Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-08-30
2002-12-10
Nguyen, Hoa T. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S320000
Reexamination Certificate
active
06493195
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistance element whose electrical resistance changes depending on the magnetic field, a manufacturing method of the magnetoresistance element, a magnetic field detection system employing the magnetoresistance element, and a magnetic recording system employing the magnetic field detection system.
DESCRIPTION OF THE PRIOR ART
Magnetoresistance elements or miagnetoresistance sensors have been used for heads of HDDs (Hard Disk Drives) of computers, and the magnetoresistance element realizes readout of information which has been stored in a high-density record medium. The magnetoresistance element (magnetoresistance head) changes its electrical resistance depending on the intensity and direction of the magnetic field around it. Therefore, if a constant voltage is applied to the magnetoresistance head, current passing through the magnetoresistance head changes as the magnetic field changes (as the position of the magnetoresistance head in relation to the record medium changes), thereby the information which has been stored in the record medium can be read out as a current signal.
Concretely, the magnetoresistance element basically behaves based on the AMR (Anisotropic MagnetoResistance) effect. In the case of the AMR effect, a component of an electrical resistance vector can be expressed as:
R=A
·cos
2
&thgr;
where &thgr; is the angle between the direction of magnetization of the magnetoresistance element and the direction of a sense current passing through the magnetoresistance element. With regard to the AMR effect, a detailed description has been given in a document: D. A. Thompson et al. “Memory, Storage and Related Applications”, IEEE Trans. on Mag. MAG-11, Page 1039 (1975).
In a magnetoresistance sensor employing the AMR effect, the so-called Barkhausen noise occurs. In order to reduce the Barkhausen noise, a longitudinal bias magnetic field is generally applied to the magnetoresistance sensor. The application of the longitudinal bias magnetic field is usually implemented by antiferromagnetic material such as FeMn, NiMn, Ni oxide, etc. Incidentally, the “FeMn” and “NiMn” are chemical symbols, and hereafter, such chemical symbols will be used for the sake of brevity of expression.
In recent years, new types of magnetoresistance effects which are called “giant magnetoresistance effect”, “spin valve effect”, etc. have been reported and have attracted considerable attention. Such effects, which are stronger than the conventional AMR effect, can be observed in an artificial lattice which is composed of ferromagnetic layers and non-magnetic conduction layers which are stacked alternately. The behavior of electrical resistance of such an artificial lattice has been explained from the viewpoint of spin-dependent transfer of conduction electrons between the ferromagnetic layers through the non-magnetic conduction layers, or spin-dependent scattering of the conduction electrons at the interfaces between the layers. In a magnetoresistance sensor composed of such an artificial lattice, an in-plane resistance of a pair of ferromagnetic layers separated by a non-magnetic conduction layer changes as:
R=B
·cos&phgr;
where &phgr; is the angle between magnetization directions of the two ferromagnetic layers. The magnetoresistance sensor employing the giant magnetoresistance effect of such an artificial lattice is more highly sensitive (larger &Dgr;R) than the magnetoresistance sensors employing the AMR effect.
In Japanese Patent Application Laid-Open No.HEI2-61572 (Japanese Gazette Containing the Patent No.2651015), a layered magnetic structure which exhibits a large magnetoresistance effect due to anti-parallel magnetization directions between magnetic layers has been disclosed. The layered structure is composed of a first permalloy layer, a second permalloy layer, an interlayer between the two permalloy layers, and a pinning (fixing) layer below the second permalloy layer. The two permalloy layers having opposite magnetization directions are separated by the interlayer (5 nm Au layer, for example), and the magnetization of the second permalloy layer is pinned (fixed) by the pinning layer which is preferably implemented by an FeMn layer.
In Japanese Patent Application Laid-Open No.HEI4-358310 (Japanese Publication of Examined Patent Applications No.HEI8-21166) and Japanese Patent Application Laid-Open No.HEI6-203340 (Japanese Gazette Containing the Patent No.2725987), a layered magnetic structure named “spin valve” has been disclosed. The layered magnetic structure includes a first ferromagnetic layer (soft), a second ferromagnetic layer and a non-magnetic metal layer which separates the two ferromagnetic layers. The angle between the magnetization directions of the two ferromagnetic layers is 90 degrees when a magnetic field applied thereto is 0, and the in-plane electrical resistance of the non-coupled two ferromagnetic layers separated by the non-magnetic metal layer changes proportionally to the aforementioned “cos &phgr;” (where &phgr; is the angle between magnetization directions of the two ferromagnetic layers), independently of the direction of the sense current passing through the spin valve magnetoresistance sensor.
A magnetoresistance sensor employing a ferromagnetic tunnel junction has been disclosed in Japanese Patent Application Laid-Open No.HEI10-162327.
FIG. 1
is a vertical sectional view showing an example of a conventional magnetoresistance element which is employed as a magnetoresistance sensor. Referring to the magnetoresistance element
102
shown in
FIG. 1
, a lower gap layer
106
is formed on a lower shield layer
104
which is formed on an unshown substrate, and a lower electrode layer
108
is formed on the lower gap layer
106
. A magnetoresistance effect layer
110
is formed on the lower electrode layer
108
, and a upper electrode layer
112
is formed on the magnetoresistance effect layer
110
. The upper electrode layer
112
is composed of a first upper electrode layer
114
and a second upper electrode layer
116
. The first upper electrode layer
114
is formed directly on the magnetoresistance effect layer
110
so as to cover the magnetoresistance effect layer
110
, and the second upper is electrode layer
116
is formed on the first upper electrode layer
114
. An upper gap layer
113
is formed on the upper electrode layer
112
, and an upper shield layer
115
is formed on the upper gap layer
113
.
The surface
118
on the left-hand end of the structure shown in
FIG. 1
is the so-called ABS (Air Bearing Surface). When information stored in a magnetic recording medium is read out by the magnetoresistance element
102
, the magnetoresistance element
102
is positioned so that the ABS
118
will face the surface of the magnetic recording medium and a narrow gap will be formed between the ABS
118
and the surface.
In the manufacturing process of the magnetoresistance element
102
, the lower electrode layer
108
is generally formed by the following process (1) or (2).
(1) An electrode layer to be formed as the lower electrode layer
108
is deposited on the entire surface of the lower gap layer
106
, and a photoresist layer (pattern) is formed on the electrode layer. Subsequently, unnecessary part of the electrode layer is removed by means of milling so that the lower electrode layer
108
will be patterned to a predetermined shape. Thereafter, the photoresist layer remaining on the patterned lower electrode layer
108
is removed by use of a release agent.
(2) A photoresist layer for lift-off is formed on part of the surface of the lower gap layer
106
, and an electrode layer to be formed as the lower electrode layer
108
is deposited on the photoresist layer and the lower gap layer
106
. Thereafter, the photoresist layer is removed by use of a release agent (lift-off).
FIG. 2
is a vertical sectional view showing a stage in the above process (1) just after the step for patterning the lower electrode layer
108
. After the patterning step, the photoresist laye
Fukami Eizo
Hayashi Kazuhiko
Honjo Hiroaki
Ishiwata Nobuyuki
Kamijo Atsushi
NEC Corporation
Nguyen Hoa T.
Watko Julie Anne
Young & Thompson
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