Page 45 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

26 Chapterfour

In 1906, the American inventor Lee de Forest introduced a third electrode
into his version of a vacuum tube. The resulting triode could be used as both an
amplifier and a switch. De Forest’s triodes revolutionized the broadcasting
industry (he presented the first live opera broadcast and the first news report on
radio). Furthermore, their ability to act as switches was to have a tremendous
impact on digital computing.
One of the most famous early electronic digital computers is the electronic
numerical integrator and calculator (ENIAC) , which was constructed at the
University of Pennsylvania between 1943 and 1946. Occupying 1,000 square
feet, weighing in at 30 tons, and employing 18,000 vacuum tubes, ENIAC was
a monster. . . but it was a monster that could perform fourteen multiplications
or 5,000 additions a second, which was way faster than the relay-based Harvard
Mark 1.
However, in addition to requiring enough power to light a small town,
ENIAC’s vacuum tubes were horrendously unreliable, so researchers started
looking for a smaller, faster, and more dependable alternative that didn’t
demand as much power. . .

Sem icond u ct or s

Most materials are conductors, insulators, or something in-between, but a
special class of materials known as semiconductors can be persuaded to exhibit
both conducting and insulating properties. The first semiconductor to undergo
evaluation was the element germanium (chemical symbol Ge). However, for
a variety of reasons, silicon (chemical symbol Si) replaced germanium as the
semiconductor of choice. As silicon is the main constituent of sand and one
of the most common elements on earth (silicon accounts for approximately
28% of the earth‘s crust), we aren’t in any danger of running out of it in the
foreseeable future.
Pure crystalline silicon acts as an insulator; however, scientists at Bell
Laboratories in the United States found that, by inserting certain impurities
into the crystal lattice, they could make silicon act as a conductor. The process
of inserting the impurities is known as doping, and the most commonly used
dopants are boron atoms with three electrons in their outermost electron shells
and phosphorus atoms with five.