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Main List | 
Recording Head/ Head Materials
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Magnetic recording heads are constructed
from a variety of materials; magnetic
alloys, metal conductors, ceramic
and polymer insulators in a complex
three dimensional structure with very
precise tolerances.
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Key
components of this structure are the reading
and writing elements that permit information
to be stored and retrieved from the rotating
hard disk. The Recording head Materials
group provides the latest materials for
read and write elements for development
of Hitachi recording heads for products
by the Storage Technology Division (STD).
In addition, these new materials are also
used by the Recording Head Process Technology
group for incorporation into even more advanced
head designs. The mission of this research
activity begins with advancements at the
leading edge of recording physics and materials
science. Subsequently the focus is on how
these new materials and magnetic phenomena
can be used or modified to meet specific
requirements of present and future recording
heads. |
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effort includes continuing research and
development of giant magnetoresistive (GMR)
spin valve head structures. The GMR effect
was discovered in 1988 at very low temperatures
and high magnetic fields in epitaxially
grown multilayer films. Through research
at the forefront of the physics of
magnetic materials, investigators in the
Hitachi Recording Head Materials group developed
the spin valve structure based on a new
understanding of the underlying physics
of the GMR effect. This spin valve structure
could be fabricated from materials that
are easily deposited by sputtering, a well
known manufacturing process, and could operate
at disk drive ambient temperatures. Most
importantly, spin valves respond to the
small magnetic fields arising from stored
information on the recording disk. The source
of the GMR effect is electrons that begin
their trajectories in one ferromagnetic
film, travel through a conducting spacer,
and are scattered in a second ferromagnetic
film. These electrons have trajectories
which are influenced by spin dependent scattering
within the films and interfaces of the multilayer
structure. The disk's magnetic field minimizes
this scattering in one of the films resulting
in a change in resistance and a bit of information
is sensed. Electrons traveling elsewhere
in the structure do not contribute to the
GMR effect but limit the GMR relative resistance
change to less than 25%. IBM has pioneered
the use of spin valve sensors, introducing
the first GMR heads in a disk drive product
in 1997, and has led the industry in replacing
the predecessor MR sensor technology. In
2000, nearly 90% of all recording heads
manufactured in the industry are estimated
to be GMR. |
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Users
of magnetic hard disk drives
require increasing capacity
and performance. Areal density
of disk drive products has
increased by a factor of over
7 million since the first
disk drive was made available
to a customer (IBM RAMAC,
1957). At present the rate
of areal density growth is
an astonishing 100% per year,
requiring continuous improvements
in all aspects of recording
head design and also the other
disk drive components. For
sensor materials this means
that the GMR signal must continually
increase with each new product
generation.
These increasing requirements
for disk drive improvements
provides a unending challenge
to extend GMR technology to
its limits, and then to look
beyond. A magnetic tunnel
junction device could be the
next read sensor technology.
In this structure electrons
pass from one ferromagnetic
film to the adjacent film
by quantum mechanical tunneling
through a very thin insulator
barrier. Similar to GMT structures,
the electrons that start their
trajectory in one ferromagnetic
film and are scattered in
the next film yield a magnetoresistance,
but in magnetic tunneling
structures all of the tunneling
electrons contribute to the
effect resulting in MR values
of > 30%.
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The
write element design in a recording
head also requires continuing
innovation to maintain efficient
writing at higher areal densities
and performances . Finer line
photolithography is required
for the pole tip width to achieve
a narrow track width, thinner
gap insulators to write increased
linear bit density. In addition,
an increased head inductance
could involve more turns of
copper coils in a smallergeometry.
Good writing performance is
achieved by increases in magnetic
write field even as the structure
itself is scaled to smaller
dimensions. This requires the
application of materials in
the pole structure with higher
4 M
magnetization, in fact magnetic
materials with a magnetization
larger than Fe could be required.
The Recording Head Materials
group has an ongoing program
to explore these high magnetization
pole materials and to address
high density recording and the
effects of these materials in
the design of advanced write
heads. Determining the limits
for increasing magnetization
is a fundamental charter for
this group. The writer and reader
elements of a head operate at
progressively frequencies as
data rate increases, based on
increasing linear density and
disk rotation speed. These frequencies
could approach a gigahertz or
greater resulting in the generation
of significant heat within head
which could adversely effect
the recording head and limit
its operation. An effort is
in place to understand thermal
effects in heads and to improve
thermal management of heat during
the recording process. This
includes three dimensional modeling
of complete head structures,
and investigating the use of
high thermal conductivity materials.
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Hitachi's
recording head technology has been a key factor
in achieving fast growth in areal density. This
is evident from the abrupt increase in the slope
of the areal density growth curve for lab demonstrations
of advanced heads at about 1997 or at 5 Gbits/in2.
This acceleration in areal density learning was
made possible through the introduction of GMR
spin valve sensors, advanced inductive writers,
high coercivity disks, improvements in head flyability
and better electronic detection. |
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To
create and develop the materials and
the designs for new heads, both required
to maintain this growth, is a significant
challenge to this group. A dedicated
and talented team is in place to meet
this challenge.
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