Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-03-26
2004-10-05
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06801413
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic sensor and a magnetic head. More particularly, the present invention relates to a magnetic sensor, of a CPP (current perpendicular to plane) type, for supplying a current in the direction perpendicular to the surface of a magnetic sensor layer. The magnetic sensor is used in a reproduction head, i.e., a read head, of a magnetic recording apparatus such as a hard disk drive (HDD). The magnetic sensor is characterized in that the resistivity (specific resistance) of a hard layer, of a hard magnetic material, acting as a magnetic domain control layer is controlled. The present invention also relates to a magnetic recording apparatus using the magnetic sensor of the present invention.
2. Description of the Related Art
As is well known, a magnetic sensor is principally used as a magnetic head of the HDD, i.e., a recording apparatus of a computer. Up to several years ago, the magnetic head for HDD had a sensing means, for a magnetic field, based on an induction current generated in a coil.
In recent years, however, the demand for a higher density and a higher speed has led to magnetic heads being provided with magnetic sensors capable of sensing a magnetic field by itself. The sensor is a magnetic sensor utilizing the magnetoresistive (MR) effect. Currently, there is a tendency to use a magnetic head utilizing the giant magnetoresistive (GMR) effect.
With the progress toward a higher recording density in the HDD as described above, the recording area per bit has been reduced and also the magnetic field generated has been reduced. In fact, the recording density of an HDD now available on the commercial market is about 10 to 20 Gbit/in
2
, and is increasing at a rate of doubling every year.
As it is necessary to respond to the above-described decreasing magnetic field range and to allow sensing of a very small change in the external magnetic field, at present, a magnetic head based on the spin valve GMR effect is widely used.
The magnetic sensor showing the spin valve GMR effect comprises a magnetic layer (pinned layer) with a fixed direction of magnetization and a magnetic layer (free layer) with a free direction of magnetization, and in the magnetic sensor, the electrical resistance can be changed by a variation in the angle between the directions of magnetization in these two magnetic layers. However, for this magnetic sensor, if a magnetic domain is contained in the free layer, it can generate Barkhausen noise, and therefore, to avoid the noise, the magnetic domain must be controlled. As a layer of a hard magnetic material (hard layer) is currently used as a magnetic domain control layer, an example of the magnetic sensor utilizing the spin valve GMR effect will be explained hereinafter with reference to
FIGS. 1A and 1B
.
FIG. 1A
is a sectional view schematically showing a prior art magnetic sensor (SV-CIP element) utilizing the spin valve GMR effect, and
FIG. 1B
is an enlarged view of the dashed circle (section
1
B) in FIG.
1
A.
First, a lower magnetic shield layer
63
of a NiFe alloy or the like is formed, through a base layer
62
of Al
2
O
3
or the like, on an Al
2
O
3
—TiC substrate
61
which is a body of a slider. A spin valve layer
65
is formed through a lower read gap layer
64
of Al
2
O
3
or the like, and after patterning to a predetermined shape, a hard layer
66
, made of a high coercive force layer of CoCrPt or the like, acting as a magnetic domain control layer, is formed on the two ends of the spin valve layer
65
. Then, a conductive layer of W/Ti/Ta multilayer or the like is deposited to form a read electrode
67
.
Next, an upper magnetic shield layer
69
of a NiFe alloy or the like is formed through an upper read gap layer
68
of Al
2
O
3
or the like, thereby completing a basic configuration of a read head utilizing a spin valve element.
In this instance, the spin valve layer
65
is formed by depositing a base layer (underlayer)
70
of Ta having a thickness of 5 nm, a free layer
71
of NiFe having a thickness of 4 nm, a free layer
72
of CoFe having a thickness of 2.5 nm, an intermediate layer
73
of Cu having a thickness of 2.5 nm, a pinned layer
74
of CoFe having a thickness of 2.5 nm, a antiferromagnetic layer
75
of PdPtMn having a thickness of 25 nm and a cap layer
76
of Ta having a thickness of 5 nm, in this order, by a sputtering process while applying a magnetic field of 80 [Oe], for example.
For example, the composition of NiFe is Ni
81
Fe
19
, that of CoFe is Co
90
Fe
10
, and that of PdPtMn is Pd
31
Pt
17
Mn
52
.
The illustrated magnetic sensor is of CIP (current in plane) type, in which, as shown by arrows, a current is supplied in parallel to the surface of the spin valve layer
65
, i.e. the surface of the magnetic sensor layer. As the hard layer
66
is arranged under the read electrode
67
, its resistivity has no substantial effect on the characteristic (GMR characteristic) of the magnetic sensor.
In the formation of the read gap layer, the thinnest material capable of providing an insulation such as Al
2
O
3
or SiO
2
formed by CVD or the like is currently used. However, the minimum thickness of these materials is about 20 nm. Thus, in view of the fact that if the bit length becomes shorter, the thickness of the read gap layer cannot be reduced any further, the only possibility is to reduce the thickness of the magnetic sensor layer itself. However, apparently, the reduction in the thickness of the magnetic sensor layer is also restricted.
To avoid the above problems while satisfying the recording density of an HDD of not less than 80 Gbit/in
2
, it is necessarily considered to use a spin valve element (SV-CPP element) or TMR (tunnel magnetoresistive) element based on a CPP (current perpendicular to plane) system in which a current is supplied in the direction (at least the direction containing a perpendicular component) perpendicular to the surface of the magnetic sensor layer, because these elements do not require a read gap layer.
An example of the prior art read head of CPP type will be explained hereinafter with reference to FIG.
2
.
FIG. 2
is a sectional view schematically showing the prior art SV-CPP element. As illustrated, a lower electrode
82
of NiFe capable of also acting as a lower magnetic shield layer and a spin valve layer
83
are formed on an Al
2
O
3
—TiC substrate
81
. The spin valve layer
83
is etched to a predetermined pattern, followed by the lift-off process. In the lift-off process, a hard layer
84
of CoCrPt or the like and an insulating layer
85
of Al
2
O
3
or the like are formed, on which an NiFe upper electrode
86
of NiFe capable of also acting as an upper magnetic shield layer is formed.
As described above, with the SV-CPP element, a read gap layer is not required. Further, as the upper and lower electrodes can also act as a magnetic shield layer, a whole thickness of the element can be reduced as compared with the SV-CIP element described above.
In this magnetic sensor of a CPP type, however, there is a problem that since the hard layer
84
is in direct contact with the spin valve layer
83
, the sense current can escape as shown by arrows in
FIG. 2
to the hard layer
84
, thereby causing a reduction in the GMR characteristic.
To prevent the reduction in the GMR characteristic, the following methods are conceived:
Method 1:
As shown in
FIG. 3
, an insulating layer
87
is inserted between the hard layer
84
and the spin valve layer
83
so that the hard layer
84
may not be in direct contact with the spin valve layer
83
.
Method 2:
As shown in
FIG. 4
, the hard layer
84
and the spin valve layer
83
are in direct contact with each other. The current supplied to the hard layer
84
, however, is reduced by applying the specific arrangement (overlay structure) of the upper electrode
86
of NiFe.
Method 3:
As shown in
FIG. 5
, a magnetic insulating material such as a ferrite is used as the hard layer
88
.
Among these three methods, the method 1 is not suitable b
Nagasaka Keiichi
Seyama Yoshihiko
Shimizu Yutaka
Tanaka Atsushi
Cao Allen
Fujitsu Limited
Greer Burns & Crain Ltd.
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