Flash Memory Verify Control for Threshold Voltage Variation
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Solution Overview
Problem
Existing semiconductor storage devices face challenges in maintaining reliability due to variations in threshold voltage distributions of memory cell transistors, leading to inefficiencies in write operations and potential data retention issues.
Innovation Solution
A semiconductor storage device with a controller that monitors and classifies memory cell transistors based on threshold voltage distribution widths, adjusting write operations to optimize reliability by modifying verify operations based on the classification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of verify operations is increased to ensure data retention, then reliability is improved, but write operation time and productivity are worsened
Solution Approach 1:
The patent applies local quality by classifying memory cell transistors into different groups based on their threshold voltage distribution widths. Different verify operations are then applied to different groups: transistors with wider threshold voltage distributions receive additional verify operations to ensure data retention, while transistors with narrower distributions use standard verify operations. This localized differentiation ensures reliability where needed without unnecessarily increasing write operation time across the entire memory array.
2Productivity
If standard write operations are used for all memory cell transistors, then productivity is maintained, but reliability deteriorates due to threshold voltage variations
Solution Approach 1:
The patent implements dynamics by making the write operation process adaptive rather than static. The controller dynamically adjusts the verify operation sequence based on the classified groups of memory cell transistors. For transistors in groups with wider threshold voltage distributions, the system dynamically adds additional verify operations. This dynamic adjustment allows the system to maintain high productivity for most transistors while ensuring reliability for those with greater variability, resolving the contradiction between standardized efficiency and targeted reliability.
Data Source
AI summary
A semiconductor storage device that is capable of improving reliability includes: a non-volatile memory provided with a block including a plurality of memory cell transistors connected to a word line; and a controller configured to monitor a threshold voltage distribution width of the plurality of memory cell transistors after performing at least one of an erasing operation on the block and a preliminary write operation on the plurality of memory cell transistors and to classify the plurality of memory cell transistors according to the threshold voltage distribution width of the plurality of memory cell transistors.