High speed low power magnetic devices based on current induced spin-momentum transfer

• US 7,170,778 B2
• Filed: 10/13/2005
• Issued: 01/30/2007
• Est. Priority Date: 08/19/2003
• Status: Active Grant

• Current Assignee: New York University
• Original Assignee: New York University
• Inventors: Kent, Andrew, Ozyilmaz, Barbaros, Gonzalez Garcia, Enrique
• Primary Examiner(s): Nguyen; Viet Q.
• Application Number:
  US11/250,791
• Publication Number:
  US 20060030058A1
• Time in Patent Office: 474 Days
• Field of Search: 365/171, 365/158, 365/173, 365/97, 365/225.6, 365/66
• US Class Current: 365/171
• 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 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: G11C 11/1673 Reading or sensing circuits or methods
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: G11C 11/5607 using magnetic storage elements
• CPC Class Codes: H01F 10/123 having a L10 crystallographic structure, e.g. [Co,Fe][Pt,Pd] thin films
• CPC Class Codes: H01F 10/325 the spacer being noble metal
• CPC Class Codes: H01F 10/3286 Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
• CPC Class Codes: H01L 29/82 controllable by variation of the magnetic field applied to the device
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

The present invention generally relates to the field of magnetic devices for memory cells that can serve as non-volatile memory. More specifically, the present invention describes a high speed and low power method by which a spin polarized electrical current can be used to control and switch the magnetization direction of a magnetic region in such a device. The magnetic device comprises a pinned magnetic layer with a fixed magnetization direction, a free magnetic layer with a free magnetization direction, and a read-out magnetic layer with a fixed magnetization direction. The pinned magnetic layer and the free magnetic layer are separated by a non-magnetic layer, and the free magnetic layer and the read-out magnetic layer are separated by another non-magnetic layer. The magnetization directions of the pinned and free layers generally do not point along the same axis. The non-magnetic layers minimize the magnetic interaction between the magnetic layers. A current is applied to the device to induce a torque that alters the magnetic state of the device so that it can act as a magnetic memory for writing information. The resistance, which depends on the magnetic state of the device, is measured to thereby read out the information stored in the device.

Claims

1. A method of magnetic switching using current induced spin-momentum transfer, said method comprising the steps of:

applying an electric current to a magnetic device comprising a pinned magnetic layer having a pinned magnetic vector and a free magnetic layer having a magnetization vector with at least a first and second stable magnetic state vector;

transferring the spin-momentum of the pinned magnetic layer to the free magnetic layer while the electric current is applied; and

stopping said electric current application when the magnetization vector of the free magnetic layer changes from one of said magnetic state vectors to the other of said magnetic state vectors.

2. The method of magnetic switching according to claim 1, wherein the magnetic

device further comprises a read-out magnetic layer having a fixed magnetization vector.

3. The method of magnetic switching according to claim 2 further comprising the step of:

utilizing the fixed magnetization vector of the read-out magnetic layer to determine a state of the free magnetic layer.

4. The method of magnetic switching according to claim 1, wherein said electric current comprises two current pulses wherein one of said two current pulses includes a negative current pulse and the other of said two current pulses includes a positive current pulse.

5. The method of magnetic switching according to claim 2, wherein the first stable magnetic state vector is parallel to the magnetization vector of the read-out magnetic layer, and the second stable magnetic state vector is anti-parallel to the magnetization vector of the read-out magnetic layer.

6. The method of magnetic switching according to claim 2, wherein the free magnetic layer further includes third and fourth stable magnetic state vectors, said first, second, third and fourth stable magnetic state vectors being coplanar with each other and each oriented in a respective direction such that the directions are separated by approximately 90°

, and the magnetization vector of the read-out layer having an in-plane component that is neither parallel nor separated by 45°

with respect to each of the stable magnetic state vectors of the free magnetic layer, and

the stopping step is performed when the magnetization vector of the free magnetic layer has rotated to one of the at least first, second, third, and fourth stable magnetic state vectors.

7. The method of magnetic switching according to claim 2, further comprising the step of applying the current through the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer.

8. A method of writing and reading data in a magnetic memory device comprising the steps of:

applying an electric current to a magnetic device comprising a pinned magnetic layer having a pinned magnetic vector and a free magnetic layer having a magnetization vector with at least first and second stable magnetic state vectors, and a read-out magnetic layer having a fixed magnetization vector, wherein the electric current comprises two current pulses wherein one of the two current pulses includes a negative current pulse and the other of the two current pulses includes a positive current pulse;

transferring the spin-momentum of the pinned magnetic layer to the free magnetic layer while the electric current is applied; and

stopping the electric current when the magnetization vector of the free magnetic layer has rotated to one of the at least first and second stable magnetic state vectors while the electric current is applied; and

measuring a resistance through at least the read-out magnetic layer and the free magnetic layer.

9. The method of writing and reading data in a magnetic memory device according to claim 8, further comprising the step of:

utilizing the fixed magnetization vector of the read-out magnetic layer to determine a state of the free magnetic layer of the magnetic device.

10. The method of writing and reading data in a magnetic memory device according to claim 8, further comprising the step of:

utilizing the pinned magnetization vector of the pinned magnetic layer to determine a state of the free magnetic layer of the magnetic device.

11. The method of writing and reading data in a magnetic memory device according to claim 8, wherein the current applying step occurs in a sub-nanosecond period of time.

12. The method of writing and reading data in a magnetic memory device according to claim 8, wherein the first stable magnetic state is parallel to the magnetization vector of the read-out magnetic layer, and the second stable magnetic state is anti-parallel to the magnetization vector of the read-out magnetic layer.

13. The method of writing and reading data in a magnetic memory device according to claim 8, wherein the free magnetic layer further includes third and fourth stable magnetic state vectors, said first, second, third, and fourth stable magnetic state vectors being co-planar with each other and each oriented in a respective direction such that the directions are separated by approximately 90°

, and the magnetization vector of the read-out layer having an in-plane component that is neither parallel nor separated by 45°

with respect to each of the stable magnetic state vectors of the free magnetic layer, and

the stopping step is performed when the magnetization vector of the free magnetic layer has rotated to one of the at least first, second, third, and fourth stable magnetic state vectors.

14. The method of writing and reading data in a magnetic memory device according to claim 8, further comprising the step of applying current through the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer.

15. The method of writing and reading data in a magnetic memory device according to claim 8, further comprising the step of measuring the resistance across the magnetic device.

16. A magnetic device comprising:

a pinned magnetic layer with a magnetization vector having a fixed magnetization direction;

a free magnetic layer with at least one magnetization vector having a changeable magnetization direction; and

a first non-magnetic layer spatially separating said free magnetic layer and said pinned magnetic layer.

17. The magnetic device according to claim 16, wherein one of said magnetization directions of said pinned magnetic layer and said free magnetic layer lie along an axis which is different than at least one of the axes along which the other magnetization directions lie.

18. The magnetic device according to claim 16 further comprising:

a read-out magnetic layer with a magnetization vector having a fixed magnetization direction; and

a second non-magnetic layer spatially separating said free magnetic layer and said read-out magnetic layer.

19. The magnetic device according to claim 18, wherein one of said magnetization directions of said pinned magnetic layer, said free magnetic layer, and said read-out magnetic layer lies along an axis which is different than at least one of the axes along which the other magnetization directions lie.

20. The magnetic device according to claim 16, wherein:

said fixed magnetization direction of said pinned magnetic layer is perpendicular to a plane of said free magnetic layer; and

said changeable magnetization direction of said free magnetic layer is perpendicular to an axis extending longitudinally through said magnetic device.

21. The magnetic device according to claim 18, wherein said changeable magnetization direction of said free magnetic layer and said fixed magnetization direction of said read-out layer switch between being in anti-parallel alignment and parallel alignment.

22. The magnetic device according to claim 16, wherein the mutual magnetic interaction between said free magnetic layer and said pinned magnetic layer is minimized.

23. The magnetic device according to claim 18, wherein said magnetization direction of said magnetization vector of said free magnetic layer represents a bit of information.

24. The magnetic device according to claim 16, wherein:

said magnetic device is substantially pillar-shaped and having a characteristic dimension less than 200 nm; and

said pinned magnetic layer, said first non-magnetic layer, and said free magnetic layer are each approximately 1 nm to 50 nm thick.

25. The magnetic device according to claim 18, wherein:

said magnetic device is substantially pillar-shaped and having a characteristic dimension less than 200 nm; and

said pinned magnetic layer, said first non-magnetic layer, said free magnetic layer, said second non-magnetic layer, and said read-out magnetic layer are each approximately 1 nm to 50 urn thick.

26. The magnetic device according to claim 16, wherein said pinned magnetic layer and said free magnetic layer are comprised of a member of the group consisting of Co, Ni, Fe, an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, an alloy of Co, Ni, and Fe, and permalloy Ni_1-xFe_x.

27. The magnetic device according to claim 18, wherein said pinned magnetic layer, said free magnetic layer, and said read-out magnetic layer are comprised of a member of the group consisting of Co, Ni, Fe, an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, an alloy of Co, Ni, and Fe, and permalloy Ni_1-xFe_x.

28. The magnetic device according to claim 16, wherein said pinned magnetic layer and said free magnetic layer are comprised of a non-magnetic metal and a member of the group consisting of an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, an alloy of Co, Ni, and Fe, such that said non-magnetic metal and said member are ferromagnetically ordered at room temperature.

29. The magnetic device according to claim 18, wherein said pinned magnetic layer, said free magnetic layer, and said read-out magnetic layer are comprised of a non-magnetic metal and a member of the group consisting of an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, an alloy of Co, Ni, and Fe, such that said non-magnetic metal and said member are ferromagnetically ordered at room temperature.

30. The magnetic device according to claim 28, wherein said non-magnetic metal is a member of the group consisting of Cu, Pd, Pt, and NiMnSb.

31. The magnetic device according to claim 29, wherein said non-magnetic metal is a member of the group consisting of Cu, Pd, Pt, and NiMnSb.

32. The magnetic device according to claim 16, wherein said pinned magnetic layer and said free magnetic layer comprise either CrO₂ or Fe₃O₄.

33. The magnetic device according to claim 16, wherein said non-magnetic layer is comprised of at least one member of the group consisting of Cu, Cr, Au, Ag, and Al.

34. The magnetic device according to claim 18, wherein said non-magnetic layers are comprised of at least one member of the group consisting of Cu, Cr, Au, Ag, and Al.

35. The magnetic device according to claim 18, wherein the mutual magnetic interaction between said free magnetic layer and said read-out magnetic layer is minimized.

36. A memory system including a memory cell comprising:

a pinned magnetic layer with a magnetization vector having a fixed magnetization direction;

a free magnetic layer with at least one magnetization vector having a changeable magnetization direction;

a first non-magnetic layer spatially separating said free magnetic layer and said pinned magnetic layer;

a read-out magnetic layer with a magnetization vector having a fixed magnetization direction; and

a second non-magnetic layer spatially separating said free magnetic layer and said read-out magnetic layer.

37. The memory system according to claim 36, wherein one of said magnetization directions of said pinned magnetic layer, said free magnetic layer, and said read-out magnetic layer lies along an axis which is different than at least one of the axes along which said other magnetization directions lie.

38. The memory system according to claim 36, further comprising a means for measuring the resistance between said pinned magnetic layer and said read-out magnetic layer.

39. The memory system according to claim 38, wherein said resistance measuring means comprises a voltmeter connected to said pinned magnetic layer and said read-out magnetic layer.

40. The memory system according to claim 36, further comprising an electric current source connected to said pinned magnetic layer and said read out layer so that an electric current can traverse said memory cell, wherein said electric current comprises at least one current pulse.

41. The memory system according to claim 40, wherein said electric current comprises two current pulses, wherein one of said two current pulses is a negative current pulse and the other of said two current pulses is a positive current pulse.

42. The memory system according to claim 40, wherein said electric current is applied in a sub-nanosecond period of time.

43. The memory system according to claim 36, wherein the mutual magnetic interaction between said free magnetic layer and said read-out magnetic layer is minimized.

46. The memory system according to claim 36, wherein the mutual magnetic interaction between said free magnetic layer and said pinned magnetic layer is minimized.

44. A method of performing a logical operation comprising the steps of:

applying first and second electric current input signals to a magnetic device comprising a pinned magnetic layer having a pinned magnetic vector, a free magnetic layer having a magnetization vector with at least a first and second stable magnetic state vector, and a read-out magnetic layer having a fixed magnetization vector, wherein said first and second stable magnetic state vectors are not parallel to the pinned magnetic vector; and

transferring the spin-momentum of the pinned magnetic layer to the free magnetic layer while the first and second electric current input signals are applied so that the magnetization vector of the free magnetic layer changes from one of said magnetic state vectors to the other of said magnetic state vectors if a sum of the first and second current input signals exceeds a predetermined level;

else, maintaining the magnetization vector of the free magnetic layer if the sum of the first and second current input signals does not exceed the predetermined level.

45. The method of performing a logical operation according to claim 44, further comprising the step of:

switching the magnetization vector of the free magnetic layer from one of said magnetic state vectors to the other of said magnetic state vectors.