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Silicon Introduction
Silicon is an amzing substance known as a semiconductor. The base material is actually sand. Once fabricated, assembled and tested, these bits of fabricated sand touch almost every aspect of our lives, business, and social behavior. Sand is purified, crystallized, and extruded into a tubular form called polysilicon. It is cut into wafers, polished, and sold to wafer fabs. It has been used for centuries to make cast iron, bricks, and pottery. In ultra-pure form, the controlled addition of minute amounts of certain impurities (called dopants) alters theatomic structure of the silicon. The silicon can then be made to act as a conductor or a nonconductor, depending upon the polarity of an electrical charge applied to it. Hence, the generic term semiconductor. Silicon has two distinct regions differentiated by the way in which they favor current flow. An area that favors positive current flow, logically named "p" and the area that favors negative current flow named "n." Impurities allow these current flow tendencies in the "p" and "n" regions to reproduced at will. ( See figure three)
A semiconductor is a unique material with physical properties somewhere in between a conductor like aluminum and an insulator like glass. Examples include germanium, the semiconductor used for the first transistors, and silicon, the basic material in the integrated circuit. Researchers exploited the unique properties of a semiconductor to create the transistor effect--that is, the ability to change its conductivity properties using an electric current.
Germanium is the semiconductor material that the the first transistor. It was used in the first years of transistor development until techniques were invented to utilize the much more abundant silicon. Germanium is a grayish white element with brilliant metallic luster and a crystalline structure with a diamond pattern.
Silicon is the most popular semiconductor material in the world. It is a gray, crystalline element. It has four electrons, thus possessing the material characteristics of a semiconductor. It is never found as a free element in nature, but its dioxide and other compounds constitute nearly 9/10ths of the earth's crust. Its most common form is sand or sandstone. Initially, it was very hard to use to create transistors due to its high melting point, brittleness, and other difficult characteristics. But, with advanced silicon processing techniques developed in the 1950's silicon eventually became the semiconductor material of choice over germanium due to its abundance and durability.
Silicon is grown from a crystal to form a cylinder shaped 'log.' Slicing the logs into sections 1/40 of an inch thick creates bare wafers.
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