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For the last 40 years, computer-chip manufacturers have been constantly improving the performance of their products by shrinking the size of transistors—the building blocks of processors and memory chips. Having gone from dimensions of a few microns in the early 1970s to 45 nm in Intel’s latest prototypes, the number of transistors that can be etched on a given area of silicon has been doubling every 18 months. This exponential trend, which is known as Moore’s law, has been the driving force behind the relentless miniaturization of microelectronic devices. However, we are now approaching the physical limits of existing technology. Chips are getting too hot and are now so small that electrons can tunnel between the transistor electrodes and degrade device performance. Unless we can find a way to solve these problems, within a decade it will be impossible to reduce the size of semiconductor transistors any further.