Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2000-02-04
2002-09-17
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C360S324100, C360S324200, C427S130000, C428S900000
Reexamination Certificate
active
06452385
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistive effect (MR) sensor utilizing a giant magnetoresistive effect (GMR) such as spin valve effect or a spin tunnel magnetoresistive effect (TMR), and to a manufacturing method of the MR sensor. Such MR sensor is used for various magneto-electronic detection devices, typically magnetic heads mounted in magnetic record and reproduction devices such as hard disk drive (HDD) units.
DESCRIPTION OF THE RELATED ART
Recently, thin-film magnetic heads with MR read sensors based on spin valve effect of GMR characteristics are proposed (U.S. Pat. Nos. 5,206,590 and 5,4212,571) in order to satisfy the requirement for ever increasing data storage densities in today's magnetic storage systems like hard disk drive units.
The spin valve effect structure includes first and second thin-film layers of a ferromagnetic material separated by a thin-film layer of nonmagnetic and electrically conductive material, and a layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide exchange bias magnetic field by exchange coupling at the interface of the layers. The magnetization direction in the second ferromagnetic layer is constrained or maintained by the exchange coupling, hereinafter the second layer is called “pinned layer”. On the other hand the magnetization direction of the first ferromagnetic layer is free to rotate in response to an externally applied magnetic field, hereinafter the first layer is called “free layer”. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magneto-resistance greatly changes and giant magneto-resistance characteristics are obtained.
The output characteristic of the spin valve MR (SVMR) sensor depends upon the angular difference of magnetization between the free and pinned layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field. That of the pinned layer is fixed to a specific direction (called as “pinned direction”) by the exchange coupling between this layer and adjacently formed anti-ferromagnetic layer.
During operation of the SVMR sensor, it is required that magnetization in the free layer changes under conditions with no wall motion. This is because the magnetization change accompanied by wall motion is irreversible change and responds slower than the magnetization change accompanied by no wall motion, and therefore causes noise component called Barkhausen noise to produce. Thus, in general, bias magnetic field (longitudinal bias) from hard magnets disposed at end edges of the free layer is applied to the free layer so as to suppress the wall motion.
However, if the SVMR sensor is used under high temperature environment, change in the magnetization or pinned direction in the pinned layer and/or change in the magnetic characteristics of the free layer itself may occur due to the longitudinal bias applied to the sensor causing degradation of the sensor output to provide. Therefore, it is necessary to hold down the intensity of the longitudinal bias to the value of necessary minimum.
U.S. Pat. No. 5,528,440 discloses a method for stabilizing the magnetic domain of a free layer of a SVMR sensor by applying longitudinal bias from an additional anti-ferromagnetic material layer and an additional ferromagnetic material layer disposed at end edges of the free layer, to suppress wall motion during operation of the SVMR sensor. According to this method, since the longitudinal bias is produced by exchange coupling between the additional anti-ferromagnetic material and ferromagnetic material layers disposed at end edges, it is possible to apply the longitudinal bias to only end regions of the free layer. Thus, the value of magnetic field applied to the whole multi-layered structure of the sensor will be kept lower than that of the sensor using the hard magnet biasing structure resulting the degradation of the sensor output under high temperature environment to reduce.
Such SVMR sensor with the additional or second anti-ferromagnetic material layer for providing the longitudinal bias will be fabricated by depositing a first anti-ferromagnetic material layer, a pinned layer, a nonmagnetic metallic layer, a free layer and a protection layer on a substrate in this order, by milling the protection layer to expose end regions of the free layer and by depositing an additional ferromagnetic material layer and the second anti-ferromagnetic material layer for providing the longitudinal bias on the exposed end regions of the free layer. However, when milling the protection layer to expose the end regions of the free layer, material elements of the milled protection layer will diffuse into the free layer causing the exchange coupling for providing the longitudinal bias may be prevented at the interface between the surface of the free layer and the additional ferromagnetic material layer.
Known is a technique for cleaning the surface of MR sensor elements in order to obtain good exchange coupling for providing the longitudinal bias. For example, Japanese patent unexamined publication Nos.7(1995)-210834 and 7(1995)-244821 disclose removing of a film of oxide produced over the surfaces of MR sensor elements when anti-ferromagnetic material layers for the longitudinal bias are formed after patterning the MR sensor elements to a predetermined shape.
However, these known techniques concern cleaning of the surface of anisotropy MR sensors but not of GMR sensors such as SVMR sensors. Furthermore, these techniques cannot solve the problems due to diffusion of material elements of other layer into the free layer. Also, there is no teaching in these prior arts as to when the cleaning of the surface of the MR sensor should be executed during the manufacturing process of the MR sensor or the magnetic head.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a MR sensor and a manufacturing method of the MR sensor, whereby excellent exchange coupling can be provided between a free layer and ferromagnetic material and anti-ferromagnetic material layers for producing a longitudinal bias magnetic field.
According to the present invention, a manufacturing method of a MR sensor includes forming a MR multi-layered structure of a first anti-ferromagnetic material layer, a first ferromagnetic material layer (pinned layer) which receives bias magnetic field caused by exchange coupling with the first anti-ferromagnetic material layer, a nonmagnetic material layer and a second ferromagnetic material layer (free layer) which changes its magnetization direction in response to magnetic signal applied thereto, depositing a protection layer on the MR multi-layered structure, removing full depth of at least end regions of the protection layer and a partial depth of end regions of the second ferromagnetic material layer, and forming a second anti-ferromagnetic material layer for exchange coupling to control magnetic domain in the second ferromagnetic material layer, on at least the end regions of the second ferromagnetic material layer. The removing is executed before annealing for controlling magnetization direction of the first anti-ferromagnetic material layer.
When a second anti-ferromagnetic material layer for exchange coupling to control magnetic domain in the free layer, a partial depth of end regions of the free layer is removed. By thus removing a partial depth of end regions of the free layer, diffused parts of the free layer into which component elements of the protection layer are diffused during removing the protection layer can be certainly eliminated from the free layer, and therefore excellent exchange coupling can be provided between the free layer and the second anti-ferromagnetic material layer for supplying the longitudinal bias to the free layer.
Also, since the removing of the partial depth of the free layer is executed before the annealing for c
Araki Satoru
Shimazawa Koji
Tsuchiya Yoshihiro
Armstrong Westerman & Hattori, LLP
Strecker Gerard R.
TDK Corporation
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