Hitachi have demonstrated the technical feasibility of magnetic recording at 610Gbit/in2, considerably exceeding the previously demonstrated capabilities of current perpendicular recording technology found in current HDDs.
These results hold the potential for a 2.5x increase in
the storage capacities of current-generation HDDs.
Hitachi and Hitachi GST have together verified an areal
recording density of 610 Gbit/in2, using conventional
perpendicular magnetic recording with continuous
recording media and a software detection model. This
achievement provides further evidence that hard drive
capacities have the potential to advance at a rate of
40% annually. Application of this technology to future
HDD products is expected to result in products that
deliver larger capacities, smaller sizes and greater
Hitachi presented its findings at The Magnetic Recording
Conference (TMRC), taking place in Singapore from 29th
to 31st , July 2008.
"These results are based on many years of experience
with design optimization and material technology for
perpendicular recording heads and media. We applied this
knowledge to the development of heads and media with an
ultra-narrow track pitch of 65nm, indispensable in
achieving a recording density of 610 Gbit/in2.
Development of iterative signal processing technology
for high density recording further increased density and
capacity," said Hiroaki Odawara, Research Director,
Storage Technology Research Center, Central Research
Laboratory, Hitachi, Ltd.
Perpendicular magnetic recording is now the current
mainstream HDD technology. Hitachi GST demonstrated 230
Gbit/in2 in April 2005, 345 Gbit/in2 in September 2006,
and has now shown extendability to 610 Gbit/in2. This
growth supports the theory that technology can support
storage capacity growth of 40% annually. It has been
predicted, however, that the current perpendicular
recording, which uses a continuous film media will
eventually reach a limit in achievable recording
density, and therefore, new head and media using
alternative technology such discrete track recording,
bit patterned media and thermally-assisted recording,
are also being considered. These new methods are still
being developed, but hold potential for much greater
advancements in areal density growth.
Write- and read- head technology for 65nm level track
Continued hard drive advancements require the ability to
squeeze more and more, and thus, smaller and smaller
data bits onto the recording media, necessitating a
decrease in recording track pitch, as well as continued
miniaturization of the recording heads to read those
bits. As the track pitch narrows, the magnetic field
from the write-head interferes with the recorded data in
an adjacent track, causing problems such as rewriting or
even deletion of data.
To minimize this effect and contain the magnetic field
of the head to the relevant track, researchers at
Hitachi and Hitachi GST developed a wrap-around shield
('WAS') write head for narrow pitch tracks by employing
a WAS structure, where the main magnetic pole of the
write-head is wrapped with a magnetic shield. A TMR
(Tunneling Magneto-Resistive) head, able to maintain a
sufficient S/N ratio, was also developed for when the
sensor width is narrowed. Technology to optimize the
write- and read-head was developed using a separated
write- and read- head, and analyzing the performance of
New media technology with high S/N ratio for 65nm
level track pitch
A recording layer was developed with an anisotropy field
gradually increasing in the thickness direction.
Generally, the greater the anisotropy field, the more
difficult it is to reverse the direction of the magnetic
current. However, Hitachi found that in the newly
developed recording layer, reversal in a magnetic moment
occurs from the area with a low anisotropy field, and
this in turn, assists reversal in the areas with a high
anisotropy field, thus maintaining high thermal
stability as well as achieving high writing capability.
The signal and noise information of the media was also
analyzed based on a micro-magnetic model, and an optimal
design for the head-and-media combination was developed.
Micro-magnetic models consider magnetic material as a
composite of minute magnets (magnetic moments) and
analyzes the behavior of these magnetic moments.
Without Reed-Solomon error correction code
In conventional hard drives, in order to read data
without errors, an error correction code is attached
when data is recorded. The code, however, occupies
recording area, thus reducing user space. A new signal
processing technique, iterative decoding, which does not
require a Reed-Solomon error correction code, was
developed for the hard drive. This new technique
increases user space by approximately 4%, enabling a
further increase in storage capacity equivalent to an
HDD with a recording density of 635 Gb/in2.
Hitachi believes that HDDs are an indispensable storage
resource for digital home appliances and recording
equipment such as large-scale corporate or public
databases, PCs and HDD recorders. As the volume of
information worldwide continues to grow rapidly, even
greater HDD capacity will become necessary.