LONDON Nonvolatile memory supplier Numonyx BV (Rolle, Switzerland) is working on adding multilevel cell (MLC) capability to its phase-change memory technology but the work is not a priority, according to Paolo Cappelletti, vice president of technology development at Numonyx.
An alternative technology, which allows planes of phase-change memory to be stacked, could be a better way to add memory capacity on the same footprint, Cappelletti said, but that technology is also some way from commericialization. Numonyx is working on the stacking approach with parent company Intel and that collaboration was the subject of a paper at the International Electron Devices Meeting in Baltimore this week.
The two companies disclosed the fact they were working on the multilayer technology, which includes a non-memory effect phase-change select transistor (PCMS) in October 2009. The researchers have used a 64-megabit test chip to demonstrate a vertically integrated memory cell that comprises one PCM element layered with an ovonic threshold switch (OTS) in a cross-point array.
The non-memory effect phase-change switch is "the best select device we have seen not in silicon," according to Cappelletti. However, although multilayer memory is attractive it is still in development and does not yet have a clear point of introduction on the PCM technology road-map.
"We are working, and keep working, on MLC but the focus and the priority is applications," Cappelletti told EE Times in a telephone interview. Cappelletti pointed out that PCM does not need to compete with high capacity NAND flash memory, which has already achieved 32-Gbit capacity in a 30-nm process technology. "The role of PCM stand-alone memory is to exploit, from a system point of view, fast random access, single-bit write and extended cycle life. Competing with NAND is not the focus. Wireless applications and NOR replacement is an interesting proposition," he added.