Page 235 - An Introduction to Microelectromechanical Systems Engineering

214 MEM Structures and Systems in RF Applications

a smaller size and lower bill-of-materials cost than if a separate hermetic package
were used.
The gap between the cantilever and the underlying electrodes must be suffi-
ciently large that the isolation is high when open. Furthermore, the cantilever must
be stiff enough that it is not damaged and closure does not accidentally occur when
the device is shocked (switches have demonstrated a shock tolerance of 30,000G).
These criteria lead to a higher actuation voltage than is available in many systems.
To resolve this problem, charge-pump circuitry supplies the needed drive voltage
from a 1.5-V input. When closed, which takes 10 µs, the measured insertion loss of
the switch is less than 0.2 dB from dc to 2 GHz. For the package alone, the insertion
loss is nearly “invisible” to the circuit at 0.06 dB, which has enabled this packaging
scheme to be used for other RF devices as well as switches. The isolation when open
is 40 dB. Goals are an insertion loss of 0.2 dB over 24–40 GHz, a lifetime of 10 11
cycles, and 1-W cold-switched power handling.

Summary

The most notable members of the RF MEMS family, micromachined variable
capacitors, inductors, resonators, filters, and switches were described, with research
or commercial examples of each. There are different advantages of these devices,
compared to their conventional counterparts, including smaller size, lower cost,
higher Q, lower loss, and the ability to be integrated on the same chip as circuitry. A
common theme in RF MEMS is the reduction of parasites. We are presently at the
dawn of an era of commercial use of RF MEMS.

References

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Communications,” Proceedings of the IEEE, Vol. 86, No. 8, August 1998, pp. 1756–1786.
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[7] U.S. Patent 6,549,394, April 15, 2003.
[8] Dec, A., and K. Suyama, “Micromachined Electro-Mechanically Tunable Capacitors and
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