NAND Time Tag Word Line Shift for Edge Read Disturb

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Solution Overview

Problem

In non-volatile memory systems, particularly for NAND flash memory, the disturb effect on edge word lines during read operations leads to increased failed bit counts due to the interference with time tag values, affecting both user data and time stamp values.

Innovation Solution

Implementing a time tag word line shift approach where an alternative word line is used to acquire time tag values when the predetermined time tag acquisition word line is an edge word line, thereby reducing the disturb effect and minimizing failed bit counts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If time tag values are acquired from edge word lines during read operations, then time tag information can be retrieved, but disturb effect increases causing failed bit count spikes

Engineering Contradiction:

Improvetime tag information retrievalVSAvoidfailed bit count

Core Design Contradiction:

Loss of informationVSReliability

Solution Approach 1:

The patent extracts the time tag acquisition function from edge word lines and relocates it to non-edge word lines. Specifically, time tag values are acquired from word lines that are not adjacent to programmed word lines, thereby eliminating the disturb effect that causes failed bit count spikes while maintaining the ability to retrieve time tag information.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces non-edge word lines as intermediaries to acquire time tag values. Instead of directly reading from edge word lines which cause disturb effects, the system uses non-edge word lines as mediators to obtain time tag information, thus reducing the harmful interference with user data.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If edge word lines are used for time tag acquisition, then data retrieval can be performed, but disturb effect on adjacent word lines increases

Engineering Contradiction:

Improvedata retrieval operationVSAvoiddisturb effect

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent removes the time tag acquisition function from edge word lines and relocates it to non-edge word lines. This extraction eliminates the source of the disturb effect that propagates to adjacent programmed word lines, while still enabling time tag information to be retrieved for data operations.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful disturb effect into a beneficial design decision by deliberately avoiding edge word lines for time tag acquisition. By selecting non-edge word lines, the system prevents the disturb effect from affecting adjacent word lines, thereby improving overall data integrity during retrieval operations.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS12488837B2Time tag word line shift to reduce failed bit count spikes for edge word lines

Publication Date: 2025.12.02 SANDISK TECHNOLOGIES LLC

AI summary

When an open block of NAND memory is read, this places the edge word lines under a set of bias conditions that can lead to disturbs. When time tag values are stored on predefined word lines, and the predefined word line is an edge word line, this can degrade not just the user data on the word line, but also the time tag values, leading to a failed bit count spike. To address this problem, a time tag word line shift approach is introduced where, if a predetermined time tag acquisition word line is an edge word line, another word line is instead used to acquire the time tag value.