Reference STATE OF THE ART Stan Augarten

ISBN 0-89919-195-9

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Photo of
The Distant Future
Josephson Junctions


Computer scientists are obsessed with speed, their obsession motivated by the harsh economics of the computer business as much as by personal and financial ambition. Computer manufacturers are constantly striving to shave billionths of a second off the performance times of their products - long-term efforts that lead some companies to spend tens of millions of dollars. For the faster a computer, the more tasks it can execute in a given period, and the better it can earn its keep.

  Of course, most computers are perfectly adequate for the vast majority of their users; it doesn't matter to most personal computer owners whether their machines need two millionths of a second to multiply two numbers or only half that. But there's a certain rarefied class of operators - NASA, the military, the National Weather Bureau - for whom no machine is ever fast enough. These are the people who buy supercomputers like the Cray-1, built by Cray Research Inc. of Minnesota, which can carry out more than a hundred million operations a second. Supercomputers are used for such highly complex chores as weather predictions and airplane air-flow analysis.

  For all their phenomenal speed, supercomputers still require hours to perform some calculations, and it may be impossible to boost their speed significantly with conventional semiconductor technology. High-speed chips generate excessive amounts of heat, particularly if they're packed closely together. Scientists at IBM have therefore been experimenting with an exotic class of ICs called Josephson junctions, which are designed to operate in tubs of liquid helium at temperatures only a few degrees above absolute zero.

  As envisioned by IBM, a Josephson junction computer would consist of a central core of about fifty to a hundred chips, all packed tightly in a cube about two inches to a side and immersed in liquid helium. The entire apparatus, core and tub, would probably be about the size of a refrigerator. By cooling the circuitry to almost absolute zero (-459.7º F) and reducing the lengths of the connecting wires to a bare minimum, a Josephson junction computer might attain speeds of one billionth of a second per operation, or less, ten times faster than today's quickest computers. A full-scale Josephson junction device has yet to be made, but IBM expects to have one by the early 1990s, if not sooner.

In this close-up of a Josephson junction chip, the junctions themselves lie beneath the four circles in the brown regions. Ultrafast switches, they can be turned on in as little as six trillionths of a second and are made of lead or niobium - both semiconductors - separated by a thin layer of insulating oxide. The narrowest lines in this photo are about 0.00001 inches wide. Actual size of the portion show here: 0.001 x 0.00112 inches. Photo of


©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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