Page 21 - Semiconductor For Micro- and Nanotechnology An Introduction For Engineers

Introduction
behavior, and indeed, semiconductor foundries offer both real metals
(aluminium, among others) and polysilicon as “metallic” layers.
1.2.2 The Diode Family
The simplest device that one can make using both P and N doping is the
diode. The diode is explained in Section 7.6.4. The diode is a one-way
valve with two electrical terminals, and allows current to flow through it
in only one direction. The diode provides opportunities for many applica-
tions. It is used to contact metal wires to silicon substrates as a Shottkey
diode. The diode can be made to emit light (LEDs). Diodes can detect
electromagnetic radiation as photo-detectors, and they form the basis of
semiconductor lasers. Not all of these effects are possible using silicon,
and why this is so is also explained later on.

1.2.3 The Transistor Family

This is the true fame of silicon, for it is possible to make this versatile
device in quantities unheard of elsewhere in the engineering world.
Imagine selling a product with more than 10 9 working parts! Through
CMOS (complimentary metal oxide semiconductor) it is possible to cre-
ate reliable transistors that require extraordinary little power (but remem-
ber that very little times 10 9 can easily amount to a lot). The trend in
miniaturization, a reduction in lateral dimensions, increase in operation
speed, and reduction in power consumption, is unparalleled in engineer-
ing history. Top that up with a parallel manufacturing step that does not
essentially depend on the number of working parts, and the stage is set
for the revolution that we have witnessed.

The transistor is useful as a switch inside the logic gates of digital chips
such as the memories, processors and communications chips of modern
computers. It is also an excellent amplifier, and hence found everywhere
where high quality analog circuitry is required. Other uses include mag-
netic sensing and chemical sensing.

20 Semiconductors for Micro and Nanosystem Technology