Multifunctional electrode
View Patent ↗A nonvolatile memory element is disclosed comprising a first electrode, a near-stoichiometric metal oxide memory layer having bistable resistance, and a second electrode in contact with the near-stoichiometric metal oxide memory layer. At least one electrode is a resistive electrode comprising a sub-stoichiometric transition metal nitride or oxynitride, and has a resistivity between 0.1 and 10 Ωcm. The resistive electrode provides the functionality of an embedded current-limiting resistor and also serves as a source and sink of oxygen vacancies for setting and resetting the resistance state of the metal oxide layer. Novel fabrication methods for the second electrode are also disclosed.
1. A nonvolatile memory element comprising
a first layer, wherein the first layer is operable as a first electrode;
a second layer,
wherein the second layer is operable as a resistive switching layer,
wherein the second layer comprises a compound comprising Me 1 v Me 2 w Si x O y N z , where Me 1 and Me 2 are metals, v≧0, w≧0, x≧0, y>0, and z≧0, and at least one of v, w, and x is greater than zero, and
wherein the compound has near-stoichiometric composition and bistable resistance; and
a third layer, wherein the third layer is operable as a second electrode;
wherein at least one of the first layer or the third layer is a layer comprising a substoichiometric nitride or substoichiometric oxynitride, and having a resistivity between 0.1 and 10 Ωcm; and
wherein a resistivity or defect density of the substoichiometric nitride or substoichiometric oxynitride is consistent with sputtered atoms impinging on the growing second layer at an incident angle greater than about 55 degrees relative to a surface normal.
2. The nonvolatile memory element of claim 1 , wherein the at least one of the first layer or the third layer is in contact with the second layer.
3. The nonvolatile memory element of claim 1 , wherein both the first layer and the third layer are resistive layers.
4. The nonvolatile memory element of claim 2 , wherein the at least one of the first layer or the third layer is operable as a source of oxygen vacancies that can migrate into the second layer during the set cycle, and is operable as a sink for oxygen vacancies that can migrate out of the second layer during the reset cycle.
5. The nonvolatile memory element of claim 1 , wherein the second layer comprises a transition metal oxide or transition metal oxynitride.
6. The nonvolatile memory element of claim 1 , wherein the at least one of the first layer or the third layer comprises a transition metal nitride or transition metal oxynitride.
7. The nonvolatile memory element of claim 6 , wherein the transition metal comprises hafnium, tantalum, zirconium, lanthanum, niobium, or tungsten.
8. The nonvolatile memory element of claim 1 , wherein Me 1 and Me 2 are each selected from the group consisting of tantalum, niobium, hafnium, yttrium, zirconium, lanthanum, vanadium, titanium, tungsten, nickel, and aluminum.
9. A method of forming a nonvolatile memory element the method comprising:
forming a first layer, wherein the first layer is operable as a first electrode;
forming a second layer,
wherein the second layer is operable as a resistive switching layer,
wherein the second layer comprises a compound comprising Me 1 v Me 2 w Si x O y N z , where Me 1 and Me 2 are metals, v≧0, w≧0, x≧0, y>0, and z≧0, and at least one of v, w, and x is greater than zero,
wherein the compound has near-stoichiometric composition and bistable resistance; and
forming a third layer, wherein the third layer is operable as a second electrode;
wherein the second layer is disposed between the first and third layers;
wherein at least one of the first and third layers is a layer comprising a sub-stoichiometric nitride or sub-stoichiometric oxynitride, and having a resistivity between 0.1 and 10 Ωcm; and
wherein the substoichiometric nitride or substoichiometric oxynitride is formed by reactive sputtering in an atmosphere comprising nitrogen or a combination of nitrogen and oxygen.
10. The method of claim 9 , wherein both the first and third layers have a resistivity between 0.1 and 10 Ωcm.
11. The method of claim 9 , wherein the at least one of the first layer or the third layer is in contact with the second layer.
12. The method of claim 9 , wherein the atmosphere has a total pressure between about 1 and about 5 mTorr.
13. The method of claim 9 , wherein the atmosphere has a total pressure between about 10 and about 50 mTorr.
14. The method of claim 9 , wherein the substoichiometric nitride or substoichiometric oxynitride is formed by reactive sputtering wherein the sputtered atoms impinge on the growing second electrode layer at an incident angle greater than about 55 degrees relative to the surface normal.
15. The method of claim 9 , wherein the substoichiometric nitride or substoichiometric oxynitride is formed by reactive sputtering wherein a substrate bias voltage is set substantially higher than a bias voltage at which a minimum resistivity occurs in the substoichiometric transition metal nitride or substoichiometric oxynitride.
16. The method of claim 9 , wherein the second layer comprises a transition metal oxide or transition metal oxynitride.
17. The method of claim 16 , wherein the transition metal comprises hafnium, tantalum, zirconium, lanthanum, niobium, or tungsten.
18. The method of claim 9 , wherein Me 1 and Me 2 are each selected from the group consisting of tantalum, niobium, hafnium, yttrium, zirconium, lanthanum, vanadium, titanium, tungsten, nickel, and aluminum.
19. The method of claim 9 , wherein the at least one of the first layer or the third layer comprises a transition metal nitride or transition metal oxynitride.