Tilted synthetic antiferromagnet polarizer/reference layer for STT-MRAM bits
Embodiments disclosed herein generally relate to a multilayer magnetic device, and specifically to a spin-torque transfer magnetoresistive random access memory (STT-MRAM) device which provides for a reduction in the amount of current required for switching individual bits. As such, a polarizing reference layer consisting of a synthetic antiferromagnet (SAF) structure with an in-plane magnetized ferromagnet film indirectly exchange coupled to a magnetic film with perpendicular magnetic anisotropy (PMA) is disclosed. By tuning the exchange coupling strength and the PMA, the layers of the SAF may both be canted such that either may be used as a tilted polarizer for either an in-plane free layer or a free layer with PMA.
1. A multilayer magnetic device, comprising:
a free layer;
a spacer layer coupled to the free layer wherein the free layer is only directly connected to the spacer layer; and
a reference layer structure comprising:
an in-plane ferromagnet layer, wherein the in-plane ferromagnet layer has an equilibrium axis parallel with a first surface;
a nonmagnetic metal layer disposed on the first surface of the in-plane ferromagnet layer; and
a perpendicular magnetic anisotropy ferromagnet layer disposed on the nonmagnetic metal layer, wherein the perpendicular magnetic anisotropy ferromagnet layer has an equilibrium axis perpendicular to the first surface, wherein magnetizations of both the in-plane ferromagnet layer and the perpendicular magnetic anisotropy ferromagnet layer are each tilted away from respective equilibrium axes.
2. The multilayer magnetic device of claim 1 , wherein the in-plane ferromagnet layer has a thickness of between about 0.5 nm and 10 nm.
3. The multilayer magnetic device of claim 1 , wherein the perpendicular magnetic anisotropy ferromagnet layer has a thickness of between about 2 nm and about 8 nm.
4. The multilayer magnetic device of claim 1 , wherein the nonmagnetic metal layer comprises ruthenium.
5. The multilayer magnetic device of claim 1 , wherein the metal layer has a thickness of between about 2 angstroms and about 10 angstroms.
6. The multilayer magnetic device of claim 1 , wherein the in-plane ferromagnet layer comprises one of Ni, Fe, Co, B, Ge, Mn, and combinations and mixtures thereof, and wherein the perpendicular magnetic anisotropy ferromagnet layer is a single ferromagnet comprising one of Ni, Fe, Co, combinations or mixtures thereof, or an alloy of Ni, Fe, Co comprising a combination with B, Ge, Pt and/or Mn, or superlattices of Co and Pt, Co and Pd, Co and Ni, or combinations and mixtures thereof.
7. A multilayer magnetic device, comprising:
a free layer;
a spacer layer coupled to the free layer wherein the free layer is only directly connected to the spacer layer; and
a reference layer structure comprising:
an in-plane ferromagnet layer, wherein the in-plane ferromagnet layer has an equilibrium axis parallel with a first surface;
a nonmagnetic metal layer disposed on the first surface of the in-plane ferromagnet layer; and
a perpendicular magnetic anisotropy ferromagnet layer disposed on the nonmagnetic metal layer, wherein the perpendicular magnetic anisotropy ferromagnet layer has an equilibrium axis perpendicular to the first surface, wherein magnetizations of both the in-plane ferromagnet layer and the perpendicular magnetic anisotropy ferromagnet layer are each tilted away from respective equilibrium axes, and wherein the perpendicular magnetic anisotropy ferromagnet layer maintains a saturation magnetization (Ms) greater than about 500 emu/cm 3 .
8. A magnetoresistive random access memory storage device, comprising:
a reference layer structure, comprising:
a first layer, comprising an in-plane ferromagnet layer or a tilted perpendicular magnetic anisotropy polarizing layer, wherein the in-plane ferromagnet layer has an equilibrium axis parallel with a first surface, wherein the tilted perpendicular magnetic anisotropy polarizing layer has an equilibrium axis perpendicular to the first surface;
a nonmagnetic metal layer disposed on the first surface of the first layer, wherein the metal layer comprises ruthenium; and
a perpendicular magnetic anisotropy ferromagnet layer disposed on the metal layer, wherein the perpendicular magnetic anisotropy ferromagnet layer has an equilibrium axis perpendicular to the first surface, wherein magnetizations of both the first layer and the perpendicular magnetic anisotropy ferromagnet layer are each tilted away from respective equilibrium axes;
a spacer layer; and
a free layer, wherein the spacer layer is coupled to the reference layer structure and the free layer and the free layer only directly connects to the spacer layer.
9. The magnetoresistive random access memory storage device of claim 8 , wherein the first layer and the perpendicular magnetic anisotropy ferromagnet layer are each tilted between about 5 degrees and about 35 degrees from equilibrium.
10. The magnetoresistive random access memory storage device of claim 8 , wherein the first layer has a thickness of between about 0.5 nm and about 10 nm.
11. The magnetoresistive random access memory storage device of claim 8 , wherein the perpendicular magnetic anisotropy ferromagnet layer has a thickness of between about 2 nm and about 8 nm.
12. The magnetoresistive random access memory storage device of claim 8 , wherein the spacer layer comprises at least one of MgO, AlOx, an oxide containing material, Cu, Ag, or combinations and mixtures thereof.
13. A magnetoresistive random access memory storage device, comprising:
a reference layer structure, comprising:
a first layer, comprising an in-plane ferromagnet layer or a tilted perpendicular magnetic anisotropy polarizing layer, wherein the in-plane ferromagnet layer has an equilibrium axis parallel with a first surface, wherein the tilted perpendicular magnetic anisotropy polarizing layer has an equilibrium axis perpendicular to the first surface;
a nonmagnetic metal layer disposed on the first surface of the first layer, wherein the metal layer comprises ruthenium; and
a perpendicular magnetic anisotropy ferromagnet layer disposed on the metal layer, wherein the perpendicular magnetic anisotropy ferromagnet layer has an equilibrium axes perpendicular to the first surface, wherein magnetizations of both the first layer and the perpendicular magnetic anisotropy ferromagnet layer are each tilted away from respective equilibrium axes;
a spacer layer; and
a free layer, wherein the spacer layer is coupled to the reference layer structure and the free layer, wherein the first layer maintains a saturation magnetization (Ms) greater than about 700 emu/cm 3 and the free layer only directly connects to the spacer layer.