Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-01
2001-07-24
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324110, C360S327320
Reexamination Certificate
active
06266217
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a magnetic head having a head face and comprising a multilayer structure with a flux guide, a magnetoresistive sensor and an intermediate layer of an insulating oxide present between the flux guide and said sensor.
A magnetic head of this type is known from Funkschau 24/1988, pp. 37-40 “Mit Dünnschichtköpfen in neue Dimensionen” Mathias Krogmann. The known magnetic head has a head face for cooperation with a magnetic recording medium and is also provided with a magnetic yoke which comprises a magnetoresistive sensor and flux guides. The magnetic yoke adjoins the head face, while said sensor is spaced apart therefrom. The magnetoresistive sensor comprises a strip-shaped element of a magnetoresistive material. When the recording medium is being scanned, the magnetic yoke is in its immediate vicinity, or is in contact with, the recording medium moving with respect to the magnetic head. Information-representing magnetic fields of the recording medium then cause changes in the magnetization of the strip-shaped element and modulate its resistance due to the effect referred to as the magnetoresistive effect. This effect implies that, due to magnetic fields, the direction of magnetization in the magnetoresistive sensor rotates, at which the electrical resistance changes. These resistance changes may be measured by a suitable detection system and converted into an output signal which is a function of the information stored in the recording medium.
Since the change of the electrical resistance of a magnetoresistive element under the influence of an external magnetic field is quadratic in this field, it is common practice to improve the operation of the magnetic head by linearizing the resistance-magnetic field characteristic. To this end, the magnetoresistive element is biased in such a way that the direction of magnetization at a signal field which is equal to zero extends at an angle of approximately 45° to the direction of the sense current through the element. In the known magnetoresistive sensor, this is realized by using an easy axis of magnetization which is parallel or substantially parallel to the longitudinal axis of the magnetoresistive element, and by an electric biasing which is achieved by means of equipotential strips of satisfactorily conducting material on the element, which strips cause a current direction at an angle of approximately 45° to the longitudinal axis of the element. The known magnetic head further has a bias winding for generating a magnetic auxiliary field parallel to the plane of the strip-shaped element and perpendicular to the easy axis of magnetization. By means of the auxiliary field, fields which are due to the sense current and influence the angle between current and magnetization, and other disturbances of the optimum angle between current and magnetization can be compensated.
Starting from a ferrite substrate, the known magnetic head is built up in layers. During manufacture, the bias winding, the magnetoresistive element, the equipotential strips and the flux guides are formed successively, while SiO
2
layers are provided between the substrate and the bias winding, between the bias winding and the magnetoresistive element and between the magnetoresistive element and the flux guides. These layers are required to insulate various electrically conducting layers in order to inhibit short circuits.
The known magnetic head is necessarily composed of a relatively large number of layers. This has the drawback that the manufacture of the known magnetic head is cumbersome due to the large number of deposition and structuring steps to be performed, so that the manufacturing process is time consuming and costly.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a magnetic head of the type described in the opening paragraph, which can be manufactured in a limited number of process steps.
The magnetic head according to the invention is characterized in that the intermediate layer comprises an anti-ferromagnetic oxide.
The invention is based on the recognition that such an oxide, used between a flux guide and a magnetoresistive sensor, fulfils a double function, with the insulating properties of the anti-ferromagnetic oxide ensuring the required electrical separation between the flux guide and the magnetoresistive sensor, on the one hand, and generating the desired magnetic biasing of the sensor due to exchange coupling with the magnetoresistive material of the sensor, on the other hand.
The use of the intermediate layer of an anti-ferromagnetic oxide therefore reduces the number of layers required in a thin-film magnetoresistive head. It is to be noted that the anti-ferromagnetic layers hitherto used for exchange-biasing are metal layers such as FeMn, NiMn or Tb
0.25
Co
0.75
. Metals are electric conductors and therefore unsuitable for the above-mentioned application.
The intermediate layer extending between a flux guide and a sensor may be formed successfully by sputtering a suitable anti-ferromagnetic oxide such as NiO
1+&dgr;
, with &dgr;<0.05. If desired, the intermediate layer may be built up in layers in order to obtain an intermediate layer having a relatively high resistance. To this end, a suitable deposition process comprises two process steps, in which an anti-ferromagnetic oxide is deposited at a relatively high sputtering pressure, for example 15 mTorr, in one of the process steps, while the anti-ferromagnetic oxide is deposited at a relatively low sputtering pressure, particularly smaller than 3 mTorr, in the other process step.
The magnetic head according to the invention is applicable as a read head or as a read head unit in a read/write head and may be implemented with one or more magnetoresistive sensors. The magnetic head is suitable for video, data, audio or multimedia uses. Moreover, the magnetic head according to the invention is suitable as a magnetic field sensor in, for example, medical apparatus.
An embodiment of the magnetic head according to the invention is characterized in that the anti-ferromagnetic oxide is NiO
1±&dgr;
, with &dgr;<0.18, or Ni
x
Co
1−x
O
1±&dgr;
, with 0.5≦x<1 and &dgr;=0.18.
It has been found by experiment that an insulating separation layer of 0.15 &mgr;m is possible by means of said nickel oxide deposited by sputtering, which layer is considerably thinner than is feasible with the usual insulating oxides which are also deposited by means of sputtering. A thinner separation layer leads to a higher sensitivity of the magnetic head and thus to a larger output.
It is to be noted that exchange biasing is possible to a relatively high temperature, which is sufficiently high for normal uses, particularly 80° C. or more for the indicated nickel cobalt oxide with a cobalt fraction ≧0.5 and at a layer thickness of 5 nm minimum.
It is to be noted that the use of anti-ferromagnetic oxides, particularly NiO and Co
x
Ni
1−x
O for biasing magnetoresistive elements is known per se from Applied Physics Letters 60 (24), Jun. 15, 1992, pp. 3060-3062; “Exchange anisotropy in coupled films of Ni
81
Fe
19
with NiO and Co
x
Ni
1−x
O” (herein incorporated by reference). In this publication, NiO and Co
x
Ni
l−
O, which are corrosion-resistant as oxides, are presented as alternatives to the anti-ferromagnet FeMn which is very sensitive to corrosion.
An embodiment of the magnetic head according to the invention is characterized in that the intermediate layer is a multilayer. A suitable multilayer is composed of, for example, a layer of NiO
1±&dgr;
(&dgr;≦0.18) alternating with a layer of CoO
1±&egr;
(&egr;≦0.18). At short multilayer periods (&Lgr;≦4 nm), such a multilayer may give a stronger biasing at room temperature than a mixed oxide. In this connection, reference is made to Journal of Applied Physics 73 (10), May 15, 1993, pp. 6892, 6894; “CoO—NiO superlattices: Interlayer interactions and exchange anisotropy with Ni
81
Fe
19
” (herein incorporated by reference).
An emb
Ruigrok Jacobus J. M.
Van Der Zaag Pieter J.
Belk Michael E
Evans Jefferson
U.S. Philips Corporation
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