Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-08-26
2002-07-23
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S314000
Reexamination Certificate
active
06424508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head used in a magnetic disk device, a magnetic tape device and so forth, and more particularly, to a magnetic tunnel junction magnetoresistive head (MR head) having a high sensitivity.
2. Description of the Prior Art
A magnetic information recording device such as a magnetic disk device, a magnetic tape device and so forth has been always required to record information at a higher density. Since a higher recording density causes reduction of a reproduced signal of a magnetic head, it is essential to develop more practical magnetic head in order to improve a recording density.
Predominant one of current high-density magnetic recording magnetic heads is a so-called composite magnetic head corresponding to a composition of a read magnetic head and a write magnetic head. In order to improve a reproducing sensitivity, there has been used as a read head an MR head based on a magnetoresistive effect or a giant magnetoresistive (GMR) head based on a GMR effect which has a higher sensitivity.
The change rates of the electric resistance caused by the magnetoresistive (MR) and giant magnetoresistive (GMR) field used in a prior art magnetic head are about 2-3% and about 5-10%, respectively. The larger the change rate of the electric resistance is the higher the reproduced output of the magnetic head is. Therefore, there has been demanded a magnetoresistive material having a higher change rate of the electric resistance. As one of materials potentially providing a higher change rate of the electric resistance, there is a material having a tunnel junction magnetoresistive effect (which will be referred to as a tunnel junction MR, hereinafter).
The tunnel junction MR is a phenomenon in which an electric resistance in a tunnel junction between two stacked ferromagnetic layers with an insulated layer disposed therebetween varies with the angle formed by the magnetization directions of the respective ferromagnetic layers. That is, the tunnel junction MR material has the maximum electric resistance when the magnetization directions of the both layers are oriented parallel to each other but in opposite directions, and has the minimum electric resistance when the magnetization directions are oriented parallel to each other. Accordingly, if one of the magnetization directions of the ferromagnetic layers is pinned or fixed while the other is rotated according to an external magnetic field, the electric resistance of the tunnel junction MR material is correspondingly changed. This effect is highly similar to that of a GMR spin valve film. However, the current must be passed parallel to the ferromagnetic layers in the spin valve film, whereas the current must be passed through the tunnel junction (in a direction perpendicular to the junction) in the tunnel MR material. In the spin valve film, even when the current is passed through the ferromagnetic layers in a direction perpendicular to the interface therebetween, the electric resistance becomes very small and the change in the electric resistance becomes small, because the intermediate layer is electrically conductive. On the other hand, in the tunnel junction MR material, the change in the electric resistance is much larger than that of the spin valve film, because the intermediate layer is a thin insulated layer. In order to put the tunnel junction MR material in practical use, the electric resistance of the tunnel junction MR material should be small enough to have the order of 10 to 10
2
ohms. Since the tunnel junction resistance is abruptly increased when the thickness of the insulated layer provided between the magnetic layers increases, it is demanded in the tunnel junction MR material that the insulated layer is very thin and has a high insulating property. In the original tunnel junction MR material, the stable formation of its element was very difficult, because it was difficult to form the insulated layer. However, recent studies have found that a good insulated layer of aluminum oxide can be formed, so that there can be formed a tunnel junction MR film, which has the change rate of about 20% at room temperature, with a good reproducibility.
In JP-A-10-162327, a magnetoresistive head which uses a magnetic tunnel junction and linearly responds to a magnetic field from a magnetic medium is disclosed.
Hereinafter, in connection with aforementioned explanation, a ferromagnetic layer, which has the fixed magnetization direction, of ferromagnetic layers forming the tunnel junction of the tunnel junction MR is called “a magnetization pinned layer”, and the other having the freely rotatable magnetization direction is called “a magnetization free layer”.
In a prior art MR (GMR) head of a most general structure, current is passed from one of electrodes formed in an identical plane to the other electrode through an MR (GMR) layer. On the other hand, in a tunnel junction MR head, unlike the prior art MR or GMR head, current must be passed through the tunnel junction in a direction perpendicular thereto. To this end, one electrode must be disposed below the tunnel junction made up of the magnetization pinned layer, an insulated layer and the magnetization free layer to pass a detection current between one electrode and the other electrode connected to an upper part of the tunnel junction. It is also required to provide layers for applying a bias magnetic field, which directs the magnetization of the magnetization free layer uniformly in a desirable direction and is for linearly responding to a magnetic field from a medium, at both ends of the magnetization free layer. In this connection, however, these layers must be isolated from the electrodes, the magnetization pinned layer and the magnetization free layer. In this way, the tunnel junction MR head of the structure wherein any of the electrodes, the magnetization pinned layer and the magnetization free layer are not in the same plane, is largely different in structure from the prior art MR (GMR) head. Therefore it is difficult to manufacture the tunnel junction MR head with use of a process of manufacturing the prior art MR head.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a tunnel junction MR head of a structure similar to that of the prior art head, which can be easily manufactured with use of the manufacturing process of the prior art head.
A magnetic head is manufactured by machiningly cutting magnetic heads formed on a substrate into individual separate heads and by polishing a surface of each head opposed to a medium. In an ordinary MR head structure, a part of an MR layer is exposed to an air bearing surface and is mechanically cut and polished simultaneously with the substrate at the time of the machining and polishing. In the tunnel junction MR head, the thickness of an insulated layer between a magnetization free layer and a magnetization pinned layer is as very small as 20 angstroms or less. In this way, since two ferromagnetic layers are provided adjacent to each other via the thin insulated layer therebetween, the electrical short-circuiting takes place easily between the two ferromagnetic layers in the cutting or polishing step. This problem results from the structural fact that the two ferromagnetic layers arranged as spaced by a very small interval therebetween are both exposed to the air bearing surface.
A second object of the present invention is to provide a tunnel junction MR head which can prevent the electrical short-circuiting between such ferromagnetic layers and can have a high reliability.
In order to attain the first object of the present invention, first and second tunnel junctions are formed at both ends of a magnetization free layer. The word “the end of the magnetization free layer” as used herein means two regions of the magnetization free layer in a track direction separated by its central line and provided at both sides of the central line. The first tunnel junction is defined by one end of the magnetization free layer,
Ishii Izuru
Tadokoro Shigeru
Chen Tianjie
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Miller Brian E.
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