Magnetoresistive memory element having a metal oxide tunnel barrier
A magnetoresistive memory array including a plurality of magnetoresistive memory elements wherein each magnetoresistive memory element comprises a free layer including at least one ferromagnetic layer having perpendicular magnetic anisotropy, a fixed layer, and a tunnel barrier, disposed between and in contact with the free and fixed layers. The tunnel barrier includes a first metal-oxide layer, having a thickness between 1 and 10 Angstroms, a second metal-oxide layer, having a thickness between 3 and 6 Angstroms, disposed on the first metal-oxide layer, and a third metal-oxide layer, having a thickness between 3 and 6 Angstroms, disposed over the second metal-oxide layer. In one embodiment, the third metal-oxide layer is in contact with the free layer or fixed layer. The tunnel barrier may also include a fourth metal-oxide layer, having a thickness between 1 and 10 Angstroms, disposed between the second and third metal-oxide layers.
1. A magnetoresistive memory array including a plurality of magnetoresistive memory elements, wherein each magnetoresistive memory element comprising:
a free layer including at least one ferromagnetic layer having perpendicular magnetic anisotropy;
a fixed layer including at least one ferromagnetic layer; and
a tunnel barrier, disposed between and in contact with the free layer and the fixed layer, the tunnel barrier including:
a first metal-oxide layer, having a thickness between 1 and 10 Angstroms;
a second metal-oxide layer, having a thickness between 3 and 6 Angstroms, disposed on the first metal-oxide layer;
a third metal-oxide layer, having a thickness between 3 and 6 Angstroms, disposed on the second metal-oxide layer; and
a fourth metal-oxide layer, having a thickness between 1 and 10 Angstroms, disposed over the third metal-oxide layer, wherein the fourth metal-oxide layer is in contact with (i) the at least one ferromagnetic layer of the free layer or (ii) the at least one ferromagnetic layer of the fixed layer.
2. The magnetoresistive memory array of claim 1 wherein the first metal-oxide layer, second metal-oxide layer, third metal-oxide layer and fourth metal-oxide layer are magnesium-oxide layers.
3. The magnetoresistive memory array of claim 1 wherein the first metal-oxide layer has a first resistance-area product, second metal-oxide layer has a second resistance-area product, third metal-oxide layer has a third resistance-area product, and fourth metal-oxide layer has a fourth resistance-area product.
4. The magnetoresistive memory array of claim 1 wherein the first metal-oxide layer includes a first oxidation level, second metal-oxide layer includes a second oxidation level and wherein the second oxidation level is greater than the first oxidation level.
5. The magnetoresistive memory array of claim 1 wherein the third metal-oxide layer includes a third oxidation level and wherein the third oxidation level is greater than the first oxidation level.
6. The magnetoresistive memory array of claim 1 wherein the fourth metal-oxide layer includes a fourth oxidation level and wherein the fourth oxidation level is greater than the first oxidation level.
7. The magnetoresistive memory array of claim 1 wherein the fourth metal-oxide layer includes a fourth oxidation level and wherein the fourth oxidation level is less than the second oxidation level or third oxidation level.
8. A magnetoresistive memory array including a plurality of magnetoresistive memory elements, wherein each magnetoresistive memory element comprising:
a free layer including at least one ferromagnetic layer having perpendicular magnetic anisotropy;
a fixed layer including at least one ferromagnetic layer; and
a tunnel barrier, disposed between and in contact with the free layer and the fixed layer, the tunnel barrier including:
a first magnesium-oxide layer, having a thickness between 1 and 10 Angstroms, wherein the first magnesium-oxide layer is in contact with the fixed layer;
a second magnesium-oxide layer, having a thickness between 3 and 6 Angstroms; and
a third magnesium-oxide layer, having a thickness between 1 and 10 Angstroms, wherein the third magnesium-oxide layer is in contact with the free layer and wherein the second magnesium-oxide layer is disposed between the first and third magnesium-oxide layers.
9. The magnetoresistive memory array of claim 8 wherein the first magnesium-oxide layer has a first resistance-area product, second magnesium-oxide layer has a second resistance-area product, and third magnesium-oxide layer has a third resistance-area product.
10. The magnetoresistive memory array of claim 9 wherein the first resistance-area product is less than the second resistance-area product.
11. The magnetoresistive memory array of claim 9 wherein the third resistance-area product is less than the second resistance-area product.
12. The magnetoresistive memory array of claim 9 wherein the first resistance-area product is less than the third resistance-area product.
13. The magnetoresistive memory array of claim 8 wherein the first magnesium-oxide layer includes a first oxidation level, second magnesium-oxide layer includes a second oxidation level and wherein the second oxidation level is greater than the first oxidation level.
14. The magnetoresistive memory array of claim 8 wherein:
the tunnel barrier is in contact with the at least one ferromagnetic layer of the free layer and wherein the one ferromagnetic layer of the free layer includes iron; and
the tunnel barrier is in contact with the at least one ferromagnetic layer of the fixed layer and wherein the one ferromagnetic layer of the fixed layer is iron.
15. The magnetoresistive memory array of claim 8 wherein:
the tunnel barrier is in contact with the at least one ferromagnetic layer of the free layer or the at least one ferromagnetic layer of the fixed layer, and
the at least one ferromagnetic layer of the free layer or the at least one ferromagnetic layer of the fixed layer is an iron alloy.
16. The magnetoresistive memory array of claim 8 wherein:
the tunnel barrier is in contact with the at least one ferromagnetic layer of the free layer or the at least one ferromagnetic layer of the fixed layer, and
the at least one ferromagnetic layer of the free layer or the at least one ferromagnetic layer of the fixed layer is a cobalt-iron-boron alloy.
17. A magnetoresistive memory array including a plurality of magnetoresistive memory elements, wherein each magnetoresistive memory element comprising:
a free layer including at least one ferromagnetic layer having perpendicular magnetic anisotropy;
a fixed layer including at least one ferromagnetic layer; and
a tunnel barrier, disposed between and in contact with the free layer and the fixed layer, the tunnel barrier including:
a first magnesium-oxide layer, having a thickness between 1 and 10 Angstroms and a first resistance-area product;
a second magnesium-oxide layer, having a thickness between 3 and 6 Angstroms and a second resistance-area product, disposed over the first magnesium-oxide layer; and
a third magnesium-oxide layer, having a thickness between 3 and 6 Angstroms, disposed over the second magnesium-oxide layer, wherein the third magnesium-oxide layer is in contact with (i) the free layer or (ii) the fixed layer.
18. The magnetoresistive memory array of claim 17 wherein the first resistance-area product is less than the second resistance-area product.
19. The magnetoresistive memory array of claim 18 wherein the first resistance-area product is less than the resistance-area product of the third magnesium-oxide layer.
20. The magnetoresistive memory array of claim 18 wherein the resistance-area product of the third magnesium-oxide layer is less than the second resistance-area product.