SanDisk Eyes Bringing 3bit/cell NAND to SSDs

Nov 27, 2008
Junichi Ooshita, Nikkei Microdevices
Don Barnetson, senior director of Marketing, Solid State Drive Business Unit of SanDisk, discussing the company's SSD business strategy
Don Barnetson, senior director of Marketing, Solid State Drive Business Unit of SanDisk, discussing the company's SSD business strategy
[Click to enlarge image]
SanDisk's plan to advance miniaturization and multi-valuing of NAND flash memory
SanDisk's plan to advance miniaturization and multi-valuing of NAND flash memory
[Click to enlarge image]
A new file management system called "ExtremeFFS" will be introduced in SSDs in 2009.
A new file management system called "ExtremeFFS" will be introduced in SSDs in 2009.
[Click to enlarge image]

SanDisk Corp explained its business strategy for SSDs (solid state drives), which are expected to be the next "killer application" of NAND flash memory, at a press conference in Tokyo Nov 26, 2008.

The company is planning to mount 3bit/cell NAND flash, which can be produced at a lower cost than the current 2bit/cell product, on SSDs, said Don Barnetson, senior director of Marketing, Solid State Drive Business Unit of SanDisk.

Barnetson said that it is difficult to incorporate the current 3bit/cell products in SSDs in view of their rewrite speeds and times. Still, he said, "Please wait a little while for our announcement (of commercialization). We are now preparing a technology to solve those issues." The company seemed to be planning to introduce 3bit/cell NAND flash for SSDs sometime in 2009 or 2010.

Taking advantage of "in-house production"

SanDisk is ahead of its rival manufacturers in miniaturization and multiple level cell (MLC) technologies, which hold the key to reducing NAND flash memory cost. The company has already started to mass-produce its 56nm 3bit/cell product and 43nm 2bit/cell product, planning the volume production of its 43nm 3 to 4bit/cell products at the end of 2008. And it will advance the process technology to 3Xnm in the second half of 2009.

It is initially difficult to embed such stat-of-the-art chips in SSDs, for which quality requirement is strict, because rewrite speeds and times become lower at device level as a result of further miniaturization and multi-valuing, Barnetson said.

However, taking advantage of the fact that "SanDisk can provide controller, firmware and all the other elements needed for SSDs by itself," the company intends to enable its most-advanced chips to be mounted on SSDs and further differentiate itself from its rivals, Barnetson said.

New file management system

In November 2008, SanDisk announced a new file management system dubbed "ExtremeFFS" as one of such technologies to differentiate itself from its rivals. This system can accelerate write speeds by up to 100 times compared with existing systems, while increasing rewrite endurance at the same time. It will be used in the SSD embedded with 2bit/cell NAND flash in 2009.

With the ExtremeFFS, SanDisk improved its file management technology in the following three respects. First, the new system can manage data by page unit, which is a smaller data storage unit compared with the prior block unit.

Second, it can perform different actions in parallel via multiple channels. For example, while the user is writing data and doing "garbage collection" (liberating unused memory) via one channel, data can be read out via a different channel.

Third, the new system can "learn" the user's pattern of using data and localize data storage areas in accordance with factors including how often the data has been used.

To equip 3bit/cell NAND flash in an SSD, "We need one more step of improvement besides ExtremeFFS," Barnetson said. Though specific measures have not been revealed, SanDisk seems to already have a clear prospect.