Reference STATE OF THE ART Stan Augarten

ISBN 0-89919-195-9
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The Near Future
Chips Made Out of Gallium Arsenide

ROCKWELL INTERNATIONAL


Silicon isn't the only substance ICs can be made of. The allow gallium arsenide, a combination of the elements gallium and arsenic, is also suitable for the fabrication of chips and has been the object of a great deal of experimentation at some of the larger semiconductor firms for several years. ICs made out of gallium arsenide will probably be on the market, for certain select uses, within a few years

  Gallium arsenide chips outperform silicon ICs in several respects. First, they are much faster conveyors of current. All things being equal, the electron mobility of gallium arsenide is six times greater than that of silicon; in actual practice, the disparity is somewhat smaller. If a typical high-speed silicon IC - an 8-bit multiplier comprised of bipolar transistors - were pitted against an equivalent gallium arsenide chip, the former might require about fifteen to thirty billionths of a second to multiply two 8-bit numbers, the latter only 5.25 billionths of a second.

  Second, gallium arsenide ICs consume less power. Third, they are far more resistant to radiation, which makes them very useful in military, aerospace, and certain industrial applications. Finally, in some respects they're appreciably easier to manufacture. In the fabrication of a silicon chip, silicon dioxide, an insulator, is used to isolate portions of the IC from each other and so to forestall shortcircuiting; in the creation of a gallium arsenide IC, however, this step is unnecessary, because gallium can be engineered to function as its own insulator.

  For all its advantages, gallium arsenide is somewhat more costly than silicon and is also highly toxic, so expensive precautions must be taken in the manufacturing process. It's unlikely, therefore, that the alloy will ever acquire more than a small fraction of the semiconductor market. It will undoubtedly be used chiefly in sophisticated applications, such as fast computers, airborne radar, electronic countermeasure systems, and satellite communications equipment, in which its high speed and resistance to radiation are of prime importance.

A so-called parallel multiplier, this IC can multiply two 8-bit numbers in only 5.25 billionths of a second - three to six times faster than the fastest silicon chips. This IC, shown on a wafer, has 1,008 logic gates. Actual size: 0.057 x 0.070 inches. Photo of

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STATE OF THE ART
©Copyright Stan Augarten
This book is provided for general reference. The National Museum of American History and the Smithsonian Institution make no claims as to the accuracy or completeness of this work.

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