Soft Program Method for Non-Volatile Memory Threshold Distribution
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Solution Overview
Problem
Conventional soft program operations in non-volatile memory devices result in wide threshold voltage distribution of erased cells, leading to reduced read margin and potential data errors due to premature termination of the soft program process when a single cell in a block exceeds the verifying voltage.
Innovation Solution
A method that involves performing a soft program to increase the threshold voltage of memory cells, verifying if cells are programmed beyond a specific voltage, and repeating the process until all cell strings have cells programmed above the verifying voltage, using a verifying voltage of 0V to maintain efficiency and improve read margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a soft program operation is performed on the whole block when only one cell exceeds the verifying voltage, then the soft program process is terminated early, but the threshold voltage distribution of erased cells becomes wide
Solution Approach 1:
The patent divides the block into multiple cell strings and performs soft program operations and verifying operations on each cell string individually rather than treating the entire block as a single unit. This segmentation allows the process to continue on other cell strings even when one cell string meets the verification criteria, thereby maintaining tight threshold voltage distribution while improving overall operation efficiency.
Solution Approach 2:
The patent applies soft program operations to all cell strings in the block rather than stopping when a single cell string is verified. This excessive action ensures that all cell strings receive adequate programming, resulting in tight threshold voltage distribution across the entire block, while the verifying operation efficiently monitors progress without requiring full completion of all cell strings.
2Measurement precision
If a negative verifying voltage is applied to verify soft program operation, then the verification accuracy is improved, but the operation complexity and time increase
Solution Approach 1:
The patent changes the verifying voltage parameter from a traditional negative voltage to 0V, simplifying the voltage application circuitry and reducing operation complexity. The method compensates for the reduced voltage differential by optimizing the sensing operation and bit line evaluation, maintaining verification accuracy while significantly reducing the time and complexity associated with applying and monitoring negative voltages.
Data Source
AI summary
A soft program method in a non-volatile memory device for performing a soft program step so as to improve threshold voltage distribution of an erased cell is disclosed. The soft program method in a non-volatile memory device includes performing a soft program for increasing threshold voltages of memory cells by a given level, wherein an erase operation is performed about the memory cells, performing a verifying operation for verifying whether or not a cell programmed to a voltage more than a verifying voltage is existed in each of cell strings, and performing repeatedly the soft program until it is verified that whole cell strings have one or more cell programmed to the voltage more than the verifying voltage.