IBM connects chips for better bandwidth

The technology, called through-silicon vias, or TSV, involves connecting different components--processors and memory, for example--or different cores inside of two respective chips through thousands of tiny wires that will carry data back and forth. Now, chips mostly transfer data over channels called buses, which can get overwhelmed, embodied in wires. With TSV, far more data can be transferred per second in a less energy-intensive manner.

IBM is not the first company to talk about TSV (Intel is), but could be one of the first to commercially exploit them. IBM will deliver samples of communication chips with TSV to customers later this year and begin commercial production in 2008. TSV will reduce power consumption in silicon germanium chips, a favorite of IBM's, by around 40 percent. In these chips, microscopic holes will be drilled into the chip and filled with tungsten to create the TSVs.

"Wire bonds have pretty high levels of noise, which can limit the capability of some of the transistors," said Lisa Su, vice president for IBM's Semiconductor Research and Development Center.

In three to five years, TSV could also be used to join memory directly to its power processors, obviating the need for another component called a memory controller. TSV in this scenario, could improve performance by 10 percent and reduce power consumption by 20 percent. IBM also hopes to bring it to the chips in its BlueGene supercomputers.

TSVs additionally economize on motherboard space because chips are stacked into vertical towers. Several chip companies stack chips vertically in packages now, but these chips are generally wired together through buses, so they achieve the space advantages but not all of the bandwidth benefits. Typically, bus ports are on the side of chips. TSVs sprout from the comparatively spacious lower or upper surface of a chip and drill through the silicon.

Packaging chips together through TSV also potentially will change how chips get sold. Rather than buy processors and memory or different communications chips from different vendors, computer makers will buy complete packages of prewired chips. Thus, companies like IBM or Intel will potentially find themselves selling standard types of memory again because it will be prepackaged with its premier semiconductors.

Although it doesn't grab the headlines like new processors, chip interconnects and packaging has been a hotbed of innovation in recent years because designers believe it's one of the areas where significant performance gains can be made. Matrix Semiconductor, a start-up that got bought by SanDisk, for instance, devised a way to make 3D memory chips, while Sun Microsystems has been working on proximity communication, which lets chips talk to each other by being close to each other.

Rambus, meanwhile, has been showing off Loki, a chip-to-chip interconnect that can pass 6.25 gigabits of information per second at a low 2.2 milliwatts per gigabit.

For the novelty factor, Rambus earlier this year hooked up a system so that Loki would be powered by two AA batteries. The chip churned for more than 40 hours and passed 3.6 petabits of data before it conked. That's 3.6 million gigabits or 3.6 quadrillion bits of data.

Intel has been working on TSV since 2005 and showed off an 80-core chip with TSV that linked memory chips to the different processor cores at its developer forum last year. The TSV, Rattner said, was a more notable accomplishment than putting 80 cores on the same piece of silicon.

Intel, though, has not laid out how it will bring TSV to market and the company has said that a substantial amount of research needs to be conducted before TSV moves into volume production. One problem: the processor generates more heat than memory, so combining them in one package requires intricate thermal management.

IBM in part leapfrogged Intel because of its application. Connecting a processor to memory is a more daunting task than using TSV to reduce noise in communication chips.

"What really is new here is that we (IBM) found a way to get it into production really quick," said Su.

Earlier this year at the International Solid State Circuits Conference3, IBM researchers mentioned that the company was experimenting with TSV.