Bottom electrode geometry for phase change memory
View Patent ↗A PCRAM cell has a gradated or layered resistivity bottom electrode with higher resistivity closer to a phase change material, to provide partial heating near the interface between the cell and the bottom electrode, preventing separation of the amorphous GST region from the bottom electrode, and reducing the programming current requirements. The bottom electrode can also be tapered to have a smaller cross-sectional area at the top of the bottom electrode than at the bottom of the bottom electrode.
1. A phase change memory cell, comprising:
a single layer bottom electrode having a gradated resistivity with lower resistivity at a bottom of the bottom electrode and gradually increasing in resistivity to a substantially higher resistivity at a top of the bottom electrode;
a phase change material on top of the bottom electrode; and
a top electrode over the phase change material.
2. The memory cell of claim 1 , wherein the bottom electrode has a conical shape with a cross-sectional area that decreases toward the top of the bottom electrode.
3. The memory cell of claim 1 , wherein the bottom of the bottom electrode has a resistivity less than 1 milliOhm.cm.
4. The memory cell of claim 1 , wherein the top of the bottom electrode has a resistivity greater than 1 milliOhm.cm.
5. The memory cell of claim 1 , wherein the phase change material is a chalcogenide.
6. The memory cell of claim 1 , wherein the phase change material is a Germanium-Antimony-Tellurium alloy.
7. A memory device, comprising:
an array of phase change memory cells arranged in rows and columns;
control circuitry to read, write and erase the memory cells; and
address circuitry to latch address signals provided on address input connections;
wherein each memory cell comprises:
a single-layer bottom electrode having a gradated resistivity with lower resistivity at a bottom of the bottom electrode gradually increasing in resistivity to a substantially higher resistivity at a top of the bottom electrode;
a phase change material on top of the bottom electrode; and
a top electrode over the phase change material.
8. The memory device of claim 7 , wherein the bottom electrode has a decreasing in size cross-sectional area, with a smallest cross-sectional area at the top of the bottom electrode.
9. The memory device of claim 7 , wherein the bottom of the bottom electrode has a resistivity less than 1 milliOhm.cm.
10. The memory device of claim 7 , wherein the top of the bottom electrode has a resistivity greater than 1 milliOhm.cm.
11. The memory device of claim 7 , wherein the phase change material is a chalcogenide.
12. The memory device of claim 7 , wherein the phase change material is a Germanium-Antimony-Tellurium alloy.
13. A processing system, comprising:
a processor; and
a memory device coupled to the processor to store data provided by the processor and to provide data to the processor, the memory comprising:
an array of phase change memory cells arranged in rows and columns and accessed by bitlines and word lines;
control circuitry to read, write and erase the memory cells; and
address circuitry to latch address signals provided on address input connections;
wherein each memory cell comprises:
a phase change memory cell having a single-layer bottom electrode with a gradated resistivity with lower resistivity at a bottom of the bottom electrode gradually increasing in resistivity to a substantially higher resistivity at a top of the bottom electrode, a phase change material on top of the bottom electrode, and a top electrode over the phase change material.
14. The processing system of claim 13 , wherein each bottom electrode of each memory cell is tapered in a conical shape having its largest cross-sectional area at the bottom of the bottom electrode, and its smallest cross-sectional area at the top of the bottom electrode.
15. A phase change memory cell, comprising:
a single layer bottom electrode having a lower resistivity at a bottom of the bottom electrode gradually increasing in resistivity to a substantially higher resistivity at a top of the bottom electrode;
a phase change material on top of the bottom electrode; and
a top electrode over the phase change material.