Memory chips have been called the crude oil of the twenty-first century. They are used in a wide variety of electronic applications from children's toys to sophisticated communication satellites. The current generation of memory chip (64Mb) is capable of storing about 3,355 pages of text on a piece the size of a dime.
What is a Semiconductor?
A number of elements are classified as semiconductors including silicon, zinc, and germanium. These elements have the ability to conduct electrical current, and they can be regulated in the amount of their conductivity. Silicon is the most widely used semiconductor material because it is easily obtained.
Silicon is basically extracted from sand. 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 the atomic 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.
Semiconductor materials were studied in laboratories as early as 1830. The first materials studied were a group of elements and compounds that were usually poor conductors if heated. Shining light on some of them would generate an electrical current that could pass through them in one direction only.
By 1874, electricity was being used not only to carry power, but to carry information. The telegraph, telephone, and later the radio were the earliest devices in an industry that would eventually be called electronics.
Radio receivers required a device called a rectifier to detect signals. Ferdinand Braun used the rectifying properties of the galena crystal, a semiconductor material composed of lead sulfide, to create the cat's whisker diode for this purpose. Thus was born the first semiconductor device.
The Integrated CircuitUntil 1959, all electronic components were discrete: that is, they performed only one function, and many of them had to be wired together to create a functional circuit. Although a great number of identical discrete transistors could be fabricated on a single wafer, they then had to be cut up and individually packaged in tiny cans. Packaging each component and hand wiring the components into circuits was extremely inefficient. The military sought more efficient methods of making circuits.
New technologies emerged and integrated circuits were soon developed with various components (transistors, resistors, and capacitors) formed on the same chip, but interconnection of the various components still required tedious hand wiring.
In 1959, Jean Hoerni and Robert Noyce developed a new process called planar technology at Fairchild Semiconductor which enabled them to diffuse various layers onto the surface of a silicon wafer to make a transistor, leaving a layer of protective oxide on the junctions. This process allowed metal interconnections to be evaporated onto the flat transistor surface and replaced the hand wiring. The new process used silicon instead of germanium, and made commercial production of ICs possible.
The initial resistance to the new IC technology gave way to enormous popularity. By the end of the 1960s, nearly 90% of all the components manufactured were integrated circuits.