Balanced three-level read disturb management in a memory device

1. A method comprising:

receiving a read request for a memory array;

retrieving a value of a read counter for a block associated with the read request;

refreshing valid word lines in the block if the value of the read counter exceeds a first threshold;

identifying a set of valid word lines in the block if the value of the read counter exceeds a second threshold, the second threshold lower than the first threshold;

identifying a subset of the set of valid word lines, the subset of the set of valid word lines including word lines having an error rate above a pre-configured error rate threshold;

refreshing the subset of the set of valid word lines; and

marking each word line in the subset of the set of valid word lines as invalid.

2. The method of claim 1 , further comprising incrementing the read counter for the block prior to retrieving a value of the read counter.

3. The method of claim 1 , further comprising setting the value of the read counter to zero after refreshing the valid word lines.

4. The method of claim 1 , wherein identifying the set of valid word lines comprises identifying at least two valid word lines in the block.

5. The method of claim 1 , further comprising:

identifying a single valid word line in the block if the value of the read counter exceeds a third threshold, the third threshold lower than both the second and first thresholds; and

refreshing the single valid word line if the single valid word line has an error rate above the pre-configured error rate threshold.

6. The method of claim 5 , further comprising marking the single valid word line as invalid after refreshing the single valid word line.

7. A device comprising:

a memory array;

a volatile memory device, the volatile memory device comprising a data structure representing blocks and word lines in the memory array, the data structure storing data associated with a plurality of blocks of the memory array; and

a controller, the controller configured to:

receive a read request for a memory array,

retrieve a value of a read counter for a block associated with the read request from the data structure stored in the volatile memory device,

refresh valid word lines in the block if the value of the read counter exceeds a first threshold,

identify a set of valid word lines associated with the block in the data structure if the value of the read counter exceeds a second threshold, the second threshold lower than the first threshold,

identify a subset of the set of valid word lines in the data structure, the subset of the set of valid word lines including word lines having an error rate above a pre-configured error rate threshold,

refresh the subset of the set of valid word lines, and

mark each word line in the subset of the set of valid word lines as invalid by updating corresponding word line data structures in the data structure, the updating including setting a Boolean flag in the corresponding word line data structures.

8. The device of claim 7 , the controller further configured to increment the read counter for the block prior to retrieving a value of the read counter.

9. The device of claim 7 , the controller further configured to set the value of the read counter to zero after refreshing the valid word lines.

10. The device of claim 7 , wherein identifying the set of valid word lines comprises identifying at least two valid word lines in the block.

11. The device of claim 7 , the controller further configured to:

identify a single valid word line in the block if the value of the read counter exceeds a third threshold, the third threshold lower than both the second and first thresholds; and

refresh the single valid word line if the single valid word line has an error rate above the pre-configured error rate threshold.

12. The device of claim 11 , the controller further configured to mark the single valid word line as invalid after refreshing the single valid word line.

13. A non-transitory computer-readable storage medium for tangibly storing computer program instructions capable of being executed by a computer processor, the computer program instructions defining the steps of:

receiving a read request for a memory array;

retrieving a value of a read counter for a block associated with the read request;

refreshing valid word lines in the block if the value of the read counter exceeds a first threshold;

identifying a set of valid word lines in the block if the value of the read counter exceeds a second threshold, the second threshold lower than the first threshold;

identifying a subset of the set of valid word lines, the subset of the set of valid word lines including word lines having an error rate above a pre-configured error rate threshold;

refreshing the subset of the set of valid word lines; and

marking each word line in the subset of the set of valid word lines as invalid.

14. The non-transitory computer-readable storage medium of claim 13 , the computer program instructions further defining the step of incrementing the read counter for the block prior to retrieving a value of the read counter.

15. The non-transitory computer-readable storage medium of claim 13 , the computer program instructions further defining the step of setting the value of the read counter to zero after refreshing the valid word lines.

16. The non-transitory computer-readable storage medium of claim 13 , the computer program instructions further defining the steps of:

identifying a single valid word line in the block if the value of the read counter exceeds a third threshold, the third threshold lower than both the second and first thresholds; and

refreshing the single valid word line if the single valid word line has an error rate above the pre-configured error rate threshold.

17. The non-transitory computer-readable storage medium of claim 16 , the computer program instructions further defining the step of marking the single valid word line as invalid.