Since World War II, no invention has made a larger impact on the communications field than the transistor, which replaced old-fashioned vacuum tubes in electronic equipment. The transistor revolutionized electronic technology and created a billion dollar industry that sells everything from popular consumer items--such as home computer games, pocket calculatos, and portable stereos--to the complex electronic systems used by business and industry.
In the 1930s researchers were aware of the limitations of vacuum tubes, which were used to increase electric current, a process called amplification, and to force it to flow in only one direction, which is known as rectification. Vacuum tubes were bulky and fragile, and they consumed a lot of power. The tubes also had a tendency to overheat, so they needed large, reliable cooling systems, and when radar was developed during World War II, vacuum tubes were unable to provide the range of frequencies, power, and voltages needed for radar circuits. After the war, when scientists began trying to develop bigger and better computers, they were frustrated by the huge, complex arrays of vacuum tubes and cooling systems that were required.
In 1945 Bell Telephone Laboratories established a research team to develop a "solid-state" electronic device that could amplify and control electrical current without using moving parts or vacuum tubes. The most promising replacements were semiconductors --materials such as silicon and germanium that can strengthen an electrical current, create a current, and either conduct or resist a current, which means they can semi-conduct a current by switching it on and off. At that time, semiconductors had been used to rectify electrical current, but no one knew how to make them amplify it.
Bell's research team, which included American physicists William Shockley, John Bardeen, and Walter Houser Brattain, began studying semiconducting materials with the hope of applying them to electric circuits. Shockley theorized that electrical current could be amplified by using semiconductors and metallic conductors. When Shockley's initial experiments failed, Bardeen explained that what was needed was a connection between the two materials to enable current to flow.
Bardeen, Brattain, and Shockley then performed several ground-breaking experiments. They mounted a germanium oxide semiconductor on a metal base and then placed the semiconductor between two fine metal wires, which served as metallic contacts through which the current flowed. By 1948 the team had successfully amplified electrical current by a factor of fifty using the world's first point contact resistor, or transistor. Tiny changes in the current induced great variations in the power output. In 1956 the three scientists were awarded the Nobel Prize in physics for their work in transistors and semiconductors.
Still, the operation of the transistor was not well understood. Shockley suggested an important improvement: placing a positively charged region between two negatively charged regions, all contained within a single crystal of semiconducting material. In the negative, or n-type region, current is carried by electrons, which are negatively charged. In the positive p-type region, current flows through " holes"--spaces left behind by vacated electrons. These holes act as positive charges by accepting electrons from the negative region. Shockley's transistor proved easier to manufacture than the point-contact type as well as more versatile in electronic applications. The positive and negative regions were created by adding tiny amounts of such chemicals as arsenic, borium, and gallium to the semiconductor to alter its electrical properties. Today this process is called doping the semiconductor, and Shockley's improved device is known as the junction or bipolar transistor.
With financial support from the United States military, Bell Labs redesigned electronic equipment to accommodate transistors and soon found many valuable markets for the device. During the 1950s transistors began to be used in telephone switching equipment, hearing aids, radios, and computers. IBM introduced a computer that used only five percent as much power as vacuum-tube models in 1955. Then, in 1958, scientists learned how to integrate many transistors on a single piece of semiconducting material. These electronic devices are called integrated circuits, or silicon chips. By the early 1970s mass-production of computer chips had led to the commercial introduction of small, powerful microprocessors.
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