NAND Flash Shielding Lines Reduce Capacitance Coupling
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Solution Overview
Problem
In NAND flash memory devices, the capacitance-coupling effect between wordlines and selection lines during programming operations leads to unintended programming of program-inhibited cells, causing degradation in the distribution profile of threshold voltages, especially when multiple data bits are stored.
Innovation Solution
The introduction of shielding lines between wordlines and selection lines, which apply a shielding voltage to reduce capacitance-coupling effects, thereby preventing voltage leaks and maintaining the cut-off state of selection transistors during programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capacitance-coupling effect between wordlines and selection lines is utilized for self-boosting, then programming operation can be simplified, but unintended programming of program-inhibited cells occurs and threshold voltage distribution degrades
Solution Approach 1:
A shielding line is introduced as an intermediary element between the wordline and the selection line. This shielding line acts as a mediator that blocks the harmful capacitance-coupling effect from affecting the selection line, while allowing the useful self-boosting effect to continue in the memory cell channel. The shielding line is connected to ground through a capacitor, enabling it to filter out high-frequency noise from the wordline that would otherwise couple into the selection line and cause unintended programming.
Solution Approach 2:
The solution applies local quality by creating a localized shielding structure only in the critical region where the wordline and selection line interact. The shielding line is positioned specifically between these two lines and connected to ground through a capacitor, providing targeted protection against capacitance-coupling effects only where needed, rather than requiring global shielding of the entire memory array. This localized approach maintains the overall simplicity of the programming operation while fixing the specific reliability issue.
2Reliability
If shielding lines are added between wordlines and selection lines, then unintended programming is prevented and reliability improves, but device structure becomes more complex
Solution Approach 1:
The shielding structure is segmented into discrete units, with each shielding line serving a specific memory cell or small group of cells. Rather than implementing a continuous shielding structure across the entire memory array, the solution divides the shielding function into multiple independent segments, each with its own shielding line and capacitor connection. This segmentation reduces the overall complexity by allowing modular implementation and reducing the total amount of shielding material and connections required.
Solution Approach 2:
The shielding line serves as an intermediary element that simplifies the overall device structure by providing a dedicated path for noise filtering. Instead of requiring complex filtering circuits or multiple interconnected shielding structures, the intermediary shielding line with its simple capacitor-to-ground connection provides effective noise blocking in a minimalistic manner, reducing the overall structural complexity while maintaining high reliability.
3Productivity
If pass voltage is applied to wordlines during programming, then programming speed is improved, but voltage leaks through capacitance-coupling and causes self-boosting in program-inhibited cells
Solution Approach 1:
The shielding line acts as an intermediary barrier between the wordline and the selection line, blocking the harmful voltage leaks that occur during programming operations. When pass voltage is applied to the wordline for high-speed programming, the shielding line with its ground capacitor connection filters out the capacitive coupling noise, preventing it from reaching the selection line and causing unintended self-boosting in program-inhibited cells, thus maintaining both high speed and accuracy.
Solution Approach 2:
The solution converts the harmful capacitance-coupling effect into a beneficial filtered signal. The shielding line captures the capacitive noise from the wordline and redirects it to ground through the capacitor, transforming what would be harmful voltage leaks into a controlled filtering action. This approach allows the full pass voltage to be applied to the wordline for high-speed programming while the shielding structure benevolently absorbs and dissipates the harmful coupling effects.
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 solution effectively prevents the unintended programming of program-inhibited cells by minimizing voltage leaks, maintaining accurate threshold voltage distribution profiles and ensuring reliable multi-level memory cell operations.
Implementation Method 1
the capacitance-coupling effect between the wordline and the selection line may be generated. The capacitance-coupling effect may boost the channel voltage
Data Source
AI summary
A method of programming a flash memory includes applying a shielding voltage to at least one shielding line, which is interposed between a plurality of wordlines and a selection line and operable to reduce capacitance-coupling between the wordline and the selection line during the programming operation, and applying a program voltage to memory cells through one of the wordlines.