Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-09-16
2001-11-06
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S900000, C365S173000, C365S171000
Reexamination Certificate
active
06312840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic tunnelling element in which a pair of magnetic layers are laminated via a tunnel barrier layer and in which the tunnel current is caused to flow from one to the other magnetic layer, with the conductance of the tunnel current being changed in dependence upon the ratio of polarization of magnetization of the paired magnetic layers. This invention also relates to a method for manufacturing the magnetic tunnelling element.
2. Description of the Related Art
It has been reported that, if, in a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers, a pre-set voltage is applied across the paired magnetic metal layers as electrodes, a magnetic tunnelling effect is displayed, in which the conductance of the tunnel current flowing in the insulating layer is changed in dependence upon the relative angle of magnetization of the paired magnetic metal layers. That is, a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers exhibits a magneto-resistance effect with respect to the tunnel current flowing in the insulating layer.
In this magnetic tunnelling effect, the specific magnetoresistance can be theoretically calculated based on the ratio of polarization of magnetization of the paired magnetic metal layers. In particular, if Fe is used as the material of the paired magnetic metal layers, expectation may be made of the specific magnetoresistance amounting approximately to 40%.
Therefore, a magnetic tunnelling element having a layered structure comprised of a thin insulating layer sandwiched between paired magnetic metal layers is stirring up notice as an element for detecting an external magnetic field.
In the above-described magnetic tunnelling element, a metal oxide is routinely used as the thin insulating layer. However, if a metal oxide is used as an insulating layer, pinholes etc tend to be formed, such that shorting tends to be induced between the paired magnetic metal layers. There are occasions wherein, if a metal oxide is used as an insulating layer, the metal oxidation degree is insufficient, such that the tunnel barrier is incomplete such that the magnetic tunnelling effect is not displayed.
In the conventional magnetic tunnelling element, changes in conductance of the current in dependence upon the relative angle of magnetization of the paired magnetic metal layers, laminated via an insulating layer in-between, that is the magnetic tunnelling effect, were detected. However, with the conventional magnetic tunnelling element, it is difficult to demonstrate the magnetic tunnelling effect reliably such that the conventional magnetic tunnelling element cannot be used for practical application.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic tunnelling element in which the tunnel current flows positively in the insulating layer to exhibit the magnetic tunnelling effect in stability.
In one aspect, the present invention provides a magnetic tunnelling element including a first magnetic layer, a tunnel barrier layer formed on the first magnetic layer; and a second magnetic layer formed on the tunnel barrier layer formed on the tunnel barrier layer, the tunnel current flowing between the first magnetic layer and the second magnetic layer via the tunnel barrier layer. The surface of the first magnetic layer carrying the tunnel barrier layer has a surface roughness (Ra) of 0.3 nm or less.
With the magnetic tunnelling element according to the present invention, as described above, since the surface of the first magnetic metal layer carrying the tunnel barrier layer has an average surface roughness (Ra) of 0.3 nm or less, the tunnel barrier layer 2 has its surface planarized to a high degree, so that, with the present magnetic tunnelling element, the interface between the first magnetic metal layer and the tunnel barrier layer and that between the second magnetic metal layer and the tunnel barrier layer are in optimum states to display the magnetic tunnelling effect reliably.
In another aspect, the present invention provides a method for manufacturing a magnetic tunnelling element at least including a first magnetic metal layer, a tunnel barrier layer and a second magnetic metal layer, laminated together, in which the method includes the steps of forming the first magnetic layer so that its major surface will have an average roughness (Ra) of 0.3 nm or less, forming the tunnel barrier layer on the major surface of the first magnetic metal layer and forming the second magnetic metal layer on the tunnel barrier layer.
With the manufacturing method for the magnetic tunnelling element according to the present invention, since the first magnetic metal layer is formed so that its major surface will be of the average surface roughness (RA) of 0.3 nm or less, the tunnel barrier layer formed on this major surface can be of optimum surface properties. Therefore, with this technique, the first magnetic metal layer and the tunnel barrier layer can be formed to optimum states.
In particular, with the magnetic tunnelling element according to the present invention, the surface roughness (Ra) of the surface of the first magnetic metal layer carrying the tunnel barrier layer is 0.3 nm or less. Thus, with the present magnetic tunnelling element, the tunnel current is allowed to flow positively between the first magnetic metal layer and the second magnetic metal layer in the vicinity of the tunnel barrier layer. Therefore, the magnetic tunnelling element of the present invention positively exhibits the high magnetic tunnelling effect.
Also, with the present manufacturing method for the magnetic tunnelling element, the first magnetic metal layer is formed so that its major surface will have an average roughness (Ra) of 0.3 nm or less. Thus, with the present technique, the magnetic tunnelling element can be provided which allows the current to flow reliably between the first magnetic metal layer and the second magnetic metal layer in the vicinity of the tunnel barrier layer. Therefore, with the present manufacturing method for the magnetic tunnelling element, a magnetic tunnelling element exhibiting a high magnetic tunnelling effect can be manufactured reliably.
Since the high magnetic tunnelling effect can be realized in the present invention, the present invention can be applied with advantage to a high output magnetic head.
REFERENCES:
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patent: 0 898 315 A1 (1999-02-01), None
Indo “Influence of Interlayer Roughness on Magnetoresistance Effect,.” JMMM 198-199 (1999).*
J.S. Moodera, et al., Ferromagnetic-Insulation-Ferromagnetic Tunneling: Spin-Dependent Tunneling and Large Magnetoresistance in Trilayer Junctions (Invited), Journal of Applied Physics, U.S. American Inst. of Physics, New York, vol. 279, No. 8, Part 02A, Apr. 15, 1996, pp. 4724-4729, XP000695592.
B.G. Park, et al., Dependence of tunneling magnetoresistance on CoFe interfacial layer thickness in NiFe/Al203/NiFe tunnel junctions, IEEE Transactions on Magnetics, vol. 35, No. 5, Sep., 1999, pp. 2919-2921, XP002128404.
Y. Indo, et al., Influence of interlayer roughness on magnetoresistance effect of ferromagnetic tunneling junctions, Journal of Magnetism and Magnetic Materials, vol. 198, Jun., 1999, pp. 155-157, XP000874195.
Ikeda Yoshito
Kumagai Seiji
Nakashio Eiji
Sugawara Junichi
Kiliman Leszek
Sonnenschein Nath & Rosenthal
Sony Corporation
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