NAND Memory Virtual Channel via Fixed Charge Layer
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Solution Overview
Problem
Nonvolatile memory systems face compatibility issues due to different standards, and scaling to small dimensions leads to 'short channel effects' which increase source/drain resistance and are not effectively mitigated by existing methods.
Innovation Solution
A nonvolatile memory array is formed with a plurality of floating gate memory cells connected in series, using source/drain regions with an inversion layer created by a fixed charge layer, and control gates extending between floating gates, eliminating the need for dopant implants and reducing short channel effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are scaled to small dimensions, then memory density is improved, but short channel effects increase and source/drain resistance worsens
Solution Approach 1:
A fixed charge layer is introduced as an intermediary element between the substrate and the floating gate. This fixed charge layer creates a virtual channel through electrostatic induction, serving as a mediator that enables current flow without requiring direct metallurgical junctions. The fixed charge layer compensates for the increased source/drain resistance by providing an additional conduction path through induced carriers, thereby resolving the contradiction between high memory density and acceptable source/drain resistance in scaled devices.
Solution Approach 2:
The invention changes the fundamental parameter of channel formation from metallurgical doping to electrostatic induction. By using a fixed charge layer to induce a virtual channel, the method alters the physical state and mechanism of charge carrier generation, enabling effective conduction in scaled devices without the harmful short channel effects associated with traditional dopant implants.
2Reliability
If dopant implants are used to form source/drain regions, then electrical connection is improved, but short channel effects increase
Solution Approach 1:
The fixed charge layer acts as an intermediary that eliminates the need for dopant implants. Instead of using metallurgical junctions created by doping, the fixed charge layer induces a virtual channel that provides electrical connection without the harmful short channel effects. This intermediary mechanism decouples the need for electrical connection from the harmful doping process.
Solution Approach 2:
The invention substitutes the mechanical/chemical process of dopant implantation with an electrostatic field effect. Rather than physically implanting atoms to create conductive regions, the fixed charge layer uses electrostatic induction to create a virtual channel, replacing the mechanical doping process with a field-based mechanism that avoids short channel 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 configuration reduces short channel effects and source/drain resistance, enabling more efficient and compatible nonvolatile memory systems by forming a 'virtual channel' without metallurgical junctions, improving performance and compatibility across different standards.
Implementation Method 1
a source/drain region including an inversion layer created by a fixed charge within a fixed charge layer portion that extends over the source/drain region
Data Source
AI summary
A string of nonvolatile memory cells are connected together by source/drain regions that include an inversion layer created by fixed charge in an overlying layer. Control gates extend between floating gates so that two control gates couple to a floating gate. A fixed charge layer may be formed by plasma nitridation.