Page 210 - An Introduction to Microelectromechanical Systems Engineering

CHAPTER 7
MEM Structures and Systems in RF

Applications

“The discovery of electrical waves has not merely scientific interest though that
alone inspired it... it has had a profound influence on civilization; it has been instru-
mental in providing the methods which may bring all inhabitants of the world
within hearing distance of each other and has potentialities social, educational and
political which we are only beginning to realize.”
—Sir Joseph. J. Thomson, on James Maxwell’s discovery of
electromagnetic waves in James Clerk Maxwell: A Commemorative
Volume 1831–1931, The University Press: Cambridge, UK, 1931.

Radio-frequency (RF) MEM devices have been in research and development for
years, with scores of papers published annually. There are unpublicized devices in
use in small volume in commercial and military applications, but only recently have
such devices gone into high-volume production. Current and future RF MEMS
devices will be competitive with more conventional components on the basis of vol-
ume, mass, cost, and performance. The largest potential market is in cellular tele-
phone handsets, with hundreds of millions of units sold each year. Other portable
electronics markets, where the aforementioned qualities are major considerations,
include cordless phones for home use, wireless computer networking, radios, and
global positioning system (GPS) receivers. Satellites, missile guidance, military
radar, and test equipment are separate markets of importance, with lower potential
sales volumes but higher unit prices.
Opening the cover of a modern cellular telephone reveals a myriad of discrete
passive and active components occupying substantial volume and weight. The mar-
ket’s continued push for small portable telephones argues a convincing economic
case for the miniaturization of components. MEMS technology promises to deliver
miniature integrated solutions including variable capacitors, inductors, oscillators,
filters, and switches to potentially replace conventional discrete components.

Signal Integrity in RF MEMS

A requirement for any RF device is maintaining signal integrity: transmitting desired
signals with low loss, minimizing reflections, not permitting external signals or
noise to join the transmitted signal, and filtering out or not generating undesired
signals, such as higher-frequency harmonics. At high frequencies, these seemingly
simple requirements are not readily attained.

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