NAND Memory XOR Set Programming Direction Balance
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Solution Overview
Problem
The increasing number of word lines in memory devices leads to inconsistent programming, resulting in variable bit error rates and a higher risk of memory device failure due to uneven distribution of strong and weak word lines across XOR sets.
Innovation Solution
Programming word lines of different dies in alternating directions, with approximately half programmed in a normal order and the other half in a reverse order, to distribute strong and weak word lines more evenly across XOR sets, reducing the concentration of weak word lines in any single XOR set.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of word lines is increased to improve memory density, then memory capacity is improved, but programming consistency deteriorates
Solution Approach 1:
The patent segments the word lines into multiple XOR sets, where each set contains word lines from different dies. This segmentation allows independent programming of different XOR sets, improving programming consistency by reducing the impact of variations in individual word lines while maintaining high memory capacity through increased word line count.
2Device complexity
If word lines are programmed in a single direction, then programming process is simple, but XOR set reliability deteriorates
Solution Approach 1:
The patent applies reverse programming to certain XOR sets while using normal programming for others. Specifically, XOR sets with odd indices are programmed in reverse order (from highest to lowest word line indices) while XOR sets with even indices are programmed in normal order (from lowest to highest word line indices). This inversion strategy balances the distribution of strong and weak word lines across XOR sets, improving reliability without significantly increasing process complexity.
3Ease of operation
If all dies are programmed in the same direction, then programming control is simple, but bit error rate increases
Solution Approach 1:
The patent applies different programming directions to different XOR sets based on their local characteristics. By identifying which XOR sets benefit from reverse programming and applying it selectively, the patent reduces bit error rates locally in those sets while maintaining simple control overall through systematic assignment of programming directions to XOR sets.
Data Source
AI summary
The memory device includes a plurality of dies, and each die includes a plurality of blocks with a plurality of word lines. Some of the word lines are arranged in a plurality of exclusive OR (XOR) sets with each XOR set containing word lines in the same positions across the plurality of dies. The memory device further includes a controller that is configured to program the word lines of the blocks of at least one of the dies in a first programming direction. The controller is further configured to program the word lines of the blocks of at least one other die in a second programming direction that is opposite of the first programming direction.