Magnetic memory array with magnetic tunnel junction memory cells

Details Magnetic memory array with magnetic tunnel junction memory cells Magnetic memory array with magnetic tunnel junction memory cells

1999-09-03

2000-12-26

Nelms, David

Static information storage and retrieval

Systems using particular element

Magnetic thin film

365171, 365 8, 365158, G11C 1114

Patent

active

061669482

ABSTRACT:
An improved magnetic tunnel junction (MTJ) memory cell for use in a nonvolatile magnetic random access memory (MRAM) array has a free layer formed as two ferromagnetic films that are magnetostatically coupled antiparallel to one another by their respective dipole fields. The magnetostatic or dipolar coupling of the two ferromagnetic films occurs across a nonferromagnetic spacer layer that is selected to prevent exchange coupling between the two ferromagnetic films. The magnetic moments of the two ferromagnetic films are antiparallel to another so that the multilayer free layer structure has a reduced net magnetic moment. In the presence of an applied magnetic field, such as during writing to the cell, the moments of the two ferromagnetic films switch directions substantially simultaneously, so that the net magnetic moment of the multilayer free layer structure can have two possible orientations relative to the orientation of the fixed or pinned layer of the MTJ cell, thus resulting in the two stable magnetic states of the MTJ cell. The reduced net magnetic moment of the multilayer free layer structure reduces the magnetostatic coupling between the multilayer free layer and the pinned ferromagnetic layer in the MTJ cell, as well as the magnetostatic coupling between adjacent MTJ cells in the array. As a result, the cells, and thus the MRAM array, can be made smaller.

REFERENCES:
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S. Parkin et al., "Oscillations in Exchange Coupling and Magnetoresistance in Metallic Superlattice Structures: Co/Ru, Co/Cr, and Fe/Cr", Physical Review Letters, The American Physical Society, vol. 64, No. 19, May 7, 1990, pp. 2304-2307.
K. Moon et al., "Exchange-Biased Magnetic Tunnel Junctions: Dependence of Offset Field on Junction Width", Applied Physics Letters, American Institute of Physics, vol. 74, No. 24, Jun. 14, 1999, pp. 3690-3692.

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