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No toys to throw from the PRAM

Phase-change memory could be going nowhere slowly

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Comment Phase-change memory (PCM or Phase-change RAM - PRAM) seems to be changing its phase, from promising-newcomer-technology to fading-candidate-going-nowhere.

PCM is a memory technology involving a change of material state and electrical resistance in a memory cell's chalcogenide layer. The theoretical attractions are that it is non-volatile, like flash, bit-addressable, like DRAM, and high-density. In practice it has proved difficult to commercialise. Problems with the technology have taken years to solve, resulting in low density product using relatively large process geometries, such as 90nm and 65nm – and apparently large power draws as well.

Meanwhile NAND flash memories are currently being fabricated using sub-30nm processes with sub-10nm geometries in prospect.

There are two PCM developers: Micron, through acquiring Numonyx, and Samsung, and they have to contend with other follow-on technology candidates to succeed NAND, such as Resistive RAM and HP's Memristor, while developing their PRAM products. It could be that NAND is viable for long enough for one of the PRAM alternatives to come to the fore and render PRAM pointless.

Our understanding is that Samsung has shipped limited quantities of a 512Mbit PRAM device but neither it nor Micron has yet shipped a 1Gbit capacity chip. The Micron Numonyx 1Gbit device, which was supposed to ship last year, uses a 45nm process whereas Samsung's is based on a 58nm process.

Talking at CeBIT, Steve MacDonald, an EMEA executive at Micron, one of the two PCM suppliers, said Micron is continuing its PCM development work and: "Eventually it may replace NOR for entry-level NOR applications. It is already in the embedded market with serial and parallel PCM ... We believe NAND will be viable for the next five years [with] geometries below 20nm. But below 10nm? I don't know."

He said that: "Samsung has announced PCM but we haven't seen anything coming out yet."

Samsung talked about its PRAM toys at the 2011 International Solid-State Circuits Conference in San Francisco last month, and said OEMs face a non-compatibility obstacle in moving from flash memory to PRAM. But it seems to El Reg the OEMs also face a bigger obstacle in that PRAM doesn't offer them anything significantly better than their existing flash memory components and may not do so until 2017.

Technologies like that in Anobit's digital signal processing controllers, and over-provisioning to combat limited endurance, as well as better flash-optimised system software, could enable NAND to persist to the point that PRAM becomes redundant.

With millions of dollars invested in the technology it will be a hard decision for either Micron or Samsung to move on from PRAM to something else. Perhaps the pair of them would be better off partnering in PRAM and not competing? ®

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