Background threshold voltage shifting using base and delta threshold voltage shift values in non-volatile memory

Patent metadata

Field	Value
Publication number	US-9583205-B2
Application number	US-201614987724-A
Country	US
Kind code	B2
Filing date	Jan 4, 2016
Priority date	Sep 29, 2014
Publication date	Feb 28, 2017
Grant date	Feb 28, 2017

Abstract

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.

First claim

What is claimed is:

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 (TVSΔ) 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
re-calibrating a base threshold voltage shift (TVS BASE ) value, the one or more TVS Δ values, or both the 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.

2. The method as recited in claim 1 , comprising resetting the one or more TVS Δ 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 , 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.

6. The method as recited in claim 1 , 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 6 , 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. The method as recited in claim 1 , comprising grouping together physical non-volatile pages which have similar TVS Δ values into a page group.

11. A computer-implemented method for managing threshold voltage shifts in non-volatile memory, comprising:
determining, by a processor after writing data to a non-volatile memory block, one or more base threshold voltage shift (TVS BASE ) values configured to track permanent changes in underlying threshold voltage distributions due to cycling of the non-volatile memory block;
calculating by the processor an overall threshold voltage shift value for the data written to the non-volatile memory block, the overall threshold voltage shift value being a function of the one or more TVS BASE values; and
storing by the processor the overall threshold voltage shift value.

12. The method as recited in claim 11 , comprising resetting the one or more TVS Δ values when the non-volatile memory block is erased.

13. The method as recited in claim 11 , comprising determining, by the processor after the writing of data to the 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.

14. The method as recited in claim 11 , comprising applying, by the processor, the overall threshold voltage shift value to a read operation of the data stored to the non-volatile memory block upon receiving a read request.

15. The method as recited in claim 11 , 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 overall threshold voltage shift value; and
storing the one or more TVS BASE values and the program/erase cycle count since last calibration to the non-volatile controller memory.

16. The method as recited in claim 11 , comprising re-calibrating the one or more TVS BASE values during a background health check after a predetermined number of background health checks without calibration are performed, wherein the predetermined number of background health checks without calibration is from 1 to 5.

17. The method as recited in claim 11 , wherein at least one of the one or more TVSBASE values and the one or more TVS Δ values are determined periodically in the background without interrupting normal operations directed at the non-volatile memory block.

18. The method as recited in claim 11 , comprising:
grouping together physical non-volatile pages which have similar TVS BASE and TVS Δ values into a page group; and
creating a mapping that correlates the TVS BASE values as tracked per page group to actual read voltage shift values.

19. A computer program product for managing threshold voltage shifts in non-volatile memory, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions being readable and/or executable by a processor to cause the processor to:
calculate, by the processor, an overall threshold voltage shift value for the data written to the non-volatile memory block, the overall threshold voltage shift value being a function of a base threshold voltage shift (TVS BASE ) value and delta threshold voltage shift (TVS Δ ) value to be used when writing data to the non-volatile memory block, the TVS BASE value representing a permanent change in underlying threshold voltage distributions due to cycling of the non-volatile memory block, the TVS Δ value representing a temporary change with respect to a change in the underlying threshold voltage distributions due to retention and/or read disturb errors; and
apply, by the processor, the overall threshold voltage shift value to a read operation of the data stored to the non-volatile memory block upon receiving a read request.

20. The computer program product as recited in claim 19 , comprising re-calibrating the one or more TVS BASE values during a background health check after a predetermined number of background health checks without calibration are performed, wherein the predetermined number of background health checks without calibration is from 1 to 5.

Assignees

• IBM

Inventors

• Camp Charles J
• Fisher Timothy J
• Fry Aaron D
• Ioannou Nikolas
• Koltsidas Ioannis
• Papandreou Nikolaos
• Parnell Thomas
• Pletka Roman
• Pozidis Charalampos
• Tomic Sasa

Classifications

• G11C16/3427 Primary

  Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written · CPC title

• G11C2029/0409

  Online test · CPC title

• G11C29/021

  in voltage or current generators · CPC title

• G11C16/10

  Programming or data input circuits · CPC title

• G11C16/14

  Circuits for erasing electrically, e.g. erase voltage switching circuits · CPC title