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The development of the transistor and integrated circuits is one of the most important technological achievements of the twentieth century. Radio, television, long-distance telephones, and computers were developed using vacuum tubes and electrical relays, but with the development of the transistor and integrated circuits, electronic devices became smaller, more efficient, more reliable and more affordable. Digital electronic devices can now be found everywhere: in home appliances, automobiles, ships, airplanes, wristwatches, calculators, super computers, desktop computers, portable computers, communications satellites, robots, automated factories, recording studios, home theatres, the film and television industry.

The semiconductor industry began shortly after World War II when researchers at Bell Labs (now Lucent) in New Jersey, USA, invented the first primitive transistors. Their discoveries arose from research into the atomic structure of a class of elements known as semiconductors.

The simplest semiconductor device is the diode. It has many applications in electronic circuits because it permits electricity to flow through it in only one direction.

In the 1950s, when transistor radios first appeared, the most common form of transistor was the bipolar transistor. It could be used as an amplifier or as an electronic switch. At that time each transistor had to be packaged in its own small container with three wires or leads which were soldered together to make complex circuits.

By the 1960s, following the lead of Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor, semiconductor manufacturers were developing techniques which allowed them to create several transistors on one piece of silicon - the integrated circuit. With dozens, then hundreds, and today millions of transistors crammed into one tiny piece of silicon, family of more energy efficient transistors - field-effect transistors - also had to be developed.

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In order to understand why semiconductors behave as they do, it is necessary to examine the atomic structure of elements, and how it affects their electrical properties. The number of protons and electrons in an atom, and the way in which they are ordered affects the electrical properties of the element. Elements in which electrons can move easily are known as conductors; those which have high resistance to the flow of electrical current are known as insulators; and then there is a small group of insulators which can be altered to become semiconductors. During the manufacturing process, semiconductors can be transformed into P-type or N-type semiconductor by the addition of other elements.

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In the early twentieth century, scientists began to uncover the secrets of the atom. They found that the atom consisted of a nucleus, containing neutrons and protons, around which orbit electrons. These high energy particles are held together by the electrical attraction between the positive protons and the negative electrons. This description of the atomic structure is known as the Bohr model. Later research showed that the protons, neutrons and electrons are in fact made of up even smaller particles. For more information on quantum physics, visit the web sites of these major research facilities: Fermi National Accelerator Laboratory in the United States and CERN in Switzerland. Releasing the tremendous power locked in the atom can create nuclear energy and atomic bombs. Knowledge of the atomic structure also enabled researchers to develop the transistor.

Normally there are an equal number of electrons and protons in every atom, and the number of electron-proton pairs (the atomic number) determines the physical and electrical properties of the element. If an electrical force removes or adds electrons to the atom, it becomes a positive ion (missing electron) or a negative ion (extra electron). The electrons orbit the central nucleus at different energy levels known as orbital rings or shells

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Electrical conductors are elements with only one to three electrons in the outer shell of each atom. The best conductors - copper, gold and silver - have only one electron in the outer shell, mercury has two and aluminium has three. Because the outer shell is not filled, the electrons tend to move easily from one atom to another within the element. Because the movement is random, no electrical change results in the absence of an electrical force. However, when a voltage is applied to a conductor, the negative electrons will move rapidly towards the positive voltage. This is known as current flow.