Non-Volatile Memory Partial Erase Algorithm
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Solution Overview
Problem
The increasing size of cell strings in non-volatile memory devices leads to program disturbance, causing degradation in memory cell characteristics, particularly evident in the threshold voltage distribution of high-level word lines during program operations.
Innovation Solution
Implementing a partial erase algorithm that differentiates between high-level and low-level word lines, performing a partial erase operation on each group to maintain initial erase states and prevent program disturbance, with the controller managing the sequence of erase and program operations to protect memory cell characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of word lines in one block is increased to increase integration degree, then the storage capacity is improved, but program disturbance occurs causing degradation in memory cell characteristics
Solution Approach 1:
The patent divides the block into multiple segments based on word line groups (first word line group and second word line group). During program operations, only the necessary word line groups are erased and programmed, while other groups remain in erase state. This segmentation prevents program disturbance from affecting the entire block, thereby maintaining memory cell characteristics while allowing increased integration degree.
Solution Approach 2:
The patent performs preliminary erase operations on specific word line groups before program operations. By erasing only the necessary word line groups (e.g., first word line group) before programming, and leaving other groups (e.g., second word line group) in erase state, the patent prevents program disturbance from propagating to non-programmed areas, thus protecting memory cell characteristics.
2Loss of information
If conventional block-based erase operation is performed on all word lines, then data erasure is complete, but threshold voltage distribution shifts due to program disturbance
Solution Approach 1:
The patent applies different operations to different word line groups based on their specific needs. The first word line group undergoes erase and program operations, while the second word line group remains in erase state. This local differentiation prevents unnecessary program disturbance in the second group, maintaining its threshold voltage distribution integrity while still achieving complete data erasure in the first group.
Solution Approach 2:
Instead of performing erase and program operations on all word lines (excessive action), the patent performs these operations only on the necessary first word line group (partial action). The second word line group is left untouched in erase state, avoiding unnecessary program disturbance and threshold voltage shifts while still achieving the required data erasure and programming objectives.
Data Source
AI summary
A method for operating a non-volatile memory device includes selecting a word line of a plurality of word lines in response to a program command and an received address, determining whether the selected word line is a word line set among the word lines, performing an erase operation on a second word line group of the word lines in response to a result of the determining, and performing a program operation on the selected word line.