Page 286 - An Introduction to Microelectromechanical Systems Engineering

Glossary 265

frequencies in a mid-band range but blocks the transmission of frequencies above or
below this band—outside of the corner frequencies.
Finesse A measure of optical loss in an optical resonator, such as an etalon.
Imperfections in the reflective surfaces that bound the resonator and in the material
between them degrade the finesse. It is the ratio of the free spectral range (FSR), the
spectral separation between two adjacent transmission peaks of the resonator, to
the full width at half maximum (FWHM), the spectral width of the transmission
peak at its 50% point.

FIT An acronym for failure in time, it is a measure of reliability equal to
-9
10 failure/hr.
Foundry A service facility capable of prototyping and fabricating semiconductor
circuits or MEMS. Foundry services typically offer a set of standard fabrication
processes. A few provide custom design services.
Frequency degeneracy The situation when two or more resonant modes oscillate
at exactly the same frequency. When a number of identical oscillators are coupled
with each other, their frequencies become degenerate. The coupling generally lifts
this degeneracy by splitting the frequencies apart. The amount of separation
depends on the strength of the coupling.
Genomics The study of genes and their functions.
Grating Also known as diffraction grating, it consists of a repeating array of lines
spaced apart by a distance close to that of the wavelength of light. Incoming light is
diffracted by the grating into a multitude of higher orders that form an angle with
the incident light beam. A grating can be either transmissive or reflective. See Bragg
grating.

Helmholtz cavity Also known as a Helmholtz resonator, in acoustics it is a hol-
low air-filled cavity having an inlet opening for sound and an outlet. The cavity is an
acoustic oscillator with a characteristic resonant frequency determined by both the
air volume and the geometry of the inlet and outlet ports. It is commonly used in
acoustics for frequency tuning.

Hole In physics, it is a vacant position in a semiconductor left by the absence of
an electron. The concept is analogous to a bubble in water left by the absence of liq-
uid. A hole is a carrier of positive electric charge and participates in electric
conduction.

Hybridization In biochemistry, it is the process when two DNA strands having
complementary sequences of nucleotides match up and bind with each other.
Impedance A measure of the total resistance to electrical current flow. In acous-
tics, it is a measure of the total resistance to the propagation of acoustic pressure
waves through a medium. Impedance is generally a complex number.
Insertion loss In a linear system, such as a filter, it is the attenuation, measured in
decibels, of an input signal with frequency content within the system bandwidth.
Ideally, it is zero.

Ion implantation A high-energy process capable of embedding impurity dopant
atoms within the surface of a semiconductor substrate. It is usually followed by a