Flash Memory Read-Voltage Detection for Unstable Cells
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Solution Overview
Problem
Flash memory systems face issues with read errors due to insufficient charge accumulation on floating gates, leading to data corruption and instability, especially when power is suddenly cut off during programming operations, resulting in uncorrectable errors and invalid data.
Innovation Solution
A memory system that employs a memory controller using both standard and correction read voltages to analyze the distribution of data in SSDs, determining the validity and correcting data by adjusting the read voltage levels, thereby identifying and addressing unstable memory cells and preventing read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a standard read voltage is used to read data from memory cells, then the read operation is simple and fast, but read errors occur when charge accumulation on floating gates is insufficient
Solution Approach 1:
The patent applies parameter changes by introducing a correction read voltage with a different voltage level than the standard read voltage. When read errors are detected using the standard read voltage, the system switches to the correction read voltage to re-read the data. This changes the electrical parameter (voltage level) to accommodate memory cells with insufficient charge accumulation, thereby resolving the contradiction between fast reading and accurate reading.
2Duration of action of moving object
If power is suddenly cut off during programming operation, then the programming process is interrupted, but data stored in the page becomes uncorrectable
Solution Approach 1:
The patent implements preliminary action by performing an initial status check of memory cells before allowing normal read operations. This preliminary detection identifies memory cells that may have insufficient charge accumulation or were improperly programmed due to power interruption. By detecting these unstable cells in advance, the system can apply correction voltages or mark them as invalid, preventing subsequent read errors and ensuring data integrity.
3Reliability
If correction read voltage is applied to detect unstable memory cells, then read errors are reduced, but additional read operations increase time consumption
Solution Approach 1:
The patent applies self-service by implementing a self-detection and self-correction mechanism within the memory system. The memory controller automatically performs initial status checks, detects unstable memory cells, and applies correction read voltages without requiring external intervention. This automated process minimizes the overhead time by integrating the correction operations into the existing read workflow, allowing the system to serve itself in identifying and correcting potential read errors.
Data Source
AI summary
A circuit is operated to detect unstable memory cells from among a plurality of memory cells in at least one page. A determination is made from an initial status of data stored in a memory cell whether no read error occurs when the data is read at a standard read voltage level, whether a read error occurs and the read error is correctable, and whether a read error occurs and the read error is uncorrectable. Responsive to determining that a read error occurs that is correctable, a further determination is made as to whether the memory cell is correctable by reading the data stored in the memory cell at a correction read voltage level, which has a different voltage level from the standard read voltage level, and by determining whether a read error occurring in the data read at the correction read voltage level is correctable or uncorrectable.