Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-08-17
2003-12-16
Ometz, David L. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06665154
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the general field of magnetic recording disks with particular reference to read heads and leads that connect thereto.
BACKGROUND OF THE INVENTION
The present invention is concerned with the manufacture of the read element in a magnetic disk system. This is a thin slice of material, located between two magnetic shields, whose electrical resistivity changes on exposure to a magnetic field. Magneto-resistance can be significantly increased by means of a structure known as a spin valve (SV). The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The key elements of a spin valve structure are two magnetic layers separated by a non-magnetic layer. The thickness of the non-magnetic layer is chosen so that the magnetic layers are sufficiently far apart for exchange effects to be negligible but are close enough to be within the mean free path of conduction elections in the material. If the two magnetic layers are magnetized in opposite directions and a current is passed through them along the direction of magnetization, half the electrons in each layer will be subject to increased scattering while half will be unaffected (to a first approximation). Furthermore, only the unaffected electrons will have mean free paths long enough for them to have a high probability of crossing the non magnetic layer. Once these electrons have crossed the non-magnetic layer, they are immediately subject to increased scattering, thereby becoming unlikely to return to their original side, the overall result being a significant increase in the resistance of the entire structure.
In order to make use of the GMR effect, the direction of magnetization of one the layers must be permanently fixed, or pinned. Pinning is achieved by first magnetizing the layer (by depositing and/or annealing it in the presence of a magnetic field) and then permanently maintaining the magnetization by over coating with a layer of antiferromagnetic (AFM) material. The other layer, by contrast, is a “free layer” whose direction of magnetization can be readily changed by an external field (such as that associated with a bit at the surface of a magnetic disk). Structures in which the pinned layer is at the top are referred to as top spin valves.
An example of a top spin valve structure is show in
FIG. 1
where layer
11
is a dielectric layer (acting as a substrate), layer
15
is the free layer, layer
14
is the non-magnetic layer, layer
13
is the pinned layer, and layer
12
is the pinning layer. Together, these four layers make up GMR stack
18
.
FIG. 2
illustrates a bottom spin valve structure where, as can be seen, pinned layer
13
is at the bottom of the stack. Also seen in both
FIGS. 1 and 2
are conductive leads
16
which make a butt contact to the sidewalls of stack
18
. It should be noted that both
FIGS. 1 and 2
are highly schematic and do not depict the actual detailed physical structure of a real unit. Such items as seed layers, glue layers, and longitudinal bias layers, for example, are not shown in these diagrams.
As track widths in magnetic recordings grow ever smaller, it has been found that, among the narrow track width magnetic readers, lead overlaid spin valve heads have several advantages over butted contiguous junction designs of the type illustrated in
FIGS. 1 and 2
. These advantages include larger signal output and better head stability [1-2].
However, in any overlaid design there is always present at least one high resistance layer between the GMR layer and the conductive leads. In particular, both top and bottom spin valve designs always include high resistivity lead stabilization layers above and, particularly, below the lead material. This is illustrated in
FIG. 3
where conductive lead
116
(preferably gold, because of its low tendency to be subject to electro-migration, but other materials such as copper or ruthenium are also possible) has stabilization layers
31
and
32
at its top and bottom surfaces respectively. Tantalum is preferred for layers
31
and
32
.
In the case of a top spin valve design, in addition to layer
31
, the high resistivity antiferromagnetic layer
12
(see
FIG. 1
) also comes between the conductive lead and the active layers of the GMR stack. The presence of these intervening high resistance layers results in significant magnetic read width broadening which limits the effectiveness of this design for narrow track width applications.
The present invention provides a solution to this problem.
The two publications referenced above are:
[1] S. H. Liao, Cheng Horng, Ben Hu, Y. Zheng, Min Li, and Kochan Ju, 8 111 Joint MMM-Intermag Conf. Paper BB04, San Antonio, 2001.
[2] K. Nakamoto et al, J. Magn. Soc. Jpn., 21,261(1997).
A routine search of the prior art was also performed with the following patent references of interest being found:
In U.S. Pat. No. 6,208,492, Pinarbasi shows a top SV, but the lead is on an AFM. In U.S. Pat. No. 6,201,669, Kakihara discloses a SV with a lead on the GMR. Yuan et al. (U.S. Pat. No. 5,705,973), Barr et al. (U.S. Pat. No. 6,134,089), and Grill (U.S. Pat. No. 5,920,446) are all related patents.
SUMMARY OF THE INVENTION
It has been an object of at least one embodiment of the present invention to provide a GMR based magnetic read head.
Another object of at least one embodiment of the present invention has been that said read head have conductive leads of the overlaid type.
Still another object of at least one embodiment of the present invention has been to provide a process for the manufacture of said read head.
A further object of at least one embodiment of the present invention has been that said read head be largely free of read width broadening.
A still further object of at least one embodiment of the present invention has been that said read head have operating characteristics at least as good as comparable structures of the prior art.
These objects have been achieved by inserting a highly conductive channeling layer between the GMR stack and the conducting lead laminate. This arrangement ensures that, at the intersection between the leads and the GMR stack, virtually all the current moves out of the free layer. This means that the effective read width of the device is very close to the physical read width that is defined by the spacing between the two leads. A process for manufacturing the device is also described.
REFERENCES:
patent: 5705973 (1998-01-01), Yuan et al.
patent: 5883764 (1999-03-01), Pinarbasi
patent: 5920446 (1999-07-01), Gill
patent: 6040962 (2000-03-01), Kanazawa et al.
patent: 6134089 (2000-10-01), Barr et al.
patent: 6201669 (2001-03-01), Kakihara
patent: 6208492 (2001-03-01), Pinarbasi
patent: 6219207 (2001-04-01), Pinarbasi
patent: 6226158 (2001-05-01), Pinarbasi
patent: 6344953 (2002-02-01), Kautzky et al.
patent: 6359760 (2002-03-01), Kanno
patent: 6493194 (2002-12-01), Sakaguchi et al.
patent: 6507465 (2003-01-01), Nakamoto et al.
patent: 2000-99926 (2000-04-01), None
S.H. Liao et al., “A Study on the Extendability of Spin Valve Heads for High Density Recording,” 8 111 Joint MMM-Intermas Conf. Paper BB04, San Antonio, 2001.
K. Nakamoto et al., “Numerical Analysis of Spin-Valve Heads with Overlapping Leads,” J. Magn. Soc. Jpn., vol. 21, No. 4-2, p. 261-264, (1997).
Ju Kochan
Lee Rod
Zheng You Feng
Ackerman Stephen B.
Headway Technologies Inc.
Ometz David L.
Saile George O.
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