Individually Controllable Shield Plates for NAND Flash Memory
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Solution Overview
Problem
As device dimensions are scaled down in semiconductor memory, floating gate-to-floating gate coupling becomes problematic, leading to widened threshold voltage distribution and reduced coupling ratio from the control gate to the floating gate, affecting the programming efficiency of non-volatile storage devices like NAND flash memory.
Innovation Solution
The introduction of individually controllable shield plates between non-volatile storage elements, which are electrically conductive and independently controllable, to reduce electromagnetic coupling and optimize programming, reading, and erasing operations by providing a conductive path and allowing reduced program voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If device dimensions are scaled down, then storage density is improved, but floating gate-to-floating gate coupling increases causing widened threshold voltage distribution
Solution Approach 1:
The patent introduces shield plates as intermediary conductive structures positioned between adjacent floating gates. These shield plates act as mediators to control and reduce the electromagnetic coupling between neighboring floating gates, thereby preventing the widening of threshold voltage distribution that occurs when device dimensions are scaled down while maintaining high storage density.
Solution Approach 2:
The patent modifies the electrical parameters of the system by introducing independently controllable conductive shield plates that can be biased at different voltages. By changing the voltage potential of the shield plates, the coupling strength between adjacent floating gates can be dynamically adjusted, allowing optimization of threshold voltage distribution while maintaining scaled-down device dimensions for high storage density.
2Quantity of substance
If device dimensions are scaled down, then storage density is improved, but coupling ratio from control gate to floating gate is reduced
Solution Approach 1:
The patent compensates for the reduced control gate to floating gate coupling ratio caused by scaling by introducing shield plates that can be biased at elevated voltages. These shield plates serve as intermediate coupling elements that enhance the effective coupling between the control gate and floating gate, thereby maintaining reliable programming operation despite the reduced direct coupling ratio in scaled-down devices.
Solution Approach 2:
The shield plates function as intermediary conductive structures that facilitate enhanced coupling between the control gate and floating gate. By positioning these conductive plates strategically and biasing them appropriately, the patent creates an intermediate coupling path that compensates for the weakened direct coupling resulting from reduced device dimensions, thus maintaining programming reliability while achieving high storage density.
3Reliability
If shield plates are added between storage elements, then program disturb is reduced, but device complexity increases
Solution Approach 1:
The patent merges the shield plate structure with existing device components by integrating the conductive shield plates into the fabrication process alongside the formation of interlayer dielectric layers and word line contacts. This merging approach allows the shield plates to be formed using modified versions of existing process steps, thereby reducing the overall device complexity increase that would result from completely separate additional processing steps.
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 configuration reduces program disturb and improves the operating window for non-volatile storage devices by minimizing floating gate-to-floating gate coupling, enhancing the accuracy and efficiency of data storage and retrieval processes.
Implementation Method 1
floating gate-to-floating gate coupling becomes problematic... individually controllable shield plates between non-volatile storage elements... to reduce electromagnetic coupling
Data Source
AI summary
A non-volatile storage having individually controllable shield plates between storage elements. The shield plates are formed by depositing a conductive material such as doped polysilicon between storage elements and their associated word lines, and providing contacts for the shield plates. The shield plates reduce electromagnetic coupling between floating gates of the storage elements, and can be used to optimize programming, read and erase operations. In one approach, the shield plates provide a field induced conductivity between storage elements in a NAND string during a sense operation so that source/drain implants are not needed in the substrate. In some control schemes, alternating high and low voltages are applied to the shield plates. In other control schemes, a common voltage is applied to the shield plates.