Fundamental studies of Au contacts in MEMS RF switches
01 Feb 2005-Tribology Letters (Kluwer Academic Publishers-Plenum Publishers)-Vol. 18, Iss: 2, pp 215-230
TL;DR: In this article, the effects of contact force and electric current on contact resistance (R), microadhesion, and reliability/durability of hot-switched gold (Au) contacts were conducted using a micro/nanoadhesion apparatus as a switch simulator.
Abstract: Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications. However, there is little understanding of the factors determining the performance and reliability of these devices. Fundamental studies of hot-switched gold (Au) contacts were conducted using a micro/nanoadhesion apparatus as a switch simulator. Experiments were conducted in a well defined air environment under precisely controlled operating conditions. Fundamental properties were connected to performance with an emphasis on the effects of contact force and electric current on contact resistance (R), microadhesion, and reliability/durability. Electric current had the most profound effect on switch performance. Observations at low current (1–10 μA) include: (1) slightly higher R; (2) asperity creep; (3) high adhesion after rapid switching; (4) switch bouncing; and (5) reasonable durability. Conversely, observations at high current (1–10 mA) include: (1) slightly lower R; (2) melting; (3) no measurable adhesion; (4) less propensity for switch bouncing; (5) necking of contacts; and (6) poor reliability and durability due to switch shorting. Low current behavior was dominated by the propensity to form smooth surface contacts by hammering, which led to high van der Waals force. High current behavior was dominated by the formation of Au nanowires that bridge the contact during separation. Data suggest the presence of an adventitious film containing carbon and oxygen. Aging of the contacts in air was found to reduce adhesion.
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TL;DR: In this article, a review of the important characteristics of the contact interface such as modeling and material choice is discussed. And a brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers.
Abstract: Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined.
122 citations
TL;DR: In this article, three noble metals, platinum (Pt), rhodium (Rh), ruthenium (Ru), and their alloys with gold (Au) were deposited as thin films on silicon (Si) substrates.
Abstract: The proper selection of electrical contact materials is one of the critical steps in designing a metal contact microelectromechanical system (MEMS) switch. Ideally, the contact should have both very low contact resistance and high wear resistance. Unfortunately this combination cannot be easily achieved with the contact materials currently used in macroswitches because the available contact force in microswitches is generally insufficient (less than 1mN) to break through nonconductive surface layers. As a step in the materials selection process, three noble metals, platinum (Pt), rhodium (Rh), ruthenium (Ru), and their alloys with gold (Au) were deposited as thin films on silicon (Si) substrates. The contact resistances of these materials and their evolution with cycling were measured using a specially developed scanning probe microscope test station. These results were then compared to measurements of material hardness and resistivity. The initial contact resistances of the noble metals alloyed with Au a...
119 citations
TL;DR: In this article, the electro-mechanical response of radio frequency (RF) microelectromechanical (MEM) switches due to variations in surface roughness and finite asperity deformations was analyzed.
Abstract: Modeling predictions and experimental measurements were obtained to characterize the electro-mechanical response of radio frequency (RF) microelectromechanical (MEM) switches due to variations in surface roughness and finite asperity deformations. Three-dimensional surface roughness profiles were generated, based on a Weierstrass–Mandelbrot fractal representation, to match the measured roughness characteristics of contact bumps of manufactured RF MEMS switches. Contact asperity deformations due to applied contact pressures were then obtained by a creep constitutive formulation. The contact pressure is derived from the interrelated effects of roughness characteristics, material hardening and softening, temperature increases due to Joule heating and contact forces. This modeling framework was used to understand how contact resistance evolves due to changes in the real contact area, the number of asperities in contact, and the temperature and resistivity profiles at the contact points. The numerical predictions were qualitatively consistent with the experimental measurements and observations of how contact resistance evolves as a function of deformation time history. This study provides a framework that is based on integrated modeling and experimental measurements, which can be used in the design of reliable RF MEMS devices with extended life cycles.
100 citations
TL;DR: A review of surface science studies on passive two-dimensional substrates compare to and contrast with studies performed on, or by, micro-and nano-electro-mechanical (MEMS) devices as discussed by the authors.
100 citations
TL;DR: This paper reviews the significant successes in MEMS products from a reliability perspective including ink jet printhead, inertial sensors, pressure sensors, micro-mirror arrays, and the emerging applications of RF switches and resonators.
92 citations
References
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Book•
01 Jan 1985
TL;DR: The forces between atoms and molecules are discussed in detail in this article, including the van der Waals forces between surfaces, and the forces between particles and surfaces, as well as their interactions with other forces.
Abstract: The Forces between Atoms and Molecules. Principles and Concepts. Historical Perspective. Some Thermodynamic Aspects of Intermolecular Forces. Strong Intermolecular Forces: Covalent and Coulomb Interactions. Interactions Involving Polar Molecules. Interactions Involving the Polarization of Molecules. van der Waals Forces. Repulsive Forces, Total Intermolecular Pair Potentials, and Liquid Structure. Special Interactions. Hydrogen-Bonding, Hydrophobic, and Hydrophilic Interactions. The Forces between Particles and Surfaces. Some Unifying Concepts in Intermolecular and Interparticle Forces. Contrasts between Intermolecular, Interparticle, and Intersurface Forces. van der Waals Forces between Surfaces. Electrostatic Forces between Surfaces in Liquids. Solvation, Structural and Hydration Forces. Steric and Fluctuation Forces. Adhesion. Fluid-Like Structures and Self-Assembling Systems. Micelles, Bilayers, and Biological Membranes. Thermodynamic Principles of Self-Assembly. Aggregation of Amphiphilic Molecules into Micelles, Bilayers, Vesicles, and Biological Membranes. The Interactions between Lipid Bilayers and Biological Membranes. References. Index.
18,048 citations
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01 Jan 1997TL;DR: The second edition of the Fundamentals of Microfabrication as discussed by the authors provides an in-depth coverage of the science of miniaturization, its methods, and materials, from the fundamentals of lithography through bonding and packaging to quantum structures and molecular engineering.
Abstract: MEMS technology and applications have grown at a tremendous pace, while structural dimensions have grown smaller and smaller, reaching down even to the molecular level. With this movement have come new types of applications and rapid advances in the technologies and techniques needed to fabricate the increasingly miniature devices that are literally changing our world.A bestseller in its first edition, Fundamentals of Microfabrication, Second Edition reflects the many developments in methods, materials, and applications that have emerged recently. Renowned author Marc Madou has added exercise sets to each chapter, thus answering the need for a textbook in this field.Fundamentals of Microfabrication, Second Edition offers unique, in-depth coverage of the science of miniaturization, its methods, and materials. From the fundamentals of lithography through bonding and packaging to quantum structures and molecular engineering, it provides the background, tools, and directions you need to confidently choose fabrication methods and materials for a particular miniaturization problem.New in the Second EditionRevised chapters that reflect the many recent advances in the fieldUpdated and enhanced discussions of topics including DNA arrays, microfluidics, micromolding techniques, and nanotechnology In-depth coverage of bio-MEMs, RF-MEMs, high-temperature, and optical MEMs.Many more links to the WebProblem sets in each chapter
2,334 citations
TL;DR: In this article, the electrostatic microswitch is used in a number of existing circuits and systems, including radio front-ends, capacitor banks, and time-delay networks, for quasi-optical beam steering and electrically reconfigurable antennas.
Abstract: This paper deals with a relatively new area of radio-frequency (RF) technology based on microelectro-mechanical systems (MEMS). RF MEMS provides a class of new devices and components which display superior high-frequency performance relative to conventional (usually semiconductor) devices, and which enable new system capabilities. In addition, MEMS devices are designed and fabricated by techniques similar to those of very large-scale integration, and can be manufactured by traditional batch-processing methods. In this paper, the only device addressed is the electrostatic microswitch - perhaps the paradigm RF-MEMS device. Through its superior performance characteristics, the microswitch is being developed in a number of existing circuits and systems, including radio front-ends, capacitor banks, and time-delay networks. The superior performance combined with ultra-low-power dissipation and large-scale integration should enable new system functionality as well. Two possibilities addressed here are quasi-optical beam steering and electrically reconfigurable antennas.
685 citations
TL;DR: The recent progress in MEMS for radio frequency (RF) applications from a device perspective is reviewed in this article, where switches and relays, tunable capacitors, integrated inductors, mechanical resonators and filters, and some representative microwave and millimetre-wave components are discussed.
Abstract: This paper reviews the recent progress in MEMS for radio frequency (RF) applications from a device perspective. RF MEMS devices reviewed include switches and relays, tunable capacitors, integrated inductors, mechanical resonators and filters, and some representative microwave and millimetre-wave components. Important device parameters are highlighted, as they have significant contributions to the performance of the final products in which the devices are used. The challenges and statuses of these RF MEMS devices are outlined and discussed. The intent of this topical review is to provide perspective to newcomers in the field, and empower potential end-users with an overall device picture, current status, and a vision of their ultimate performance capabilities.
552 citations
01 Aug 1998
TL;DR: An overview of recent progress in the development of micromachined devices for use in wireless communication subsystems is presented in this article, where specific applications are reviewed for each of these components with emphasis on methods for miniaturization and performance enhancement of existing and further wireless transceivers.
Abstract: An overview of recent progress in the research and development of micromachined devices for use in wireless communication subsystems is presented. Among the specific devices described are tunable micromachined capacitors, integrated high-Q inductors, micromachined low-loss microwave and millimeter-wave filters, low-loss micromechanical switches, microscale vibrating mechanical resonators with Q's in the tens of thousands, and miniature antennas for millimeter-wave applications. Specific applications are reviewed for each of these components with emphasis on methods for miniaturization and performance enhancement of existing and further wireless transceivers.
481 citations