Variable resistance element having gradient of diffusion coefficient of ion conducting layer
A structure for a variable-resistance element using an electrochemical reaction. The structure limits a position at which metal cross-linking breaks to a position most preferred for cross-linking break: namely, a part of an ion conduction layer closest to a first electrode. Also provided is a method for manufacturing the variable-resistance element, which has a first electrode serving as a source for a metal ion(s), a second electrode which is less ionizable (i.e. has a higher redox potential) than the first electrode, and an ion conduction layer which is interposed between the first and second electrodes and can conduct the metal ion(s). There is a first region in the ion conduction layer, adjacent to the first electrode, having a diffusion coefficient that increases continuously towards the first electrode right upto contacting the first electrode.
1. A variable resistance element, comprising:
a first electrode that serves as a source of a metal ion(s);
a second electrode that is less ionizable than said first electrode; and
an ion conducting layer that is disposed between said first electrode and said second electrode and is capable of conducting said metal ion; wherein
said ion conducting layer includes a first region which has a first diffusion coefficient successively increasing toward said first electrode up to contacting said first electrode, said first region being disposed adjacent to said first electrode, and
said ion conducting layer has a single maximum diffusion coefficient at a boundary with said first electrode,
said ion conducting layer further includes a second region which has a second diffusion coefficient that is constant;
said second region is formed between said first region and said second electrode; and
said second diffusion coefficient in said second region is equal to or less than a minimum value of said first diffusion coefficient in said first region.
2. The variable resistance element according to claim 1 , wherein
said ion conducting layer comprises a compound(s) including two or more elements; and
said first region having a gradient of said first diffusion coefficient is formed by varying a composition ratio of said two or more elements in a vertical direction of the layer, that is, in a direction across said first electrode and said second electrode.
3. The variable resistance element according to claim 2 , wherein
said compound(s) including two or more elements is (are) composed of a metal, and nitrogen and/or a chalcogen element(s) that belongs to group 16 of a periodic table.
4. The variable resistance element according to claim 3 , wherein said ion conducting layer comprises metal oxide or metal oxynitride.
5. The variable resistance element according to claim 4 , wherein said ion conducting layer comprises tantalum oxide or tantalum oxynitride.
6. A variable resistance element, comprising:
a first electrode that serves as a source of a metal ion(s);
a second electrode that is less ionizable than said first electrode; and
an ion conducting layer that is disposed between said first electrode and said second electrode and is capable of conducting said metal ion; wherein
said ion conducting layer includes a first region which has a first diffusion coefficient successively increasing toward said first electrode up to contacting said first electrode, said first region being disposed adjacent to said first electrode, wherein
said ion conducting layer further includes a second region which has a second diffusion coefficient that is constant;
said second region is formed between said first region and said second electrode; and
said second diffusion coefficient in said second region is equal to or less than a minimum value of said first diffusion coefficient in said first region.
7. A variable resistance element, comprising:
a first electrode that serves as a source of a metal ion(s);
a second electrode that is less ionizable than said first electrode; and
an ion conducting layer that is disposed between said first electrode and said second electrode and is capable of conducting said metal ion; wherein
said ion conducting layer includes a first region which has a first diffusion coefficient successively increasing toward said first electrode up to contacting said first electrode, said first region being disposed adjacent to said first electrode, wherein
said ion conducting layer includes impurity; and
said first region having a gradient of said first diffusion coefficient is formed by varying an amount of said impurity in a vertical direction of the layer, that is, in a direction across said first electrode and said second electrode.
8. The variable resistance element according to claim 7 , wherein
said ion conducting layer comprises tantalum oxide or tantalum oxynitride including silicon as said impurity.
9. A variable resistance element, comprising:
a first electrode that serves as a source of a metal ion(s);
a second electrode that is less ionizable than said first electrode; and
an ion conducting layer that is disposed between said first electrode and said second electrode and is capable of conducting said metal ion; wherein
said ion conducting layer includes a first region which has a first diffusion coefficient successively increasing toward said first electrode up to contacting said first electrode, said first region being disposed adjacent to said first electrode, wherein
said ion conducting layer has a first temperature dependence of the diffusion coefficient on a first side adjacent to said first electrode greater than a second temperature dependence of the diffusion coefficient on a second side adjacent to said second electrode.
10. The variable resistance element according to claim 9 , wherein
an operation of transition from a high resistance state to a low resistance state is performed in a temperature range in which said ion conducting layer has a first gradient of the diffusion coefficient on said first side adjacent to said first electrode greater than a second gradient of the diffusion coefficient on said second side adjacent to said second electrode.