Magnetoresistive structure having a metal oxide tunnel barrier and method of manufacturing same
In one aspect, the present inventions are directed to a magnetoresistive structure having a tunnel junction, and a process for manufacturing such a structure. The tunnel barrier may be formed between a free layer and a fixed layer in a plurality of repeating process of depositing a metal material and oxidizing at least a portion of the metal material. Where the tunnel barrier is formed by deposition of at least three metal materials interceded by an associated oxidization thereof, the oxidation dose associated with the second metal material may be greater than the oxidation doses associated with the first and third metal materials. In certain embodiments, the fixed layer may include a discontinuous layer of a metal, for example, Ta, in the fixed layer between two layers of a ferromagnetic material.
1. A method of manufacturing a tunnel barrier of a magnetoresistive structure including first and second ferromagnetic layers, wherein the tunnel barrier is disposed between the first and second ferromagnetic layers, the method comprising:
depositing a first metal material over the first ferromagnetic layer;
oxidizing at least a portion of the first metal material to a first oxidation dose to provide a first metal oxide;
depositing a second metal material over the first metal oxide;
oxidizing at least a portion of the second metal material to a second oxidation dose to provide a second metal oxide, wherein the second oxidation dose is greater than the first oxidation dose;
depositing a third metal material over the second metal oxide; and
oxidizing at least a portion of the third metal material to a third oxidation dose to provide a third metal oxide, wherein the third oxidation dose is less than the second oxidation dose.
2. The method of claim 1 wherein the first, second, and third metal materials include magnesium.
3. The method of claim 1 wherein depositing the first, second and third metal materials further comprise:
depositing the first, second and third metal materials having a thickness in a range of 3 to 6 Angstroms.
4. The method of claim 1 wherein oxidizing the first, second, and third metal materials comprises:
oxidizing the first, second, and third metal materials using at least one of natural oxidation, exposure to oxygen radicals, an argon and oxygen plasma, and an ion beam.
5. The method of claim 1 wherein depositing the first, second, and third metal materials comprises:
depositing the first, second, and third metal materials using a sputtering process.
6. The method of claim 1 wherein:
the second oxidation dose is at least 100 times greater than the first oxidation dose, and
the second oxidation dose is at least 20 times greater than the third oxidation dose.
7. The method of claim 1 wherein:
the second oxidation dose is at least 1000 times greater than the first oxidation dose, and
the second oxidation dose is at least 100 times greater than the third oxidation dose.
8. A method for manufacturing a magnetoresistive structure, the method comprising:
depositing a first layer of ferromagnetic material;
forming a tunnel barrier over the first layer of ferromagnetic material, wherein forming the tunnel barrier includes:
depositing a first metal material,
oxidizing at least a portion of the first metal material to a first oxidation dose to provide a first metal oxide,
depositing a second metal material over the first metal oxide,
oxidizing at least a portion of the second metal material to a second oxidation dose to provide a second metal oxide, wherein the second oxidation dose is greater than the first oxidation dose,
depositing a third metal material over the second metal oxide, and
oxidizing at least a portion of the third metal material to a third oxidation dose to provide a third metal oxide, wherein the third oxidation dose is greater than the first oxidation dose; and
depositing a second layer of ferromagnetic material over the third metal oxide of the tunnel barrier.
9. The method of claim 8 wherein:
depositing the first, second and third metal materials comprises depositing each of the first, second, and third metal materials having a thickness of between 3 to 6 Angstroms,
the second oxidation dose is at least 1000 times greater than the first oxidation dose, and
the third oxidation dose is at least 10 times greater than the first oxidation dose.
10. The method of claim 8 wherein:
depositing the first, second and third metal materials comprises depositing the first, second, and third metal materials wherein each have a thickness of between 3 to 6 Angstroms,
one or more of the first, second, and third metal materials is/are magnesium,
the second oxidation dose is at least 1000 times greater than the first oxidation dose, and
the second oxidation dose is at least 20 times greater than the third oxidation dose.
11. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing an iron alloy layer; and
wherein the tunnel barrier is formed on the iron alloy layer.
12. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing a cobalt-iron-boron alloy layer, wherein the tunnel barrier is formed on the cobalt-iron-boron alloy layer.
13. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing a cobalt alloy layer; and
wherein the tunnel barrier is formed on the cobalt alloy layer.
14. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing a third layer of ferromagnetic material;
depositing a fourth layer of ferromagnetic material;
depositing a coupling layer, wherein the coupling layer is disposed between and adjacent to the third and fourth layers of ferromagnetic material to provide antiferromagnetic coupling therebetween;
depositing a cobalt alloy layer on the fourth layer of ferromagnetic material, wherein the tunnel barrier is formed over the cobalt alloy layer.
15. The method of claim 14 wherein the cobalt alloy layer is an iron-cobalt alloy layer.
16. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing a third layer of ferromagnetic material;
depositing a fourth layer of ferromagnetic material;
depositing a coupling layer, wherein the coupling layer is disposed between and adjacent to the third and fourth layers of ferromagnetic material to provide antiferromagnetic coupling therebetween;
depositing an iron alloy layer on the fourth layer of ferromagnetic material, wherein the tunnel barrier is formed over the iron alloy layer.
17. A method of manufacturing a tunnel barrier of a magnetoresistive structure including first and second ferromagnetic layers, wherein the tunnel barrier is disposed between the first and second ferromagnetic layers, the method comprising:
depositing a first metal material over the first ferromagnetic layer;
oxidizing at least a portion of the first metal material to a first oxidation dose to provide a first metal oxide;
depositing a second metal material over the first metal oxide;
oxidizing at least a portion of the second metal material to a second oxidation dose to provide a second metal oxide, wherein the second oxidation dose is greater than the first oxidation dose;
depositing a third metal material over the second metal oxide; and
oxidizing at least a portion of the third metal material to a third oxidation dose to provide a third metal oxide;
depositing a fourth metal material over the third metal oxide; and
oxidizing at least a portion of the fourth metal material to a fourth oxidation dose to provide a fourth metal oxide, wherein the second and third oxidation doses are greater than the fourth oxidation dose.
18. The method of claim 17 wherein:
at least one of the first, second, third and fourth metal materials includes magnesium, and
the second and third oxidation doses are at least 1000 times greater than the first oxidation dose.
19. The method of claim 17 wherein:
the second and third oxidation doses are at least 1000 times greater than the first oxidation dose, and
the fourth oxidation dose is at least 5 times greater than the first oxidation dose.
20. The method of claim 17 wherein the second and/or third oxidation doses are at least 1000 times greater than the first oxidation dose.
21. The method of claim 8 wherein depositing the first layer of ferromagnetic material comprises:
depositing a layer including at least one of iron or cobalt; and
wherein the tunnel barrier is formed on the layer including at least one of iron or cobalt.