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9.9 Option - The Age of Silicon: 7. Limits to current devices

Extract from Physics Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

gather, process and analyse information and use available evidence to discuss the possibility that there may be a limit on the growth of computer power and this may require a reconceptualisation of the way computers are designed

• There is a physical limit to how small you can make a transistor before it fails as a binary switch (about 4 nm). Thus, making smaller and smaller transistors on silicon-based substrates will eventually hit this limitation. If we want faster, more powerful computers, other kinds of computers will need to be made.
  
  
• A good starting point is Moore's law from Wikipedia's free web-based encyclopedia.
  
  Moore's law (so called) provides a context for discussing the change in computing power or complexity. Gordon Moore (he worked for Intel and Intel make ICs) had an article published in Electronics Magazine, 19 April 1965 titled "Cramming more components onto integrated circuits". In that article he said:
  
  The complexity for minimum component costs has increased at a rate of roughly a factor of two per year ... Certainly over the short term this rate can be expected to continue, if not to increase. Over the longer term, the rate of increase is a bit more uncertain, although there is no reason to believe it will not remain nearly constant for at least 10 years. That means by 1975, the number of components per integrated circuit for minimum cost will be 65,000. I believe that such a large circuit can be built on a single wafer.
  
  
• The initial observation proved remarkably accurate and in 1975 he projected that the complexity would double every two years into the future. The original observation was dubbed "Moore's Law" by Caltech professor, Carver Mead. Since then a popular form of the law (complexity will double every eighteen months) has become the goal that IC and memory (hard disk and random access) manufacturers have set themselves.
  
  
• It is predicted that the limitation (4 nm) to the size of silicon-based transistors will be reached in less than twenty years. By then, it is predicted that new technology will be ready to replace silicon-based transistors and that Moore's Law will continue into the foreseeable future on the back of this new technology.
  
  
• Speculation based on information from Intel and AMD (two of the biggest chip manufacturers) has it that using nickel gates in their silicon-based transistors will allow smaller transistors to be made but they still be bigger than the 4 nm limit mentioned above. This is just a refinement on current technology. Gallium Arsenide is already replacing silicon, but transitors made on that substrate are not able to be made smaller than the 4 nm limit.
  
  
• The ABC's News in Science website carried a story (28 August 2000) about a successful test of molecular-sized switches that worked hundreds of times. This represents a first step toward the goal of molecular computers. This article reports on a chip using molecular switches Densest IC ever made Andre Kesteloot, Amateur Radio Research and Development Corporation Jan 27, 2007. Another possibility is to implant computer-technology into humans (cyborg technology). The combined power of the two may provide advantages to humans, but is it really the next generation of computers or another way of using what we already have?

identify that the increased speed of computers has been accompanied by a decrease in size of circuit elements

• The increase in speed since the first personal computers (PCs) generally appeared (1980s) is due to the increased sophistication of manufacturing processes making silicon based ICs. These processes have allowed the switching transistors to be reduced in size and placed closer together on the silicon substrate.

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