Perpendicular magnetic random access memory (MRAM) device with a stable reference cell
View Patent ↗A magnetic random access memory (MRAM) element is configured to store a state when electric current flows therethrough. The MRAM element includes a first magnetic tunnel junction (MTJ) for storing a data bit and a reference bit MTJ for storing a reference bit. The data bit MTJ and reference bit MTJ are preferred to be of identical structure that includes a magnetic free layer (FL) having a switchable magnetization with a direction that is perpendicular to a film plane. The direction of magnetization of the FL is determinative of the data bit stored in the at least one MTJ. The identical structure further includes a magnetic reference layer (RL) having a magnetization with a direction that is perpendicular to the film plane, and a magnetic pinned layer (PL) having a magnetization with a direction that is perpendicular to the film plane. The direction of magnetization of the RL and the PL are anti-parallel relative to each other in the data bit MTJ for storing data bit, wherein when electric current is applied to the first MTJ, the magnetization orientation of the FL switches during a write operation, whereas, the direction of magnetization the RL and the PL remain the same. The direction of magnetization of the FL, the RL and the PL are parallel relative to each other in the reference bit MTJ for storing reference bit, the magnetization orientation of the FL does not switch under normal read operations.
1. A magnetic random access memory (MRAM) whose memory elements are configured to store a state when electric current flows therethrough comprising:
a plurality of magnetic tunnel junctions (MTJs) including at least one data bit MTJ and at least one reference bit MTJ,
each of the plurality of MTJs including,
a free layer (FL) having a switchable magnetization with a direction that is perpendicular to a film plane, the direction of magnetization of the FL being determinative of data stored in the MTJ;
a reference layer (RL) having a fixed magnetization with a direction that is perpendicular to the film plane; and
a pinned layer (PL) having a fixed magnetization with a direction that is perpendicular to the film plane,
wherein the directions of magnetization of the RL and that of the PL of the data bit MTJ are anti-parallel to each other;
further wherein the reference bit MTJ is used to compare with the data bit MTJ to retrieve the data stored in the data bit MTJ, the directions of magnetizations of the RL and the PL of the reference bit MTJ being parallel to each other.
2. The MRAM of claim 1 , wherein each of the plurality of MTJs further includes a junction layer (JL) positioned between the FL and the RL, wherein a change of the magnetization direction of the FL relative to the magnetization of the RL produces a resistance change across the data bit MTJ.
3. The MRAM of claim 1 , wherein each of the plurality of MTJs further includes a spacer layer (SL) disposed immediately adjacent to the PL.
4. The MRAM of claim 1 , wherein the plurality of MTJs are formed on a same die.
5. The MRAM of claim 1 , wherein the plurality of MTJs have substantially a same structure.
6. The MRAM of claim 1 , wherein the directions of magnetizations of the RL and PL of the data bit MTJ and that of the reference bit MTJ are effectuated either during manufacturing of the MRAM element or thereafter.
7. The MRAM of claim 2 , wherein the JL is made of a material comprising: magnesium oxide (MgO), alumina, zirconium oxide (ZnO), copper (Cu), or Cu nano-pillars within an oxide.
8. The MRAM of claim 1 , wherein the direction of the magnetization of each of the data bit MTJs is switched by spin transfer torque (STT) effect from the electric current flowing through the each of the data bit MTJs.
9. The MRAM of claim 2 , wherein the PL and RL are disposed on a same side of the JL opposing the FL in each MTJ.
10. The MRAM of claim 9 , wherein each MTJ further includes a spacer layer (SL) disposed immediately adjacent to the PL, the PL being separated from the RL by the SL.
11. The MRAM of claim 2 , wherein the PL and FL are disposed on a same side of the JL and opposing the RL in each MTJ.
12. The MRAM of claim 11 , wherein each MTJ further includes a spacer layer (SL) disposed immediately adjacent to the PL, wherein the PL is separated from the FL by the SL.
13. The MRAM of claim 3 , wherein the SL is made of a non-magnetic layer.
14. The MRAM of claim 13 , wherein the SL is made of a material comprising: ruthenium (Ru), tantalum (Ta), titanium (Ti), magnesium oxide (MgO), copper (Cu), hafnium (Hf), zirconium oxide (ZnO), iron manganese (IrMn), platinum manganese (PtMn), iron ruthenium (FeRu), or alumina.
15. The MRAM of claim 10 , wherein the SL produces an anti-ferromagnetic exchange coupling between the RL and the PL.
16. The MRAM of claim 10 , wherein the SL eliminates any type of exchange coupling between the RL and the PL.
17. The MRAM of claim 10 , wherein the SL produces a ferromagnetic exchange coupling between the RL and the PL.
18. The MRAM of claim 12 , wherein the SL produces an anti-ferromagnetic exchange coupling between the FL and the PL.
19. The MRAM of claim 12 , wherein the SL substantially eliminates any type of exchange coupling between the FL and the PL.
20. The MRAM of claim 15 , wherein the SL produces a ferromagnetic exchange coupling between the FL and the PL.
21. The MRAM of claim 1 , wherein the PL produces an effective perpendicular magnetic field that is operable to reduce an effective perpendicular magnetic field produced by the RL within the FL of the data bit MTJ.
22. The MRAM of claim 1 , wherein the PL produces an effective perpendicular magnetic field that is operable to enhance an effective perpendicular magnetic field produced by the RL within the FL of the reference bit MTJ.
23. A magnetic random access memory (MRAM) whose memory elements are configured to store a state when electric current flows therethrough comprising:
a plurality of magnetic tunnel junctions (MTJs) having a same structure, the MTJ of each of which including,
a magnetic free layer (FL) having a first magnetization;
a magnetic reference layer (RL) having a second magnetization;
a magnetic pinned layer (PL) having a third magnetization; and
a junction layer (JL) positioned between the FL and the RL,
wherein a change of the first magnetization direction relative to the second magnetization produces a resistance change across the MTJ,
wherein at least one of the plurality of MTJs is a data bit MTJ,
wherein at least one of the plurality of MTJs is a reference bit MTJ that is used to compare with the data bit MTJ to retrieve the data stored in the data bit MTJ,
further, wherein the directions of the second magnetization and the third magnetization are anti-parallel in the data bit MTJ while being parallel in the reference bit MTJ.
24. The MRAM of claim 23 , wherein the first magnetization, the second magnetization and the third magnetization are all perpendicular to film planes of the magnetic FL, the magnetic RL, and the magnetic PL.
25. The MRAM of claim 23 , wherein the magnetic RL and the magnetic PL each has associated therewith a perpendicular field component produced in the magnetic FL, and the perpendicular field components of the magnetic RL and the magnetic PL substantially cancel each other in the magnetic FL of the data bit MTJ.
26. The MRAM of claim 23 , wherein the magnetic RL and the magnetic PL each has associated therewith a perpendicular field component produced in the magnetic FL, and the perpendicular field components of the magnetic RL and the magnetic PL enhance each other in the magnetic FL of the reference bit MTJ.
27. The MRAM of claim 23 , wherein the magnetic RL and the magnetic PL each has associated therewith a field component produced in the magnetic FL, and the field components of the magnetic RL and the magnetic PL substantially cancel each other in the magnetic FL of the data bit MTJ.
28. The MRAM of claim 23 , wherein the magnetic RL and the magnetic PL each has associated therewith a field component produced in the magnetic FL, and the field components of the magnetic RL and the magnetic PL enhance each other in the reference bit MTJ.
29. The MRAM of claim 23 , wherein the plurality of MTJs are formed on a same die.
30. A magnetic random access memory (MRAM) whose memory elements are configured to store a state when electric current flows therethrough comprising:
a plurality of magnetic tunnel junctions (MTJs) having an identical structure, an MTJ of the plurality of MTJs including,
at least one magnetic free layer (FL) having a first magnetization;
at least one magnetic reference layer (RL) having a second magnetization; and
at least one magnetic pinned layer (PL) having a third magnetization,
wherein directions of the second magnetization and the third magnetization are anti-parallel in at least a first MTJ while being parallel in at least a second MTJ, and
wherein in the first MTJ, the first magnetization switches during a write operation while the second and the third magnetizations are unchanged.
31. The MRAM of claim 30 , wherein the first magnetization, the second magnetization and the third magnetization are all perpendicular to film planes of the magnetic FL, the magnetic RL and the magnetic PL.
32. The MRAM of claim 31 , wherein perpendicular field components from the magnetic RL and the magnetic PL substantially cancel each other in the magnetic FL of the first MTJ.
33. The MRAM of claim 31 , wherein perpendicular field components from the magnetic RL and the magnetic PL enhance each other in the magnetic FL of the second MTJ.
34. The MRAM of claim 30 , wherein at least one magnetic field component from each of the magnetic RL and the magnetic PL substantially cancel each other in the magnetic FL of the first MTJ.
35. The MRAM of claim 34 , wherein the at least one magnetic field component from each of the magnetic RL and the magnetic PL enhance each other in the magnetic FL of the second MTJ.
36. The MRAM of claim 30 , wherein the plurality of MTJs are formed on a same die.