3D NAND Initialization via Dummy String Selection Line
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Solution Overview
Problem
The challenge in downscaling NAND flash memory devices lies in achieving sharp threshold distributions for string selection transistors in 3D non-volatile memory devices without causing interlayer disturbances, and the use of dummy string selection transistors complicates this process, especially when trying to integrate more memory layers.
Innovation Solution
A method is introduced that initializes 3D non-volatile memory devices by programming string selection transistors using a dummy string selection line, where incremental step pulse programming techniques are applied to achieve sharp threshold values without disturbing other memory cells, and the dummy string selection transistor is programmed to function as a string selection transistor, allowing for increased integration density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dummy string selection transistors are incorporated into memory strings for initialization, then string selection transistors can be programmed to have sharp threshold distributions, but device complexity increases and integration density is reduced
Solution Approach 1:
The patent extracts the dummy string selection line from the traditional initialization structure and repositions it to intersect with channel lines at a specific location. This extraction allows the dummy line to be used for programming string selection transistors without requiring additional dummy transistors within the memory strings, thereby reducing device complexity while maintaining threshold distribution sharpness.
Solution Approach 2:
The dummy string selection line is designed to serve multiple functions: it intersects with channel lines to enable programming of string selection transistors, and its intersection point can be controlled to program transistors at different locations. This multi-functionality eliminates the need for separate dummy transistors, reducing overall device complexity while achieving sharp threshold distributions.
2Quantity of substance
If more memory layers are integrated to increase density, then integration density improves, but interlayer disturbances increase making initialization more difficult
Solution Approach 1:
The dummy string selection line acts as an intermediary structure that enables controlled programming of string selection transistors across multiple memory layers. By positioning the intersection of the dummy line with channel lines at a specific location, the patent can program string selection transistors without causing disturbances to other memory layers, thus allowing high integration density while minimizing interlayer interference.
Solution Approach 2:
The patent applies local quality by controlling the intersection position of the dummy string selection line with channel lines. This localized control allows programming to be performed at specific locations without affecting other areas, enabling the initialization of string selection transistors in high-density multi-layer structures without causing interlayer disturbances.
3Reliability
If programming bias is applied to selected wordline for reliable program operation, then program reliability improves, but disturbance to other memory cells sharing the same wordline increases
Solution Approach 1:
The patent segments the programming process by using the dummy string selection line to selectively program string selection transistors independent of the main wordline programming operation. The intersection of the dummy line with channel lines creates a segmented approach where string selection transistors can be initialized without applying programming bias to the main wordline, thus avoiding disturbance to other memory cells while maintaining program reliability.
Data Source
AI summary
A 3D non-volatile memory device may include a dummy string selection line, string selection lines, wordlines, bitlines, a ground selection line, and memory layers. Each of the memory layers comprising channel lines respectively coupled to the bitlines via first ends and coupled to a common source line of the memory layer via second ends. The dummy string selection line, the string selection lines, the wordlines, and the ground selection line intersect with the channel lines, and each of the channel lines defines a memory string. Initializing the 3D non-volatile memory device may include programming string selection transistors coupled with the string selection lines to have one or more threshold values, and programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the string selection transistors function as string selection transistors.