Micron is first to market with phase-change memory (PCM)

[ScienceRocks]

Micron is first to market with phase-change memory (PCM)
Micron is first to market with phase-change memory (PCM) - TechSpot News

By Rick Burgess

We've been hearing about phase-change memory (PCM) for the past several years, but it appears Micron will be the first manufacturer to bring this flash-alternative to commercial markets. According to Micron, PCM will be landing on feature phones first with plans for smartphones and tablets to come later.

If you're wondering why feature phones, Micron says it'll be stamping out a boards with 1GB of PCM (45nm) accompanied by 512MB of LPDDR2 (mobile DDR). Smartphone and tablet users expect higher capacities, but PCM is very much in its infancy. Micron is likely taking a slow and steady approach before working with higher densities and smaller packages.

PCM is a type of non-volatile memory which appears to be best suited for applications where NAND flash is currently used. NAND flash is typically found in USB storage drives, SSDs, memory cards and most other commercial products where permanent data storage without a power source is important. PCM does this too.

What makes PCM different though is how it stores data. PCM works by triggering (pdf) a poly-crystalline solid to become amorphous, switching from its once crystalline state. This change is induced by applying jolts of electricity to specific areas of the material, creating heat and triggering those state changes. This type of localized "current injection" can be done with great precision, allowing PCM to manipulate individual "cells" as single bits, similar to SLC flash memory.

Unlike NAND flash though, PCM is bit-alterable. That means there's no need for PCM controllers to erase bits between re-writes. This is one reason current flash offerings have write speeds far below their read performance.

One more interesting bit -- if PCM becomes fast enough, we may see the marriage of storage and system memory. In fact, Micron mentions this in this brief PCM demo.

Because system memory has needed to be both fast and affordable, the industry has been using volatile memory solutions like EDO, SDR and DDR for decades. Respective to their own time periods, these DRAMs offer great speed, but instantaneously lose any information they contain when the host device is powered off. Thus, for reasons of price and volatility, storage devices and system memory have remained two very separate things.

Like flash, PCM doesn't suffer from this memory loss. Unlike flash though, PCM and competing non-volatile technologies have the potential to rival the performance of DRAM. If these non-volatile memory technologies become fast enough, cheap enough and large enough -- quite a few variables, I know -- there may be little reason to keep memory and storage devices separate.

http://en.wikipedia.org/wiki/Phase-change_memory

 

[ScienceRocks]

Write speeds for phase-change memory reach record limits

Scientists bring us closer to wider use of phase-change memory (PRAM) chips.


by Melissae Fellet - June 22 2012, 8:40am PDT

Physical Sciences
38

DRAM in computers is erased when a computer is turned off.

commons.wikimedia,org

By pre-organizing atoms in a bit of phase-change memory, information can be written in less than one nanosecond, the fastest for such memory. With write speeds comparable to the memory that powers our computers, phase change memory could one day help computers boot up instantly.

Phase-change memory stores information based on the organization of atoms in a material, often a mixture of germanium, antimony, and tellurium (Ge2Sb2Te5 or GST). A voltage pulse heats the metal and disordered atoms in the crystal rearrange into an ordered crystal. Restoring the disordered arrangement by melting the glassy material erases the information. A computer reads each bit by detecting the lower electrical resistance of the ordered crystal.

Micron sells small phase-change memory (PRAM) chips. Companies like IBM and Samsung are working on PRAM chips too.

Phase-change memory could one day replace flash memory in our cellphones, just as Samsung briefly tried in a commercial smartphone. PRAM can top the density and write times of flash memory. And like flash, PRAM is nonvolatile, meaning that it retains its information even when a device is powered off.

That makes phase-change memory an intriguing candidate to replace the volatile DRAM that powers our computers. But a computer that boots up instantly using PRAM is still a long way off, partly because the materials can’t be switched from disordered to ordered, or written quickly enough. Most phase-change materials crystallize slower than the 1-10 nanoseconds it takes to write a bit of DRAM. And materials that crystallize faster at PRAM operating temperatures tend to naturally organize at lower temperatures too, says Stephen Elliott of the University of Cambridge. Therefore, they slowly crystallize and erase themselves over time.

Elliott and his colleagues have boosted the crystallization time, and thus the write speed, of a stable PRAM bit. They pre-organized the atoms in a chunk of Ge2Sb2Te5 using a weak electric field. The scientists sandwiched a 50nm-wide cylinder of GST between two titanium electrodes and applied 0.3V of potential across the material. A 500-picosecond burst of 1V electrical potential triggered the crystallization, which is about 10 times faster than the best speed using a germanium-tellurium material.
Write speeds for phase-change memory reach record limits | Ars Technica