Background threshold voltage shifting using base and delta threshold voltage shift values in non-volatile memory
In one embodiment, a computer-implemented method includes determining, by a processor, after the writing of data to a non-volatile memory block, one or more delta threshold voltage shift (TVS Δ ) values configured to track temporary changes with respect to changes in the underlying threshold voltage distributions due to retention and/or read disturb errors. One or more overall threshold voltage shift values is calculated for the data written to the non-volatile memory block, the one or more overall threshold voltage shift values being a function of the one or more TVS Δ values to be used when writing data to the non-volatile memory block. The one or more overall threshold voltage shift values are stored.
1. A computer-implemented method, comprising:
determining, by a processor, after writing data to a non-volatile memory block, one or more delta threshold voltage shift (TVS Δ ) values configured to track temporary changes with respect to changes in the underlying threshold voltage distributions due to retention and/or read disturb errors;
calculate one or more overall threshold voltage shift values for the data written to the non-volatile memory block, the one or more overall threshold voltage shift values being a function of the one or more TVS Δ values to be used when writing data to the non-volatile memory block;
storing the one or more overall threshold voltage shift values;
reading one or more TVS values from a non-volatile controller memory;
resetting a program/erase cycle count since last calibration after calibrating the one or more overall threshold voltage shift values; and
storing, to the non-volatile controller memory, the one or more TVS Δ values and the program/erase cycle count since last calibration.
2. The method as recited in claim 1 , comprising resetting the one or more TVS 66 values when the non-volatile memory block is erased.
3. The method as recited in claim 1 , comprising applying the one or more overall threshold voltage shift values to a read operation of the data stored to the non-volatile memory block upon receiving a read request.
4. The method as recited in claim 1 , comprising:
reading one or more TVS values from a non-volatile controller memory;
resetting a program/erase cycle count since last calibration after calibrating the one or more overall threshold voltage shift values; and
storing the one or more TVS Δ values, and the program/erase cycle count since last calibration to the non-volatile controller memory.
5. The method as recited in claim 1 , comprising re-calibrating at least one value selected from a group consisting of: a base threshold voltage shift (TVS BASE ) value and the one or more TVS Δ values during a background health check after a predetermined number of background health checks without calibration are performed.
6. The method as recited in claim 5 , wherein the predetermined number of background health checks without calibration is from 1 to 5.
7. The method as recited in claim 6 , wherein a block is marked for re-calibration when a program/erase cycle count since last calibration exceeds a predetermined threshold, wherein blocks marked for re-calibration are forced to be calibrated in a read sweep background health check, and wherein the blocks are unmarked after re-calibration is completed.
8. The method as recited in claim 7 , wherein the re-calibration is not performed when a program/erase cycle count is lower than a predetermined threshold.
9. The method as recited in claim 1 , wherein the one or more TVS Δ values are determined periodically in the background without interrupting normal operations directed at the non-volatile memory block.
10. A computer-implemented method, comprising:
determining, by a processor, after writing data to a non-volatile memory block, one or more delta threshold voltage shift (TVS Δ ) values configured to track temporary changes with respect to changes in the underlying threshold voltage distributions due to retention and/or read disturb errors;
calculate one or more overall threshold voltage shift values for the data written to the non-volatile memory block, the one or more overall threshold voltage shift values being a function of the one or more TVS Δ values to be used when writing data to the non-volatile memory block; and
storing the one or more overall threshold voltage shift values; and
grouping together physical non-volatile pages which have similar TVS Δ values into a page group.
11. The method as recited in claim 10 , comprising resetting the one or more TVS Δ values when the non-volatile memory block is erased.
12. The method as recited in claim 10 , comprising applying the one or more overall threshold voltage shift values to a read operation of the data stored to the non-volatile memory block upon receiving a read request.
13. The method as recited in claim 10 , comprising:
reading one or more TVS values from a non-volatile controller memory;
resetting a program/erase cycle count since last calibration after calibrating the one or more overall threshold voltage shift values; and
storing the one or more TVS Δ values and the program/erase cycle count since last calibration to the non-volatile controller memory.
14. The method as recited in claim 10 , wherein each overall threshold voltage shift value equals a sum of a corresponding base threshold voltage shift (TVS BASE ) value and a corresponding TVS Δ value, the TVS BASE value configured to track permanent changes in underlying threshold voltage distributions due to cycling of the non-volatile memory block.
15. The method as recited in claim 10 , comprising re-calibrating at least one value selected from a group consisting of: a base threshold voltage shift (TVS BASE ) value and the one or more TVS Δ values during a background health check after a predetermined number of background health checks without calibration are performed.
16. The method as recited in claim 15 , wherein the predetermined number of background health checks without calibration is from 1 to 5.
17. The method as recited in claim 16 , wherein a block is marked for re-calibration when a program/erase cycle count since last calibration exceeds a predetermined threshold, wherein blocks marked for re-calibration are forced to be calibrated in a read sweep background health check, and wherein the blocks are unmarked after re-calibration is completed.
18. The method as recited in claim 16 , wherein the re-calibration is not performed when a program/erase cycle count is lower than a predetermined threshold.
19. The method as recited in claim 10 , wherein the one or more TVS Δ values are determined periodically in the background without interrupting normal operations directed at the non-volatile memory block.
20. A computer-implemented method, comprising:
determining, by a processor, after writing data to a non-volatile memory block, one or more delta threshold voltage shift (TVS Δ ) values configured to track temporary changes with respect to changes in the underlying threshold voltage distributions due to retention and/or read disturb errors;
calculate one or more overall threshold voltage shift values for the data written to the non-volatile memory block, the one or more overall threshold voltage shift values being a function of the one or more TVS Δ values to be used when writing data to the non-volatile memory block; and
storing the one or more overall threshold voltage shift values,
wherein each overall threshold voltage shift value equals a sum of a corresponding base threshold voltage shift (TVS BASE ) value and a corresponding TVS Δ value, the TVS BASE value being configured to track permanent changes in underlying threshold voltage distributions due to cycling of the non-volatile memory block.