Nanocrystal memory

Freescale Semiconductor has manufactured the world's first 24Mbit memory array based on silicon nanocrystals, a major step toward replacing conventional floating gate-based flash memories.

The 24Mbit memory array technology was manufactured at Freescale's Austin Technology & Manufacturing Center using 90nm CMOS bulk technology.

As the industry begins manufacturing at smaller geometries — 90-nm and smaller — embedding floating gate-based flash becomes difficult to produce cost-effectively. At those dimensions, the chip area consumed by the 9-12V high-voltage transistors required to write and erase the conventional flash module cannot be scaled down.

Furthermore, engineers cannot reduce the high voltage in floating gate-based flash without compromising reliability or risking memory failures and loss of data.

Silicon nanocrystal memories are part of an advanced class of memory technologies called thin-film storage. They 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.