Modified double magnetic tunnel junction structure suitable for BEOL integration

1. A modified double magnetic tunnel junction (mDMTJ) structure comprising:

a first magnetic reference layer;

a first tunnel barrier layer having a first surface in direct physical contact with a surface of the first magnetic reference layer;

a non-magnetic, spin-conducting metallic layer having a first surface in direct physical contact with a second surface of the first tunnel barrier layer which is opposite the first surface of the first tunnel barrier layer;

a magnetic free layer having a first surface in direct physical contact with a second surface of the non-magnetic, spin-conducting metallic layer which is opposite the first surface of the non-magnetic, spin-conducting metallic layer;

a second tunnel barrier layer having a first surface contacting a second surface of the magnetic free layer which is opposite the first surface of the magnetic free layer, and

a second magnetic reference layer having a first surface contacting a second surface of the second tunnel barrier layer which is opposite the first surface of the second tunnel barrier layer.

2. The mDMTJ structure of claim 1 , wherein the first magnetic reference layer is located at a bottom portion of the mDMTJ structure, and the second magnetic reference layer is located at a top portion of the mDMTJ structure.

3. The mDMTJ structure of claim 2 , wherein the second magnetic reference layer comprises a lower magnetic reference layer, an anti-ferromagnetic coupling layer, and an upper magnetic reference layer.

4. The mDMTJ structure of claim 2 , wherein the first tunnel barrier layer and the second tunnel barrier layer have a same lateral dimension.

5. The mDMTJ structure of claim 2 , wherein the first tunnel barrier layer has a first lateral dimension, and the second tunnel barrier layer has a second lateral dimension that is less than the first lateral dimension.

6. The mDMTJ structure of claim 5 , wherein the magnetic free layer is located on a pedestal portion of the non-magnetic, spin-conducting metallic layer, the pedestal portion of the non-magnetic, spin-conducting metallic layer has the second lateral dimension, and a remaining portion of the non-magnetic, spin-conducting metallic layer has the first lateral dimension.

7. The mDMTJ structure of claim 1 , wherein the second magnetic reference layer is located at a bottom portion of the mDMTJ structure, and the first reference layer is located at a top portion of the mDMTJ structure.

8. The mDMTJ structure of claim 7 , wherein the second magnetic reference layer comprises a lower magnetic reference layer, an anti-ferromagnetic coupling layer, and an upper magnetic reference layer.

9. The mDMTJ structure of claim 7 , wherein the first tunnel barrier layer and the second tunnel barrier layer have a same lateral dimension.

10. The mDMTJ structure of claim 7 , wherein the first tunnel barrier layer has a first lateral dimension, and the second tunnel barrier layer has a second lateral dimension that is less than the first lateral dimension.

11. The mDMTJ structure of claim 10 , wherein the magnetic free layer contacts a lower portion of the non-magnetic, spin-conducting metallic layer, the lower portion of the non-magnetic, spin-conducting metallic layer has the second lateral dimension, and an upper portion of the non-magnetic, spin-conducting metallic layer has the lateral first dimension.

12. A spin-transfer torque (STT) magnetic tunnel junction (MTJ) memory element comprising:

a modified double magnetic tunnel junction (mDMTJ) structure sandwiched between a first electrode and a second electrode, wherein the mDMTJ structure comprises a first magnetic reference layer, a first tunnel barrier layer having a first surface in direct physical contact with a surface of the first magnetic reference layer, a non-magnetic, spin-conducting metallic layer having a first surface in direct physical contact with a second surface of the first tunnel barrier layer which is opposite the first surface of the first tunnel barrier layer, a magnetic free layer having a first surface in direct physical contact with a second surface of the non-magnetic, spin-conducting metallic layer which is opposite the first surface of the non-magnetic, spin-conducting metallic layer, a second tunnel barrier layer having a first surface contacting a second surface of the magnetic free layer which is opposite the first surface of the magnetic free layer, and a second magnetic reference layer having a first surface contacting a second surface of the second tunnel barrier layer which is opposite the first surface of the second tunnel barrier layer.

13. The STT MTJ memory element of claim 12 , wherein the first magnetic reference layer is located at a bottom portion of the mDMTJ structure, and the second magnetic reference layer is located at a top portion of the mDMTJ structure.

14. The STT MTJ memory element of claim 13 , wherein the second magnetic reference layer comprises a lower magnetic reference layer, an anti-ferromagnetic coupling layer, and an upper magnetic reference layer.

15. The STT MTJ memory element of claim 13 , wherein the first tunnel barrier layer and the second tunnel barrier layer have a same lateral dimension.

16. The STT MTJ memory element of claim 13 , wherein the first tunnel barrier layer has a first lateral dimension, and the second tunnel barrier layer has a second lateral dimension that is less than the first lateral dimension.

17. The STT MTJ memory element of claim 16 , wherein the magnetic free layer is located on a pedestal portion of the non-magnetic, spin-conducting metallic layer, the pedestal portion of the non-magnetic, spin-conducting metallic layer has the second lateral dimension, and a remaining portion of the non-magnetic, spin-conducting metallic layer has the first lateral dimension.

18. The STT MTJ memory element of claim 12 , wherein the second magnetic reference layer is located at a bottom portion of the mDMTJ structure, and the first reference layer is located at a top portion of the mDMTJ structure.

19. The STT MTJ memory element of claim 18 , wherein the second magnetic reference layer comprises a lower magnetic reference layer, an anti-ferromagnetic coupling layer, and an upper magnetic reference layer.

20. The STT MTJ memory element of claim 18 , wherein the first tunnel barrier layer and the second tunnel barrier layer have a same lateral dimension.

21. The STT MTJ memory element of claim 18 , wherein the first tunnel barrier layer has a first lateral dimension, and the second tunnel barrier layer has a second lateral dimension that is less than the first lateral dimension.

22. The STT MTJ memory element of claim 21 , wherein the magnetic free contacts a lower portion of the non-magnetic, spin-conducting metallic layer, the lower portion of the non-magnetic, spin-conducting metallic layer has the second lateral dimension, and an upper portion of the non-magnetic, spin-conducting metallic layer has the first lateral dimension.

23. A method of forming a modified double magnetic tunnel junction (mDMTJ) structure, the method comprising:

forming a lower material stack of the mDMTJ structure, wherein the lower material stack comprises, from bottom to top, a first magnetic reference layer, a first tunnel barrier layer, and a non-magnetic, spin-conducting metallic layer; and

forming an upper material stack of the mDMTJ structure on a physically exposed topmost surface of the lower material stack of the mDMTJ structure, wherein the upper material stack comprises, from bottom to top, a magnetic free layer, a second tunnel barrier layer, a magnetic free layer, and a second magnetic reference layer, wherein the non-magnetic, spin-conducting layer has a first surface in direct physical contact with a surface of the first tunnel barrier layer, and a second surface, opposite the first surface, that is in direct physical contact with a surface of the magnetic free layer.

24. The method of claim 23 , wherein the upper material stack includes another non-magnetic, spin-conducting metallic layer of a same non-magnetic, spin-conducting metallic material as the non-magnetic, spin-conducting metallic layer of the lower material stack, wherein the another non-magnetic, spin-conducting metallic layer of the upper material stack forms an interface with the non-magnetic, spin-conducting metallic layer of the lower material stack.

25. A method of forming a magnetoresistive random access memory (MRAM), the method comprising:

forming a lower material stack of the mDMTJ structure, wherein the lower material stack comprises, from bottom to top, a second magnetic reference layer, a second tunnel barrier layer, and a magnetic free layer; and

forming an upper material stack of the mDMTJ structure on a physically exposed topmost surface of the lower material stack of the mDMTJ structure, wherein the upper material stack comprises, from bottom to top, a non-magnetic, spin-conducting metallic layer, a first tunnel barrier layer, and a first magnetic reference layer, wherein the non-magnetic, spin-conducting layer has a first surface in direct physical contact with a surface of the first tunnel barrier layer, and a second surface, opposite the first surface, that is in direct physical contact with a surface of the magnetic free layer.

26. The method of claim 25 , wherein the lower material stack includes another non-magnetic, spin-conducting metallic layer of a same non-magnetic, spin-conducting metallic material as the non-magnetic, spin-conducting metallic layer of the upper material stack, wherein the another non-magnetic, spin-conducting metallic layer of the lower material stack forms an interface with the non-magnetic, spin-conducting metallic layer of the upper material stack.