Dynamic Pass Voltage for Flash Memory Read-Disturb Reduction
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Solution Overview
Problem
Flash memory devices face issues with 'read disturb' mechanism, where multiple sensing operations can perturb the threshold voltage of memory cells, leading to sensing errors and reduced performance characteristics.
Innovation Solution
Applying a dynamic pass voltage to unselected access lines during sensing operations, which can decrease in magnitude, such as negatively ramping from 5.8V to 5.6V, helps reduce the perturbation of unselected memory cells and minimizes sensing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a constant pass voltage is applied to unselected access lines during sensing operations, then memory cells can be sensed, but threshold voltage perturbations occur leading to sensing errors
Solution Approach 1:
The patent applies a dynamic pass voltage that varies over time during the sensing operation, specifically decreasing from an initial value to a final value. This dynamic adjustment reduces threshold voltage perturbations in unselected memory cells while maintaining proper sensing operation, thereby resolving the contradiction between sensing accuracy and threshold voltage stability.
Solution Approach 2:
The patent changes the pass voltage parameter from a constant value to a time-varying value that decreases during the sensing operation. This parameter change allows the system to maintain sensing functionality while reducing the harmful effects of read disturb, thus improving both sensing accuracy and threshold voltage stability.
2Productivity
If multiple sensing operations are performed on memory cells, then data can be read repeatedly, but read disturb effects perturb threshold voltages causing sensing errors
Solution Approach 1:
By implementing a dynamic pass voltage that decreases during each sensing operation, the patent reduces the cumulative read disturb effect that occurs with multiple sensing operations. This allows repeated data reading while maintaining sensing accuracy and preventing threshold voltage perturbations from causing errors.
Solution Approach 2:
The patent applies a decreasing pass voltage as a preliminary protective measure against read disturb effects before they can cause significant threshold voltage perturbations. This preventive approach allows multiple sensing operations to be performed without accumulating harmful effects that would lead to sensing errors.
3Ease of operation
If a high pass voltage is applied to ensure proper sensing operation, then sensing can be performed, but significant threshold voltage perturbations occur in unselected memory cells
Solution Approach 1:
The patent uses a dynamic pass voltage that starts at a higher value to ensure proper sensing operation and then decreases to reduce threshold voltage perturbations. This time-varying approach maintains sensing reliability while minimizing harmful effects on unselected memory cells.
Solution Approach 2:
The patent implements a pass voltage that changes periodically during the sensing operation, specifically decreasing over time. This periodic adjustment allows the system to maintain proper sensing operation initially while progressively reducing the harmful threshold voltage perturbations that would otherwise occur with a constant high pass voltage.
Data Source
AI summary
The present disclosure includes methods, devices, modules, and systems for operating memory cells. One method embodiment includes applying sensing voltages to selected access lines for sensing selected memory cells. The method also includes applying a dynamic pass voltage to unselected access lines while the sensing voltages are applied.