Dielectric Cap Above Floating Gate Reduces Leakage Current
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Solution Overview
Problem
Non-volatile memory devices face challenges in reducing leakage current due to strong electric fields in the inter-poly dielectric region, particularly at the corners of the floating gate and control gate, which increases as feature sizes decrease, and existing high dielectric constant materials suffer from oxygen diffusion and electrical defects.
Innovation Solution
A dielectric cap is formed above the floating gate, reducing the electric field strength at the top of the floating gate and inhibiting leakage current by implanting oxygen and heating the floating gate to create a dielectric cap from the implanted oxygen and silicon, while maintaining sufficient capacitive coupling between the floating gate and control gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inter-poly dielectric thickness is reduced to increase capacitive coupling, then the coupling ratio is improved, but the leakage current increases due to stronger electric fields
Solution Approach 1:
The inter-poly dielectric layer is segmented into two distinct parts: a thin region that maintains strong capacitive coupling between control gate and floating gate, and a thick region that provides electrical isolation to prevent leakage current. This segmentation allows each region to optimize its function independently.
Solution Approach 2:
Different thicknesses of the inter-poly dielectric are applied to different spatial locations: a first thickness in the coupling region for high capacitance and a second thickness in the isolation region for low leakage. This local quality variation resolves the contradiction by making the dielectric thickness position-dependent rather than uniform.
2Reliability
If high dielectric constant materials are used to increase capacitive coupling, then the coupling ratio is improved, but oxygen diffusion and electrical defects increase
Solution Approach 1:
Instead of changing the dielectric material's intrinsic properties (dielectric constant), the invention changes the geometric parameter (thickness) of the dielectric layer to achieve the desired capacitive coupling. This avoids the harmful effects associated with high-K materials while still improving coupling ratio.
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
The dielectric cap effectively reduces leakage current without significantly impacting capacitive coupling, thereby addressing the challenge of increasing electric field strengths in smaller memory cell structures and minimizing defects associated with high dielectric constant materials.
Implementation Method 1
forming a dielectric cap above the floating gate... by implanting oxygen and heating the floating gate to create a dielectric cap from the implanted oxygen and silicon
Implementation Method 2
reducing the electric field strength at the top of the floating gate and inhibiting leakage current
Implementation Method 3
capacitive coupling between the control gate and floating gate... The threshold voltage of the memory cell is controlled by the amount of charge that is retained on the floating gate
Data Source
AI summary
A memory system is disclosed that includes a set of non-volatile storage elements. A given memory cell has a dielectric cap above the floating gate. In one embodiment, the dielectric cap resides between the floating gate and a conformal IPD layer. The dielectric cap reduces the leakage current between the floating gate and a control gate. The dielectric cap achieves this reduction by reducing the strength of the electric field at the top of the floating gate, which is where the electric field would be strongest without the dielectric cap for a floating gate having a narrow stem.