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MirrorBit flash moves to production

Posted: 02 Apr 2007 ?? ?Print Version ?Bookmark and Share

Keywords:MirrorBit flash memory? MirrorBit Quad chips? media content storage? NAND?

After nearly five years of development, Spansion Inc. has pushed its 4bit-per-cell MirrorBit flash memory technology into production in devices with densities ranging from 256Mbits to 2Gbits. The company is targeting read-intensive applications, such as media content storage, but promises to increase the write performance of the new MirrorBit Quad chips later this year.

Spansion is the first company to commercialize 4bit-per-cell flash, doubling the capacity of current 2bit-per-cell offerings. The inaugural batch of MirrorBit Quad chips will be produced in a 90nm process at Spansion's Fab 25 in Austin, Texas, and will be drop-in compatible with other industry-standard NAND products, the company said.

The first-generation devices "are suitable for low-cost, read-intensive storage applications," said Greg Wong, a flash analyst at Web-Feet Research. "To expand into the broader storage market occupied by NAND, Spansion intends to expand device densities and increase performance in subsequent generations."

Wong noted that low-end cards using MirrorBit Quad, which is based on a NOR architecture, will write at about 2-3MBps. And while endurance for 70nm multilevel-cell NAND is about 10,000 write cycles, he suspects the MirrorBit Quad specification is probably significantly lower. "Spansion told us that they expect both the performance and endurance to improve with subsequent generations so that it becomes competitive with NANDbut I'm not sure whether that is possible," Wong said.

Later this year, Spansion will reveal plans for 65nm products that will target applications such as digital film, MP3 players, game cartridges and USB flash drives. Spansion also wants to promote MirrorBit Quad for embedded applications, such as e-books and GPS navigation systems. Gary Montgomery, director of Spansion's Removable Storage Business Unit, said write performance will increase as needed for the specific applications. "Rather than trying to build a general-purpose part that does a wide range of things fairly well, we are designing parts that will tend to do those specific things better," he said.

Quad cell uses two charge regions and four charge levels.

When it comes to media content storage, it is read performance and data retention that matter most, Montgomery said, followed by cost. Spansion believes that MirrorBit Quad will be cheaper than its NAND competitors in its initial density ranges.

"Because it is going to be released in the 256Mbit to 2Gbit density range, it will act as a replacement for CDs, DVDs and other content delivery devices," said Adrienne Downey, non-volatile-memory analyst for Semico Research Corp. "As long as it is reliable, its size advantage over not only CDs and DVDs, but other flash devices as well is substantial."

Unlike Intel's StrataFlash, which uses four levels of charge to create 2bits per cell, Spansion's MirrorBit Quad requires a combination of multilevel and multibit technologies, putting four levels of charge in each of the two physical bit locations within the cell. So now, the cell stores 16 combinations of charge, or the equivalent of 4bits per cell.

- Mike Clendenin
EE Times

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