Storage system and method for program reordering to mitigate program disturbs
A storage system has a memory that is organized in wordlines. Each wordline has a number of strings. A controller in the storage system changes, in each of the wordlines, which of the strings is a last string programmed. Doing so can unmask a program disturb error when triple-level cells in the memory are used as pseudo-multi-level cells. By unmasking the program disturb error, the controller can detect and correct the error.
1. A storage system comprising:
a memory comprising memory cells configured to store X number of bits per memory cell, wherein X is a positive integer and wherein the memory is organized into a plurality of wordlines, wherein each wordline comprises a plurality of programming segments; and
a controller configured to:
for each of a plurality of program cycles, change, in each of the plurality of wordlines and with respect to a prior wordline, which of the plurality of programming segments is a last programming segment programmed;
after the plurality of program cycles, observe a pattern showing that an error repeatedly occurred on a certain programming segment of the plurality of programming segments;
based on the observed pattern, select the certain programming segment to be the last programming segment programmed;
detect a number of program disturb errors in the memory; and
correct the program disturb errors using the error correction operation.
2. The storage system of claim 1 , wherein the memory comprises triple-level cells.
3. The storage system of claim 1 , wherein the memory comprises quad-level cells.
4. The storage system of claim 1 , wherein the controller is further configured to change, in each of the plurality of wordlines, a programming order of at least one other one of the plurality of programming segments.
5. The storage system of claim 4 , wherein the controller is further configured to change, in each of the plurality of wordlines, a programming order of all of the plurality of programming segments.
6. The storage system of claim 1 , wherein the controller is further configured to program a first programming segment in each of the plurality of wordlines first.
7. The storage system of claim 1 , wherein the memory further comprises a plurality of memory dies, and wherein the controller is further configured to change a programming order of at least one of the plurality of programming segments across memory dies.
8. The storage system of claim 1 , wherein the memory further comprises a block of memory cells, and wherein the controller is further configured to change a programming order of at least one of the plurality of programming segments across program-erase cycles of the block.
9. The storage system of claim 1 , wherein the memory further comprises a plurality of blocks of memory cells, and wherein the controller is further configured to randomize a starting programming segment to be programmed in each of the plurality of blocks.
10. The storage system of claim 1 , wherein the controller is further configured to randomize a starting programming segment to be programmed in each of the plurality of wordlines.
11. The storage system of claim 1 , wherein the memory comprises a three-dimensional memory.
12. In a storage system comprising a memory comprising memory cells configured to store X number of bits per memory cell, wherein X is a positive integer, wherein the memory is organized into a plurality of wordlines, wherein each wordline comprises a plurality of programming segments, and wherein the memory comprises a plurality of memory dies organized in a stripe, a method comprising:
changing, in each memory die in the stripe, which of the plurality of programming segments is a last programming segment programmed;
observing a pattern showing that an error repeatedly occurred on a certain programming segment of the plurality of programming segments;
based on the observed pattern, selecting the certain programming segment to be the last programming segment programmed;
detecting a number of program disturb errors in the memory; and
correcting the program disturb errors using the error correction operation.
13. The method of claim 12 , further comprising:
determining whether data was programmed successfully into a current programming segment.
14. The method of claim 13 , further comprising:
in response to determining that the data was not programmed successfully, generating an error report.
15. The method of claim 13 , further comprising:
in response to determining that the data was programmed successfully, determining whether there are any more programming segments available to be programed.
16. A storage system comprising:
a memory comprising memory cells configured to store X number of bits per memory cell, wherein X is a positive integer and wherein the memory is organized into a plurality of wordlines, wherein each wordline comprises a plurality of programming segments;
means for, for each of a plurality of program cycles, changing, in each of the plurality of wordlines and with respect to a prior wordline, which of the plurality of programming segments is a last programming segment programmed;
means for, after the plurality of program cycles, observing a pattern showing that an error repeatedly occurred on a certain programming segment of the plurality of programming segments;
means for, based on the observed pattern, selecting the certain programming segment to be the last programming segment programmed;
means for detecting a number of program disturb errors in the memory; and
means for correcting the program disturb errors using the error correction operation.