3D Flash Memory GSL Removal for Channel Potential Control
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Solution Overview
Problem
Conventional 3D flash memory devices face a trade-off between securing channel potential in non-selected strings and maintaining memory integration, as they require ground selection lines (GSLs) that hinder integration improvements.
Innovation Solution
A 3D flash memory structure with a GSL removal design, utilizing a dummy word line at the lowermost end and back gates to manage channel potential, along with a double or single substrate structure to enhance integration and reduce leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground selection lines (GSLs) are used to secure channel potential in non-selected strings, then channel potential is secured and leakage current is controlled, but memory integration is hindered due to increased structural complexity
Solution Approach 1:
The patent removes the ground selection line (GSL) from the memory structure entirely. Instead of using a separate GSL to control channel potential, the invention repurposes the lowermost word line (WL0) to serve this function, thereby eliminating the harmful element (GSL) that was causing structural complexity while maintaining the necessary control function through an existing component
Solution Approach 2:
The lowermost word line (WL0) is assigned multiple functions: it serves as both a word line for selecting memory cells and as a ground selection line for controlling channel potential in non-selected strings. This multi-functionality eliminates the need for a separate GSL, reducing structural complexity while maintaining reliability
2Adaptability or versatility
If multiple common source lines are used to connect cell strings, then channel potential can be controlled in different string groups, but the number of control lines increases leading to higher complexity
Solution Approach 1:
The patent combines the control functions of multiple common source lines into a single common source line. By removing the GSL that was used to control different string groups, all cell strings share a common source line, reducing the number of control lines while maintaining adaptability through selective string selection using string selection lines (SSL) and bit lines
Data Source
AI summary
Disclosed are a three-dimensional flash memory, to which a GSL-removed structure is applied, and an operating method thereof.According to an embodiment, the three-dimensional flash memory comprises: a plurality of word lines which are formed extending in a horizontal direction on a substrate and are sequentially stacked; and a plurality of strings passing through the plurality of word lines and formed extending in one direction on the substrate, wherein each of the plurality of strings comprises a channel layer formed extending in the one direction and a charge storage layer formed extending in the one direction to surround the channel layer, and the channel layer and the charge storage layer constitute a plurality of memory cells corresponding to the plurality of word lines, and the channel layer comprises a back gate formed extending in the one direction while at least a part thereof is surrounded by the channel layer and an insulation film formed extending in the one direction between the back gate and the channel layer, and each of the plurality of strings includes the back gate. Accordingly, the three-dimensional flash memory has a GSL-removed structure.