Early Source-Side Boosting for NAND Flash Program Disturb

Solution Overview

Problem

Program disturb occurs in NAND flash memory devices during programming, causing shifts in threshold voltage of unselected non-volatile storage elements, which limits the operating window and affects data integrity.

Innovation Solution

A method is introduced that 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 stabilize the channel regions, thereby reducing program disturb by increasing drain side boosting efficiency and reversing the lateral field direction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional programming is applied to NAND flash memory, then programming speed is achieved, but program disturb occurs causing threshold voltage shifts in unselected storage elements

Engineering Contradiction:

Improveprogramming speedVSAvoiddata integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary boosting to the source side channel potential before the drain side channel potential during programming. This early source side boosting prepares the channel regions to withstand the programming process, preventing threshold voltage shifts in unselected storage elements while maintaining programming speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies different boosting strategies to different regions of the NAND string - specifically boosting the source side channel potential earlier and more aggressively than the drain side. This localized differential boosting addresses program disturb in the source region without affecting the overall programming performance of the entire memory structure.

Inventive Principle:

Principle #3Local quality

2Reliability

If pass voltage is applied to isolate channel regions, then program disturb is reduced, but boosting efficiency decreases

Engineering Contradiction:

Improveprogram disturb reductionVSAvoidboosting efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies preliminary boosting to the source side channel potential before the drain side channel potential during programming. This early source side boosting prepares the channel regions to withstand the programming process, preventing threshold voltage shifts in unselected storage elements while maintaining programming speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies different boosting strategies to different regions of the NAND string - specifically boosting the source side channel potential earlier and more aggressively than the drain side. This localized differential boosting addresses program disturb in the source region without affecting the overall programming performance of the entire memory structure.

Inventive Principle:

Principle #3Local quality

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 significantly reduces program disturb failures by ensuring sufficient boosting of the drain side channel potential, maintaining data integrity and extending the operating window for non-volatile storage devices.

Implementation Method 1

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 stabilize the channel regions

Methodology Applied

Scientific EffectElectrostatic potential control: Electric Field

Implementation Method 2

reversing the lateral field direction

Methodology Applied

Scientific EffectElectric field reversal: Electric Field

Data Source

PatentEP2078302B1Reducing program disturb in non-volatile storage using early source-side boosting

Publication Date: 2010.11.24 SANDISK CORP

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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.