SPIN TRANSFER TORQUE MAGNETIC RANDOM ACCESS MEMORY (STTMRAM) HAVING GRADED SYNTHETIC FREE LAYER

• US 20140015078A1
• Filed: 09/16/2013
• Published: 01/16/2014
• Est. Priority Date: 07/26/2010
• Status: Active Grant

• Current Assignee: Avalanche Technology Incorporated
• Original Assignee: Avalanche Technology Incorporated
• Inventors: Huai, Yiming, Ranjan, Rajiv Yadav, Malmhall, Roger Klas, Zhou, Yuchen
• Granted Patent: US 8,779,537 B2
• Time in Patent Office: Days
• US Class Current: 257/421
• 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: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• 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 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/80 Constructional details
• CPC Class Codes: H10N 50/85 Magnetic active materials

Abstract

A spin transfer torque memory random access memory (STTMRAM) element is capable of switching states when electrical current is applied thereto for storing data and includes the following layers. An anti-ferromagnetic layer, a fixed layer formed on top of the anti-ferromagnetic layer, a barrier layer formed on top of the second magnetic layer of the fixed layer, and a free layer including a first magnetic layer formed on top of the barrier layer, a second magnetic layer formed on top of the first magnetic layer, a nonmagnetic insulating layer formed on top of the second magnetic layer and a third magnetic layer formed on top of the non-magnetic insulating layer. A capping layer is formed on top of the non-magnetic insulating layer.

Claims

1. A spin transfer torque magnetic random access memory (STTMRAM) element comprising:

an anti-ferromagnetic layer;

a magnetic fixed layer structure formed on top of said anti-ferromagnetic layer, said magnetic fixed layer comprising two invariable magnetic sublayers having opposite magnetization directions with an anti-ferromagnetic coupling sublayer interposed therebetween;

a magnetic free layer separated from said magnetic fixed layer by an insulating tunnel barrier layer, said magnetic free layer comprising;

a first variable magnetic sublayer formed on top of said insulating tunnel barrier layer;

a second variable magnetic sublayer formed on top of said first magnetic sublayer; and

a third variable magnetic sublayer separated from said second variable magnetic sublayer by a coupling sublayer, said coupling sublayer including at least a non-magnetic insulating layer and a non-magnetic conductive layer,

wherein said first and second variable magnetic sublayers have substantially the same magnetization direction that is substantially opposite to the magnetization direction of said third variable magnetic sublayer; and

a capping layer formed on top of said third variable magnetic layer of said magnetic free layer.

2. The STTMRAM element according to claim 1, wherein said second variable magnetic sublayer of said magnetic free layer has a lower saturation magnetization than said first and third variable magnetic sublayers of said magnetic free layer.

3. The STTMRAM element according to claim 1, wherein said insulating tunnel barrier layer is formed of magnesium oxide (MgO).

4. The STTMRAM element according to claim 1, wherein said first, second, and third variable magnetic layers each comprises a material selected from the group consisting of iron, nickel, cobalt, platinum, copper, boron, tantalum, titanium, chromium, terbium, samarium, neodymium, gadolinium, silicon oxide, titanium oxide, magnesium oxide, tantalum oxide, aluminum oxide, and any combination thereof.

5. The STTMRAM element according to claim 1, wherein said first, second, and third variable magnetic layers each is a magnetic alloy comprising cobalt, iron, and boron.

6. The STTMRAM element according to claim 1, wherein said coupling sublayer of said magnetic free layer comprises a non-magnetic insulating layer and a non-magnetic conductive layer.

7. The STTMRAM element according to claim 6, wherein said non-magnetic insulating layer is formed of magnesium oxide (MgO) and said non-magnetic conductive layer is formed of tantalum (Ta).

8. The STTMRAM element according to claim 1, wherein said coupling sublayer of said magnetic free layer comprises a non-magnetic insulating layer formed on top of said second variable magnetic sublayer and a non-magnetic conductive layer formed on top of said non-magnetic insulating layer.

9. The STTMRAM element according to claim 8, wherein said non-magnetic insulating layer is formed of magnesium oxide (MgO) and said non-magnetic conductive layer is formed of tantalum (Ta).

10. The STTMRAM element according to claim 1, wherein said coupling sublayer of said magnetic free layer has a multi-layer structure comprising a plurality of alternated non-magnetic insulating layers and non-magnetic conductive layers.

11. The STTMRAM element according to claim 10, wherein said non-magnetic insulating layers are formed of magnesium oxide (MgO) and said non-magnetic conductive layers are formed of tantalum (Ta).

12. The STTMRAM element according to claim 1, wherein said coupling sublayer of said magnetic free layer comprises a non-magnetic insulating layer and a non-magnetic conductive layer with a dead magnetic layer interposed therebetween.

13. The STTMRAM element according to claim 12, wherein said non-magnetic insulating layer is formed of magnesium oxide (MgO) and said non-magnetic conductive layer is formed of tantalum (Ta).

14. The STTMRAM element according to claim 12, wherein said dead magnetic layer comprises a magnetic material with a thickness of about 0.5 nm or less, thereby not having a magnetization.

15. A spin transfer torque magnetic random access memory (STTMRAM) element comprising:

an anti-ferromagnetic layer;

a magnetic fixed layer structure formed on top of said anti-ferromagnetic layer, said magnetic fixed layer comprising two invariable magnetic sublayers having opposite magnetization directions with an anti-ferromagnetic coupling sublayer interposed therebetween;

a magnetic free layer separated from said magnetic fixed layer by an insulating tunnel barrier layer, said magnetic free layer comprising;

a first variable magnetic sublayer formed on top of said insulating tunnel barrier layer;

a second variable magnetic sublayer formed on top of said first magnetic sublayer; and

a third variable magnetic sublayer separated from said second variable magnetic sublayer by a coupling sublayer, said coupling sublayer including at least a non-magnetic insulating layer and a non-magnetic conductive layer,

wherein said first and second variable magnetic sublayers have substantially the same magnetization direction that is substantially opposite to the magnetization direction of said third variable magnetic sublayer;

a non-magnetic insulating top layer formed on top of said third variable magnetic layer of said magnetic free layer; and

a capping layer formed on top of said non-magnetic insulating top layer.

16. The STTMRAM element according to claim 15, wherein said second variable magnetic sublayer of said magnetic free layer has a lower saturation magnetization than said first and third variable magnetic sublayers of said magnetic free layer.

17. The STTMRAM element according to claim 15, wherein said insulating tunnel barrier layer is formed of magnesium oxide (MgO).

18. The STTMRAM element according to claim 15, wherein said first, second, and third variable magnetic layers each comprises a material selected from the group consisting of iron, nickel, cobalt, platinum, copper, boron, tantalum, titanium, chromium, terbium, samarium, neodymium, gadolinium, silicon oxide, titanium oxide, magnesium oxide, tantalum oxide, aluminum oxide, and any combination thereof.

19. The STTMRAM element according to claim 15, wherein said first, second, and third variable magnetic layers each is a magnetic alloy comprising cobalt, iron, and boron.

20. The STTMRAM element according to claim 15, wherein said coupling sublayer of said magnetic free layer comprises a non-magnetic insulating layer and a non-magnetic conductive layer.

21. The STTMRAM element according to claim 20, wherein said non-magnetic insulating layer is formed of magnesium oxide (MgO) and said non-magnetic conductive layer is formed of tantalum (Ta).

22. The STTMRAM element according to claim 15, wherein said coupling sublayer of said magnetic free layer has a multi-layer structure comprising a plurality of alternated non-magnetic insulating layers and non-magnetic conductive layers.

23. The STTMRAM element according to claim 22, wherein said non-magnetic insulating layers are formed of magnesium oxide (MgO) and said non-magnetic conductive layers are formed of tantalum (Ta).

24. The STTMRAM element according to claim 15, wherein said coupling sublayer of said magnetic free layer comprises a non-magnetic insulating layer and a non-magnetic conductive layer with a dead magnetic layer interposed therebetween.

25. The STTMRAM element according to claim 24, wherein said non-magnetic insulating layer is formed of magnesium oxide (MgO) and said non-magnetic conductive layer is formed of tantalum (Ta).

26. The STTMRAM element according to claim 24, wherein said dead magnetic layer comprises a magnetic material with a thickness of about 0.5 nm or less, thereby not having a magnetization.

27. A spin transfer torque magnetic random access memory (STTMRAM) element comprising:

an anti-ferromagnetic layer;

a magnetic fixed layer structure formed on top of said anti-ferromagnetic layer, said magnetic fixed layer comprising two invariable magnetic sublayers having opposite magnetization directions with an anti-ferromagnetic coupling sublayer interposed therebetween;

a magnetic free layer separated from said magnetic fixed layer by a magnesium oxide (MgO) tunnel barrier layer, said magnetic free layer comprising;

a first variable magnetic sublayer formed on top of said MgO tunnel barrier layer;

a second variable magnetic sublayer formed on top of said first magnetic sublayer; and

a third variable magnetic sublayer separated from said second variable magnetic sublayer by a coupling sublayer, said coupling sublayer including a MgO layer and a Ta layer formed thereon,

wherein said first, second, and third magnetic sublayers each is formed of a magnetic alloy comprising, cobalt, iron, and boron, said first and second variable magnetic sublayers have substantially the same magnetization direction that is substantially opposite to the magnetization direction of said third variable magnetic sublayer, said second variable magnetic sublayer has a lower saturation magnetization than said first and third variable magnetic sublayers; and

a capping layer formed on top of said third variable magnetic layer of said magnetic free layer.