Forming nonvolatile memory elements by diffusing oxygen into electrodes
View Patent ↗Provided are methods of forming nonvolatile memory elements including resistance switching layers. A method involves diffusing oxygen from a precursor layer to one or more reactive electrodes by annealing. At least one electrode in a memory element is reactive, while another may be inert. The precursor layer is converted into a resistance switching layer as a result of this diffusion. The precursor layer may initially include a stoichiometric oxide that generally does not exhibit resistance switching characteristics until oxygen vacancies are created. Metals forming such oxides may be more electronegative than metals forming a reactive electrode. The reactive electrode may have substantially no oxygen at least prior to annealing. Annealing may be performed at 250-400° C. in the presence of hydrogen. These methods simplify process control and may be used to form nonvolatile memory elements including resistance switching layers less than 20 Angstroms thick.
1. A method of forming a nonvolatile memory element, the method comprising:
forming a first layer, the first layer comprising a first metal, wherein the first layer is operable as a first electrode;
forming a second layer, the second layer comprising an oxide of a second metal that is more electronegative than the first metal; and
annealing the first layer and the second layer,
wherein oxygen diffuses from the second layer into the first layer;
wherein the second layer exhibits resistance switching characteristics after annealing; and
wherein the annealing is performed in a hydrogen containing environment comprising no more than 10 weight percent of hydrogen.
2. The method of claim 1 , wherein the second metal comprises aluminum and the first metal comprises tantalum.
3. The method of claim 1 , wherein the second metal comprises hafnium and the first metal comprises tantalum.
4. The method of claim 1 , wherein the second layer is formed after forming the first layer.
5. The method of claim 1 , wherein the second layer directly interfaces the first layer.
6. The method of claim 1 , wherein the first metal comprises one or more of aluminum, titanium, chromium, molybdenum, tungsten, or niobium.
7. The method of claim 1 , wherein, prior to annealing, the oxide of the second metal has a concentration of oxygen vacancies of less than 0.1 atomic percent.
8. The method of claim 1 , wherein, after annealing, the oxide of the second metal has a concentration of oxygen vacancies of at least 0.5 atomic percent.
9. The method of claim 1 , wherein annealing is performed at a temperature of between 250° C. and 400° C.
10. The method of claim 9 , wherein a duration of the annealing is less than 30 minutes.
11. The method of claim 1 , wherein the second layer has a thickness of less than about 20 Angstroms.
12. The method of claim 1 , wherein the first layer is a part of a bit line or a word line in the nonvolatile memory element.
13. The method of claim 1 , further comprising forming a third layer on an opposite side of the second layer with respect to the first layer, wherein the third layer is operable as a second electrode of the nonvolatile memory element.
14. The method of claim 13 , wherein, during annealing, substantially no oxygen diffuses from the second layer into the first layer.
15. The method of claim 14 , wherein the third layer comprises one or more of titanium nitride, tantalum nitride, platinum, gold, iridium oxide, or ruthenium oxide.
16. The method of claim 13 , wherein the third layer comprises the first metal and wherein, during annealing, oxygen diffuses from the second layer into the third layer.
17. A method of forming a nonvolatile memory element, the method comprising:
forming a first layer, the first layer comprising a first metal, wherein the first layer is operable as a first electrode;
forming a second layer, the second layer comprising an oxide of a second metal that is more electronegative than the first metal; and
forming a third layer, the third layer comprising an oxygen resistant material, wherein the third layer is operable as a second electrode, and wherein the second layer is positioned between the first layer and the third layer;
annealing the first layer, the second layer, and the third layer at a temperature of between 250° C. and 400° C.;
wherein oxygen diffuses from the second layer into the first layer but substantially no oxygen diffuses from the second layer into the third layer;
wherein the second layer exhibits resistance switching characteristics after annealing; and
wherein, after the annealing, a concentration of oxygen vacancies in the second layer is uneven.
18. A nonvolatile memory element comprising:
a first layer comprising a first metal and an oxide of the first metal, wherein the first layer is operable as a first electrode;
a second layer comprising an oxide of a second metal that is more electronegative than the first metal, wherein the oxide of the second metal comprises oxygen vacancies at least at an interface between the second layer and the first layer such that the second layer is operable as a resistance switching layer; and
a third layer comprising an oxygen resistant material, wherein the third layer is operable as a second electrode, and wherein the second layer is positioned between the first layer and the third layer.