Table salt to boost hard disk density by six times

SINGAPORE: A team of scientists used nanopatterning to closely pack more of the miniature structures that hold information in the form of bits, per unit area.

Joel Yang, from Institute of Materials Research and Engineering's (IMRE), a research institute of Singapore’s Agency for Science, Technology and Research (A*STAR), and his research team working with peers from A*STAR’s DSI and NUS, used nano-patterning to create uniform arrays of magnetic bits that can potentially store up to 3.3 Terabit/in2 of information, which is six times the recording density of current devices.

This means that a hard disk drive that holds 1 Terabyte (TB) of data today could, in the future, hold 6 TB of information in the same size using this new technology.

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The key ingredient in the much enhanced patterning method that he pioneered is sodium chloride, the chemical grade of regular table salt.

Conventional hard disks have randomly distributed nanoscopic magnetic grains - with a few tens of grains used to form one bit — that enable the latest hard disk models to hold up to 0.5 Terabit/in2 of information. The IMRE-led team used the bit-patterned media approach, where magnetic islands are patterned in a regular fashion, with each single island able to store one bit of information.

“What we have shown is that bits can be patterned more densely together by reducing the number of processing steps”, said Joel Yang, the IMRE scientist who heads the project. Current technology uses very tiny ‘grains’ of about 7-8 nm in size deposited on the surface of storage media.

However, information or a single bit, is stored in a cluster of these ‘grains’ and not in any single ‘grain’. IMRE’s bits are about 10nm in size but store information in a single structure.

The method has been demonstrated to achieve data-storage capability at 1.9 Terabit/in2, though bits of up to 3.3 Terabit/in2 densities were fabricated.

“In addition to making the bits, we demonstrated that they can be used to store data,” explained Yang.

The secret of the research lies in the use of an extremely high-resolution e-beam lithography process that produces super fine nano-sized structures. Yang discovered that by adding sodium chloride to a developer solution used in existing lithography processes, he was able to produce highly defined nanostructures down to 4.5 nm half pitch, without the need for expensive equipment upgrades.

This ‘salty developer solution’ method was invented by Yang when he was a graduate student at the Massachusetts Institute of Technology.

This work is the result of a collaborative effort with Prof Vivian Ng’s group at NUS, and Yunjie Chen, Siang Huei Leong, and Tianli Huang from A*STAR DSI’s 10 Terabit/in2 Magnetic Recording programme.

The researchers are now looking at increasing the storage density further.