Appendix G
Glossary
Abrasive: A hard and
wear-resistant material (such as a ceramic) used to wear, grind, or cut away
other material.
Absolute zero: The lowest
temperature theoretically possible, corresponding to –273.15° Celsius.
Acceptor: An impurity atom
which has fewer valence electrons than the atom it replaces. When introduced
into a semiconductor it produces a hole.
Accuracy: The degree of
correctness with which the measuring system yields the “true value”
of a measured quantity, where the “true value” refers to an
accepted standard, such as a standard meter or volt. Typically described in
terms of a maximum percentage of deviation expected based on a full-scale
reading.
Actin: A soluble protein found in muscle
cells. It is the main component of the thin filaments.
Affinity: A thermodynamic
measurement of the strength of binding between molecules, say between an
antibody and antigen. Each antibody/antigen pair has an association constant, Ka,
expressed in L/mol.
AFM: For atomic force microscopy. A variant of the
STM method. In AFM, the surface is probed mechanically rather than
electronically.
Algorithm: A set of
well-defined mathematical rules or operations for solving a problem in a finite
number of steps.
AM 1: The air mass 1 spectrum of a light
source is equivalent to that of sunlight at the earth’s surface when the
sun is at zenith.
Amino acids: Naturally
occurring biological molecules with a variety of functions. Among the amino
acids, there are 20 that are used as building blocks for making proteins.
Amorphous silicon: Silicon lacking a
preferred crystalline orientation, typically consisting of extremely fine
grains each measuring a few nanometers in size.
Ampere (amp) [A]: Measure of
electric current: 1A = 1 coulomb/second.
Amperometric sensor: Amperometric
sensors involve a heterogeneous electron transfer as a result of an
oxidation/reduction of an electro-active species at a sensing electrode
surface. A current is measured at a certain imposed voltage of the sensing
electrode with respect to the reference electrode. Analytical information is
obtained from the current-concentration relationship at that given applied
potential.
a.m.u: See atomic mass
unit.
Analyte: A chemical species
targeted for qualitative or quantitative analysis.
Angiography: The X-ray study of
the blood vessels. An angiogram uses a radiopaque substance, or dye, to make
the blood vessels visible under X-ray
Angstrom [Å]: Measure of length:
1 Å= 10–10 m.
Anisotropic: Exhibiting
different values of a property in different crystallographic directions.
Anneal: Heat process used
to remove stress, crystallize, or render deposited material more uniform.
Anode: The electrode in an electrochemical
cell or galvanic couple that experiences oxidation, or gives up electrons.
Anodic bonding: A process to bond
silicon to glass, specifically Pyrex® or equivalent.
Antibiotic: An organic
substance that suppresses multiplication of bacteria, but that is not poisonous
to humans or animals. The first antibiotic was pencillin, isolated by Alexander
Fleming from fungi in 1929. The discovery of antibiotics produced a
revolutionary breakthrough in the treatment of many diseases that had
previously resisted any medical treatment, such as pneumonia and tuberculosis.
However, the broad and uncontrolled reliance on antibiotics caused bacteria to
develop a resistance to them. As a result, traditional antibiotics are now much
less effective than they were during the first decades of their application.
Antibiotics are utterly irrelevant in combating viral diseases.
Antibody: A large protein
that specifically recognizes foreign structures such as bacteria or viruses and
triggers an immune response against them.
Antigen: A molecule or part
of a molecule that triggers an immune response following molecular recognition
by an antibody.
Arrhenius equation: The equation
representing the rate constant as k = AeEa/RT , where A
represents the product of the collision frequency and a steric factor, and e-Ea/RT
is fraction of collisions with sufficient energy to produce a reaction.
ASIC: For application-specific
integrated circuit. An electronic integrated circuit with a functionality
designed specifically for one particular application; for example, the
detection of minute changes in capacitance and conversion into an output
voltage.
Atomic mass unit (a.m.u.): A unit of mass
used to express relative atomic masses. It is equal to 1/12 of the mass of an
atom of the isotope carbon-12 and is equal to 1.66033 ´ 10–27.
Atomic number (also proton number Z): The number of
protons within the atomic nucleus of a chemical element.
Atomic weight: The weighted
average mass of the atoms in a naturally occuring element.
ATP: For adenosine triphosphate. A building block
for making DNA and RNA, ATP also is the most important carrier of chemical
energy in all cells. To use the stored energy, the cell cleaves off the
outermost of the three phosphate groups contained in the molecule, yielding ADP
(adenosine diphosphate) and an inorganic phosphate ion.
Austenite: Face-centered
cubic iron; also iron and steel alloys that have the FCC crystal structure.
Avogadro’s number: The number of
atoms in exactly 12 grams of pure 12C, equal to 6.022 ´ 1012.
Bacteria: Single-cell
microorganisms. The world of bacteria is extraordinarily varied and plays an
immense role in ensuring the existence of other living things on earth. Many
bacteria survive in the most primitive conditions, requiring for their
multiplication only the simplest molecules containing chemical elements that
are part of biological molecules. Thus, to meet their carbon needs, some
bacteria need only petroleum; they get their nitrogen and oxygen from the air.
Bacteria are everywhere: they cause the souring of milk or broth; they dwell
inside us, helping us to digest food (E. coli); and they also cause many
infectious diseases.
Band gap: The energy
difference between the conduction and valence bands, and equal in magnitude to
the energy required to create an electron-hole pair.
Band gap energy (Eg): For semiconductors
and insulators, the energies that lie between the valence and conduction bands;
for intrinsic materials, electrons are forbidden to have energies within this
range.
Bandwidth: The range of
frequencies over which the measurement system can operate within a specified
error range.
Base: One of the
building blocks of DNA or RNA. A nitrogen-containing base combines with sugar
and phosphate molecules to make a nucleotide. The four bases in DNA are adenine
(A), guanine (G), cytosine (C), and thymine (T).
Base pair: Two nucleotides
held together by a weak bond between complementary bases. In DNA molecules,
adenine is paired with thymine and guanine is paired with cytosine.
BAW: For bulk acoustic
wave.
BCC: See body-centered
cubic.
Bilayer lipid membrane (BLM): The structure
found in most biological membranes, in which two layers of lipid molecules are
so arranged that their hydrophobic parts interpenetrate, whereas their
hydrophilic parts form the two surfaces of the bilayer.
Bimetallic actuation: The resulting
motion when a stack of two materials having dissimilar coefficients of thermal
expansion is heated. One material expands more than the other, giving rise to
bending stresses. The amount of bending is proportional to the temperature of
the stack and the difference in coefficients of thermal expansion.
Binary: Numbering system
based on powers of 2 using only the digits 0 and 1, called bits.
Binding energy: The amount of
energy required in order to remove a particle from a given system. For example,
the binding energy of the electron in a hydrogen atom is given by the energy
required to remove the electron far from the nucleus.
Bioluminescence: Generation of
light from metabolic energy. In addition to fireflies, bioluminescence is found
in dozens of other species including fish, jellyfish, and mushrooms.
Biosensor: The term biosensor is a general
designation that denotes either a sensor to detect a biological substance or a
sensor which incorporates the use of biological molecules such as antibodies or
enzymes. Biosensors are a subcategory of chemical sensors.
Bipolar-junction transistor: Transistor with
n-type and p-type semiconductors having base-emitter and collector-base
junctions.
Bit: See binary.
BLM: See bilayer lipid
membrane.
Body-centered cubic (BCC): A common crystal
structure found in some elemental metals. Within the cubic unit cell, atoms are
located at corner and cell center positions.
Bond pad: A metal area on a
die or wafer to which a gold or aluminum wire is bonded. The wire and bond pad
provide electrical connectivity between electrical components on the die and
electronic circuitry external to the die.
Brazing: A metal joining
technique that uses a molten filler metal alloy having a melting temperature
greater than about 425˚C (800˚F).
Breakdown: Failure of a
material resulting from an electrical overload. The resulting damage may be in
the form of thermal damage (melting or burning) or electrical damage (loss
of polarization in piezoelectric materials).
Brownian motion: A chaotic motion
of microparticles suspended in a liquid, as a consequence of thermal agitation
of molecules.
Bulk micromachining: A class of
micromachining processes that yields micromechanical structures with
thicknesses in the tens or hundreds of micrometers. Very often, it also refers
to micromechanical structures formed using wet anisotropic etch solutions, such
as potassium hydroxide.
Bus: Transmission medium for electrical
or optical signals that perform a particular function, such as computer
control.
Byte: A group of eight bits that can
represent any of 28 = 256 different entities.
Calibration: A process of
adapting a sensor output to a known physical quantity to improve sensor output
accuracy.
Capacitance (C): The charge-storing
ability of a capacitor, defined as the magnitude of charge stored on either
plate divided by the applied voltage. A 1-F capacitor charged to 1 V contains C
of charge (see also capacitor) and 1 C is an amount of charge equal to
that of about 6.24 ´ 1018
electrons.
Capacitor: Energy storage
circuit element having two conductors separated by an insulator.
Catalysis: Acceleration of a
chemical reaction by lowering the energy barrier achieved by a catalyst. The
strict definition of catalysis requires that the catalyst not be affected by
the overall reaction.
Cathode: The electrode in
an electrochemical cell or galvanic couple at which a reduction reaction
occurs; in other words the electrode receiving electrons from an external
circuit.
CD: For critical dimension or compact disc.
Cells: The basic structural units of life.
Ceramic: A nonmetallic
material made from clay and hardened by firing at high temperature; it contains
minute silicate crystals suspended in a glassy cement.
Cermet: A composite
material consisting of a combination of ceramic and metallic meterials. The
most common cermets are the cemented carbides, composed of an extremely hard
ceramic (e.g., WC, TiC), bonded together by a ductile metal such as cobalt or
nickel.
Chaperons: Specialized
proteins that carry out, inside the cell, the folding of a polyamino acid chain
(newly synthesized on ribosome) into a native protein molecule.
Chemical vapor deposition (CVD): A process based on
the principle of initiating a chemical reaction in a vacuum chamber, resulting
in the deposition of a reacted species on a heated substrate. Materials that
can be deposited by CVD include polysilicon, silicon dioxide, and silicon
nitride.
Chip: A die (unpackaged semiconductor
device) cut from a silicon wafer, incorporating semiconductor circuit elements
such as a sensor, actuator, resistor, diode, transistor, and/or capacitor.
Cholesterol: A complex organic
molecule of the steroid class. In moderate quantities, it is necessary for
building the cell membrane and serves as the predecessor for a number of
hormones (including sex hormones). Excess cholesterol in blood leads to
artherosclerosis.
Chromatography: The general name
for a series of methods for separating mixtures by employing a system with a
mobile phase and a stationary phase.
Chromophore: The part of a
molecule that is responsible for its color or more generally for its response
to light.
Chromosome: A complex
structured set of DNA with proteins inside the cell nucleus. It stores genetic
information.
Cloning: Obtaining a large
number of cells from the same cell. Now also used in relation to DNA molecules.
Cluster: A structure
consisting of a small number of (metal) atoms.
CMOS: For complementary metal oxide
semiconductor. Integrated circuit containing n-channel and p-channel
MOSFETs.
Codon: A triplet of nucleotides that is
part of the genetic code and specifies the particular amino acid to be added to
a growing chain to make a protein.
Coefficient of thermal expansion (CTE): The rate of change
in length of an object as a function of temperature. In general, CTE = (DL/L)/DT, where (DL/L) is the fractional change in length corresponding to a DT change in temperature. It is measured in inverse unites of
temperature (l° C).
Collagen: A protein of
connecting tissue. A major example of a protein that, not being an enzyme,
plays a structural role. Collagen is the principal component of bones and
tendons. In everyday life, it is known as gelatin. It is used to
make things such as jellies, glue, and gelatins.
Collector: One region of a
bipolar transistor. In an npn transistor the electrons flow into this region
when the device is switched ON.
Conduction band: The range of
energies in a semiconductor in which an electron is able to move relatively
easily through a crystal, and therefore contribute towards the process of
electrical conduction. An electron in this band is called a conduction electron.
Conductor: Material such as
the metals copper or aluminum that conducts electricity via the motion of
electrons.
Copolymer: A polymer that
consists of two or more dissimilar monomer units in combination in its molecular
chains. Also a polymer formed from the polymerization of more than one type of
monomer.
Corrosion: Deteriorative loss
of a metal as a result of dissolution environmental reactions.
Coulomb [C]: Measure of
electrical charge: 1 C is an amount of charge equal to that of about 6.24 ´ 1018 electrons.
Covalent bond: A primary
interatomic bond that is formed by the sharing of electrons between neighboring
atoms.
Creep: The time-dependent permanent
deformation that occurs under stress; for most materials it is important only
at elevated temperatures.
Critical temperature: Usually
abbreviated by Tc –-the temperature below which a
material becomes a superconductor. The recently discovered materials with
critical temperatures in excess of about 30 Kelvin are referred to as high Tc superconductors.
Critical thickness: The maximum
thickness of a layer of strained material which can be grown before the crystal
structure is disrupted.
Cross-linked polymer: A polymer in which
adjacent linear molecular chains are joined at various positions by covalent
bonds.
Cross-sensitivity: The influence of
one measurand on the sensitivity of a sensor, another measurand.
Cross talk: Electromagnetic
noise transmitted between leads or circuits in close proximity to each other.
Crystal: The regular
arrangement of atoms which is present in virtually all solids.
Crystal structure: For crystalline
materials, the manner in which atoms or ions are arrrayed in space. It is
defined in terms of the unit cell geometry and the atom positions within the
unit cell.
CTE: See coefficient of thermal
expansion.
Curie temperature (also Curie point) (Tc): The temperature
above which a ferromagnetic or ferrimagnetic material becomes paramagnetic. For
iron the Curie point is 760˚C and for nickel 356˚C.
Current [A]: Measure of rate of
flow of electric charge. A one-ampere current is a flow of 1 C of charge per
second.
Current density: A measure of the
amount of current flowing through a wire divided by the cross-sectional area of
the wire.
Cutoff: Condition in a
diode or bipolar-junction transistor in which the potential across a p-n
junction prevents current flow.
CVD: See chemical vapor
deposition.
Cyclotron: A type of particle
accelerator in which an ion introduced at the center is accelerated in an
expanding spiral path by use of alternating electrical fields in the presence
of a magnetic field.
Cytoplasm: The content of a
cell without the nucleus.
Debye shielding: The Debye length
in front of a sensing electrode depends on the ionic strength of the electrolyte
used. In a 0.001N NaCl the Debye length measures 96.5 Å, while for a 1.0
N solution it is reduced to 3.0 Å. An adsorbed protein can stick out from
the surface for as much as 50 to 100 Å. As a result, the charges which
could contribute to the surface potential will be shielded in a 1.0 N solution.
To make more sensitive measurements a solution of low ionic strength should be
used.
Degradation: A term used to
describe the deteriorative processes that occur with polymeric materials,
including swelling, dissolution, and chain scission.
Denaturation: The breaking down
of the three-dimensional structure of a protein resulting in the loss of its
function.
Density of states: A measure of the
number of electrons allowed over a given small energy range. The density of
states is very low at the extremes of the valence and conduction bands and
increases towards the middle of these bands.
Deoxyribonucleic acid: See DNA.
Depletion layer: The region around
a p-n junction which is depleted of carriers. This forms because the conduction
electrons and holes in this region have recombined as a result of the diffusion
of carriers across the interface.
Design: To plan and
delineate with an end in mind and subject to constraints.
Devitrification: The process in
which a glass (noncrystalline or vitreous solid) transforms to a crystalline
solid.
Dialysis: A phenomenon in
which a semipermeable membrane allows transfer of both solvent molecules and
small solute molecules and ions.
Diamagnetism: A weak form of
induced or nonpermanent magnetism for which the magnetic susceptibility is
negative. A type of magnetism associated with paired electrons, which causes a
substance to be repelled from the inducing magnetic field.
Die: See chip.
Dielectric: Any material that
is electrically insulating.
Dielectric (breakdown) strength: The magnitude of
an electric field necessary to cause significant current passage through a
dielectric material.
Dielectric constant (e): The ratio of the
permittivity of a medium to that of a vacuum. Also called the relative
dielectric constant or relative permittivity.
Dielectric displacement: The magnitude of
charge per unit area of capacitor plate.
Diffusion: A thermochemical
process whereby controlled dopants are introduced into a substrate.
Diffusion coefficient: The constant of
proportionality between the diffusion flux and the concentration gradient
in Fick’s first law. Its magnitude is indicative of the rate of atomic
diffusion.
Digital: Refers to systems
employing only quantized (discrete) states to convey information.
Dimer: A molecule formed
by the joining of two identical monomers.
Diode: Two-terminal
device that conducts current well in one direction and poorly in the other.
Dip: For dual in-line package. Common ceramic or
plastic enclosure for an integrated circuit.
Dipole (electric): A pair of equal
yet opposite electrical charges that are separated by a small distance.
Direct gap semiconductor: A material in
which the recombination of conduction electrons and holes is an efficient
process.
Dislocation: A linear
crystalline defect around which there is atomic misalignment. Plastic
deformation corresponds to the motion of dislocations in response to an applied
shear stress. Edge, screw, and mixed dislocations are possible.
DNA
(deoxyribonucleic acid): Biololgical chain molecule built from four kinds of
building blocks, the nucleotides. DNA, normally found as a double helix spiral
of two complementary strands, is the carrier of genetic information in all
cellular life forms and many viruses.
DNA polymerase: An enzyme
responsible for DNA synthesis on the DNA template. The process is called DNA
replication.
DNA probes: A DNA or nucleic
acid probe is a short strand of DNA that locates and binds to its complementary
sequence in samples containing single strands of DNA or RNA enabling
identification of specific sequences. Nucleic acid probe assays exploit the
fundamental hybridization reaction that occurs spontaneously between two
complementary DNA:DNA or DNA:RNA strands. As in immunoassays, detection of the
hybrid requires that the probe be labeled. Various direct and indirect methods
have been devised for the detection of the hybrid. Direct labeling involves
attaching the label directly to the probe sequence; indirect labeling binds an
antibody to the DNA:DNA or DNA:RNA hybrid. As in immunoassays,
non-isotopically-labeled probes are preferred over radio-labeled probes
primarily because of radiation hazards, disposal problems, and short reagent
shelf life. In addition, the factors determining the detection limits of hybridization
assays based on labeled probes are similar to those in immunoassays. Therefore,
the development of a simple, inexpensive, and sensitive direct detection system
which eliminates the use of labels is highly desirable.
DNA sequencing: There are two main
classical methods for sequencing DNA, The first method, developed by Allan
Maxam and Walter Gilbert, involves chemicals used to cleave the DNA at certain
positions, generating a set of fragments that differ by one nucleotide. The
second method, developed by Fred Sanger and Alan Coulson, involves enzymatic
synthesis of DNA strands that terminate in a modified nucleotide. Analysis of
fragments is similar for both methods and involves gel electrophoresis and
autoradiography or fluorescence. The enzymatic method has largely replaced the
chemical method as the technique of choice, although there are some situations
where chemical sequencing can provide data more easily than the enzymatic
method.
Domain: A region of a
ferromagnetic or ferrimagnetic material in which all atomic or ionic magnetic
moments are aligned in the same direction.
Donor: An impurity which
has more valence electrons than the atom that it replaces. This generally gives
rise to a conduction electron.
Doping: Process of
introducing impurity atoms into a semiconductor to affect its conductivity.
Double heterostructure laser: A laser in which
the active region is enclosed between the two heterojunctions. The distinction
from a quantum well laser is that the wave-like nature of the electrons and
holes does not play a significant role.
Drain: The region of a MOSFET through
which the carriers flow out of the device.
DRAM: For dynamic random access
memory. Memory
in which each stored bit must be refreshed periodically.
Drift: Gradual departure of the instrument
output from the calibrated value. An undesired slow change of the output
signal.
DSP: For digital signal processing. A process by which
a sampled and digitized data stream (real-time data such as sound or images) is
modified in order to extract relevant information. Also, a digital signal
processor.
Dynamic characteristics: A description of
an instrument's behavior between the time a measured quantity changes value and
the time the instrument obtains a steady response.
Dynamic error: The error that
occurs when the output does not precisely follow the transient response of the
measured quantity.
Dynamic range: The ratio of the
largest to the smallest values of a range, often expressed in decibels.
Ductility: A measure of a
material’s ability to undergo plastic deformation before fracture;
expressed as percent elongation (%EL) or percent area reduction (%AR) from a
tensile test.
EDP: Ethylene diamine pyrocatechol.
Effective mass: An electron in a
crystal appears to be accelerated more rapidly by an electric field than we
would expect. We explain this by saying that the electron has an effective
mass. It is important to remember that this is a property of the crystal, not
of the electron.
EIA: See enzyme
immunoassay.
EIS: See electrolyte/insulator/silicon.
Elastic deformation: A nonpermanent
deformation that totally recovers upon release of an applied stress.
Elastomer: A polymeric
material that may experience large and reversible elastic deformations.
Electrical breakdown: Condition in
which, particularly with high electric field, a nominal insulator becomes
electrically conducting.
Electric field [V/m]: In simplest form,
the potential difference between two points divided by the distance between the
two.
Electroluminescence: In electrical
engineering: the emission of visible light by a p-n junction across which a
forward-biased voltage is applied. In electrochemistry: emission of light by a
molecule which is being reduced or oxidized on a biased electrode. If the
exciting cause is a photon, rather than an electron, the process is called photoluminescence.
Electrolyte: A solution through
which an electric current may be carried by the motion of ions.
Electromigration: The physical
destruction of a wire caused by the movement of ions from their position in the
crystal. The effect is typically caused when a narrow wire is subject to a
large current density.
Electromotive force (emf) series: A series of
chemical elements arranged in order of their electromotive force. The
electromotive force is the greatest potential difference that can be generated
by a particular source of electric current. In practice this potential may be
observable only when the source is not supplying current, because of its internal
resistance.
Electronegative: Describing
elements that tend to gain electrons and form negative ions. The halogens are
typical electronegative elements.
Electron-hole pair: The excitation of
a valence electron into the conduction band leaves behind a hole in the valence
band. Thus the two carriers are created simultaneously.
Electron state (level): One of a set of
discrete, quantized energies that are allowed for electrons. In the atomic case
each state is specified by 4 quantum numbers.
EMI: For electromagnetic
interference.
Emitter: One region of a
bipolar transistor. In an npn transistor the electrons flow out of this region
into the base.
Energy [J]: Capacity for
performing work or to cause heat flow. Like work itself, it is measured in
joules.
Enthalpy (H): A property of a
system equal to E + PV, where E is the internal energy of the system, P is the
presssure of the system, and V is the volume of the system. At constant pressure
the change in enthalpy equals the energy flow as heat.
Enzyme: A large molecule,
usually a protein, that catalyzes biological reactions.
Enzyme immunoassay (EIA): In an EIA, an
enzyme-labeled antibody or antigen is used for the detection and quantification
of the antigen-antibody reaction. In an electrochemical EIA, the
enzyme-catalyzed reaction is monitored electrochemically (amperometric,
potentiometric, voltammetric, or conductometric). In EIA, the antibody-antigen
reaction furnishes the needed specificity. The enzyme label provides the
sensitivity via chemical amplification.
Epitaxial or epi: A single-crystal
semiconductor layer grown upon a single-crystal substrate having the same
crystallographic characteristics as the substrate material.
EPROM: For electrically programmable
read-only memory. Nonvolatile memory device.
Escherichia coli: A bacterium living
in natural conditions in man’s bowels. Abbreviated E. coli. Frequently
used in research by molecular biologists.
Eukaryotes: Organisms having a
cell nucleus.
Exciton: A system composed
of a conduction electron and a hole which are attracted togther by their
opposing electrical charges and therefore move through the crystal as a single
entity.
Exclusion principle: A fundamental rule
in quantum theory. It states that no more than two electrons are allowed to
occupy a given quantum state at any one time.
Exon: A DNA segment that stores
information about a part of the amino acid sequence of protein.
Expression: Realization of the
genetic information encoded in DNA leading to the synthesis of a protein or a
stable RNA. The term is used in particular when a foreign gene is introduced
into a host cell, which then expresses the gene, that is, produces a
recombinant protein, or when the rate of synthesis is artificially enhanced
(overexpression).
Extrinsic: Characterizes
doped, rather than pure, semiconductor.
Fab: For fabrication, a term referring
to the making of semiconductor devices such as microprocessors.
Face-centered cubic (FCC): A crystal structure
found in common elemental metals. Within the cubic unit cell, atoms are located
at all corner and face-centered positions.
Farad: The unit of capacitance. See capacitance.
Faraday: A constant
representing the charge on one mole of electrons; 96, 485 coulombs.
FCC: See face-centered
cubic.
FEA: For finite element analysis.
Fermi energy: A quantity which
is characteristic of the energy of the electron in a material. At absolute zero
the Fermi energy corresponds to the highest energy electrons, that is, all the
states with lower energy are occupied by electrons and all the ones with higher
energy are vacant. At higher temperatures the Fermi energy corresponds to the
average maximum energy of the electron, that is, there are as many electrons
above the Fermi energy as there are vacant states below it.
Ferroelectric material: A dielectric
material such as Rochelle salt and barium titanate with a domain structure
containing dipoles (asymmetric distributions of electrical charge) which
spontaneously align. Their domain structure makes them analogous to
ferromagnetic materials. They exhibit hysteresis and usually the piezoelectric
effect.
Ferromagnetism: Permanent and
large magnetizations found in some metals (e.g., Fe, Ni, and Co), resulting
from the parallel alignment of neighboring magnetic moments.
FET: For field-effect transistor. Semiconductor
device whose insulated gate electrode controls current flow.
Fiber-optic: Relates to
transmission of information as modulated light in tiny transparent fibers
instead of copper wires.
Fick’s first law: The diffusion flux
is proportional to the concentration gradient. This relationship is employed
for steady-state diffusion situations.
Fick’s second law: The time rate of
change of concentration is proportional to the second derivative of
concentration. This relationship is employed in non-steady-state diffusion
situations.
Filler: An inert foreign
substance added to a polymer to improve or modify its properties.
Firing: A high temperature
heat treatment that increases the density and strength of a ceramic piece.
Flat-band potential: See electrolyte/insulator/silicon
(EIS).
Flip-flop: Binary device
whose outputs change value only in response to an input pulse.
Fluorescence: Luminescence (see
also
luminescence) which persists less than a second after the exciting cause
has been removed. If the luminescence persists significantly longer it is
called phosphorescence.
FM: For frequency modulation. Information coding
scheme in which the frequency of a steady wave is changed.
Forward bias: The conducting
bias for a p-n junction rectifier that assures electron flow to the n side of
the junction.
Free energy (G): A thermodynamic
quantity that is a function of the enthalpy (H), the Kelvin temperature (T),
and the entropy (S) of a system; G=H-TS. At equilibrium, the free energy is at
a minimum. Under certain conditions the change in free energy for a process is
equal to the maximum useful work.
Frequency: Number of times
per second that a quantity representing a signal, such as a voltage, changes
state. Also, the number of waves (cycles) per second that pass a given point in
space.
Frequency response: Two relations
between sets of inputs and outputs. One relates frequencies to the output-input
amplitude ratio; the other relates frequencies to the phase difference between
the output and input.
Gain: The ratio of the amplitude of an
output to input signal.
Galvanic corrosion: The preferential
corrosion of the more chemically active of two metals electrically coupled and
exposed to an electrolyte.
Gate: Circuit whose logical output
variables are determined by its inputs.
Gauss: The cgs unit used in measuring
magnetic induction.
Gel: A polymer network
saturated with a solvent. Like a solid substance, a gel retains its form (e.g.,
gelatins and jellies). Electrophoresis in gels is widely used in decoding DNA
sequences, in genetic engineering, and in investigating circular DNA.
Gene: The physical unit
of inheritance, made up of a particular sequence of nucleotides on a particular
site on a particular chromosome.
Gene expression: The conversion of
the gene’s nucleotide sequence into an actual process or structure in the
cell. Some genes are expressed only at certain times during an organism’s
life and not at others.
Genetic code: The sequence of
nucleotides in a gene, coded in triplets (codons). The genetic code determines
the sequence of amino acids in protein synthesis.
Genetic engineering: An applied branch
of molecular biology that engages in purposeful modification of heredity by
cutting and “stitching together” DNA molecules and subsequently
building them into a living cell.
Genome: All the genes in a
complete set of chromosomes.
Genotype: A term from
classical genetics, denoting the totality of genes of the given organism. Now,
the term genome, which has the same meaning, is used more frequently.
Glass: An amorphous solid obtained when
silica is mixed with other compounds, heated above its melting point, and then
cooled rapidly.
Glass state: If a substance is
cooled below its freezing (crystallization) temperature but cannot rearrange
its atoms or molecules in the way necessary to form an ordered structure, it
remains a “vitrified” liquid. Common glass is transparent because
it is a supercooled liquid.
Glass transition temperature (Tg):
The
temperature at which, upon cooling, a noncrystalline ceramic or polymer
transforms from a supercooled liquid to a rigid glass.
Grain boundary: The interface
separating two adjoining grains having different crystallographic orientations.
Grain growth: The increase in
average grain size of a polycrystalline material. For most materials, an
elevated temperature heat treatment is necessary.
Grain size: The average grain
diameter as determined from a random cross section.
Green ceramic body: A ceramic piece,
formed as a particulate aggregate, that has been dried but not fired.
Ground: To make electrical
connection to the earth or to the chassis of a device (verb); the connection
point so used (noun).
GUI: For graphical user interface. Hardware,
software, and firmware that produces the display on modern personal computers.
Hall effect: The phenomenon
whereby a force is applied to a moving electron or hole by a magnetic field
that is applied perpendicular to the direction of motion. The force direction
is perpendicular to both the magnetic field and the particle motion directions.
Hardness: The measure of a
material’s resistance to deformation by surface indentation or by
abrasion. There are various scales in use to express hardness. The Mohs scale
is qualitative and somewhat arbitrary and ranges from 1 on the soft end for
talc to 10 for diamond. Quantitative scales are the Rockwell (indicated by HR),
Brinell (HB), Knoop (HK), and Vickers (HV). Knoop and Vickers are referred to
as microhardness testing methods on the basis of load and indenter size.
Heat capacity (Cv at constant
volume and Cp at constant pressure): The quantity of
heat required to produce a unit temperature rise per mole of material.
Helix: Structure wound up like a screw. In
biochemistry, helices are commonly found in proteins (alpha helix) and in
nucleic acids (double helix).
Heme: An iron complex.
Hemoglobin: A biomolecule
composed of four myoglobinelike units (proteins plus heme) that can bind
and transport four oxygen molecules in the blood.
HEMT: For high electron mobility
transistor. These are also called MODFETs.
Henry (H): Unit of inductance
(see
inductance). One henry (H) is the inductance of a closed circuit in
which an electromotive force of 1 volt is produced when the electric current in
the circuit varies uniformly at the rate of 1 ampere per second.
Henry’s law: The amount of gas
dissolved in a solution is directly proportional to the pressure of the gas
above the solution.
Heterostructure: A device
consisting of two (or more) different types of material. A heterojunction is
the interface between these two materials.
Hirudin: A potent clotting
inhibitor produced by leeches. The gene for this protein has now been
genetically engineered into canola plants.
Histones: Proteins that are
part of chromosomes. They form the protein core of nucleosomes.
Hole: A particle which corresponds to the
absence of an electron in the valence band of a semiconductor. The particle
behaves as though it carries a positive charge. In most semiconductors the
holes at the top of the valence band can have one of two different values of
effective mass and are referred to as light holes and heavy holes. Since their
mobility depends on their effective mass, it is often necessary to distinguish
between the two.
Home page: A site or
“page” on the World Wide Web (WWW).
Homogeneous and heterogeneous assays: A homogeneous assay
does not require a separation step to remove free antigen from bound antigen
and relies upon the fact that the function of the label is modified upon
binding, leading to a change in signal intensity. Because of high background
signal a heterogeneous approach incorporating a separation step of bound and
unbound makes the detection limit lower, approaching the values obtained by
RIA. The homogeneous assay is less technically demanding.
Hormones: Molecules of
protein and other origin that regulate many processes in the organism. The lack
or excess of a particular hormone causes many chronic ailments. Such hormones
as insulin, growth hormone, and others are widely known.
http: For hypertext transfer protocol. Transfer protocol
used on the WWW.
Human genome project: An international
research effort begun in the 1980s to map and sequence all 100,000 or so genes
found in human DNA.
Hydrophobic: Water-avoiding.
Hydrophobic interaction: Tendency of
hydrophobic molecules or parts of molecules to cluster with other hydrophobic
groups to minimize their exposure to water. Hydrophobic interactions are
important factors for the stability of cellular structures such as the double
layer membrane and the inner core of proteins.
Hyperthermophilic: Extremely
heat-loving, normally used to describe microorganisms whose optimal growth
temperature exceeds 80°C.
Hysteresis: The difference in
the output when a specific input value is approached first with an increasing
and then with a decreasing input. This phenomenon occurs in ferroelectric
materials and results in irreversible loss of energy through heat dissipation.
IC: See integrated
circuit.
Immunoglobulin G: The most common
class of antibodies present in human serum (i.e., the liquid part of blood).
Impedance: The complex ratio
of a force-like quantity (force, pressure, voltage, temperature, or electric
field) to a corresponding related velocity-like quantity (velocity, volume
velocity, current, heat flow, or magnetic field strength).
Impurity scattering: The presence of
impurities in a sample deflects the electrons and therefore gives rise to
resistance. This is particularly important when the impurities form ions.
Index of refraction (n): The ratio of the
velocity of light in a vacuum to the velocity in some medium.
Indirect gap semiconductor: A material in
which the recombination of conduction electrons and holes occurs by an
inefficient process.
Inductance [in Henry, H]: That property of
an electric circuit which tends to oppose change in current in the circuit. One
henry (H) is the inductance of a closed circuit in which an electromotive force
of 1 volt is produced when the electric current in the circuit varies uniformly
at the rate of 1 ampere per second.
Inductor: Energy storage
circuit component consisting of a coil of wire and possibly a magnetic
material.
Infrared: Invisible
electromagnetic radiation having a longer wavelength, and lower frequency, than
visible red light.
Inhibitor: A chemical
substance that, when added in relatively low concentrations, slows down a
chemical reaction.
Insertion point (in lithography
context):
Adaptation of a new lithography technique is referred to as the insertion point
of that technique.
Insulator: Material that
conducts electricity very poorly.
Insulin: A hormone
consisting of 51 amino acids in two polypeptide chains. Insulin reduces the
glucose level in the blood. Failure to produce insulin is one of the causes of
diabetes.
Integrated circuit (IC): Semiconductor
circuit, typically on a very small silicon chip, containing microfabricated
transistors, diodes, resistors, capacitors, etc.
Interference: A phenomenon which
is characteristic of waves. When the waves are in phase the interference is
constructive and the amplitude of the resultant waves is increased. When the
waves are out of phase the interference is destructive and the waves cancel
each other out.
Internet: Worldwide digital
communication network in which packets of information travel between senders
and recipients.
Interstitial diffusion: A diffusion
mechanism that causes atomic motion from interstitial site to interstitial
site.
Intrinsic semiconductor: Characterizes pure
undoped semiconductor; electrical conductivity depends only on temperature and
the band gap energy.
Intron: A DNA section that
divides exons.
I/O: Input/output information transfer between computer
and peripherals such as keyboard or printer.
Ion: An atom which has gained or lost
one or more electrons, and therefore has a net electric charge. Ionic bonding
occurs in materials where the electrons are transferred from one type of atom
to another. The bond is a result of the attractive forces between the positive
and negative ions.
Ion channels: Pores in the cell
membrane that allow and regulate the transport of ions across the membrane.
Ionic bond: A coulombic
interatomic bond existing between two adjacent and oppositely charged ions.
Ion implantation: A method of
introducing dopant atoms into a crystal by projecting them at high speed
towards the crystal surface.
Ionophore: A macro-organic
molecule capable of specifically solubilizing an inorganic ion of suitable size
in organic mediums.
ISE: For ion selective electrode. Ions in solution
are quantified by measuring the change in voltage (i.e., potentiometric)
resulting from the distribution of ions (by ion exchange controlled by the ion
exchange current io) between a sensing membrane (the ion selective
membrane) and the solution. This potential is measured at zero current with
respect to a reference electrode which is also in contact with the solution.
The potential measured is proportional to the logarithm of the analyte
concentration. The oldest and best known ISE is the pH sensor based on a glass
membrane. More recently, polymeric membranes have been formed incorporating
ionophores (see ionophore) rendering the membrane specific to
certain ions only.
ISFET: For ion
sensitive field effect transistor. A logical extension of ISEs. They can be
conceptualized by imagining that the lead from an ion selective electrode,
attached via a cable to an FET in the high impedance input stage of a
voltmeter, is made shorter until no lead exists and the selective membrane is
attached directly to the FET. For an ISFET, the property measured is the
lateral conductivity between two opposing doped regions (the source and drain)
surrounding the active area. The underlying change is a change in flat-band
voltage.
Isomorphous: Having the same
structure. In the phase diagram sense, isomorphicity means having the same
crystal structure or complete solid solubility for all compositions.
Isothermal: At a constant
temperature. In an isothermal process heat is, if necessary, supplied or
removed from the system at just the right rate to maintain constant temperature.
Isotropic: Having identical
values of a property in all crytallographic directions.
Josephson junction: A device formed by
placing a very thin layer of insulator between two superconductors. The
insulator is said to form a weak superconductor because the flow of
superconducting current across the junction is extremely sensitive to a
magnetic field.
Kilobyte (kB): 210 (=
1024, or about one thousand) bytes of information.
Kilohertz (kHz): One thousand
cycles per second (see also frequency).
Kinesin: A motor protein
used for transport processes within the cell and which migrates along the
microtubules.
Kinetic molecular theory: A model that
assumes that an ideal gas is composed of tiny particles (molecules) in constant
motion.
Label or marker: A problem endemic
in immunoassays is the absence of a chemical signal created by the
antibody-antigen binding, in contrast with an enzyme-substrate binding reaction
which produces a chemical reaction. As a result of this absence, the use of a
label or marker is usually required to detect the bound antibody-antigen
complex. Several markers have been established for use in immunoassays.
Examples of such markers are:
• Particles
(e.g., latex, gold particles, erythrocytes)
• Metal
and dye sols (e.g., Au, Palanil® Luminous Red G)
• Chemiluminescent
and bioluminescent compounds (e.g., Luciferase/luciferins, Luminol and
derivatives, Acridinium esters, Peroxidase)
• Electrochemical
active species (ions, redox species, ionophores)
• Fluorophores
(e.g., dansyl chloride DANS, rare earth metal chelates, Umbelliferones)
• Chromophores
• Liposomes
• Iodine-125,
tritium, 14C, 75Se, 57Co.
Langmuir-Blodgett film: A single layer of
molecules that has been transferred from the surface of a liquid onto a solid
substrate.
Laser: For light amplification by the
stimulated emission of radiation. Quantum device that produces coherent
light.
Laser trimming: A method for
adjusting the value of thin- or thick-film resistors by using a
computer-controlled laser system.
LCD: For liquid crystal display. Display device
employing light source and electrically alterable optically active thin film.
Leakage: The loss of all or
parts of a useful agent, as of the electric current that flows through an
insulator or the magnetic flux that passes outside useful flux circuits.
LED: For light-emitting diode. Semiconducting
diode that produces visible or infrared radiation.
Lewis acid: An electron-pair
acceptor.
Lewis base: An electron-pair
donor.
Life (lifetime): The length of time
the sensor can be used before its performance changes.
Limit of detection: The smallest
measurable input. This differs from resolution, which defines the smallest
measurable change in input. For a temperature measurement, this would provide
an indication of the lowest temperature in response to which a sensor could
generate an output.
Linear coefficient of thermal expansion: See thermal
expansion coefficient, linear.
Linearity: The degree to
which the calibration curve of a device conforms to a straight line.
Lipids: Water-insoluble
substances than can be extracted from cells by nonpolar organic solvents.
Luminescence: Defined as the
emission of light from a substance in an electronically excited state.
Depending on whether the excited state is singlet or triplet, the emission is
called fluorescence (less than 1 second decay) or phosphorescence (longer than 1
second decay). Depending on the source from which molecules get the needed extra energy, different types of
luminescence are distinguished: radioluminescence, photoluminescence (in the same
category are fluorescence and phosphorescence), chemiluminescence and
bioluminescence, electrochemiluminescence, sonochemiluminescence and
thermoluminescence.
Magnetic field strength (designated by
H) [A/m]:
Magnetic field produced by a current, independent of the presence of magnetic
material. The units of H are ampere-turns per meter, or just amperes per meter.
Magnetic flux density or magnetic
induction (designated by B): The magnetic field produced in a substance
by an external magnetic field. The units of B are tesla (T). One tesla is the
magnetic flux density given by a magnetic flux of 1 weber per square meter. One
weber is a magnetic flux that, linking a circuit of 1 turn, would produce in it
an electromotive force of 1 volt if it were reduced to zero at a uniform rate
in 1 second. Both B and H are field vectors. One henry (H) is the inductance of
a closed circuit in which an electromotive force of 1 volt is produced when the
electric current in the circuit varies uniformly at the rate of 1 ampere per
second. The magnetic field strength and flux density are related according to:
B = µH, where µ is the permeability (see permeability).
Magnetic susceptibility (cm): The
proportionality constant between the magnetization M (see magnetization) and the magnetic
field strength H. The magnetic susceptibility is unitless.
Magnetostrictive material: A material that
changes dimension in the presence of a magnetic field or generates a magnetic
field when mechanically deformed.
Majority/minority carriers: In a semiconductor
the majority carrier is the one introduced by doping the material. The minority
carriers are the other type of carrier (conduction electrons or holes) present
because of thermal excitation.
Martensite: A metastable iron
phase supersaturated in carbon that is the product of a diffusionless (a
thermal) transformation from austenite.
Mask: Pattern on glass, like a
photographic negative, for producing integrated-circuit elements on
semiconductor wafer.
MBE: For molecular beam epitaxy. One way of
producing high-quality atomically layered structures.
MCM: For multichip module. The
interconnection of two or more semiconductor chips in a semiconductor-type
package.
Mean: Numerical average of data values.
Measurand: A physical
quantity, condition, or property that is to be measured.
Mechatronics: The synergistic
combination of precision mechanical engineering with electronic control.
Megabyte (MB): 220 (=
1,048,576, or about one million) bytes of information.
Megahertz (Mhz): One million cycles
per second (see also frequency).
MEMS: Stood originally for micro-electromechanical
system.
Microscopic mechanical elements, fabricated on silicon chips by techniques
similar to those used in integrated circuit manufacture, for use as sensors,
actuators, and other devices. Today almost any miniaturized device (based on Si
technology or traditional precision engineering, chemical or mechanical) is
referred to as a MEMS device.
MESFET: The name given to
an FET structure fabricated from gallium arsenide. The principle of operation
is slightly different from that of a MOSFET because there is no oxide layer
above the gate (since gallium arsenide has no native oxide).
Messenger RNA: See mRNA.
Metallic bonding: The bond which
forms between a collection of positive ions as a result of the associated sea
of electrons. Materials which bond in this way are called metals. Owing to the large
number of essentially free electrons, these materials make good electrical
conductors.
Microphone: Device that
produces voltage or current in response to a sound wave.
Microprocessor: Chip containing
the logical elements for performing calculations and carrying out stored
instructions.
Microstructure: In materials
engineering the structural features of a material such as grain boundaries,
grain size and structure, subject to observation under a microscope, selective
etching, etc. In MEMS microstructure unfortunately is also used to designate a
micromachined feature.
Microtubules: Hollow tubes made
of subunits of the protein tubulin. They serve both for structural stability of
higher cells and as a “rail” for transport processes mediated by
the motor protein kinesin.
Miller indices: A set of 3
integers (4 for hexagonal) that designate crystallographic planes, as
determined from reciprocals of fractional axial intercepts.
MIPS: For millions of instructions per
second.
A measure of computing power.
Mitochondrion: A cigar-shaped
body located in the cytoplasm. It is the cell’s power plant, transforming
food products into adenosine triphosphoric acid (ATP) energy.
Mobility (electron, and hole): The
proportionality constant between the carrier drift velocity and applied
electric field.
Modulus of elasticity (E): The ratio of
stress to strain when deformation is totally elastic. Also the Young’s
modulus.
Molality: The molality or
molal concentration (symbol m) is the amount of substance per unit mass of
solvent or mol kg–1.
Molarity: Concentration in a
liquid solution (symbol c), in terms of the number of moles of a solute
dissolved in 106†mm3 (103 cm3)
of solution in mol l–1.
Molding (plastics): Shaping a plastic
material by forcing it, under pressure at a high temperature, into a mold
cavity.
Molecular chaperone: A protein that
helps unfolded or freshly synthesized proteins to fold to the correct
three-dimensional structure by suppressing unwanted side reactions.
Monoclonal antibodies: Produced by
injecting animals to elicit a response from lymphocytes to produce antibodies.
Lymphocytes which produce antibodies with strong binding capability can be
isolated and used to produce only one kind of antibody (monoclonal) on a
permanent basis once the lymphocytes are immortalized. This is accomplished by fusing
them (combining them genetically) with cancer cells which have the
distinction of living indefinitely in a culture. Monoclonal antibodies can be
produced repeatedly and collected for use in immunodetection.
Moore’s law (after Gordon Moore): “The number
of transistors per computer chip will double roughly every two years.”
MOSFET: For metal-oxide-semiconductor
field effect transistor. Device where gate electrode potential controls current
flow.
mRNA (messenger RNA): The information
carrier used by the ribosome during protein biosynthesis. The mRNA arises from
the process of DNA transcription. In contrast to transfer and ribosomal RNA, it
is quite short-lived. The latter two, therefore, may be called stable RNAs.
MUX: Device for combining several
signals or data streams into a single flow.
Myosin: The motor protein
that generates the force and movement in contraction of muscles.
NAND: For NOT-AND. Logic gate whose
output is the negation of that of the AND gate.
Nanotubes: Tubes with an
inner diameter in the nanometer range.
Nernst equation: An equation
relating the potential of an electrochemical cell to the concentrations of the
cell components: E = Eo + RT/zF ln C1/C2 with
z the charge exchanged at the electrode and C1 and C2
concentrations of two electroactive compounds.
NOR: For NOT-OR. Logic gate whose
output is the negation of that of the OR gate.
NOT: Logic gate whose output is binary 1
when its input is 0, and whose output is a 0 when its input is a 1.
n-type semiconductor: Characterizes a
semiconductor containing predominantly mobile electrons (see also p-type
semiconductor).
Nucleation: The initial stage
in a phase transformation, evidenced by the formation of small particles
(nuclei) of the new phase, which are capable of growing.
Nucleosome: The principal
structural element of the chromosome. It consists of a protein (histone) core,
on which is wound DNA with a length of 140 base pairs, thus making about two
turns.
Nucleotide: A monomer of the
nucleic acids composed of a five-carbon sugar, a nitrogen-containing base, and
phosphoric acid.
Nucleotide sequence (or base sequence): The particular
arrangement of nucleotides along a strip of DNA. Genes are defined as a
particular nucleotide sequence.
Nucleus: Part of the cell
containing the chromosomes.
Ohm (W): Unit of
resistance. One ohm is the electrical resistance between two points of a
conductor when a constant potential difference of 1 volt, applied to these
points, produces a current of 1 ampere in the conductor.
Ohmmeter: Tool for measuring
electrical resistance.
Op-amp: For operational
amplifier. Semiconductor amplifier characterized by high gain and high
internal resistance.
OR: Logic gate whose output is a binary
1 if any of its inputs is a 1; zero otherwise.
Organelles: Compartments of
the eukaryotic cell, which are separated from the cytoplasm by a membrane and
fulfill specialized function. Examples are mitochondria (energy metabolism) and
chloroplasts (photosynthesis).
Oscillator: Circuit that
produces an alternating voltage (current) when supplied by a steady (DC) energy
source.
Osmosis: The flow of
solvent into a solution through a semipermeable membrane.
Osmotic pressure
(p):
The pressure that must be applied to a solution to stop osmosis: p = MRT.
Oxidation: The removal of one
or more electrons from an atom, ion, or molecule.
Package: Protective
enclosure for a chip or a sensor, typically made of plastic or ceramic.
Paramagnetism: A relatively weak
form of magnetism resulting from the independent alignment of atomic dipoles
(magnetic) with an applied magnetic field. Also a type of induced magnetism,
associated with unpaired electrons, that causes a substance to be zapped into
the inducing magnetic field.
Phase: A term describing the specific
stage that a wave is at in its cycle. In general we are interested in
determining the phase of one wave relative to another. If the peaks of the
waves coincide we say that they are in phase; if the peak of one coincides with
the trough of the other then they are out of phase.
Phase shift: A time difference
between the input and output signals.
Phase transformation: A change in the
number and/or character of the phases that make up the microstructure of an
alloy.
Phenotype: A notion of
classical genetics signifying the totality of external characteristics and
properties of a living organism, which have evolved in the course of its
development.
Phonon: A single quantum
of vibrational or elastic energy.
Phosphorescence: Luminescence that
occurs at times greater than on the order of a second after an electron
excitation event (see also luminescence).
Photodiode: Semiconductor
diode that produces voltage (current) in response to illumination (see also phototransistor).
Photolithography: The process which
is most commonly used to transfer the layout of an integrated circuit on to a
wafer.
Photomicrograph: The picture made
with a microscope.
Phototransistor: Transistor that,
when powered, produces amplified voltage (current) in response to illumination.
Piezoelectric material: A ferroelectric
material in which an electrical potential difference is created due to
mechanical deformation, or conversely, in which the application of a voltage
causes dimensional changes in the material.
Pinhole: The term embraces
a wide variety of oxide defects and is used in a broad sense today. Listed in
this category are cracks caused by thermal contraction after oxidation or by
handling, and regions of oxide with low dielectric strength caused by dust
particles, inadequate masking, contamination, or poor resist adhesion.
Pin-out: Diagram showing
the relations between connecting pins and internal components for electronic
devices.
Pixel: For picture element. Smallest element
of an image, such as a dot on a computer monitor screen.
Pitting: A form of very
localized corrosion wherein small pits or holes form, usually in a vertical
direction.
pK value: A measure of the
strength of an acid on a logarithmic scale. The pK value is given by log10
(1/Ka), where Ka is the acid dissociation constant. pK
values often are used to compare the strengths of different acids.
Planck’s constant: The fundamental
constant associated with quantum theory. The energy of a photon is equal to
Planck’s constant multiplied by the speed of light and divided by the
wavelength of the light.
Plasmid: A small circle of
bacterial DNA separate from the single bacterial chromosome and capable of
replicating independently. Plasmids are also occasionally found in certain
fungi and plants.
Plastic deformation: Permanent or
nonrecoverable deformation, accompanied by permanent atomic displacement.
Plasticizer: A low molecular
weight polymer additive that enhances flexibility and workability and reduces
stiffness and brittleness.
p-n junction: A device formed
from a single crystal containing regions which are doped p-type and n-type.
Among other applications the device can be used as a diode or in a p-n junction
laser.
Point defect: A crystalline
defect associated with one or several atomic sites.
Poisson’s ratio (n): For elastic
deformation, the negative ratio of lateral and axial strains that result from
an applied axial stress.
Polarization (P): The total electric
dipole moment per unit volume of dielectric material.
Polyclonal antibodies: Antibodies
produced by an animal’s white blood cells (lymphocytes, specifically) in
response to an antigen. This response occurs naturally or can purposely be
created by injecting an animal, such as a rabbit or goat, with a specific
antigen. More than one kind of antibody is produced since more than one
lymphocyte is producing antibodies. This is referred to as polyclonal. The polyclonal
antibodies are isolated from the animal and can be used for detection purposes.
Because the antibodies are actually a mixture with different affinities
(binding capability) for the antigen of interest, some variability in
performance can occur from one test to another or one batch of antibodies to
another.
Polymerase chain reaction (PCR): A method for
making multiple copies of fragments of DNA. It uses a heat-stable DNA
polymerase enzyme and cycles of heating and cooling to successively split apart
the strands of double-stranded DNA and uses the single strands as templates for
building new double-stranded DNA.
Polypeptide: Any polymer made
of amino acid building blocks. Used in particular for those cases when the
polymer is unstructured—as opposed to a protein, which is a polypeptide
that normally adopts a well-defined three-dimensional structure.
Polysilicon: Polycrystalline
silicon used as conductor in integrated circuits, and especially FETs.
Potentiometric device: Monitors the
voltage between a sensing electrode and a reference electrode. A high input
impedance voltmeter is used to minimize current flow. The voltage typically is
proportional to the logarithm of the analyte concentration.
Power [W]: Product of voltage
and current in a component; also, refers to the field of electric energy
supply.
Precision: The degree of
reproducibility among several independent measurements of the same true value
under specified conditions.
Primary structure: First level of
structure in proteins, comprising the order or sequence of amino acids in the
polypeptide chain.
Primer: A single-stranded
oligonucleotide (DNA or RNA) that binds, via complementary pairing, to DNA or
RNA single-stranded molecules and serves for the priming of polymerases working
on both DNA and RNA.
Printed circuit board: Selectively
metallized insulating sheet for supporting and interconnecting circuit
components.
Protein biosynthesis: The process of
linking up amino acid building blocks to form a protein molecule. It is carried
out by the ribosome together with a set of other cellular factors.
Protein folding: The process in
which the linear chain of amino acids (i.e., polypeptide) arising from protein
biosynthesis or from denaturation of a protein forms a three-dimensional
structure stabilized by many weak interactions. Most proteins have to be folded
to be biologically active.
Proteins: Molecules made up
of long chains of amino acids. They build tissues and carry out many critical
functions in the body. Proteins literally make us what we are.
p-type semiconductor: A semiconductor
for which the predominant charge carriers responsible for electrical conduction
are holes.
Pyroelectricity: The property of
certain crystals, such as tourmaline, of acquiring opposite electrical charges
on opposite faces when heated.
Q factor: A rating, applied
to coils, capacitors, and resonant circuits, equal to the reactance divided by
the resistance. The ratio of energy stored to energy dissipated per cycle in an
electrical or mechanical system.
Q particles: Nanometer-sized
particles of semiconductor materials, whose behavior is governed by
quantum-mechanical effects.
Quantization: The concept that
energy can occur only in discrete units called quanta.
Quantum dot: An artificial
structure in which the carriers exhibit wave-like properties along all three
dimensions.
Quantum Hall effect: The anomalous
results obtained from the Hall effect when the carriers are confined in one
dimension.
Quantum well: An artificial
structure in which the carriers are confined in one dimension. In other words
the electrons exhibit wave-like properties in one dimension but behave as free
electrons in the other two dimensions. A quantum well laser uses these
properties to produce a semiconductor laser which is far more efficient than a
p-n junction laser.
Quantum wire: An artificial
structure in which carriers are confined in two dimensions. The carriers are
free to travel along the axis of the wire, but exhibit wave-like properties in
the other directions.
RAM: For random access memory. Read-write memory
with elements accessible in any order.
Range: The difference between the minimum
and maximum values of sensor output in the intended operating range. Defines
the overall operating limits of a sensor.
Reactance: Portion of
impedance that characterizes nondissipative, energy storage effects (see
also
impedance).
Reactant: A starting
substance in a chemical reaction. It appears to the left of the arrow in a
chemical reaction.
Recombinant DNA: Novel DNA made by
joining DNA fragments from different sources.
Recombination: The process by
which a conduction electron is reunited with a hole. As a result both carriers
are annihilated and there is a release of energy (usually in the form of a
photon).
Recrystallization: The formation of a
new set of strain-free grains within a previously cold-worked material due to
an annealing heat treatment.
Rectifier: Device that
converts bi-directional to one-way current flow.
Reduction: The addition of
one or more electrons to an atom, ion, or molecule.
Reflection: Deflection of a
light beam at the interface between 2 media.
Refraction: Bending of a light
beam when passing from one medium to another, at different velocities of light.
Refractory: A metal or ceramic
that does not deteriorate rapidly or does not melt when exposed to extremely
high temperatures.
Reliability (life, multi-use vs. single,
calibration vs. accuracy drift): How well a sensor maintains both precision
and accuracy over its expected lifetime. Also includes the robustness of the
sensor.
Repeatability: The exactness with
which a measuring instrument repeats indications when it measures the same
property under the same conditions.
Residual stress: A persisting
stress in a material free of external forces or temperature gradients.
Resistance [W-ohm]: Characteristic of
a resistor. In a 1-ohm resistance a current of 1 A produces a voltage drop of 1
V.
Resistivity (r): The reciprocal of
electrical conductivity, and a measure of a material’s resistance to
passing electric current.
Resistor: Energy dissipative
element consisting of a poor conductor in series with connecting wires.
Resolution: The smallest
measurable change in input that will produce a small but noticeable change in
the output. In the context of chemical separations, defines the completeness of
separation.
Resonant frequency: The frequency at
which a moving member or a circuit has a maximum output for a given input.
Resonant
tunneling: A process in which the probability of an electron tunneling
through a barrier increases dramatically for a specific energy. This principle
is applied in the resonant tunneling transistor.
Response time: The time it takes
for the sensor's output to reach its final value. A measure of how quickly the
sensor will respond to changes in the environment. In general, this parameter
is a measure of the speed of the sensor and must be compared with the speed of
the process.
Restriction endonuclease (or enzyme): An enzyme that
cuts a DNA molecule at a particular base sequence.
Reverse bias: The insulating
bias for a p-n junction rectifier; electrons flow into the p side of the
junction.
RF: For radio frequency. Refers to
alternating voltages and currents having frequencies between 9 kHz and 3 MHz.
RHEED: For reflection high-energy
electron diffraction.
Rhodopsin: A protein molecule
that plays a key role in transforming light into the visual signal in the eye.
Ribonucleic acid: See RNA.
Ribosome: A complex of more
than 50 proteins and several RNA molecules, which carries out the synthesis of
proteins following the genetic instructions read from the messenger RNA with
the help of transfer RNAs and various protein factors.
rms: For root mean square.
RNA (ribonucleic acid): A nucleotide chain
that differs from DNA in having the sugar ribose instead of deoxyribose and
having the base uracil instead of thymine. RNA helps translate the instructions
encoded in DNA to build proteins.
RNA polymerase: An enzyme
synthesizing messenger RNA on the DNA template, which carries out the
transcription process.
ROM: For read only memory. Memory used for
permanent storage of unalterable data; nonvolatile memory.
Sacrificial anode: An active metal or
alloy that corrodes and protects another metal or alloy to which it is
electrically coupled.
Sacrificial layer: A thin film that
is later removed to release a microstructure from its substrate.
Scanning electron microscope (SEM): A microscope
producing an image by using reflected electron beams that scan the surface of a
specimen.
Scanning tunneling microscope (STM): A technique that
uses the quantum-mechanical effect called tunneling (i.e., that
electrons can jump through “forbidden” space across very short
distances) to probe surfaces at nearly atomic resolution.
Secondary structure: Certain structural
features of proteins that can directly form from the linear protein chain.
Secondary structure elements include alpha helices and beta-pleated sheets.
Selectivity: The ability of a
sensor to measure only one metric or, in the case of a chemical sensor, to
measure only a single chemical species.
SEM: See scanning
electron microscope.
Semiconductor: Nonmetallic
material, such as silicon, whose electrical conductivity is moderate and
alterable by doping.
Sensitivity: The amount of
change in a sensor's output in response to a change at a sensor's input over
the sensor's entire range. Provides an indication of a sensor's ability to
detect changes. For some sensors, the sensitivity is defined as the input
parameter change required to produce a standardized output change.
SHE: See standard
hydrogen electrode.
Signal-to-noise-ratio: The ratio of the
output signal with an input signal to the output signal with no input signal.
Single crystal: A crystalline
solid for which the periodic and repeated atomic pattern extends throughout its
entirety without interruption.
Sintering: Particle
coalescence of a powdered aggregate by diffusion that is accomplished by firing
at an elevated temperature.
SI units: International
system of units based on the metric system and units derived from the metric
system.
Slip: Plastic deformation resulting from
dislocation motion; also, the shear displacement of 2 adjacent planes of atoms.
Slip casting: A forming
technique used to shape ceramic materials. A slip or suspension of solid
particles in water is poured into a porous mold. A solid layer forms on the
inside wall as water is absorbed by the mold, leaving a shell (or a solid
piece) in the shape of the mold.
Smart sensor: A sensor in which
the electronics that process the output from the sensor are partially or fully
integrated on a single chip.
Solvent: The component of a
solution that dissolves a solute.
Source: The region of an
FET through which the carriers flow into the device.
Span: The difference between the highest
and lowest scale values of an instrument.
Specific heat: The heat capacity
per unit mass of material.
Specific modulus (specific stiffness): The ratio of
elastic modulus to specific gravity for a material.
Specific strength: The ration of
tensile strength to specific gravity for a material.
Spinning: Fiber forming
process. A multitude of fibers are spun as molten material is forced through
many small orifices.
Spontaneous emission: A randomly
occurring process in which a conduction electron recombines with a hole to
produce a photon.
Squeeze-film damping: Effect of ambient
fluid and spacing on the vertical movement of a structural member with respect
to a substrate.
Stability: The ability of a
sensor to retain specified characteristics after being subjected to designated
environmental or electrical test conditions.
Stabilizer: A polymer additive
that counteracts deteriorative processes.
Standard atmosphere: A unit of pressure
equal to 760 mm Hg.
Standard hydrogen electrode (SHE): A platinum
conductor in contact with a 1 M H+ ions (???) and bathed by hydrogen
gas at one atmosphere.
Steady-state diffusion: The diffusion
condition for which there is no net accumulation or depletion of diffusing
species. The diffusion flux is independent of time.
Step response: The response of a
system to an instantaneous jump in the input signal.
Stiction: Static friction;
adhering of thin micromachined layers to a substrate.
Stimulated emission: A process in which
the presence of one photon induces recombination of an electron and hole to
produce another identical photon.
STM: See scanning
tunneling microscope.
Stoichiometry: For ionic
compounds, the state of having exactly the ratio of cations to anions specified
by the chemical formula. Stoichiometric quantities refer to quantities of
reactants mixed in exactly the correct amounts so that all are used up at the
same time.
Strain (symbol e): The change in
gauge length of a specimen, in the direction of an applied stress, divided by
its original gauge length.
Strain gauge: An element (wire
or foil) that measures a strain based on electrical resistance changes of the
gauge that result from a change in length or dimension strain of the wire or
foil.
Stress concentration: The concentration
or amplification of an applied stress at the tip of a notch or small crack.
Stress corrosion (cracking): A form of failure
resulting from the combined action of a tensile stress and a corrosion
environment, occuring at lower stress levels than required when the corrosion
environment is absent.
Superconductivity: A phenomenon
characterized by the disappearance of the electrical resistivity at
temperatures approaching 0 K.
Superconductor: A state of matter,
generally achieved at extremely low temperatures, in which (among other things)
the material exhibits no resistance to the flow of a direct current.
Superlattice: An artificial
structure formed by constructing a large number of quantum wells side by side,
separated by thin barrier layers. Interaction of electrons in neighboring wells
produces a series of allowed minibands.
Surface plasmon: A collective
motion of electrons in the surface of a metal conductor, excited by the impact
of light of appropriate wavelength at a particular angle.
Synchrotron: A particle
accelerator providing synchronized particles and high-energy X-rays.
Systematic error: An error that always
occurs in the same direction.
TAB bonding: Tape automated
bonding. Semiconductor packaging technique that uses a tiny lead-frame to
connect circuitry on the surface of the chip to a substrate instead of wire
bonds.
TEM: See transmission
electron microscope.
Tensile strength (TS): The maximum
engineering stress, in tension, sustainable without fracture; also called ultimate
(tensile) strength.
Tertiary structure: Comprises the
complete folded structure of a native protein, including through-space links
(tertiary contacts) between separate elements of secondary structure.
Tesla [T]: Unit of magnetic
induction: 1 T = 1 weber/m2 (also, 1T = 104 gauss).
TFT: For thin film transistor.
Thermal conductivity (k): For steady-state
heat flow, the proportionality constant between the heat flux and the
temperature gradient. Also, a parameter characterizing the ability of a
material to conduct heat.
Thermal expansion coefficient, linear
(a):
The fractional change in length divided by the change in temperature.
Thermal fatigue: A type of fatigue
failure that introduces the cyclic stresses by fluctuating thermal stresses.
Thermal shock: The fracture of a
brittle material resulting from stresses introduced by a rapid temperature
change.
Thermal stress: A residual stress
introduced within a body resulting from a change in temperature.
Thermistor: A
temperature-measuring device that contains a resistor or semiconductor whose
resistance varies with temperature.
Thermocouple: A
temperature-measuring device, which contains a pair of end-joined dissimilar
conductors in which an electromotive force is developed by thermoelectric
effects when the joined ends and the free ends of the conductors are a
different temperature.
Thermophilic: Heat-loving.
Thermoplastic polymer: A substance that
when molded to a certain shape under appropriate conditions can later be
remelted.
Thermoset polymer: A substance that
when molded to a certain shape under pressure and high temperatures cannot be
softened again or dissolved.
Threshold: The smallest input
signal that will cause a readable change in the output signal.
Time constant: The time it takes
for the output change to reach 63% of its final value.
Toughness: A measure of the
amount of energy absorbed by a material as it fractures, indicated by the total
area under the material’s tensile stress-strain curve.
Transcription: Copying of the
genetic information from DNA onto RNA by the enzyme RNA polymerase. The
regulation of transcription by specialized proteins, the transcription factors,
is a central switchboard for all life processes in a cell.
Transduction (self-generating or
modulating): The conversion of the signal to be measured into another,
more easily accessible form. Source of energy for transmission of the sensor
signal.
Transduction mode (direct or indirect): How the sensor
acquires the desired information from the material. In general, this parameter
is an indication of the ability of the sensor signal to provide information
regarding a material property or state of interest.
Transfer RNA. See tRNA.
Transformer: Device using
magnetically linked inductors to change AC voltage level.
Transgenic organism: An organism into
which the genes of other species have been engineered.
Transient response: The response of
the sensor to a step change in the measurand.
Translation: Another term for
protein biosynthesis, used to emphasize the aspect that the ribosome
“translates” the 4-letter genetic code used in DNA and RNA into the
20-letter amino acid code of the proteins.
Transmission: Refers to system
for carrying electric power at voltages above 100,000 volts.
Transmission electron microscope (TEM): A microscope that
produces an image by using electron beams to transmit (pass through) the
specimen, making examination of internal features at high magnifications
possible.
Transistor: Semiconductor
device used for amplification and switching.
Tribology: The science and
technology of two interacting surfaces in relative motion and of related
subjects and practices. The popular equivalent is friction, wear, and
lubrication in surfaces sliding against each other, as in bearing and gears.
tRNA (transfer RNA): Stable RNA
molecules that act as specific carriers for the amino acid molecules to be
incorporated in protein biosynthesis.
TS: See tensile
strength.
Turn-on-voltage: Applied voltage
required to produce conduction in a diode.
ULSI: For ultra large scale
integration. A chip with over 1,000,000 components.
Unit cell: The basic
structural unit of a crystal structure, defined in terms of atom (or ion)
positions within a parallelepiped volume.
URL: For universal resource locator. Address of a World
Wide Web site.
Usenet: Interlinked
bulletin board available via Internet and commercial on-line services.
UV: For ultraviolet. Characterization
of short-wavelength light for exposing photoresist in making semiconductor
devices.
Valence band: The electron
energy band that contains the valence electrons in solid materials.
Valence electrons: Those electrons in
the outermost orbit of an atom. On forming a solid these electrons interact to
produce the valence band. In a semiconductor or insulator this band is full.
van der Waals bond: A secondary,
permanent or induced, interatomic bond between adjacent molecular dipoles.
Viscoelasticity: A type of
deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation.
Viscosity (symbol is h): The ratio of the
magnitude of an applied shear stress to the velocity gradient that it produces;
in other words, a measure of a noncrystalline material’s resistance to
permanent deformation.
Vitrification: During firing of a
ceramic body, the formation of a liquid phase that becomes a glass-bonding
matrix upon cooling.
VLSI: For very large scale
integration. A chip with 100,000 to 1,000,000 components.
Volt: Unit of electrical potential
difference (see voltage).
Voltage [V]: Potential
difference between two points: energy to move a 1-C charge through a 1-V
potential difference is 1-J.
Wafer: Semiconductor disk out of which
integrated circuits are made (see also chip, mask).
Watt (W): Unit of power. One
watt is the power that in 1 second gives rise to an energy of 1 joule.
Weber: Unit of magnetic flux. One weber is
a magnetic flux that linking a circuit of 1 turn would produce in it an
electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1
second.
Weight percent (wt%): Concentration
specification on the basis of weight (or mass) of a particular element relative
to the total alloy weight (or mass).
Whisker: A very thin,
single crystal of high perfection which has an extremely large
length-to-diameter ratio. Whiskers are used as the reinforcing phase in some
composites.
World Wide Web (WWW): Graphical
hypertext system linking many Internet computers.
WWW: See World Wide Web.
Yielding: The onset of
plastic deformation.
Yield strength: The stress
required to produce a very slight yet specified amount of plastic strain; a
strain offset of 0.002 is commonly used.
Zener diode: Semiconductor
diode that has a well-defined turn-on voltage for conduction in the reverse
direction.
Zero offset: The output of a
sensor at zero input for a specified supply voltage or current.
Zone refining: A metallurgical
process for obtaining a highly pure metal that depends on continuously melting
the impure material and recrystallizing the pure metal.