MAGNETIC TUNNEL JUNCTION MAGNETIC MEMORY

• US 20080247072A1
• Filed: 03/31/2008
• Published: 10/09/2008
• Est. Priority Date: 03/29/2007
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Inventors: Sousa, Ricardo, Nozieres, Jean-Pierre, Prejbeanu, Ioan Lucian, Redon, Olivier, Dieny, Bernard
• Granted Patent: US 7,957,181 B2
• Time in Patent Office: Days
• US Class Current: 360/59
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: H10B 61/22 of the field-effect transistor [FET] type
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/85 Magnetic active materials
• CPC Class Codes: Y10S 977/933 Spintronics or quantum computing
• CPC Class Codes: Y10S 977/935 Spin dependent tunnel, SDT, junction, e.g. tunneling magnetoresistance, TMR

Abstract

This magnetic memory with a thermally-assisted write, every storage cell of which consists of at least one magnetic tunnel junction, said tunnel junction comprising at least:

one magnetic reference layer, the magnetization of which is always oriented in the same direction at the time of the read of the storage cell;
one so-called “free” magnetic storage layer, the magnetization direction of which is variable;
one insulating layer sandwiched between the reference layer and the storage layer.

The magnetization direction of the reference layer is polarized in a direction that is substantially always the same at the time of a read due to magnetostatic interaction with another fixed-magnetization layer called the “polarizing layer”.

Claims

1. A magnetic memory with a thermally-assisted write, every storage cell of which consists of at least one magnetic tunnel junction, said tunnel junction comprising at least:

one magnetic reference layer, the magnetization of which is always oriented in the same direction at the time of the read of the storage cell;

one so-called “

free”

magnetic storage layer, the magnetization direction of which is variable;

one insulating layer sandwiched between the reference layer and the storage layer,

wherein the magnetization direction of the reference layer is polarized in a direction that is substantially always the same at the time of a read due to magnetostatic interaction with another fixed-magnetization layer called the “

polarizing layer” and

in that the polarizing layer is arranged so that it is subjected, during read phases and write phases, to thermal variations that are less than those to which the reference layer with which it interacts magnetostatically is subjected.

2. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein a layer of low thermal conductivity is placed between the reference layer and the polarizing layer in order to limit the thermal variations of the polarizing layer during read and write phases.

3. A magnetic memory with a thermally-assisted write as claimed in claim 2, wherein the layer of low thermal conductivity placed between the reference layer and the polarizing layer is made of GeSbTe or BiTe.

4. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the storage layer comprises a bilayer that associates firstly a layer of a ferromagnetic material, typically selected from the group comprising Permalloy (Ni₈₀Fe₂₀) and Co₉₀Fe₁₀ and secondly an antiferromagnetic layer having a moderate blocking temperature.

5. A magnetic memory with a thermally-assisted write as claimed in claim 4, wherein the bilayer of the storage layer has planar magnetization.

6. A magnetic memory with a thermally-assisted write as claimed in claim 4, wherein the antiferromagnetic layer having a moderate blocking temperature consists of an IrMn alloy having a composition close to Ir₂₀Mn₈₀.

7. A magnetic memory with a thermally-assisted write as claimed in claim 4, wherein the selected respective thickness of the layers made of a ferromagnetic and antiferromagnetic material constituting the storage layer is 1 to 4 nm for the former and 4 to 8 nm for the latter.

8. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer comprises a bilayer which associates firstly a layer of a ferromagnetic material, typically a Co_1-xFe_x alloy, x being 0 to 0.50, and secondly an antiferromagnetic layer having a high blocking temperature.

9. A magnetic memory with a thermally-assisted write as claimed in claim 8, wherein the antiferromagnetic layer that fixes the magnetization direction of the polarizing layer is made of PtMn or IrMn.

10. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein if a magnetic field is used for writing, it is used to accentuate the magnetization orientation of the reference layer.

11. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the ferromagnetic polarizing layer is made of a material with high coercivity made from a material selected from the group comprising Co₈₀Cr₂₀ and SmCo.

12. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer is inserted in the line which ensures electrical connection to the storage cell and in that its magnetization direction is substantially perpendicular to the length of the line.

13. A magnetic memory with a thermally-assisted write as claimed in claim 12, wherein the conductive line consists of the polarizing layer, an antiferromagnetic pinning layer and is supplemented by a non-magnetic conductive layer, said polarizing and antiferromagnetic pinning layers being of the same kind as that in claim 9 or 11.

14. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the reference layer is made of a ferromagnetic material selected from the group comprising an alloy of CoFe (Co₉₀Fe₁₀, Co₇₀Fe₃₀, Co₇₀Fe₁₀B₁₀), of NiFe (Ni₈₀Fe₂₀) or a 1 nm CoFe/2 nm NiFe bilayer.

15. A magnetic memory with a thermally-assisted write as claimed in claim 14, wherein the thickness of the reference layer is 1 to 4 nm.

16. A magnetic memory with a thermally-assisted write as claimed in claim 4, wherein the side of the storage layer opposite the tunnel barrier is in contact with a layer of very low thermal conductivity used as a thermal barrier.

17. A magnetic memory with a thermally-assisted write as claimed in claim 16, wherein the layer acting as a thermal barrier is made of a material selected from the group comprising BiTe and GeSbTe having a thickness of 2 to 10 nm.

18. A magnetic memory with a thermally-assisted write as claimed in claim 5, wherein every storage cell consists of a double magnetic tunnel junction having a single storage layer in common, said storage layer being inserted between the two tunnel barriers, each tunnel barrier having, on the side opposite the storage layer, a reference layer, the magnetization of which is maintained in a fixed direction at the time of a read by magnetostatic interaction with a pinned magnetization polarizing layer, the two reference layers being separated from the two polarizing layers with which they are respectively magnetostatically coupled by a thermal barrier.

19. A magnetic memory with a thermally-assisted write as claimed in claim 18, wherein the storage layer consists of a tri-layer comprising a central antiferromagnetic layer with a moderate blocking temperature made of a material selected from the group comprising IrMn, PtMn and PtPdMn sandwiched between two ferromagnetic layers of soft materials in contact with the tunnel barriers, said ferromagnetic layers being made of Ni₈₀Fe₂₀, Co_100-xFe_x where x is typically 0 to 30, Co_100-x-yFe_xB_y, where x is typically 0 to 30 and y is typically 0 to 20.

20. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer consists of permanent magnets placed either side of the storage cell.

21. A magnetic memory with a thermally-assisted write as claimed in claim 20, wherein the permanent magnets are placed at the level of the reference layer.

22. A magnetic memory with a thermally-assisted write as claimed in claim 20, wherein the permanent magnets consist of layers of strongly magnetic ferromagnetic materials with high coercive fields selected from the group comprising SmCo, CoPt, CoCrPt and FePt.

23. A magnetic memory with a thermally-assisted write as claimed in claim 20, wherein the permanent magnets consist of strongly magnetic ferromagnetic materials, particularly those based on a CoFe alloy and pinned by an antiferromagnetic layer with a high blocking temperature in excess of 200°

C. in particular.

24. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer that interacts magnetostatically with the reference layer consists of a permanent magnet located above the memory.

25. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the reference layer consists of a number of ferromagnetic layers which are antiferromagnetically coupled through a non-magnetic spacer, especially one made of ruthenium.

26. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer consists of a number of ferromagnetic layers which are antiferromagnetically coupled through a non-magnetic spacer, especially one made of ruthenium.

27. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the reference layer is laminated and produced by inserting, into a first magnetic material, especially CoFe, thin layers of a second material with a low thermal conductivity, especially GeSbTe or Ta.

28. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the polarizing layer is laminated and produced by inserting, into a first magnetic material, especially CoFe, thin layers of a second material with a low thermal conductivity, especially GeSbTe or Ta.

29. A magnetic memory as claimed in claim 25, wherein at least one of the ferromagnetic layers which are antiferromagnetically coupled and which constitute the reference layer is itself laminated and produced by inserting into this ferromagnetic layer, thin layers of a second material with a low thermal conductivity, especially GeSbTe or Ta.

30. A magnetic memory as claimed in claim 26, wherein at least one of the ferromagnetic layers which are antiferromagnetically coupled and which constitute the polarizing layer is itself laminated and produced by inserting into this ferromagnetic layer, thin layers of a second material with a low thermal conductivity, especially GeSbTe or Ta.

31. A magnetic memory with a thermally-assisted write as claimed in any of claims 26, 28 and 30, wherein the polarizing layer is pinned by an antiferromagnetic layer, especially one made of PtMn, with the laminated reference layer being polarized by said polarizing layer by antiferromagnetic coupling through a spacer made of ruthenium, this coupling being added to the magnetostatic coupling between these layers.

32. A magnetic memory with a thermally-assisted write as claimed in claim 1, wherein the reference layer is in contact with the tunnel barrier of the magnetic tunnel junction, with the last constituent layer of the reference layer which is in contact with said tunnel barrier being likely to be made of a ferromagnetic material selected from the group comprising CoFe and CoFeB.

33. A magnetic memory with a thermally-assisted write as claimed in claim 25, wherein the number of stacks coupled in anti-parallel by one ruthenium layer and consisting of the laminated reference layer/laminated polarizing layer assembly is greater than two, with the stack farthest from the tunnel barrier being pinned by interaction with a layer made of an antiferromagnetic material.

34. A magnetic memory with a thermally-assisted write as claimed in claim 33, wherein the ferromagnetic layers that are in immediate contact with the tunnel barrier of the magnetic tunnel junction and the ruthenium layer are thicker than those within the laminated layers.