GMR Read Head Design

1
GMR Read Head Design
Jun Wan Department of Physics and
Astronomy University of Delaware
2
Real Recording Density Growth in HDD
GMR is a key device for ultra-high-density
storage devices up to 100Gb/in2.
3
Introduction of GMR
GMR devices have a basic structure two
ferromagnetic metal films separated magnetically
by a nonmagnetic metallic film. The electric
resistance R of these structures depends on the
relative angle 2ø between the magnetizations of
both ferromagnetic films
RR ?R(1-cos2ø)/2
?RR -R
Ferromagnetic metal
Nonmagnetic metal
Ferromagnetic metal
4
Manufacturing GMR Head Elements
Head elements are produced using several
processes that include photolithography, vacuum
deposition and ion beam etching. Multiple layers
of metals and alloys are vacuum-deposited to
achieve high sensitivity to magnetic
perturbations.
5
GMR Read head Structure
The MR element in a shield gap is composed of a
spin-valve film (SV), with a cap layer(CL), and
under layer(UL) leads (L) and hard magnets(HM).
The easy axis of the FL makes a right angle
against that of PL. The direction of the signal
field is parallel to the easy axis of PL. and
and perpendicular to that of FL.
6
MR Elements
TH
Tw
L
L
HM
HM
UL
CL
SV
In the overlaid structure, the size of SV is
larger than Tw, which makes the process of SV
element easier and increase the active area of FL
in the Tw region.
Tw Track width TH MR height
A bias field HL is generated to the FL. The stray
field from the PL also produce HM to the FL. It
is necessary to balance the HL and HM to make the
bias field to be zero
7
Output of Spin Valve Heads
?VaI ?Rs (TW/TH) Ø /(MF tF) a is a
constant. TW and TH are track width and MR
height. Ø is the flux from the media. MF and tF
are the saturation magnetization and the
thickness of the FL of the spin valve film. The
ratio TW/TH is almost constant. Therefore higher
output is obtained when the spin valve has a
larger ?Rs and a smaller MF tF.
8
Spin Valves for GMR Read Heads
1. Single-spin-valve The magnetization
of one ferromagnetic layer is pinned exchange
coupling with an antiferromagnetic overlayer 2.
Pseudo-spin-valve The two ferromagnetic
films have different coercive forces. . 3.
SAF-spin-valve The PL and FL are made of
the synthetic antiferromagnetic layers (SAL),
which consist of two ferromagnetic films
separated by a conductive nonmagnetic layer.
9
Single-Spin-Valve
The FL is unusually composed of soft magnetic
materials so that can change the magnetic
direction with an application of a small magnetic
field. The NM layer is a separate layer to
eliminate the magnetic coupling between the FL
and PL and to realize free magnetic rotation in
the FL.The AF magnetically couples with the PL
across the interface and cause the exchange bias
effect on the PL.
Structure of single spin-valve film
The prototype of the single spin valve film is
Ni80Fe20/Cu/Ni80Fe20/Fe50Mn50. PtMn-based spin
valves show excellent thermal stability of he MR
properties owing to high TB gt 350oC and widely
used for read heads
10
Pseudo- Spin-Valve
The pseudo-spin-valve is composed of a hard
magnetic layer,HM, and a soft magnetic layer,SM,
magnetically separated with a nonmagnetic
layer,NM.with a small magnetic field that causes
magnetization reversal of SM, but not of HM.
However pseudo-spin-valve shows a irreversible MR
curve with the magnetic field. They can be used
for MRAM devices.
Structure of pseudo- spin-valve film
11
SAF Spin Valve
The free layer is composed of the first and the
second magnetic layer, FL1 and FL2,
antiferromagnetically coupled to each other
across the nonmagnetic layer and the pinned layer
is composed of antiferromagnetically coupled PL1
and PL2 across the nonmagnetic layer. SAF spin
valve can reduce MF without degrading the MR
ration, therefore higher output can be obtained.
FL1
Ru
SAF FL
FL2
Cu
Structure of SAF spin valve
PL2
Ru
SAF PL
PL1
AF
12
Challenges
The decrease in bit size with the development of
high-density recording makes the size of the MR
element smaller and smaller, resulting in an
increase of the current density of MR element,
which has a upper limit. Therefore we need new MR
element. TMR(tunneling magnetoresistance) and
CPP(current perpendicular to the plane) MR are
two candidates beyond 100Gb/in2.