Multi-level resistive memory cell using different crystallization speeds

1. An integrated circuit comprising:

a first electrode;

a second electrode;

a first resistivity changing material between the first electrode and the second electrode; and

a second resistivity changing material between the first electrode and the second electrode;

wherein the first resistivity changing material and the second resistivity changing material have different crystallization speeds, and

wherein the first electrode, the second electrode, the first resistivity changing material, and the second resistivity changing material are aligned.

2. The integrated circuit of claim 1 , further comprising:

a diffusion barrier between the first resistivity changing material and the second resistivity changing material.

3. The integrated circuit of claim 1 , further comprising:

shunt resistors surrounding at least one of the first resistivity changing material and the second resistivity changing material.

4. The integrated circuit of claim 1 , wherein the first resistivity changing material and the second resistivity changing material have different cross-sectional widths.

5. A memory cell comprising:

a first electrode;

a first resistivity changing material directly contacting the first electrode and vertically adjacent the first electrode;

a second resistivity changing material vertically adjacent the first resistivity changing material; and

a second electrode directly contacting the second resistivity changing material,

wherein the first resistivity changing material and the second resistivity changing material have different crystallization speeds.

6. The memory cell of claim 5 , further comprising:

a diffusion barrier directly contacting the first resistivity changing material and the second resistivity changing material.

7. The memory of cell of claim 6 , wherein the diffusion barrier comprise one of TiN, TaN, W, Al, WN, TaSiN, TiSiN, TiAlN, C, and Cu.

8. The memory of cell of claim 5 , wherein the first electrode and the second electrode comprise one of TiN, TaN, W, Al, WN, TaSiN, TiSiN, TiAlN, C and Cu.

9. The memory cell of claim 5 , further comprising:

shunt resistors laterally surrounding at least one of the first resistivity changing material and the second resistivity changing material.

10. The memory cell of claim 5 , wherein the first resistivity changing material and the second resistivity changing material have different cross-sectional widths.

11. The memory cell of claim 5 , further comprising:

insulation material laterally surrounding the first electrode, the first resistivity changing material, the second resistivity changing material, and the second electrode.

12. A memory cell comprising:

a first electrode;

a first phase change material layer over the first electrode;

a second phase change material layer over the first phase change material layer; and

a second electrode over the second phase change material layer,

wherein the first phase change material layer and the second phase change material layer have different crystallization speeds.

13. The memory cell of claim 12 , further comprising:

a diffusion barrier between the first phase change material layer and the second phase change material layer.

14. The memory of cell of claim 13 , wherein the diffusion barrier comprise one of TiN, TaN, W, Al, WN, TaSiN, TiSiN, TiAlN, C, and Cu.

15. The memory of cell of claim 12 , wherein the first electrode and the second electrode comprise one of TiN, TaN, W, Al, WN, TaSiN, TiSiN, TiAlN, C and Cu.

16. The memory cell of claim 12 , further comprising:

shunt resistors laterally surrounding at least one of the first phase change material layer and the second phase change material layer.

17. The memory cell of claim 12 , wherein the first phase change material layer and the second phase change material layer have different cross-sectional widths.

18. The memory cell of claim 12 , further comprising:

insulation material laterally surrounding the first electrode, the first phase change material layer, the second phase change material layer, and the second electrode.