Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2001-07-10
2004-09-28
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06798616
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to inductive write heads used in magnetic media storage devices, and more particularly to magneto-resistive disk drive heads.
BACKGROUND ART
A computer disk drive stores-and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on the surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” into which the read/write sensors are imbedded during fabrication. The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads have become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
In a magneto-resistive (MR) sensor changes in the strength and orientation of magnetic fluxes are sensed as changes in electric resistance, as an MR read head encounters changes in magnetic data, as on a computer hard drive. In such an MR sensor, the read head operates based on the anisotropic magneto-resistance (AMR) effect in which the resistance of the read element varies in proportion to the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the sensor. This effect is relatively weak in magnitude, and consequently more attention has been paid in recent years to what is referred to as “spin valve (SV) effect” or “giant magneto-resistance (GMR) effect” because of its relatively large magnitude of effect.
In this type of MR sensor, the resistance of a layered magnetic sensor varies due to both spin-depending transfer of conduction electrons between magnetic layers (M1, M2) via a non-magnetic layer (N), and spin-depending scattering at the interfaces between the layers accompanying the transfer of conduction electrons. The in-plane resistance between the pair of ferromagnetic layers (M1, M2), separated by a non-magnetic layer (N), varies in proportion to the cosine of the angle between the magnetization in the two ferromagnetic layers.
In ferromagnetic materials, scattering of electrons depends on the spin on the carriers. Resistivity is proportional to the scattering of electrons. Electrons with A spins parallel to the magnetization direction experience very little scattering and hence provide a low-resistance path. If magnetization of one side of this triple layer (M2) is pinned and M1 is gradually rotated from a parallel to an anti-parallel direction, the resistance of the structure increases in proportion to the cosine of the angle of magnetizations of the two layers M1, and M2. The spin valve is sensitive at low fields because the ferromagnetic layers are uncoupled, therefore a small magnetic field from the magnetic media can rotate the magnetization in one layer relative to the other.
A constant current passes through the sensing region from one electrode terminal (not shown) to another electrode terminal. The total electric resistance of the spin valve changes in proportion to a cosine of an angle between the magnetization direction of the pinned magnetic layer (M2) and the magnetization direction of the free magnetic layer (M1). When the total electric resistance is changed, a voltage difference between the electrode terminals changes and is sensed as read information.
This type of head for writing data is generally configured with two poles separated by a gap layer of non-magnetic material. A typical prior art read/write head is shown in FIG.
4
. Layers are generally deposited upon one another and typically include a shield layer
54
, a dual gap layer
56
, which surround a Magneto-resistive sensor, called MR sensor
58
, a pole piece layer, which will be referred to as the bottom pole or P
1
60
, a non-magnetic gap layer
62
, a first insulation layer or I
1
64
, upon which the coils
38
lie, and a second insulation layer, usually referred to as I
2
66
, which is generally made from photo-resist material. The top pole
42
is next, and is also commonly referred to as P
2
. The bottom and top poles
60
,
42
each have bottom and top pole tips
72
,
74
respectively with pole write gap
76
between them. The Air Bearing Surface ABS
46
and the coating layer
48
are also shown, as well as a back gap
78
. The top and bottom poles
42
,
60
typically extend from the ABS
46
in a roughly parallel manner until the top pole
42
veers upward to accommodate the thickness of the coils
38
and insulation layers I
1
64
and I
2
66
. The bottom pole
60
may also include an extension portion called a pedestal
84
.
There are other features which are only apparent from a top or isometric view of the write head. As seen in
FIG. 3
, the top pole
42
has a main body portion
86
and a narrower portion, commonly referred to as a pole tip or nose
88
. The narrow dimension of the top and bottom poles
42
,
60
at the write gap
76
determine the track width and also serve to channel the magnetic flux to increase the flux density across the write gap
76
. The point at which the nose begins to widen is known as the flare line
90
. This is shown in prior art
FIGS. 5B
,
6
B and
8
A and B.
The write head is a complex shape in 3 dimensions which cannot be understood by only one view. As seen from the cross-sections
5
A and
6
A, axes are shown for the x and y directions as the z axis is normal to the plane of the paper in these views. In this view, the top pole P
2
42
has a flat portion covering the main portion of the coils
38
, which then begins to curve as the pole approaches the ABS
46
so that the distance between the top pole
42
and the bottom pole P
1
60
narrows. This curved contour portion
92
has a contour boundary
94
, at which point the top pole
42
typically includes a flat portion
96
as it approaches the top pole tip
74
(see FIG.
4
).
FIGS. 5A and B
and
6
A and B are corresponding cross-sectional and top plan views of two prior art write head architectures.
FIGS. 5B and 6B
are top plan views similar to
FIG. 3
of the top pole P
2
42
, and includes axes x and z, the y axis being normal to the plane of the page. As the top pole curved contour
92
curves in the x and y dimensions, the flare
90
widens in the x and z dimensions.
FIG. 8A
shows an isometric view of the prior art write head
42
with the three axes indicated for reference.
When the flare line
90
of the head lies within the contour boundary
94
, then a portion of the pole nose
88
is also curved, or to put it another way, the contour boundary
94
lies closer to the ABS
46
than the flare point
90
. Thus the flat portion
96
of the pole nose
88
is small, as seen in
FIG. 6B and 8A
and B, or practically non-existent as in FIG.
5
B.
There are several difficulties in manufacturing write heads such as the ones shown in
FIGS. 5A-B
,
6
A-B and
8
A and B. The performance of a write head in many ways is related to how close the flair position can be located to the air bearing surface. The closer it is, the more high performance media that can be written, and the smaller the track width that can be written. The problem in the manufacturing process is to control the structure and the position of the flare. It is much easier to control the fabrication of a structure when it is on a flat surface than it is on a curved surface. This process typically involves photo-lithography, and when light comes down onto a sloped surface, it tends to reflect and scatter out. In contrast, when light comes onto a flat surface, it has a tendency to reflect off the bottom and come back up rather than scattering out. This makes it easier to control the dimensions from a photo-lithography
He Qing
Seagle David J.
Wang Lien-Chang
Zhao Ming
Letscher George J.
Magee Christopher R
Stetina Brunda Garred & Brucker
Western Digital (Fremont) Inc.
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