| US 7,569,902 B2 | ||
| Enhanced toggle-MRAM memory device | ||
| Hideo Fujiwara, Duncanville, Ala. (US); and Sheng-Yuan Wang, Milpitas, Calif. (US) | ||
| Assigned to Board of Trustees of the University of Alabama, Tuscaloosa, Ala. (US) | ||
| Filed on Oct. 30, 2006, as Appl. No. 11/589,676. | ||
| Claims priority of provisional application 60/731537, filed on Oct. 28, 2005. | ||
| Prior Publication US 2007/0097742 A1, May 03, 2007 | ||
| Int. Cl. G11C 11/02 (2006.01); H01L 29/82 (2006.01) | ||
| U.S. Cl. 257—421 [257/427; 257/E29.323; 365/158] | 23 Claims |
| 1. A magnetic memory device comprising:
one or more memory layer structures having an anti-parallel magnetization configuration, each said memory layer structure
comprising;
a first ferromagnetic layer having a first uniaxial magnetic anisotropy comprised of a first induced uniaxial anisotropy or
a first shape magnetic anisotropy, wherein said first shape magnetic anisotropy has a first shape magnetic anisotropy easy
axis and a first shape magnetic anisotropy hard axis and said first induced uniaxial magnetic anisotropy has a first induced
uniaxial magnetic anisotropy easy axis and a first induced uniaxial magnetic anisotropy hard axis;
a second ferromagnetic layer having a second uniaxial magnetic anisotropy comprised of a second induced uniaxial anisotropy
or a second shape magnetic anisotropy, wherein said second shape magnetic anisotropy has a second shape magnetic anisotropy
easy axis and a second shape magnetic anisotropy hard axis and said second induced uniaxial magnetic anisotropy has a second
induced uniaxial magnetic anisotropy easy axis and a second induced uniaxial magnetic anisotropy hard axis and said second
induced uniaxial magnetic anisotropy easy axis is set substantially parallel to said first induced uniaxial magnetic anisotropy
easy axis making a common induced uniaxial anisotropy easy axis;
an intermediate layer substantially between said first and said second ferromagnetic layers;
magnetostatic coupling having a magnetostatic coupling strength between said first ferromagnetic layer and said second ferromagnetic
layer, wherein said magnetostatic coupling causes the anti-parallel magnetization confignration of said memory layer structure
to be stable without the application of an external magnetic field such that said magnetic memory device has a stable magnetization
direction and said stable magnetization direction is parallel to said common induced uniaxial anisotropy easy axis;
a first current path positioned such that a first magnetic field generated by passage of current through the first current
path lies in a direction of about +(−) 45° from the common induced uniaxial magnetic anisotropy easy axis; and
a second current path positioned such that a second magnetic field generated by passage of current through the second current
path lies in a direction of about −(+) 45° from the common induced uniaxial magnetic anisotropy easy axis;
wherein each said memory layer structure is configured such that the magnetic memory device has a normalized total anisotropy
field (hk,total) and coupling field (hcouple) such that there is a relationship: a(hcouple−1)+b(hcouple2−1)2≤hk,total≤0.05(hcouple−1), with 25>hcouple>1;
wherein said magnetic memory device operates in a toggle writing mode by applying a current to the first current path and
second current path, such that the first magnetic field and the second magnetic field are generated temporally successive
to each other, but overlapping so that the second magnetic field is present before the first magnetic field has dissipated,
wherein for the relationship: a(hcouple−1)+b(h2couple−1)2≤hk,total≤0.05(hcouple−1), a can be between and including −0.81 to −0.26 and b can be between and including −0.002 and −0.004.
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