Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-09-16
2001-06-26
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06252749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin film magnetic heads mounted on, for example, hard disk drives. To be more specific, it relates to thin film magnetic heads composed of a gap layer formed over and/or under a magnetoresistive element layer, which gap layer comprises an improved material or structure so as to have an enhanced thermal conductivity.
2. Description of the Related Art
FIG. 16
is an enlarged sectional view of a conventional thin film magnetic head illustrated from an opposite side of a recording medium.
This thin film magnetic head is a reading head with the use of magnetoresistance effect, and mounted, for instance, on a trailing side edge of a constitutive slider of a floating type head. Onto the thin film magnetic head (reading head) shown in
FIG. 16
, a so-called inductive head for writing can be laminated.
The reference numeral
1
in
FIG. 16
indicates a lower shield layer composed of, for example, sendust or a Ni—Fe alloy (Permalloy; trade mark). Onto the lower shield layer
1
is formed a lower gap layer
20
composed of a non-magnetic material such as Al
2
O
3
(aluminium oxide), and onto the lower gap layer
20
, a magnetoresistive element layer
16
is formed.
The magnetoresistive element layer
16
can be classified into an anisotropic magnetoresistive (AMR) element using an element having magnetoresistance effect, and a giant magnetoresistive (GMR) element using an element having giant magnetoresistance effect. For providing higher recording density, a GMR element having a superior regeneration sensitivity is preferably employed. There are some species of structures which produce giant magnetoresistance effect, among which a structure called as a spin-valve type thin film element is comparatively simple and can change its resistance even in a weak magnetic field. The spin-valve type thin film element has the simplest structure composed of four layers, i.e., a free magnetic layer (a Ni—Fe alloy), a non-magnetic electrically conductive layer (Cu), a pinned magnetic layer (a Ni—Fe alloy) and an antiferromagnetic layer (e.g., an Fe—Mn alloy).
As illustrated in
FIG. 16
, hard bias layer
4
as longitudinal bias layer is formed on both sides of the magnetoresistive element layer
16
, and electrode layer
5
composed of a non-magnetic electrically conductive material having a small electric resistance such as Cu (copper) or W (tungsten) is formed on the hard bias layer
4
, respectively. When the magnetoresistive element layer
16
is composed of the aforementioned spin-valve type thin film element and a sensing current is applied to the electrode layers
5
, the sensing current is to flow in the pinned magnetic layer, non-magnetic electrically conductive layer and free magnetic layer of the spin-valve type thin film element.
Onto the electrode layer
5
an upper gap layer
21
composed of a non-magnetic material such as aluminium oxide is formed, and onto the upper gap layer
21
, an upper shield layer
7
composed of sendust or Permalloy is formed, as shown in FIG.
16
.
To enhance the regeneration sensitivity of the magnetoresistive element layer
16
for providing a high recording density, the density of a current from the electrode layer
5
should be increased. Increase of the current density, however, invites increase of heat generation from the magnetoresistive element layer
16
and hence elevation of the temperature of element of the magnetoresistive element layer. This is because the gap layers
20
and
21
formed under and over the magnetoresistive element layer
16
are each composed of an insulation film having a low thermal conductivity such as Al
2
O
3
.
By way of illustration, when the magnetoresistive element layer
16
is composed of a spin-valve type thin film element, elevation of the temperature of element of the magnetoresistive element layer
16
results in diffusion of nickel in the Ni—Fe alloy constituting the pinned magnetic layer and free magnetic layer, and of copper constituting the non-magnetic layer, which leads to collapse of multilayer structure of the element. The collapse of the multilayer structure in turn decreases a change rate of resistance and hence decreases the regeneration sensitivity. Not only in spin-valve type thin film elements but also in thin film magnetic heads using AMR effect, elevation of the temperature of element invites electromigration so as to impair the durability and to shorten the life time of the elements.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above problems. Accordingly, it is an object of the present invention to provide a thin film magnetic head composed of gap layers formed under and over a magnetoresistive element layer and having an improved material or structure and hence an enhanced thermal conductivity. In the thin film magnetic head, heat generated in the element can be escaped to an upper and lower shield layers and hence the current density can be increased and the regeneration sensitivity of the magnetoresistive element layer can be enhanced.
To be more specific, the present invention provides in one aspect a thin film magnetic head being composed of a lower shield layer, a lower gap layer formed on the lower shield layer, a magnetoresistive element layer formed on the lower gap layer, an electrode layer for giving a sensing current to the magnetoresistive element layer, an upper gap layer formed on the electrode layer, and an upper shield layer formed on the upper gap layer, wherein at least one of the lower gap layer and the upper gap layer is composed of an insulation film comprising at least one member selected from the group consisting of AlN, SiC, diamond-like carbon (DLC), BN, MgO, SiAlON, AlON, Si
3
N
4
, SiCO, SiN, SiON and SiCON.
Each of the above-mentioned insulation films has a higher thermal conductivity than Al
2
O
3
conventionally used as gap layers.
In the present invention, it is preferred that the insulation film has a film structure composed of, in toto, a crystalline phase. This is because such a crystalline phase in toto improves the thermal conductivity of insulation film.
The aforementioned insulation film can have a film structure composed of a crystalline phase mixed with a small amount of an amorphous phase. An excessive amount of amorphous phase, however, results in an excessively low thermal conductivity of the insulation film. Accordingly, the amorphous phase should be minimized in quantity.
The insulation film may be incorporated with non-magnetic metal grains. Since the non-magnetic metal grains have a higher thermal conductivity than the insulation film, incorporation of the non-magnetic metal grains into the insulation film provides a higher thermal conductivity.
The non-magnetic metal grains are preferably composed of at least one member selected from the group consisting of Cu, Ag, Au, Ti and Cr.
The non-magnetic metal grains may preferably have an average grain size of several nanometers or less. An excess average grain size increases the volume ratio of non-magnetic metal grains in the gap layers and decreases the volume ratio of the insulation film, and hence insulation properties are deteriorated or decayed.
Therefore, the average grain size of non-magnetic metal grains should advantageously be minimized.
Of the aforementioned insulation films, a film composed of AlN can advantageously be employed as the insulation film for its good crystallinity and high thermal conductivity.
In particular, when the insulation film is composed of AlN, it is preferable that a crystal face of a crystalline phase is preferred-oriented in the direction perpendicular to a plane of the film, for enhancing the thermal conductivity of the AlN film.
To be more specific, it is preferable that a (002) plane or a (220) plane of the crystalline phase is oriented in a direction perpendicular to a plane of the film.
The (002) plane of the crystalline phase is advantageously preferred-oriented in the direction perpendicular to the plane of the film. To be more specific, i
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Evans Jefferson
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