Early Source-Side Boosting for NAND Flash Program Disturb
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Solution Overview
Problem
Program disturb occurs in non-volatile storage elements during the programming of NAND flash memory, where the threshold voltage of unselected or previously programmed storage elements is shifted due to the programming of other elements, leading to inefficiencies and potential data loss.
Innovation Solution
The method involves boosting the source side channel potential before the drain side channel potential during programming, using a higher pass voltage on the source side word lines to isolate and pre-charge the drain side channel, thereby reducing electron leakage and enhancing boosting efficiency, which helps in minimizing program disturb.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional programming is applied to NAND flash memory, then programming speed is maintained, but program disturb occurs causing threshold voltage shifts in unselected storage elements
Solution Approach 1:
The patent applies preliminary boosting to the source side channel before the drain side channel during programming. By pre-charging the source side channel with a higher pass voltage, the patent creates a voltage gradient that prevents electron leakage into unselected storage elements before programming occurs, thereby reducing program disturb while maintaining programming efficiency
Solution Approach 2:
The patent applies different boosting strategies to different regions of the channel. The source side channel receives a higher pass voltage and is boosted earlier than the drain side channel, creating localized voltage differences that prevent electron leakage specifically at the source side while allowing normal programming at the drain side
2Manufacturing precision
If electrons are injected into the floating gate for programming, then the storage element transitions to programmed state, but electron leakage causes threshold voltage shifts in inhibited storage elements
Solution Approach 1:
The patent pre-charges the source side channel with a higher pass voltage before programming begins. This preliminary action creates a potential barrier that prevents electrons from leaking into the channel of inhibited storage elements, thereby maintaining precise threshold voltage control in unselected elements
Solution Approach 2:
The patent uses the channel potential as an intermediary mechanism to control electron flow. By adjusting the channel potential through selective boosting, the patent creates a barrier that mediates between the programmed elements (where electron injection is desired) and inhibited elements (where electron leakage must be prevented)
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 program disturb failures by increasing the drain side boosting efficiency and maintaining the integrity of programmed and unprogrammed states, improving the overall operating window for non-volatile storage devices.
Implementation Method 1
boosting a first region of a substrate... boosting a first region of the substrate on a source side of the selected word line
Implementation Method 2
electrons from the channel of a cell or memory element, e.g., storage element, to be injected into the floating gate
Data Source
AI summary
Program disturb is reduced in non-volatile storage by boosting unselected NAND strings in an array so that a source side channel, on a source side of a selected word line, is boosted before a drain side channel, on a drain side of the selected word line. In one approach, a first boost mode is used when the selected word line is a lower or intermediate word line. In the first boost mode, boosting of the source and drain side channels is initiated concurrently. A second boost mode is used when the selected word line is a higher word line. In the second boost mode, boosting of the source side channel occurs early relative to the boosting of the drain side channel. Either boost mode include an isolation voltage which tends to isolate the source and drain side channels from one another.