Multiple String Select Lines for Non-Volatile Memory
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Solution Overview
Problem
NAND flash memory devices face challenges in maintaining high read performance and data retention while preserving faster program and erase speeds, due to issues like program disturbances and reduced memory windows caused by pass voltage adjustments.
Innovation Solution
The implementation of a non-volatile memory device with multiple string select lines, which applies different voltages to string select lines to counterbalance program voltage, thereby enhancing data retention and read performance by reducing unwanted electron transfer to unselected memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the pass voltage is increased to maintain program operation duration, then the program operation can be completed, but program disturbance to unselected cells increases
Solution Approach 1:
The string select line is divided into multiple segments (first SSL and second SSL) that can be independently controlled. This segmentation allows different voltage levels to be applied to different portions of the select line, enabling precise control over which cells are affected during program operations and reducing unwanted program disturbance to unselected cells.
Solution Approach 2:
Different voltage levels are applied to different segments of the string select line based on their specific function. The first SSL receives a first voltage level while the second SSL receives a second voltage level, creating local quality differences that optimize both program operation completion and reduction of program disturbance to unselected cells.
2Object-affected harmful factors
If the pass voltage is decreased to reduce program disturbance, then program disturbance is reduced, but the memory window is reduced
Solution Approach 1:
The string select line is divided into multiple segments (first SSL and second SSL) that can be independently controlled. This segmentation allows different voltage levels to be applied to different portions of the select line, enabling precise control over which cells are affected during program operations and reducing unwanted program disturbance to unselected cells.
Solution Approach 2:
Different voltage levels are applied to different segments of the string select line based on their specific function. The first SSL receives a first voltage level while the second SSL receives a second voltage level, creating local quality differences that optimize both program operation completion and reduction of program disturbance to unselected cells.
3Reliability
If multiple string select lines with different voltages are applied, then program disturbance is reduced and memory window is enlarged, but device complexity increases
Solution Approach 1:
The string select line is divided into multiple segments (first SSL and second SSL) that can be independently controlled. This segmentation allows different voltage levels to be applied to different portions of the select line, enabling precise control over which cells are affected during program operations and reducing unwanted program disturbance to unselected cells.
Solution Approach 2:
The multiple string select lines serve multiple functions: they select specific memory cells for programming, they prevent program disturbance to unselected cells, and they maintain the memory window. By making the SSL structure multi-functional, the patent reduces the need for additional separate components to achieve these same goals.
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 effectively reduces program disturbances, enlarges the memory window, and maintains accurate read performance by controlling the potential barrier of the substrate, ensuring improved data retention and operational efficiency.
Implementation Method 1
NAND flash memory devices program memory cells using Fowler-Nordheim tunneling, which can pull electrons from a substrate into a floating gate and fill its traps due to high voltage (or potential) drop between a word line and the substrate.
Data Source
AI summary
Methods and apparatuses are contemplated herein for enhancing the program performance of nonvolatile memory devices. In an example embodiment, a nonvolatile memory device comprises a 3D array of nonvolatile memory cells including a plurality of layers, each layer comprising NAND strings of nonvolatile memory cells, the NAND strings coupled to a bit line, and a plurality SSLs and word lines, the SSLs and the word lines arranged orthogonally to the NAND strings, the word lines establishing the nonvolatile memory cells at cross-points between surfaces of the plurality of NAND strings and the word lines, each of the NAND strings further comprising a plurality of SSL transistors coupling the SSLs to the NAND strings, wherein at least a first SSL being configured to receive a first voltage and a second SSL configured to receive at second voltage, and wherein the second SSL being nearer to the word lines.