Memory Controller IVS Charge Loss Evaluation for Data Integrity
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Solution Overview
Problem
Flash memory devices with charge trap flash (CTF) cells experience initial verify shift (IVS), leading to data loss due to threshold voltage variations over time, which are influenced by factors like erase count and temperature, requiring separate management methods to maintain data integrity.
Innovation Solution
A memory controller is configured to program evaluation data into CTF memory cells, periodically perform charge loss evaluation by detecting threshold voltage variations, and adjust read voltages based on the stored results to mitigate data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If charge trap flash (CTF) memory cells are used for storage, then data can be retained without power supply, but threshold voltage changes over time cause data loss due to initial verify shift (IVS)
Solution Approach 1:
The patent performs preliminary charge loss evaluation by programming evaluation data into memory cells and measuring threshold voltage variations after predetermined time periods. This advance evaluation creates a charge loss evaluation table that predicts future threshold voltage drift, allowing the system to proactively adjust read voltages before actual data corruption occurs, thus maintaining data integrity while preserving long-term retention capabilities
Solution Approach 2:
The patent implements a feedback mechanism where measured threshold voltage variations from charge loss evaluation are used to dynamically adjust read voltages. The charge loss evaluation table stores historical data that continuously refines the adjustment strategy, creating a closed-loop system that compensates for IVS effects and maintains reliable data reading over extended retention periods
2Measurement precision
If read voltages are adjusted to compensate for threshold voltage variation, then data reading accuracy improves, but additional evaluation and adjustment operations increase system complexity
Solution Approach 1:
The patent uses evaluation data as a representative copy to assess charge loss characteristics without requiring evaluation of all actual data storage operations. By programming test patterns and measuring threshold voltage shifts in evaluation memory cells, the system derives charge loss evaluation tables that accurately reflect overall memory device behavior, simplifying the complexity while maintaining measurement precision
Solution Approach 2:
The charge loss evaluation table serves multiple functions: it characterizes threshold voltage drift over time, predicts future IVS effects, and provides adjustment parameters for read voltage compensation. This multi-functional approach consolidates what could be separate complex operations into a single unified evaluation mechanism, improving read accuracy without proportionally increasing system complexity
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 solution ensures improved reliability of nonvolatile memory systems by periodically evaluating and adjusting read voltages, thereby reducing errors caused by IVS and maintaining data integrity over time.
Implementation Method 1
detecting threshold voltage variation of the desired memory cells over a period based on the time elapsed from the time point when the evaluation data is programmed
Data Source
AI summary
An operating method of a memory controller configured to control a nonvolatile memory device including a plurality of memory cells is provided. The operating method includes: programming evaluation data into desired memory cells among the plurality of memory cells; performing initial verify shift (IVS) charge loss evaluation on the desired memory cells after a time elapses from a time point when the evaluation data is programmed, the IVScharge loss evaluation including an operation of detecting threshold voltage variation of the desired memory cells over a period based on the time elapsed from the time point when the evaluation data is programmed; and storing a result of the IVScharge loss evaluation; and adjusting levels of a plurality of read voltages used in the nonvolatile memory device based on the stored result of the charge loss evaluation.