Precessional spin current structure with non-magnetic insertion layer for MRAM
A magnetoresistive random-access memory (MRAM) is disclosed. MRAM device has a magnetic tunnel junction stack having a significantly improved performance of the free layer in the magnetic tunnel junction structure. The MRAM device utilizes a precessional spin current (PSC) magnetic structure in conjunction with a perpendicular MTJ where the in-plane magnetization direction of the PSC magnetic layer is free to rotate. The precessional spin current magnetic layer a first and second precessional spin current ferromagnetic layer separated by a nonmagnetic precessional spin current insertion layer.
1. A magnetic device, comprising
a first synthetic antiferromagnetic structure in a first plane, the first synthetic antiferromagnetic structure including a magnetic reference layer, the magnetic reference layer having a magnetization vector that is perpendicular to the first plane and having a fixed magnetization direction;
a nonmagnetic tunnel barrier layer in a second plane and disposed over the magnetic reference layer;
a free magnetic layer in a third plane and disposed over the nonmagnetic tunnel barrier layer, the free magnetic layer having a magnetization vector that is perpendicular to the third plane and having a magnetization direction that can precess from a first magnetization direction to a second magnetization direction, the magnetic reference layer, the nonmagnetic tunnel barrier layer and the free magnetic layer forming a magnetic tunnel junction;
a nonmagnetic spacer layer in a fourth plane and disposed over the free magnetic layer, the non-magnetic spacer layer comprising MgO;
a precessional spin current magnetic structure in a fifth plane that is physically separated from the free magnetic layer, and magnetically and electronically coupled to the free magnetic layer by the nonmagnetic spacer layer, the precessional spin current magnetic structure having a magnetization vector with a magnetization direction in the fifth plane which can freely rotate in any magnetic direction in the fifth plane, the precessional spin current magnetic structure comprising a first precessional spin current ferromagnetic layer, a nonmagnetic precessional spin current insertion layer and a second precessional spin current ferromagnetic layer, the first precessional spin current ferromagnetic layer being disposed over the nonmagnetic spacer layer, the nonmagnetic precessional spin current insertion layer being disposed over the first precessional spin current ferromagnetic layer, and the second precessional spin current ferromagnetic layer being disposed over the nonmagnetic precessional spin current insertion layer, wherein the nonmagnetic precessional spin current insertion layer is constructed of a thin film of Ru; and
a capping layer in a sixth plane and disposed over the precessional spin current magnetic structure;
wherein electrons of an electrical current passing through the precessional spin current magnetic structure are aligned in the magnetic direction of the precessional spin current magnetic and injected into the nonmagnetic spacer, the free magnetic layer, the nonmagnetic tunnel barrier layer, and the magnetic reference layer, and wherein the magnetization direction of the precessional spin current magnetic structure precesses and is free to follow precession of the magnetization direction of the free magnetic layer, thereby causing spin transfer torque to assist switching of the magnetization vector of the free magnetic layer.
2. The magnetic device of claim 1 wherein the nonmagnetic precessional spin current insertion layer is constructed of a material having a spin diffusion length exceeding two (2) nanometers.
3. The magnetic device of claim 1 wherein the thin film of Ru has a thickness of at least one nanometer.
4. The magnetic device of claim 1 wherein the thin film of Ru has a thickness of 1.5 nanometers.
5. The magnetic device of claim 1 , wherein the first precessional spin current ferromagnetic layer comprises a thin film of Fe, the nonmagnetic precessional spin current insertion layer comprises a material with a long spin diffusion length, and the second precessional spin current ferromagnetic layer comprises a thin film of CoFeB.
6. The magnetic device of claim 5 , wherein the thin film of Fe has a thickness of 0.4 nanometers.
7. The magnetic device of claim 5 , wherein the thin film of Fe has a thickness of 0.6 nanometers.
8. The magnetic device of claim 5 wherein the thin film of CoFeB is comprised of forty percent Co, forty percent Fe and twenty percent B.
9. The magnetic device of claim 8 wherein the thin film of CoFeB has a thickness of 1.7 nanometers.
10. The magnetic device of claim 8 wherein the thin film of CoFeB has a thickness of 1.85 nanometers.
11. The magnetic device of claim 5 , wherein the material with a long spin diffusion length is selected from the group consisting of Ru, Cu, Ag, Au, Mg and Al.
12. The magnetic device of claim 1 wherein the free magnetic layer has an effective magnetic anisotropy such that its easy axis magnetization axis points away from the perpendicular direction and forms an angle with respect to perpendicular plane.