Memory Controller Program Disturb Mitigation

Solution Overview

Problem

Memory systems with nonvolatile devices face issues with program disturb due to sudden power-offs, where repeated over-write operations on selected pages can cause threshold voltage changes in unselected pages, leading to errors and data retention problems.

Innovation Solution

A memory system with a controller that determines the probability of program disturb in unselected pages sharing a word line with a selected page after a sudden power-off, and decides whether to perform an over-write operation or skip it, potentially selecting a different page for the operation based on the probability assessment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an over-write operation is performed on a selected page after sudden power-off, then data integrity of the selected page is improved, but program disturb occurs in unselected pages sharing the same word line

Engineering Contradiction:

Improvedata integrityVSAvoidprogram disturb

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The memory controller performs a read operation on unselected pages sharing the same word line before executing the over-write operation on the selected page. This preliminary action detects whether program disturb has already occurred, allowing the system to conditionally execute the over-write operation only when safe, thus preventing further program disturb while maintaining data integrity when needed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the read operation results from unselected pages as feedback to determine whether to proceed with the over-write operation. Based on the detected program disturb status, the controller dynamically adjusts its decision to perform or skip the over-write operation, creating a closed-loop control mechanism that balances data integrity and program disturb prevention

Inventive Principle:

Principle #23Feedback

2Duration of action of stationary object

If the memory controller always performs over-write operation after sudden power-off, then data retention in selected page is improved, but threshold voltage changes occur in unselected pages leading to errors

Engineering Contradiction:

Improvedata retentionVSAvoidthreshold voltage stability

Core Design Contradiction:

Duration of action of stationary objectVSManufacturing precision

Solution Approach 1:

The memory controller performs a read operation on unselected pages before executing the over-write operation on the selected page. This preliminary action detects whether program disturb has already occurred, allowing the system to conditionally execute the over-write operation only when safe, thus preventing further program disturb while maintaining data integrity when needed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the read operation results from unselected pages as feedback to determine whether to proceed with the over-write operation. Based on the detected program disturb status, the controller dynamically adjusts its decision to perform or skip the over-write operation, creating a closed-loop control mechanism that balances data integrity and program disturb prevention

Inventive Principle:

Principle #23Feedback

3Manufacturing precision

If the memory controller skips the over-write operation to prevent program disturb, then threshold voltage stability in unselected pages is improved, but data integrity in the selected page deteriorates

Engineering Contradiction:

Improvethreshold voltage stabilityVSAvoiddata integrity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The memory controller performs a read operation on unselected pages before executing the over-write operation on the selected page. This preliminary action detects whether program disturb has already occurred, allowing the system to conditionally execute the over-write operation only when safe, thus preventing further program disturb while maintaining data integrity when needed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the read operation results from unselected pages as feedback to determine whether to proceed with the over-write operation. Based on the detected program disturb status, the controller dynamically adjusts its decision to perform or skip the over-write operation, creating a closed-loop control mechanism that balances data integrity and program disturb prevention

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10936421B2Memory system having storage device and memory controller and operating method thereof

Publication Date: 2021.03.02 MIMIRIP LLC

AI summary

A memory system includes: a storage device including a plurality pages for storing data; and a memory controller configured to determine, when sudden power-off occurs, whether there is a high probability of a program disturb of unselected pages sharing a word line coupled to a selected page among the pages in rebooting, and output a command to perform an over-write operation for programming data in the selected page or skip the over-write operation, based on a result of the determination.