CPP Magnetoresistive device with reduced edge effect and...

Details CPP Magnetoresistive device with reduced edge effect and... CPP Magnetoresistive device with reduced edge effect and...

1998-11-09

2001-03-06

Miller, Brian E. (Department: 2754)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

C360S319000, C360S320000

Reexamination Certificate

active

06198609

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to magnetic disk drives, more particularly to magnetoresistive (MR) read heads, and most particularly to methods and structures for current-perpendicular-to-plane (CPP) operation of submicron GMR heads.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In
FIGS. 1A and 1B
, a magnetic disk drive
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 SI 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 to the arm
20
, and at its other end to a read/write head or transducer
24
. The transducer
24
typically includes an inductive write element with a sensor read element (shown in FIG.
1
C). 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 of the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
. Various magnetic “tracks” of information can be 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 drives is well known to those skilled in the art
FIG. 1C
depicts a magnetic read/write head
30
including a read element
32
and a write element
34
. The edges of the read element
32
and write element
34
also define an air bearing surface ABS, in a plane
33
, which faces the surface of the magnetic disk
16
.
Read element
32
includes a first shield
36
, a second shield
38
, and a read sensor
40
that is located between the first shield
36
and the second shield
38
. One type of read sensor
40
is a magnetoresistive (MR) sensor which can be a variety of types, such as anisotropic magnetoresistive (AMR), spin valve, and giant magneto-resistive (GMR). The particular read sensor
40
shown is a multilayer GMR, formed of successive layer pairs
42
of various materials. Such an MR device typically can be formed by depositing the layer pairs
42
one upon the next to form a multilayer wafer (not shown). The material of each layer and the ordering of layers are appropriately selected to achieve a desired read performance. Multiple portions of the wafer are then removed to provide multiple read sensors
40
.
Write element
34
of
FIG. 1C
is typically an inductive write element and includes a first yoke element
44
and the second shield
38
, which forms a second yoke element, defining a write gap
46
therebetween. The first yoke element
44
and second yoke element
38
are configured and arranged relative to each other such that the write gap
46
has a particular throat height, TH. Also included in write element
34
, is a conductive coil
48
that is positioned within a dielectric medium
50
. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk
16
.
The operation of the read element
32
can be better understood with reference to the cross-sectional view of read element
32
in
FIG. 1D. A
sense current I is caused to flow
15
through the read sensor
40
. While in
FIG. 1D
the sense current is shown injected through the shields (which act as leads), in other configurations the read sensor electrically isolated from the shields, with additional leads injecting the sense current I. Specifically,
FIG. 1D
depicts a four-point configuration, where a lead lies between each shield and the read sensor. In such a configuration, the sense current I passes through the first shield
36
, through a first sense lead
37
, then through the read sensor
40
to a second sense lead
39
and to the second shield
38
. As the sense current I passes through, the read sensor exhibits a resistive response, resulting in an output voltage that can be quantified by measuring the voltage drop across the two sense leads
37
,
39
. The higher the output voltage, the greater the precision and sensitivity of the read sensor in sensing magnetic fields from the magnetic medium
16
.
The output voltage is affected by various characteristics of the read element
32
. For example, the greater the component of a sense current that flows perpendicular to the read sensor layers, as indicated by the vector CPP, the greater the output voltage. This component of sense current is the current-perpendicular-to-plane, CPP, component. For example, the sense current I of
FIG. 1D
is CPP. On the other hand, the component of a sense current that flows along (or parallel to) the read sensor layers
42
is the current-in-plane, CIP, component. Such current would occur in the read sensor
40
of
FIG. 1D
perpendicular to the sense current I either parallel to, as indicated by the vector CIP, or through the plane of the view.
In the configuration of
FIG. 1D
, the first and second shields
36
,
38
are conductive and are in electrical contact with the read sensor
40
. Here, the sense current I of the read sensor
40
flows, for example, from the first shield
36
to the second shield
38
through the read sensor
40
. As the sense current I flows through the read sensor
40
, the current flows substantially perpendicularly to the orientation of the layers
42
of the read sensor
40
. Thus, substantially all of the sense current I is CPP, i.e., the read sensor
40
operates in CPP mode. Other read sensors may be designed to operate with varying CPP and CIP components of the sense current. However, it is desirable to maximize the CPP component to maximize the output voltage of the read sensor. The design and manufacture of such magnetoresistive heads, such as read sensor
40
, are well known to those skilled in the art.
Although current GMR read sensors such as read sensor
40
have been used in the past, their performance is limited. In particular, various aspects of the read sensor fabrication can result in undesirable edge circuit paths between edges E of the read sensor layers. For example, as is shown in
FIG. 1E
, if etching is performed on multiple layers in the same operation, there can be redeposition
43
of the etched material of one layer upon the etched edge of another layer. Also, during lapping of the read sensor to form the air bearing surface ABS, or during a cutting operation to remove a single read sensor from a wafer, material can be smeared from one layer to another layer. In addition, when the read sensor layers are exposed to high temperatures diffusion might occur between the layers. When particular redeposition, smearing, or diffusion occurs between conductive layers, circuit paths can be formed between those layers at their edges E. Additionally, while such circuit paths can be formed between layers of a variety of types of read sensors, the problem can be more extensive or more likely in read sensors which have layers of smaller thicknesses, for example GMR sensors.
When such circuit paths are formed, the sense current I can be disrupted, as is illustrated by the charge flow lines
44
of FIG.
1
E. The charge, illustrated by charge flow lines
44
a
, that flows through the sensor in a region away from the edges E, the edge-free sensor portion
46
, is substantially unaffected by the edge circuit paths and is primarily in CPP mode. However, the charge, illustrated by charge flow lines
44
b
and
44
c
, that flows through the sensor in a region nearer to the edges E, the edge sensor portion
48
, can be shunted away from a direct path between the first shield
36
and the second shield
38
. Such shunting reduces the sensitivity of the device because current is directed away from and around the multilayer. The shunted portion of the current does not typically exhibit any MR or GMR effect because an edge circuit path is typically an unstructured mixture of materials that have been re-sputtered or re-deposited f

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