Ferroelectric memory cell recovery
View Patent ↗Methods, systems, and devices for recovering fatigued ferroelectric memory cells are described. Recovery voltages may be applied to a ferroelectric memory cell that is fatigued due to repeated access (read or write) operations. The recovery voltage may have a greater amplitude than the access voltage and may include multiple voltage pulses or a constant voltage. The recovery operation may be performed in the background as the memory array operates, or it may be performed when a host device is not actively using the memory array. The recovery operations may be performed periodically or may include discrete series of pulses distributed among several instances.
1. A method, comprising:
determining that a parameter of a memory cell of a memory array has satisfied a fatigue threshold; and
applying a recovery voltage to the memory cell based at least in part on determining that the parameter of the memory cell has satisfied the fatigue threshold.
2. The method of claim 1 , further comprising:
applying a test voltage having an amplitude less than an amplitude of an access voltage, wherein determining that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on applying the test voltage.
3. The method of claim 1 , further comprising:
determining a failure to sense a value stored on the memory cell based at least in part on a test sense window being smaller than a sense window used during an access operation, wherein determining that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on detecting the failure to sense the value.
4. The method of claim 1 , further comprising:
applying error correction to an unknown logic value, wherein determining that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on applying the error correction.
5. The method of claim 1 , further comprising:
determining that a timer satisfies a threshold, wherein determining that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on determining that the timer satisfies the threshold.
6. The method of claim 1 , further comprising:
counting a number of access operations performed on the memory cell in which the memory cell has reached a remnant polarization threshold; and
determining that the number of access operations satisfies a threshold, wherein determining that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on determining that the number of access operations satisfies the threshold.
7. The method of claim 1 , wherein the recovery voltage is different from an access voltage applied during an access operation of the memory cell.
8. The method of claim 1 , wherein the memory cell is a ferroelectric memory cell.
9. The method of claim 1 , further comprising:
storing a logic state of the memory cell based at least in part on determining that the parameter of the memory cell has satisfied the fatigue threshold; and
re-writing the logic state to the memory cell after applying the recovery voltage.
10. The method of claim 1 , wherein a duration of the application of the recovery voltage, or a number of repetitions of the application of the recovery voltage, or both are based at least in part on the recovery voltage.
11. The method of claim 1 , wherein the recovery voltage comprises at least one of:
a plurality of bipolar voltage pulses;
a plurality of unipolar voltage pulses; or
a voltage with a constant amplitude.
12. A circuit, comprising:
a memory array including a plurality of memory cells; and
a memory controller operable to:
initiate a fatigue recovery operation for a memory cell of the plurality of memory cells;
determine that a parameter of the memory cell has satisfied a fatigue threshold; and
apply a recovery voltage to the memory cell of the plurality of memory cells based at least in part on the determination that the parameter has satisfied the fatigue threshold.
13. The circuit of claim 12 , wherein the recovery voltage is different from an access voltage of an access operation.
14. The circuit of claim 12 , wherein the memory controller is further operable to:
apply a test voltage having different from an access voltage of an access operation, wherein the determination that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on applying the test voltage.
15. The circuit of claim 12 , wherein the memory controller is further operable to:
determine a failure to sense a value stored on the memory cell based at least in part on a test sense window being smaller than a sense window used during an access operation, wherein the determination that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on determining the failure to sense the value.
16. The circuit of claim 12 , wherein the memory controller is further operable to:
apply error correction to an unknown logic value, wherein the determination that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on applying the error correction.
17. The circuit of claim 12 , wherein the memory controller is further operable to:
determine that a timer satisfies a threshold, wherein the determination that the parameter of the memory cell has satisfied the fatigue threshold is based at least in part on determining that the timer satisfies the threshold.
18. A method, comprising:
determining that a memory cell has satisfied a fatigue threshold based at least in part on a number of access operations that have been performed on the memory cell; and
applying a recovery voltage to the memory cell based at least in part on determining that the memory cell has satisfied the fatigue threshold.
19. The method of claim 18 , further comprising:
pulsing the recovery voltage until a number of repetitions of the application of the recovery voltage satisfies a recovery threshold, wherein applying the recovery voltage is based at least in part on the pulsing of the recovery voltage.
20. The method of claim 18 , further comprising:
incrementing a counter each time an access operation is performed on the memory cell; and
determining that the counter satisfies a count threshold, wherein determining that the memory cell has satisfied the fatigue threshold is based at least in part on determining that the counter satisfies the count threshold.