Charge-Trapping Layer Refractive Index Gradient for 3D Memory
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Solution Overview
Problem
In three-dimensional charge-trapping memory devices, lateral diffusion of electrons between memory cells due to a uniform refractive index in the charge-trapping layer leads to charge loss and impaired data retention, affecting the ability to read programmed states accurately.
Innovation Solution
Increasing the refractive index of the charge-trapping layer portions adjacent to word line layers by removing sacrificial material, doping, and depositing metal in the word line layers, thereby creating a refractive index gradient that reduces lateral charge migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform refractive index is used in the charge-trapping layer, then the manufacturing process is simple, but lateral diffusion of electrons occurs causing charge loss and impaired data retention
Solution Approach 1:
The charge-trapping layer is designed with spatially varying refractive index properties. Specifically, the layer adjacent to the first control gate has a first refractive index, while the layer adjacent to the second control gate has a second refractive index that is higher than the first. This local differentiation suppresses lateral electron diffusion at critical interfaces while maintaining manufacturing feasibility through selective doping or material composition variation in different regions of the charge-trapping layer.
2Reliability
If the refractive index of the charge-trapping layer is increased adjacent to word line layers, then lateral charge migration is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The refractive index of the charge-trapping layer is modified by changing its physical or chemical parameters. This is achieved through selective doping processes, variation in material composition (e.g., different ratios of oxides, nitrides, or other charge-trapping materials), or control of layer thickness in different regions. These parameter changes increase the refractive index adjacent to word line layers to suppress lateral charge migration, while the modifications are integrated into existing fabrication workflows to manage complexity.
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
Enhances data retention by suppressing lateral charge diffusion, maintaining the integrity of programmed states and improving the readability of memory cells.
Implementation Method 1
A charge-trapping layer can be used in memory devices to store a charge which represents a data state
Implementation Method 2
lateral diffusion of electrons between memory cells due to a uniform refractive index in the charge-trapping layer leads to charge loss
Data Source
AI summary
Techniques are provided for fabricating a three-dimensional, charge-trapping memory device with improved long term data retention. A corresponding three-dimensional, charge-trapping memory device is also provided which includes a stack of alternating word line layers and dielectric layers. A charge-trapping layer is deposited in a memory hole. The refractive index of portions of the charge-trapping layer which are adjacent to the word line layers is increased relative to the refractive index of portions of the charge-trapping layer which are adjacent to the dielectric layers. This can be achieved by doping the portions of the charge-trapping layer which are adjacent to the word line layers. In one approach, the charge-trapping layer is SiON and is doped with Si or N. In another approach, the charge-trapping layer is HfO and is doped with Hf. In another approach, the charge-trapping layer is HfSiON and is doped with Hf, Si or N.