Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
1999-07-19
2001-09-18
Tran, Minh Loan (Department: 2826)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000, C257S295000
Reexamination Certificate
active
06292389
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic elements for information storage and/or sensing and a fabricating method thereof, and more particularly, to a method of fabricating and thus defining the magnetic element to improve magnetic field response.
BACKGROUND OF THE INVENTION
This application is related to a co-pending application that bears U.S. Pat. No. 5,940,319, entitled “MAGNETIC RANDOM ACCESS MEMORY AND FABRICATING METHOD THEREOF,” filed on Aug. 31, 1998, assigned to the same assignee and incorporated herein by this reference, co-pending application that bears U.S. Pat. No. 6,024,885, entitled “PROCESS OF PATTERNING MAGNETIC FILMS” filed on Dec. 8, 1997, assigned to the same assignee and incorporated herein by this reference and issued U.S. Pat. No. 5,768,181, entitled “MAGNETIC DEVICE HAVING MULTI-LAYER WITH INSULATING AND CONDUCTIVE LAYERS”, issued Jun. 16, 1998, assigned to the same assignee and incorporated herein by this reference.
Typically, a magnetic element, such as a magnetic memory element, has a structure that includes ferromagnetic layers separated by a non-magnetic layer. Information is stored as directions of magnetization vectors in magnetic layers. Magnetic vectors in one magnetic layer, for instance, are magnetically fixed or pinned, while the magnetization direction of the other magnetic layer is free to switch between the same and opposite directions that are called “Parallel” and “Antiparallel” states, respectively. In response to Parallel and Antiparallel states, the magnetic memory element represents two different resistances. The resistance has minimum and maximum values when the magnetization vectors of the two magnetic layers point in substantially the same and opposite directions, respectively. Accordingly, a detection of changes in resistance allows a device, such as an MRAM device, to provide information stored in the magnetic memory element. The difference between the minimum and maximum resistance values, divided by the minimum resistance is known as the magnetoresistance ratio (MR).
An MRAM device integrates magnetic elements, more particularly magnetic memory elements, and other circuits, for example, a control circuit for magnetic memory elements, comparators for detecting states in a magnetic memory element, input/output circuits, etc. These circuits are fabricated in the process of CMOS (complementary metal-oxide semiconductor) technology in order to lower the power consumption of the device.
In addition, magnetic elements structurally include very thin layers, some of which are tens of angstroms thick. The performance of the magnetic element is sensitive to the surface conditions on which the magnetic layers are deposited. Accordingly, it is necessary to make a flat surface to prevent the characteristics of a magnetic element from degrading.
During typical magnetic element fabrication, such as MRAM element fabrication, which includes metal films grown by sputter deposition, evaporation, or epitaxy techniques, the film surfaces are not absolutely flat but instead exhibit surface or interface waviness. This waviness of the surfaces and/or interfaces of the ferromagnetic layers is the cause of magnetic coupling between the free ferromagnetic layer and the other ferromagnetic layers, such as the fixed layer or pinned layer, which is known as topological coupling or Néel's orange peel coupling. Such coupling is typically undesirable in magnetic elements because it creates an offset in the response of the free layer to an external magnetic field.
The ferromagnetic coupling strength is proportional to surface magnetic charge density and is defined as the inverse of an exponential of the interlayer thickness. As disclosed in U.S. Pat. No. 5,764,567, issued Jun. 9, 1998, and entitled “MAGNETIC TUNNEL JUNCTION DEVICE WITH NONFERROMAGNETIC INTERFACE LAYER FOR IMPROVED MAGNETIC FIELD RESPONSE”, by adding a non-magnetic copper layer next to the aluminum oxide tunnel barrier in a magnetic tunnel junction structure, hence increasing the separation between the magnetic layers, reduced ferromagnetic orange peel coupling, or topological coupling, is achieved. However, the addition of the copper layer will lower the MR of the tunnel junction, and thus degrade device performance. In addition, the inclusion of the copper layer will increase the complexity for etching the material.
Accordingly, it is a purpose of the present invention to provide an improved magnetic element with improved field response.
It is another purpose of the present invention to provide an improved magnetic element that includes reduced ferromagnetic coupling, more particularly ferromagnetic coupling of topological origin.
It is a still further purpose of the present invention to provide a method of forming a magnetic element with improved field response.
It is still a further purpose of the present invention to provide a method of forming a magnetic element with improved field response which is amenable to high throughput manufacturing.
SUMMARY OF THE INVENTION
These needs and others are substantially met through provision of a magnetic element including a first electrode, a second electrode and a spacer layer. The first electrode includes a fixed ferromagnetic layer whose magnetization is fixed in a preferred direction in the presence of an applied magnetic field, the fixed ferromagnetic layer having a thickness t
1
. A second electrode is included and comprises a free ferromagnetic layer whose magnetization is free to rotate in the presence of an applied magnetic field, the free ferromagnetic layer having a thickness t
2
. A spacer layer is located between the fixed ferromagnetic layer of the first electrode and the free ferromagnetic layer of the second electrode for permitting tunneling current in a direction generally perpendicular to the fixed and free ferromagnetic layers, the spacer layer having a thickness t
3
, where 0.25t
3
<t
1
<2t
3
, such that the net magnetic field at the interface between the free layer and the spacer layer, due to the topology of the other ferromagnetic surfaces, is near zero. The magnetic element further includes a metal lead and a substrate, the metal lead, the first and second electrodes and the spacer layer being formed on the substrate. Additionally disclosed is a method of fabricating the magnetic element with improved field response.
REFERENCES:
patent: 5764567 (1998-06-01), Parkin
patent: 1000422 (1998-01-01), None
“Topological coupling in spin valve type multilayers,” Zhang et al., IEEE Transactions on Magnetics, vol. 32, No. 5, Sep. 1996, pp. 4630-4635.
“Spin dependent tunnel/spin-valve devices with different pinning structures made by photolithography,” Wang et al, Journal of Applied Physics, Bo. 85, No. 8, Apr. 1999, pp. 5255-5257.
Chen Eugene Youjun
Shi Jing
Slaughter Jon Michael
Koch William E.
Motorola Inc.
Tran Minh Loan
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