Local Backgate RF CNT FET Devices

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Solution Overview

Problem

Current carbon-nanotube (CNT) field effect transistors face challenges due to high parasitic capacitance from global backgates, limiting their high-frequency performance, and the inefficiency of removing metallic tubes, which are undesirable for device operation.

Innovation Solution

A radio-frequency (RF) CNT field effect transistor (FET) device with a local backgate and a high-κ gate dielectric layer is developed, where the local backgate is used to deplete semi-conducting CNTs and burn out metallic CNTs, reducing parasitic capacitance and enabling RF performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a global backgate is used to remove metallic tubes, then metallic tube removal is achieved, but parasitic capacitance increases significantly

Engineering Contradiction:

Improvemetallic tube removalVSAvoidparasitic capacitance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent divides the backgate into local segments positioned beneath individual CNT channels rather than using a single global backgate. This segmentation reduces the total gate capacitance while maintaining effective metallic tube removal in each local region through controlled depletion of semi-conducting tubes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements local backgates with specific geometric configurations optimized for each CNT channel region. Each local backgate is positioned and dimensioned to provide appropriate depletion control for its associated channel, reducing overall parasitic capacitance while maintaining effective metallic tube removal where needed.

Inventive Principle:

Principle #3Local quality

2Reliability

If a global backgate is used, then metallic tube removal is effective, but high-frequency performance is limited

Engineering Contradiction:

Improvemetallic tube removalVSAvoidfrequency performance

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

By segmenting the backgate into local regions, the total gate capacitance is reduced, which directly improves the frequency response and speed of the device while maintaining effective metallic tube removal in each segmented region.

Inventive Principle:

Principle #1Segmentation

3Productivity

If standard CVD process is used, then CNT growth is achieved, but one-third of tubes grow as metallic tubes which are undesirable

Engineering Contradiction:

ImproveCNT growth efficiencyVSAvoidtube quality

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent uses the local backgate depletion mechanism to selectively remove metallic tubes from the CNT channel after growth. By applying appropriate voltages to the local backgate, semi-conducting tubes are depleted while metallic tubes conduct high current that oxidizes and removes them, extracting the unwanted metallic component from the CNT population.

Inventive Principle:

Principle #2Taking out (Extraction)

4Reliability

If high current is passed through metallic tubes for removal, then metallic tubes are oxidized and removed, but the process requires precise control to avoid damaging semi-conducting tubes

Engineering Contradiction:

Improvemetallic tube removalVSAvoidprocess control

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs preliminary depletion of semi-conducting tubes by applying voltage to the local backgate before passing high current through the metallic tubes. This preliminary action ensures that semi-conducting tubes are already depleted and protected, allowing subsequent high current passage to selectively remove only metallic tubes without damaging the semi-conducting ones.

Inventive Principle:

Principle #10Preliminary action

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 local backgate structure significantly reduces capacitance, enhancing the on/off ratio and allowing for higher frequency performance while effectively removing metallic tubes, thus improving the overall performance of CNT FET devices.

Implementation Method 1

a local backgate positioned below the semi-conducting CNTs, separated by a gate dielectric, in which the local backgate is capable of RF performance

Methodology Applied

Scientific EffectElectrical field effect: Electric Field

Implementation Method 2

In an oxygen environment, this high current will oxidize the metallic tubes, leaving behind most of the depleted semi-conducting tubes

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

depositing high-κ gate dielectric layer on top of the local backgate structure

Methodology Applied

Scientific EffectDielectric property: Dielectric

Data Source

PatentUS10224413B1Radio-frequency carbon-nanotube field effect transistor devices with local backgates and methods for making same

Publication Date: 2019.03.05 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

A radio-frequency (RF) carbon-nanotube (CNT) field effect transistor (FET) device. The device includes a source contact, a drain contact, semi-conducting CNTs positioned between the source and drain contacts, high-.kappa. gate dielectric, and a local backgate positioned below the semi-conducting CNTs, in which the local backgate is capable of RF performance and is capable of being used in a backgate burnout process used to enhance the semiconducting to metallic tube ratio of the device.