Flash Memory Pre-Charging to Reduce Program Disturb

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Solution Overview

Problem

In flash memory systems, program disturb occurs when programming one cell on a word line inadvertently programs adjacent unselected cells, due to the application of program voltage to all cells connected to the word line, leading to errors and data integrity issues.

Innovation Solution

Pre-charging unselected groups of non-volatile storage elements to a higher boosted potential before applying the program voltage to the selected word line, using different pre-charge enable voltages for cells that may have undergone partial programming to ensure proper pre-charging and reduce program disturb.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If program voltage is applied to all cells connected to a word line, then programming of selected cells is achieved, but program disturb occurs in adjacent unselected cells

Engineering Contradiction:

Improveprogramming speedVSAvoiddata integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent divides the word line into multiple segments or groups, applying different pre-charge voltages to different segments. Selected cells receive appropriate pre-charge voltages to enable programming, while unselected cells receive different voltages to prevent program disturb, thus resolving the contradiction between programming efficiency and data integrity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different pre-charge voltages to different regions or groups of cells along the word line based on their selection status. This localized differentiation ensures that only selected cells are programmed while protecting unselected cells from program disturb, maintaining both productivity and reliability

Inventive Principle:

Principle #3Local quality

2Reliability

If pre-charge voltage is applied to unselected cells, then program disturb is reduced, but device complexity increases due to multiple voltage levels

Engineering Contradiction:

Improvedata integrityVSAvoidvoltage control complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies pre-charge voltages selectively to only those cell groups that require protection from program disturb, rather than uniformly to all cells. This partial application of pre-charge reduces the complexity of voltage control while still achieving the reliability goal of preventing program disturb in unselected cells

Inventive Principle:

Principle #16Partial or excessive action

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 method effectively reduces or eliminates program disturb by ensuring that unselected cells are adequately pre-charged, preventing unintended programming and enhancing data integrity during the programming process.

Implementation Method 1

Pre-charging unselected groups of non-volatile storage elements to a higher boosted potential before applying the program voltage to the selected word line

Methodology Applied

Scientific EffectElectrical potential difference: Electric Field

Data Source

PatentUS7468918B2Systems for programming non-volatile memory with reduced program disturb by removing pre-charge dependency on word line data

Publication Date: 2008.12.23 SANDISK TECHNOLOGIES LLC

AI summary

Unselected groups of non-volatile storage elements are boosted during programming to reduce or eliminate program disturb for targeted, but unselected memory cells connected to a selected word line. Prior to applying a program voltage to the selected word line and boosting the unselected groups, the unselected groups are pre-charged to further reduce or eliminate program disturb by providing a larger boosted potential for the unselected groups. During pre-charging, one or more pre-charge enable signals are provided at higher voltages for certain memory cells that may have undergone partial programming.