NAND Flash Read Parameter Adjustment for Back Pattern Effect
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Solution Overview
Problem
The back pattern effect in NAND flash memory systems leads to errors during data reading due to changes in channel resistance and threshold voltage shifts as more memory cells are programmed, causing conductivity issues and inaccurate current flow.
Innovation Solution
Measuring resistance information for groups of connected non-volatile storage elements and adjusting read parameters to account for the condition of neighboring memory cells, allowing for compensation during the read process to mitigate the back pattern effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple memory cells in a NAND string are programmed sequentially, then the memory capacity is increased, but the channel resistance increases and causes threshold voltage shifts leading to read errors
Solution Approach 1:
The patent applies preliminary action by measuring the resistance of unselected memory cells before reading the selected memory cell. This resistance measurement is performed in advance to detect the back pattern effect condition, allowing the system to compensate for threshold voltage shifts before they affect the read accuracy. The resistance information obtained from unselected cells is used to adjust read parameters proactively.
Solution Approach 2:
The patent implements feedback by using the measured resistance information from unselected memory cells to dynamically adjust the read parameters for selected memory cells. The system continuously monitors resistance changes in unselected cells and feeds this information back to modify the read operation, creating a closed-loop control system that compensates for the back pattern effect in real-time.
2Measurement precision
If resistance measurement is performed for each NAND string, then read accuracy is improved, but the operation time increases
Solution Approach 1:
The patent merges the resistance measurement operation with the existing read operation by measuring the resistance of unselected memory cells during the same time period when the selected memory cell is being read. This combined approach allows resistance information to be obtained without requiring separate measurement cycles, thereby improving read accuracy while minimizing additional time overhead.
Solution Approach 2:
The system performs self-service by utilizing the natural signal paths and circuitry already present during read operations to measure resistance. The same bit lines and word lines used for reading selected cells are also used to sense the resistance of unselected cells, eliminating the need for dedicated measurement circuits or separate measurement phases.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves data reading accuracy by compensating for resistance changes and threshold voltage shifts, reducing errors and maintaining reliable data retrieval in NAND flash memory systems.
Implementation Method 1
measuring, with the managing circuit, resistance information for one or more groups of connected non-volatile storage elements
Data Source
AI summary
When reading data from a non-volatile storage element that is part of a group of connected non-volatile storage elements, resistance information is measured for the group. One or more read parameters are set based on the measured resistance information. The read process is then performed using the one or more parameters.