NEXT-GENERATION SEMICONDUCTORS
SEMICONDUCTOR SAFARI Exotic materials beyond silicon By Dan Green
At this moment, the semiconductor industry is justifiably focused on the impending inflection in Moore’s Law, the famous technology projection that underlies the astonishing progress of the microelectronics era, and its potential impact on the continuing advance and dominance of silicon technology. That means it’s worthwhile to consider another visionary perspective in the history of microsystems. As the nascent Advanced Research Projects Agency (ARPA) passed its one-year anniversary in 1959, Prof. Richard Feynman at Caltech delivered one of his most famous and consequential talks, titled “There’s plenty of room at the bottom.”
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DEFENSE ADVANCED RESEARCH PROJECTS AGENCY I 60 YEARS
DARPA’s MIMIC technology, particularly the techniques of integration that came out of it, enabled the DOD to make radios and radar systems that engage the spectrum at higher frequencies and bandwidths than ever before. U.S. AIR FORCE PHOTO BY TECH. SGT. GREGORY BROOK
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imilar to Gordon Moore, Feynman anticipated many of the opportunities for technological advance that lie within the realm of microscale systems. However, Feynman took a much broader view that highlighted the exotic possibilities that would emerge with the ability to manipulate structures at the atomic scale. DARPA has played a central role in bringing many of these “exotic” structures, including semiconductors, to life with capabilities beyond the binary-processing feats that silicon electronics have been pulling off for half a century. Feynman’s talk inspired a resurgent interest in the 1980s as his speculative notions of nanotechnology and the ability to tailor materials at the atomic scale were becoming tantalizingly close to realization. At that time, emerging crystal growth techniques were enabling the creation of a class of materials known as compound semiconductors, where the exact chemical composition or alloy could be varied at the atomic level on a layer-by-layer basis. In particular, gallium arsenide (GaAs) and its alloys emerged as new wonder materials that allowed transistors to operate well beyond the performance limits of silicon. DARPA identified the potential for the new GaAs transistors to move electrons faster and therefore operate at higher frequencies in the electromagnetic spectrum. While this new technology would not displace silicon technology for highly integrated digital logic, DARPA anticipated its value to enable the next generation of radar and communications systems. To that end, DARPA in 1988 took over the baton
