Patent Number: 6,166,948

Title: Magnetic memory array with magnetic tunnel junction memory cells having flux-closed free layers

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.

Inventors: Parkin; Stuart Stephen Papworth (San Jose, CA), Thomas; Luc (San Jose, CA)

Assignee: International Business Machines Corporation

International Classification: H01F 10/32 (20060101); G11C 11/16 (20060101); G11C 11/02 (20060101); H01F 10/00 (20060101); G11C 011/14 ()

Expiration Date: 12/26/2017