Flash Memory Block SLC Mode Recovery for MSB Programming Failures

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Solution Overview

Problem

Conventional multi-level cell (MLC) memory systems often classify a memory block as a bad block when the most significant bit (MSB) fails to be programmed, leading to unavailability of normal cells for least significant bit (LSB) programming, resulting in inefficient use of flash memory.

Innovation Solution

The memory system operates a memory block including a fail cell in a single level cell (SLC) mode when the MSB fails to be programmed, without classifying it as a bad block, allowing continued use of the block for LSB programming, with the operation mode stored in a spare field or meta-block within the flash memory.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a memory block with MSB programming failure is classified as a bad block, then programming reliability is ensured, but memory capacity is reduced due to unavailable cells

Engineering Contradiction:

Improveprogramming reliabilityVSAvoidmemory capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The memory block is segmented into two operational modes: MLC mode for cells with successful MSB programming and SLC mode for cells with MSB programming failure but successful LSB programming. This segmentation allows the system to preserve usable capacity by isolating and independently managing failed cells rather than discarding the entire block.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The operational parameter of the memory block is dynamically changed based on programming results. When MSB programming fails, the block's operating mode parameter is switched from MLC (2-bit) to SLC (1-bit), allowing the same physical cells to continue serving storage purposes at a reduced data density level.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If multi-level cell mode is used to increase memory capacity, then storage density is improved, but programming failure rate increases

Engineering Contradiction:

Improvememory capacityVSAvoidprogramming success rate

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The system performs preliminary verification of LSB programming success before attempting MSB programming. This cushioning approach ensures that only blocks with successfully programmed LSB are subjected to the riskier MSB programming operation, and failed blocks are gracefully degraded to SLC mode rather than being completely lost.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The programming failure in MSB is converted into a beneficial outcome by automatically switching the block to SLC mode. What would traditionally be a harmful failure resulting in bad block classification is transformed into an opportunity to preserve capacity through adaptive mode switching, turning a negative event into a positive resource utilization strategy.

Inventive Principle:

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

Data Source

PatentUS7505338B2Memory systems and memory cards that use a bad block due to a programming failure therein in single level cell mode and methods of operating the same

Publication Date: 2009.03.17 SAMSUNG ELECTRONICS CO LTD

AI summary

A memory system includes a host, a flash memory that is configured to store multi-bit data in one memory cell, and a memory controller that is configured to control programming of multi-bit data provided by the host into the flash memory. When an nth bit is normally programmed, and a fail occurs in programming an n+1th bit in the flash memory, a memory block of the flash memory including a fail cell is operated in an operation mode of the nth or lesser bit. Related memory systems and methods are also provided.