Asymmetric Ground Selection Lines for Independent NAND Cell Strings
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Solution Overview
Problem
The manufacturing process of flash memory devices is complicated, making it difficult to form independent lines, which affects the reliability and performance and increases power consumption.
Innovation Solution
A memory device with asymmetric ground selection lines, where ground selection transistors are connected in units of rows, allowing for independent control of each cell string, and are formed in multiple layers to ensure proper connection through a word line replacement process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If independent ground selection lines are formed for each cell string, then reliability and performance are improved, but manufacturing complexity increases
Solution Approach 1:
The ground selection lines are segmented into multiple independent lines (first ground selection line, second ground selection line, third ground selection line, fourth ground selection line), each connected to specific cell strings. This segmentation allows independent control of each cell string while maintaining manufacturing feasibility through systematic arrangement.
Solution Approach 2:
The patent introduces a vertical stacking dimension with upper and lower ground selection lines at different heights above the substrate. This three-dimensional arrangement allows more ground selection lines to be formed without increasing planar manufacturing complexity, as lines can be connected through vertical vias and layered structures.
2Reliability
If various lines are controlled in units of cell string, then reliability and performance are improved, but manufacturing complexity increases
Solution Approach 1:
The control lines are segmented and assigned to specific cell string groups. The first ground selection line controls first and second cell strings, the second ground selection line controls third cell string, and additional lines control other cell strings. This segmentation enables independent cell string control while using a manageable number of lines.
Solution Approach 2:
Each ground selection line is designed to serve multiple functions: controlling ground potential for connected cell strings, enabling independent read/write operations, and supporting various memory operations (read, program, erase). This multi-functionality reduces the total number of lines needed while maintaining comprehensive control.
3Use of energy by moving object
If asymmetric ground selection lines are implemented, then power consumption is reduced, but device structure becomes more complex
Solution Approach 1:
The ground selection lines are arranged asymmetrically with respect to their connections. The first ground selection line connects to first and second cell strings, while the second ground selection line connects only to the third cell string. This asymmetric configuration allows selective activation of ground lines during operations, reducing unnecessary power consumption compared to symmetric configurations where all lines would need to be activated.
Data Source
AI summary
A memory device includes a substrate, a first cell string, second cell string, and third cell string, each connected to a first bit line and formed in a direction perpendicular to a top surface of the substrate, a first upper ground selection line connected to the first cell string, a second upper ground selection line separated from the first upper ground selection line and connected to the second and third cell strings, a first lower ground selection line connected to the first and second cell strings, and a second lower ground selection line separated from the first lower ground selection line and connected to the third cell string.