Graphene Gate Electrode for Non-Volatile Memory

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Solution Overview

Problem

Conventional non-volatile memory devices face issues with reduced operating speed and data retention characteristics due to defects in the Al2O3 film and TaN electrode interface, leading to early erase saturation and limited memory window improvement, especially when using TaN electrodes with mid-gap work function, which are not compatible with CMOS technology.

Innovation Solution

The use of graphene as a gate electrode with a high work function, combined with a metal electrode and appropriate blocking oxide, to reduce tunneling current and enhance data retention, allowing for improved memory characteristics and device reliability, while being compatible with CMOS technology.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If TaN electrode with mid-gap work function is used, then device compatibility with CMOS technology is achieved, but erase saturation occurs early and memory window improvement is limited

Engineering Contradiction:

ImproveCMOS compatibilityVSAvoiddata retention characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the work function parameter of the gate electrode material from mid-gap (TaN) to high work function (graphene with work function > 4.5 eV). This parameter change prevents erase saturation and improves memory window while maintaining CMOS compatibility through appropriate material selection and fabrication processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite gate electrode structure combining graphene with metal electrodes (such as Pt, Ir, or Ru) and blocking oxide layers. This composite structure achieves both high work function for improved memory characteristics and compatibility with existing CMOS fabrication technologies.

Inventive Principle:

Principle #40Composite materials

2Device complexity

If Al2O3 film and TaN electrode interface is used, then device structure is simplified, but defects occur at the interface causing deterioration in operating speed and data retention

Engineering Contradiction:

Improvedevice structureVSAvoidoperating speed and data retention

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent introduces an intermediate blocking oxide layer (such as SiO2 or HfO2) between the Al2O3 film and the gate electrode. This intermediary layer prevents direct contact between the gate electrode and tunnel oxide, reducing interface defects and improving data retention characteristics while maintaining the simplified device structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies different material properties at different locations: using high-quality blocking oxide layers with specific dielectric properties at the gate electrode interface, while maintaining the overall simplified Al2O3-based device structure. This local optimization of material quality prevents interface defects without increasing overall device complexity.

Inventive Principle:

Principle #3Local quality

3Productivity

If cell area is reduced for improved integration, then extent of integration is improved, but operating speed and data retention characteristics deteriorate

Engineering Contradiction:

Improveextent of integrationVSAvoidoperating speed and data retention characteristics

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the electrical parameters of the gate electrode (work function, carrier concentration) to compensate for the reduced cell area. By optimizing the graphene gate electrode's electrical characteristics, the patent maintains operating speed and data retention characteristics even as the physical dimensions are reduced for higher integration.

Inventive Principle:

Principle #35Parameter changes

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

Graphene gate electrodes significantly improve operating speed, memory window, and data retention by reducing defects and leakage current, preventing erase saturation, and maintaining high flat band voltage for extended periods, thus enhancing the overall performance of non-volatile memory devices and MOSFETs.

Implementation Method 1

charges are tunneled into the charge trap layer 12 by F-N tunneling (Fowler-Nordheim tunneling) and become trapped therein

Methodology Applied

Scientific EffectFowler-Nordheim tunneling:

Implementation Method 2

graphene which is a novel material that has a high work function and does not cause the deterioration of a lower insulating film

Methodology Applied

Scientific EffectWork function:

Data Source

PatentUS8638614B2Non-volatile memory device and MOSFET using graphene gate electrode

Publication Date: 2014.01.28 KOREA ADVANCED INST OF SCI & TECH

AI summary

Disclosed herein is a method of remarkably improving the memory characteristics of a non-volatile memory device and the device reliability of the MOSFET using graphene which is a novel material that has a high work function and does not cause the deterioration of a lower insulating film.