Introduction and Overview Results for Potential, Capacitance, and Electric Field

Analytical Results, Advantages, and Prospects

Motivation and Objective The purpose of this project is to study novel carbon

nanotube-embedded chemical sensors that can detectenvironmentally toxic microscopic agents.

Carbon nanotubes (CNTs) are rolled sheets of carbonwith atoms arranged in a hexagonal pattern. CNTsmeasure about a millionth of a millimeter in diameter andshow great promise for applications in nanotechnology.Use of CNTs in nanoelectronics can lead to nanoscalesensitive devices.

To investigate the electrical properties of such sensors,CNT-embedded metal-oxide-semiconductor structuresare analyzed using numerical modeling.

Traditional Chemicapacitive SensorClean: Contaminated:

When a particle attaches to the metal plate, it is detectedby measuring the capacitance change across the oxide.

Nanotube-embedded Chemicapacitive Sensor Nanotubes replace the metal plate in the proposed design. CNT-embedded sensors are advantageous because they

are more sensitive to toxic agents.

Clean: Contaminated:

The Poisson Equation The Poisson equation is solved to obtain the electrostatic

potential, capacitance, and electric field of sensor devices:

2D Solution: Nonuniform Mesh with Nonuniformwithout Particle

2D Solution: Nonuniform Mesh with Nanotube andParticle

Electric Field at Nanotube The particle disrupts the electric field, which causes the

capacitance to change.Without Particle: With Particle:Capacitance = 0.127 pF/cm Capacitance = 0.136 pF/cm

q where is the electrostatic potential; is the dielectric constant; is the net charge density; q is the electronic charge

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NanotubeNanotube

Analytical Solutions

Conclusions: The numerical solutions show unequivocally that the

proposed design for a nanotube sensor is advantageousover the traditional design in terms of sensitivity uponthe insertion of a particle.

According to our calculated results, the highest sensitivityoccurs in sensors which have a high gate width (x-direction) and a low oxide thickness (y-direction).

A higher sensitivity allows detection at a lowerconcentration of toxic agents.

Due to the smaller size of the carbon nanotube sensor,these proposed sensors respond more quickly— adifference that may be lifesaving.

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Gate Width (x-direction) (nm)

Percent Difference in Capacitance vs. Gate Width% Difference in nanotube sensor with particle on the left

% Difference in nanotube sensor with particle on the right

% Difference in traditional sensor with particle on the left

% Difference in traditional sensor with particle on the right

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Oxide Thickness (y-direction) (nm)

Percent Difference in Capacitance vs. Oxide Thickness

% Difference in traditional sensor with particle on the left

% Difference in nanotube sensor with particle on the left

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Electrostatic Potential InterfacePoint representing particle

4 points representing nanotube

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