Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-02-17
2003-03-18
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06535365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic tunneling structure, and in particular a magnetic tunneling structure formed of two magnetic layers having an insulating tunneling barrier layer sandwiched therebetween.
2. Background of the Related Art
Magnetic storage technology is currently enjoying a 60% compound annual growth rate, with data rate increases of 30-40% per year. This has enabled the hard disk drive industry to drive storage costs down by approximately 40% per year. This rate of improvement shows no signs of diminishing and promises to continue at the present rate or even to accelerate.
While many factors such as fly height, media, etc. can also be improved, magnetic recording heads capable of higher speeds and densities are the key to continuing this trend. The magnetic sensing used so far, is done by a change in magnetoresistance (MR) induced in the sensing head. Research on magnetoresistance has been particularly active in recent years towards this goal. The materials explored so far exploit the giant magnetoresistance (GMR) effect in heterogeneous magnetic systems, such as layered and granular solids, where the dominant mechanism responsible for GMR is spin-dependent electron scattering, which is greatly enhanced in heterogeneous media. To extend the recording density beyond approximately 10 Gbytes/in
2
, a current perpendicular to the plane (CPP) mode GMR head was proposed in 1995. GMR materials in this configuration have low electrical impedance complicating their use in disk drives. A second type of magnetoresistance effect occurs in manganese perovskites. These materials display even larger magnetoresistance (MR), named “colossal” magnetoresistance (CMR), but the effects only occur in a large field and have a strong temperature dependence. The potential of CMR for low-field and room-temperature applications has yet to be determined.
Another promising source of large magnetoresistance effects has been magnetic tunnel junctions (MTJs). Magnetic tunneling structures generally have two magnetic electrodes with different coercivities separated by a very thin insulating layer. A tunneling effect manifests depending upon the relative angles of magnetization of the two ferromagnetic layers. Since the directions of the magnetizations can be altered by an external field, the tunneling resistance is sensitive to the field. According to known theories, a range of field exists where the spins in both electrodes are antiparallel and the tunneling resistance as a function of the magnetic field will be larger. For all other field values, the spins in both electrodes are parallel and the resistance will have a lower value.
Although MTJ structures have been studied for more than twenty years, it is only recently that significant changes in MR (~20-30% at room temperature) have been observed, for absolute resistance values in the 10
2
kilo-ohm range for micron-size devices. All the structures studied that have yielded high MR values at room temperature, consist of polycrystalline magnetic layers separated by a thin aluminum oxide insulating layer. Different magnetic materials and/or shapes have been employed to create the two different anisotropys in some cases. Other devices have employed an antiferromagnetic layer to pin one of the ferromagnetic layers.
For example, U.S. Pat. No. 5,835,314 to Moodera, which is hereby incorporated by reference, discloses a magnetic tunneling junction
20
comprising a substrate
22
, a seeding layer
24
, a first ferromagnetic layer
12
, an insulating tunnel barrier layer
14
, and a second ferromagnetic layer
10
. The first ferromagnetic material layer is formed of Cobalt Iron and the second ferromagnetic material layer is formed of either Cobalt or Nickel Iron. The insulating tunnel barrier layer is formed of Aluminum Oxide or other nitrides.
U.S. Pat. No. 5,953,248 to Chen, which is hereby incorporated by reference, discloses magnetic tunneling injunction
10
comprising a supporting substrate
11
, a magnetoresistive structure
12
supported on the substrate, an electrically insulating material layer
13
positioned on the structure
12
and a magnetoresistive structure
15
positioned on the electrically insulating material layer
13
. The magnetoresistive structure
15
comprises an antiferromagnetically coupled multi-layer structure including magnetoresistive layers
17
and
18
having a nonmagnetic conductive layer
19
situated in parallel juxtaposition between the magnetoresistive layers
17
and
18
. The magnetoresistive layers
17
and
18
may be single layers of ferromagnetic material such as a layer of Nickel, Iron, Cobalt, or alloys thereof, or alternatively, either of layers
17
and
18
can be a composite ferromagnetic layer, such a layer of Nickel-Iron-Cobalt covering a layer of Cobalt-Iron or three layer structures including layers of Cobalt-Iron and Nickel-Iron-Cobalt and Cobalt-Iron with Cobalt-Iron at the interface with adjacent layers. The magnetoresistive structure
12
is similar to the structure
15
and includes magnetoresistive layers
25
and
26
separated by a non-magnetic conducting layer
27
. Chen notes that only the layers
17
and
26
, adjacent to the electrically insulating material layer
13
, contribute to the magnetoresistance of the magnetic tunneling injunction
10
. Chen teaches Aluminum Oxide as an example of the electrically insulating material layer
13
.
U.S. Pat. No. 5,793,697 to Scheurelein and U.S. Pat. No. 5,640,343 to Gallagher, which are hereby incorporated by reference, each discloses a magnetic tunneling junction comprising a template layer
15
, such as Pt, a initial ferromagnetic layer
16
, such as Permalloy (Ni—Fe), an antiferromagnetic layer
18
, such as Mn—Fe, a fixed ferromagnetic layer
10
, such a Co—Fe or Permalloy, a thin tunneling barrier layer
22
of Alumna (Al
2
O
3
), a soft ferromagnetic layer
24
, such as a sandwich of thin Co—Fe with Permalloy, and a contact layer
25
, such as Pt.
SUMMARY OF THE INVENTION
An object of the invention is to solve at least the problems and/or disadvantages associated with prior art devices and to provide at least the advantages described hereinafter.
It is an object of the invention to provide a novel magnetic tunneling structure.
It is another object of the invention to provide a magnetic tunneling structure with improved magnetoresistive effect in comparison to conventional magnetic tunneling structures.
It is a still further object of the invention to provide a magnetic tunneling structure with lower absolute electrical impedance in comparison to conventional magnetic tunneling structures.
It is an additional object of the invention to provide a magnetic tunneling structure with a higher degree of polarization of the ferromagnetic layers in comparison to conventional magnetic tunneling structures.
It is another object of the invention to provide a magnetic tunneling structure with a lower tunneling barrier in comparison to conventional magnetic tunneling structures.
It is yet another object of the invention to provide a magnetic tunneling structure reduced in size in comparison to conventional magnetic tunneling structures.
It is a further object of the invention to provide a magnetic tunneling structure having an oxide-free tunneling barrier.
It is a further object to provide a magnetic tunneling structure with reduced oxidation between the ferromagnetic layers and the insulating tunneling barrier layer.
To achieve the above objects, a magnetic tunneling structure is provided that comprises, first and second ferromagnetic layers and an insulating tunneling barrier layer disposed between the first and second ferromagnetic layers, wherein the first ferromagnetic layer is a single crystalline layer and the second ferromagnetic layer is a polycrystalline layer. The single crystalline layer and the polycrystalline layer work in combination to provide two states of magnetization. The multilayer structure may be disposed on a substrate, for example, silicon; however, other mater
Clarke Roy
Lukaszew Rosa A.
Sheng Yongning
Uher Ctirad
Evans Jefferson
Fleshner & Kim LLP
The Regents of the University of Michigan
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