QLC Flash Memory Data Recovery via Multi-Pass Programming
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Solution Overview
Problem
Quadruple-level cell (QLC) flash memory faces challenges with slower read and write speeds and higher error rates due to its higher storage density, requiring advanced write management mechanisms to enhance data integrity and storage reliability.
Innovation Solution
The method involves converting lower-level memory cell blocks to higher-level blocks through multiple programming operations without garbage collection, and employing specific programming schemes for data recovery using minimal data backup to ensure data integrity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If QLC flash memory is used to increase storage density, then storage capacity is improved, but read/write speed and data reliability deteriorate
Solution Approach 1:
The patent segments the programming process into multiple passes (first programming pass, second programming pass, third programming pass) to program different pages (lower page, middle page, upper page) sequentially. This segmentation allows the system to manage the complexity of QLC programming by breaking it down into manageable stages, improving reliability while maintaining high storage density
Solution Approach 2:
The patent performs preliminary actions by backing up data from lower pages to middle pages before proceeding with subsequent programming operations. This preliminary data protection mechanism ensures that original data is preserved before being overwritten or modified in later programming passes, thereby maintaining data integrity and reliability in high-density QLC storage
2Quantity of substance
If QLC flash memory is used to increase storage density, then storage capacity is improved, but error rate increases
Solution Approach 1:
The patent performs preliminary data backup by copying data from lower pages to middle pages before subsequent programming operations. This creates a safety mechanism that preserves original data before potential modifications, directly addressing the reliability challenge of QLC memory
Solution Approach 2:
The patent implements verification mechanisms where programmed data is read back and verified after each programming pass. This feedback loop allows the system to detect and correct errors early in the programming process, ensuring data integrity despite the higher error susceptibility of QLC cells with 16 charge states
3Productivity
If multiple programming operations are performed without garbage collection, then writing efficiency is improved, but data management complexity increases
Solution Approach 1:
The patent enables the memory system to manage its own data through self-service mechanisms. The controller automatically performs data backup, verification, and recovery operations without requiring external garbage collection interventions. This self-managing approach simplifies the overall system architecture while maintaining writing efficiency in QLC flash memory
Data Source
AI summary
A data recovery method for a flash memory includes: during a first programming pass, programming a memory cell of the flash memory to a specific charge state, thereby to store middle page data and lower page data into the memory cell; reading the memory cell to back up one of the middle page data and the lower page data stored in the memory cell to another memory cell in the flash memory; upon detecting an error during or after a second programming pass, based on a current voltage of the memory cell and the backed-up one of the middle page data and the lower page data from the another memory cell of the flash memory, recovering the middle page data and the lower page data of the memory cell; and writing back the recovered middle page data and the recovered lower page data to the flash memory.