Hardware Reference
In-Depth Information
This magnetic alloy has twice the magnetization capability of raw ferrite and enables the head to
write to the higher coercivity thin-film media needed at higher densities. MIG heads also produce a
sharper gradient in the magnetic field for a better-defined magnetic pulse. Double-sided MIG heads
offer even higher coercivity capability than the single-sided designs.
Because of these increases in capabilities through improved designs, MIG heads were for a time the
most popular head design and were used in many hard disk drives in the late 1980s and early 1990s,
and most recently in LS-120 (SuperDisk) drives.
Thin-Film
Thin-film heads are manufactured much the same way as a semiconductor chip—through a
photolithographic process. This process creates many thousands of heads on a single circular wafer
and produces a small, high-quality product.
TF heads have an extremely narrow and controlled head gap that is created by sputtering a hard
aluminum material. Because this material completely encloses the gap, the area is well protected,
minimizing the chance of damage from contact with the spinning disk. The core is a combination of
iron and nickel alloy that has two to four times more magnetic power than a ferrite head core.
TF heads produce a sharply defined magnetic pulse that enables them to write at extremely high
densities. Because they do not have a conventional coil, TF heads are more immune to variations in
coil impedance. These small, lightweight heads can float at a much lower height than the ferrite and
MIG heads; in some designs, the floating height is 2 micro-inches or less. Because the reduced height
enables the heads to pick up and transmit a much stronger signal from the platters, the signal-to-noise
ratio increases and improves accuracy. At the high track and linear densities of some drives, a
standard ferrite head would not be capable of picking out the data signal from the background noise.
Another advantage of TF heads is that their small size enables the platters to be stacked closer
together, enabling more platters to fit into the same space.
Many of the drives in the 100MB-2GB range used TF heads, especially in the smaller form factors.
TF heads displaced MIG heads as the most popular head design, but they have now themselves been
displaced by newer magneto-resistive heads.
Magneto-Resistive Heads
Magneto-resistive heads, sometimes also referred to as the anisotropic magneto-resistant (AMR)
heads, are capable of increasing density four times or greater as compared to the previous inductive-
only heads. IBM introduced the first commercially available drive with MR heads in 1991, in a 1GB
3 1/2-inch model, and other manufacturers quickly followed suit.
All heads are detectors; that is, they are designed to detect the flux transitions in the media and
convert them back to electrical signals that can be interpreted as data. One problem with magnetic
recording is the ever-increasing desire for more and more density, which is putting more information
(flux transitions) in a smaller and smaller space. As the magnetic domains on the disk get smaller, the
signal from the heads during reading operations becomes weaker; distinguishing the true signal from
the random noise or stray fields present becomes difficult. A more efficient read head, which is a
more efficient way to detect these transitions on the disk, is therefore necessary.
Another magnetic effect that is well known today is being used in modern drives. When a wire is
passed through a magnetic field, not only does the wire generate a small current, but the resistance of
the wire also changes. Standard read heads use the head as a tiny generator, relying on the fact that the
