Threshold-Programmed Word Lines for NAND Sub-Block Access
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Solution Overview
Problem
As NAND memory blocks increase in size and density, accessing less than all of the block, such as a sub-block or subset of the blocks, is challenging due to processing difficulties with independently biasable select gates, particularly at the source side of three-dimensional NAND structures.
Innovation Solution
Implementing word line based selectors where multiple word lines are programmed with different sets of threshold voltages to allow individual access of sub-blocks, reducing read disturbs and power consumption while avoiding processing difficulties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If independently biasable select gates are used to access sub-blocks, then sub-block access capability is improved, but processing difficulty increases
Solution Approach 1:
The patent combines the select gate functionality with existing word lines by programming multiple threshold voltage states into the same word line structure. This merging eliminates the need for separate independently biasable select gates, thereby maintaining sub-block access capability while avoiding the processing difficulties associated with additional gate structures.
Solution Approach 2:
The word lines are designed to serve multiple functions: they act as both data access lines and sub-block selection lines. By programming different threshold voltage states into the word lines, they can selectively enable or disable access to different sub-blocks, providing universal functionality that replaces dedicated select gates.
2Adaptability or versatility
If traditional select gate structures are used, then sub-block separation is achieved, but read disturbances increase
Solution Approach 1:
The patent replaces the physical select gate structure with an electrical field-based selection mechanism. By applying specific voltage levels to word lines with different threshold voltages, sub-block selection is achieved through electrical control rather than physical gate structures, thereby reducing read disturbances to non-selected cells.
3Quantity of substance
If higher density NAND memory blocks are used, then storage capacity is improved, but access control to sub-blocks becomes more difficult
Solution Approach 1:
The patent utilizes parameter changes in the word line threshold voltages to achieve sub-block access control in high-density NAND memory. By programming word lines with distinct threshold voltage values, the system can selectively activate or deactivate access to different sub-blocks, maintaining ease of access control despite increased storage capacity and density.
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
Enables efficient access to sub-blocks in NAND memory, reducing read disturbances and power consumption, and increasing operating speeds without the processing challenges of traditional select gate structures.
Implementation Method 1
multiple word lines are programmed with different sets of threshold voltages to allow individual access of sub-blocks
Data Source
AI summary
As block sizes in NAND memory continue to increase in size and density, in can be useful to access less than all of the block, such as sub-block or subset of the blocks NAND strings, in order to reduce read disturbs, reduce power consumption, and increase operating speeds. Although this sort of separation of sub-block can be achieved by independently biasable select gates, the sort of select gate structure can face processing difficulties, particularly at the source side of three dimensional NAND structures. To avoid these difficulties while still providing individually selectable sub-blocks, the following introduces word line based selectors, where multiple word lines of a blocks are programmed with different sets of threshold voltages, allowing them to be biased for individual access of sub-blocks.