Vertical NAND Flash Pre-Pulse Control for Read Disturbance
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Solution Overview
Problem
In vertical NAND flash memory systems, the application of pre-pulses to remove boosting charges from unselected strings during read operations can slow down processing speed, leading to potential read disturbances due to hot carrier injection.
Innovation Solution
A program method for nonvolatile memory devices that includes determining the operation mode, applying a pre-pulse to unselected string selection lines only when necessary, and varying the pre-pulse duration based on the target state of the memory cell to optimize data integrity and processing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-pulses are applied to remove boosting charges from unselected strings, then read disturbance is reduced, but processing speed is slowed down
Solution Approach 1:
The patent applies dynamic control by adjusting the pre-pulse time period based on the target state of memory cells. When memory cells are programmed to higher states requiring more charge removal, a longer pre-pulse time period is applied. When fewer charges need removal, a shorter pre-pulse time period is used. This dynamic adjustment optimizes the balance between read disturbance reduction and processing speed by applying the minimum necessary pre-pulse duration for each operational context.
2Reliability
If pre-pulses are applied to all unselected strings, then read disturbance is reduced, but device complexity increases
Solution Approach 1:
The patent implements local quality control by selectively applying pre-pulses to specific unselected strings based on their individual charge states and the read operation requirements. Rather than uniformly applying pre-pulses to all unselected strings, the control logic determines which specific strings require charge removal and applies pre-pulses only to those strings. This localized approach reduces unnecessary control complexity while maintaining data integrity where it is actually needed.
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 effectively reduces read disturbances while maintaining or improving processing speed by selectively applying pre-pulses based on operational modes and memory cell states, ensuring data integrity without compromising program speed.
Implementation Method 1
the probability that read disturbance is generated by hot carrier injection may be high
Data Source
AI summary
A program method of a nonvolatile memory device is provided, which includes programming a memory cell in one string selected from a plurality of vertical strings; determining whether a mode of operation of the nonvolatile memory device is a pre-pulse mode; when the mode of operation is determined to be the pre-pulse mode, applying a pre-pulse having a predetermined level to a string selection line connected with a gate of a string selection transistor of at least one unselected vertical string of the plurality of vertical strings for a particular time period; and performing a verification operation on the programmed memory cell.