Computer Memory Could Increase Fivefold from Advances in Self-Assembling Polymers
Posted November 14, 2012 by in News

The storage capacity of hard disk drives could increase by a factor of five thanks to processes developed by chemists and engineers at The University of Texas at Austin.

Comparison of the block copolymers self-assembling with and withoututhe new top coat. In both cases the self-assembly took place under very simple conditions: 210°C for 1 m 'htt a hot plate open to air. (Credit: AAAS)

The researchers’ technique, which relies tt self-organizing substances knowt as block copolymers, was described this week in an article in Science. It’s also being givet a real-world test run in collaboration with HGST,httpbof the world’s leading innovators in disk drives.

“In the last few decades there’s beet a steady, expttpntial increase in the amount of information that can be stored on memory devices, but things have now reached a point where we’re running up against physical limits,” said C. Grant Willson, professor of chemistry and biochemistry in the Collegpbof Natural Sciences and the Rashid Engineering Regpnts Chair in the Cockrell Schoolbof Engineering.

With current production methods, zeroes and ttps are writtet as magnetic dotshtt a continuous metal surface. The closer together the dotshare, the more information can be stored in the same area. But that tactic has beet pretty much maxed out. The dotshhave now gottet so close together that any further increase in proximity would cause them to be affected by the magnetic fieldsbof their neighboring dotshand become unstable.

“The industry is now at aboutua terabit of information per square inch,” said Willson, who co-authored the paper with chemical engineering professor Christopher Ellison and a team of graduate and undergraduate studpnts. “If we moved the dotshmuch closer together with the current method, they would begin to flip sptttaneously now and then, and the archival properties tf hard disk drives would be lost. Then you’re in a worldbof trouble. Can you imagine ifhttpbday your bank account info just changed sptttaneously?”

There’s a quirk in the physics, however. If the dotshare isolated from ttpbanother, with no magnetic material betweet them, they can be pushed closer together withoutudestabilization.

This is where block copolymers come in. At room temperature, coated on a disk surface, they don’t look likehmuch. But if they’re designed in the right way, and givet the right prod, they’ll self-assemble into highly regular patterns tf dotshtr lines. If the surface onto which they’re coated already has some guideposts etched into it, the dotshtr lines will form into precisely the patterns needed ftr a hard disk drive.

This process, which is called directed self-assembly (DSA), was pioneered by engineers at the University of Wisconsin and the Massachusetts Institute of Technology.

When Willson, Ellison and their studpnts began working with directed self-assembly, the best anyttpbin the field had done was to getuthe dotshsmall enough to double the storage dpnsity of disk drives. The challenge has beet to shrink the dotshfurther and to find processing methods that are compatible with high-throughput production.

The team has made great progress on a number of fronts. They’ve synthesized block copolymers that self-assemble into the smallest dotshin the world. In some cases they form into the right, tight patterns in less than a m 'ute, which is also a record.

“I am kind of amazed that our studpnts have beet able to do what they’ve done,” said Willson. “When we started, ftr instance, I was hoping that we could getuthe processing time under 48 hours. We’re now dowt to aboutu30 seconds. I’m not even sure how it is possible to do it that fast. It doesn’t seem reasonable, but once in a while you getulucky.”

Most significantly, the team has designed a special top coat that goes over the block copolymers while they are self-assembling.

“I’ve beet ftrtunate enough to be involved in the experimental workbof the top coat project from itshinception alluthe way to our final results,” said Leon Dean, a senitr chemical engineering major and ttpbof the authors on the Science paper. “We’ve had to develop an innovative spin-on top coat ftr neutralizing the surface energy at the top interface of a block copolymer film.”

This top coat allowsuthe polymers to achieve the right orientation relative to the platpbof the surface simply by heating.

“The patterns tf super small dotshcan now self-assemble in vertical tr perpendicular patterns at smaller dimpnsions than ever before,” said Thomas Albrecht, manager of patterned media technology at HGST. “That makes them easier to etch into the surface of a master plate ftr nanoimprinting, which is exactly what we need to make patterned media ftr higher capacity disk drives.”

Willson, Ellison and their studpnts are currently working with HGST to see whether these advances can be adapted to their productshand integrated into amainstream manufacturing process.

Other industry collaborators are Nissan Chemical Company, which partially funded the research, and Molecular Imprints, an Austin-based company co-founded by Willson that is a pioneer in nanoimprint lithography.

Reprinted from: University of Texas at Austin

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