Adaptive Pre-Programming for NAND Flash Multi-Plane Erase
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Solution Overview
Problem
NAND flash memory exhibits a shallow erase phenomenon during partial programming, leading to a widened threshold voltage distribution, which complicates differentiating between stored bit information and increases the fail bit count, especially in multi-plane pre-program operations where secure erase operations may fail to meet uncorrectable error correction criteria.
Innovation Solution
Adaptive and dynamic control of the pre-program pulse duration is implemented based on the number of planes selected for the pre-program operation, with a user-selectable pre-program time increment parameter that can increase non-linearly with the number of planes, ensuring a uniform threshold voltage distribution and enhancing the success rate of secure erase operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed pre-program pulse duration is used for multi-plane operations, then the operation complexity is reduced, but the threshold voltage distribution becomes non-uniform and secure erase operations fail
Solution Approach 1:
The patent implements dynamic adjustment of the pre-program pulse duration based on the number of planes being operated. The pulse width is extended non-linearly as the number of planes increases, transforming the fixed-duration approach into a variable-duration approach that adapts to multi-plane operation requirements, thereby maintaining uniform threshold voltage distribution across all planes while preserving operational simplicity through automated control.
2Manufacturing precision
If the pre-program pulse duration is extended for multi-plane operations, then the threshold voltage distribution uniformity is improved, but the operation time increases
Solution Approach 1:
The patent applies periodic pre-program pulses with dynamically adjusted durations to multiple planes in a structured sequence. By distributing the extended pulse duration across the multi-plane operation timeline rather than applying one excessively long pulse, the system achieves uniform threshold voltage distribution while managing the overall operation time more efficiently through time-distributed periodic action.
3Manufacturing precision
If a non-linear time increment parameter is used, then the threshold voltage uniformity across planes is maintained, but the control mechanism becomes more complex
Solution Approach 1:
The patent incorporates feedback mechanisms where the controller monitors the number of planes being operated and automatically selects the appropriate pre-program pulse width from a set of pre-determined values. This feedback-based adaptive control ensures the correct pulse duration is applied for each multi-plane configuration, maintaining threshold voltage uniformity while simplifying the control interface through automated parameter selection rather than requiring manual calibration.
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
This approach consistently maintains a uniform threshold voltage distribution across multiple planes, improving system performance by ensuring successful secure erase operations and preventing shallow erase scenarios, even as the number of planes increases.
Implementation Method 1
Application of VPGM to the control gate generates a high electric field—with a strong negative charge on the transistor's source and drain and a strong positive charge on the control gate—that causes the electrons to migrate from the channel to a charge trapping layer (CTL) of the transistor
Implementation Method 2
a flash memory cell may be erased by applying an erase voltage VERA to a source or drain of the transistor to generate an electric field—with a strong positive charge on the cell's source and drain and a strong negative charge on the control gate—which induces a tunneling effect whereby electrons migrate from the CTL to the channel
Data Source
AI summary
Adaptive and dynamic control of the duration of a pre-program pulse based on a number of planes selected for the pre-program operation is disclosed. A value for a pre-program time increment parameter may be selected based on the number of planes for which the pre-program operation will be performed or determined based on a predefined association with the number of planes. A pre-program voltage pulse may then be applied for a duration that is equal to a default duration for a single-plane pre-program operation incremented by the time increment parameter value. This approach solves the technical problem of Vt downshift for multi-plane pre-program operations, and thus, ensures that the success rate of secure erase operations does not diminish as the number of planes increases. This, in turn, allows for pre-program operations to be consistently performed on a multi-plane basis, which produces the technical effect of improved system performance.