The way IBM describes its racetrack memory – yet another candidate for "memory of the future" – it's easy to be left with the impression that Big Blue is out on its own with this one. Stacey Higginbotham breathlessly opines: "IBM sure has some seriously crazy semiconductor researchers locked in its basement. These guys question everything when it comes to advancing chip technology."
Maybe IBM does. But it's not alone. What IBM claimed in the press release was that a memory 100 times denser than today's flash devices is on its way:
"The devices would not only store vastly more information in the same space, but also require much less power and generate much less heat, and be practically unbreakable; the result: massive amounts of personal storage that could run on a single battery for weeks at a time and last for decades."
Sounds great. When can I buy one? Not any time soon if you look more closely at what IBM's release is based on. The journal Science has published a paper on the work of Stuart Parkin's group at its Almaden lab in San Jose that describes a tweak to a type of magnetic memory. It's a bit like a solid-state disk state. You store bits magnetically: the state depends on which way the stored field points, either forwards or backwards along a metal wire.
With a disk drive, you read the bits by passing them at high speed under a magnetic head. With domain-wall memory, you push the bits along until they pass by a circuit that can read the state of the field. This is where IBM came up with its moniker of 'racetrack' memory. In reality, it's a bit more like a sushi counter: you have to wait until the bits you want slide into view. In that respect, it works a bit like a NAND flash memory, albeit with much longer chains of bits. And so, the main application, if and when this type of memory appears, is going to be in media players where you simply want to suck bits from it in a more or less continuous stream.
In principle, domain-wall devices sound great, and there are other groups pushing ahead on the research in addition to Parkin's, although he has a key patent on the technology. When Professor Russell Cowburn's group at Imperial College, London reported making logic switches using this approach, they explained why the world might want to switch from silicon semiconductors to this new way of working. Because you make the circuits out of conductors instead of semiconductors, you get a lot more electrons into a small space. That makes it, in principle, easier to scale down in size. On top of that, you don't have to mess with all the complicated steps that silicon technology needs: you simply lay down tracks of a simple magnetic alloy.
Now the bad news. There are still some big problems with this type of memory. The one that is likely to trip it up is power. Parkin's team describes in the Science paper a way of pushing the bits along a short wire – just three bits in a row – using current. The previous devices use magnetic fields. By using pulses of electric current to push the domains along the wire instead of magnetic fields, it should be easier to make the devices - chipmakers have been dealing with that kind of circuit for years; the idea trying to control magnetic fields on a chip is far less well developed. But it's not just IBM doing it.
Professor Teruo Ono's team in Kyoto published in Applied Physics Express in January a description of their work on current-driven domain walls, and they name-check quite a few groups doing work in the same area. What Ono's team points out clearly, and you find people with similar concerns in the Science news item as well, is that using current to push the bits along demands a lot of juice. 100 million amps per square centimetre. The wires are tiny, so you don't have to put the entire generating capacity of a small nation into the chip, but this is two orders of magnitude more juice than the magnetic memories that are going into production today. And they consume a lot more power than electronics engineers want, which is why Freescale Semiconductor's magnetic memories are going 