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MEMS are rapidly moving from the research laboratory to the mar­ ketplace. Many market studies indicate not only a tremendous market potential of MEMS devices; year by year we see the actual market grow as the technology matures. In fact, these days, many large silicon foundries have a MEMS group exploring this promising technology, including such giants as INTEL and Motorola. Yet MEMS are fundamentally different from microelectronics. This means that companies with an established track record in these branches need to adapt their skills, whereas companies that want to enter the "miniaturization" market need to establish an entirely new set of capabil­ ities. The same can be said of engineers with classical training, who will also need to be educated toward their future professional activity in the MEMS field. Here are some questions that a company or technologist may ask: I have an existing product with miniaturization market poten­ tial. Which technology should I adopt? What are the manufacturing options available for miniaturiza­ tion? What are the qualitative differences? How do we maintainamarketleadforproductsbased onMEMS? Is there CAD support?Can we outsource manufacturing? Which skills in our current capability need only adaptation? What skills need to be added? Professors Jan Korvink and Oliver Paul have set out to answer these questions in a form that addresses the needs of companies, commercial practitioners, and technologists.



1. Microtransducer Operation

Rooted in mechanical, electrical, and chemical engineering and relying on physical insight, biological techniques, and materials science know-how, microelectromechanical systems (MEMS) engineering is a fundamentally interdisciplinary field. Its fascinating diversity often forces the research and development engineer to take into account a broader range of issues than in many classical, well-established technical disciplines. Simultaneously, the diversity creates the impression of a lack of unity, contrasting strongly with the classical disciplines of science and engineering. These are usually able to offer a core of thoughts stripped of unnecessary details, with well-established foundations and lines of thought, and representations accepted by the majority of researchers active in the field. More peripheral aspects of the disciplines can be built up from a solid basis of knowledge.
Oliver Paul

2. Material Properties: Measurement and Data

The performance of MEMS strongly depends on the properties of materials used not only as functional materials but also as structural materials. Therefore, the materials used for MEMS are required to possess many properties for applications with electrical, mechanical, thermal, magnetic, optical, and chemical requirements according to the specification of individual MEMS. Most of the MEMS use single-crystal silicon (SCS) as a substrate material because of its superior electrical and mechanical properties. The superiority of electrical properties of SCS has been widely accepted from the time they were first used as a substrate of large-scale integrations (LSIs). Furthermore, SCS has been used as a structural material for mechanical sensors such as piezoresistive pressure sensors and acceleration sensors since the early 1960s.[1] The great success of silicon-based mechanical sensors is attributable to the excellent mechanical properties of SCS as well as its well-established piezoresistive effect. A detailed account of mechanical sensors and their applications is given in Chapter 10.
Osamu Tabata, Toshiyuki Tsuchiya

3. MEMS and NEMS Simulation

Because MEMS and NEMS touch on so many application areas, the ideal simulation tool must follow suite and provide a vast range of coupled multidomain physical effects. In reality, no single tool caters to all the needs of the MEMS community. Hence, MEMS designers carry the burden tofind theappropriate toolsand strategy for their task. Fortunately, many alternative routes exist to achieve a given goal, but some insight is needed to get the most out of the simulators, especially if the target isto use simulation to achieve a design advantage. In this chapter we take a closer look at what is out there, and at the key features of each simulation method. We develop a simulation strategy to maximize the benefit from simulation, picking out a couple of key areas that are currently the focusof commercial applications. Toround off the chapter, we illustrate the ideas with some concrete applications from our own work.
Jan G. Korvink, Evgenii B. Rudnyi, Andreas Greiner, Zhenyu Liu

4. System-Level Simulation of Microsystems

Microelectromechanical systems require a multidisciplinary approach to design, including knowledge of fabrication technology, mechanics, electromechanics, and electronics. In the majority of cases, good MEMS design requires the evaluation of tradeoffs among the fabrication process, micromechanical topology, and sizing. Sensor interface circuits, signal conditioning, and feedback provide additional interactions that affect design choices. This chapter provides an introductory overview to the system-level simulation of microsystems in support of the design effort. Discussion is devoted to microelectromechanical structures with electronics. However, the general methods outlined here have equal applicability in other microsystems, such as microfluidic and micro-optical systems.
Gary K. Fedder

5. Thermal-Based Microsensors

Users require inexpensive, reliable sensors and actuators compatible with modern signal processing circuitry. This demand can be satisfied by microsensors and microactuators (microelectromechanical systems, MEMS), notably based on silicon with on-chip circuitry fabricated by using integrated circuit (IC) technology. A large number of such MEMS are based on thermal and thermoelectric principles. They use thermoresistive and thermoelectric thin films for sensor or actuator operation and the concepts of micromachining for device optimization. Indeed, a variety of thermal-based microsensors and microactuators fabricated by standard semiconductor technologies have been demonstrated. [14]
Friedemann Vöelklein

6. Photon Detectors

Current interest in hydrogenated amorphous silicon (a-Si:H) technology extends well beyond active-matrix liquid-crystal displays and solar cells; it stems from the variety of desired material and technological attributes.[13] The high optical absorption; low-temperature deposition (<300°C); high uniformity over large areas; few constraints on substrate size, material, or topology; standard integrated circuit lithography processes; and low capital equipment cost associated with the a-Si:H material offer a viable technological alternative for improved imaging of optical signals and high-energy radiation. Notable application areas include contact imaging for document scanning, digital copiers, and fax machines; color sensors/imaging; position/motion detection; and radiation detection/imaging of high-energy X-rays in biomedical applications, gamma-ray space telescopes, airport security systems, and nondestructive testing of the mechanical integrity of materials or structures.
Arokia Nathan, Karim S. Karim

7. Free-Space Optical MEMS

Microelectromechanical systems (MEMS) technology enables the creation of micro-optical elements that are inherently suited to cost-effective manufacturability and scalability because the processes are derived from the very mature semiconductor microfabrication industry. The inherent advantages of applying microelectronics technology to silicon micromechanical devices, including optical MEMS, were presented in 1982 by Petersen in the now-classic paper, “Silicon as a mechanical material.” [1] The ability to steer or direct light is a key requirement for free-space optical systems. In the 20 years since Petersen’s silicon scanner,[2] the field of optical MEMS has seen explosive growth.[3,4] In the 1980s and early 1990s, displays were the main driving force for the development of micromirror arrays. Portable digital displays are now commonplace, and head-mount displays are also commercially available. In the past decade, telecommunications have become the market driver for optical MEMS. The demand for routing ever-increasing Internet traffic through fiberoptic networks pushes the development of both digital and scanning micromirror systems for large port-count, all-optical switches. In the health care arena, scanning optical devices promise low-cost, optical cross-sectioning endoscopic microscopy for in vivo diagnostics.
Ming C. Wu, Pamela R. Patterson

8. Integrated Micro-Optics

Microelectromechanical systems (MEMS), as the name suggests, are predisposed to the use of electrons and mechanical movement. By adding optics to the palette of MEMS capabilities, the resultant micro-opto-electromechanical systems (MOEMS) or micro-opto-mechanical systems (MOMS) provide increased functionality while retaining the attractive features of MEMS technology. As the spectrum of potential applications can thus be substantially increased, research and development work on optical MEMS has recently seen considerable activity.[1,2]
Hans Zappe

9. Microsensors for Magnetic Fields

The devices and microsystems for measuring magnetic fields have the unique ability to reveal realities that cannot be perceived by the human senses. These transducers, which measure magnetic fields in a range not less than 15 to 16 orders of magnitude and are universal in their applications, are in continuous development.This chapter discusses recent progress in the most frequently used magnetic-field microsensors and MEMS, which are perfectly compatible with microelectronic technologies, most of which are silicon technologies. Up-to-date results are analyzed and abundant information is presented about the following topics: physical mechanisms of the origin of magnetosensitivity,device designs, sensor characteristics and the methods for their determination, biasing and inter-face circuits, the means for performance improvement and overcoming the basic transducer limitations, the most current and prospective applications, anddevelopment trends. Ample references torelevantliterature are included for all modifications of Hall effect devices (orthogonal and parallel field); micromagnetodiodes; magnetoresistors (including feromagnetic versions such as giant magnetoresistance elements); microsensors based on AniBv semiconductors; MOSFET, bipolar, CMOS, unijunction,and split-drain magnetotransistors and related devices; carrier-domain magnetometers; functional multisensorsfor the magnetic field, temperature, and light; 2-D and 3-D vector microsystems for the magnetic field; and magnetogradiometers and digital stochastic magnetotransducers.
Chavdar Roumenin

10. Mechanical Microsensors

Micromachining technologies have enabled a reduction in the size of mechanical sensors and an increase in their functionality to unprecedented levels of miniaturization. In many applications, precision-machined devices already existed when micromachined solutions entered the market. To replace established solutions, mechanical microsensors had to prove their competitiveness with respect to cost, size, and performance. Success stories were due to enhanced functionality, increased accuracy and performance, and higher reliability, at lower device, packaging, and mounting costs. In many applications, such as the automotive area, which was and still remains the strongest driver for MEMS-based sensor sys- tems, sensor cost is one of the most important factors deciding the success and the degree of market penetration of a new system. Starting with the replacement of older sensor generations established in already-existing systems like the airbag, mainly for cost reasons, mechanical microsensors are currently enabling completely new systems that critically rely on them. One well-known example is the Electronic Stability Program (ESP) or Vehicle Dynamics Control (VDC) system, which would not have been affordable and would not have reached today’s performance if it had to rely on classical mechanical sensor approaches.
Franz Laermer

11. Semiconductor-Based Chemical Microsensors

The detection of molecules or chemical compounds is a general analytical task in the efforts of chemists to obtain qualitative and/or quantitative time-and spatially resolved information on specific chemical components.[1] Examples of qualitative information include the presence or absence of certain odorant, toxic, carcinogenic, or hazardous compounds. Examples of quantitative information include concentrations, activities, or partial pressures of such specific compounds exceeding, e.g., a certain threshold-limited value or the lower explosive limits of combustible gases.
Andreas Hierlemann, Henry Baltes

12. Microfluidics

The field of microfluidics has become one of the most dynamic disciplines of microtechnology. On the one hand, microfluidics offers the mere benefits of miniaturization, enabling many fields of application, in particular where small liquid volumes, transportable and cheap devices, or integrated process control are beneficial. On the other hand, microfluidics provides an elegant and often exclusive access to the nanoworld of biomolecular chemistry and cell handling, leveraging many novel biotechnological applications. This chapter first outlines the fluidic properties and working principles underlying microfluidic devices, such as diffusion, heat transport, interfacial surface tension, and electrokinetic effects. It then introduces fabrication techniques and sketches microfluidic components for flow control, pumping, physical sensing, and dispensing and their applications in (bio-)analytical chemistry, drug discovery, and chemical process engineering.
Jens Ducrée, Peter Koltay, Roland Zengerle

13. Biomedical Systems

The phenomenal success and widespread proliferation of microelectronic devices can be attributed in large part to the mass production technologies that have been developed for their manufacture. These microfabrication techniques have been honed to maximize device yield and microelectromechanical systems (MEMS) capitalize on these semiconductor microfabrication tools to create miniature systems that meld electronic and mechanical functions. Miniaturization brings with it the benefits of smaller devices that cost less, require less power, and incorporate greater functionality. The use of microsystems in biomedical applications holds the promise of improving patient care in a minimally invasive manner while simultaneously reducing health care costs.
Whye-Kei Lye, Michael Reed

14. Microactuators

This chapter provides the information necessary to understand the capabilities and limitations of existing electrically operated microactuators so that a microactuator can be selected or designed for a specific application and set of design constraints. It begins by providing introductory information about the field of microelectromechanical systems (MEMS), with the specific perspective of microactuator development. A brief but broad discussion of the transduction mechanisms used by microactuators is presented. Microactuators based on electromechanical transduction mechanisms are then described and analyzed, and specific examples are cited. References to published work are provided as existence proofs and for in-depth study of the individual cases.
Jack W. Judy

15. Micromachining Technology

The term micromachining usually refers to the fabrication of micromechanical structures with the aid of etching techniques to remove part of the substrate or a thin film. Silicon has excellent mechanical properties,[1] making it an ideal material for machining. An early silicon (pressure) sensor was made by Honeywell in 1962 using isotropic etching.[2] In 1966, Honeywell developed a technique to fabricate thin membranes using mechanical milling. Crystal-orientation-dependent etchants led to more precise definition of structures and increased interest.[3] Anisotropic etching was introduced in 1976. An early silicon pressure sensor, based on anisotropic etching, was made by Greenwood in 1984.[4] Surface micromachining also dates back to the 1960s. Early examples included metal mechanical layers.[5] Basically, surface micromachining involves the formation of mechanical structures from thin films on the surface of the wafer. The 1980s saw the growth of silicon-based surface micromachining using a polysilicon mechanical layer.[6,7] In recent years, a number of new technologies have been developed using both silicon and alternative materials. These include the epi-processes where the epilayer is used as a mechanical layer and a number of deep plasma etching processes. This chapter concentrates on silicon-based micromachining processes.
Paddy J. French, Pasqualina M. Sarro

16. LIGA Technology for R&D and Industrial Applications

The LIGA process[1] was first developed at the Forschungszentrum Karlsruhe GmbH. It is currently used worldwide by numerous other research institutes and by industry. LIGA allows for the manufacturing of microcomponents with almost arbitrary lateral geometry and resolution in the micron range, but with structure heights into the millimeter range. The typical materials used are polymers, metals, and ceramics, thus covering a wide range of “nonsilicon” candidates. The main process steps have given the technique its name, LIGA, a German acronym consisting of LI (Lithographie for lithography), G (Galvanik for electroplating), and A (Abformung for replication techniques, such as molding). In the classical understanding of LIGA, the lithography step is performed using the highly collimated and energetic X-rays of a synchrotron that can penetrate with little scattering into hundreds of microns of polymer resist and hence pattern it with extremely sharp, smooth, and vertical sidewalls. In addition, due to the short wavelengths of the X-rays, the spatial resolution of the process is very high, thus allowing for extremely high aspect ratios, i.e., the ratio of width over thickness of a structure. The overall process development requires establishing an entire process chain, e.g., a mask-making procedure, since X-ray masks need to be patterned with relatively high-aspect-ratio absorbing structures in a LIGA-like process, or an adopted sacrificial layer technique.
Ulrike Wallrabe, Volker Salle

17. 17 Interface Circuitry and Microsystems

Sensing physical or chemical quantities is a fundamental task in information processing and control systems. A sensing element or transducer converts the quantity to be measured into an electrical signal, such as a voltage, a current, or a resistive or capacitive variation. The data obtained from the transducers then have to be translated into a form understandable by humans, computers, or measurement systems. An electronic circuit called a sensor interface usually performs this task. The functions implemented by a sensor interface can range from simple amplification or filtering to A/D conversion, calibration, digital signal processing, interfacing with other electronic devices or displays, and data transmission (through a bus or, recently, through a wireless connection, such as Bluetooth).
Piero Malcovati, Franco Maloberti


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