November 28, 2005 — Freescale Semiconductor, Austin, TX, has brought silicon nanocrystal memory technology a little closer to commercial reality. The company reports that it has produced a 24Mbit memory array based on Si nanocrystals, a denser, faster, nonvolatile option that may take the place of floating gate-based flash memories, due to the expectation that conventional embedded flash memory technology may reach its scaling limits within four years.
Claudine Simson, Freescale CTO, explained, “Silicon nanocrystal technology offers lower operating voltages, reduced memory-module size, simpler process flow, and lower manufacturing costs. Additionally, it requires no new materials or wafer fabrication equipment, allowing for immediate compatibility with existing production wafer fabs.”
Thin-film storage technologies such as Si nanocrystal memories are more scalable than floating gate-based flash because tunnel oxide thickness can be reduced without affecting 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; the same defects would result in significant charge loss from a conventional floating gate. A thinner tunnel oxide permits lower-voltage operation, decreasing the memory module area needed to generate bit-cell programming voltages.