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Motorola to boost 0.13µ PowerPCs with low-k dielectrics

Speed jumps put Moto back in the Apple game?

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Speculation that Motorola may soon cease to be a supplier of processors to Apple may be premature. The chip maker yesterday said it had successfully implemented low-k dielectric materials in its 0.18 micron silicon-on-insulator (SOI) processors, bringing an estimated 20 per cent speed bump to the PowerPC line.

Motorola expects to roll out the process on its 0.13 micron chips this month.

The company didn't mention specific models, but on the basis of the kind of chips it said it's planning to implement low-k dielectric materials in, candidate processors include the MPC7457, which has yet to ship but is set to take Motorola's G4 family beyond 1GHz.

"Our goal is to stay with a frequency doubling every 18 months or so, and get into the 2GHz range for PowerPC, but at very low power consumption of, say, 20W," said Dirk Wristers, director of device/integration for Motorola's MOS-13 wafer fab, according to an EE Times report. "The frequency could be higher if we were at higher power."

Low-k dielectric materials are used to improve the insulation between processor circuits. As chips get smaller and their circuit lines come closer together signals in nearby circuits increasingly interfere with each other, effectively slowing the ability of the component transistors to switch on and off. Getting the switch speed up involves raising the voltage and thus the power the transistor - and in turn the whole chip - consumes.

Reducing that cross-circuit interference with low-k dielectrics allows transistors to switch more quickly and draw less power. The trouble is, implementing low-k dielectrics has not proved easy - new materials require new methods, all of which must be thoroughly proved before they can be implemented in commercial products.

Wristers claimed that some chip vendors - he didn't name names - are now waiting for the switch from 0.13 micron fabrication processes to 0.09 micron (90nm) before implementing low-k dielectrics. The implication in his comment is that since Motorola can use the technology in its 0.13 micron chips, it will be able to really run with it when it makes the transition to 90nm.

With Apple expected to announce a shift to IBM's 64-bit PowerPC 970 processor in just a few weeks' time, the timing of Motorola's announcement takes on a new relevance. Speculation is already mounting that Apple will drop Motorola for IBM, ditching the G4 for a mix of 970s and Big Blue's rumoured AltiVec-enabled G3-class processors.

Motorola's top-end product is the 7457, announced earlier this year but not yet in volume production. The 7457 is essentially a 7455 with double the on-die L2 cache (512KB) and fabbed at 0.13 micron rather than 0.18 micron. Older Motorola roadmaps show the 7457 topping out at 1.3GHz. Implementing low-k dielectrics could lift that ceiling significantly.

Interestingly, Motorola said it had been delivering low-k dielectric 0.18 micron SOI processors for a full quarter. The 7455, used by Apple in its Power Macs - is just such a chip.

The promise of much faster G4-class processors than anticipated calls into question suggestions not only that Apple will ditch Motorola across the range, but that its sees the 970 as a PowerBook solution, at least in the short term.

If Wristers claims can be taken a face value, Motorola's implementation of low-k dielectrics, with its implications for major power consumption reductions, make it a strong contender for PowerBook - and possibly iBook - processors going forward. Curiously, Motorola's announcement that 0.13 micron parts with low-k dielectrics will appear within weeks comes not only just ahead of Apple's Worldwide Developers Conference (WWDC), but hot on the heels of major price cuts on Apple's 12in and 15in PowerBook models. Price cuts are typically a signal that models are to be refreshed.

Motorola has come under fire from Mac users over the past 18 months for failing to deliver processors to Apple capable of matching the broad-brush performance lead of Intel's top-end CPUs. Last year, high clock frequency processors were notably absent from Motorola's roadmaps. Low-k dielectric materials may allow Motorola to rectify that, but only significant clock-speed hikes are going to satisfy Mac buffs frustrated by the chip maker's efforts to date.

Indeed, even if Motorola can match or exceed the performance expectations surrounding IBM's 970, Mac users are still likely to prefer the 'new blood' IBM is bringing to the platform.

The real choice, though, is Apple's. We suspect it will choose a multi-vendor approach, utilising chips from IBM and Motorola by matching processor characteristics to application: G4 for mobile machines and consumer desktops, 970 for pro desktops and servers. ®

Related Link

Silicon Strategies: Motorola claims 20% benefit from low-k at 0.18-micron

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