Page 20 - Semiconductor For Micro- and Nanotechnology An Introduction For Engineers

Popular Definitions and Acronyms
1.2 Popular Definitions and Acronyms
The microelectronic and microsystem world is replete with terminology
and acronyms. The number of terms grows at a tremendous pace, without
regard to aesthetics and grammar. Their use is ruled by expedience. Nev-
ertheless, a small number have survived remarkably long. We list only a
few of the most important, for those completely new to the field.

1.2.1 Semiconductors versus Conductors and Insulators
A semiconductor such as silicon provides the technologist with a very
special opportunity. In its pure state, it is almost electrically insulating.
Being in column IV of the periodic table, it is exceptionally balanced,
and comfortably allows one to replace the one or other atom of its crystal
with atoms from column III or V (which we will term P and N type dop-
ing). Doing so has a remarkable effect, for silicon then becomes conduc-
tive, and hence the name “semiconductor”. Three important features are
easily controlled. The density of “impurity” atoms can vary to give a tre-
mendously wide control over the conductivity (or resistance) of the bulk
material. Secondly, we can decide whether electrons, with negative
charge, or holes, with positive charge, are the dominant mechanism of
current flow, just by changing to an acceptor or donor atom, i.e., by
choosing P or N type doping. Finally, we can “place” the conductive
pockets in the upper surface of a silicon wafer, and with a suitable geom-
etry, create entire electronic circuits.

If silicon is exposed to a hot oxygen atmosphere, it forms amorphous sil-
icon dioxide, which is a very good insulator. This is useful to make
capacitor devices, with the SiO as the dielectric material, to form the
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gate insulation for a transistor, and of course to protect the top surface of
a chip.

Silicon can also be grown as a doped amorphous film. In this state we
lose some of the special properties of semiconductors that we will
explore in this book. In the amorphous form we almost have metal-like

Semiconductors for Micro and Nanosystem Technology 19