A COATING of microscopic polystyrene beads can dramatically increase the memory capacity of hard discs, as well as cutting the time a computer takes to access the data.
Since the early 1990s, the capacity of hard discs has doubled roughly every 18 months. The computer industry faces constant pressure to pack ever more data onto hard discs, for example, to support better graphics for games, or to store a library of digital movies. But the pace is beginning to ease. 鈥淭he slowdown has been coming for a few years,鈥� says James Porter, an industry analyst and founder of Disk Trend in Mountain View, California.
Now Manfred Albrecht from the University of Konstanz in Germany and colleagues from the Hitachi San Jose Research Center in California have come up with a novel way to increase the amount of data discs can store.
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鈥淚f the bits shrink much more, even subtle temperature variations would be enough to corrupt their data鈥�
All personal computers and network servers contain magnetic hard discs a few centimetres in diameter. The data they store takes the form of binary bits 鈥� either 1s or 0s 鈥� which are written to the disc by changing the direction of the magnetic field in successive bits. A read/write head follows a spiralling track across the disc鈥檚 surface, like the needle of a vinyl record player, and reads the magnetic fields.
The disc surface is made up of grains of magnetic material. A single bit is typically recorded on an area about 50 nanometres square that contains hundreds of these grains. Such an area contains data when the magnetic fields of all these grains point the same way. The problem engineers are now encountering is that making the bits smaller destabilises the orientation of the grains鈥� magnetic fields. If the bits shrink much more, even subtle temperature fluctuations would be enough to flip their field and corrupt the data.
Albrecht鈥檚 technique is to coat the disc with microscopic polystyrene beads, which gives it a pimpled surface. This layer is then covered with a magnetic film, which settles in round caps on top of each sphere and in the gullies between them. The effect is a surface made of many separate magnets. The beads鈥� isolation makes their fields more stable, so each bead can record a bit.
Albrecht鈥檚 team has developed a quick and cheap way of assembling the rafts of spheres. They simply stir the beads into a liquid and coat a surface with the mixture. As the liquid evaporates, the beads deposit in a single layer (Nature Materials, DOI: 10.1038/nmat1324).
鈥淭his way of trying to pattern media cheaply is interesting,鈥� says Michel Despont, who works on storage technologies at IBM鈥檚 Zurich Research Laboratory in Switzerland. 鈥淲hat is clear is this is just the beginning.鈥�
The team is still developing the technique but Albrecht expects to reduce the size of the beads from about 50 nanometres at present to about 10 nanometres.
