Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
1998-01-21
2001-08-14
Miller, Brian E. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Core
C360S123090
Reexamination Certificate
active
06275354
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to magnetic heads and in particular to low profile magnetic heads incorporating toroidal coils capable of transducing high areal density signals at high data transfer rates.
BACKGROUND OF THE INVENTION
Magnetic recording media in the form of tapes or disks have widely been used for data storage. Magnetic heads are commonly employed to perform the tasks of interacting with these recording media.
FIG. 1
shows a conventional magnetic head
2
comprising a flat inductive coil
4
sandwiched between a first yoke layer
6
and a second yoke layer
8
. The two magnetic yoke layers
6
and
8
contact each other at a back closure region
10
at one end to form a magnetic path
9
and define a narrow transducing gap
12
at another end. During data writing, electrical current representing information passes through a pair of electrical leads
11
and
13
and through the inductive coil
4
to induce magnetic flux along the magnetic path
9
. The induced magnetic flux reaches the narrow gap
12
and magnetizes a moving recording medium (not shown) disposed close by.
During data reading, magnetic flux emanating from a recorded medium (not shown) is intercepted by the narrow gap
12
. The intercepted magnetic flux flows along the continuous magnetic path
9
defined by the two yoke layers
6
and
8
and induces electrical current in the inductive coil
4
. The induced current in the coil
4
, which is directed through the electrical leads
11
and
13
, corresponds to the data stored on the recording medium.
As shown in
FIG. 1
, the inductive coil
4
of the head
2
is geometrically flat in topology. As is known in the art, when current passes though a structure, such as the coil
4
, induced magnetic flux is mostly generated at the central region adjacent to the axis
14
of the coil
4
. It is the back closure region
10
, with its relatively wide physical area and high permeability, that captures the induced magnetic flux for transmission to the gap
12
during data writing. The magnetic flux has to pass through a long magnetic path
9
which is defined by the second yoke layer
8
. This arrangement is undesirable in several aspects. First, the long magnetic path
9
contributes substantially to the reluctance of the magnetic head
2
and renders the head
2
less effective in flux transmission. To compensate for the inefficiency, the coil
4
is normally wound with a large number of turns. As a consequence, the inductance of the coil is further increased. A magnetic head with high inductance is sluggish in response to writing current during the data writing mode and incapable of reading media at a high rate during the data reading mode. Furthermore, the long magnetic path with the irregular geometrical topology is the main source of magnetic domain instabilities, which is especially enhanced at the back closure region
10
where a highly unstable domain pattern, commonly called the “spider web” pattern, resides. The constant merging and splitting of the unstable magnetic domains in the yoke layers
6
and
8
during operation significantly produces Barkhausen noise (also called popcorn noise) to the head
2
and accordingly lowers the signal-to-noise ratio (SNR) of the head. To compound the situation further, the coil
4
with the large number of windings is also high in ohmic resistance which is a key contributor to Johnson noise. As a consequence, the SNR is further degraded.
To solve the aforementioned problems, different kinds of magnetic heads have been suggested.
FIG. 2
illustrates a prior art magnetic head described in Cohen et al., “Toroidal Head Supports High Data Transfer Rates”, Data Storage, February 1997, pp 23-28.
FIG. 2
shows a magnetic head
16
that includes a toroidal coil
18
formed of two coil segments
18
A and
18
B. The first coil segment
18
A is connected in series to the second coil segment
18
B. Electrical leads
20
and
22
are connected to the first and second coil segments
18
A and
18
B, respectively. The first coil segment
18
A wraps around a first yoke layer
24
. In a similar manner, the second coil segment
18
B surrounds a second yoke layer
26
. The two yoke layers
24
and
26
contact each other at a back closure region
28
at one end, and define a narrow transducing gap
30
at another end. With this arrangement, a continuous magnetic path
36
with the transducing gap
30
is defined by the two yoke layers
24
and
26
.
During data writing, writing current I passes through the coil
18
via the electrical leads
20
and
22
. Magnetic flux is accordingly induced in the coil
18
. In a similar fashion as with the coil
4
shown in
FIG. 1
, the coil segments
18
A and
18
B, being spiral structures, generate magnetic flux around the areas adjacent to the coil axes
32
and
34
, respectively. The induced flux flows directly through the two yoke layers
24
and
26
without relying on the back closure region
28
for flux collecting. The head
16
is more efficient in controlling flux flow, and consequently has better performance.
Advantageous as it appears, the head
16
still requires the coil
18
to be wound with a large number of coil turns. Therefore, the head
16
has undesirable high inductance.
In Cohen et al., the authors are fully aware of the detrimental effects of the high coil inductance on head performance. In fact, Cohen et al. specifically state that the head inductance L is proportional to the square of the number of coil windings N, while the output signal generated by the head
16
only increases linearly with the number of coil windings N. The prior art head
16
is fabricated with a large number of coil turns N, required to effectively drive the two long yoke layers
24
and
26
which are high in magnetic reluctance. There are two coil segments
18
A and
18
B sandwiched between the two yoke layers
24
and
26
which exacerbate the curvature of the second yoke layer
26
. Consequently a longer second yoke layer
26
is required to define the magnetic path
36
. With a longer and more curved magnetic path
36
, more coil windings are needed to drive the yoke layers
24
and
26
in order to supply sufficient field strength from the narrow gap layer
30
. The overall effect is that the head
16
is burdened with a high inductance.
Data storage products are now built with smaller geometrical sizes and with higher storage capacities. To interact with these storage products having narrow track widths and high areal densities, a magnetic head needs to have low head inductance, thereby providing sufficient agility and responsiveness to the head during normal operation. Also, the head must provide a high SNR such that valid signals are not overshadowed by background noise. Furthermore, the head must be small in physical geometry and thus be compatible with miniaturized air bearing sliders which are designed to accommodate the rapid movements of the actuator arms of the disk drives. All of these features impose stringent requirements in the design and manufacturing of a magnetic head.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a magnetic head with a magnetic path which is efficient in flux flow enabling the head to perform with agility and sensitivity.
It is another object of the invention to provide a magnetic head with low inductance allowing the head to operate with high frequency signals.
It is yet another object of the invention to provide a magnetic head characterized by a high signal-to-noise ratio.
It is still another object of the invention to provide a magnetic head that is easy to fabricate and with low manufacturing cost.
In an embodiment of the invention, a magnetic head includes first and second magnetic yoke layers having a toroidal coil encompassing one of the yoke layers. The yoke layers contact each other at a back closure region at one end, and define a transducing gap at the other end. The axis of the toroidal coil is positioned to pass within the encompassed yoke layer. During the data writing mode, electrical current passin
Crue Billy Wayne
Huai Yiming
Shen Yong
Shi Zhupei
Kallman Nathan N.
Miller Brian E.
Read-Rite Corporation
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