NAND Flash Channel Isolation Switching for Program Disturb Reduction

Solution Overview

Problem

Program disturb occurs in non-volatile storage elements during the programming of NAND flash memory, where the threshold voltage of unselected storage elements is shifted due to programming of other elements, affecting both programmed and erased states, leading to operational limitations.

Innovation Solution

Implementing a non-volatile storage system with a source side boosting scheme, where the NAND string is boosted on the source side before the drain side, and specific voltage configurations are applied to word lines to isolate and control channel regions, reducing program disturb by managing electric fields and charge injection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If program voltage is applied to control gate during programming operation, then storage elements can be programmed, but program disturb occurs causing threshold voltage shift in unselected storage elements

Engineering Contradiction:

Improveprogramming speedVSAvoidthreshold voltage stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent segments the channel into multiple regions by applying different voltages to different word lines. The selected word line region receives high voltage for programming, while unselected word line regions receive low voltage to isolate and prevent program disturb, effectively dividing the channel into programmed and unprogrammed segments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by providing different voltage conditions to different spatial locations within the channel. The selected channel region receives high voltage for electron injection, while unselected regions maintain low voltage to prevent hot carrier generation, creating localized programming action without affecting other regions.

Inventive Principle:

Principle #3Local quality

2Productivity

If high voltage is applied to boost channel for programming, then programming efficiency improves, but hot carrier injection occurs causing program disturb

Engineering Contradiction:

Improveprogramming efficiencyVSAvoidhot carrier injection

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent segments the channel into multiple regions by applying different voltages to different word lines. The selected word line region receives high voltage for programming, while unselected word line regions receive low voltage to isolate and prevent program disturb, effectively dividing the channel into programmed and unprogrammed segments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by providing different voltage conditions to different spatial locations within the channel. The selected channel region receives high voltage for electron injection, while unselected regions maintain low voltage to prevent hot carrier generation, creating localized programming action without affecting other regions.

Inventive Principle:

Principle #3Local quality

3Productivity

If multiple storage elements are programmed in parallel, then programming speed increases, but program disturb affects both programmed and erased states

Engineering Contradiction:

Improveparallel programming capabilityVSAvoidstate integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent segments the channel into multiple regions by applying different voltages to different word lines. The selected word line region receives high voltage for programming, while unselected word line regions receive low voltage to isolate and prevent program disturb, effectively dividing the channel into programmed and unprogrammed segments.

Inventive Principle:

Principle #1Segmentation

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 by maintaining the integrity of threshold voltages, enhancing the operating window for non-volatile storage devices and preventing hot carrier injection, thus improving data retention and programming accuracy.

Implementation Method 1

specific voltage configurations are applied to word lines to isolate and control channel regions, reducing program disturb by managing electric fields and charge injection

Methodology Applied

Scientific EffectElectric field control: Electric Field

Implementation Method 2

managing electric fields and charge injection... preventing hot carrier injection

Methodology Applied

Scientific EffectCharge injection: Electron Beam

Data Source

PatentUS7463522B2Non-volatile storage with boosting using channel isolation switching

Publication Date: 2008.12.09 SANDISK TECHNOLOGIES LLC

AI summary

Non-volatile storage in which program disturb is reduced by preventing source side boosting in selected NAND strings. A self-boosting mode which includes an isolation word line is used. A channel area of an inhibited NAND string is boosted on a source side of the isolation word line before the channel is boosted on a drain side of the isolation word line. Further, storage elements near the isolation word line are kept in a conducting state during the source side boosting so that the source side channel is connected to the drain side channel. In this way, in selected NAND strings, source side boosting can not occur and thus program disturb due to source side boosting can be prevented. After the source side boosting, the source side channel is isolated from the drain side channel, and drain side boosting is performed.