Page 287 - An Introduction to Microelectromechanical Systems Engineering

266 Glossary

high-temperature diffusion or anneal step. Implantation is useful in the doping of
piezoresistors, embedded electrical interconnects in a silicon substrate, and thin
polysilicon films.
International Telecommunication Union (ITU) The ITU, headquartered in
Geneva, Switzerland, is an international organization within the United Nations,
where governments and companies coordinate global telecommunication networks,
services, and standards.
Liquidus temperature In metallurgy, the phase state of an alloy changes with tem-
perature, pressure, and mole percentage of its constituents. At a constant pressure,
there are three distinct regions in the phase diagram. At low temperatures, the alloy
is a solid. At high temperatures, it is a liquid. A third intermediate region defines a
plastic-like, mixed liquid and solid state. The dividing line between the liquid state
and the plastic-like state is the liquidus line. The dividing line between the solid state
and the plastic-like state is the solidus line. For each molar composition, there is a
liquidus and a solidus temperature. At the eutectic composition, the two tempera-
tures are identical; in other words, the two lines coalesce and the plastic-like phase
vanishes.
Lithography A process common in microfabrication for delineating a pattern
image in a photosensitive polymer. The polymer, or photoresist, can then be used as
a masking layer to transfer the pattern into the underlying substrate.
Lorentz force In physics, it is the force on a current-conducting element inside a
magnetic field. Its magnitude is equal to the current multiplied by the magnetic flux
density and the length of the conductor. Its direction is orthogonal to both the mag-
netic field and electric current. For a free charge, the force is equal to the product of
the charge, the velocity, and the magentic flux density.
LPCVD An acronym for low-pressure chemical-vapor deposition.
MESFET An acronym for metal-semiconductor field effect transistor. A type of
electronic transistor useful for operation at very high frequencies. It is very common
in electronic circuits made of gallium arsenide (GaAs).
Microelectromechanical systems (MEMS) A generic descriptive term, common
in the United States, for a broad technology with the objective of miniaturizing
complex systems by integrating a diverse set of functions into a small package or a
single die.
Micromachining A term describing the set of design and fabrication tools for the
machining of microstructures and very small mechanical features in a substrate fre-
quently made of silicon.

Microwave The electromagnetic frequency range variously defined as starting at
about 1 GHz and extending to 30 GHz or even 3 THz (the far infrared). The range of
30 GHz to 300 GHz, with wavelengths in vacuum of 1 cm to 1 mm, is referred to as
the millimeter-wave range.

MTTF An acronym for mean time to failures for nonrepairable systems. A typi-
cal figure for robust electronic equipment is in excess of 500,000 hours. It means