Read Disturb Detection in Open Flash Memory Blocks
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Solution Overview
Problem
Non-volatile memory systems, such as flash memory, face read disturb errors when reading from open blocks due to unintended programming of neighboring cells, which complicates data retention and accuracy, especially as block sizes increase, requiring efficient detection and correction methods to prevent data degradation.
Innovation Solution
A modified erase verify operation is implemented, applying a higher voltage to programmed wordlines and the usual bias voltage to unprogrammed wordlines during erase verify operations to detect read disturb errors, allowing for real-time detection and correction without significant processing time or resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If read operations are performed on open blocks, then data access is enabled, but read disturb errors occur causing unintended programming of neighboring cells
Solution Approach 1:
The patent applies a preliminary detect operation before programming operations on open blocks. This detect operation identifies unprogrammed wordlines that may have suffered read disturb errors, allowing the system to take corrective action (such as erasing affected blocks) before data corruption occurs, thus preventing reliability issues while maintaining ease of operation
Solution Approach 2:
The patent implements a feedback mechanism where the detect operation monitors the state of unprogrammed wordlines during open block operations. Based on the detect results, the system dynamically adjusts subsequent programming operations, enabling data access while preventing read disturb errors through closed-loop control
2Quantity of substance
If block size is increased, then storage capacity is improved, but read disturb errors increase due to more neighboring cells
Solution Approach 1:
The patent segments the detection process by specifically targeting unprogrammed wordlines within open blocks for detect operations. This segmentation allows the system to handle large blocks by focusing detection efforts only on vulnerable unprogrammed regions, enabling increased storage capacity while mitigating read disturb errors through selective monitoring
Solution Approach 2:
The patent changes the detection parameter by applying detect operations with specific voltage conditions tailored for unprogrammed wordlines. This parameter change enables the system to distinguish between programmed and unprogrammed cells, allowing larger block sizes while maintaining error detection capability through adjusted detection thresholds
3Measurement precision
If detect operation is applied to all wordlines, then read disturb detection is comprehensive, but processing time and resource usage increase significantly
Solution Approach 1:
The patent extracts and focuses detection efforts specifically on unprogrammed wordlines within open blocks, excluding already-programmed wordlines from detect operations. This extraction approach maintains detection accuracy for vulnerable cells while significantly reducing processing time and resource usage by limiting the detection scope to only necessary regions
4Reliability
If frequent detect operations are performed, then data accuracy is maintained, but productivity decreases due to additional processing steps
Solution Approach 1:
The patent applies partial detect operations only to unprogrammed wordlines in open blocks rather than all wordlines. This partial action approach maintains data accuracy for vulnerable unprogrammed cells while minimizing the impact on programming productivity by avoiding redundant detection of already-programmed wordlines
Data Source
AI summary
A storage device with a memory may include read disturb detection for open blocks. An open or partially programmed block may develop read disturb errors from reading of the programmed portion of the open block. The detection of any read disturb effects may be necessary for continued programming of the open block and may include verifying that wordlines in the unprogrammed portion of the open block are in the erase state. A modified erase verify operation for the open block is used in which programmed wordlines are subject to a higher erase verify read voltage, while the unprogrammed wordlines are subject to an erase verify bias voltage.