MRAM cell using multiple axes magnetization and method of operation

1. A magnetic random access memory cell, comprising:

a reference layer structure that includes an anti-ferromagnetic layer structure pinning a magnetization orientation of the reference layer structure, the reference layer structure being magnetically polarizable bidirectional and parallel to more than one axis by a magnetic field applied during a writing procedure so as to store information of more than one bit in the reference layer structure while heating the anti-ferromagnetic layer structure above its blocking temperature; and

a free layer structure adjacent the reference layer structure, the reference layer structure having a higher magnetic coercivity than the free layer structure.

2. The magnetic random access memory cell of claim 1 , further comprising a non-magnetic tunnel barrier layer structure disposed between said reference layer structure and said free layer structure,

wherein said reference layer structure has a higher magnetic coercivity than said free layer structure and said reference layer structure is magnetically polarizable bidirectional and parallel to two different axes by the magnetic field applied during the writing procedure.

3. The magnetic random access memory cell of claim 2 , further comprising a word line electrode and a bit line electrode for generating the magnetic field.

4. The magnetic random access memory cell of claim 3 , wherein the free layer structure has an easy axis parallel to the magnetic field generated by one of the electrodes.

5. The magnetic random access memory cell of claim 3 , wherein the bit line electrode is electrically coupled to the memory cell and the free layer structure has an easy axis parallel to the magnetic field generated by the bit line electrode.

6. The magnetic random access memory cell of claim 4 , wherein the free layer structure comprises a cobalt iron boron layer having uniaxial anisotropy defining said easy axis.

7. The magnetic random access memory cell of claim 4 , wherein the free layer structure comprises a cobalt iron boron layer having a thickness of approximately 15-25 Angstroms.

8. The magnetic random access memory cell of claim 1 , wherein the anti-ferromagnetic layer structure comprises an iridium or an iron manganese layer.

9. The magnetic random access memory cell of claim 8 , wherein the anti-ferromagnetic layer structure has a thickness of approximately 20-150 Angstroms.

10. The magnetic random access memory cell of claim 1 , wherein the anti-ferromagnetic layer structure comprises a cobalt iron layer or a cobalt iron boron layer.

11. The magnetic random access memory cell of claim 10 , wherein the cobalt iron layer or the cobalt iron boron layer has a thickness of approximately 18 Angstroms.

12. The magnetic random access memory cell of claim 1 , further comprising a heating current source providing heating current to the magnetic random access memory cell, thereby heating the anti-ferromagnetic layer structure.

13. A magnetic random access memory cell, comprising:

a reference layer structure that includes an anti-ferromagnetic layer structure pinning a magnetization orientation of the reference layer structure;

a free layer structure; and

a non-magnetic tunnel barrier layer structure disposed between the reference layer structure and the free layer structure, the reference layer structure having a higher magnetic coercivity than the free layer structure and the reference layer structure being magnetically polarizable bidirectional and parallel to a magnetic field generated by a bit line electrode and parallel to a magnetic field generated by a word line electrode during a writing procedure so as to store information of more than one bit in the reference layer structure while heating the anti-ferromagnetic layer structure above its blocking temperature.

14. The magnetic random access memory cell of claim 13 , wherein:

the bit line electrode is electrically coupled to the memory cell; and

the free layer structure has an easy axis parallel to the magnetic field generated by the bit line electrode.

15. The magnetic random access memory cell of claim 13 , wherein the anti-ferromagnetic layer structure comprises an artificial anti-ferromagnetic layer structure.

16. The magnetic random access memory cell of claim 15 , wherein the artificial anti-ferromagnetic layer structure comprises:

a first magnetic layer having a first magnetic moment;

a second magnetic layer having a second magnetic moment; and

an anti-ferromagnetic layer disposed between the first and second magnetic layers, the first magnetic layer being in contact with the non-magnetic tunnel barrier layer structure.

17. A magnetic random access memory cell, comprising:

a reference layer structure that includes an anti-ferromagnetic layer structure pinning a magnetization orientation of the reference layer structure, wherein the anti-ferromagnetic layer structure comprises an artificial anti-ferromagnetic layer structure, the artificial anti-ferromagnetic layer structure comprising a first magnetic layer having a first magnetic moment, a second magnetic layer having a second magnetic moment, and an anti-ferromagnetic layer disposed between the first and second magnetic layers;

a free layer structure; and

a non-magnetic tunnel barrier layer structure disposed between the reference layer structure and the free layer structure, the first magnetic layer being in contact with the non-magnetic tunnel barrier layer structure, the reference layer structure having a higher magnetic coercivity than the free layer structure, and the reference layer structure being magnetically polarizable bidirectional and parallel to a magnetic field generated by a bit line electrode and parallel to a magnetic field generated by a word line electrode during a writing procedure so as to store information in the reference layer structure while heating the anti-ferromagnetic layer structure above its blocking temperature;

wherein at room-temperature the first magnetic moment and the second magnetic moment are balanced resulting in an absence of a magnetic offset field of the artificial anti-ferromagnetic layer structure, and at high temperature the first magnetic moment dominates over the second magnetic moment.

18. The magnetic random access memory cell of claim 16 , wherein the first magnetic layer comprises cobalt iron boron and the anti-ferromagnetic layer comprises ruthenium.

19. The magnetic random access memory cell of claim 18 , wherein the first magnetic layer has a thickness of approximately 18 Angstroms.

20. The magnetic random access memory cell of claim 13 , wherein the anti-ferromagnetic layer structure comprises an iron manganese layer.

21. The magnetic random access memory cell of claim 20 , wherein the iron manganese layer has a thickness of approximately 120 Angstroms.

22. The magnetic random access memory cell of claim 13 , wherein the free layer structure comprises an artificial anti-ferromagnetic layer structure.

23. The magnetic random access memory cell of claim 22 , wherein the artificial anti-ferromagnetic layer structure comprises a first magnetic layer having a first magnetic moment, a second magnetic layer having a second magnetic moment and an anti-ferromagnetic layer disposed between said first and said second magnetic layers, said first magnetic layer being in contact with the non-magnetic tunnel barrier layer structure.

24. A magnetic random access memory cell, comprising:

a reference layer structure that includes an anti-ferromagnetic layer structure pinning a magnetization orientation of the reference layer structure;

a free layer structure, wherein the free layer structure comprises an artificial anti-ferromagnetic layer structure, the artificial anti-ferromagnetic layer structure comprising a first magnetic layer having a first magnetic moment, a second magnetic layer having a second magnetic moment and an anti-ferromagnetic layer disposed between the first and the second magnetic layers; and

a non-magnetic tunnel barrier layer structure disposed between the reference layer structure and the free layer structure, the first magnetic layer being in contact with the non-magnetic tunnel barrier layer structure, the reference layer structure having a higher magnetic coercivity than the free layer structure, and the reference layer structure being magnetically polarizable bidirectional and parallel to a magnetic field generated by a bit line electrode and parallel to a magnetic field generated by a word line electrode during a writing procedure so as to store information in the reference layer structure while heating the anti-ferromagnetic layer structure above its blocking temperature;

wherein at room-temperature the second magnetic moment dominates over the first magnetic moment.

25. The magnetic random access memory cell of claim 24 , wherein at room-temperature the second magnetic moment is about twice the first magnetic moment in amount.

26. The magnetic random access memory cell of claim 24 , wherein at high temperature the first and the second magnetic moments are substantially balanced resulting in a substantial absence of a magnetic offset field of the free layer structure.

27. The magnetic random access memory cell of claim 23 , wherein the first magnetic layer comprises cobalt iron boron and the anti-ferromagnetic layer comprises ruthenium.

28. The magnetic random access memory cell of claim 23 , wherein the first magnetic layer has a thickness of approximately 25 Angstroms.

29. A method of writing to a magnetic access memory cell, the method comprising:

providing a magnetic access memory cell that includes a free layer structure adjacent a reference layer structure; and

applying a magnetic field thereby polarizing the reference layer structure in one of two possible directions parallel to one out of more than one possible axes so as to store information of more than one bit in the reference layer structure.

30. The method of claim 29 , further comprising, while applying the magnetic field, heating the memory cell by applying a heating current.

31. The method of claim 29 , wherein applying the magnetic field comprises generating the magnetic field by a field current through at least one of more than one field electrodes.

32. The method of claim 31 , wherein generating the magnetic field comprises generating the magnetic field by the field current through a bit line electrode or through a word line electrode of the magnetic access memory cell.

33. The method of claim 31 , wherein generating the magnetic field comprises generating the magnetic field by the field current through a bit line electrode and through a word line electrode of the magnetic access memory cell.

34. A method of reading a magnetic access memory cell, the method comprising:

providing a magnetic access memory cell that includes a free layer structure adjacent a reference layer structure;

applying a magnetic field thereby polarizing the free layer structure parallel to each axis of a plurality of axes; and

determining a tunnel magneto resistance status of the magnetic access memory cell thereby reading information of more than one bit.

35. A method of operating a magnetic access memory cell for reading, the method comprising:

providing a magnetic access memory cell that includes a free layer structure adjacent a reference layer structure;

applying a magnetic field thereby polarizing the free layer structure parallel to an axis of a plurality of axes; and

determining an axis aligned tunnel magneto resistance status and, if the axis aligned tunnel magneto resistance status represents neither a logical ‘0’ state nor a logical ‘1’ state, applying a magnetic field polarizing the free layer structure parallel to an other axis of the plurality of axes and again determining the axis aligned tunnel magneto resistance status.

36. The method of claim 35 , wherein applying the magnetic field comprises generating the magnetic field by a field current through at least one of more than one field electrodes.

37. The method of claim 36 , wherein generating the magnetic field comprises generating the magnetic field by the field current through a bit line electrode or through a word line electrode of the magnetic access memory cell.

38. The method of claim 36 , wherein generating the magnetic field comprises generating the magnetic field by the field current through a bit line electrode and through a word line electrode of the magnetic access memory cell.

39. A method of operating a magnetic access memory cell for reading, the method comprising:

pulsing a field current through a bit line electrode;

pulsing a first read current through the magnetic access memory cell for determining a first axis aligned tunnel magneto resistance status;

pulsing a field current through a word line electrode; and

pulsing a second read current through the magnetic access memory cell for determining a second axis aligned tunnel magneto resistance status.

40. A method of operating a magnetic access memory cell for reading, the method comprising:

pulsing a field current through a bit line electrode;

pulsing a first read current through the magnetic access memory cell for determining a first axis aligned tunnel magneto resistance status;

pulsing a field current through a word line electrode; and

pulsing a second read current through the magnetic access memory cell for determining a second axis aligned tunnel magneto resistance status;

wherein the pulsing the field current through the word line electrode and the pulsing the second read current through the magnetic access memory cell are at least partially overlapping.

41. The method of claim 35 , wherein determining the axis aligned tunnel magneto resistance status is used to read more than one bit of information from the magnetic access memory cell.

42. The method of claim 39 , wherein pulsing the first read current and pulsing the second read current are used to read more than one bit of information from the magnetic access memory cell.