was described The pressure-driven microactive catheter, with its extremely small size and high safety, should promote the application of catheterization in 12 Micro Electronic and Mechanical Systems complex intravascular surgery, which is at present not possible with conventional surgical tools For further improvements, microchannels for drug delivery and/or blood sampling could be attached to the bellows This can be achieved by simply adding microchannel templates on the master mold of the bellows Furthermore, the nonelectrical actuation mechanism of this catheter, which has a 3-D membrane microstructure, can be widely extended to safe medical tools and microactuators in the microrobotics field Conclusions and perspectives In this chapter, the concept of 3-D membrane microdevices was introduced and the development of the MeME process was described To utilize its characteristics, the concept was applied to actual devices in two different fields First, focusing on the efficient transfer of substances and heat in 3-D membrane microchannels, an artificial capillary network chip was developed for tissue engineering purposes Second, utilizing the high elastic deformability of 3-D membrane microstructures, hollow bellows composed of folded microchambers and microchannels were developed to realize a pressure-driven microactive catheter Biological organisms are fundamentally characterized by a 3-D membrane microstructure From intracellular organelles to vascular networks, from plant leaves to insect wings, the exquisite architectures prevalent in nature greatly inspires us to develop novel micro/nanodevices The study of 3-D membrane microdevices has just emerged out of the proof-of-concept stage To further expand the scope of applications of 3-D membrane microdevices, our laboratory is actively engaged in the exploration of a variety of materials applicable to the MeME process and improvement of the resolutions of the MeME process toward the nanometer scale With its unique advantages, the 3-D membrane microdevice technology should contribute to drug delivery, tissue engineering, electric power generation, smart skin development and many other fields in the near future References Bryant, S & Anseth, K (2002) Hydrogel properties influence ECM production by chondrocytes photoencapsulated in poly(ethylene glycol) hydrogels Journal of Biomedical Materials Research, Vol 59, Issue 1, 63-72 Bunch, T.J., Bruce, G.K., Mahapatra S., Johnson S.B., Miller D.V., Sarabanda A.V., Milton M.A & Packer D.L (2005) Mechanisms of phrenic nerve injury during radiofrequency ablation at the pulmonary vein orifice Journal of Cardiovascular Electrophysiology, Vol 16, Issue 12, 1318-1325 Fang, B.K., Ju, M.S & Lin, C.C.K (2007) A new approach to develop ionic polymer–metal composites (IPMC) actuator: Fabrication and control for active catheter systems Sensors and Actuators A, Vol 137, Issue 2, 321-329 Giselbrecht, S., Gietzelt, T., Gottwald, E., Trautmann, C., Truckenmüller, R., Weibezahn, K.F & Welle, A (2006) 3D tissue culture substrates produced by microthermoforming of pre-processed polymer films Biomedical Microdevices, Vol 8, Issue 3, 191-199 Membrane Micro Emboss (MeME) Process for 3-D Membrane Microdevice 13 Ikeuchi, M & Ikuta, K (2005), Fabrication of biodegradable membrane micro-channels for artificial blood capillary networks using membrane micro embossing (MeME) Transactions of JSMBE Vol 43, Issue 4, 646-652 Ikeuchi, M & Ikuta, K (2006,a) The membrane micro emboss (MeME) process for fabricating 3-D microfluidic device formed from thin polymer membrane Proc μTAS’06, pp 693-695, ISBN4-9903269-0-3-C3043, Tokyo, Nov 2006 Ikeuchi, M & Ikuta, K (2006,b) On-site size-selective particle sampling using mesoporous polymer membrane microfluidic device Proc μTAS’06, pp 1169-1171, ISBN49903269-0-3-C3043, Tokyo, Nov 2006 Ikeuchi, M & Ikuta, K (2008) Membrane micro emboss following excimer laser ablation (MeME-X) process for pressure-driven micro active catheter Proc MEMS’08, pp 62-65, ISBN978-1-4244-1792-6, Tucson, Jan 2008 Ikuta, K & Hirowatari, K (1993) Real three dimensional micro fabrication using stereo lithography and metal molding Proc MEMS’93, pp 42-47, ISBN0-7803-0957-X, Fort Lauderdale, Feb 1993 Ikuta, K., Ichikawa, H., Suzuki, K & Yamamoto, T (2003) Safety active catheter with multisegments driven by innovative hydro-pressure micro actuators Proc MEMS’03, pp 130-135, ISBN0-7803-7744-3, Kyoto, Jan 2003 King, K., Wang, C., Mofrad, M., Vacanti, J.P & Borenstein, J (2004) Biodegradable microfluidics Advanced Materials, Vol 16, 2007-2012 Konishi, S., Nokata, M., Jeong, O.C., Kusuda, S., Sakakibara, T., Kuwayama, M & Tsutsumi, H Pneumatic micro hand and miniaturized parallel link robot for micro manipulation robot system, Proc ICRA’06, pp 1036-1041, ISBN0-7803-9505-0, Orlando, May 2006 Liu, V & Bhatia, S (2002) Three-dimensional photopatterning of hydrogels containing living cells Biomedical Microdevices, Vol 4, Issue 4, 257-266 Liua, M.C., Hob, D & Tai, Y.C (2008) Monolithic fabrication of three-dimensional microfluidic networks for constructing cell culture array with an ”integrated combinatorial mixer Sensors and Actuators B, Vol 129, Issue 2, 826-833 Manecke, G.R., Brown, J.C Landau, A.A., Kapelanski, D.P., St Laurent, C.M & Auger, W.R (2002) An unusual case of pulmonary artery catheter malfunction Anesthesia Analgesia, Vol 95, 302-304 Mineta, T., Mitsui, T., Watanabe, Y., Kobayashi, S., Haga, Y & Esashi, M (2002) An active guide wire with shape memory alloy bending actuator fabricated by room temperature process Sensors and Actuators A, Vol 97-98, 632-637 Sekiya, S., Shimizu, T., Yamato, M., Kikuchi, A & Okano, T (2006) Bioengineered cardiac cell sheet grafts have intrinsic angiogenic potential Biochemical and Biophysical Research Communications, Vol 341, Issue 2, 573-82 Truckenmuller, R., Rummler, Z., Schaller, T & Schomburg, W.K (2002) Low-cost thermoforming of micro fluidic analysis chips Journal of Micromechanics and Microengineering, Vol 12, 375–379 14 Micro Electronic and Mechanical Systems Zhenga, J., Webstera, J.R., Mastrangelob, C.H., Ugazc, V.M., Burnsd M.A & Burkee, D.T (2007) Integrated plastic microfluidic device for ssDNA separation Sensors and Actuators B, Vol 125, Issue 1, 343-351 A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications Chris Gould and Noel Shammas Staffordshire University UK Introduction Thermoelectric technology can be used to generate a small amount of electrical power, typically in the µW or mW range, if a temperature difference is maintained between two terminals of a thermoelectric module Alternatively, a thermoelectric module can operate as a heat pump, providing heating or cooling of an object connected to one side of a thermoelectric module if a DC current is applied to the module’s input terminals This chapter reviews the development of microelectromechanical systems (MEMS) based thermoelectric devices suitable for micro-power generation, heating and cooling applications The chapter begins with a brief overview of thermoelectric technology, macrothermoelectric module construction and operation Micro-thermoelectric modules are introduced, and a review of recent developments in research, commercial development, and typical application of MEMS based micro-thermoelectric devices is made The chapter draws conclusions on the development and potential application of MEMS based thermoelectric devices suitable for thermoelectric cooling, heating and micro-power generation Overview of thermoelectric technology, module construction and operation 2.1 Overview of thermoelectric technology Thermoelectricity utilises the Seebeck, Peltier and Thomson effects that were first observed between 1821 and 1851 (Nolas et al, 2001) Practical thermoelectric devices emerged in the 1960’s and have developed significantly since then with a number of manufacturers now marketing thermoelectric modules for cooling, heating and power generation applications Thermoelectric power generation is mainly influenced by the Seebeck effect, with thermoelectric cooling and heating influenced predominantly by the Peltier effect The Thomson effect does not have a major influence although it should always be included in detailed calculations (Rowe, 2006) For power generation applications, a small amount of electrical power, typically in the µW or mW range, can be generated by a thermoelectric module if a temperature difference is maintained between two terminals of a thermoelectric module Alternatively, a thermoelectric module can operate as a heat pump, providing 16 Micro Electronic and Mechanical Systems heating or cooling of an object connected to one side of a thermoelectric module if a DC current is applied to the module’s input terminals The technology has achieved commercial success in mini-refrigeration, cooling and space-craft power applications, with the consumer market for mini-refrigerators and coolers currently the most successful commercial application (Hachiuma and Fukuda, 2007) Future developments in thermoelectric technology will include the need to reduce the size, and improve the performance, of current thermoelectric devices in order to address thermal problems in microelectronics, and create localised low-power energy sources for electronic systems 2.2 Standard thermoelectric module construction Standard thermoelectric modules are constructed from P-type and N-type thermo-elements, often referred to as thermoelectric couples, connected electrically in series and thermally in parallel Each couple is constructed from two ‘pellets’ of semiconductor material usually made from Bismuth Telluride One of these pellets is doped to create a P-type pellet, the other is doped to produce an N-type pellet The two pellets are physically linked together on one side, usually with a small strip of copper, and placed between two ceramic plates The ceramic plates perform two functions; they serve as a foundation on which to mount the thermo-element; and also electrically insulate the thermo-element (Riffat and Ma, 2003) A single couple of a thermoelectric module is shown below in Fig Fig A single couple of a thermoelectric module The thermo-element, or couple, is then connected electrically in series and thermally in parallel to other couples Standard thermoelectric modules typically contain a minimum of couples, rising to 127 couples for larger devices A schematic diagram of a thermoelectric module is shown in Fig Fig A schematic diagram of a thermoelectric module 2.3 Thermoelectric module configuration A thermoelectric module can cool or lower the temperature of an object, if the object is attached to the ‘cold’ side of the module, often referred to as ‘TC’, and DC electrical power is applied to the module’s terminals Heat from the object will be absorbed by the ‘cold’ side of the thermoelectric module, and transferred or ‘pumped’ through to the ‘hot’ side of the A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications 17 module ‘TH’ due to the Peltier effect Normally, the hot side of the module will be attached to a heat sink in order to reject this heat into the atmosphere A thermoelectric module operating as a thermoelectric cooler or heat-pump is shown below in Fig If the polarity of the DC current applied to the thermoelectric module terminals is now reversed, the module will heat the object connected to the cold side of the module, with the other side of the module now cooling down In this condition, the thermoelectric module is referred to as a thermoelectric heater Fig A thermoelectric module operating as a thermoelectric cooler or heat-pump A thermoelectric module can also be used to generate a small amount of electrical power, typically in the µW or mW range, if a temperature difference is maintained between both sides of the module Normally, one side of the module is attached to a heat source and is referred to as the ‘hot’ side or ‘TH’ The other side of the module is usually attached to a heat sink and is called the ‘cold’ side or ‘TC’ The heat sink is used to create a temperature difference between the cold and hot sides of the module If a resistive load (RL) is connected across the module’s output terminals, electrical power will be generated in the resistive load when a temperature difference exists between the hot and cold sides of the module, due to the Seebeck effect A thermoelectric module, operating as a thermoelectric power generator, is shown below in Fig Fig A thermoelectric module operating as a thermoelectric power generator 18 Micro Electronic and Mechanical Systems 2.4 Operation of standard thermoelectric modules Semiconductor theory can be used to describe the operation of thermoelectric devices In Fig 5, a single thermoelectric couple is connected to operate as a heat pump Fig A single thermoelectric couple connected as a heat pump When a DC voltage is applied to the module terminals, electrical current flows from the positive terminal of the supply voltage to the negative terminal This is shown as an anticlockwise current flow in the configuration shown in Fig The negative charge carriers, i.e the electrons, in the n-type bismuth telluride pellet are attracted by the positive pole of the supply voltage, and repelled by the negative potential Similarly, the positive charge carriers, i.e the holes, in the p-type material are attracted by the negative potential of the supply voltage, and repelled by the positive potential, and move in an opposite direction to the electron flow It is these charge carriers that actually transfer the heat from one side of the thermoelectric couple to the other side in the direction of charge carrier movement In the n-type pellet, the negatively charged electrons are the charge carriers and absorb heat from the ‘cold’ side of the thermoelectric couple and transfer or ‘pump’ this heat to the ‘hot’ side of the couple in a clock-wise direction Similarly, the positively charged carriers in the p-type pellet, the holes, absorb heat from the cold side of the couple and transfer this heat to the hot side of the couple in an anti-clockwise direction Practical thermoelectric modules are manufactured with several of these thermoelectric couples connected electrically in series and thermally in parallel Arranging the thermoelectric couples in this way allows the heat to be pumped in the same direction According to (Rowe, 2006), the energy efficiency of a thermoelectric device, operating in a cooling or refrigeration mode, is measured by its Coefficient of Performance (COP), found by: COP = Heat absorbed Electrical power input (1) For thermoelectric power generation, if a temperature difference is maintained between two sides of the module, thermal energy is moving through the n-type and p-type pellets As these pellets are electrically conductive, charge carries are transported by this heat This movement of heat and charge carriers creates an electrical voltage, called the Seebeck voltage If a resistive load is connected across the module’s output terminals, current will flow in the load and an electrical voltage will be generated A thermoelectric couple connected as a thermoelectric power generator is shown in Fig A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications 19 Fig A single thermoelectric couple connected as a thermoelectric power generator The efficiency of a thermoelectric module, operating as a power generator, can be found by: η = Energy supplied to the load Heat energy absorbed at the hot junction (2) In thermoelectricity, efficiency is normally expressed as a function of the temperature over which the device is operated, referred to as the dimensionless thermoelectric figure-of-merit ZT The thermoelectric figure of merit ZT can be found by: ZT = α 2σ λ (3) where α is the Seebeck coefficient, σ is the electrical conductivity, and λ is the total thermal conductivity (Sales, 2007) Thermoelectric phenomena are exhibited in almost all conducting materials, with the exception of superconductors below specific temperatures Materials which possess a ZT > 0.5 are usually regarded as thermoelectric materials (Rowe, 2006) The best thermoelectric materials used in commercial macro-thermoelectric devices, Bi2Te3-Sb2Te3 alloys, operating around room temperature, have typical values of α=225µV/K, σ = 105/Ωm, and λ = 1.5 W/mK, which results in ZT ≈ (Sales, 2007) Bismuth Telluride is the most common material used in standard thermoelectric modules, as it exhibits the most pronounced thermoelectric effect around room temperature Other material combinations are also used including; Alloys based on bismuth in combination with antimony, tellurium and selenium; lead telluride; and silicon germanium alloys (Rowe, 2006) 2.5 Development of micro-thermoelectric modules Standard thermoelectric modules range in size from x x mm3 to around 50 x 50 x 50 mm3 Although, in principle, the dimensions can be reduced further, the fabrication of conventional thermoelectric modules for power generation or heating and cooling applications is a bulk technology, and is incompatible with microelectronic fabrication processes (Volklein & Meier, 2006) The development of micro-thermoelectric devices that are compatible with standard microelectronic technology and manufacturing processes have the potential to enhance the performance of microelectronic systems, achieve significant 20 Micro Electronic and Mechanical Systems reductions in size, improve the performance of thermoelectric devices, and open up new areas of research and commercial application Until recently, thermoelectric devices have been confined to niche applications because of their relatively low conversion efficiency and thermoelectric figure-of-merit ZT when compared with other technologies (Riffat & Ma, 2003) For thermoelectric power generation, current thermoelectric efficiencies are between 5% to 10% (Nuwayhid et al, 2005), with a practical thermoelectric figure-of-merit ZT ~ For thermoelectric cooling and refrigeration, a COP of 0.5 is typical, which is lower than that achieved by conventional refrigeration techniques (Bass et al, 2004) According to (Stabler, 2006), since the early 1990’s, materials with ZT > have been discovered, and reports of ZT ~ are widely known today with evidence that higher values of ZT are possible (Vining, 2007) Improving the efficiency and thermoelectric figure-of-merit ZT, reducing the cost of thermoelectric devices, and the use of alternative materials that are more widely available are focus areas for current research activity However, thermoelectric technology does have several advantages over other technologies; For cooling or refrigeration applications, thermoelectric modules not use any chlorofluorocarbons or other materials that require periodic replenishment; they can achieve precise temperature control to within +/- 0.1°C; the same thermoelectric device can be used for heating or cooling and can cool to temperatures below 0°C (Riffat & Ma, 2003); the modules are electrically quite in operation and are relatively small in size and weight (Alaoui & Salameh, 2001); and not import dust or any other particles that could cause an electrical short circuit Thermoelectric MEMS devices 3.1 Overview There is an increasing amount of published research in support of developing MEMS based thermoelectric devices MEMS technology, combined with microelectronics and micromachining techniques, has been successfully and widely utilised in micro-sensor and micro-actuator applications, and there is significant commercial value in developing next generation thermoelectric devices for applications in power generation and integrated circuit cooling (Huang et al, 2007) Current micro-sensors and micro-actuators may also be based on thermal and thermoelectric principles, and use thin-film technology to achieve sensing and actuator functionality, with micromachining techniques to achieve device optimisation (Volklein & Meier, 2006) According to (Min, 2006), the development of thermoelectric devices compatible with standard semiconductor manufacturing processes has the potential to address many applications in microelectronics, with MEMS technology, along with nanotechnology, of significant interest to thermoelectric manufacturers and researchers It is anticipated that these technologies can be used to reduce the size, and improve the performance, of thermoelectric devices suitable for micro-power generation, heating and cooling applications Current MEMS based devices will also benefit from incorporating thermoelectric technology, for example where a MEMS based device has an electrical power consumption in the micro-watt range, this could potentially be supplied by thermoelectric devices (Huesgen et al, 2008), or where there is a need for temperature stabilisation of MEMS based microelectronic components and circuits (Li et al, 2003) 3.2 Emerging thermoelectric MEMS based devices Research into manufacturing a thermoelectric MEMS based device, using thin-film technology, has resulted in the proposal of different device structures; a vertical device A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications 21 structure; and a horizontal device structure (Min, 2006) Commercially available microthermoelectric devices, based on thin-film technology, have also recently started to emerge According to (Vining, 2007), two start-up companies have started to market thermoelectric devices based on thin-film technology One company has developed thermoelectric devices based on a MEMS like process that use a sputtering deposition method and Bi2Te3 related materials Another company has developed thermoelectric devices based on Bi2Te3-Sb2Te3 superlattice technology (Bottner et al, 2007; 2005; 2004; 2002) describe in some detail the development of thin-film MEMS like thermoelectric devices using a sputtering deposition technique Similarly, (Venkatsubramanian et al, 2007) and (Koester et al, 2006) describe the development of commercial thermoelectric devices using superlattice nanoscale materials The concept of MEMS like thermoelectric devices for cooling and micro-power generation applications, using a thin-film sputtering deposition technique, is to have a common vertical architecture of thermoelectric devices that use standard silicon/silicondioxide wafers as a substrate One of these wafers is used to create an n-type semiconductor using Bi2Te3 related materials, and another, separate wafer is used to create a p-type semiconductor The Bi2Te3 related material is deposited using a sputtering method, and after dry etching to create the device structure, the wafers are then sawn in order to create a single n-type and p-type die The n-type and p-type die are then soldered together to create a thermoelectric couple (Bottner, 2005) Another approach to creating micro-thermoelectric devices, that are compatible with modern semiconductor processing techniques, is the development of thin-film thermoelectric devices using nanoscale materials According to (Venkatsubramanian et al, 2007), significant developments have occurred in the last few years in the area of nanoscale thermoelectric materials using superlattices and self-assembled quantum dots Thin-film thermoelectric superlattices can be manufactured using Planar semiconductor device technology and are compatible with standard microelectronic processing and packaging tools There are a number of other examples of recently published work into MEMS based thermoelectric devices Although not an exhaustive list, a basic literature search will highlight activity by (Liu et al, 2007) on the integration of micro-thermoelectric devices into a silicon based light-emitting diode (LED) in order to stabilise the LED’s temperature; a planar multi-stage micro-thermoelectric device for cooling applications is presented by (Hwang et al, 2008); and the development of two micro-thermoelectric cooling devices, one based on a column-type telluride material, and another using a bridge-type polysilicon material and fabricated using MEMS based techniques by (Huang et al, 2008) 3.3 Future application of MEMS based thermoelectric devices MEMS based thermoelectric devices can be used in thermoelectric cooling, heating and micro-power generation applications The miniaturisation of thermoelectric modules, and the potentially higher thermoelectric performance that can be obtained, will also allow the development of new applications to emerge Micro-thermoelectric devices, fabricated in thin-film technology, have achieved sufficient miniaturisation to be integrated inside semiconductor packaged devices, rather than having to be mounted onto the outside of a semiconductor device, as is normal with a macrothermoelectric module As the semiconductor industry further reduces the size of transistors in integrated circuits, a trend is to fabricate more of the external circuitry inside the semiconductor packaging Removing the heat within these integrated circuits is becoming 22 Micro Electronic and Mechanical Systems more of a design challenge, and the miniaturisation of cooling devices can be used to solve these problems (Baliga, 2005) Historically, the motivation for using thermoelectric technology to cool microelectronic integrated circuits in the computer industry has been to increase their clock speed below ambient temperatures Increasing microprocessor performance has usually been accompanied by an increase in power and on-chip power density Both of these present a challenge in cooling microelectric devices (Mahajan et al, 2006) The computer industry may begin to approach the limit of forced-air cooled systems and will need to find alternative solutions (Sharp et al, 2006) Localised areas of high heat flux on microprocessors can produce ‘hot spots’ that limit their reliability and performance, and are becoming more severe as local power density and overall die power consumption increase Although a macro-thermoelectric module can be used in this application to provide cooling of the entire integrated circuit, microthermoelectric cooling of these localised regions of higher temperature or ‘hot spots’ may provide a better alternative According to (Snyder et al, 2006), embedded thin-film microthermoelectric devices is a promising approach to reduce the temperature of localised, high heat flux hot spots generated by modern microprocessors Micro-thermoelectric devices are also suitable for addressing other thermal management problems in microelectronics, and could be used to cool or stabilise the temperature of laser diodes, and provide a faster response time than conventional cooling techniques It may also be possible to integrate a micro-thermoelectric device inside the laser diode packaging (Baliga, 2005) Infra-red detectors, charge coupled devices (CCD), light-emitting diodes (LED) and other optoelectronic devices may also benefit from micro-thermoelectric cooling Thermoelectric micro-power generation and energy harvesting is also a target market for micro-thermoelectric devices (Bottner et al, 2007) believes that self-powered electronic sensor systems will require MEMS like manufacturing of micro-thermoelectric devices to meet the high volume requirements of this market Energy harvesting or scavenging systems can be designed to replace batteries in autonomous sensor and wireless systems, and it has been shown that body heat can be used as an energy source to power low-energy devices, including a wrist watch or hearing-aid (Weber at al, 2006) Micro-thermoelectric power generators could also be used to supply power to electronic devices for wearable electronics applications (Bottner, 2002) Conclusion Thermoelectric technology can be used in cooling, heating and micro-power generation applications Macro-thermoelectric devices have developed significantly since their introduction in the 1960’s, and have achieved commercial success in mini-refrigeration, cooling and space-craft power applications There is a requirement to reduce the size, and improve the performance, of current thermoelectric devices in order to address the need to solve thermal problems in microelectronics, and create localised low-power energy sources for electronic systems The miniaturisation and development of MEMS based thermoelectric devices has the potential to improve the performance of thermoelectric devices, and create new applications for the technology Thermoelectric MEMS based devices, based on thin-film technology, that are compatible with modern semiconductor processing techniques have now started to enter the market place Thermoelectric devices based on a MEMS like process that use a sputtering deposition method and Bi2Te3 related materials, and thermoelectric devices manufactured using Bi2Te3-Sb2Te3 superlattice technology are two recent entries into the thermoelectric market place A Review of Thermoelectric MEMS Devices for Micro-power Generation, Heating and Cooling Applications 23 It is anticipated that MEMS based thermoelectric devices can address the need to solve thermal problems in microelectronics, including the cooling of integrated circuits in the computer industry, and the cooling of optoelectronic and telecommunication devices Micro-thermoelectric power generation is also expected to supply low-level localised power to other electronic components and systems, and provide a power source for energy harvesting systems References Alaoui, C.; Salameh, Z.M (2001) Solid State Heater Cooler: Design and Evaluation, Proceedings LESCOPE, pp 139-145, 2001 Baliga, J (2005) Thermoelectric Cooling Prepares for the Small Stage Semiconductor International, October 2005, pp 42 Bass, J.C.; Allen, D.T ; Ghamaty, S ; Elsner, N.B (2004) New Technology for Thermoelectric Cooling, Proceedings of 20th IEEE Semiconductor Thermal Measurement and Management Symposium, pp 18-20, ISBN 0-7803-8363-X, March 2004 Bottner, H.; Nurnus, J.; Schubert, A.; Volkert, F (2007) New high density micro structured thermogenerators for stand alone sensor systems, Proceedings of 25th International Conference on Thermoelectrics (ICT2007), pp 306-309, ISBN 978-1-4244-2262-3, Jeju Island, June 2007 Bottner, H (2005) Micropelt Miniaturized Thermoelectric Devices: Small Size, High Cooling Power Densities, Short Response Time, Proceedings of 24th International Conference on Thermoelectrics (ICT2005), pp 1-8, ISBN 0-7803-9552-2, June 2005 Bottner, H.; Nurnus, J.; Gavrikov, A.; Kuhner, G.; Jagle, M.; Kunzel, C.; Eberhard, D.; Plescher, G.; 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– Macro to Nano, D.M Rowe (Ed.), pp 47-1 - 47–16, CRC Taylor & Francis Group, ISBN 0-8493-2264-2, Boca Raton, Florida Weber, J.; Potje-Kamloth, K.; Haase, F.; Detemple, F.; Volklein, F.; Doll, T (2006) Coin-sized coiled-up polymer foil thermoelectric power generator for wearable electronics Sensors and Actuators A, Vol 132, 2006, pp 325-330 Micro Power Generation from Micro Fuel Cell Combined with Micro Methanol Reformer Taegyu Kim Chosun University Republic of Korea Introduction 1.1 Background Thanks to the breakthroughs in microfabrication technologies, numerous concepts of microsystems including micro aerial vehicles, microbots, and nanosatellites have been proposed Contrary to ordinary electronic devices, these microsystems perform mechanical work and require the extended operation As their functions are getting complex and advanced, their energy consumption is also increasing exponentially In order to activate these microsystems, a high density power source in a small scale is required However, present portable devices still extract power from existing batteries The energy density of the current batteries is too low to support these microsystems (Holladay et al., 2004) Therefore, a new micro power source is essential for the successful development of new microsystems Various concepts for micro power generations have been introduced such as micro engines, micro gas turbines, thermoelectric generators combined with a micro combustor, and micro fuel cells All of these concepts extract energy from a chemical fuel that have energy density much greater than that of the existing batteries The first challenge to micro power source was the miniaturization of conventional heat engines However, the development of micro heat engine reached a deadlock due to the difficulties of microfabrication and realization of miniaturized fast moving components and kinematics‘ mechanism to generate power in micro scale Micro fuel cells have drawn attention as a primary candidate for a micro power source due to its distinctive merits that are absence of moving parts and high efficiencies The fuel cell is an electrochemical device that directly converts chemical energy to electric energy Due to its different energy conversion path, the fuel cell has high thermal efficiency compared to the heat engines The energy density of the fuel cell is higher than that of the existing batteries because it uses a chemical fuel such as hydrogen (Nguyen & Chan, 2006) There are several types of fuel cell as summarized in Table (O’Hayre et al., 2006), such as polymer electrolyte membrane fuel cell (PEMFC), phosphoric acid fuel cell (PAFC), alkaline fuel cell (AFC), molten carbon fuel cell (MCFC), and solid oxide fuel cell (SOFC) Of these fuel cells, PEMFC is suitable to a micro power device due to its low operating temperature and solid phase of electrolyte Direct methanol fuel cell (DMFC) is a kind of PEMFC except that it directly uses methanol instead of hydrogen as a fuel Formic acid, chemical hydrides, and other alcohols can be used as a direct fuel ... with standard microelectronic technology and manufacturing processes have the potential to enhance the performance of microelectronic systems, achieve significant 20 Micro Electronic and Mechanical. .. which we call “3-D membrane microdevices” (Fig.1b) Fig Schematics of (a) conventional “bulk“ microdevice and (b) “3-D membrane microdevice“ Micro Electronic and Mechanical Systems The purpose of this... Setomoto and Tadashi Hattori 12 5 VIII 10 Micro- Electro-Discharge Machining Technologies for MEMS 14 3 Kenichi Takahata 11 Mechanical Properties of MEMS Materials 16 5 Zdravko Stanimirović and Ivanka