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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."
PCM is interesting stuff. Here's some info:
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.
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.
Sig Battery depleted. Reverting to safe mode.
Yes you are being paranoid. You already run a serious risk of losing all your data when you drop your Cell, so nothing changes here.
Other things will break first.
Sig Battery depleted. Reverting to safe mode.
Yep. PCM natively supports per-bit writing without the need to re-write the rest of the block.
Apparently the crystal bond is very weak. I wouldn't want to lose my data because I dropped my cellphone. Perhaps I'm being paranoid?
Keep in mind that your intuitions about how substances will react to shocks are all based on objects of a particular size. Small objects are much less likely to break under a given amount of acceleration than large objects are. For an example of what I mean:
My guess is that this memory will be at least as shock-resistant as current flash memory.
I don't care if it's 90,000 hectares. That lake was not my doing.
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.
Those who would give up liberty to obtain working drivers, deserve neither liberty nor working drivers.
I was pretty sure they cleared that "glass is a liquid with a high viscosity" myth in one of those "Myths my science teacher taught me" books. This should help clear that up for you though: http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html
Glass is an amorphous solid, not a liquid.
Don't just stand there, get that other dog!
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
whois gawk date unzip strip find touch finger mount join nice man top fsck grep eject more yes exit umount sleep dump
without it's firmware it wouldn't boot, but yes, re-programming the phone brought it back to life.
I see the new temps Samsung has hit are high enough that this will not be a problem for them.
whois gawk date unzip strip find touch finger mount join nice man top fsck grep eject more yes exit umount sleep dump
Kidding aside, thanks for the rundown. It now makes sense. :) One thing I don't understand, though, is the write cycle life. Does the phase change substance gradually settle into a third state? Or does the heating mechanism 'wear out'?
According to this detailed paper, it's being conservatively limited to a million writes for now because they have no real experience from which to determine true write lifetime. Right now, they don't know which will fail first: the phase-change material, or the BJT driver transistor.
Man is the animal that laughs.
And occasionally whores for Karma.