Nano-scale arrays enable terabit disk storage
by Chappell Brown, EETimes
Silicon Strategies
12/03/2003, 9:09 AM ET
HANCOCK, New Hampshire -- Fundamental materials research is pushing magnetic media densities to new highs.
At the Materials Research Society in Boston this week Bruce Terris from the Hitachi San Jose Research Center described a process for creating cobalt-palladium nanometer scale islands on silicon dioxide that he believes could carry magnetic media densities into the terabit/square-inch realm.
While theoretical predictions point to a physical limit somewhere around 100-Gbits per square inch for current approaches, the nano-island technique manages to avoid some of the factors leading to that limit. The process was developed in a joint project with researchers at nearby IBM Almaden Research Center.
The process has the ability to create vertically polarized magnetic domains, which reduce the crosstalk between neighboring bits. Previously, IBM researchers produced a medium using vertical domains that could store 200-Gbits per square inch.
The second innovation is a regular nano-patterning process that isolates individual magnetic domains on islands, which is essential in beating the thermal limit imposed by physics. The ability of magnetic domains to hold their magnetic polarization decreases linearly with their size, and the basic limit occurs when that figure matches the thermal energy of the magnetic medium. At that point, thermal noise would be able to switch magnetic orientations randomly.
Nano-imprint lithography was used to create an etch mask on a silicon dioxide substrate. Next, multiple layers of cobalt and palladium were sputtered onto the silicon dioxide islands. Because the resulting domains were isolated and not in a continuous film, they showed higher values for coercivity and thus were more resistant to thermal effects. Other projects are attempting to find nano-structured materials that isolate magnetic particles.
Integration potential
A research group at Rochester Institute of Technology presented a process that can integrate arrays of soft magnetic particles onto semiconductors for incorporation into circuits. Soft spinel ferrite nano-particles were suspended in an alcohol solution containing magnesium nitrate, which binds to the particles and gives them an electric charge. The solution, deposited over a silicon substrate, is then subjected to electrophoresis, which uses an electrostatic field to distribute them over the surface. The process was used to build integrated microtoroidal magnets and inductors. The researchers expect that the technique will be able to realize other devices, such as microtransformers.
Di-block copolymers are a popular medium for creating regular nano-structures because of their self-assembling properties. The polymers consist of two species that form a regular alternating structure on a molecular scale. One species can be opened up using a process called ring-opening meta-thesis polymerization, and a material of interest deposited into the cavity.
A project at the University of Maryland (College Park) used the system to create arrays of 5-nm to 15-nm diameter iron-oxide nano-particles suspended in the polymer and separated by around 37-nm.
The self-assembly properties of organic molecules are being used by a group at Germany's University of Duisburg-Essen to create regular nano-arrays of iron-platinum magnetic particles.
Magnetic nano-particles were first created by sintering, and then coated with organic phospho-lipids. When deposited on silicon substrates, the coated particles spontaneously organized themselves into a regular hexagonal pattern with a spacing of 1.2-nm. This regularity is critical to getting higher data storage densities, the researchers said. |
