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

awesome

[Anonymous Coward]

i've been waiting for pcram to show it's head in consumer electronics for a while now. it has the advantages of being hundreds of times faster than flash along with having at least ten times the write-cycle life. it could turn out to be the OLED to DRAM's LCD.

the main disadvantage is that it's rather heat-sensitive, since writing is accomplished by melting crystals with a low melting temperature.

Re:awesome

[fractoid]

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.

Well... unless you count lithium battery fires... :P Although I suppose they'd count as 'destructive events'.

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'?

Re:awesome

[TheRaven64]

Because it's a very old question. People used to look at old glass, notice that it was thicker at the bottom, and assume that it had flowed. It turns out that, back when this glass was made, you made sheets of glass by spinning a blob until it became a disc. You then let this cool and cut it into the right shapes. The parts along the edge were thicker. Any glass that was installed with the thick bit at the top had more weight on weaker glass than sheets installed the other way up, and so cracked, broke, and was replaced. The only bits that survive are the ones where the glass was installed with the thick part at the bottom. More modern glass sheets are made by floating the molten glass on top of another liquid and so do not have this deformity and do not appear to flow.

Asking why old windows are thinner at the top is like asking why the sun moves across the sky to contradict the heliocentric view of the solar system, and so deserves a funny moderation.

hmmmm

[socceroos]

I wonder how long they'd last. 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?

CDRW

[afidel]

This sound very similar to the phase change crystals in CDRW disks though obviously they are reading these electrically rather than optically since at 20nm you're well into the x-ray part of the spectrum.

Laugh, but....

[WindBourne]

Security for afterlife may be interesting. The more so if somebody thinks that their system or even the ram is bad. Unless it is physically ran through a fire, there will be something of use.

Re:And What About...

[John Marter]

And also, will this get past the requirement for flash of writing out in largish chunks?

Primary advantage, so far unmentioned...

[KonoWatakushi]

Perhaps the single most important advantage of PRAM has not even been mentioned yet. PRAM does not require the stupid block erase semantics of Flash--you can read or write as much or as little as you want, at whatever alignment, with no impact on performance. This also means that an SSD will be very simple, require no caches at all, and still have blazing fast write performance, even for synchronous writes.

PRAM will still require ECC algorithms, wear leveling, and bad block remapping, but on the spectrum of controller complexity, it is a lot closer to DRAM than Flash. (Incidentally, the same can be said of performance.) Reads and writes would still be buffered for queuing purposes, but this is very different from a cache; it is simply to allow requests to be pipelined from the storage controller.

Compared with the very simple constant time operations with PRAM, Flash is a dog. The controller must cache writes while it reads, erases, and otherwise shuffles blocks around. Moreover, as the controller operates with volatile memory, it must do this very slowly and carefully, or a power failure could severely corrupt the disk. (There are Flash SSDs with an onboard super capacitor to work around this, but they are obscenely expensive.)

Due to their inherent nature, even the best Flash SSDs have severely asymmetric read/write performance. The fact that only one company (Intel) has managed to produce a decent controller also betrays the immense complexity required to eek out even moderately acceptable random write performance. In my opinion, so called "SSDs" made with Flash don't even deserve that moniker, as they are more like a fast hard disk. (They still have a sort of geometry which constrains performance, and aren't anywhere near as fast as DRAM.)

PRAM will fix that, offering performance similar to a DRAM SSD. There are many companies banking on Phase-change RAM to displace Flash memory, Intel included. The wikipedia page has a lot more info, but basically, PRAM is superior to Flash in every way, except that the data on a prewritten chip won't survive a trip through the wave soldering machine.