Programmable conductor memory cell structure and method therefor
View Patent ↗In programmable conductor memory cells, metal ions precipitate out of a glass electrolyte element in response to an applied electric field in one direction only, causing a conductive pathway to grow from cathode to anode. The amount of conductive pathway growth, and therefore the programming, depends, in part, on the availability of metal ions. It is important that the metal ions come only from the solid solution of the memory cell body. If additional metal ions are supplied from other sources, such as the sidewall edge at the anode interface, the amount of metal ions may not be directly related to the strength of the electric field, and the programming will not respond consistently from cell to cell. The embodiments described herein provide new and novel structures that block interface diffusion paths for metal ions, leaving diffusion from the bulk glass electrolyte as the only supply of metal ions for conductive pathway formation.
1. A method of forming a programmable conductor memory cell comprising:
forming a cathode;
forming a glass electrolyte element in contact with the cathode;
forming an insulating layer over the glass electrolyte element;
forming an anode via in the insulating layer, thereby exposing a surface of the glass electrolyte element;
depositing a layer of spacer material that conforms to contours of the anode via and the insulating layer;
preferentially etching horizontal portions of the spacer material to expose a central portion of the surface of the glass electrolyte element; and
depositing a layer of conducting material sufficiently thick to fill the anode via and to provide a conducting layer over the insulting layer, thus forming an anode.
2. The method of claim 1 , wherein forming the glass electrolyte element comprises forming a germanium-selenium glass and introducing silver ions into the glass by deposition of a silver layer over the glass and subsequently diffusing silver from the silver layer into the glass.
3. The method of claim 2 , wherein diffusing silver into the glass comprises photodissolution.
4. The method of claim 1 , wherein forming the glass electrolyte element comprises forming a first germanium selenide layer, an intervening metal selenide layer over the germanium selenide layer, and a second germanium selenide layer over the intervening metal selenide layer.
5. The method of claim 1 , wherein forming the insulating layer comprises depositing silicon nitride.
6. The method of claim 1 , wherein the anode via is formed to a width between about 200 nm and 300 nm.
7. The method of claim 1 , wherein depositing the layer of spacer material comprises depositing a layer of insulating material.
8. The method of claim 7 , wherein depositing the layer of spacer materials comprises depositing a layer of silicon nitride.
9. The method of claim 8 , wherein the layer of spacer material is deposited to a thickness between about 5 nm and 30 nm.
10. The method of claim 1 , wherein preferentially etching comprises reactive ion etching.
11. The method of claim 1 , wherein depositing a layer of conducting material comprises depositing silver.
12. A method of forming a programmable conductor memory cell comprising:
forming a cathode;
forming a glass electrolyte element in contact with the cathode and having a sidewall edge;
forming an insulating layer over the glass electrolyte element and covering the sidewall edge;
forming an opening in the insulating layer, to expose a surface of the glass electrolyte element without exposing the sidewall edge; and
depositing a layer of conducting material into the opening to contact only the central portion of the surface of the glass electrolyte element, thus forming an anode.
13. The method of claim 12 , wherein forming the opening comprises:
etching a via through the insulating layer;
blanket depositing a spacer material layer; and
preferentially etching horizontal portions of the spacer material layer to expose the central portion of the surface of the glass electrolyte element.
14. The method of claim 13 , wherein the spacer material comprises an insulating material.
15. The method of claim 12 , wherein the insulating material is silicon nitride.
16. The method of claim 12 , wherein forming the opening in the insulating layer comprises patterning and etching using a mask with an opening smaller and in width than the glass electrolyte element and having the opening arranged concentrically over the glass electrolyte element.