The neat division between NOR and NAND flash is crumbling as cell phones take on multimedia functions. Traditional thinking is that NOR is good for storing code, NAND for saving data.

With multilevel-cell technology extending NOR densities by storing two bits per cell, NOR devices can be partitioned for both code execution and data storage. That's the plan for Intel's StrataFlash, AMD-Fujitsu's MirrorBit and the multilevel-cell memories from Infineon's partnership with Saifun Semiconductors.

The NAND flash market also is attracting new players. STMicroelectronics and Hynix will jointly develop and manufacture NAND chips, starting with 512-Mbit products later this year.

ST and Hynix enter a booming NAND flash market, one that Alan Niebel, president of Web-Feet Re-search (Monterey, Calif.), predicts will grow from $2 billion in 2002 to $9.44 billion in 2007. More to the point, NAND local storage in cell phones will increase from $150 million this year to $1.4 billion in 2006.

The ST-Hynix move also is defensive, because NAND has the potential to drive NOR out of certain system designs. The thinking is that if code is moved at bootup from a NAND device directly to a pseudostatic RAM, bypassing the NOR chip, that would bring cost advantages for phones where data storage demands are large, said Niebel.

NAND costs much less per bit than NOR, since the NAND serial architecture matches many memory capacitors with few switching transistors. "As NAND gets to equal performance with NOR, then it comes down to a price war," Niebel said.

Intel's flash product manager, Scott Dunagan, argues that moving code from NAND to shadow RAM has a cost in terms of power. As systems put chips into deep-sleep mode, the power drain at wake-up to move code repeatedly out of a NAND chip will be huge. Much better to partition a high-density StrataFlash device for XIP (execute in place) of code as well as data storage, he said.

For some high-end phones, NOR could be stacked with the baseband processor, and NAND and DRAM with a separate multimedia processor, said Philippe Berge, director of marketing for ST's memory group.

One thing is clear: As cell phones and PDAs begin to store photos, video and sound, NAND is becoming the digital papyrus for our mobile multimedia society.

David Lammers covers SoC process equipment. Contact him at dlammers@cmp.com.

http://www.eet.com/