Melting Memory Chips In Mass Production

chill writes "Nature is reporting that 'South Korean manufacturer Samsung Electronics announced this week that it has begun mass production of a new kind of memory chip that stores information by melting and freezing tiny crystals. Known as phase-change memory (PCM), the idea was first proposed by physicists in the 1960s.' With transistor-equivalent cells only 20 nm wide, switching time is around 16 ns. The first target market is cell phones, but the companies behind the technology see applications in PCs, servers, and other devices as well."

Comments

Durability and Other Limitations

[mrbene]

PCM is interesting stuff. Here's some info:

• It's expected re-write lifetime is magnitudes larger than that of Flash.
• It'll be heat sensitive - weak crystal bonds will 'fail' if the module gets too hot. This also means interesting challenges around soldering.
• While Flash memory units become less usable the smaller they are (due to bleeding of info from weird electromagnetic interactions at very small scale), PCMs become more usable, as they require less energy to go through the "melt and refreeze" steps.
• It'll be in the manufacturers best interest to direct the heat directly at the PCMs themselves, since this is the most energy efficient solution. They're probably going to run cold.

Re:And What About...

[georgewilliamherbert]

Lifetime - significantly better than Flash, 3 plus orders of magnitude more write/erase cycles before there's degradation.

Impact on overall computer heat & energy required to use - lower read power than Flash, no maintenance power (DRAM requires rewrite cycles as the bits decay)

Expected size - Initial model is 0.5 GB (512 MB) per chip. That's on a much larger fab process than current CPUs or DRAM though - expect that to increase rapidly once demand is established.

Re:awesome

[icebike]

Rather heat sensitive, in comparison to other technologies, but the critical temperature of GeTe grystals is around 446 Celcius.

At room temp this stuff is rhombohedral structure, at at 446C it changes to a cubic structure. The size of these tiny crystals is so small that this temperature is easily reached.

Note that no liquid phase is involved here, its simply changing from a glass structure to a crystal structure.

This 446C temperature is not likely to be reached in the absence of other heat related destructive events, regardless of how tight your jeans are.

Re:awesome

[Tweenk]

Note that no liquid phase is involved here, its simply changing from a glass structure to a crystal structure.

No. Glass is a form of liquid - it has no translational symmetry at the molecular level. Rhomboedral or cubic structures are not glasses because they do have translational symmetry and are therefore crystalline. The change is between two types of crystal lattice.

Re:awesome

[qeveren]

Glass is an amorphous solid, not a liquid.

Re:awesome

[networkBoy]

The crystals are melted by passing a current through a BJT transistor. The heat given off melts the calcoginide(sp?) material. Reducing the current quickly causes it to freeze in an amorphous state, cooling it slowly produces a crystal. The resistance of the two phases is different, thus having memory.

Pros:
*Naturally rad hardened since it is a physical state, not a charge like flash and DRAM.
*Easy to erase in manufacture (the reflow temp is high enough to erase the whole memory)
*3D memory arrays are possible. The same material can be used (with metal) to make a transistor, thus you can make layers of arrays. Traditional flash is one layer deep as it requires doped Si for the transistor.

Cons:
*In prototypes we've seen cell phones erase themselves when left in a closed up black car on a black dash with a black interior on a hot Phoenix AZ summer day.
*you can't factory program the memory, it must be programmed after reflow onto the device. (flash can be ordered from the factory pre-programmed in large unit orders).
*Manufacturing defects have been an issue (bubbles in the calcoginide material.

I used to work for a company developing this stuff. We had prototype units in modified production cell phones as long as two years ago (when I left). Not sure if some of the cons have been fixed since then.
-nB