Page 289 - An Introduction to Microelectromechanical Systems Engineering

268 Glossary

Piezoelectricity The property exhibited by a class of materials to develop a volt-
age in response to applied mechanical stress or pressure. Conversely, an externally
applied electrical voltage strains and deforms the material.
Piezoresistivity The property of a certain class of materials, including impurity
doped silicon, to change their electrical resistivity in response to mechanical stress.

Plasma etching A class of etch processes capable of selectively removing material,
including silicon, by chemical reaction with one or more gases. The reactive gases
are ionized in a plasma inside a vacuum chamber by means of electrical or electro-
magnetic energy. A plasma is an electrically neutral, highly ionized gas composed of
ions, electrons, and neutral particles.

Polysilicon Abbreviation for polycrystalline silicon. An aggregate of small crys-
talline grains of silicon, each with a different preferred orientation. The grains may
vary in dimensions from a few nanometers to a few micrometers.
Polymerase chain reaction (PCR) In biochemistry, it is an amplification process
invented in the 1980s for creating billions of identical replicas of a DNA fragment.
Primitive unit The smallest repeating block of a crystal lattice.
Proteomics The study of the full set of proteins encoded by a genome.
p-type doping see doping.

p-n diode see doping.
Quadrature The situation when two periodic signals of same frequency, f , are
L
out of phase by a quarter of a cycle, or 90º. For example, sine and cosine waveforms
are in quadrature (or phase quadrature). One important application is in communi-
cations and RF circuits. Separation is possible by heterodyning (multiplication) with
another signal of frequency f . The amplitudes at the two new frequencies, (f + f )
R R L
and (f – f ), are proportional to the amplitude sum and difference, respectively, of
R L
the signals in quadrature.
Quality factor Physically, it is 2π multiplied by the ratio of the energy stored to
the energy lost during one oscillation cycle of a resonator. It arises from energy loss
mechanisms, such as resistive heating in electrical networks, or viscous damping or
friction at grain boundaries in mechanical systems. Practically, it is the ratio of the
resonant frequency to the spectral bandwidth measured at 3 dB below the resonant
peak of an electrical or mechanical system. The sharper the resonance is, the higher
the quality factor gets. It is a measure of the frequency stability of oscillators. In an
RLC electrical circuit, it is equal to LC R.
Radio Frequency (RF) Also known as radio spectrum, it is a general term that
refers to the portion of the electromagnetic spectrum between 3 kHz and 300 GHz.
In the United States, the Department of Commerce and the Federal Communications
Commission are responsible for regulating the frequency allocations in this spectrum.
Reduction Chemical process by which the atoms of an element gain electrons and
increases their negative valence. Reduction neutralizes positive ions in an aqueous
solution.
Resistivity The material property, usually measured in Ω•cm, that, along with
the physical dimensions, determines the resistance of a resistor in Ω.