Memory Threshold Offset Calibration for Die and Workload Variation
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Solution Overview
Problem
Existing memory sub-systems fail to adaptively adjust threshold voltage offset bins due to die-to-die variation, data retention behavior differences, workload variation, and cross-temperature differences, leading to sub-optimal performance and increased error rates.
Innovation Solution
Implement a memory sub-system controller that updates threshold voltage offset bins based on calibration measurements triggered by program erase cycle counts, workload changes, or temperature changes, using techniques like parallel auto-read calibration and vectorized read level calibration to dynamically adjust offset bins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed threshold voltage offset bins are used, then device complexity is reduced, but reliability deteriorates due to die-to-die variation and data retention behavior differences
Solution Approach 1:
The patent implements dynamic threshold voltage offset bins that automatically adjust based on calibration measurements. The calibration system continuously monitors data retention behavior and die-to-die variations, then updates the offset bins to maintain optimal read margins. This dynamic adaptation resolves the contradiction by allowing the system to maintain high reliability through continuous adjustment while keeping the underlying hardware architecture relatively simple.
Solution Approach 2:
The patent employs feedback mechanisms where calibration measurements are performed periodically or triggered by specific events (e.g., program-erase cycle thresholds). The results of these measurements feed back into adjusting the threshold voltage offset bins. This closed-loop feedback system enables the memory device to self-correct for variations and maintain reliability without requiring complex real-time control circuitry.
2Reliability
If adaptive calibration is implemented, then reliability is improved, but productivity deteriorates due to increased calibration time and processing overhead
Solution Approach 1:
The patent implements periodic calibration where threshold voltage offset bins are updated at predetermined intervals or based on program-erase cycle counters rather than continuously. This periodic approach maintains reliability by regularly correcting for drift and variations while minimizing the impact on productivity by limiting calibration operations to necessary intervals.
Solution Approach 2:
The patent applies calibration selectively rather than uniformly across all memory blocks simultaneously. By performing calibration on representative samples or subsets of memory devices and extrapolating results, or by calibrating only when threshold criteria are met, the system achieves adequate reliability improvement without the full productivity cost of comprehensive continuous calibration.
3Measurement precision
If continuous calibration is performed, then measurement precision is improved, but loss of time increases due to frequent calibration operations
Solution Approach 1:
The patent uses periodic calibration triggered by program-erase cycle thresholds or time-based intervals rather than continuous calibration. This approach maintains measurement precision by regularly updating offset bins to account for drift and variations, while minimizing time loss by performing calibration only when necessary based on predetermined criteria.
Solution Approach 2:
The patent performs preliminary calibration measurements during manufacturing or initial device setup to establish baseline offset bins. These preliminary calibrations provide initial measurement precision, and subsequent calibrations are performed only when drift or variations exceed predetermined thresholds, thereby reducing overall calibration time while maintaining adequate precision throughout the device lifecycle.
Data Source
AI summary
A system includes a memory device and a processing device, operatively coupled with the memory device, to perform operations including: determining whether a workload change associated with a segment of the memory device satisfies a first threshold criterion for triggering an offset bin update; responsive to determining that the workload change satisfies the first threshold criterion, performing a calibration measurement of a center of a voltage valley for each state of each cell in the segment of the memory device; repeating the calibration measurement until a result of the calibration measurement is less than or equal to a threshold value; and updating a threshold voltage offset bin associated with the segment of the memory device based on the result of the calibration measurement.