Page 162 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Integrated Circuits (ICs)

In the 1950s, transistors and other electronic components were available
only in individual packages. These discrete components were laid out on
a circuit board and hand connected using separate wires. At that time, an
electronic gate capable of storing a single binary bit of data cost more than $2.
By comparison, in the early 1990s, enough gates to store 5,000 bits of data cost
less than a cent. This vast reduction in price was primarily due to the invention
of the integrated circuit (IC).l
A functional electronic circuit requires transistors, resistors, diodes, etc.
and the connections between them. A monolithic integrated circuit (the
”monolithic” qualifier is usually omitted) has all of these components formed
on the surface layer of a sliver, or chip, of a single piece of semiconductor;
hence the term monolithic, meaning “seamless.” Although a variety of semi-
conductor materials are available, the most commonly used is silicon, and
integrated circuits are popularly known as “silicon chips.” Unless otherwise
noted, the remainder of these discussions will assume integrated circuits based
on silicon as the semiconductor.

An Overview of the Fabrication Process
The construction of integrated circuits requires one of most exacting pro-
duction processes ever developed. The environment must be at least a thousand
times cleaner than that of an operating theater, and impurities in materials
have to be so low as to be measured in parts per billion.2 The process begins
with the growing of a single crystal of pure silicon in the form of a cylinder with
a diameter that can be anywhere up to 300 mm.3 The cylinder is cut into paper-
thin slices called wafers, which are approximately 0.2 mm thick (Figure 14-1).

1 In conversation, IC is pronounced by spelling it out as “I-C”.
2 If you took a bag of flour and added a grain of salt, this would be impure by comparison.
3 This 300 mm value was true as of 2002. However, in 1995 (when the first edition of this tome
hit the streets), the maximum diameter was 200 mm, so who knows what it will be in the future?