Your Guide to the Year in Science: 2008

Breaking the Law

Forty years ago, engineer Gordon Moore famously predicted that the number of transistors that could fit on a silicon chip would double roughly every two years, making computers ever faster and more efficient. That truism will hit a brick wall in the next 15 years, as transistors approach the size of single atoms and manipulating them proves ever more difficult. This year, IBM will begin selling its work-around to the transistor-density problem, a vertically stackable chip that moves data 1,000 times as fast as what we use now.

If you open up your cellphone today, you'll probably find a pseudo-3-D chip inside-stacking ordinary chips on top of each other increases computing power without taking up too much space. It's the long wires that connect two chips around their outer edges that limit their ultimate processing speeds. Without better connections between the two chip layers, their utility is restricted to whatever can be shunted through a few small wires.

IBM's solution is to make 3-D chips with vertical interconnections called through-silicon vias (TSVs). Instead of connecting the chips along the outer edges, TSVs tunnel down through the chip and connect to the next layer directly below it. The trick was in getting metal into the tiny holes that serve as the wires between the layers. Other companies aren't far behind. Samsung plans to use TSVs to make stacked DRAM chips and hopes to incorporate them into high-density flash memory.

What will this mean for us? TSV chips will be extremely speedy processors, and because chips with different functions can be made separately and later stacked, prices for multifunctional chip stacks will probably drop. One thing is certain, says interconnection expert Larry Smith of Sematech, a consortium that studies semiconductor manufacture: "Products will continue to get smaller, thinner and lighter."-Melinda Wenner

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