The self-assembling of materials known as block copolymers could provide a low-cost, efficient way to fabricate ultra-high-density computer memory. Block copolymers, which are made of chemically different polymers linked together, can arrange themselves into arrays of nanoscale dots on surfaces, which could be used as templates for creating tiny magnetic bits that store data on hard disks. Until now, though, there was no simple, quick way to coax the block copolymer to make the desired arrays over large areas.

Researchers at the University of California, Berkeley, and the University of Massachusetts Amherst have found a simple way to coat square inches of substrate with block copolymers. The highly ordered pattern formed by the copolymers could be used to create hard disks with 10 terabits squeezed into a square inch, the researchers report this week in Science.

Today's hard disks carry 200 gigabits per square inch of data. Existing magnetic storage technology could potentially allow densities up to one terabit per square inch. Each bit on a hard disk is a small area of magnetic material with its magnetic field aligned in one direction. These islands are irregularly shaped and sit edge to edge on the disk. As densities go beyond one terabit per square inch, the tiny bit areas will need to be defined and not overlap so that they can be read accurately.

Block copolymers could help shrink magnetic bit dimensions. When a solution of a block copolymer is spread out on a surface, the polymers arrange themselves in precise nanoscale arrangements. Hard-disk makers such as Hitachi Global Storage Technologies, in San Jose, CA, are working with materials in which one polymer lines up as parallel cylinders inside the other polymer. The cylinders, which stick up from the surface, could then be etched away, and the empty holes filled with magnetic material. Each little dot of magnetic material would be a bit.

The catch is that the cylinders don't arrange themselves straight, says Ting Xu, a materials-science and engineering professor at the University of California, Berkeley, and one of the researchers on the new work. "They're randomly oriented with respect to the surface," she says. "You can't use those because the disk reader will have difficulty identifying where the bit is."