Reserved Word-Line SLC Mode for MLC Flash Reliability
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Solution Overview
Problem
Multilevel cell (MLC) flash memory devices face instability issues, leading to higher Bit Error Rates (BER) in the first and last word-lines of blocks, which can shorten the lifespan of data storage devices, and existing management mechanisms are inadequate to address these issues without increasing costs.
Innovation Solution
Implementing a method where the controller selects blocks with reserved and non-reserved word-lines, using Single Level Cell (SLC) writing mode for the first and last word-lines to reduce error rates, thereby extending the device's lifespan without significant additional cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If MLC flash memory is used to increase storage capacity and reduce cost, then the storage density increases, but the bit error rate in first and last word-lines increases significantly
Solution Approach 1:
The patent applies local quality by treating first and last word-lines differently from intermediate word-lines. Specifically, it designates certain word-lines as reserved word-lines and applies SLC writing mode (more reliable) only to these critical word-lines, while using MLC mode for intermediate word-lines. This localized differentiation resolves the contradiction by maintaining high storage density in intermediate word-lines while ensuring reliability in first and last word-lines through SLC mode.
Solution Approach 2:
The patent segments the word-lines into three categories: first word-lines, intermediate word-lines, and last word-lines. It further segments the writing mode application by using SLC mode for first and last word-lines (reserved word-lines) and MLC mode for intermediate word-lines. This segmentation allows the system to optimize for reliability where needed while maintaining high storage capacity elsewhere.
2Reliability
If reserved word-lines are designated and SLC writing mode is applied to reduce bit error rate, then reliability improves, but device complexity increases
Solution Approach 1:
The patent implements self-service by automatically designating reserved word-lines and automatically selecting appropriate writing modes based on word-line position. The controller autonomously determines which word-lines are first, intermediate, or last, and applies the appropriate writing mode without requiring external intervention or complex management mechanisms. This automation reduces the perceived complexity for the user while maintaining high reliability.
Solution Approach 2:
The patent changes the writing mode parameter (from MLC to SLC) based on the position parameter of the word-line. By dynamically adjusting the writing mode parameter according to whether the word-line is a first, intermediate, or last word-line, the system achieves high reliability without requiring permanent hardware changes or complex management structures. The parameter change is simple and rule-based.
Data Source
AI summary
A method for controlling operations of a data storage device, the associated data storage device and the controller thereof are provided. The method can comprise: selecting a block of multiple blocks of a non-volatile (NV) memory element of a plurality of NV memory elements; receiving a data-writing command from a host device; generating a plurality of operating commands corresponding to the data-writing command, and sending the plurality of operating commands to the NV memory to perform data-writing on a plurality of non-reserved word-lines of the block, wherein the block comprises the plurality of non-reserved word-lines and a plurality of reserved word-lines, and each non-reserved word-line of the plurality of non-reserved word-lines comprises multiple pages; and writing user data into a reserved word-line of the plurality of reserved word-lines through a single level cell (SLC) writing mode, to make the reserved word-line comprise a single page.