Numonyx looks to bright future for NOR Flash and phase-change memory

With the current focus of attention on NAND flash as the drama queen of non-volatile memory, there is a tendency to overlook the importance of NOR Flash. And in this oversight, one hardly hears any more about the best contender for next big thing in the memory arena, phase-change memory. But Numonyx, the non-volatile memory vendor formed by carving out pieces of Intel and ST Microelectronics, is bullish on NOR and has phase-change memory very much in its sights.

Glen Hawk, vice president and general manager at Numonyx, sees NOR moving beyond its traditional role in code and static-parameter storage. At one extreme, Hawk agrees with the emphasis that Spansion has put on NOR/NAND combinations as an alternative to the enormous power appetite of DRAM in server farms. But Hawk sees this specific application as just part of a larger picture.

"As we move to finer geometries, scaling NAND Flash is getting more and more problematic," Hawk said. "We are seeing issues such as dropping endurance and rising error rates. In many cases, vendors are concentrating on cost and simply telling customers that they will have to compensate for these issues in their systems designs. We have seen some systems that use twice the necessary amount of NAND Flash simply to overcome the problems with the chips."

Hawk says Numonyx prefers another approach—using alternative technologies to compensate for NAND’s scaling problems without imposing systems design changes on the user. "For example, there are lots of instances where judicious use of NOR arrays can compensate for NAND’s problems," Hawk said. But eventually, even with help multi-level NAND runs out of steam, as the available cell area simply becomes too small to support enough stored charge. At that point phase-change memory comes to the fore.

"Today, we are sampling a 128 Mbit phase-change part, and we are getting good feedback on it," Hawk said. "But frankly, it is a specialty device at this point. To understand the technology better we chose to do the chip in 90 nm, so it is a full node behind the current Flash devices. For most applications today, conventional NOR Flash is a better choice.

"But there are two points that will make phase-change memory vital in the future. First, scaling. By the time we get to the 45 nm node next year, I think we will see growing interest in phase-change. And by the 32 nm node, the case for phase-change will be compelling. At that point, we believe it will be the only technology capable of providing backward-compatible non-volatile devices.

"The second point is process compatibility. It is a real problem to integrate Flash with a CMOS logic process. But we have already established that the phase-change technology integrates very well with standard CMOS. And it offers significant performance advantages, such as the ability to execute code in place."

This creates the possibility for new architectural options on SoCs and microcontrollers that don’t carry the penalties of either embedded Flash or embedded DRAM. If Numonyx continues to be happy with their initial adventure into phase-change memory, watch this space.