Nanocrystals to breathe new life into Flash

Austin (TX) - Flash sales are booming more than ever, but the memory technology may be gone sooner than you think - potential replacements have been lining up for years and keep gaining ground in production cost and scalability. But there are ideas that could extend the life span of Flash: Freescale today announced the first 24 Mbit nanocrystal Flash device.

The debate about how long Flash will be able of beating the forces of economics has been going on for at least five years. It's no secret that Flash will hit a barrier sometime in the near future, most likely in 2008 or 2009, when it will make little financial sense to keep scaling the memory devices for greater capacities, when other technologies may be superior in power consumption and read and write performance.

Despite its 17-year history, Flash has gained popularity only in more recent years. Sales of memory devices are still accelerating and scaling advances into the 90nm space allowed the technology to compete with small and entry level harddisk drives. But Flash may run out of steam soon, as engineers currently believe that Flash memory chips with structures smaller than 32 nm or 20 nm structures may make little sense. However, nanocrystals have been developed to become a life extension for Flash. Freescale is first to provide a foundation to that vision.

The company said that it has manufactured the world's first 24 Mbit memory array based on silicon nanocrystals, which could be a major step toward replacing conventional floating gate-based flash memories. The device uses 90 nm CMOS bulk technology and can be manufactured in existing wafer fabs, according to Freescale. While the production process requires silicon nanocrystals to be deposited with perfect uniformity and integration approaches, the technology still is expected to lower overall Flash production cost. Freescale claims that nanocrystal Flash will cost 10 to 15 percent less than today's Flash memory.

Freescale explained that nanocrystals also are more scaleable than conventional floating gate-based flash technology, as their tunnel oxide thickness can be reduced without impacting data retention. The charge is stored on isolated nanocrystals and is lost only from those few nanocrystals that align with defects in the tunnel oxide - while the same defects would result in significant charge loss from a conventional floating gate. A thinner tunnel oxide permits lower-voltage operation, the company said, and substantially reduces the memory module area needed to generate the bit-cell programming voltages. According to the potential of shrinking the oxide layer enables a decrease in supply voltage from around 9 volts today to about 6 volts in nanocrystal flash.

Bruce White, manager in Freescale's advanced materials, memories and interconnects divisions says that a reduction of voltage will be key in scaling Flash memories in the future. While nanocrystals will target embedded Flash in industrial or automotive segments first, the technology could also make its way into consumer Flash memory cards someday. However, Freescale did not decide on actual development of such a device. With the hurdle of a 24 Mbit Flash memory device being cleared, White said that Freescale will be working in the near future on creating "high-quality" oxide to work in conjunction with nanocrystals.

Freescales plans to offer commercial nancrystal flash by the end of 2007 or early in 2008. The first widely available nancrystal Flash is likely to be manufactured in a 65 nm process and offer a capacity of 24 or 32 Mbit.