3D NAND Memory Program Disturb Reduction via Pre-Charging
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Solution Overview
Problem
Residual electrons trapped in dummy cells of unselected strings in 3D NAND memory devices cause program disturb to neighboring selected memory cells during the programming process, leading to reduced channel potential and programming errors.
Innovation Solution
Applying specific voltage sequences during the pre-charging and boosting phases to redirect and remove residual electrons from middle dummy cells to top memory cells, ensuring they do not interfere with the selected memory cells, by using distinct voltages on various word lines to control the channel potential and isolate the unselected string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a program voltage is applied to the control gate and bit line is grounded during programming, then electrons are injected into the charging storage region to program the memory cell, but residual electrons trapped in dummy cells of unselected strings cause program disturb to neighboring selected memory cells
Solution Approach 1:
The patent applies a preliminary action by performing a pre-charging phase before the main programming operation. During this pre-charging phase, a first voltage is applied to word lines above dummy word lines and a second voltage is applied to the second neighboring word line above the selected word line. This preliminary voltage application redistributes residual electrons trapped in dummy cells before the programming voltage is applied, preventing program disturb to selected memory cells while maintaining programming accuracy
2Device complexity
If different word lines are controlled via identical voltages during precharging section as disclosed in US 9,640,273B1, then the programming process is simplified, but residual electrons in unselected strings still cause program disturb to selected memory cells
Solution Approach 1:
The patent applies local quality by differentiating voltage control for different word lines during the pre-charging phase. Specifically, a first voltage is applied to word lines located vertically above dummy word lines, while a second distinct voltage is applied to the second neighboring word line located vertically above the selected word line. This localized differentiation in voltage application effectively removes residual electrons from unselected strings without causing program disturb, while maintaining manageable voltage control complexity through systematic voltage assignment
3Reliability
If residual electrons are removed from dummy cells to prevent program disturb, then programming accuracy is improved, but the programming process complexity increases due to additional voltage control steps
Solution Approach 1:
The patent applies segmentation by dividing the word lines into distinct groups that receive different voltage treatments during pre-charging. Word lines above dummy word lines receive a first voltage, while the second neighboring word line above the selected word line receives a second voltage. This segmented approach to voltage control systematically removes residual electrons from specific regions (dummy cells) without affecting selected memory cells, improving programming accuracy while keeping the process complexity manageable through organized voltage assignment
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
Effectively reduces program disturb by removing residual electrons from unselected strings, maintaining the integrity of the selected memory cell's channel potential and improving programming accuracy without increasing the complexity of the programming process.
Implementation Method 1
During a pre-charging phase, a first voltage is applied to a plurality of word lines... a second voltage is applied to a second neighboring word line... During a boosting phase, the second voltage is applied to the second neighboring word line and a plurality of first word lines, and a third voltage is applied to a first neighboring word line
Data Source
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AI summary
A method of performing a programming operation to a three dimensional (3D) NAND memory device is disclosed. The method makes residual electrons trapped in storage regions of middle dummy memory cells of the unselected string of the 3D NAND memory device to be removed during the pre-charging phase, so as to reduce program disturb to the selected string which neighbors the unselected string.