Page 291 - An Introduction to Microelectromechanical Systems Engineering

270 Glossary

TEC see Thermoelectric cooler.

Temperature coefficient of expansion (TCE) see coefficient of thermal expansion.
Temperature coefficient of resistance (TCR) The rate of increase in resistance as
a function of temperature. In general, TCR =(∆R/R)/∆T, where (∆R/R) is the frac-
tional change in resistance corresponding to a ∆T change in temperature. It is meas-
ured in inverse units of temperature (/ºC).
Thermocompression bond A bonding process involving the melting of an inter-
mediate layer between two substrates pressed against each other. Frequently, the
intermediate layer is made of glass or gold.
Thermoelectric cooler (TEC) Also known as a Peltier cooler, it is a device that is
capable of transferring heat from one side to another. It is common in controlling
the temperature of small dice or objects. The device consists of many semiconductor
junctions in parallel that use the Peltier effect.

VGA An acronym for video graphics adapter, it identifies displays with a resolu-
tion of 640 × 480 pixels. SVGA, XGA, and SXGA denote displays with resolutions
of 800 × 600, 1,024 × 768, and 1,280 × 1,024 pixels, respectively.
Wavelength A characteristic of a wave, it represents the distance between identi-
cal points in two adjacent cycles of an oscillating waveform. In electromagnetic
waves, wavelength and frequency are inversely related by the velocity of the wave. In
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vacuum, the velocity is the speed of light equal to3×10 m/s. In a transmission line,
the velocity depends on the dielectric constant, frequency, and geometry and is in the
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range of2×10 m/s. Thus, a 2-GHz signal has a wavelength of around 100 mm.
Wavelength division multiplexing (WDM) A protocol in fiber-optic communica-
tion in which digital data is multiplexed on different wavelengths in a single fiber.
This effectively increases the bandwidth available in one fiber by increasing the
number of channels.

Wavelength locker A device used in fiber optical telecommunications that locks
the wavelength of a laser to a specific value that is often preset by the ITU.
Wet anisotropic etching Process of etching or removal of material from a silicon
substrate with the etch front delineated by crystallographic planes. Potassium
hydroxide and tetramethyl ammonium hydroxides are two examples.
Wheatstone bridge An electrical circuit consisting of four resistors forming two
branches electrically connected in parallel, with each branch consisting of two resis-
tors electrically in series. It is useful to measure an imbalance in the values of the four
resistors.
Wireless RF communication without the use of wires or other transmission lines.
Young’s modulus Also known as modulus of elasticity, it is a material constant
(in units of pressure) relating mechanical stress to elastic strain. It is indicative of the
stiffness of the material. For example, diamond has a very high Young’s modulus,
whereas soft polymers have low values. It often depends on orientation in crystalline
materials.