Apparatuses and methods for determining stability of a memory cell
View Patent ↗Examples described include apparatuses and methods for determining stability of memory cells. Resistance variable memory cells may be used. Once a memory cell is placed in a low or high resistance state responsive to set or reset pulses, the stability of the state may be determined, such as by providing another pulse to the memory cell or otherwise stressing the cell. The another pulse may be of an opposite polarity to the set or reset pulses already applied. If the memory cell is no longer in the target state after providing the another pulse, additional set or reset pulses may be applied to achieve a stable state.
1. A method comprising:
providing a plurality of state pulses to a resistance variable memory cell to determine whether the resistance variable memory cell satisfies a programming criterion by entering a first state;
responsive to a resistance of a resistance variable memory cell indicating the resistance variable memory cell satisfies the programming criterion, providing a pulse to the resistance variable memory cell, wherein a polarity of the plurality of state pulses is opposite of a polarity of the pulse;
determining a resistance of the resistance variable memory cell after providing the pulse to the resistance variable memory cell to determine whether the resistance variable memory cell satisfies a stability criterion by remaining in the first state; and
responsive to the resistance of the resistance variable memory cell indicating the resistance variable memory cell satisfies the stability criterion by remaining in the first state, designating the resistance variable memory cell as stable.
2. The method of claim 1 , further comprising sensing the resistance of the resistance variable memory cell.
3. The method of claim 1 , further comprising, after providing a first state pulse of the plurality of state pulses, providing another state pulse of the plurality of state pulses having a magnitude greater than the first state pulse responsive to the resistance of the resistance variable memory cell indicating the resistance variable memory cell did not satisfy the programming criterion following the first state pulse.
4. The method of claim 3 , wherein the first state is one of a set state or a reset state.
5. The method of claim 1 , wherein a magnitude of the first state pulse is greater than a magnitude of the pulse.
6. A method comprising:
providing a plurality of state pulses having a first polarity to a resistance variable memory cell to determine whether the resistance variable memory cell satisfies a programming criterion;
stressing the resistance variable memory cell in a target state by providing a at least one pulse to the resistance variable memory cell of an opposite polarity of the plurality of state pulses to determine whether the resistance variable memory cell satisfies a stability criterion responsive to a resistance of the resistance variable memory cell indicating the resistance variable memory cell satisfies the programming criterion;
determining whether the resistance variable memory cell remains in the target state; and
responsive to the resistance variable cell remaining in the target state in satisfaction of the stability criterion, designating the resistance variable cell as stable.
7. The method of claim 6 , wherein stressing the resistance variable cell comprises providing at least one pulse to the resistance variable cell.
8. The method of claim 7 , further comprising, responsive to the resistance variable cell changing to a state other than the target state after stressing the resistance variable cell:
providing a target state pulse to the resistance variable memory cell to place the resistance variable memory cell into the target state; and
stressing the resistance variable memory cell a second time.
9. The method of claim 8 , further comprising designating the resistance variable cell as unstable responsive to the resistance variable cell changing to a state other than the target state after stressing the resistance variable cell a threshold number of times.
10. The method of claim 9 , wherein the target state is one of a low resistance state or a high resistance state, and wherein the state other than the target state is the other of the low resistance state and the high resistance state.
11. The method of claim 6 , further comprising indirectly sensing the resistance of the resistance variable memory cell.
12. A method comprising:
providing a series of pulses to a resistance variable memory cell to place the resistance variable memory cell in a first state, wherein each successive pulse in the series of pulses increases in magnitude; and
determining, after provision of each individual pulse in the series of pulses, whether the resistance variable memory cell is in a second state;
responsive to determining that the variable memory cell is in the first state, providing a stress pulse to the resistance variable memory cell, wherein providing the stress pulse to the resistance variable memory cells comprises providing at least one pulse to the resistance variable memory cell of an opposite polarity of the series of pulses; and
responsive to a resistance of the resistance variable memory cell indicating the resistance variable memory cell is in the second state after providing the stress pulse, designating the resistance variable memory cell as defective.
13. The method of claim 12 , further comprising, responsive to the resistance variable memory cell remaining in the first state after stressing the resistance variable memory cell, designating the resistance variable memory cell as stable in the first state.
14. The method of claim 13 , further comprising determining whether the resistance variable memory cell is stable in the second state after designating the resistance variable memory cell as stable in the first state.
15. The method of claim 14 , wherein determining whether the resistance variable memory cell is stable in the second state comprises:
providing a second pulse to the resistance variable memory cell to place the resistance variable memory cell in the second state; and
responsive to the resistance variable memory cell being in the second state after provision of the second pulse, providing a second stress pulse to the resistance variable memory cell.
16. The method of claim 14 , storing an indication that the resistance variable memory cell is stable responsive to determining that the resistance variable memory cell is stable in the first state and is stable in the second state.