Spin-orbit torque magnetoresistive random access memory with magnetic field-free current-induced perpendicular magnetization reversal
Spin-orbit torque magnetoresistive random-access memory (SOT-MRAM) cells that undergo perpendicular magnetization switching in the absence of an in-plane magnetic field and methods for their operation are provided. The SOT-MRAM cells use cobalt-iron-boron alloys, cobalt-iron alloys, metallic cobalt, and/or metallic iron as the ferromagnetic free layer in a magnetic tunnel junction. By designing the ferromagnetic layer with appropriate lateral dimensions and operating the SOT-MRAM cells with an appropriate charge current density, deterministic perpendicular magnetization switching is achieved without the need to apply an external in-plane bias collinear with the charge current.
1. A field free method of deterministically switching a spin-orbit torque magnetoresistive random-access memory cell, the memory cell comprising:
a structurally symmetric circular magnetic tunnel junction comprising:
a free layer comprising CoFeB, CoFe, metallic cobalt, or metallic iron and having a perpendicular direction of magnetization;
a pinned layer comprising a ferromagnetic material having a fixed perpendicular direction of magnetization; and
a barrier layer comprising an electrically insulating material separating the free layer from the pinned layer;
a structurally symmetric spin current layer comprising a non-magnetic material in contact with the free layer at an interface, wherein the spin current layer is not interfaced with a strain-inducing layer; and
a write line in electrical communication with the spin current layer; and
a read line in electrical communication with the magnetic tunnel junction,
the method comprising:
passing an in-plane write current through the spin current layer in the absence of a colinear in-plane magnetic field, whereby an out-of-plane spin current running parallel with the direction of magnetization of the free layer is generated in the spin current layer, giving rise to a spin torque in the free layer that deterministically fully reverses the perpendicular direction of magnetization of the free layer, wherein the reversal of the perpendicular direction of magnetization is not strain-mediated; and
passing a read current through the magnetic tunnel junction and measuring the resistance of the magnetic tunnel junction.
2. The method of claim 1 , wherein the free layer comprises CoFeB and has a diameter in the range from 40 nm to 63 nm, and the write current density is less than 1.75×10 13 A/m 2 .
3. The method of claim 2 , wherein the free layer has a diameter of less than 60 nm.
4. The method of claim 2 , wherein the write current density is in the range from 1.75×10 13 A/m 2 to 1.10×10 13 A/m 2 .
5. The method of claim 2 , wherein the spin current layer comprises platinum.
6. The method of claim 5 , wherein the free layer comprises metallic cobalt and has a diameter in the range from 45 nm to 75 nm, and the write current density is less than 1.60×10 13 A/m 2 .
7. The method of claim 6 , wherein the write current density is in the range from 1.60×10 13 A/m 2 to 1.00×10 13 A/m 2 .
8. The method of claim 6 , wherein the spin current layer comprises platinum.
9. The method of claim 1 , wherein the free layer comprises metallic cobalt and has a diameter of in the range from 45 nm to 75 nm, and the write current density is less than 1.60×10 13 A/m 2 .
10. The method of claim 9 , wherein the write current density is in the range from 1.60×10 13 A/m 2 to 1.00×10 13 A/m 2 .
11. The method of claim 9 , wherein the spin current layer comprises platinum.
12. The method of claim 1 , wherein the free layer comprises CoFe.
13. The method of claim 12 , wherein the spin current layer comprises platinum.
14. The method of claim 1 , wherein the free layer comprises metallic iron.
15. The method of claim 14 , wherein the spin current layer comprises platinum.
16. A spin-orbit torque magnetic random-access memory cell comprising:
a structurally symmetric circular magnetic tunnel junction comprising:
a free layer comprising CoFeB, CoFe, metallic cobalt, or metallic iron and having a perpendicular magnetic anisotropy, the free layer having a diameter in the size range from 35 nm to 80 nm;
a pinned layer comprising a ferromagnetic material having a fixed perpendicular direction of magnetization; and
a barrier layer comprising an electrically insulating material separating the free layer from the pinned layer; and
a structurally symmetric spin current layer comprising a non-magnetic material in contact with the free layer at an interface, wherein the Dyzaloshinskii-Moriya interaction at the interface is in the range from 0.2 mJ/m 2 to 3.2 mJ/m 2 .
17. The cell of claim 16 , further comprising:
a write line in electrical communication with the spin current layer; and
a read line in electrical communication with the magnetic tunnel junction.
18. The cell of claim 16 , wherein the free layer comprises CoFeB and has a diameter in the range from 40 nm to 63 nm.
19. The cell of claim 18 , wherein the free layer has a diameter of less than 60 nm.
20. The cell of claim 16 , wherein the free layer comprises metallic cobalt and has a diameter in the size range from 45 nm to 75 nm.
21. The cell of claim 16 , wherein the free layer comprises CoFe.
22. The cell of claim 16 , wherein the free layer comprises metallic iron.
23. The method of claim 1 , wherein the free layer has a diameter in the size range from 35 nm to 80 nm and the Dyzaloshinskii-Moriya interaction at the interface is in the range from 0.2 mJ/m 2 to 3.2 mJ/m 2 .
24. The method of claim 23 , wherein the Dyzaloshinskii-Moriya interaction at the interface is in the range from 0.4 to 2.1 mJ/m 2 .
25. The cell of claim 16 , wherein the Dyzaloshinskii-Moriya interaction at the interface is in the range from 0.4 mJ/m 2 to 2.1 mJ/m 2 .