Enhanced Read Retry Algorithm for Flash Memory Data Recovery
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Solution Overview
Problem
Existing data recovery methods fail to effectively handle open connections in memory blocks, leading to data loss due to uncharged select gate source (SGS) or other open word lines, causing defective parts per million (DDPM) issues and uncorrected error correction codes (UECC) during read operations.
Innovation Solution
An Enhanced Read Retry (ERR) algorithm is implemented, which flags unsuccessful read operations and increases voltage or bias time on select gate drain (SGD), dummy word lines, data word lines, and select gate source (SGS) to facilitate data recovery, potentially applying multiple pulses or combinations of voltage and time adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If default read recovery is used, then simple error handling is maintained, but data loss occurs due to open connections and uncharged SGS
Solution Approach 1:
The error handling process is segmented into multiple distinct phases: initial read operation, failure detection, voltage increase phase, and retry read operation. Each phase handles a specific aspect of the error recovery process, allowing systematic addressing of open connections and uncharged SGS conditions without overwhelming complexity.
Solution Approach 2:
The system performs preliminary actions by increasing voltage on select gate drain, dummy word lines, data word lines, and select gate source before attempting the retry read operation. This preliminary voltage adjustment prepares the memory structure to overcome the open connection and uncharged SGS conditions that caused the initial failure.
2Reliability
If voltage is increased on WLs to facilitate data recovery, then data recovery success rate improves, but energy consumption increases
Solution Approach 1:
The voltage increase is applied periodically and selectively only when read failures are detected, rather than continuously. The system monitors read operation outcomes and applies voltage adjustments only when necessary, creating a periodic action pattern that reduces overall energy consumption while maintaining high data recovery success rate when needed.
Solution Approach 2:
The system changes the voltage parameter dynamically based on the specific failure conditions detected during read operations. By adjusting voltage levels adaptively rather than using fixed high voltage, the system achieves effective data recovery while minimizing unnecessary energy consumption in successful reads.
3Reliability
If multiple voltage levels and bias times are applied, then open row issues are detected and data recovery is enabled, but read operation time increases
Solution Approach 1:
The system implements feedback mechanisms that monitor read operation outcomes and use this information to determine whether voltage increase and retry operations are necessary. The feedback from read failures triggers the enhanced error handling sequence, while successful reads proceed without time-consuming voltage adjustments, thus balancing detection capability with operation time.
Solution Approach 2:
The system applies partial action by implementing voltage increase and extended bias time only for the specific word lines and select gates that fail during read operations, rather than applying these time-consuming adjustments to all memory structures. This selective partial action reduces overall read operation time while maintaining effective open row detection and data recovery for problematic areas.
Data Source
AI summary
A flash memory includes an improved error handling algorithm for data recovery. Rather than running a default read recovery only, an Enhance Read Retry (ERR) process also is performed. After running a default read recovery, WLs are flagged with an error flag if the read was unsuccessful. The flag triggers ERR mode. ERR mode implements increase of the row read bias or implements increase of row read time or implements multiple pulses at the same voltage, or a combination of all three.