Multi-Wall Carbon Nanotube FET Gate Structure

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Solution Overview

Problem

Carbon nanotube-based field effect transistors are susceptible to surface traps due to their extremely small diameter, leading to noise and degradation of high-speed switching and high-frequency characteristics.

Innovation Solution

A field effect transistor design where the outer wall of a multi-wall carbon nanotube is removed in the gate formation region to expose the inner wall, allowing the outer wall to act as a passivation film and gate electrode, effectively shielding the inner wall channel from surface traps.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a carbon nanotube is used as the channel region in a field effect transistor, then high-speed switching capability and long ballistic conduction length are achieved, but surface traps at the outermost wall cause noise and degradation of electrical conduction

Engineering Contradiction:

Improvehigh-speed switching capabilityVSAvoidsurface traps affecting electrical conduction

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

An intermediary layer comprising the outer wall of the multi-wall carbon nanotube is introduced between the gate electrode and the inner wall channel. This outer wall acts as a protective mediator that shields the inner wall from surface traps while allowing the gate to control the channel, thus resolving the contradiction between maintaining high-speed switching and eliminating surface trap effects

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The structure employs a nested configuration where the inner wall carbon nanotube (channel) is surrounded by the outer wall carbon nanotube (passivation layer). This nested arrangement allows the inner channel to benefit from the protective shielding of the outer wall, eliminating surface trap effects while preserving the high-speed switching characteristics

Inventive Principle:

Principle #7Nested doll (Nesting)

2Object-affected harmful factors

If a passivation film is formed on the carbon nanotube surface to reduce surface traps, then electrical conduction is improved, but traps in the passivation film or at the interface cannot be completely eliminated

Engineering Contradiction:

Improvesurface trapsVSAvoidresidual traps in passivation film

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The outer wall of the multi-wall carbon nanotube serves its dual function: it acts as both the structural channel and the passivation layer. This self-service approach eliminates the need for separate passivation films that would introduce additional interface traps, as the carbon nanotube itself provides the protective function without introducing new trap sources

Inventive Principle:

Principle #25Self-service

3Productivity

If the diameter of the carbon nanotube is reduced to achieve higher performance, then ballistic conduction length increases, but the innermost wall becomes more susceptible to surface traps

Engineering Contradiction:

Improveballistic conduction lengthVSAvoidsurface traps at outermost wall

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The nested structure allows the inner wall to maintain a small diameter for long ballistic conduction while the outer wall provides protective shielding. This resolves the contradiction by allowing the channel to be small for high performance while being protected from surface effects by the surrounding outer wall

Inventive Principle:

Principle #7Nested doll (Nesting)

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 design enhances the high-speed switching and high-frequency performance by reducing the impact of surface traps, maintaining high current density and allowing operation on low-cost substrates without substrate constraints.

Implementation Method 1

the outer wall to act as a passivation film and gate electrode, effectively shielding the inner wall channel from surface traps

Methodology Applied

Scientific EffectPassivation:

Data Source

PatentUS7755115B2Field effect transistor using carbon nanotube of two or more walls having the outer walls at the gate and source/drain regions removed

Publication Date: 2010.07.13 FUJITSU LTD

AI summary

A field effect transistor according to the present invention includes a carbon nanotube of two or more walls having an inner wall and an outer wall, source and drain electrodes formed on both sides of the carbon nanotube, and a gate electrode formed in a gate formation region of the carbon nanotube, wherein the outer wall of the carbon nanotube is removed in the gate formation region to expose the inner wall, an insulation film is formed on the exposed inner wall, the gate electrode is formed on the exposed inner wall via the insulation film or via a Schottky junction, the source and drain electrodes are formed in contact with the outer wall and inner wall, and the carbon nanotube between the source and drain electrodes and the insulation film is covered by the outer wall.