Design and pull-in voltage optimization of series metal-to-metal contact RF MEMS switch

RF MEMS: Theory, Design, and Technology

Abstract: From the Publisher: Practical and theoretical coverage of RF MEMS for circuits and devices New RF and microwave frequency MEMS (microeletromechanical systems) have potentially enormous and widespread applications in the telecommunications industry. Components based on this technology–such as switches, varactors, and phase shifters–exhibit virtually no power consumption or loss, making them ideally suited for use in modern telecommunications and wireless devices. This book sets out the basics of RF MEMS and describes how to design practical devices and circuits. As well as covering fundamentals, Gabriel Rebeiz offers expert tips for designers and presents a range of real-world applications. Throughout, the author utilizes actual engineering examples to illustrate basic principles in theory and practice. Detailed discussion of cutting-edge fabrication and packaging techniques is provided. Suitable as a tutorial for electrical and computer engineering students, or as an up-to-date reference for practicing circuit designers, RF MEMS provides the most comprehensive available survey of this new and important technology. Author Biography: Gabriel M. Rebeiz received his PhD from the California Institute of Technology, and is Professor of Electrical and Computer Engineering at the University of Michigan, Ann Arbor. In 1991 he was the recipient of the National Science Foundation Presidential Young Investigator Award, and in 2000 was the corecipient of the IEEE Microwave Prize. A Fellow of the IEEE and a consultant to Rockwell, Samsung, Intel, Standard MEMS, and Agilent, he has published extensively in the field of microwave technology and in the area of RF MEMS.

RF-MEMS switches for reconfigurable integrated circuits

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.

MEMS for wireless communications: 'from RF-MEMS components to RF-MEMS-SiP'

Abstract: Wireless communication has led to an explosive growth of emerging consumer and military applications of radio frequency (RF), microwave and millimeter wave circuits and systems. Future personal (hand-held) and ground communications systems as well as communications satellites necessitate the use of highly integrated RF front-ends, featuring small size, low weight, high performance and low cost. Continuing chip scaling has contributed to the extent that off-chip, bulky passive RF components, such as high-Q inductors, ceramic and SAW filters, varactor diodes and discrete PIN diode switches, have become limiting. Micro-machining or MEMS technology is now rapidly emerging as an enabling technology to yield a new generation of high-performance RF-MEMS passives to replace these off-chip passives in wireless communication (sub)systems. This paper reviews the progress in RF-MEMS from a device and integration perspective. The worldwide state-of-the-art of RF-MEMS devices including switches, variable capacitors, resonators and filters are described. Next, it is stipulated how integration of RF-MEMS passives with other passives (as inductors, LC filters, SAW devices, couplers and power dividers) and, active circuitry (ASICs, RFICs) can lead to the so-called RF-MEMS system-in-a-package (RF-MEMS-SiP) modules. The evolution of the RF-MEMS-SiP technology is illustrated using IMEC's microwave multi-layer thin-film MCM-D technology which today already serves as a technology platform for RF-SiP.

Mechanical design and optimization of capacitive micromachined switch

Abstract: Design and optimization of a shunt capacitive micromachined switch is presented. The micromachined switch consists of a thin metal membrane called the “bridge” suspended over a center conductor, and fixed at both ends to the ground conductors of a coplanar waveguide (CPW) line. A static electromechanical model considering the residual stress effects is developed to predict the effective stiffness constant and the critical collapse voltage of the bridge for several typical bridge geometries. The deformation of the bridge and its contact behavior with the dielectric layer are analyzed using the finite element method (FEM) in order to explore a good contact field with different bridge geometries. Furthermore, a nonlinear dynamic model that captures the effects of electrostatic forces, elastic deformation, residual stress, inertia, and squeeze film damping is developed, and is used for predicting the switching speed (including the switching-down and the switching-up time) and the Q -factor. The effects of variation of important parameters on the mechanical performance have been studied in detail, and the results are expected to be useful in the design of optimum shunt capacitive micromachined switch. The results may also be useful in the design of actuators with membranes or bridges.

Metal contact reliability of RF MEMS switches

Abstract: It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential applications have been investigated such as Tx/Rx antenna switching, frequency band selection, tunable matching networks for PA and antenna, tunable filters, and antenna reconfiguration. However, none of these applications have been materialized in high volume products to a large extent because of reliability concerns, particularly those related to the metal contacts. The subject of the metal contact in a switch was studied extensively in the history of developing miniaturized switches, such as the reed switches for telecommunication applications. While such studies are highly relevant, they do not address the issues encountered in the sub 100μN, low contact force regime in which most MEMS switches operate. At such low forces, the contact resistance is extremely sensitive to even a trace amount of contamination on the contact surfaces. Significant work was done to develop wafer cleaning processes and storage techniques for maintaining the cleanliness. To preserve contact cleanliness over the switch service lifetime, several hermetic packaging technologies were developed and their effectiveness in protecting the contacts from contamination was examined. The contact reliability is also very much influenced by the contact metal selection. When pure Au, a relatively soft metal, was used as the contact material, significant stiction problems occurred when clean switches were cycled in an N 2 environment. In addition, various mechanical damages occurred after extended switching cycling tests. Harder metals, while more resistant to deformation and stiction, are more sensitive to chemical reactions, particularly oxidation. They also lead to higher contact resistance because of their lower electrical conductivity and smaller real contact areas at a given contact force. Contact reliability issues could also be tackled by improving mechanical designs. A novel collapsing switch capable of generating large contact forces (>300μN) was shown to be less vulnerable to contamination and stiction.