Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-05-31
2003-10-21
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120
Reexamination Certificate
active
06636395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnetic transducer, a thin film magnetic head using the same, and a method of manufacturing the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive element (hereinafter sometimes referred to as an MR element) that is a type of magnetic transducer and a recording head having an inductive magnetic transducer, is widely used as the thin film magnetic head.
MR elements include an AMR element using a magnetic film (an AMR film) exhibiting an anisotropic magnetoresistive effect (an AMR effect), a GMR element using a magnetic film (a GMR film) exhibiting a giant magnetoresistive effect (a GMR effect), and so on.
The reproducing head using the AMR element is called an AMR head or simply an MR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as the reproducing head whose surface recording density exceeds 1 gigabit per square inch, and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch. As the GMR film, a “multilayered type (antiferromagnetic type)” film, an “inductive ferromagnetic type” film, a “granular type” film, a “spin valve type” film and the like are proposed. Of these types of films, the spin valve type GMR film is considered to have a relatively simple structure, to exhibit a great change in resistance even under a low magnetic field and to be suitable for mass production.
FIG. 54
is a sectional side view of a general structure of a composite thin film magnetic head
800
(hereinafter simply referred to as a thin film magnetic head) using an MR element using a spin valve type GMR film (hereinafter referred to as a spin valve film). The thin film magnetic head
800
has a substrate
801
made of, for example, Al
2
O
3
. TiC (altic). A bottom shield layer
803
made of a magnetic material is stacked on the substrate
801
with an insulating layer
802
made of, for example, Al
2
O
3
(alumina) in between. A bottom shield gap layer
804
and a top shield gap layer
806
made of, for example, Al
2
O
3
or AlN (aluminum nitride) are stacked on the bottom shield layer
803
. A stack
805
, which is the above-mentioned spin valve film, is buried between the bottom shield gap layer
804
and the top shield gap layer
806
.
A top shield layer
807
(also serving as a bottom pole) made of a magnetic material is formed on the top shield gap layer
806
. A top pole layer
810
is located facing the top shield layer
807
with a write gap layer
808
made of, for example, Al
2
O
3
in between. Thin film coils
811
buried in an insulating layer
809
are formed between the top shield layer
807
and the top pole layer
810
. The bottom shield layer
803
, the bottom shield gap layer
804
, the stack
805
and the top shield gap layer
806
compose a reproducing head for reading out information from a magnetic recording medium. The top shield layer
807
, the write gap layer
808
, the insulating layer
809
, the top pole layer
810
and the thin film coils
811
compose a recording head for writing information on the magnetic recording medium. A surface indicated by reference symbol S in
FIG. 54
corresponds to a medium facing surface (an air bearing surface: ABS) of the thin film magnetic head
800
facing the magnetic recording medium such as a hard disk.
The structure of the stack
805
which is the spin valve film will be described with reference to
FIGS. 55 and 56
.
FIG. 55
is a cross sectional view of the stack
805
parallel to the medium facing surface S (i.e., a cross sectional view taken along the line LV—LV of FIG.
54
).
FIG. 56
is a cross sectional view of the stack
805
perpendicular to the medium facing surface S (i.e., an enlarged view of the stack
805
shown in FIG.
54
). The spin valve film is basically composed of a multilayered film having a stacked structure comprising four layers: an antiferromagnetic layer
851
made of, for example, PtMn (platinum-manganese alloy); a pinned layer
852
which is a magnetic layer made of, for example, Co (cobalt); a nonmagnetic metal layer
853
made of, for example, Cu (copper); and a free layer
854
made of, for example, NiFe (permalloy). When heat treatment takes place at, for example, 250 degrees centigrade in a state in which the pinned layer
852
and the antiferromagnetic layer
851
are stacked, the orientation of magnetization of the pinned layer
852
is fixed in, for example, the direction indicated by reference symbol Y in
FIG. 56
by an exchange anisotropic magnetic field generated by exchange coupling occurring on an interface between the antiferromagnetic layer
851
and the pinned layer
852
. Since the free layer
854
is separated from the antiferromagnetic layer
851
by the nonmagnetic metal layer
853
, the orientation of magnetization thereof is not fixed but changes in accordance with an external magnetic field.
Reproduction of information in the MR element using the above-mentioned spin valve film, i.e., detection of a signal magnetic field from the magnetic recording medium is performed in the following manner. First, a sense current, which is a constant direct current, is passed through the pinned layer
852
, the nonmagnetic metal layer
853
and the free layer
854
in, for example, the direction indicated by reference symbol X in FIG.
55
. On receiving the signal magnetic field from the magnetic recording medium, the orientation of magnetization of the free layer
854
changes. Electrical resistance changes in accordance with a relative angle between the orientation of magnetization of the free layer
854
and the (fixed) orientation of magnetization of the pinned layer
852
, and thus information is detected as a voltage change caused by a change in electrical resistance.
Generally, a distance between the medium facing surface S of the MR element and the opposite surface is called an MR height (MR-H). In the case of the MR element using the spin valve film, the MR height is determined in accordance with the distance between the medium facing surface S of the free layer and the opposite face. A read track width Tw of the MR element decreases as a recording density increases. Also, the MR height of the MR element tends to decrease as the read track width decreases. For example, the MR height is equal to 0.6 &mgr;m when the read track width of the MR element is equal to 1 &mgr;m, while the MR height is equal to 0.3 &mgr;m when the read track width of the MR element is equal to 0.5 &mgr;m.
As described above, a size reduction of the MR element advances. However, with the advance in the size reduction, the following problem arises due to heat generated in the MR element. That is, heat generated in the MR element is dissipated into the top and bottom shield layers (the shield layers
803
and
807
shown in
FIG. 54
) through the top and bottom shield gap layers. However, when the reproducing track width and the MR height of the MR element are reduced, a heat dissipation area of the MR element (i.e., the product of the reproducing track width and the MR height) is considerably reduced. Heat generation by the MR element incident to the reduction in the heat dissipation area becomes a factor that causes electro migration (a phenomenon in which a local void is created because of metal atoms migrating through a conductor) or interlayer diffusion. As a result, a problem exists: the longevity of the MR element decreases.
Japanese Patent Application Laid-open Nos. Hei 6-223331 and 10-222816 disclose a technique in which layers (a shield layer, an insulating layer, a substrate, etc.) around an MR element are made of a material having high thermal conductivity so that heat generated in the MR element is efficiently dissipated. However, when the
Davis David
Oliff & Berridge PLC.
TDK Corporation
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