Methods for initializing and/or resetting GMR heads by...

Details Methods for initializing and/or resetting GMR heads by... Methods for initializing and/or resetting GMR heads by...

1998-12-23

2001-08-14

Strecker, Gerard R. (Department: 2862)

Electricity: measuring and testing

Magnetic

Magnetic information storage element testing

C324S228000, C324S232000, C324S252000, C029S603080, C360S324000

Reexamination Certificate

active

06275028

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an apparatus and methods for maintaining or recovering the performance and the functions of a magnetic recording head utilizing a giant magnetoresistive (GMR) effect in the manufacturing process in which the head is used in a hard disk drive (HDD).
2. Description of Related Art
The magnetic recording head using the GMR effect (hereinafter referred to as GMR head) provides a sensitivity three times or more of that of the magnetic recording head using the ordinary magnetoresistance (MR) effect (AMR head hereinafter referred to as MR head). On the other hand, better sensitivity means more liability to damage by an external stimulus than the conventional MR head. For instance, GMR head is susceptible to the effect of a stimulus such as electrostatic discharge (hereinafter, referred to as ESD). The ESD means that, when two materials are put in contact with or separated from each other through abrasion, pressurization, or collision, static electricity is generated on both materials and remains on an insulating material or insulated conductor (charging), and the residual static electricity is instantly discharged when it is put in contact with a material. In addition, stimuli such as electrical overstress (hereinafter referred to as EOS) and thermal stress (or temperature stress) also have undesirable effects on the performance of GMR heads.
Accordingly, in the manufacturing process in which GMR heads are finally assembled into an HDD, maintaining the head performance by decreasing the possibility of undergoing such damages and recovering the function of GMR heads having experienced such damages become important.
Through the diagrammatical view of
FIG. 1
, each process level is defined. The “wafer level” (a) is a stage at which GMR elements (GMR heads) are formed into a multilayered structure at the stage of a wafer
10
. The multilayered structure is described later in FIG.
2
. The “row level” (b) is the stage at which GMR elements are taken out from the wafer into a strip
12
to form a row. In these levels (a) and (b), GMR heads may get exposed to an external stimulus through a step such as cutting, washing, lapping, or polishing. Although, in the FIG.
1
(
a
) a diagrammatical expression is given so that one rectangle corresponds to one of the GMR elements, it is possible to actually extract many more GMR elements than those shown in this diagrammatical view. The “HGA level” (c) is a head gimbal assembly (HGA) level, and more particularly a stage at which a GMR element is attached to the end face of a slider
14
, which is mounted on a suspension assembly
16
for supporting the slider
14
. In fact, the size of the GMR element is much smaller as compared with the size of the slider (the end face of the slider). The “HSA level” (d) is a level at which a plurality of HGAs are collected into a stack
18
, and for a rotary actuator, they form an assembly rotatable on a pivot in unison. The “file level” (e) is a stage at which they are assembled into an HDD
20
and data writing and reading are allowed.
A class of GMR elements is known as spin valve (SV) magnetoresistance sensors as explained below. The SV magnetoresistance sensor is a sensor in which the electrical resistance between two uncoupled ferromagnetic layers varies as cosine of the angle between the magnetized directions of the two layers, independently of the direction of current. Thus, the SV sensor is different from the anisotropic magnetoresistance (AMR) in which electrical resistance varies as cos
2
(square of cosine) of the angle between the magnetized direction and the direction of current.
FIG. 2
is a perspective view showing the multilayered structure made up of the respective layers forming a spin valve (SV) sensor
30
. An underlayer or a buffer layer
33
is disposed on a substrate
31
as needed, and subsequently, a first thin-film layer
35
formed of a soft ferromagnetic material provided as a free layer is disposed on the buffer layer
33
. In the presence of an external magnetic field, the magnetization of the free layer
35
can freely rotate (the dotted arrows). If no external magnetic field exists, the magnetized direction matches the direction of the solid arrow
32
. A thin-film nonmagnetic metallic spacer layer
37
is subsequently disposed on the free layer
35
followed by disposing a second thin-film layer
39
of ferromagnetic material (pinned layer) on the spacer layer
37
followed by disposing a thin-film layer
41
made of anti-ferromagnetic material having a relatively high electrical resistance on the pinned layer
39
. There is an exchange coupling interaction between the pinned layer
39
and the anti-ferromagnetic layer
41
.
Ferromagnetic end regions
42
and
43
are formed adjacent to the end portions of the free layer
35
on the substrate
31
. In the present invention thin layers of permanent magnet are provided as substitutes for the ferromagnetic layers
42
and
43
. Layers
62
and
63
formed over layers
42
and
43
, respectively, are electrical leads used for allowing current to flow in the SV sensor
30
. The current for resetting the GMR head, which is described later, flows through the GMR head from the layer
62
to the layer
63
or from layer
63
to layer
62
. That is, in the direction of applying a current or a voltage pulse to the GMR element. The direction in which the current flows is decided in the design, but the current flows in the direction in which the magnetic field generated by the current helps the magnetization of the pinned layer. This direction is the longitudinal direction of the GMR element represented by a rectangle in FIG.
1
(
a
), the direction vertical to the longitudinal direction of the suspension assembly
16
in FIG.
1
(
c
), and the direction in which a current i flows in FIG.
5
.
Furthermore, it should be noted that the stacking sequence of the layers
35
,
37
,
39
, and
41
may be reversed to a stacking sequence of
41
,
39
,
37
, and
35
. The combination of the layers
35
,
37
, and
39
is necessary for achieving the function of the SV sensor, but there is a choice as to the stacking sequence to provide better characteristics. In the present invention, the stacking sequence which is opposite to the stacking sequence shown in
FIG. 2
is employed. The so-called air bearing surface of a magnetic recording disk is in the direction vertical to the direction of a signal field h. It is because the GMR element is attached to the surface corresponding to the end portion of the slider, as seen from FIG.
1
(
c
) and FIG.
10
.
The operation of orienting the polarity of the magnetized direction of the free layer by hard biasing by the use of an external magnetic field is called “initialization.” Directly affected by the initialization are the thin layers
42
and
43
of permanent magnets where the magnetization of the end regions
42
and
43
is preferably biased in the longitudinal direction. The magnetized direction of the free layer is maintained by the layers
42
and
43
. Note that the magnetization direction can be reversed by reversing the polarity of the external magnetic field (reversing the direction).
The GMR head needs to be magnetically and thermally stable, and in this respect, the stability of the exchange coupling between the ferromagnetic pinned layer
39
and the antiferromagnetic (AFM) thin-film layer
41
becomes a problem. In the manufacturing process in which the assembling is sequentially proceeded in the respective levels (a) to (e) of
FIG. 1
described above, the exchange coupling may be weakened or completely disconnected by the damage caused by an external stimulus, so that the originally required function of the GMR head cannot be maintained.
To recover the function of the GMR head, an operation called reset is effective. The “reset” is to adjust the magnetized direction of the pinned layer.
The reason why the magnetized direction of the pinned layer can be adjusted is that, if the GMR head is heated to a tempe

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