Cell-to-cell program interference aware data recovery when ECC fails with an optimum read reference voltage

1. An apparatus comprising:

a memory configured to store data, the memory comprising a plurality of memory modules each having a size less than a total size of the memory; and

a controller configured to process a plurality of read/write operations and recover data stored in the memory determined to exceed a maximum number of errors after performing a first read operation using a first read reference voltage, wherein the controller (i) performs a second read operation using a second read reference voltage, (ii) identifies a victim cell having a threshold voltage in a region between the first read reference voltage and the second read reference voltage, (iii) performs a third read operation on aggressor cells of the victim cell, and (iv) performs a fourth read operation using the first read reference voltage with bit-fixed values on the victim cell based on a type of interference from the aggressor cells.

2. The apparatus according to claim 1 , wherein the aggressor cells are one or more cells adjacent to the victim cell.

3. The apparatus according to claim 1 , wherein the controller identifies a plurality of victim cells.

4. The apparatus according to claim 1 , wherein the first read reference voltage is an optimum read reference voltage and the optimum read reference voltage achieves a minimum raw bit-error rate.

5. The apparatus according to claim 4 , wherein the optimum read reference voltage is a voltage value at a cross point of two neighboring threshold voltage distributions.

6. The apparatus according to claim 1 , wherein the second read reference voltage is near the first read reference voltage.

7. The apparatus according to claim 1 , wherein the second read reference voltage is slightly greater than the first read reference voltage.

8. The apparatus according to claim 7 , wherein the bit-fixed value on the victim cell is unchanged when the type of interference is small.

9. The apparatus according to claim 7 , wherein the bit-fixed value on the victim cell is flipped when the type of interference is large.

10. The apparatus according to claim 1 , wherein the second read reference voltage is slightly less than the first read reference voltage.

11. The apparatus according to claim 10 , wherein the bit-fixed value on the victim cell is flipped when the type of interference is small.

12. The apparatus according to claim 10 , wherein the bit-fixed value on the victim cell is unchanged when the type of interference is large.

13. The apparatus according to claim 1 , wherein the bit-fixed value allows low-density parity check codes to jump out of trapping sets.

14. The apparatus according to claim 1 , wherein the interference comprises cell-to-cell program interference.

15. The apparatus according to claim 1 , wherein the controller is further configured to recover data stored in the memory determined to exceed a maximum number of errors after performing the fourth read operation and the controller (i) performs a fifth read operation using a third read reference voltage, (ii) identifies a victim cell having a threshold voltage in a region between the first read reference voltage and the third read reference voltage, (iii) performs a sixth read operation on aggressor cells of the victim cell, and (iv) performs a seventh read operation using the first read reference voltage with bit-fixed values on the victim cell based on a type of interference from the aggressor cells.

16. The apparatus according to claim 15 , wherein the second read reference voltage is slightly greater than the first read reference voltage and the third read reference voltage is slightly less than the first read reference voltage.

17. The apparatus according to claim 15 , wherein the second read reference voltage is slightly less than the first read reference voltage and the third read reference voltage is slightly greater than the first read reference voltage.

18. The apparatus according to claim 1 , wherein the third read operation performed on the aggressor cells is performed using the first read reference voltage.

19. A method for implementing data recovery in response to exceeding a maximum number of errors after performing a first read operation using a first read reference voltage, comprising the steps of:

(A) processing a plurality of read/write operations to/from a memory, the memory comprising a plurality of memory units each having a size less than a total size of the memory;

(B) performing a second read operation using a second read reference voltage;

(C) identifying a victim cell having a threshold voltage in a region between the first read reference voltage and the second read reference voltage;

(D) performing a third read operation on aggressor cells of the victim cell; and

(E) performing a fourth read operation using the first read reference voltage with bit-fixed values on the victim cell based on a type of interference from the aggressor cells.

20. An apparatus comprising:

an interface configured to process a plurality of read/write operations to/from a memory; and

a control circuit configured to recover data stored in the memory determined to exceed a maximum number of errors after performing a first read operation using a first read reference voltage, wherein the controller (i) performs a second read operation using a second read reference voltage, (ii) identifies a victim cell having a threshold voltage in a region between the first read reference voltage and the second read reference voltage, (iii) performs a third read operation on aggressor cells of the victim cell, and (iv) performs a fourth read operation using the first read reference voltage with bit-fixed values on the victim cell based on a type of interference from the aggressor cells.