IBM has 60Gbit/cm2 storage density on tip of its tongue

IBM has 60Gbit/cm2 storage density on tip of its tongueSteve Bush
Data could be stored at a density of 60Gbit/cm2 (400Gbit/in2) if work at IBM’s Zurich Research Laboratory ever makes it to production. The best magnetic hard drives are now achieving around 2Gbit/cm2.
The storage medium is a sheet of polymethylmethacrylate (the same material in ‘Perspex’ clear plastic sheets)and the storage technique involves melting tiny pits in it using an atomic force microscope (AFM) technique.
The tip of the AFM is sprung and in constant contact with the polymer surface. Springing is through a U-shaped cantilever which also acts as an electrical conductor to allow the tip to be resistance-heated.
To write, the tip is heated to 400?C so that the tip melts into the polymer under spring pressure, like a hot knife on butter.
To read, the tip is warmed to a temperature that will not melt the polymer (350?C)and dragged along the surface. When the tip drops into a pit, it is cooled by thermal conduction. The change in temperature can be read as a change of resistance. The whole assembly could be the size of a conventional chip.
“We have an array of 32 by 32 AFM tips in a 3 x 3mm patch on a single silicon chip. Because it has a thousand legs we call it The Millipede,” said project leader Peter Vettiger.
The tips are on a 92?m pitch grid and can produce 40nm pits. By moving the whole array slightly, the pits can be made with a 40nm spacing.
This means that each tip can be made to produce over 2,000 pits before it begins to overwrite pits from its neighbouring tip. As the array moves in two dimensions, each tip can actually access over 5 million pits.
1024 tips in the array can therefore be used to service 5 billion pits. According to Vettiger this estimate could be a little conservative. “I think the array could finally store around 10Gbit on 3 x 3mm of polymer,”he said.
Although no way of erasing individual bits has yet been proposed, erasure of an area is possible by heating the polymer to melt it back to a flat surface.
Vettiger points out that the work is at a very early stage, but he sees small devices based on an array moving over a similarly sized area of polymer, “for consumer audio-visual and PDA applications”, and bigger stores where the array can jump to a fresh area of polymer.


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