Nonvolatile Memory Data Retention via Segmented Reference Currents
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Solution Overview
Problem
Multi-level threshold voltage algorithms in nonvolatile memory cells are vulnerable to data errors due to charge leakage and margin loss, as the narrowing of threshold voltage states increases sensitivity to read disturbs and charge loss.
Innovation Solution
The implementation of a nonvolatile memory integrated circuit with reference current circuitry and sense amplifier circuitry that generates multiple reference currents with varying sensing windows to differentiate between low and high threshold voltage states, allowing for more precise sensing and detection of charge loss, thereby reducing data errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level threshold voltage algorithm is used to increase storage density, then storage density is improved, but data retention deteriorates due to charge leakage and margin loss
Solution Approach 1:
The patent divides the sensing operation into multiple segments by using different reference currents for different threshold voltage ranges. The first reference current senses a first threshold voltage range, the second reference current senses a second threshold voltage range, and the third reference current senses a third threshold voltage range. This segmentation allows precise detection of charge loss in multi-level cells without requiring large margins between threshold voltage states, thereby maintaining high storage density while improving data retention through early charge loss detection
Solution Approach 2:
The patent changes the sensing parameters by using multiple reference currents with different threshold voltage levels instead of a single reference current. This parameter change enables the system to adaptively sense different threshold voltage ranges, allowing narrow threshold voltage margins to be maintained while still detecting charge loss accurately, thus resolving the contradiction between high storage density and data retention
2Quantity of substance
If threshold voltage states are bunched closer together to increase storage density, then storage density is improved, but measurement precision deteriorates due to reduced margin between states
Solution Approach 1:
The patent implements dynamic sensing by selecting different reference currents based on the detected threshold voltage range. The system dynamically adapts the sensing parameters to match the specific threshold voltage state being measured, allowing precise differentiation of closely-bunched threshold voltage states. This dynamic approach maintains measurement precision even when threshold voltage states are closely spaced for high storage density
Solution Approach 2:
The patent changes the sensing parameters by using multiple reference currents with different threshold voltage levels. Each reference current is optimized for sensing a specific threshold voltage range, enabling precise measurement of closely-bunched threshold voltage states. This parameter change allows the system to maintain high measurement precision while supporting high storage density through closely-spaced threshold voltage states
3Quantity of substance
If charge loss margin is reduced to improve storage density, then storage density is improved, but reliability deteriorates due to increased vulnerability to charge leakage
Solution Approach 1:
The patent performs preliminary detection of charge loss by using multiple reference currents to sense threshold voltage changes before they result in data errors. The system continuously monitors threshold voltage using appropriate reference currents and detects charge loss early, allowing corrective action to be taken before data integrity is compromised. This preliminary detection enables reduced charge loss margins while maintaining reliability
Solution Approach 2:
The patent implements feedback by using the sensing results from multiple reference currents to monitor threshold voltage changes and detect charge loss. The system uses the comparison results between different reference current sensing operations to determine when charge loss has occurred, providing continuous feedback on memory cell status. This feedback mechanism enables early detection of charge leakage, allowing the system to maintain reduced charge loss margins while ensuring data retention reliability
Data Source
AI summary
Disclosed are apparatuses, methods, and manufacturing methods relating to improving data retention in nonvolatile memory. In many embodiments, monitor reference currents in addition to a normal reference current are used to determine whether to refresh the data memory.