Hardware Reference
In-Depth Information
Thin-Film
Thin-film heads are manufactured much the same way as a semiconductor chip—through
aphotolithographicprocess.Thisprocesscreatesmanythousandsofheadsonasinglecir-
cular 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
wellprotected,minimizingthechanceofdamagefromcontactwiththespinningdisk.The
core is a combination of iron and nickel alloy that has two to four times more magnetic
power than a ferrite head core.
TFheadsproduceasharplydefinedmagneticpulsethatenablesthemtowriteatextremely
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 to-
gether, 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
previousinductive-onlyheads.IBMintroducedthefirstcommerciallyavailabledrivewith
MR heads in 1991, in a 1GB 3 1/2-inch model, and other manufacturers quickly followed
suit.
Allheadsaredetectors;thatis,theyaredesignedtodetectthefluxtransitionsinthemedia
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 mag-
netic domains on the disk get smaller, the signal from the heads during reading opera-
tionsbecomesweaker;distinguishingthetruesignalfromtherandomnoiseorstrayfields
present becomes difficult. A more efficient read head, which is a more efficient way to
detect these transitions on the disk, is therefore necessary.
