Adaptive NAND Voltage Offsets for Program-Verify Reliability
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Solution Overview
Problem
The reliability of NAND devices decreases with an increase in program-erase cycles due to imbalanced threshold voltage distributions and edge margins, leading to reliability and data retention issues.
Innovation Solution
Implementing a memory sub-system that applies read level adjustments in addition to a step decrease in program voltage based on the number of program-erase cycles, using voltage offset values stored in metadata or a look-up table, determined by threshold voltage data collected during manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If program voltage is decreased to reduce programming time and energy consumption, then productivity and energy efficiency improve, but reliability deteriorates due to imbalanced threshold voltage distributions and reduced edge margins
Solution Approach 1:
The patent applies dynamics by making the program voltage adaptive rather than fixed. The controller dynamically adjusts program voltage based on real-time monitoring of threshold voltage distributions and edge margins during programming operations. This allows the system to optimize voltage levels for each specific programming condition, achieving both speed and reliability.
Solution Approach 2:
The patent changes the program voltage parameter dynamically during operation. By monitoring threshold voltage distributions and edge margins, the system adjusts voltage parameters in real-time to maintain optimal programming conditions, preventing reliability issues while maintaining high productivity.
2Reliability
If read voltage levels are adjusted to improve read reliability, then read accuracy improves, but device complexity increases due to additional voltage levels and control mechanisms
Solution Approach 1:
The patent implements feedback by monitoring threshold voltage distributions and edge margins during read operations. Based on this feedback, the controller dynamically adjusts read voltage levels to optimize read accuracy. This feedback mechanism allows the system to adapt to varying conditions without requiring complex predetermined voltage tables.
Solution Approach 2:
The read voltage levels are made dynamic rather than static. The system continuously monitors programming conditions and adjusts read voltages accordingly, allowing the same hardware to handle varying reliability requirements without additional complex voltage control circuits.
3Reliability
If program-verify operations are performed to ensure data integrity, then reliability improves, but productivity decreases due to additional operation cycles
Solution Approach 1:
The patent applies partial action by performing program-verify operations selectively rather than universally. The controller determines when verify operations are necessary based on monitored threshold voltage distributions and edge margins, skipping verify steps when conditions indicate sufficient programming accuracy, thus maintaining reliability while improving throughput.
Solution Approach 2:
Feedback from threshold voltage monitoring during programming operations allows the system to determine when program-verify steps are necessary. This feedback mechanism enables the system to reduce unnecessary verify operations, improving productivity while maintaining data integrity through targeted verification.
Data Source
AI summary
A an example method of adjusting voltage offsets utilized by memory access operations based on values of a chosen media endurance metric includes the operations of: identifying a value of a media endurance metric associated with one or more memory blocks of a memory device; performing a programming operation on the one or more memory blocks; identifying a program-verify voltage level associated with the one or more memory blocks; determining a program-verify voltage offset associated with the program-verify voltage level and the value of the media endurance metric; and performing, using the program-verify voltage level and the program-verify voltage offset, a program-verify operation on the one or more memory blocks.