Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-16
2004-07-27
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C360S324000, C360S324100, C360S324110, C360S324120, C427S130000
Reexamination Certificate
active
06767655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magneto-resistive elements that are widely used, for example, in magnetic random access memory (MRAM) used in data communication terminals, for example, and to manufacturing methods for the same.
2. Description of the Related Art
It is known that when a current flows through a multilayer film including ferromagnetic material/intermediate layer/ferromagnetic material in a direction traverse to the intermediate layer, a magneto-resistive effect occurs due to the spin tunneling effect if the intermediate layer is a tunneling insulating layer, and a magneto-resistive effect occurs due to the CPP (current perpendicular to the plane)-GMR effect if the intermediate layer is a conductive metal, such as Cu. Both magneto-resistive effects depend on the size of the angle between the magnetizations of the magnetic materials sandwiching the intermediate layers (magnetization displacement angle). In the former, the magneto-resistive effect occurs due to changes of the transition probability of tunneling electrons flowing through the two magnetic layers depending on the magnetization displacement angle, and in the latter the magneto-resistive effect occurs due to changes in the spin-dependent scattering.
When such a TMR element is used for a magnetic head or an MRAM device, one of the two magnetic layers sandwiching the intermediate layer can serve as a pinned magnetic layer, in which magnetization rotations with respect to an external field are difficult, by layering an antiferromagnetic material of FeMn or IrMn onto it, whereas the other layer serves as a free magnetic layer, in which magnetization rotations with respect to an external field are easy (spin-valve element).
When applying these vertical current-type resistive elements for example to a magnetic head or memory elements of an MRAM, for example in a reproduction element for tape media, then the area of the intermediate layer through which current flows should be not larger than several 1000 &mgr;m
2
, in order to achieve the demanded high recording densities or high installation densities. Especially in HDDs and MRAMs or the like, an element area of not more than several &mgr;m
2
is desired. If the element area is large, magnetic domains form relatively easily in the free magnetic layer Therefore, there are the problems of Barkhausen noise due to magnetic wall transitions when used as a reproduction element, and instabilities of the switching magnetization when used for the memory operation of MRAMs. On the other hand, in a region, in which the film thickness of the free magnetic layer with respect to the element area cannot be ignored, the demagnetizing field due to shape anisotropies becomes large, so that especially when used as a reproduction head, the decrease of the reproduction sensitivity brought about by an increase of the coercivity becomes a problem. When used as an MRAM, the increase of the reversal magnetic field becomes a problem.
In order to suppress the demagnetizing field, the film thickness of the free magnetic layer can be made thinner. However, at submicron dimensions, the film thickness of the magnetic layer necessary to suppress the demagnetizing field becomes less than 1 nm, which is below the physical film thickness limit of magnetic films.
Using the TMR elements for an MRAM, a thermal process at about 400° C. is performed in a semiconductor process of hydrogen sintering or a passivation process. However, it has been reported that in conventional pinned layers, in which IrMn or FeMn is arranged in contact with a magnetic layer, the MR is decreased by the decrease of the spin polarizability of the magnetic layer due to diffusion of Mn at temperatures of about 300° C. or above, and the decrease of the pinning magnetic field due to the dilution of the composition of the antiferromagnetic material (see S. Cardoso et.al., J. Appl.Phys. 87, 6058(2000)).
In previously proposed methods for reading non-volatile MRAM elements, the read-out is difficult when there are large variations in element resistance or in the resistance of switching element and electrode, because what is read out is the change of magnetic resistance of the magneto-resistive element with respect to the total resistance of magneto-resistive elements connected in series to a switching element and an electrode. In order to improve the SIN, a method of reading an element with the voltage between that element and a reference element has been proposed, but in that case, the higher integration of the elements becomes a problem, because the reference element is necessary (see p. 37, Proceedings of 112
th
Study Group of the Magnetics Society of Japan).
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a vertical current-type magneto-resistive element includes an intermediate layer and a pair of magnetic layers sandwiching the intermediate layer, wherein one of the magnetic layers is a free magnetic layer in which magnetization rotation with respect to an external magnetic field is easier than in the other magnetic layer, wherein the free magnetic layer is a multilayer film including at least one non-magnetic layer and magnetic layers sandwiching the non-magnetic layer, and wherein an element area through which current flows is not larger than 1000 &mgr;m
2
, preferably not larger than 10 &mgr;m
2
, more preferably not larger than 1 &mgr;m
2
, most preferably not larger than 0.1 &mgr;m
2
. The element area is defined by the area of the intermediate layer through which the current flows perpendicular to the film plane. Providing the free magnetic layer as a multilayer structure of magnetic and non-magnetic layers suppresses the demagnetizing field, which increases as the element area becomes smaller. Here, the magnetic and non-magnetic layers can be single layers or multilayers. It is preferable that the free magnetic layer performs magnetization rotation at an external magnetic field causing magnetization rotation that is at least 50 Oe (ca. 4 kA/m) smaller than that required for magnetization rotation of the other magnetic layers (usually, the pinned magnetic layer). Especially when the element is used for a memory, it is preferable that magnetization rotation at a value of 10 to 500 Oe is possible.
It is preferable that, in particular near 0.5 nm of the interface with the intermediate layer, the magnetic layers are made of a ferromagnetic or ferrimagnetic material including at least 50 wt % of (i) a Co-based amorphous material such as CoNbZr, CoTaZr, CoFeB, CoTi, CoZr, CoNb, CoMoBZr, CoVZr, CoMoSiZr, CoMoZr, CoMoVZr or CoMnB, (ii) an Fe-based microcrystal material, such as FeSiNb or Fe(Si,Al,Ta,Nb,Ti)N, (iii) a magnetic material containing at least 50 wt % of a ferromagnetic metal element selected from Fe, Co and Ni, for example ferromagnetic or dilute magnetic materials like FeCo alloy, NiFe alloy, NiFeCo alloy, FeCr, FeSiAl, FeSi, FeAl, FeCoSi, FeCoAl, FeCoSiAl, FeCoTi, Fe(Ni)Co)Pt, Fe(Ni)(Co)Pd, Fe(Ni)(Co)Rh, Fe(Ni)(Co)Ir or Fe(Ni)(Co)Ru, (iv) a nitride, such as FeN, FeTiN, FeAlN, FeSiN, FeTaN, FeCoN, FeCoTiN, FeCoAlN, FeCoSiN, FeCoTaN, (v) Fe
3
O
4
, (vi) a half metal, such as XMnSb (wherein X is at least one selected from Ni, Cu and Pt), LaSrMnO, LaCaSrMnO or CrO
2
, (vii), a spinel oxide such as a perovskite oxide, MnZn ferrite or NiZn ferrite, or (viii) a garnet oxide. In this specification, elements or layers in parentheses are optional ones.
It is preferable that the area of the free magnetic layer is wider than the element area. If the area of the free magnetic layer is substantially the same as the element area, then the MR decreases due to the influence of disturbances of the domain structure that occur at the edge of the free magnetic layer. When the area of the free magnetic layer is larger than the element area, and when the free magnetic layer is formed to cover the element area sufficiently, then the edges of the free magnetic layer are separated from the element area, so that the magnetization direction inside the fre
Hiramoto Masayoshi
Iijima Kenji
Matukawa Nozomu
Odagawa Akihiro
Sakakima Hiroshi
Matsushita Electric - Industrial Co., Ltd.
Thibodeau Paul
Uhlir Nikolas J
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