GMR read sensors with non-uniform height

Details GMR read sensors with non-uniform height GMR read sensors with non-uniform height

2000-04-25

2002-08-13

Evans, Jefferson (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

C360S324120

Reexamination Certificate

active

06433973

ABSTRACT:

BACKGROUND
Magnetic sensors utilizing the GMR effect, frequently referred to as “spin valve” sensors, are known in the art. A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-magnetic layer. One of the ferromagnetic layers is called the “pinned layer” because it is magnetically pinned or oriented in a fixed and unchanging direction by either an adjacent anti-ferromagnetic layer or some other mechanism, commonly referred to as the “pinning layer,” through anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the “free” or “unpinned” layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields.
FIG. 1
shows the conventional design structures for a horizontal GMR head sensor
100
. The Cu layer
102
is sandwiched between the pinning layer
101
and the free layer
103
, with the air bearing surface (ABS)
104
on the bottom of FIG.
1
. The ABS is the surface closest to the magnetic medium. The height of the layers, D, is uniform across the track direction in this case. In order to obtain optimized performance, the conventional GMR read head design requires that the height, D, of the GMR sandwich element be less than or equal to the decay length, L, of the magnetic flux captured from the magnet recording media. As shown in
FIG. 2
, L can be expressed as: L=(Tg&mgr;/2)
½
, where T is the total thickness of magnetic layers, &mgr; is the permeability of those magnetic layers, and g is half gap distance as shown in FIG.
2
. In this situation, the overall change in resistance of a GMR element is subject to a non-uniform field or flux from the media. More precisely, the magnetic flux must become zero at the lower end of the GMR strip. The situation is analogous to that of an open-circuited electric transmission line. If GMR heads are shielded and the optimum condition of D<L is satisfied, the maximum average flux in the GMR element is close to 0.5&PHgr;(0) regardless of the actual height, D, since the width of electric current path, H, is approximately equal to the height, D
max
, of GMR element as long as the height is uniform (i.e., D
min
=D
max
).
SUMMARY
In spin valve sensors, improved performance is measured by increased sensitivity, which is affected by the ability of the sensor to detect magnetoresistive changes in a magnetic medium. As a result, it is desirable to find ways to improve the sensitivity of spin valve sensors. Consequently, spin valve sensors that respond strongly in the presence of electromagnetic fields are desired.
In general, in one aspect, the invention features a magnetoresistive sensor. The sensor includes spin valve sensor layers, an air bearing surface perpendicular to a first edge region common to the spin valve sensor layers, and a non-planar surface perpendicular to a second edge region common to the spin valve sensor layers and opposite the air bearing surface.
In general, in another aspect, the invention features a method for producing a magnetoresistive sensor. This method includes forming spin valve sensor layers, wherein an air bearing surface including a plane perpendicular to a first edge region common to the spin valve sensor layers is formed, and a non-planar surface including a plane perpendicular to a second edge region common to the spin valve sensor layers and opposite the air bearing surface is formed.
Implementations may include one or more of the following features. The non-planar surface can include a substantially concave channel. The non-planar surface can include a substantially plateau region. The plurality of spin valve sensor layers can include a free magnetic layer, a first nonmagnetic layer, a first pinned magnetic layer, a second nonmagnetic layer and a second pinned magnetic layer. The height of the spin valve sensor stack can be less than 0.5 &mgr;m. The air bearing surface can be substantially parallel to a magnetically recorded surface. The non-planar surface can be formed within an electromagnetic active portion of the magnetoresistive sensor. The non-planar surface can be formed in the direction of a magnetic medium's motion.
Implementations may include one or more of the following advantages. The edge pinning effect on magnetic moment rotation in normal GMR sensor may be lessened so that the GMR sensitivity could be further enhanced. Furthermore, the actual thermal energy density generated by the sense current can be smaller than the GMR element with the same width of current path but uniform height. This type of structure design could drastically increase the sensor repeatability.
A 20-30% possible net increase of GMR element sensitivity could be expected with the use of the non-uniform height, compared with the output signal of the present GMR read heads. Furthermore, GMR elements with non-uniform height could exhibit a higher dM/dH ratio. This results in higher sensitivity than the GMR element with the same width of current path but uniform height.


REFERENCES:
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patent: 6046891 (2000-04-01), Yoda et al.
patent: 6108176 (2000-08-01), Yokoyama
A. V. Pohm, R. S. Beech, J. M. Anderson, and W. C. Black, IEEE Trans. Magn. 33, p. 2392 (1997).
A.V. Pohm, J.M. Anderson, R.S. Beech, and J.M. Daughton, IEEE Trans. Magn. 34, p. 1486 (1998).
J.M. Anderson and A.V. Pohm, J. Appl. Phys. vol. 85(8), p. 5321 (1999).
Youfeng Zheng and Jian-Gang Zhu, J. Appl. Phys. vol. 81(8), p. 5471 (1997).

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