Set pulse for phase change memory programming
View Patent ↗A memory device and method for programming the memory device, more particularly a single pulse algorithm for programming a phase change memory cell or array. The single pulse can heat the memory cell to above its melting point and reduce in signal level so that the memory cell is crystallized.
1. A method comprising:
applying an electronic signal at a first particular signal value level so as to melt a phase change memory (PCM) cell; and
decreasing the signal value level of the electronic signal being applied, after the PCM cell is melted, until a second particular non-zero signal value level is reached;
wherein the signal value level decreases in a manner so that a substantially vertical drop in signal value level does not occur between the first particular signal value level and the second particular signal value level; and
wherein said decreasing the signal value level comprises an approximately linear ramp between the first particular signal value level and the second particular signal value level.
2. The method of claim 1 , wherein the electronic signal is applied to a resistive heater.
3. The method of claim 2 , wherein said applying the electronic signal comprises applying the first particular signal value level to more than one resistive heater so as to melt more than one PCM cell.
4. The method of claim 3 , wherein the more than one PCM cell comprises a PCM cell array.
5. The method of claim 3 , wherein the signal value level decreases in a manner so that the phase change material of the more than one PCM cell crystallizes from an outer cell periphery inwardly.
6. The method of claim 2 , wherein the resistive heater physically contacts a surface of the PCM cell.
7. The method of claim 1 , wherein the electronic signal is applied to a PCM cell arranged in a self heating configuration.
8. The method of claim 7 , wherein said applying the electronic signal comprises applying the first particular signal value level to more than one PCM cell so as to melt more than one PCM cell.
9. The method of claim 1 , wherein the electronic signal comprises a current signal.
10. The method of claim 1 , wherein the signal value level decreases in a manner so that the phase change material of the PCM cell crystallizes from an outer cell periphery of the PCM cell inwardly.
11. A method comprising:
applying a single signal pulse in a manner so as to reset and then set a plurality of PCM cells, some PCM cells reaching a crystallization temperature level at a different time than others;
wherein the single signal pulse is applied at an initial level so as to produce a temperature that corresponds to or exceeds a melt temperature for a PCM cell of the plurality having the highest melt temperature.
12. The method of claim 11 , wherein the single signal pulse comprises a current pulse applied to heating elements.
13. The method of claim 11 , wherein the single signal pulse comprises a current pulse applied to PCM cells in a self heating cell architecture.
14. The method of claim 11 , wherein the single signal pulse is applied in a manner so that the plurality of PCM cells substantially become fully crystallized.
15. The method of claim 11 , wherein the single signal pulse is applied in a manner so that a change in temperature results that is at or below a rate corresponding to the rate at which the slowest PCM cell of the plurality is able to substantially fully crystallize.
16. The method of claim 11 , wherein the single signal pulse produces a later level that results in a temperature that corresponds to or is below a temperature for a PCM cell of the plurality having the lowest crystallization temperature.
17. The method of claim 11 , wherein the single signal pulse is decreased from a current at the initial level to a non-zero current at a second level in a generally smooth signal path.
18. A device comprising: a resistive heater; said resistive heater to program an array of PCM cells in a manner so that a substantially vertical drop in temperature does not occur during crystallization of the cells of the array;
said resistive heater to program the cells of the array by reducing temperature from a reset temperature level to a set temperature level; and
wherein said reset temperature comprises a temperature at or above a highest melt temperature of any cell of the array.
19. The device of claim 18 , wherein said set temperature level comprises a temperature at or below a lowest crystallization temperature of any cell of the array.
20. The device of claim 18 , wherein said device comprises an integrated circuit, wherein the array of PCM cells is substantially fully crystallized via a single pulse without state verification of any PCM cells in the array of PCM cells during application of the single pulse.
21. The device of claim 20 , wherein the PCM cells comprise joule heater programmed memory cells.
22. The device of claim 18 , further comprising a computer platform capable of adjusting parameters of a single pulse configured to program the resistive heater;
said parameters comprising a starting current, an ending current and a time dependent, connected, smooth signal path from the starting current to the ending current.
23. The device of claim 22 , wherein said computing platform includes a capability to adjust said parameters so as to make trade-offs between any of the following: programming speed, programming reliability, or programming yield.
24. The apparatus of claim 22 , wherein said computing platform includes a capability to adjust said parameters so as to reduce programming speed without significantly degrading nearly full crystallization of the array of PCM cells.
25. The method of claim 18 , wherein a single signal pulse decreases the temperature from the reset temperature level to the set temperature level in a generally smooth signal path, wherein the set temperature level is non-zero.
26. A device comprising: a resistive heater; said resistive heater to program an array of PCM cells in a manner so that a substantially vertical drop in temperature does not occur during crystallization of the cells of the array;
said resistive heater to program the cells of the array by reducing temperature from a reset temperature level to a set temperature level; and
wherein said set temperature level comprises a temperature at or below a lowest crystallization temperature of any cell of the array.