Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
1999-12-28
2001-11-20
Pianalto, Bernard (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S132000, C427S264000, C427S270000, C427S271000, C427S372200, C427S383100, C427S404000, C427S548000, C427S599000
Reexamination Certificate
active
06319544
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a magnetoresistive effect (MR) sensor utilizing the giant magnetoresistive effect (GMR) and to a method of manufacturing a magnetic head with the MR sensor, used for a magnetic recording and reproducing device such as a hard disc drive (HDD) unit.
DESCRIPTION OF THE RELATED ART
Recently, thin-film magnetic heads with MR sensors based on spin valve effect of GMR characteristics are proposed in order to realize high sensitivity and high power magnetic heads which will satisfy the requirement for ever increasing data storage densities in today's HDD units.
The spin valve effect will be obtained by a structure with first and second thin-film layers of a ferromagnetic material separated by a thin-film layer of non-magnetic and electrically conductive material, and an adjacent layer of anti-ferromagnetic material 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 GMR characteristics are obtained.
The output characteristic of the spin valve effect MR sensor depends upon the angular difference of magnetization between the free and pinned ferromagnetic layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field such as a leakage magnetic field from a magnetic recording medium. 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.
In order to provide an exchange coupling between the pinned layer and the adjacently formed anti-ferromagnetic layer made of ordered anti-ferromagnetic material, it is necessary to give the anti-ferromagnetic layer an crystal structure of the CuAu—I type by executing ordering heat treatment on a deposited anti-ferromagnetic layer under application of magnetic field.
The output characteristics of the spin valve effect MR sensor with such ordered anti-ferromagnetic layer will be improved if the thickness of the anti-ferromagnetic layer becomes thinner. Namely, in the spin valve effect MR sensor, since the anti-ferromagnetic layer and the ferromagnetic layers are connected in parallel with the conductor layer for passing the sense current, it is necessary to make the thickness of the anti-ferromagnetic layer and the ferromagnetic layers thin to increase their resistance. If the resistance of the anti-ferromagnetic layer and the ferromagnetic layers increases, the divided current passing through these layers decreases and thus a rate of the output resistance change increases. Since the thickness of the anti-ferromagnetic layer will have in general extremely greater than that of the ferromagnetic layers, it is effective to form a thinner anti-ferromagnetic layer in order to decrease the divided current passing through these layers.
In addition, since it is requested that the magnetic head has a narrower recording gap to satisfy the requirement for increasing data storage density in the recent HDD unit, the thickness of the anti-ferromagnetic layer has to decrease more.
In the spin valve effect MR sensor, the energy of the exchange coupling for magnetizing the ferromagnetic layer toward one direction will increase if the thickness of the anti-ferromagnetic layer increases. Thus, conventionally the anti-ferromagnetic layer has been designed to have a relatively large thickness such as 25 nm or more.
If the thickness of the anti-ferromagnetic layer becomes thicker than 25 nm, the MR changing rate and the sheet-resistance value of the spin valve effect sensor become low. Thus, the rate of the output resistance change of the sensor decreases under the influence of low MR changing rate and low sheet-resistance value. Also, if the thickness of the anti-ferromagnetic layer becomes thinner than 5 nm, the MR changing rate of the sensor abruptly decreases and therefore the rate of the output resistance change suddenly decreases.
As mentioned above, requirement for lowering of the divided sense current passing through the anti-ferromagnetic layer and the ferromagnetic layers and requirement for increasing of the exchange-coupling energy conflict with each other with respect to the thickness of the anti-ferromagnetic layer. Since these requirements are fundamental requirements for the spin valve effect sensor, it is very important to satisfy both of these requirements.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a manufacturing method of a MR sensor and a manufacturing method of a magnetic head with the MR sensor, whereby exchange-coupling energy can be increased without increasing the thickness of an anti-ferromagnetic layer.
The present invention relates to a method for manufacturing a MR sensor having at least an anti-ferromagnetic layer and a ferromagnetic layer, and to a method for manufacturing a magnetic head with the MR sensor. The sensor utilizes bias magnetic field provided by exchange coupling between the anti-ferromagnetic layer and the ferromagnetic layer. The sensor manufacturing method includes a step of depositing an anti-ferromagnetic layer to have a larger thickness than a target thickness, a step of ordering the deposited anti-ferromagnetic layer, and a step of thinning the ordered anti-ferromagnetic layer to have the target thickness.
The anti-ferromagnetic layer deposited to have a larger thickness than a target thickness is ordered and thereafter thinned to have the target thickness. Thus, it is possible to obtain a multi-layered MR structure with a larger exchange-coupling energy than that of a multi-layered MR structure in which an anti-ferromagnetic layer is deposited to have the target thickness from the beginning and ordered. As a result, the exchange-coupling energy between the ferromagnetic layer and the anti-ferromagnetic layer of the multi-layered MR structure can be increased without changing or increasing the thickness of the anti-ferromagnetic layer so as to keep the divided sense current passing through the anti-ferromagnetic layer at almost the same value and so as to maintain the output characteristics of the MR sensor.
Japanese unexamined patent publication No.9-69210 discloses that anti-ferromagnetic layers for magnetic domain control are etched to have a thickness so that the anti-ferromagnetic layers become magnetically inactive. Namely, in the publication, it is described that the anti-ferromagnetic layers are thinned by ion milling to destroy the magnetic exchange coupling between these anti-ferromagnetic layers and the MR layer so as to use them layers as protection layers of the MR layer. Thus, thinning of the anti-ferromagnetic layers is not executed to improve the exchange coupling but just opposite to that of the present invention. Therefore, there is no teaching in the publication that the anti-ferromagnetic layer is deposited to have a larger thickness than a target thickness, then ordered and thereafter thinned to have the target thickness.
It is preferred that the thinning step includes thinning the ordered anti-ferromagnetic layer by a thinning amount of 5 nm or more.
It is preferred that the anti-ferromagnetic layer is made of a Mn-containing compound with the CuAu—I type ordered crystal structure. In this case, preferably, the ordered anti-ferromagnetic layer is oriented along (111) crystal alignment face after the ordering.
It
Kawashima Hiroaki
Sasaki Tetsuro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Pianalto Bernard
TDK Corporation
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