Numonyx wiggles out of PCM scaling trap

Intel and Numonyx announced a way to build vertical stacks of Phase Change Memory arrays without losing performance.

Phase Change Memory (PCM) is an experimental memory technology that is non-volatile, bit-addressable - unlike flash - and capable of moving to smaller process geometries than flash which, manufacturers say, is approaching a process down-sizing limit.

It works by having the state or phase of a chemical compound altered such that its resistance to electricity changes. This can be used to signal the presence or absence of a binary digit. The compound is a Chalcogenide glass substance which changes between crystallised and amorphous, non-crystallised states when heated.

Numonyx has been working on PCM for some time, as has Samsung. Numonyx has a 128Mbit PCM die whereas Samsung has announced a 512Mbit one. It has been reckoned that Numonyx has had difficulty increasing PCM die capacity, having tried multi-level cell technology but finding that cell access speed is slow.

As announced, the Intel and Numonyx research engineers demonstrated a working 64Mb test die that has an Ovonic Threshold Switch (OTS) - termed a selector - layered on top of the array of PCM cells. They said the demo opens the door to building PCM dies with multiple, vertically-stacked layers, which would increase die capacity without compromising cell access speed.

This demo is probably vital for Numonyx as its PCM development work appears to have been stalled by its scaling problem. It can see its way now to ratchet up PCM die capacity to Samsung's 512Mb die and beyond.

But the demo is only of a single entity in such a stacked cell and the next step is to verify that stacked PCMS layers work as well. The Intel and Numonyx engineers must be confident that this can be accomplished, though. We might hear news of such a stacked PCMS die next year. ®