Double magnetic tunnel junction device

1. A method of manufacturing a double magnetic tunnel junction device, the method comprising:

forming a first magnetic tunnel junction stack;

forming a spin conducting layer on the first magnetic tunnel junction stack; and

forming a second magnetic tunnel junction stack on the spin conducting layer,

wherein the second magnetic tunnel junction stack has a width that is less than a width of the first magnetic tunnel junction stack,

wherein a width of the spin conducting layer increases in a thickness direction from a first side of the spin conducting layer adjacent to the second magnetic tunnel junction stack to a second side of the spin conducting layer adjacent to the first magnetic tunnel junction stack, and

wherein the spin conducting layer includes a curved sidewall profile.

2. The method according to claim 1 , wherein forming the first magnetic tunnel junction stack includes:

forming a first reference layer;

forming a first tunnel barrier layer on the first reference layer;

forming a first magnetic free layer on the first tunnel barrier layer; and

forming a second tunnel barrier layer on the first magnetic free layer.

3. The method according to claim 2 , further comprising:

forming an etch stop layer on the second magnetic tunnel junction stack; and

forming a metallic hard mask layer on the etch stop layer.

4. The method according to claim 1 , wherein the increasing width of the spin conducting layer is formed by etching partially through a thickness of the spin conducting layer.

5. The method according to claim 4 , further comprising forming a dielectric spacer layer on surfaces of the spin conducting layer and the second magnetic tunnel junction stack,

wherein forming the dielectric spacer layer occurs after performing the etching partially through the spin conducting layer, and wherein the dielectric spacer layer covers a portion of the underlying spin conducting layer.

6. The method according to claim 5 , further comprising etching through portions of the spin conducting layer and the first magnetic tunnel junction stack that are not covered by the dielectric spacer layer.

7. The method according to claim 1 , wherein a width of a top surface of the spin conducting layer is the same as a width of a bottom surface of the second magnetic tunnel junction stack, and wherein a width of a bottom surface of the spin conducting layer is the same as a width of a top surface of the first magnetic tunnel junction stack.

8. The method according to claim 1 , wherein the first magnetic tunnel junction stack is formed by a self-aligned patterning process.

9. The method according to claim 1 , wherein the spin conducting layer has a lower portion and an upper portion, and the lower portion has a sidewall profile that is more vertical than a sidewall profile of the upper portion.

10. The method according to claim 1 , wherein the second magnetic tunnel junction has a sidewall profile that is more vertical than a sidewall profile of the spin conducting layer.

11. A double magnetic tunnel junction device comprising:

a first magnetic tunnel junction stack;

a spin conducting layer formed on the first magnetic tunnel junction stack; and

a second magnetic tunnel junction stack formed on the spin conducting layer;

wherein the second magnetic tunnel junction stack has a width that is less than a width of the first magnetic tunnel junction stack, and

wherein a width of the spin conducting layer increases in a thickness direction from a first side of the spin conducting layer adjacent to the second magnetic tunnel junction stack to a second side of the spin conducting layer adjacent to the first magnetic tunnel junction stack, and

wherein the spin conducting layer includes a curved sidewall profile.

12. The double magnetic tunnel junction device according to claim 11 , wherein the first magnetic tunnel junction stack includes:

a first reference layer;

a first tunnel barrier layer on the first reference layer;

a first magnetic free layer on the first tunnel barrier layer; and

a second tunnel barrier layer on the first magnetic free layer.

13. The double magnetic tunnel junction device according to claim 12 , further comprising:

an etch stop layer on the second magnetic tunnel junction stack; and

a metallic hard mask layer on the etch stop layer.

14. The double magnetic tunnel junction device according to claim 11 , wherein a width of a top surface of the spin conducting layer is the same as a width of a bottom surface of the second magnetic tunnel junction stack, and wherein a width of a bottom surface of the spin conducting layer is the same as a width of a top surface of the first magnetic tunnel junction stack.

15. The double magnetic tunnel junction device according to claim 11 , wherein the first magnetic tunnel junction stack is formed by a self-aligned patterning process.

16. The double magnetic tunnel junction device according to claim 11 , further comprising:

a dielectric spacer layer formed on surfaces of the spin conducting layer and the second magnetic tunnel junction stack; and

an encapsulating dielectric layer formed on side surfaces of the dielectric spacer layer, and on side surfaces of the first magnetic tunnel junction stack.

17. The double magnetic tunnel junction device according to claim 16 , further comprising an interlayer dielectric formed on the encapsulating dielectric layer.

18. The double magnetic tunnel junction device according to claim 17 , wherein the first magnetic tunnel junction stack is formed on a via dielectric layer, and the encapsulating dielectric layer extends below a top surface of the via dielectric layer.

19. The double magnetic tunnel junction device according to claim 11 , wherein the spin conducting layer is non-magnetic, and comprises at least one material selected from the group consisting of Cu, CuN, Ag and AgSn.

20. The double magnetic tunnel junction device according to claim 11 , wherein the second magnetic tunnel junction has a sidewall profile that is more vertical than a sidewall profile of the spin conducting layer.