Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-05-02
2002-08-13
Hudspeth, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06433968
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to magnetic disk data storage systems, and more particularly to a merged read/write head having a tapered pedestal portion and method for fabricating the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In
FIGS. 1A and 1B
, a magnetic disk data storage system
10
of the prior art includes a sealed enclosure
12
, a disk drive motor
14
, a magnetic disk
16
, supported for rotation by a drive spindle S
1
of motor
14
, an actuator
18
and an arm
20
attached to an actuator spindle S
2
of actuator
18
. A suspension
22
is coupled at one end of the arm
20
, and at its other end to a read/write head or transducer
24
. The transducer
24
(which will be described in greater detail with reference to
FIG. 2A
) typically includes an inductive write element with a sensor read element. As the motor
14
rotates the magnetic disk
16
, as indicated by the arrow R, an air bearing is formed under the transducer
24
causing it to lift slightly off the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
. Alternatively, some transducers, known as contact heads, ride on the disk surface. Various magnetic “tracks” of information can be written to and/or read from the magnetic disk
16
as the actuator
18
causes the transducer
24
to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A
depicts a merged magnetic read/write head
24
including a substrate
25
above which a read element
26
and a write element
28
are disposed. Edges of the read element
26
and write element
28
also define an air bearing surface ABS, in a plane
29
, which can be aligned to face the surface of the magnetic disk
16
(see FIGS.
1
A and
1
B). The read element
26
includes a first shield
30
, an intermediate layer
32
, which functions as a second shield, and a read sensor
34
that is located within a dielectric medium
35
between the first
30
shield
30
and the second shield
32
. The most common type of read sensor
34
used in the read/write head
24
is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic flux being sensed.
The write element
28
is typically an inductive write element which includes the intermediate layer
32
, which functions as a first pole, and a second pole
38
disposed above the first pole
32
. The first pole
32
and the second pole
38
are attached to each other by a backgap portion (not shown), these three elements collectively forming a yoke (not shown). The combination of a first pole tip portion
43
and a second pole tip portion
45
near the ABS is sometimes referred to as the yoke tip portion
46
. A write gap
36
is formed between the first and second poles
32
and
38
in the yoke tip portion
46
. The write gap
36
is filled with a non-magnetic, electrically insulating material that forms a write gap material layer
37
. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer
47
that lies below the second pole
38
and extends from the yoke tip portion
46
to the backgap portion.
Also included in write element
28
is a conductive coil
48
, formed of multiple winds
49
. The conductive coil
48
is shown positioned within the first insulation layer
47
. The first insulation layer
47
thereby electrically insulates the winds
49
from each other and from the second pole
38
.
An inductive write head such as that shown in
FIGS. 2A and 2B
operates by passing a writing current through the conductive coil layer
48
. Because of the magnetic properties of the yoke, a magnetic flux is induced in the first and second poles
32
and
38
by write currents passed through the coil layer
48
. The write gap
36
allows the magnetic flux to fringe out from the yoke tip portion
46
(thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS.
A critical parameter of a magnetic write element is a trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by the geometries in the yoke tip portion
46
(see
FIG. 2A
) at the ABS. These geometries can be better understood with reference to FIG.
2
B. As can be seen from this view, the first and second poles
32
and
38
can have different widths W
1
and W
2
respectively in the yoke tip portion
46
. In the shown configuration, the trackwidth of the write element
28
is defined by the width W
2
of the second pole tip portion
45
.
The fringing gap field of the write element can be further affected by the positioning of the zero throat level ZT and by the throat height TH, which is measured from the ABS to the zero throat level, as shown in FIG.
2
A. The zero throat level is defined as the position where the first pole tip portion
43
and a second pole tip portion
45
converge at the write gap
36
. In order to prevent flux leakage from the second pole
38
into the back portions of the first pole tip portion
43
, it is desirable to provide a zero throat level in a well defined plane which is parallel to the plane of the ABS. Thus, accurate definition of the trackwidth, zero throat level and throat height is critical during the fabrication of the write element.
In order to provide accurate definition to one edge of the zero throat level a pedestal
42
may be formed on top of a first pole
32
as shown in FIG.
2
C. The pedestal
42
is typically electroplated into photoresist cavities and provides for a structure having a well defined plane at the zero throat level which is parallel to the plane of the ABS.
The performance of the write element is further dependent upon the properties of the magnetic materials used in fabricating the poles of the write element. In order to achieve greater overwrite performance, magnetic materials having a high saturation magnetic flux density Bs are preferred. A common material employed in forming the poles is high Fe content (55 at % Fe) NiFe alloy having a Bs of about 16 kG. However, high Fe content NiFe alloy has a high magnetostriction constant &lgr;s (on the order of 10
−5
) which causes undesirable domain formation in the poles. It is known that the domain wall motion in the writer is directly related to an increase in false signals (popcorn noise) in the read element, especially when the motion occurs in the first pole, which also serves as a shield for the read element. Furthermore, domain walls formed in the pedestal are easily pinned at sharp comers and also easily activated thermally. Thermal activation of pinned domains induces magnetic domain wall motion in the shield
32
of the read element
26
. The magnetic domain wall motion in shield
32
generates magnetic flux which passes through the MR sensor
34
of the read element
26
and results in a false signal in the read element
26
which degrades the performance of the magnetic read/write head
24
.
Moreover, typical fabrication processes limit the formation of desirable pedestal features. An example of one such process is shown in the process diagram of FIG.
3
. The
30
process
54
includes an operation
56
of pattern plating the second shield/first pole (S
2
/P
1
). The second shield/first pole is typically formed from NiFe alloy to a thickness of 1.6 &mgr;m. In an operation
58
, a first pole (P
1
) pedestal formed of NiFe is pattern plated above the second shield/first pole. The as-plated pedestal thickness is 2 &mgr;m. In an operation
60
, a protective alumina layer is sputter deposited on the wafer to provide electrical insulation between the first shield and the MR interconnect.
In an ope
Feng Aiguo
Shi Zhupei
Castro Angel
Hudspeth David
Read-Rite Corporation
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