Tunneling magnetoresistive device

Details Tunneling magnetoresistive device Tunneling magnetoresistive device

2001-01-31

2003-12-02

Watko, Julie Anne (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06657829

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a tunneling magnetoresistive device mounted, for example, in magnetic reproduction apparatus such as hard disks or other magnetic detector devices. More particularly, the invention relates to a tunneling magnetoresistive device that is able to obtain a stable resistance variation rate and also to a method for manufacturing the same.
2. Description of the Related Art
It is known that a GMR (giant magnetoresistive) device exhibiting a giant magnetoresistive effect is used as a read-only head mounted such as in a hard disk device, and such a GMR device has high sensitivity.
Among GMR devices, there is known a spin valve film that is relatively simple in structure and is able to change in resistance by application of a weak external magnetic field. This spin valve film most simply has a four-layered structure.
FIG. 15
is a partial schematic view showing the structure of a spin valve film.
FIG. 15
is a front view as seen from a side opposite to a recording medium.
Reference numerals
1
and
3
indicated in
FIG. 15
are, respectively, ferromagnetic layers formed of an NiFe alloy, and a non-magnetic conductive layer
2
formed of Cu or the like is interposed between the ferromagnetic layers.
With this type of spin valve film, the ferromagnetic layer
1
is a layer called a free magnetic layer, and the ferromagnetic layer
3
is a fixed magnetic layer. Hereinafter, the ferromagnetic layer
1
is called free magnetic layer, and the ferromagnetic layer
3
is called fixed magnetic layer.
As shown in
FIG. 15
, an antiferromagnetic layer
4
formed of NiMn alloy is formed in contact with the fixed magnetic layer
3
, and when annealed in a magnetic field, an exchange anisotropic magnetic field takes place between the fixed magnetic layer
3
and the anti-ferromagnetic layer
4
, thereby causing the magnetization to be fixed along a height thereof (in a direction of Y in the figure).
On the other hand, the free magnetic layer
1
is influenced by a bias layer (not shown), so that its magnetization is uniformly arranged in a direction of track width (in a direction of X in the figure), thereby permitting the magnetization to be in the crossing relation between the fixed magnetic layer
3
and the free magnetic layer
1
.
As shown in
FIG. 15
, electrode layers
5
,
5
are provided at opposite sides along the direction of track width (in a direction of X in the figure) of the laminated film covering from the free magnetic layer
1
to the anti-ferromagnetic layer
4
, respectively. It will be noted that the conductive layers
5
,
5
are each formed of Cu (copper), W (tungsten), Cr (chromium) or the like.
With the spin valve film shown in
FIG. 15
, when the direction of magnetization of the free magnetic layer
1
varies by the influence of a leakage magnetic field from a recording medium such as of a hard disk, the electric resistance varies by the relation with respect to the fixed magnetization direction of the fixed magnetic layer
3
, the leakage magnetic current from the recording medium can be detected according to the variation in voltage based on the change of electric resistance. The resistance variation rate (MR ratio) of the spin valve film ranges from approximately several to tens and several of percent.
The recent tendency toward high recording density results in the increasing areal density of a hard disk device. With a GMR device that is now in the main current, there arises a problem as to whether or not a further higher recording density (particularly, of 40 Gbits/inch
2
or over) is enabled.
As a reproduction head substituted for the GMR device, attention has now been drawn to a tunneling magnetoresistive device. The resistance variation rate (i.e. a TMR ratio) of the tunneling resistive effect device arrives at several tens of percent, so that a very high reproduction output can be obtained in comparison with the GMR device.
FIG. 16
is a schematic view showing part of a structure of a conventional tunneling magnetoresistive device.
FIG. 16
is a front view as seen from a side opposite to a recording medium.
Reference numerals
1
and
3
indicated in
FIG. 16
are, respectively, a free magnetic layer and a fixed magnetic layer, like the spin valve film shown in
FIG. 15
, and an anti-ferromagnetic layer
4
is formed on and in contact with the fixed magnetic layer
3
.
The differences in structure from the spin valve film reside in that an insulating barrier layer
6
made, for example, of Al
2
O
3
(alumina) is formed between the free magnetic layer
1
and the fixed magnetic layer
3
and that the electrodes
5
,
5
are provided on opposite sides in a direction vertical (in a direction of Z in the figure) to the film face of a multi-layered film covering from the free magnetic layer
1
to the anti-ferromagnetic layer
4
.
With the tunneling magnetoresistive device, when a voltage is applied to the two ferromagnetic layers (i.e. the free magnetic layer
1
and the fixed magnetic layer
3
), an electric current (tunnel current) flows through the insulating barrier layer
6
by the tunneling effect.
Like the spin valve film, the tunneling magnetoresistive device is so arranged that the magnetization of the fixed magnetic layer
3
is fixed in the direction of Y in the figure and the magnetization of the free magnetic layer
1
is arranged in the direction of X in the figure, and the direction of the magnetization varies by the influence of an external magnetic field.
In case where the magnetizations of the fixed magnetic layer
3
and the free magnetic layer
1
are anti-parallel to each other, the tunnel current is most unlikely to pass, with a maximum resistance value. Where the magnetizations of the fixed magnetic layer
3
and the free magnetic layer
1
are parallel to each other, the tunnel current is most likely to pass, with the resistance being minimized.
When the magnetization of the free magnetic layer
1
varies by the influence of an external magnetic field, a varied electric resistance is taken as a variation in voltage, thus permitting a leakage magnetic field from a recording medium to be detected.
The resistance variation rate (TMR ratio, or &Dgr;R
TMR
) in the tunneling magnetoresistive device is represented by 2P
P
P
F
/(1−P
P
P
F
) wherein P
P
represents a spin polarizability (i.e. the difference in number of electrons between the upspin and the downspin is normalized on the basis of the total number of electrons and this spin polarizability is hereinafter referred to simply as polarizability), and P
F
represents a polarizability of the free magnetic layer. As will be seen from the above equation, the resistance variation rate is determined by the polarizabilities of the ferromagnetic layers. As the polarizabilities increase, the resistance variation rate increases theoretically.
The tunneling magnetoresistive device per se, which is composed of the insulating barrier layer
6
interposed between the two ferromagnetic layers
1
,
3
, was known far back in the past. One of the reasons why the tunneling magnetoresistive effective device has never been put to practical use is that it is necessary to form the insulating barrier layer
6
that is thin enough to cause electrons to be tunneled, and the formation of such a thin uniform insulating barrier layer
6
is very difficult. For instance, thickness of the above-mentioned insulating barrier layer
6
is at several tens of angstroms.
In order to make the insulating barrier layer
6
thin, it has been conventional to form the insulating barrier film
6
according to the following procedure.
More particularly, after formation of an electrode layer
6
and a free magnetic layer
1
in this order as viewed from below, metallic Al is formed as a film on the free magnetic layer
1
such as by sputtering. Next, the metallic Al is oxidized according to a pure oxygen natural oxidation method or an oxygen plasma method to provide Al
2
O
3
, thereby forming an insulating barrier layer
6
.
This procedure is advantag

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