Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-07-09
2003-11-04
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06643104
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistive effect (MR) thin-film magnetic head that is applicable to a hard disk drive (HDD) apparatus and provided with a tunnel magnetoresistive effect (TMR) element or a current perpendicular to the plane giant magnetoresistive effect (CPP-GMR) element, in which a current flows in a direction perpendicular to surfaces of layers.
DESCRIPTION OF THE RELATED ART
Recently, in order to satisfy the demand for higher recording density in an HDD apparatus, higher sensitivity and larger output of a thin-film magnetic head are required. A TMR element and a CPP-GMR element meet these requirements and are beginning to receive attention. The TMR element, disclosed in Japanese patent publication No. 04103014A for example, utilizes a ferromagnetic tunnel effect and has a multi-layered structure including a lower ferromagnetic thin-film layer, a tunnel barrier layer and an upper ferromagnetic thin-film layer. The CPP-GMR element is one type of GMR element Of a multi-layered structure including a lower ferromagnetic thin-film layer, a nonmagnetic metal layer and an upper ferromagnetic thin-film layer. In the CPP-GMR element, however, a current flows in a direction perpendicular to the surfaces of laminated layers. Such CPP-GMR element is disclosed in, for example, W. P. Pratt, Jr. et al., “Perpendicular Giant Magnetoresistance of Ag/Co Multilayer,” PHYSICAL REVIEW LETTERS, Vol. 66, No. 23, pp.3060-3063, June 1991.
These elements not only offer MR ratios several times greater than that of a general GMR element such as CIP (Current-In-Plane)-GMR element in which a current flows along the surface of layers, but also implements narrow gaps between layers without difficulty. The terms “lower” in “lower ferromagnetic thin-film layer” and “upper” in “upper ferromagnetic thin-film layer” are selectively used depending on the position of the layer relative to the substrate. In general, a layer is “lower” if this layer is close to the substrate, and “upper” if the layer is away from the substrate.
FIG. 1
illustrates a CIP-GMR element with a conventional structure seen from an air bearing surface (ABS).
In the figure, reference numeral
10
denotes a lower shield layer,
11
denotes a lower shield gap layer made of an insulation material,
12
denotes a GMR multilayer consisting of a lower ferromagnetic thin-film layer (free layer)/a nonmagnetic metal layer/an upper ferromagnetic thin-film layer (pinned layer)/an anti-ferromagnetic thin-film layer,
13
denotes an upper shield gap layer formed of an insulation material,
14
denotes an upper shield layer,
15
denotes hard bias layers, and
16
denotes electrode layers, respectively.
A sense current flows in parallel to the surfaces of the layers of the GMR multilayer
12
. The GMR multilayer
12
are insulated from the lower shield layer
10
by the lower shield gap layer
11
, and from the upper shield layer
14
by the upper shield gap layer
13
.
In order to more narrow the gap of such CIP-GMR element, the lower and upper shield gap layers
11
and
13
require to be formed of a very thin insulating material with a very high dielectric strength. However, such an insulating material is difficult to make and has been the bottleneck for providing a CIP-GMR element used in a high density HDD apparatus.
FIG. 2
illustrates a TMR element or a CPP-GMR element with a conventional structure, seen from the ABS.
In the figure, reference numeral
20
denotes a lower shield layer also serving as an electrode,
21
denotes a lower gap layer made of a metal material, which also serves as an electrode,
22
denotes a TMR layer with a multi-layered structure consisting of a lower ferromagnetic thin-film layer (free layer)/a tunnel barrier layer/an upper ferromagnetic thin-film layer (pinned layer)/an anti-ferromagnetic thin-film layer, or CPP-GMR layer with a multi-layered structure consisting of a lower ferromagnetic thin-film layer (free layer)/a nonmagnetic metal layer/an upper ferromagnetic thin-film layer (pinned layer)/an anti-ferromagnetic thin-film layer,
23
denotes an upper gap layer made of a metal material, which also serves as an electrode,
24
denotes an upper shield layer also serving as an electrode,
25
denotes hard bias layers, and
26
denotes an insulation gap layer made of an insulating material, respectively. Reference numeral
22
a
denotes extended parts of the lower ferromagnetic thin-film layer (free layer) extending from the TMR multilayer or the CPP-GMR multilayer to the hard bias layers
25
along the surfaces of layers of the TMR multilayer or the CPP-GMR multilayer.
The TMR element or CPP-GMR element is electrically connected between the lower shield layer
20
and the upper shield layer
24
so that a sense current flows in a direction perpendicular to the surfaces of the layers. Therefore, a narrow gap can be implemented without inviting dielectric breakdown of the gap layer. As a result, the line recording density can be greatly improved.
The important features required for an HDD apparatus are not only high recording density but also high data transfer rate. The transfer rate greatly relies on the rotational speed of a magnetic disk as well as the frequency characteristics of a write head and a read head.
FIG. 3
shows an equivalent circuit of the CIP-GMR element, and
FIG. 4
shows an equivalent circuit of the TMR element or the CPP-GMR element.
As is apparent from
FIG. 3
, the CIP-GMR element has only an equivalent resistance R
GMR
of the GMR element across the output terminals and no other essential factor that may deteriorate its frequency characteristics. However, as shown in
FIG. 4
, the TMR element or the CPP-GMR element that utilizes the shield layers as the electrodes has not only an equivalent resistance R
TMR
of the TMR element or the CPP-GMR element across their output terminals but also a capacitance C
shield
between the shield layers and a capacitance C
TMR
of the TMR element or the CPP-GMR element itself across their output terminals. These resistance R
TMR
and capacitances C
TMR
and C
shield
form a low-pass filter causing serious deterioration of the frequency characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an MR thin-film magnetic head having a TMR element or a CPP-GMR element for example, whereby the frequency characteristics of the MR thin-film magnetic head can be greatly improved.
According to the present invention, an MR thin-film magnetic head includes a lower shield layer, an upper shield layer, a MR multilayer sandwiched between the lower shield layer and the upper shield layer, the MR multilayer being electrically connected with the lower shield layer and the upper shield layer, a current flowing through the MR multilayer in a direction perpendicular to surfaces of layers, and a lead conductor having one end electrically connected to the upper shield layer and the other end connected to a terminal electrode. The lead conductor is patterned such that an area of the lead conductor located above the lower shield layer becomes small.
Also, according to the present invention, an MR thin-film magnetic head includes a lower shield layer, a lower gap layer made of a nonmagnetic electrically conductive material and laminated on the lower shield layer, an MR multilayer in which a current flows in a direction perpendicular to surfaces of layers of the MR multilayer, the MR multilayer being formed on the lower gap layer, an upper gap layer made of a nonmagnetic electrically conductive material and formed on the MR multilayer, an insulation gap layer made of an insulation material and formed to surround the MR multilayer and the upper gap layer, an upper shield layer laminated on the upper gap layer and the insulation gap layer, a lead conductor having one end electrically connected to the lower shield layer, and a terminal electrode electrically connected the other end of the lead conductor. The lead conductor is patterned such that an area of the lead conductor located above the lowe
Beacham Christopher R
Burns Doane Swecker & Mathis L.L.P.
Letscher George J.
TDK Corporation
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