Multi-bit magnetic random access memory device

• US 20050259463A1
• Filed: 04/29/2005
• Published: 11/24/2005
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lim, Chee-kheng
• Granted Patent: US 7,502,248 B2
• Time in Patent Office: Days
• US Class Current: 365/158
• 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 11/1675 Writing or programming circuits or methods
• CPC Class Codes: G11C 11/5607 using magnetic storage elements
• CPC Class Codes: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• CPC Class Codes: H01F 10/3263 the exchange coupling being symmetric, e.g. for dual spin valve, e.g. NiO/Co/Cu/Co/Cu/Co/NiO
• 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: H01F 10/329 Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

A multi-bit magnetic random access memory device and a method for writing to and sensing the multi-bit magnetic random access memory device. The magnetic memory includes a memory cell with a multilayer structure having a plurality of data layers which can each store one bit. The structure includes a plurality of magnetically changeable ferromagnetic layers, a ferromagnetic reference layer having a fixed magnetization state, a first spacer layer separating the magnetically changeable ferromagnetic layers, and a second spacer layer separating the ferromagnetic reference layer from the magnetically changeable ferromagnetic layers. This structure allows for more than one-bit to be stored as well as for efficient writing and reduced power consumption.

Claims

1. A magnetic memory comprising:

first and second magnetically changeable ferromagnetic layers;

a ferromagnetic reference layer having a fixed magnetization state;

a first spacer layer interposed between the first and second magnetically changeable ferromagnetic layers; and

a second spacer layer interposed between the ferromagnetic reference layer from the second magnetically changeable ferromagnetic layers.

2. The magnetic memory according to claim 1, further comprising at least a third magnetically changeable ferromagnetic layer, wherein the first, second, and third magnetically changeable ferromagnetic layers are separated from one another by first, second and third spacer layers.

3. The magnetic memory according to claim 1, wherein the spacer layer is conductive.

4. The magnetic memory according to claim 1, wherein the spacer layer is non-conductive.

5. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a same ferromagnetic material.

6. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a differing ferromagnetic material.

7. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a same thickness.

8. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a differing thickness.

9. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a same saturation magnetic moment.

10. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a differing saturation magnetic moment.

11. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a same magnetocrystalline anisotropy.

12. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have a differing magnetocrystalline anisotropy.

13. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers comprise one of an in-plane magnetocrystalline anisotropy, an out-of-plane magnetocrystalline anisotropy, and a combination of an in-plane magnetocrystalline anisotropy and an out-of-plane magnetocrystalline anisotropy.

14. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers comprise an alloy of Ni, Fe and Co, or a combination thereof.

15. The magnetic memory according to claim 1, wherein each of the first and second magnetically changeable ferromagnetic layers stores one bit of binary information.

16. The magnetic memory according to claim 1, wherein the first and second magnetically changeable ferromagnetic layers have differing spin precession frequencies.

17. The magnetic memory according to claim 1, wherein a cell formed by the ferromagnetic and spacer layers includes rounded ends for suppressing magnetic domain nucleation.

18. The magnetic memory according to claim 1, wherein a cell formed by the ferromagnetic and spacer layers has as aspect ratio in a range of about 1.1 and 5.0.

40. A sensing method for a device as recited in claim 1, wherein selective writing of the first and second magnetically changeable ferromagnetic layers is performed using a combination of a saturation magnetization ratio, magnetic isotropy ratio, easy to hard axis field magnitude ratio, and/or a spin polarized current density ratio.

41. The sensing method according to claim 40, wherein when the first and second magnetically changeable ferromagnetic layers are in a (1, 1) configuration, a readback signal will be different from a (0,0) configuration by a magnetoresistance ratio of a structure including the second magnetically changeable ferromagnetic layer, the second spacer, and the reference layer.

42. The sensing method according to claim 40, wherein when the first and second magnetically changeable ferromagnetic layers are in a (1, 0) configuration, a readback signal will be different from a (0,0) configuration by a magnetoresistance ratio of a structure including the first and second magnetically changeable ferromagnetic layers and the first spacer.

43. The sensing method according to claim 40, wherein when the first and second magnetically changeable ferromagnetic layers are in a (0, 1) configuration, a readback signal will be different from a (0,0) configuration by the sum of magnetoresistance ratios of a first structure including the second magnetically changeable ferromagnetic layer, the second spacer, and the reference layer and a second structure including the first and second magnetically changeable ferromagnetic layers and the first spacer.

44. The sensing method according to claim 40, further comprising increasing readback signal states by increasing a difference between a magnetoresistance ratio of a first structure including the second magnetically changeable ferromagnetic layer, the second spacer, and the reference layer and a magnetoresistance ratio of a second structure including the first and second magnetically changeable ferromagnetic layers and the first spacer.

19. A writing method for a magnetic memory comprising a memory cell comprising at least first and second magnetically changeable ferromagnetic layers, and a ferromagnetic reference layer, the method defining a writing event comprising:

applying a first magnetic field below a switching field along a long axis of the memory cell; and

applying a second magnetic field orthogonal to the first magnetic field, wherein the first magnetic field is turned-off after the second magnetic field is turned-off.

20. The writing method for a magnetic memory according to claim 19, wherein a pulse of the first magnetic field has a longer duration than a pulse of the second magnetic field.

21. The writing method for a magnetic memory according to claim 19, wherein the first and second magnetically changeable ferromagnetic layers are independently written using a single writing event.

22. The writing method for a magnetic memory according to claim 19, wherein a pulse of the second magnetic field has a rise time which is equal to or less than 1 ns.

23. The writing method for a magnetic memory according to claim 19, wherein the first magnetically changeable ferromagnetic layer has a damping constant greater than the damping constant of the second magnetically changeable ferromagnetic layer such that a writing response time of the first magnetically changeable ferromagnetic layer is delayed to accomplish independent writing.

24. The writing method for a magnetic memory according to claim 19, wherein the pulse of the magnetic fields are shaped to generate a fast rising field to create a rise time that activates spin precession.

25. The writing method for a magnetic memory according to claim 19, wherein the pulse of the magnetic fields are shaped in one of a trapezoidal or exponential shape.

26. The writing method for a magnetic memory according to claim 19, further comprising sensing stored information in each of the first and second magnetically changeable ferromagnetic layers using a magnetoresistance effect.

27. The writing method for a magnetic memory according to claim 19, further comprising terminating the second magnetic field when the magnetization of the first magnetically changeable ferromagnetic layer has been through (n+½

) precession cycles, where n is a number of precession cycles.

28. The writing method according to claim 19, wherein a pulse duration of the first magnetic field is in a range of 0.2 to 10 ns, while a pulse duration of the second magnetic field is in a range of 0.01 to 5 ns.

29. The writing method according to claim 19, further comprising controlling at least one of a saturation magnetization and magnetic anisotropy ratio of the first and second magnetically changeable ferromagnetic layers to achieve independent writing.

30. The writing method according to claim 19, wherein the first and second magnetically changeable ferromagnetic layers and the first spacer as a structure have a differing MR ratio than a structure including the second magnetically changeable ferromagnetic layer, the second spacer, and the reference layer.

31. The writing method according to claim 19, wherein the first and second magnetically changeable ferromagnetic layers are written as (1,1) and (0,0) using a single writing event, and (1,0) and (0,1) using two writing events.

32. The writing method according to claim 19, wherein the two magnetically changeable ferromagnetic layers are written as (1,0) by first writing a 1 in both of the first and second magnetically changeable ferromagnetic layers, followed by a second writing event to write a 0 in the magnetically softer ferromagnetic layer.

33. The writing method according to claim 19, wherein the two magnetically changeable ferromagnetic layers are written as (0,1) by first writing a 0 in both magnetically changeable ferromagnetic layers, followed by a second writing event to write a 1 in the magnetically softer free layer.

34. The writing method according to claim 19, further comprising inducing orthogonal unidirectional an isotropy in one of the first and second magnetically changeable ferromagnetic layers.

35. The writing method according to claim 19, wherein the first and second magnetically changeable ferromagnetic layers are written separately using spin-polarized current induced switching by creating asymmetry in a switching current threshold for the first and second magnetically changeable ferromagnetic layers.

36. The writing method according to claim 19, wherein the first and second magnetically changeable ferromagnetic layers are written using spin polarized current induced switching in combination with an externally applied magnetic field.

37. The writing method according to claim 19, further comprising increasing a damping coefficient of one of the first and second magnetically changeable ferromagnetic layers using a capping layer.

38. The writing method according to claim 19, further comprising setting a magnetization pinning axis of the ferromagnetic reference layer orthogonal to the long axis of the memory cell.

39. The writing method according to claim 19, further comprising terminating the second magnetic field when the magnetization of one of the first and second magnetically changeable ferromagnetic layers has been through (n+½

) precession cycles, where n is the number of precession cycles.