Nonvolatile storage element and method for manufacturing same

1. A nonvolatile storage element comprising:

a first electrode;

a second electrode; and

a variable resistance layer provided between the first electrode and the second electrode, and having a resistance value that reversibly changes based on an electrical signal applied between the first electrode and the second electrode,

wherein the variable resistance layer includes a first transition metal oxide layer, a second transition metal oxide layer, and a third transition metal oxide layer, the first transition metal oxide layer having a composition expressed as MO x (where M is a transition metal and O is oxygen), the second transition metal oxide layer having a composition expressed as MO y (where x>y), and the third transition metal oxide layer having a composition expressed as MO z (where y>z),

wherein the second transition metal oxide layer is directly stacked on the first transition metal oxide layer,

wherein the third transition metal oxide layer is directly stacked on the second transition metal oxide layer, and

wherein an oxygen content atomic percentage of the first transition metal oxide layer is greater than an oxygen content atomic percentage of the second transition metal oxide layer, and the oxygen content atomic percentage of the second transition metal oxide layer is greater than an oxygen content atomic percentage of the third transition metal oxide layer.

2. The nonvolatile storage element according to claim 1 ,

wherein the first transition metal oxide layer is a layer in which a filament path is formed, the filament path being a micro region of which resistance changes.

3. The nonvolatile storage element according to claim 1 ,

wherein a filament path is formed in the first transition metal oxide layer, the filament path being a micro region of which resistance changes such that a resistance of the nonvolatile element changes, after an initial breakdown of the nonvolatile storage element is performed by applying, to the nonvolatile memory element, a voltage having an absolute value higher than an absolute value of a voltage applied in a normal operation.

4. The nonvolatile storage element according to claim 1 ,

wherein the first transition metal oxide layer is an insulating layer before an initial breakdown of the nonvolatile storage element is performed.

5. The nonvolatile storage element according to claim 1 ,

wherein the second transition metal oxide layer has a film thickness greater than a film thickness of the first transition metal oxide layer and a film thickness of the third transition metal oxide layer.

6. The nonvolatile storage element according to claim 1 ,

wherein the third transition metal oxide layer has a film thickness greater than a film thickness of the first transition metal oxide layer and a film thickness of the second transition metal oxide layer.

7. The nonvolatile storage element according to claim 1 ,

wherein the variable resistance layer further includes a fourth transition metal oxide layer stacked on the third transition metal oxide layer, the fourth transition metal oxide layer having a composition expressed as MO a (where z>a).

8. The nonvolatile storage element according to claim 1 ,

wherein the first electrode and the first transition metal oxide layer are connected to each other,

wherein the second electrode and the third transition metal oxide layer are connected to each other,

wherein the first electrode and the second electrode include respective materials having mutually different chemical elements as main components, and

wherein a standard electrode potential V1 of the first electrode, a standard electrode potential V2 of the second electrode, and a standard electrode potential Vt of the transition metal M satisfy Vt<V1 and V2<V1.

9. The nonvolatile storage element according to claim 8 ,

wherein the first electrode is provided above the second electrode.

10. The nonvolatile storage element according to claim 8 ,

wherein the first electrode is provided below the second electrode.

11. The nonvolatile storage element according to claim 1 ,

wherein the first transition metal oxide layer, the second transition metal oxide layer, and the third transition metal oxide layer comprise a tantalum oxide, a hafnium oxide, or a zirconium oxide as a variable resistance material.

12. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is tantalum, and

wherein the first transition metal oxide layer comprising TaO x , the second transition metal oxide layer comprising TaO y , and the third transition metal oxide layer comprising TaO z satisfy 2.1≦x, 0.8≦y≦1.9, and 0<z<0.8.

13. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is hathium, and

wherein the first transition metal oxide layer comprising HfO x , the second transition metal oxide layer comprising HfO y , and the third transition metal oxide layer comprising HfO z satisfy 1.8<x, 0.9≦y≦1.6, and 0<z<0.9.

14. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is zirconium, and

wherein the first transition metal oxide layer comprising ZrO x , the second transition metal oxide layer comprising ZrO y , and the third transition metal oxide layer comprising ZrO z satisfy 1.9<x, 0.9≦y≦1.4, and 0<z<0.9.

15. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is tantalum, and

wherein the first transition metal oxide layer comprising TaO x , the second transition metal oxide layer comprising TaO y , and the third transition metal oxide layer comprising TaO z satisfy 2.1≦x, 0.8≦y≦1.9, and 0.8≦z≦1.9.

16. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is hathium, and

wherein the first transition metal oxide layer comprising HfO x , the second transition metal oxide layer comprising HfO y , and the third transition metal oxide layer comprising HfO z satisfy 1.8<x, 0.9≦y≦1.6, and 0.9≦z≦1.6.

17. The nonvolatile storage element according to claim 11 ,

wherein the transition metal M is zirconium, and

wherein the first transition metal oxide layer comprising ZrO x , the second transition metal oxide layer comprising ZrO y , and the third transition metal oxide layer comprising ZrO z satisfy 1.9<x, 0.9≦y≦1.4, and 0.9≦z≦1.4.