Stress assisted current driven switching for magnetic memory applications

• US 7,282,755 B2
• Filed: 11/14/2003
• Issued: 10/16/2007
• Est. Priority Date: 11/14/2003
• Status: Expired due to Fees

• Current Assignee: Samsung Semiconductor Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Grandis, Inc. (Samsung Electronics Co. Ltd.)
• Inventors: Huai, Yiming, Pakala, Mahendra
• Primary Examiner(s): TRAN, MICHAEL THANH
• Application Number:
  US10/714,357
• Publication Number:
  US 20050106810A1
• Time in Patent Office: 1,432 Days
• Field of Search: 438/3, 365/158, 365/173
• US Class Current: 257/295
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: H01F 10/3272 by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets
• CPC Class Codes: H01F 10/3286 Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
• CPC Class Codes: H10B 61/22 of the field-effect transistor [FET] type
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

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.

Claims

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.

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.

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.

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.

2. A magnetic memory comprising:

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;

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.

8. 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;

wherein at least one layer is a free layer; and

wherein the at least one magnetic element includes at least one spin valve.

9. A magnetic memory comprising:

a plurality of magnetic elements, each of the plurality of magnetic elements being configured to be written using a 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;

wherein at least one layer is a free layer; and

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.

13. 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;

wherein the stress assist layer further includes bilayer of at least one of IrO₂/PZT, MnO/PZT, TiO_y/PZT, Al₂O₃/PZT, Al₂O₃/PMN, Al₂O₃/SrBaTiO₃, SiO₂/PZT or SiO₂/SrBaTiO₃, where PZT is PbZr_1-xTi_xO₃, wherein PMN is PbMn_1-xNb_XO₃ with PbTiO₃ and wherein x is a 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;

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 seperation layer configured to align the first magnetization and the second magnetization antiparallel.

15. 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;

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. 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;

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 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;

wherein each of the plurality of magnetic elements has at least one layer and being configured to be written using spin transferof charge carriers polarized by at least one layer having an in-plane magnetization.

18. 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;

wherein each of the plurality of magnetic elements further includes a ferromagnetic free layer and a non magnetic capping layer on the ferromagnetic free layer, the nonmagnetic capping layer reducing the perpendicular anisotropy of the ferromagnetic free layer.

19. 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;

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.

20. 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;

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.

21. 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 on 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;

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.

22. 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.

23. The magnetic memory of claim 22 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.