ST-RAM cells with perpendicular anisotropy
Magnetic spin-torque memory cells, often referred to as magnetic tunnel junction cells, which have magnetic anisotropies (i.e., magnetization orientation at zero field and zero current) of the associated ferromagnetic layers aligned perpendicular to the wafer plane, or “out-of-plane”. A memory cell may have a ferromagnetic free layer, a first pinned reference layer and a second pinned reference layer, each having a magnetic anisotropy perpendicular to the substrate. The free layer has a magnetization orientation perpendicular to the substrate that is switchable by spin torque from a first orientation to an opposite second orientation.
1. A magnetic memory cell on a substrate, the memory cell comprising a ferromagnetic free layer, a first pinned reference layer and a second pinned reference layer, each having a magnetic anisotropy perpendicular to the substrate, the first and second pinned reference layer are unbalanced synthetic antiferromagnetic (SAF) coupled structures each unbalanced synthetic antiferromagnetic (SAF) coupled structure comprising two ferromagnetic layers separated by a metallic spacer and the two ferromagnetic layers have opposing magnetizations of unequal magnitude resulting in a net magnetization, the free layer between the first pinned reference layer and the second pinned reference layer and having a magnetization orientation perpendicular to the substrate and switchable by spin torque from a first orientation to an opposite second orientation, the magnetization of the free layer coupled to each of the first pinned reference layer and the second pinned reference layer and a first nonmagnetic and insulating barrier layer positioned between the free layer and the first pinned reference layer and a second nonmagnetic and insulating barrier layer positioned between the free layer and the second pinned reference layer.
2. A magnetic memory cell on a substrate, the memory cell comprising:
a ferromagnetic free layer having a magnetic anisotropy and a magnetization perpendicular to the substrate, the magnetization switchable by spin torque;
a first pinned reference layer having a magnetic anisotropy and a magnetization pinned perpendicular to the substrate, the first pinned reference layer positioned between the substrate and the free layer;
a first nonmagnetic and insulating barrier layer positioned between the free layer and the first pinned reference layer;
a second pinned reference layer having a magnetic anisotropy and magnetization pinned perpendicular to the substrate, the free layer positioned between the first pinned reference layer and the second pinned reference layer; and
a second nonmagnetic and insulating barrier layer positioned between the free layer and the second pinned reference layer;
wherein the first pinned reference layer and the second pinned reference layer are unbalanced synthetic antiferromagnetic (SAF) coupled structures, each unbalanced synthetic antiferromagnetic (SAF) coupled structure comprising two ferromagnetic layers separated by a metallic spacer and the two ferromagnetic layers have opposing magnetizations of unequal magnitude resulting in a net magnetization and the free layer has a free layer interface area and the adjacent first pinned reference layer has a first pinned reference layer interface area, wherein the free layer interface area is less than the first pinned reference layer interface area.
3. The memory cell of claim 2 wherein the first pinned reference layer and the second pinned reference layer are the same structure.
4. The memory cell of claim 2 further comprising a first antiferromagnetic material (AFM) layer positioned between the first pinned reference layer and the substrate.
5. The memory cell of claim 2 further comprising a second antiferromagnetic material (AFM) layer, the second pinned reference layer positioned between the second AFM layer and the second nonmagnetic and insulating barrier layer.
6. The memory cell of claim 2 further comprising a first antiferromagnetic material (AFM) layer positioned between the first pinned reference layer and the substrate and a second antiferromagnetic material (AFM) layer, the second pinned reference layer positioned between the second AFM layer and the second nonmagnetic and insulating barrier layer.
7. The memory cell of claim 2 wherein the second pinned reference layer has a second pinned reference layer area that is constant and equal to the free layer interface area.
8. A magnetic memory cell on a substrate, the memory cell comprising:
a ferromagnetic free layer having a magnetic anisotropy and a magnetization perpendicular to the substrate, the magnetization switchable by spin torque;
a first pinned reference layer having a magnetic anisotropy and a magnetization pinned perpendicular to the substrate, the first pinned reference layer positioned between the substrate and the free layer;
a first nonmagnetic and insulating barrier layer positioned between the free layer and the first pinned reference layer;
a second pinned reference layer having a magnetic anisotropy and magnetization pinned perpendicular to the substrate, the free layer positioned between the first pinned reference layer and the second pinned reference layer; and
a second nonmagnetic and insulating barrier layer positioned between the free layer and the second pinned reference layer;
wherein the first pinned reference layer and the second pinned reference layer are unbalanced synthetic antiferromagnetic (SAF) coupled structures, each unbalanced synthetic antiferromagnetic (SAF) coupled structure comprising two ferromagnetic layers separated by a metallic spacer and the two ferromagnetic layers have opposing magnetizations of unequal magnitude resulting in a net magnetization and the second pinned reference layer has a second pinned reference layer interface area and the adjacent free layer has a free layer interface area, wherein the second pinned reference layer interface area is less than the free layer interface area.
9. The memory cell of claim 8 wherein the second pinned reference layer has a second pinned reference layer area that is constant and less than the free layer interface area.