Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-08-24
2001-08-07
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06271998
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thin film shielded magnetic read head device, comprising an end face extending in a first direction, in which a magnetic information carrier is movable with respect to the magnetic head device, and in a second direction, perpendicular to said first direction, the magnetic head device further comprising shield forming flux guiding elements for magnetic cooperation with the information carrier, which elements extend in the second direction and in a third direction, perpendicular to the first and the second direction, and form a flux path in the first and the third direction, and a magnetoresistive element with a spin tunnel junction structure, one of said shields forming a common contact lead for the current through said magnetoresistive element.
Such a shielded magnetic read head device is known from EP-A-0 791 916. In the head device described in said document both shields are used as a contact lead for the current through the magnetoresistive element. Therefore, the known construction is limited to a single channel head device.
SUMMARY OF THE INVENTION
The object of the invention is to provide a shielded magnetic read head device, the construction of which is applicable in both single and multi-channel read head devices.
This object is achieved by the shielded magnetic read head device according to the invention, which is characterized by a number of magnetoresistive elements with a spin tunnel junction structure forming parallel flux paths in the first and the third direction, the number of magnetoresistive elements corresponding to the number of magnetic channels of the magnetic head device.
As in this construction only one of the shields can be used as a contact lead, the head device is further characterized in that a spin tunnel junction structure and the shields are separated from each other by at least metallic nonmagnetic layers, one of which forms a contact to one of the shields, while the other metallic nonmagnetic layer forms a further contact lead and is separated from the neighbouring shield by an insulating layer.
In a shielded read head construction, several embodiments of a spin tunnel junction structure are possible. However, in a more general structure each spin tunnel junction structure will comprise a first (F
1
) and a second (F
2
) metallic layer, each of said layers having at least one ferromagnetic layer, the first and second metallic layer being separated from each other by a barrier layer consisting of Al—O, Al—N, Hf—O or suchlike oxides or nitrides.
In the following a magnetoresistive element with a spin tunnel junction structure will be indicated as a STJ-MR element. The areal dimension of a STJ-MR element is determined by the joint area of the first and the second metallic layer (F
1
and F
2
).
These two metallic layers (F
1
and F
2
) may be patterned such that they have the same dimension in the second direction. Their maximum width is then determined by the track pitch.
In accordance with a first alternative, the second metallic layer is patterned to a smaller dimension in the second direction than the first metallic layer by applying an etching process that stops at or in the barrier layer. This makes it possible to independently optimize the magnetic and micromagnetic response of the first and the second metallic layer. For example, the first metallic layer can be patterned after a picture frame, whereas the smaller second metallic layer can be used to selectively sense which part of the first metallic layer yields the optimum between a large on-track response and a small off-track response. In the case of a multichannel head, the first metallic layer may form e.g. a single picture frame structure or a single long stripe structure, whereas the second metallic layer structures are present at distances equal to N x track pitch, i.e. the distance between tracks read out simultaneously (N=1, 2, etc.).
In accordance with a second alternative, the joint area between the first and second metallic layer is selected by locally thinning the metal forming the insulating barrier before oxidation or nitridation or by thinning the insulating barrier after oxidation or nitridation. Technically, this may be possible with the help of a focused ion beam (FIB) apparatus in the etch mode, used in situ during preparation of the junction in a UHV deposition apparatus. Use is made of the exponential dependence of the tunnelling resistance on the barrier thickness.
It has already been mentioned that a more general structure of the spin tunnel junctions, as specified above in a shielded read head construction enables several specific embodiments of a spin tunnel junction structure to be achieved.
In a first embodiment, the first metallic layer (F
1
) is soft magnetic, the magnetization thereof in the quiescent state being in the second direction, and the second metallic layer (F
2
) is provided with a ferromagnetic film whose magnetization direction is pinned in the third direction by contact with an antiferromagnet, a hard magnetic ferromagnet or ferrimagnet or an artificial antiferromagnet.
In a second embodiment, the first and second metallic layers (F
1
and F
2
) are both soft magnetic, the magnetizations in said layers in the quiescent state crossing each other as a result of a stray field from an exchanged biased soft magnetic film or a thin film permanent magnet, present close to the spin tunnel junction structure further away from the end face of the magnetic head device.
In a third embodiment, the first and second metallic layers (F
1
and F
2
) are ferromagnetic having a different magnetic easy direction structure and a magnetization whose vectors rotate in opposite directions when a magnetic flux is offered to the read head device.
In a fourth embodiment, the first metallic layer (F
1
) has a multilayer structure consisting of two soft magnetic layers, separated by a metallic nonmagnetic layer, the magnetization of these soft magnetic layers in the quiescent state being antiparallel in the second direction, while the second metallic layer (F
2
) comprises a ferromagnetic film whose magnetization direction is pinned in the third direction by contact with an antiferromagnet, a hard magnetic ferromagnet or ferrimagnet or an artificial antiferromagnet.
The invention not only relates to a thin film shielded magnetic read head device as indicated above, but also to a system for reading information from a magnetic information carrier comprising such a thin film shielded magnetic read head device.
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patent: 5729410 (1998-03-01), Fontana, Jr. et al.
patent: 5986858 (1999-11-01), Sato et al.
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patent: 0791916A2 (1997-08-01), None
patent: WO 9837550 (1998-08-01), None
Adelerhof Derk J.
Coehoorn Reinder
Kools Jacques C. S.
Altman Franklin D.
Gathman Laurie E.
Ometz David L.
U.S. Philips Corporation
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