Multi-state magnetoresistance random access cell with improved memory storage density

• US 20040012994A1
• Filed: 07/17/2002
• Published: 01/22/2004
• Est. Priority Date: 07/17/2002
• Status: Active Grant

• Current Assignee: Everspin Technologies Incorporated
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Goronkin, Herber, Slaughter, Jon M., Korkin, Anatoli A., Savtchenko, Leonid
• Granted Patent: US 7,095,646 B2
• Time in Patent Office: Days
• US Class Current: 365/158
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/5607 using magnetic storage elements

Abstract

A multi-state magnetoresistive random access memory device comprising a pinned ferromagnetic region having a magnetic moment vector fixed in a preferred direction in the absence of an applied magnetic field, an non-ferromagnetic spacer layer positioned on the pinned ferromagnetic region, and a free ferromagnetic region with an anisotropy designed to provide a free magnetic moment vector within the free ferromagnetic region with N stable positions, wherein N is a whole number greater than two, positioned on the non-ferromagnetic spacer layer. The number N of stable positions can be induced by a shape anisotropy of the free ferromagnetic region wherein each N stable position has a unique resistance value.

Claims

1. A multi-state magnetoresistive random access memory device having a resistance, the device comprising:

a substrate;

a first conductive line positioned on the substrate;

a fixed ferromagnetic region positioned proximate to the first conductive line, the fixed ferromagnetic region having a fixed magnetic moment vector fixed in a preferred direction both with and without an applied magnetic field;

a non-ferromagnetic spacer layer positioned on the pinned ferromagnetic region;

a free ferromagnetic region positioned on the non-ferromagnetic spacer layer, the free ferromagnetic region having a free magnetic moment vector that is free to rotate in the presence of an applied magnetic field and where the free ferromagnetic region has an anisotropy that creates more than two stable positions for the free magnetic moment vector wherein the more than two stable positions are oriented relative to the preferred direction of the fixed magnetic moment vector such that each position produces a unique resistance; and

a second conductive line positioned at a non-zero angle to the first conductive line.

2. An apparatus as claimed in claim 1 wherein the anisotropy of the free ferromagnetic region is created by the shape of the free ferromagnetic region.

3. An apparatus as claimed in claim 2 wherein the shape of the free ferromagnetic region is defined approximately by a polar equation given as r(θ

)=1+|A·

cos(N·

θ

−

α

)|, wherein N is a whole number, θ

is an angle in degrees relative to the first and second conductive lines, r is a distance in polar coordinates that is a function of the angle θ

, α

is an angle in degrees that determines the angle of the lobes relative to the first conductive line, and A is a constant.

4. An apparatus as claimed in claim 3 wherein the constant A has a value between 0.1 and 2.0.

5. An apparatus as claimed in claim 2 wherein the shape of the free ferromagnetic layer has at least one lobe oriented parallel to the first conductive line.

6. An apparatus as claimed in claim 3 wherein the angle θ

has continuous values in the range between 0° and

360°

.

7. An apparatus as claimed in claim 1 wherein at least one of the pinned ferromagnetic region and the free ferromagnetic region includes one of iron oxide (Fe₃O₄), chromium oxide (CrO₂), oxides, and semiconductors, wherein the oxides and semiconductors are doped with one or more of iron, cobalt, nickel, magnesium, and chromium.

8. An apparatus as claimed in claim 1 wherein the anisotropy of the free ferromagnetic region is created by an intrinsic anisotropy of a material included in the free ferromagnetic region.

9. An apparatus as claimed in claim 8 wherein the intrinsic anisotropy is created by applying a magnetic field to the free ferromagnetic region.

10. An apparatus as claimed in claim 1 wherein the anisotropy of the free ferromagnetic region is created by growing the free ferromagnetic region with a preferred crystalline orientation.

11. An apparatus as claimed in claim 1 wherein the anisotropy of the free ferromagnetic region is created by growing the free ferromagnetic region with clusters or crystallites that have a shape anisotropy.

12. An apparatus as claimed in claim 1 wherein the more than two stable positions are oriented at a nonzero angle relative to the first and second conductive lines.

13. An apparatus as claimed in claim 1 wherein the magnetic moment of the fixed ferromagnetic region is at a non-zero angle relative to the first and second conductive lines.

14. An apparatus as claimed in claim 1 wherein the stable positions are induced by a shape anisotropy of the free ferromagnetic region.

15. An apparatus as claimed in claim 1 wherein the anisotropy of the free ferromagnetic region is created by the free ferromagnetic region having clusters or crystallites that have a shape anisotropy.

18. An apparatus as claimed in claim 14 wherein the shape of the free ferromagnetic region is defined approximately by a polar equation given as r(θ

)=1+|A·

cos(N·

θ

−

α

)|, wherein N is a whole number, θ

is an angle in degrees relative to the first and second conductive lines, r is a distance in polar coordinates that is a function of the angle θ

, α

is an angle in degrees that determines the angle of the lobes relative to the first conductive line, and A is a constant.

19. An apparatus as claimed in claim 18 wherein the constant A has a value between 0.1 and 2.0.

20. An apparatus as claimed in claim 18 wherein the angle θ

has continuous values in the range between 0° and

360°

.

21. An apparatus as claimed in claim 18 wherein the stable positions are induced by a shape anisotropy of the free ferromagnetic region.

22. An apparatus as claimed in claim 18 wherein the number of stable positions is equal to four.

16. A multi-state magnetoresistive random access memory device comprising:

a substrate;

a first conductive line positioned proximate to the base electrode;

a free ferromagnetic region positioned proximate to the first conductive line, the free ferromagnetic region having a free magnetic moment vector that is free to rotate in the presence of an applied magnetic field and where the free ferromagnetic region has an anisotropy that creates more than two stable positions for the free magnetic moment vector wherein the more than two stable positions are oriented relative to the preferred direction of the fixed magnetic moment vector such that each position produces a unique resistance;

a non-ferromagnetic spacer layer positioned on the free ferromagnetic region;

a fixed ferromagnetic region positioned on the non-ferromagnetic spacer layer, the fixed ferromagnetic region having a fixed magnetic moment vector fixed in a preferred direction both with and without an applied magnetic field; and

a second conductive line positioned at a non-zero angle to the first conductive line.

17. An apparatus as claimed in claim 16 wherein the shape of the free ferromagnetic layer has at least one lobe oriented parallel to the first conductive line.

23. An apparatus as claimed in claim 16 wherein the anisotropy of the free ferromagnetic region is created by an intrinsic anisotropy of a material included in the free ferromagnetic region.

24. An apparatus as claimed in claim 23 wherein the intrinsic anisotropy is created by applying a magnetic field to the free ferromagnetic region.

25. An apparatus as claimed in claim 16 wherein the anisotropy of the free ferromagnetic region is created by growing the free ferromagnetic region with a preferred crystalline orientation.

26. An apparatus as claimed in claim 16 wherein the anisotropy of the free ferromagnetic region is created by growing the free ferromagnetic region with clusters or crystallites that have a shape anisotropy.

27. An apparatus as claimed in claim 16 wherein at least one of the pinned ferromagnetic region and the free ferromagnetic region includes one of iron oxide (Fe₃O₄), chromium oxide (CrO₂), oxides, and semiconductors, wherein the oxides and semiconductors are doped with one or more of iron, cobalt, nickel, magnesium, and chromium.

28. An apparatus as claimed in claim 16 wherein the non-ferromagnetic spacer layer includes one of a dielectric material, such as aluminum oxide, and a conductive material, such as copper.

29. An apparatus as claimed in claim 16 wherein the more than two stable positions are oriented at a nonzero angle relative to the first and second conductive lines.

30. A method of fabricating a multi-state magnetoresistive random access memory device comprising the steps of:

providing a substrate defining a surface;

supporting a base electrode on the surface of the substrate;

forming a material layer between a fixed magnetoresistive region having a fixed magnetic moment vector fixed in a preferred direction both with and without an applied magnetic field and a free ferromagnetic region with a shape wherein the free ferromagnetic region is designed to provide a free magnetic moment vector with more than two stable positions, wherein the more than two stable positions are oriented at a nonzero-angle relative to the preferred direction of the fixed magnetic moment vector;

forming a bit conductive line, wherein one of the material layer and the free ferromagnetic region is positioned on the base electrode and the bit conductive line is positioned on the other of the material layer and the free ferromagnetic region.

31. A method as claimed in claim 30 further including the step of positioning a digit conductive line proximate to the base electrode.

32. A method as claimed in claim 30 further including the step of connecting an isolation transistor to the base electrode and an electrical ground.

33. A method as claimed in claim 30 wherein the material layer includes one of aluminum oxide and another suitable dielectric material.

34. A method as claimed in claim 30 wherein the material layer includes one of copper and another suitable conductive material.

35. A method as claimed in claim 30 wherein the more than two stable positions are created by an anisotropy of the free ferromagnetic region.

36. A method as claimed in claim 35 wherein the anisotropy is created by a shape anisotropy of the free ferromagnetic region.

37. A method as claimed in claim 35 wherein the anisotropy is created by an intrinsic anisotropy of a material included in the free ferromagnetic region.

38. A method as claimed in claim 37 wherein the intrinsic anisotropy is created by applying a magnetic field to the free ferromagnetic region.

39. A method as claimed in claim 35 wherein the anisotropy is created by growing the free ferromagnetic region with a preferred crystalline orientation.

40. A method as claimed in claim 35 wherein anisotropy is created by growing the free ferromagnetic region with clusters or crystallites that have a shape anisotropy.

41. A method as claimed in claim 30 wherein at least one of the pinned ferromagnetic region and the free ferromagnetic region includes one of iron oxide (Fe₃O₄), chromium oxide (CrO₂), oxides, and semiconductors, wherein the oxides and semiconductors are doped with one or more of iron, cobalt, nickel, magnesium, and chromium.

42. A method as claimed in claim 30 wherein the more than two stable positions are oriented at a nonzero angle relative to the first and second conductive lines.

43. A method of storing multiple states in a multi-state magnetoresistive random access memory device comprising the steps of:

providing a multi-state magnetoresistive random access memory device adjacent to a first conductor and a second conductor wherein the multi-state magnetoresistive random access memory device includes a first ferromagnetic region and a second ferromagnetic region separated by a non-ferromagnetic spacer layer, at least one of the first and second ferromagnetic regions include a synthetic anti-ferromagnetic region and has a free magnetic moment vector oriented in a preferred direction at a time t₀, wherein at least one of the first and second ferromagnetic regions has an anisotropy that provides the free magnetic moment vector with more than two stable positions, and wherein at least one of the first and second ferromagnetic regions has a fixed magnetic moment vector wherein the fixed magnetic moment vector is oriented in a preferred direction both with and without an applied magnetic field wherein the more than two stable positions are oriented at a nonzero angle relative to the preferred direction of the fixed magnetic moment vector;

applying a first and a second current pulse to orient the free magnetic moment vector in one of the more than two stable positions; and

turning off the first and second current pulses so that the free magnetic moment vector is aligned with one of N stable positions in the absence of an applied magnetic field.

44. A method as claimed in claim 43 further including the step of orientating the first and second conductors at a 90°

angle relative to each other.

45. A method as claimed in claim 43 further including the step of setting the preferred direction at the time t₀ to be at a non-zero angle to the first and second conductors.

46. A method as claimed in claim 43 wherein the step of causing a first and second current flow in the first and second conductors, respectively, includes using a combined current magnitude that is large enough to cause the magnetoresistive memory element to switch.

47. A method as claimed in claim 43 wherein the more than two stable positions are created by an anisotropy of the free ferromagnetic region.

48. A method as claimed in claim 47 wherein the anisotropy is created by a shape anisotropy of at least one of the first and second magnetoresistive regions.

49. A method as claimed in claim 48 wherein the shape has at least one lobe oriented parallel with one of the first conductive line and the second conductive line.

50. A method as claimed in claim 43 wherein the anisotropy is created by an intrinsic anisotropy of a material included in at least one of the first and second magnetoresistive regions.

51. A method as claimed in claim 50 wherein the intrinsic anisotropy is created by applying a magnetic field to at least one of the first and second magnetoresistive regions.

52. A method as claimed in claim 43 wherein the anisotropy is created by growing at least one of the first and second magnetoresistive regions with a preferred crystalline orientation.

53. A method as claimed in claim 43 wherein anisotropy is created by growing at least one of the first and second magnetoresistive regions with clusters or crystallites that have a shape anisotropy.

54. A method as claimed in claim 43 wherein the more than two stable positions are oriented at a nonzero angle relative to the first and second conductive lines.

55. A method as claimed in claim 43 wherein the step of causing a first and second current flow in the first and second conductors, respectively, includes using a combined current magnitude that is large enough to allow the magnetoresistive memory element to switch the free magnetic moment vector to a first position but not a second position.

56. A multi-state magnetoresistive random access memory device having a resistance, the device comprising:

a first ferromagnetic region;

a second ferromagnetic region positioned adjacent to the first ferromagnetic region to form a magnetoresistive memory device wherein one of the first and second ferromagnetic regions includes a shape having more than two magnetic moment vector stable positions, the stable positions being induced by an anisotropy of a material included within one of the first and second ferromagnetic regions.