Devices that have been beyond the reach of engineers can now be fabricated in new ways. The crucial factor has been the development of a technique by which extremely narrow rods, or nanowires, of a semiconductor can be formed. The bottom-up, self-assembly process enables accurate control of dimension, location, composition, and other properties. The materials are the same semiconductors, like Si and GaAs, that we have, for the last forty or so years, been shaping into devices and circuits. But this process has relied on top-down fabrication techniques.The top-down approach limits the dimensions of devices to what is technically achievable using lithography. This is the means by which patterns can be drawn, either in stone as the Vikings did when they carved messages into granite, or into Si as the electronics industry does today to build integrated circuits. Lithographic techniques can create device features as narrow as 130 nm and the industry sees the road ahead pretty well drawn up for line-widths down to ~50 nm. This continued progress does not come without a price; the cost of new fabs is growing extremely fast, at a pace that may limit continued progress, simply because devices and circuits become too expensive to be economically viable.

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DOI: 10.1016/S1369-7021(03)01026-5