ABSTRACT
Dielectrics are materials that are used primarily to isolate components electrically from each other or ground,
or to act as capacitive elements in devices, circuits, and systems. Their insulating properties are directly
attributable to their large energy gap between the highest filled valence band and the conduction band. The
number of electrons in the conduction band is extremely low, because the energy gap of a dielectric (5 to 7 eV)
is sufficiently large to maintain most of the electrons trapped in the lower band. As a consequence, a dielectric
subjected to an electric field, will evince only an extremely small conduction or loss current. This current will
be caused by the finite number of free electrons available in addition to other free charge carriers (ions)
associated usually with contamination by electrolytic impurities, as well as dipole orientation losses arising
with polar molecules under ac conditions. Often the two latter effects will tend to obscure the miniscule
contribution of the relatively few free electrons available. Unlike solids and liquids, vacuum and gases (in their
nonionized state) approach the conditions of a perfect insulator, i.e., they exhibit virtually no detectable loss or
leakage current.
