Phase change memory having temperature budget sensor
View Patent ↗A semiconductor device includes a plurality of memory cells, a temperature budget sensor, and a circuit. The circuit periodically compares a signal from the temperature budget sensor to a reference signal and refreshes the memory cells based on the comparison.
1. A resistive memory device comprising:
a plurality of resistive memory cells; and
a temperature budget sensor for detecting a temperature budget based on an integration of a temperature of the resistive memory device over time, the temperature budget sensor comprising a phase change material and adapted to be initialized by slightly setting the phase change material.
2. The device of claim 1 , wherein the memory cells comprise phase change memory cells.
3. The device of claim 1 , wherein the temperature budget sensor comprises a phase change memory cell.
4. The device of claim 1 , wherein the temperature budget sensor monitors a temperature budget of the device with the device powered down.
5. A memory comprising:
an array of phase change memory cells;
a temperature budget sensor for detecting a temperature budget based on an integration of a temperature of the array over time, the temperature budget sensor including a phase change material in a partially crystalline and partially amorphous state and adapted to be initialized by slightly setting the phase change material; and
a circuit for periodically comparing a signal from the phase change material of the temperature budget sensor to a reference signal and refreshing the array of phase change memory cells based on the comparison.
6. The memory of claim 5 , wherein the partially crystalline and partially amorphous state comprises a partially reset state.
7. The memory of claim 5 , wherein the partially crystalline and partially amorphous state comprises a partially set state.
8. The memory of claim 5 , wherein the temperature budget sensor comprises a phase change memory cell within the array of phase change memory cells.
9. The memory of claim 5 , wherein the circuit comprises a comparator for comparing a current signal through the phase change material of the temperature budget sensor to a reference current.
10. The memory of claim 5 , wherein the reference signal is adjusted based on a current temperature of the memory.
11. The memory of claim 5 , wherein the circuit comprises a comparator for comparing a voltage across the phase change material of the temperature budget sensor to a reference voltage.
12. A memory device comprising:
an array of phase change memory cells;
means for monitoring a temperature budget of the array of memory cells based on an integration of a temperature of the array over time, the means for monitoring comprising a phase change material;
means for initializing the means for monitoring by slightly setting the phase change material; and
means for refreshing the array of memory cells in response to the temperature budget exceeding a predefined threshold.
13. The memory device of claim 12 , wherein the means for monitoring the temperature budget comprises means for monitoring the temperature budget with the memory device powered off.
14. A method for operating a resistive memory, the method comprising:
resetting a phase change material of a temperature budget sensor;
slightly setting the phase change material of the temperature budget sensor to initialize the temperature budget sensor; and
monitoring, by the temperature budget sensor, a temperature budget of the resistive memory based on an integration of a temperature of the resistive memory over time.
15. The method of claim 14 , wherein monitoring the temperature budget comprises monitoring the temperature budget with the memory powered off.
16. The method of claim 14 , wherein monitoring the temperature budget comprises monitoring a temperature budget of a phase change memory.
17. A method for operating a memory, the method comprising:
setting a phase change memory cell to a partially crystalline and partially amorphous state;
periodically comparing a signal from the memory cell to a reference signal, the signal from the memory cell indicating a temperature budget of the memory based on an integration of a temperature of the memory over time; and
refreshing a plurality of phase change memory cells storing data in response to the comparison,
wherein setting the phase change memory cell to the partially crystalline and partially amorphous state comprises fully resetting the memory cell and then slightly setting the memory cell.
18. The method of claim 17 , wherein refreshing the plurality of memory cells storing data in response to the comparison comprises refreshing the plurality of memory cells in response to the signal from the memory cell exceeding the reference signal.
19. The method of claim 17 , wherein periodically comparing the signal from the memory cell to the reference signal comprises periodically comparing a current through the memory cell to a reference current.
20. The method of claim 17 , wherein periodically comparing the signal from the memory cell to the reference signal comprises periodically comparing a voltage across the memory cell to a reference voltage.
21. A method for operating a memory, the method comprising:
setting a phase change memory cell to a partially crystalline and partially amorphous state;
periodically comparing a signal from the memory cell to a reference signal, the signal from the memory cell indicating a temperature budget of the memory based on an integration of a temperature of the memory over time; and
refreshing a plurality of phase change memory cells storing data in response to the comparison,
wherein setting the phase change memory cell to the partially crystalline and partially amorphous state comprises partially resetting the memory cell.
22. A resistive memory device comprising:
a plurality of resistive memory cells;
a temperature budget sensor for detecting a temperature budget based on an integration of a temperature of the resistive memory device over time, the temperature budget sensor comprising a phase change material and adapted to be initialized by slightly setting the phase change material; and
a circuit for periodically comparing a signal from the temperature budget sensor to a reference signal and refreshing the resistive memory cells based on the comparison.
23. The device of claim 22 , wherein the circuit comprises a comparator for comparing a current through the temperature budget sensor to a reference current.
24. The device of claim 22 , wherein the reference signal is adjusted based on a current temperature of the device.
25. The device of claim 22 , wherein the circuit comprises a comparator for comparing a voltage across the temperature budget sensor to a reference voltage.