NAND Flash Memory String Cleaning to Control Hole Accumulation
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Solution Overview
Problem
NAND Flash memory devices experience issues with hole accumulation during program operation suspensions, leading to false increases in threshold voltage and increased fail bit counts due to negative channel coupling potentials when DSG and SSG transistors are turned off, affecting the performance and reliability of memory devices.
Innovation Solution
The solution involves turning on the DSG and/or SSG transistors to ground the channel and release accumulated holes, thereby preventing negative potential and reducing false threshold voltage increases by applying pass voltages to select and unselect memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the program operation is suspended by turning off the DSG and SSG transistors, then the program operation can be interrupted and resumed later, but hole accumulation occurs in the channel causing false threshold voltage increases and increased fail bit counts
Solution Approach 1:
Before suspending the program operation by turning off the DSG and SSG transistors, the invention applies a pass voltage to turn on the memory cells in the memory string. This preliminary action ensures that holes are released from the channel before the transistors are turned off, preventing hole accumulation and the associated false threshold voltage increases that would otherwise occur during suspension
Solution Approach 2:
The invention converts the potentially harmful effect of hole accumulation into a beneficial outcome by using the pass voltage to deliberately turn on the memory cells and release holes before suspension. This transforms what would be a harmful accumulation effect into a controlled release mechanism, ensuring accurate threshold voltages are maintained even during program operation suspension
2Productivity
If the DSG and SSG transistors are turned off during program suspension, then the program operation can be suspended, but negative channel coupling potentials are generated causing hole accumulation
Solution Approach 1:
Before turning off the DSG and SSG transistors to suspend the program operation, the invention applies a pass voltage to turn on the memory cells, which creates a counter-action that prevents the formation of negative channel coupling potentials. This preliminary anti-action eliminates the harmful effect before it can occur during the suspension state
3Loss of energy
If the program operation is suspended with DSG and SSG transistors off, then power can be saved during suspension, but fail bit counts increase due to hole accumulation
Solution Approach 1:
Before suspending the program operation, the invention applies a pass voltage to turn on the memory cells and release holes from the channel. This preliminary action prevents hole accumulation and the associated increase in fail bit counts, ensuring that the suspension can occur with transistors turned off for power savings without compromising program operation reliability
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 reduces fail bit counts and improves memory device performance by preventing hole accumulation and maintaining accurate threshold voltages during program operation suspensions.
Implementation Method 1
turn on the DSG and/or SSG transistors to ground the channel and release accumulated holes
Implementation Method 2
applying pass voltages to select and unselect memory cells
Data Source
AI summary
A memory device is disclosed. The memory device may include a memory string and a peripheral circuit. The memory string may include a drain select gate (DSG) transistor, a plurality of memory cells, and a source select gate (SSG) transistor. The peripheral circuit may be coupled to the memory string and configured to, during a program operation on a select memory cell of the plurality of memory cells: after detecting an interrupt signal, perform a clean process that includes turning on at least one of the DSG transistor or the SSG transistor.