Stress assisted current driven switching for magnetic memory applications
View Patent ↗A method and system for providing a magnetic memory is disclosed. The method and system include providing a plurality of magnetic elements and providing at least one stress-assist layer. Each of the plurality of magnetic elements is configured to be written using spin transfer. The at least one stress-assist layer is configured to exert at least one stress on at least one magnetic element of the plurality of magnetic elements during writing. The reduction of spin-transfer switching current is due to stress exerted by the stress-assist layer on the magnetic elements during writing. Stability of the magnetic memory with respect to thermal fluctuations is not compromised because the energy barrier between the two magnetization states is unchanged once the switching current is turned off.
1. A magnetic memory comprising:
a plurality of magnetic elements, each of the plurality of magnetic elements being configured to be written using spin transfer;
at least one stress-assist layer configured to exert at least one stress on at least one magnetic element of the plurality of magnetic elements during writing.
2. The magnetic memory of claim 1 wherein the at least one stress induces at least one anisotropy on the at least one magnetic element during writing, the at least one anisotropy reducing a total anisotropy energy perpendicular to a stable state of the at least one magnetic element.
3. The magnetic memory of claim 1 wherein the magnetic element includes a plurality of layers and wherein the at least one stress is in a direction perpendicular to a plane of at least one of the plurality of layers.
4. The magnetic memory of claim 3 wherein at least one layer is a free layer.
5. The magnetic memory of claim 4 wherein the free layer includes a ferromagnetic layer and a capping layer, the free layer having a high positive magnetostriction.
6. The magnetic memory of claim 5 wherein the free layer has a surface anisotropy and a total anisotropy perpendicular to a stable state of the free layer, the capping layer configured to modify the surface anisotropy to reduce the total perpendicular anisotropy and capable of including Cu, Au, Pd or Pt.
7. The magnetic memory of claim 4 wherein the at least one magnetic element includes at least one spin tunneling junction.
8. The magnetic memory of claim 4 wherein the at least one magnetic element includes at least one spin valve.
9. The magnetic memory of claim 4 wherein the at least one magnetic element includes at least one spin valve portion and at least one spin tunneling junction portion the at least one spin valve portion and the at least one spin tunneling junction portion sharing the free layer.
10. The magnetic memory of claim 9 wherein the at least one spin valve portion includes a first pinned layer having a first ferromagnetic layer closest to the free layer and wherein the at least one spin tunneling junction portion includes a second pinned layer having a second ferromagnetic layer closest to the pinned layer, the first ferromagnetic layer being pinned in a first direction, and the second ferromagnet layer being pinned in a second direction opposite to the first direction.
11. The magnetic memory of claim 1 wherein the at least one magnetic element has a plurality of sides and wherein the at least one stress-assist layer surrounds the plurality of sides of the at least one magnetic element.
12. The magnetic memory of claim 1 further comprising:
a plurality of word write lines; and
wherein the at least one stress-assist layer resides between the plurality of word lines and the at least one magnetic element.
13. The magnetic memory of claim 1 wherein the stress assist layer further includes bilayer of at least one of IrO 2 /PZT, MnO/PZT, TiO y /PZT, Al 2 O 3 /PZT, Al 2 O 3 /PMN, Al 2 O 3 /SrBaTiO 3 , SiO 2 /PZT or SiO 2 /SrBaTiO 3 , where PZT is PbZr 1-x Ti x O 3 , wherein PMN is PbMn 1-x Nb X O 3 with PbTiO 3 and wherein x is an fraction less than 1.
14. A magnetic memory comprising:
a plurality of magnetic elements, each of the plurality of magnetic elements being configured to be written using spin transfer;
at least one stress-assist layer configured to exert at least one stress on at least one magnetic element of the plurality of magnetic elements during writing, the stress-assist layer including at least one of a piezoelectric and an electrostrictive material.
15. The magnetic memory of claim 1 wherein each of the plurality of magnetic elements further includes a first lead and a second lead for driving current through the magnetic element in a perpendicular-to-a plane direction to allow the magnetic element to be written using spin transfer.
16. The magnetic memory of claim 1 wherein each of the plurality of magnetic elements includes a free layer having a first ferromagnetic layer having a first magnetization, a second ferromagnetic layer having a second magnetization, and a separation layer between the first ferromagnetic layer and the second ferromagnetic layer, the separation layer configured to align the first magnetization and the second magnetization antiparallel.
17. The magnetic memory of claim 14 wherein each of the plurality of magnetic elements further includes a first lead and a second lead for driving current through the magnetic element in a perpendicular-to-a plane direction to allow the magnetic element to be written using spin transfer.
18. The magnetic memory of claim 14 wherein each of the plurality of magnetic elements includes a free layer having a first ferromagnetic layer having a first magnetization, a second ferromagnetic layer having a second magnetization, and a separation layer between the first ferromagnetic layer and the second ferromagnetic layer, the separation layer configured to align the first magnetization and the second magnetization antiparallel.
19. The magnetic memory of claim 1 wherein each of the plurality of magnetic elements has at least one layer and being configured to be written using spin transfer of charge carriers polarized by at least one layer having an in-plane magnetization.
20. The magnetic memory of claim 1 wherein each of the plurality of magnetic elements further includes a ferromagnetic free layer and a nonmagnetic capping layer on the ferromagnetic free layer, the nonmagnetic capping layer reducing the perpendicular anisotropy of the ferromagnetic free layer.
21. The magnetic memory of claim 1 wherein the at least one stress-assist layer being adjacent to a portion of each of the plurality of magnetic elements without residing above or below any of the plurality of magnetic elements.
22. The magnetic memory of claim 1 wherein the plurality of magnetic elements includes at least one ferromagnetic layer, each of the at least one ferromagnetic layer having an in-plane magnetization.
23. The magnetic memory of claim 14 wherein each of the plurality of magnetic elements further includes a ferromagnetic free layer and a nonmagnetic capping layer on the ferromagnetic free layer, the nonmagnetic capping layer reducing the perpendicular anisotropy of the ferromagnetic free layer.
24. A magnetic memory comprising:
a plurality of magnetic elements, each of the plurality of magnetic elements being configured to be written using spin transfer, each of the plurality of magnetic elements including a ferromagnetic free layer having an perpendicular anisotropy and a nonmagnetic capping layer on the ferromagnetic free layer, the nonmagnetic capping layer reducing the perpendicular anisotropy of the ferromagnetic free layer.
25. The magnetic memory of claim 24 wherein the ferromagnetic free layer includes at least one of Co, Fe, and Ni and wherein the nonmagnetic capping layer includes at least one of Pt, Pd, Au, Ta, and Cr.