Spin-transfer torque magnetic random access memory with perpendicular magnetic anisotropy multilayers
View Patent ↗A spin-transfer torque magnetic random access memory (STTMRAM) element includes a composite fixed layer formed on top of a substrate and a tunnel layer formed upon the fixed layer and a composite free layer formed upon the tunnel barrier layer. The magnetization direction of each of the composite free layer and fixed layer being substantially perpendicular to the plane of the substrate. The composite layers are made of multiple repeats of a bilayer unit which consists of a non-magnetic insulating layer and magnetic layer with thicknesses adjusted in a range that makes the magnetization having a preferred direction perpendicular to film plane.
1. A spin transfer torque magnetic random access memory (STTMRAM) element comprising:
a composite free layer including one or more repeats of a bilayer unit that comprises an insulator layer and a magnetic layer, said magnetic layer having a variable magnetization direction substantially perpendicular to a layer plane thereof;
a magnetic pinned layer having a first fixed magnetization direction substantially perpendicular to a layer plane thereof;
a tunnel barrier layer formed between said composite free layer and said magnetic pinned layer; and
a magnetic fixed layer coupled to said magnetic pinned layer through an anti-ferromagnetic coupling layer, said magnetic fixed layer having a second fixed magnetization direction that is substantially perpendicular to a layer plane thereof and is substantially opposite to said first fixed magnetization direction.
2. The STTMRAM element of claim 1 , wherein said anti-ferromagnetic coupling layer is made of ruthenium.
3. The STTMRAM element of claim 1 , wherein said tunnel barrier is made of magnesium oxide.
4. The STTMRAM element of claim 1 , wherein said insulator layer of said bilayer unit is made of a magnesium oxide compound, said magnetic layer of said bilayer unit comprises cobalt and iron.
5. The STTMRAM element of claim 1 , wherein said insulator layer of said bilayer unit is made of an insulator material selected from the group consisting of aluminum oxide, zinc oxide, titanium oxide, strontium oxide, ruthenium oxide, silicon oxide, zirconium oxide, hafnium oxide, tantalum oxide, silicon nitride, and any combinations thereof.
6. The STTMRAM element of claim 1 , wherein said magnetic layer of said bilayer unit further comprises first and second magnetic sublayers separated by a first boron absorption layer, said first and second magnetic sublayers having said variable magnetization direction substantially perpendicular to layer planes thereof.
7. The STTMRAM element of claim 6 , wherein said first boron absorption layer is made of Ta, Ti, or Ru.
8. The STTMRAM element of claim 6 , wherein said first boron absorption layer is made of Ta, Ti, Ru, Co, Fe, Ni, or any combination thereof.
9. The STTMRAM element of claim 6 , wherein at least one of said first and second magnetic sublayers is made of a CoFeB or CoFe alloy.
10. The STTMRAM element of claim 1 , wherein said magnetic pinned layer comprises iron and cobalt.
11. The STTMRAM element of claim 1 , wherein said magnetic pinned layer further comprises third and fourth magnetic sublayers separated by a second boron absorption layer, said third and fourth magnetic sublayers having said first fixed magnetization direction substantially perpendicular to layer planes thereof.
12. The STTMRAM element of claim 11 , wherein said second boron absorption layer is made of Ta, Ti, or Ru.
13. The STTMRAM element of claim 11 , wherein said second boron absorption layer is made of Ta, Ti, Ru, Co, Fe, Ni, or any combination thereof.
14. The STTMRAM element of claim 11 , wherein at least one of said third and fourth magnetic sublayers is made of a CoFeB or CoFe alloy.
15. The STTMRAM element of claim 1 , further comprising a first magnetic insertion layer formed between said composite free layer and said tunnel barrier layer.
16. The STTMRAM element of claim 15 , wherein said first magnetic insertion layer comprises iron.
17. The STTMRAM element of claim 15 , wherein said first magnetic insertion layer is made of a magnetic metal or alloy selected from the group consisting of Co, Fe, CoFe, B, Ta, Ti, Hf, Cr, and any combinations thereof.
18. The STTMRAM element of claim 1 , further comprising a second magnetic insertion layer formed between said magnetic pinned layer and said tunnel barrier layer.
19. The STTMRAM element of claim 18 , wherein said second magnetic insertion layer comprises iron.
20. The STTMRAM element of claim 18 , wherein said second magnetic insertion layer is made of a magnetic metal or alloy selected from the group consisting of Co, Fe, CoFe, B, Ta, Ti, Hf, Cr, and any combinations thereof.