IBM Boosts Chip Performance By Stacking Silicon

IBM plans to give customers samples of chips making use of the technology in the third quarter, with commercial production starting next year.
IBM plans to manufacture next year microprocessors that make use of a breakthrough chip-stacking technology the company claims guarantees a performance boost.

The technology called "through-silicon vias" will first be used to stack memory components on top of processors for faster access to data and instructions. In traditional configurations, memory components are placed next to a processor, thereby increasing the distance between the CPU and the information it needs. Placing those components on top of the CPU brings the information closer -- about 10 micrometers versus hundreds of micrometers.

As a result, the processor can get more information faster, which speeds up its ability to do calculations. How much of a boost hasn't been determine, since it will depend on the applications running on top of the chipset. Business applications, for example, place different demands on CPUs then applications used in supercomputing. "(Nevertheless,) we know there's a performance boost," Wilfried Haensch, senior manager at IBM's Watson Research Center, said.

IBM is stacking memory components, as opposed to processors, because bringing the latter closer together would create more heat then internal cooling systems can handle. A memory chip, on the other hand, has the easier job. "It's not doing too much work, so it doesn't sweat," Haensch said. "It doesn't get hot."

The idea of stacking components on top of a processor isn't new. IBM, however, has managed to develop a way of doing it, so the chip and its components can be manufactured as a vertical package. Through-silicon via is IBM's way of stringing a wire through the layers, so information can flow through the stack to the processor. "This is conceptually a very simple thing, but from a technical perspective, it's very difficult," Haensch said.

IBM plans to give customers samples of chips making use of the technology in the third quarter, with commercial production starting next year. The first application will be in power amplifiers, which is hardware used to boost signals in wireless local area networks. IBM is starting here because the market doesn't require high-volume manufacturing at the level of the server market. It's not unusual for companies to start small and refine the manufacturing process to handle larger production levels.

Following power amplifiers, the stacking technique would be used in bringing power to a processor. By stacking power-storing capacitors on top of the CPU, the processor can more quickly draw additional power when needed. Energy consumption fluctuates on a processor depending on the workload, so having the power source closer produces a more stable performance level.

The new technology would likely find its way into the server market once the number of CPUs on a piece of silicon reaches between 10 and 20, Haensch said. Today's advanced chips have a maximum of eight processors. Chipmakers aren't expected to exceed the current number of cores until after 2010.

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