Page 284 - An Introduction to Microelectromechanical Systems Engineering

Glossary 263

Coherence A property of light that describes the statistical correlation between
the phases of optical wavefronts (i.e., the degree to which the waves of the radiation
are vibrating in phase). Temporal coherence relates to the phase correlation between
different instants in time and is a necessary characteristic to obtain interference. Spa-
tial coherence relates to the phase correlation between different points in space.
Complementarity In biochemistry, it is the specific affinity for binding between
the purines (adenine and guanine) with pyrimidines (thymine and cytosine). See
nucleotide.

Condenser microphone see capacitor microphone.
Coriolis effect Physical effect responsible for the deflection of objects moving on
the surface of a rotating body such as Earth.
Corner frequency see filter.
Decibel (dB) A unit to measure the relative difference in intensity of a physical,
electrical, optical, or acoustical signal (e.g., voltage, electric field, or pressure). It is
defined as 20 times the 10-base logarithm of the intensity ratio, or, because power is
proportional to the square of the intensity, 10 times the 10-base logarithm of the
power ratio. For example, 40 dB is equivalent to a ratio of 100 between the highest
and lowest intensities in the range. The same ratio in power would, however, be
equivalent to 20 dB.
Degeneracy see frequency degeneracy.

Detector Also photodetector, it is a semiconductor sensor that converts the opti-
cal intensity in a light beam into an electrical current. A quadrant detector is made
of four adjoining detectors and detects the spatial position of a light beam.
Die Also chip, a common term in microfabrication technology indicating a small
piece of semiconductor or glass cut or diced from a much larger wafer.
Diffusion In semiconductor fabrication, it is the process to controllably spread or
diffuse impurity dopant atoms in silicon or a semiconductor. Diffused resistors are
resistors made of one type of doping (e.g., p-type) and embedded in silicon having a
background doping of the opposite type (e.g., n-type).
Diffraction In optics, it is the effect of an incident light beam separating into mul-
tiple beams, each called a higher diffraction order upon striking an optical element
with features that approach in size the wavelength of the incident beam.

DIP An acronym for dual-in-line type of package. Made of ceramic or plastic, it is
rectangular in shape with pins (leads) on its two long sides.

Dipole Also electric dipole, it is the electric field created by two charges of equal
magnitude but opposite polarity and separated by a small distance.
Distributed-feedback laser (DFB) A category of integrated semiconductor lasers
that utilize a Bragg grating to stabilize their output optical frequency. They are
widely used in optical fiber telecommunications.
Doping Also known as impurity doping. A process of introducing into a semi-
conductor material impurities or foreign atoms—dopants—in relatively dilute con-
20
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centrations (10 ~10 cm ). The impurities alter the electrical properties of the