Battle brewing between rival flash architectures

Battle brewing between rival flash architectures
WASHINGTON — The cell phone is becoming a potential battleground for suppliers of flash memory ICs, as a band of NAND flash manufacturers gears up to raid what has long been a market stronghold of NOR vendors.

The promise of phones able to handle data, images, and even video is placing new demands on flash densities, which makers of NAND flash say will give them a competitive edge in the long run. But NOR-only suppliers like Advanced Micro Devices Inc. and Intel Corp. are defending their turf with the claim that NOR's ability to provide more robust code storage will outweigh NAND's density advantage.

NAND flash vendors Samsung Electronics Co. Ltd. and Toshiba Corp., as well as Renesas Technology Corp., which makes a similarly-gated architecture known as AND flash, already provide data storage for 2.5G and 3G handsets. Lately, however, they have also begun eyeing the code-storage functions that historically have been the domain of NOR.

Why now? In part because the NAND flash industry finally has amassed a sizable enough manufacturing infrastructure to be considered as a possible alternative.

Brian Kumagai, Toshiba's business development manager for flash memory, said as many as six cell phone makers in Asia have replaced NOR with NAND and expects the number to double by the end of the year.

Microsoft Corp. and London-based Symbian Ltd. also have weighed in by adapting their respective cell phone operating systems to support NAND flash for boot-up and code execution. Samsung felt Symbian's decision in April to support NAND in its OS 7.0 software was so overlooked that the Korean chipmaker today is making its own announcement touting the companies' cooperative effort.

In addition to OS providers, four cell phone chipset vendors, Motorola, Qualcomm, Texas Instruments, and Samsung, have added NAND support for code execution.

"It's going to be an interesting battle over the next year," said Alan Niebel, an analyst with flash memory research firm Webfeet Research Inc. (Monterey, Calif.). The general criteria on which the winner will be judged are price, speed, memory density, and the effect each will have on the component count of a given cell phone reference design, he said.

On the face of it, NAND memory is much cheaper to produce than NOR. Jim Handy, nonvolatile memory analyst at Semico Research Corp. (Los Gatos, Calif.), said the average price per megabit of NAND is now about 23 cents, compared with $1.30 for NOR.

But that only tells part of the story given that NAND must transfer the stored operating system code to a separate SRAM or DRAM component for execution.

Troy Winslow, technical advisor to the Intel flash memory group, claimed that a single NOR chip is less costly than the combination of NAND and auxiliary RAM. Winslow also noted that the additional memory needed for NAND code execution increases power consumption and adds to a mobile phone's overall parts count.

Not so, countered Ivan Greenberg, director of strategic marketing at Samsung Semiconductor Inc. (San Jose, Calif.). Greenberg argued that new "smart" phones and 3G mobile handsets already are adding low-power DRAM, even in products using NOR for code execution.

"Since DRAMs are already in these cell phones, NAND doesn't suffer any price disadvantage," he said. "By replacing NOR for code execution, NAND can lead to a much lower memory bill of materials for mobile phones."

Ian Williams, vice president of customer operations for AMD (Sunnyvale, Calif.), asserted that NAND memory needs extra error detection and correction circuitry in the code execution mode to map around bad bits that occur over time. Williams said this, too, adds cost to the NAND solution.

Density is another point of contention for the NOR and NAND camps.

"Cell phone operating systems are becoming increasingly complex and need larger memory size to store code," said Fashid Sabet, director of product technical marketing at SanDisk Corp. (Sunnyvale), which last year switched its storage products from NOR to NAND. "The new Symbian 7.0 and Microsoft Smart Phone OSes need at least 32 Mbytes or higher for flash code storage."

Sabet claimed that a single-chip 128- or 256Mbit NOR flash would be hard pressed to meet the memory demands of such new operating systems.

At present only a few NOR producers, such as AMD, Fujitsu Ltd., and Intel, are shipping 256Mbit chips. But Intel's Winslow said stacked high-density NOR die can achieve a 512Mbit package, enough, he claimed, to meet the most pressing mobile handset code execution requirements.

NAND, on the other hand, is available in densities as high as 1 and even 2 Gbits. SanDisk and Toshiba last week disclosed they have developed a new NAND memory cell structure capable of scaling to 4 Gbits and beyond.

Toshiba and SanDisk said they will produce the new NAND memory chips using 90 nm processing at their joint venture fab, FlashVision, in Yokkaichi, Japan. Initial production is slated for the first half of 2004.

In addition to sheer density, the speed of the two flash architectures has become a subject of debate.

Toshiba's Kumagai maintained that NAND flash has an average access time in burst mode of 10 ns, faster than the 25 ns to 35ns of NOR. However, AMD's Williams said NOR is faster when executing stored code.

While they are a high-profile product, cell phones are not the only market in which NOR and NAND suppliers are competing. Kumagai said networking equipment, which has been a large user of NOR for code execution, is also starting to switch to NAND. Switches and routers are also beginning to use NAND-based flash memory cards to store large amounts of OS code, according to SanDisk's Sabet.