Hybrid Erase Scheme for Non-Volatile Memory Voltage Margin

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Solution Overview

Problem

Current non-volatile memory technologies face inefficiencies in erase operations, particularly in three-dimensional memory structures, where stripe erase methods are slower and more prone to tunnel oxide wear-out compared to normal erase methods, and there is a need for a hybrid approach that combines the advantages of both to improve data retention and erase speed.

Innovation Solution

Implementing a hybrid erase scheme that follows a normal erase operation with a stripe erase operation, where every other wordline is biased differently to aggregate holes under wordlines, reducing trapped holes between them, without requiring higher erase voltages, thus optimizing erase efficiency and data retention.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If stripe erase operation is used to improve data retention, then voltage margin is improved, but erase speed decreases and tunnel oxide wear-out increases

Engineering Contradiction:

Improvedata retentionVSAvoiderase speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The erase operation is segmented into two distinct phases: a normal erase phase that erases all wordlines simultaneously for speed, followed by a stripe erase phase that selectively erases alternating wordlines to improve voltage margin. This segmentation allows each phase to optimize for its specific purpose without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The hybrid erase employs periodic alternating patterns in the stripe erase phase, where every other wordline is erased in succession rather than simultaneously. This periodic action redistributes holes uniformly across all wordlines, improving data retention while maintaining reasonable erase speed through the initial normal erase phase.

Inventive Principle:

Principle #19Periodic action

2Reliability

If stripe erase operation is used to improve data retention, then voltage margin is improved, but tunnel oxide wear-out increases

Engineering Contradiction:

Improvedata retentionVSAvoidtunnel oxide wear-out

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Instead of performing a complete stripe erase on all wordlines (excessive action), the hybrid erase applies stripe erase only to alternating wordlines (partial action). This partial application achieves the hole redistribution benefit for improved data retention while reducing the cumulative stress on tunnel oxide compared to full stripe erase.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

Inventive Principle:

Principle #1Segmentation

3Productivity

If normal erase operation is used to improve erase speed, then productivity is improved, but data retention and voltage margin deteriorate

Engineering Contradiction:

Improveerase speedVSAvoiddata retention

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The hybrid erase merges the advantages of normal erase (speed) and stripe erase (data retention) into a single composite operation. The normal erase phase provides rapid initial erasure, while the subsequent stripe erase phase corrects voltage margin issues, achieving both speed and reliability benefits.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The normal erase phase is performed first as a preliminary action to quickly erase all wordlines, establishing a baseline erased state. This preliminary fast erase is then followed by the stripe erase phase that refines the voltage margin characteristics, combining the speed benefit of the first phase with the reliability benefit of the second.

Inventive Principle:

Principle #10Preliminary 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

The hybrid erase method enhances data retention and erase speed, offering better beginning-of-life and end-of-life voltage margins while reducing erase defects and tunnel oxide wear-out, outperforming both standard normal and stripe erase techniques.

Implementation Method 1

every other wordline is biased differently to aggregate holes under wordlines, reducing trapped holes between them

Methodology Applied

Scientific EffectCharge trapping and hole aggregation:

Data Source

PatentUS20240386973A1Hybrid erase for data retention threshold voltage margin improvement

Publication Date: 2024.11.21 SANDISK TECHNOLOGIES LLC

AI summary

A storage device is disclosed. The storage device is configured to perform a hybrid erase scheme comprising: performing an erase operation including simultaneously erasing memory cells associated with a block; and performing a stripe erase operation including simultaneously erasing memory cells associated with every other wordline of the block and then simultaneously erasing memory cells associated with remaining wordlines of the block.