Nonvolatile Memory Read Voltage Adjustment for Coupling Effects
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Solution Overview
Problem
Current nonvolatile memory devices face challenges in accurately reading data from memory cells, particularly in distinguishing between erase and program states in multi-level cells, due to coupling effects from adjacent cells, which affects read operation reliability.
Innovation Solution
The method involves determining the state of a selected word line by applying different read voltages based on the number of fail bits detected, using flag cells to identify LSB or MSB programming, and adjusting select and unselect read voltages to improve read operation reliability by distinguishing between different cell states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed read voltage is applied to all word lines, then the read operation is simple, but the read accuracy deteriorates due to coupling effects from adjacent programmed cells
Solution Approach 1:
The patent applies dynamic read voltage adjustment based on the programming state of adjacent word lines. The read voltage is changed according to whether adjacent word lines are programmed, which dynamically adapts the read operation to different coupling conditions and improves read accuracy without requiring complex additional hardware
Solution Approach 2:
The patent changes the read voltage parameter based on the state of adjacent word lines. When adjacent word lines are programmed, a different read voltage is applied compared to when they are not programmed, thereby compensating for coupling effects and improving measurement precision
2Difficulty of detecting and measuring
If the read voltage is increased to distinguish erase and program states, then the detection capability improves, but the coupling effects from adjacent cells worsen
Solution Approach 1:
The patent adjusts the read voltage parameter based on the programming state of adjacent word lines rather than using a uniformly high voltage. This selective parameter adjustment improves state detection capability while avoiding excessive voltage that would worsen coupling effects
3Quantity of substance
If multi-bit data is stored in each memory cell to increase integration, then the storage capacity improves, but the difficulty of accurately reading data worsens due to overlapping threshold voltage distributions
Solution Approach 1:
The patent changes the read voltage parameter based on the programming state of adjacent word lines to compensate for coupling effects. This helps maintain threshold voltage distribution separation in multi-bit cells, thereby improving data reading accuracy while preserving high storage capacity
Data Source
AI summary
A read method of a nonvolatile memory device includes determining whether a selected word line comprises LSB (least significant bit) page only programmed memory cells by applying a first read voltage to the selected word line. In the case that the selected word line comprises LSB (least significant bit) page only programmed memory cells, counting the number of off-cells by applying the first read voltage to the selected word line. And in a read operation, changing a select read voltage being applied to the selected word line according to the number of off-cells.