Memory Controller Refresh Read for 3D NAND Data Retention

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Solution Overview

Problem

3D non-volatile memory devices experience data degradation over time due to charge loss, leading to potential data retention issues, which existing methods struggle to effectively prevent.

Innovation Solution

A method of operating a memory controller that performs a refresh read operation on non-volatile memory devices, including issuing a refresh read command to detect power states and performing read operations on memory blocks connected to word lines to maintain data retention and prevent charge degradation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If refresh read operations are performed to prevent data degradation, then data retention is improved, but power consumption increases

Engineering Contradiction:

Improvedata retentionVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic refresh read operations at strategically determined intervals based on power state transitions. The memory controller performs refresh reads after power-on states and at power-off states, creating a periodic maintenance schedule that prevents data degradation while avoiding continuous operation that would waste energy. This periodic approach balances reliability improvement with energy conservation.

Inventive Principle:

Principle #19Periodic action

2Reliability

If refresh read operations are performed frequently to maintain data accuracy, then data retention is improved, but device complexity increases

Engineering Contradiction:

Improvedata accuracyVSAvoidcontrol logic complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The memory controller autonomously determines when refresh read operations are needed by monitoring power state transitions without requiring external intervention or complex scheduling algorithms. The system self-manages the refresh operations based on inherent power management events (power-on/power-off states), reducing the need for additional complex control logic while maintaining data accuracy.

Inventive Principle:

Principle #25Self-service

3Reliability

If refresh read operations are performed to prevent charge degradation, then data retention is improved, but operation time increases

Engineering Contradiction:

Improvedata retentionVSAvoidoperation time

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent performs refresh read operations at power-state transition points (power-on and power-off states) before data degradation can significantly impact operational readiness. By proactively refreshing data at these predetermined moments, the system prevents degradation rather than reacting to it, reducing the need for continuous or frequent refresh operations during active use and thereby minimizing impact on operation time.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9984757B2Operating method of memory controller controlling non-volatile memory device performing refresh read operation

Publication Date: 2018.05.29 SAMSUNG ELECTRONICS CO LTD

AI summary

An operating method of a memory controller, configured to control a non-volatile memory device that performs a refresh read operation, detects a power on state or power off state of the non-volatile memory device and issues a refresh read command. The non-volatile memory device that receives the refresh read command is controlled to perform, one time, the refresh read operation including a read operation on one of a plurality of word lines with respect to each of the plurality of memory blocks.