Reduced diffusion in metal electrode for two-terminal memory
Providing for two-terminal memory that mitigates diffusion of external material therein is described herein. In some embodiments, a two-terminal memory cell can comprise an electrode layer. The electrode layer can be at least in part permeable to ionically or chemically reactive material, such as oxygen or the like. The two-terminal memory can further comprise a diffusion mitigation material disposed between the electrode layer and external material. This diffusion mitigation material can be selected to mitigate or prevent diffusion of the undesired element(s) or compound(s), to mitigate or avoid exposure of such element(s) or compound(s) to the electrode layer. Accordingly, degradation of the two-terminal memory as a result of contact with the undesired element(s) or compound(s) can be mitigated by various disclosed embodiments.
1. A memory cell, comprising:
a monolithic stack comprising a plurality of layers stacked in a first direction, the plurality of layers comprising:
a bottom electrode layer comprising an electrically conductive material;
a switching medium layer, above the bottom electrode layer in the first direction, comprising an electrically resistive material;
a top electrode layer, above the switching medium layer in the first direction, comprising a noble metal that produces ions at a boundary of the top electrode layer and the switching medium layer in response to an electric field applied to the memory cell, wherein the switching medium layer is at least in part permeable to the ions; and
a passivation layer, above the top electrode layer in the first direction, comprising a non-noble metal, wherein the passivation layer reduces diffusion of one or more atmospheric gasses, above the passivation layer in the first direction, into the top electrode layer and switching medium layer.
2. The memory cell of claim 1 , wherein the passivation layer is in immediate contact with the top electrode layer.
3. The memory cell of claim 1 , wherein the non-noble metal of the passivation layer is selected from a group consisting of: W, tungsten nitride, Ti, TiW, Al, Cu and TiN.
4. The memory cell of claim 1 , wherein the passivation layer is deposited above the top electrode layer in an oxygen-free environment.
5. The memory cell of claim 4 , wherein the passivation layer is deposited using a physical vapor deposition process.
6. The memory cell of claim 4 , wherein the passivation layer is deposited using a chemical vapor deposition process.
7. The memory cell of claim 1 , wherein the noble metal of the top electrode layer is Ag.
8. The memory cell of claim 1 , wherein the electrically conductive material of the bottom electrode layer comprises a conductive metal and a doped silicon material.
9. The memory cell of claim 1 , wherein the switching medium layer is comprised of an undoped amorphous Si, an amorphous compound of Si, or a Si sub-oxide.
10. The memory cell of claim 1 , wherein the passivation layer has a thickness in a range of about 10 nanometers (nm) and about 50 nm.
11. The memory cell of claim 1 , further comprising a barrier layer disposed between the switching medium layer and the top electrode layer selected from a group consisting of: Ti, TiN and TiO.
12. The memory cell of claim 11 , wherein the barrier layer has a thickness of about 3 nm to about 10 nm.
13. The memory cell of claim 1 , further comprising:
a semiconductor substrate upon which the memory cell is disposed, the semiconductor substrate comprising at least one complementary metal oxide semiconductor device;
a first metal conductor built on the semiconductor substrate and in electrical contact with the bottom electrode layer; and
a second metal conductor formed at least in part as a metal hardmask in contact with the passivation layer, wherein the first metal conductor and the second metal conductor facilitate application of a signal to the memory cell.
14. A method of fabricating a memory cell, comprising:
forming a first electrically conductive electrode layer above a substrate material;
forming an electrically resistive switching medium above the first electrically conductive electrode layer that is permeable to ions of at least one noble metal;
forming a second electrically conductive electrode layer comprising the at least one noble metal above the electrically resistive switching medium; and
forming a diffusion mitigation layer comprising a non-noble metal above the second electrically conductive electrode layer, wherein the diffusion mitigation layer is configured to mitigate diffusion of one or more atmospheric gasses above the diffusion mitigation layer into the second electrically conductive electrode layer and electrically resistive switching medium; and
wherein the second electrically conductive electrode layer is configured to generate ions at least at a surface closest to the electrically resistive switching medium in response to an electric field.
15. The method of claim 14 , wherein the non-noble metal of the diffusion mitigation layer is selected from a group consisting of W, Ti, TiN, Al, Cu, WN, and TiW.
16. The method of claim 14 , further comprising subjecting the memory cell to an ambient atmosphere after the forming the second electrically conductive electrode layer, wherein the forming the diffusion mitigation layer is performed within about 4 hours of the forming the second electrically conductive electrode layer.
17. The method of claim 14 , further comprising forming a barrier layer that is selected from a group consisting of: Ti, TiN and TiO disposed between the electrically resistive switching medium and the second electrically conductive electrode layer, wherein the barrier layer has a thickness about 10 nanometers (nm) or less, and the diffusion mitigation layer has a thickness within a range of about 10 nm to about 50 nm.
18. The method of claim 14 , further comprising subjecting the memory cell to an inert atmosphere after the forming the second electrically conductive electrode layer, wherein the forming the diffusion mitigation layer is performed within about 24 hours of the forming the second electrically conductive electrode layer.
19. A device, comprising:
an array of memory cells, where a memory cell of the array of memory cells comprises:
a monolithic stack comprising a plurality of layers stacked in a first direction, the plurality of layers comprising:
a bottom electrode layer comprising an electrically conductive material;
a switching medium layer, above the bottom electrode layer in the first direction, comprising an electrically resistive material;
a top electrode layer, above the switching medium layer in the first direction, comprising a noble metal that produces ions at a boundary of the top electrode layer and the switching medium layer in response to an electric field applied to the memory cell, wherein the switching medium layer is at least in part permeable to the ions; and
a passivation layer, above the top electrode layer in the first direction, comprising a non-noble metal, wherein the passivation layer reduces diffusion of one or more atmospheric gasses, above the passivation layer in the first direction, into the top electrode layer and switching medium layer.
20. The device of claim 19 , wherein the passivation layer is in immediate contact with the top electrode layer.