Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
2000-06-20
2001-03-20
Nguyen, Tan T. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S158000
Reexamination Certificate
active
06205053
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of nonvolatile memories. In particular, this invention is drawn to magnetic memory cells.
BACKGROUND OF THE INVENTION
One type of nonvolatile memory relies on a magnetoresistive effect referred to as the giant magnetoresistive (GMR) effect. GMR-based magnetic memory cells are multilayered structures comprising a nonmagnetic layer sandwiched by conductive magnetic layers. The magnetic state of the cell is determined by the relative orientation of a magnetic vector in one magnetic layer to a magnetic vector in another magnetic layer (e.g., parallel or anti-parallel). The resistance of the cell differs according to the relative orientations of the magnetic vectors. Accordingly the state of the cell can be determined by applying a voltage across the cell and measuring a resulting sense current.
The layers of magnetic material are typically formed as geometrically patterned films such as squares or rectangles. One disadvantage of patterned magnetic layer storage structures is that multiple magnetic domains may form in the magnetic layers, rendering the state of the cell indeterminate during read operations. Variation in the magnetic domain configuration of the cell may also lead to fluctuations in the magnetic switching field (i.e., coercivity) of the cell.
In order to reduce the ambiguities introduced by the magnetic domains, shape anisotropy is frequently introduced by increasing one dimension (e.g., length) of a layer with respect to another dimension (e.g., width) of the layer in order to reduce the number of domain states. One disadvantage of the rectangular shape as opposed to the square shape, however, is a significant reduction in the memory density.
SUMMARY OF THE INVENTION
In view of limitations of known systems and methods one embodiment of a magnetoresistive memory cell includes first and second conductive magnetic layers. One of the first and second layers is substantially “H” or “I” shaped. A separation layer is disposed between the first and second layers. In various embodiments, the separation layer is either conductive or nonconductive. In various embodiments, at least one of the first and second layers comprises one of a nickel-iron (NiFe), cobalt-iron (CoFe), or a nickel-iron-cobalt (NiFeCo) alloy.
In one embodiment, the memory cell apparatus includes conductive magnetic reference and data layers. The data layer is substantially “H” or “I” shaped. The presence of the “H” or “I” shaped geometry imparts a stabilizing uniaxial shape anisotropy to the data layer of the memory cell. A separation layer is disposed between the reference and data layers. The cell may be a tunneling magnetoresistive cell or a giant magnetoresistive cell. The separation layer is nonconductive in one embodiment and conductive in an alternative embodiment. In various embodiments, one of the reference and data layers comprises one of a nickel-iron, cobalt-iron or a nickel-iron-cobalt alloy.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.
REFERENCES:
patent: 5757695 (1998-05-01), Shi et al.
patent: 5966323 (1999-10-01), Chen et al.
Hewlett--Packard Company
Nguyen Tan T.
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