3D NAND Array Divided String Architecture Reduces Program-Disturb
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Solution Overview
Problem
Conventional 3D NAND array structures suffer from 'program-disturb' issues, which worsen with increased density and are particularly severe in Multi-Level Cell configurations, affecting the reliability of memory storage.
Innovation Solution
The introduction of a divided string architecture within the 3D NAND array, utilizing internal select gates to segment the cell string, allowing selective isolation of memory cell segments during programming, thereby reducing or eliminating program-disturb effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the 3D NAND array is increased by stacking more word line layers in one string, then the memory capacity is improved, but the program-disturb problem is increased
Solution Approach 1:
The cell string is divided into multiple segments by inserting internal select gates between groups of memory cells. Each segment can be independently selected and programmed. During programming of a specific segment, the internal select gates isolate that segment from others, preventing program-disturb from affecting unselected segments while allowing higher overall density through efficient use of the cell string structure.
2Productivity
If more word line layers are stacked in one string to increase density, then the memory array capacity is improved, but the program-disturb problem becomes more severe
Solution Approach 1:
The cell string is divided into multiple segments by inserting internal select gates between groups of memory cells. Each segment can be independently selected and programmed. During programming of a specific segment, the internal select gates isolate that segment from others, preventing program-disturb from affecting unselected segments while allowing higher overall density through efficient use of the cell string structure.
3Ease of manufacture
If conventional 3D NAND architecture is used with stacked word lines, then manufacturing complexity is reduced, but program-disturb affects reliability
Solution Approach 1:
The cell string is divided into multiple segments by inserting internal select gates between groups of memory cells. Each segment can be independently selected and programmed. During programming of a specific segment, the internal select gates isolate that segment from others, preventing program-disturb from affecting unselected segments while allowing higher overall density through efficient use of the cell string structure.
Solution Approach 2:
Internal select gates are inserted within the cell string to act as intermediary elements that control and isolate segments. These internal select gates serve as mediators between the programming signal applied to selected cells and the remaining cells in the string, preventing harmful program-disturb from propagating to unselected segments while maintaining the overall stacked architecture.
Data Source
AI summary
A 3D NAND array with divided string architecture. In one aspect, an apparatus includes a plurality of charge storing devices connected to form a cell string. The apparatus also includes one or more internal select gates connected between selected charge storing devices in the cell string. The one or more internal select gates divide the cell string into two or more segments of charge storing devices. Selectively enabling and disabling the one or more internal select gates during programming operates to isolate one or more selected segments to reduce program-disturb to remaining segments. In another embodiment, a method is provided for programming a memory cell of a cell string having internal select gates that isolate the memory cell to reduce the effects of program-disturb. In another embodiment, multiple memory cells of a cell string having internal select gates are programmed with reduced program-disturb.