A modified approach to fabrication of magnetic memory elements may lead to a new generation of stable, ultra-high-capacity hard drives.
A magnetic film patterned into an array of dots (background) is
known as a bit-patterned medium, and can store data at very high areal
densities. Each dot requires a slightly different magnetic field to
write or erase. Ranjbar and co-workers reduced this variation by adding a
continuous layer underneath the dots, made of the same material as the
dots themselves (green). By comparison, the traditional approach
(yellow) had both a wider variation, and higher average switching
fields. (Credit: Copyright A*STAR)
Information in most computer memories is stored in the form of 'bits'
represented by the polarization of tiny magnets on the surface of
memory devices such as the computer's hard drive. The capacities of
these devices have increased exponentially over the last 30 years, a
feat made possible by progressively reducing the area taken up by the
magnets storing the information. In modern machines, these magnets are
so small that reducing their size any further risks creating unstable
data, due to random flipping of the direction of polarization of the
magnets at higher densities. Now, Mojtaba Ranjbar and colleagues at the
A*STAR Data Storage Institute have honed a key technology, called
bit-patterned media, to overcome this problem and allow data to be
stored at previously unattainable densities.
Bit-patterned media technology replaces the continuous magnetic film
traditionally used in hard drives with an array of small, patterned
magnetic dots (see image), each of which stores a bit of data. By
carefully designing the size and shape of these dots, data can be stored
at very high densities without the instability that would be
encountered if a continuous film were used.
Using bit-patterned media, however, is not without its own
difficulties, chief among which is a problem known as 'switching field
distribution', whereby the magnetic field required to write or erase
data in each dot differs slightly and by an unknown amount. As a result,
the magnetic field applied by a hard drive write head may be too small,
or too large, resulting in data errors.
Previous work by other researchers sought to minimize the switching
field distribution problem by covering all of the magnetic dots with a
continuous magnetic film placed on top of the dots, which alters the
magnetic interactions between individual dots. The approach called
'capped bit-patterned media' traditionally requires different magnetic
materials for the dots and film, introducing additional fabrication
complexity.
Ranjbar and co-workers used the same material for the film and dots,
and positioned the dots above the film rather than below it. This
approach allowed a particularly simple fabrication process, in which
dots were etched in a controlled fashion, leaving a continuous, unetched
film underneath and obviating the need for a separate deposition step
to introduce a new magnetic material.
The researchers found that this simplified process successfully
reduced switching field distribution, and also lowered the field
strengths necessary for writing data. Ranjbar comments, "Combined with
the ease of fabrication, this technology should prove useful in
bit-patterned media for next-generation hard disk drives."
Story Source:
The above story is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR), via ResearchSEA.
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