MAGNETIC TUNNEL JUNCTION WITH FREE LAYER HAVING EXCHANGE COUPLED MAGNETIC ELEMENTS

• US 20120250404A1
• Filed: 03/31/2011
• Published: 10/04/2012
• Est. Priority Date: 03/31/2011
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Wang, Xiaobin, Gao, Kaizhong
• Granted Patent: US 8,742,518 B2
• Time in Patent Office: Days
• US Class Current: 365/171
• 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

Abstract

A magnetic tunnel junction device includes a reference magnetic layer and a magnetic free layer including first and second magnetic elements that are magnetically exchange coupled. The magnetic exchange coupling between the first and second magnetic elements is configured to achieve a switching current distribution less than about 200% and a long term thermal stability criterion of greater than about 60 k_BT.

Claims

1. A magnetic tunnel junction device, comprising:

a magnetic reference layer; and

a magnetic free layer comprising;

a first magnetic element;

a second magnetic element that is magnetically exchange coupled to the first magnetic element, wherein magnetic exchange coupling between the first and second magnetic elements is configured to achieve a switching current distribution less than about 200% and a long term thermal stability criterion of greater than about 60 k_BT.

2. The device of claim 1, wherein the first magnetic element has a first saturation magnetization, M_s1, and anisotropy, H_k1, and the second magnetic element has a second saturation magnetization, M_s2, and anisotropy, H_k2, and the ratio M_s2H_k2/M_s1H_k1 is less than about 0.8.

3. The device of claim 1, wherein an exchange interaction parameter, hex=J/M_s2/H_k1 is less than 0.65, where J is the exchange coupling strength between the first and second elements.

4. The device of claim 1, wherein:

the second magnetic element comprises CoPt or CoCrPt or CoCr; and

the first magnetic element comprises FePt or CoPt with L1₀ structure.

5. The device of claim 1, wherein the device comprises a multi level storage device having two magnetic tunnel junctions arranged in parallel.

6. The device of claim 1, wherein the device comprises a multi level storage device having two magnetic tunnel junctions arranged in series.

7. The device of claim 1, wherein an anisotropy of the first magnetic element is less than an anisotropy of the second magnetic element.

8. The device of claim 1, wherein a volume of the first magnetic element is less than a volume of the second magnetic element.

9. The device of claim 1, further comprising an exchange coupling layer disposed between the first and second magnetic elements.

10. The article of claim 9, wherein the exchange coupling layer is configured to achieve antiferromagnetic coupling between the first and second magnetic elements.

11. A magnetic tunnel junction device, comprising:

a magnetic reference layer; and

a magnetic free layer comprising;

a first magnetic element;

a second magnetic element, and

an exchange coupling layer disposed between the first magnetic element and the second magnetic element, the exchange coupling layer configured to control an amount of exchange coupling between the first and second magnetic elements, the exchange coupling between the first and second magnetic elements configured to achieve a predetermined switching current, a predetermined switching current distribution, and a long term thermal stability criterion.

12. The device of claim 11, wherein the exchange coupling layer is configured to provide antiferromagnetic coupling between the first and second magnetic elements and comprises Ru.

13. The device of claim 11, wherein the exchange coupling layer comprises one or more of MgO, Mg, and Ag.

14. The device of claim 11, wherein at least one of first and second magnetic elements is a ferrimagnetic material and comprises PtMn.

15. The device of claim 11, wherein the switching current distribution of the device is less than about 50%.

16. The device of claim 11, wherein the switching current distribution of the device is less than about 200%.

17. The device of claim 11, wherein the long term thermal stability criterion is about 60 k_BT.

18. The device of claim 11, wherein the first magnetic element and the second magnetic element have about the same aspect ratio and the first magnetic element has a different volume than the second magnetic element.

19. The device of claim 11, wherein the anisotropy of at least one of the first and second magnetic elements is less than about 200,000 Oe.

20. The device of claim 11, wherein the first magnetic element has a magnetization easy axis that is parallel to a magnetization easy axis of the second magnetic element.

21. A system, comprising:

an array of magnetic tunnel junction devices, each magnetic tunnel junction device comprising;

a magnetic reference layer;

a magnetic free layer comprising;

a first magnetic element;

a second magnetic element that is magnetically exchange coupled to the first magnetic element, wherein magnetic exchange coupling between the first and second magnetic elements is configured to achieve a switching current distribution less than about 200% and a long term thermal stability criterion of greater than about 60 k_BT;

circuitry configured to select a particular magnetic tunnel junction device for access; and

circuitry configured store or read data to or from the selected magnetic tunnel junction device.