NAND Memory Read Reference Voltage Search Using Dummy Data
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Solution Overview
Problem
Three-dimensional (3D) NAND flash memory systems experience increased read latency and performance degradation due to a large number of read-retry operations, which are necessary to correctly decode encoded pages.
Innovation Solution
A method is introduced that performs a single-read operation at a read reference voltage of a first level to detect bits from a set of memory cells, using previously programmed dummy data to determine original bits and calculate upper-state and lower-state failed bit counts. The read reference voltage is adjusted based on the difference between these counts to determine a best read reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple read-retry operations with adjusted read reference voltage values are performed, then the reliability of reading data from 3D NAND flash memory is improved, but the read latency increases and performance degrades
Solution Approach 1:
The patent applies preliminary action by performing a read-retry operation in advance to detect flipping bits before the actual data read operation. The detected flipping bit information is stored and reused for subsequent reads from the same memory block, eliminating the need to perform multiple read-retry operations for each read request. This preliminary detection and storage of flipping bit patterns resolves the contradiction by establishing reliability through advance error detection while minimizing read latency during actual data access.
2Measurement precision
If a large number of read-retry operations are performed to correctly decode encoded pages, then the decoding accuracy is improved, but the performance of the memory system degrades
Solution Approach 1:
The patent implements feedback by using the results of preliminary read-retry operations to identify flipping bits and adjust subsequent read operations. The detected flipping bit information feeds back into the read process, allowing the system to compensate for threshold voltage shifts and improve decoding accuracy. This feedback mechanism enables correct decoding with fewer operations, thereby maintaining high memory system performance.
3Reliability
If read reference voltage values are adjusted through multiple retry steps, then the correctness of decoded pages is improved, but the complexity of the read operation increases
Solution Approach 1:
The patent performs the complex voltage adjustment and flipping bit detection in advance during a preliminary read-retry operation. Once the flipping bit patterns are identified and stored, subsequent reads can proceed with simpler operations using the pre-acquired correction information. This preliminary action approach maintains decoded page correctness while reducing the complexity of routine read operations.
Data Source
AI summary
A method can include performing a single-read operation at a read reference voltage to detect bits from memory cells. The method can also include determining second bits corresponding to the set of memory cells, the second bits corresponding to data being initially programmed into the set of memory cell. The method can further include determining a read voltage based on the first bits and the second bits.