Nonvolatile Memory Curing Operation for Threshold Voltage Recovery
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Solution Overview
Problem
Nonvolatile semiconductor memory devices face challenges in maintaining data integrity and performance over time due to shifts in threshold voltages of memory cells after operations, leading to increased error bits and degraded performance.
Innovation Solution
A method for operating nonvolatile memory devices that involves performing a curing operation after a memory operation, where a turn-on voltage is applied to word-lines and a ground selection line, and electrons are moved back to the surface of the channel layer to recover threshold voltages, thereby reducing error bits and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If memory operations are performed continuously without interruption, then productivity is maintained, but threshold voltage shifts accumulate leading to increased error bits and degraded reliability
Solution Approach 1:
The curing operation is performed in advance or between memory operations to prevent threshold voltage shifts from accumulating to problematic levels. By proactively resetting the threshold voltages of cell transistors through the curing process (applying turn-on voltages to word-lines and ground selection line to move electrons back to the channel layer surface), the system maintains data integrity without waiting for errors to occur, thus resolving the contradiction between continuous operation and reliability maintenance
2Reliability
If a curing operation is performed after every memory operation, then threshold voltage recovery is maximized, but operation time increases due to additional processing intervals
Solution Approach 1:
Instead of performing curing operations after every single memory operation, the system applies curing selectively or periodically when threshold voltage shifts begin to affect performance. The curing operation is triggered based on operational patterns or error thresholds, applying the corrective action only when necessary rather than continuously, thus maintaining reliability while minimizing time loss
Solution Approach 2:
The curing operation is implemented as a periodic maintenance task rather than a continuous process. The system monitors operational patterns and performs curing at scheduled intervals or when specific conditions are met (such as after a certain number of program/erase cycles), ensuring threshold voltage stability while avoiding unnecessary operation delays
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The curing operation effectively recovers threshold voltages of memory cells, reducing error bits and enhancing the reliability and performance of nonvolatile memory devices by ensuring accurate data retrieval and storage.
Implementation Method 1
a turn-on voltage is applied to each of a plurality of word-lines and a ground selection line... and electrons are moved back to the surface of the channel layer to recover threshold voltages
Data Source
AI summary
A method of operating a nonvolatile memory device includes performing a first memory operation on a first memory block of a plurality of memory blocks and a curing operation on a portion of the first memory block when a status signal indicates a ready state of the nonvolatile memory device during an interval equal to or greater than a reference interval after the first memory operation is completed. The nonvolatile memory device includes the plurality of memory blocks, each memory block including a plurality of vertical strings extending in a vertical direction with respect to a substrate.