Multistage set procedure for phase change memory

1. A method in a phase change semiconductor material, comprising:

heating a phase change semiconductor material (PM) to a first temperature for a first period of time to promote nucleation of a crystalline state of the PM;

increasing the PM from the first temperature to a second temperature for a second period of time, the second temperature to promote crystal growth within the PM to set the PM to the crystalline state; and

ramping down from the second temperature over a third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature.

2. The method of claim 1 , wherein heating the PM comprises controlling an amount of current passing through the PM.

3. The method of claim 1 , wherein heating comprises controlling an intensity of laser light on the PM.

4. The method of claim 1 , wherein the first temperature for the first period of time to promote nucleation comprises a first nucleation temperature for a first sub-period of time and a second nucleation temperature for a second sub-period of time.

5. The method of claim 1 , further comprising:

initially heating the PM to a temperature higher than the first temperature to amorphize the PM prior to nucleation; and

allowing the PM to cool to a temperature lower than the first temperature prior to heating to the first temperature.

6. The method of claim 1 , wherein ramping down from the second temperature over the third period of time comprises:

decreasing from the second temperature to a third temperature and holding the third temperature for a portion of the third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature.

7. The method of claim 1 , wherein the PM is a storage cell of a phase change memory (PCM).

8. A circuit to set a chalcogenide material, comprising:

a power source to heat a phase change chalcogenide material (PM); and

a control circuit to control the power source, to heat the PM to a first temperature for a first period of time to promote nucleation of a crystalline state of the PM, increase the PM from the first temperature to a second temperature for a second period of time, the second temperature to promote crystal growth within the PM to set the PM to the crystalline state, and ramp down from the second temperature over a third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature.

9. The circuit of claim 8 , wherein the control circuit comprises a circuit coupled to the PM to control an amount of current passing through the PM.

10. The circuit of claim 8 , wherein the control circuit comprises a light source to control an intensity of laser light directed to the PM.

11. The circuit of claim 8 , wherein the first temperature for the first period of time to promote nucleation comprises a first nucleation temperature for a first sub-period of time and a second nucleation temperature for a second sub-period of time.

12. The circuit of claim 8 , further comprising the control circuit to initially heat the PM to a temperature higher than the first temperature to amorphize the PM prior to nucleation, and allow the PM to cool to a temperature lower than the first temperature prior to heating to the first temperature.

13. The circuit of claim 8 , wherein to ramp down from the second temperature over the third period of time comprises the control circuit to decrease from the second temperature to a third temperature and hold the third temperature for a portion of the third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature.

14. The circuit of claim 8 , wherein the PM is a storage cell of a phase change memory (PCM).

15. A system to implement a phase change set, comprising:

a phase-change dynamic random access memory (PRAM) including a phase change material (PM);

a power source to provide power to heat the PM; and

a controller to write to the PRAM, the controller including a control circuit to control application of heat from the power source to the PM, the controller to heat the PM to a first temperature for a first period of time to promote nucleation of a crystalline state of the PM, increase the PM from the first temperature to a second temperature for a second period of time, the second temperature to promote crystal growth within the PM to set the PM to the crystalline state, and ramp down from the second temperature over a third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature; and

a touchscreen display coupled to generate a display based on data accessed from the PRAM.

16. The system of claim 15 , wherein the controller is to control an amount of current passing through the PM.

17. The system of claim 15 , wherein the controller is to control an intensity of laser light directed to the PM.

18. The system of claim 15 , wherein the first temperature for the first period of time to promote nucleation comprises a first nucleation temperature for a first sub-period of time and a second nucleation temperature for a second sub-period of time.

19. The system of claim 15 , further comprising the controller to initially heat the PM to a temperature higher than the first temperature to amorphize the PM prior to nucleation, and allow the PM to cool to a temperature lower than the first temperature prior to heating to the first temperature.

20. The system of claim 15 , wherein to ramp down from the second temperature over the third period of time comprises the controller to decrease from the second temperature to a third temperature and hold the third temperature for a portion of the third period of time to anneal disturbance in the crystalline structure of the PM caused by overheating at the second temperature.