NDR Molecular-circuits - Nanotechnology - Lecture Slides, Slides of Nanotechnology

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Molecular circuits based on

NDR composites Alfredo D. BobadillaTexas A&M University

Outline Current silicon semiconductor technologyNDR devicesNDR behavior in molecules and nanodevicesLogic circuits based on NDR devicesThe Nanocell conceptFurther research

Introduction NDR & molecularcircuits Suggestions

OFF state Cross section of an NMOS without channel formed

ON state Cross section of an NMOS with channel formed http://en.wikipedia.org/wiki/MOSFET

N-type MOSFET (metal–oxide–semiconductor field-effect transistor )

MOSFET electrical characteristic http://en.wikipedia.org/wiki/MOSFET

Gate

Drain SourceI^ DS VGS

+ VDS

+^

The current level is controlled by the gate voltage. When switch is turned ON, the gate to source voltage is differentthan zero and a current flow through the transistor, activating the LED (light-emitting diode).V: Drain to source voltageDS^ V: Gate to source voltageGS^ I^ : Drain currentDS^

AnantAgarwaland Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007.MIT OpenCourseWare(http://ocw.mit.edu/), Massachusetts Institute of Technology.

CMOS Power Consumption

AnantAgarwaland Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007.MIT OpenCourseWare(http://ocw.mit.edu/), Massachusetts Institute of Technology.

CMOS Power Consumption

Scaling limit of digital circuits due to thermal noise AnantAgarwaland Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007.MIT OpenCourseWare(http://ocw.mit.edu/), Massachusetts Institute of Technology.

… noise hampers our ability to distinguishBetween small differences in value —e.g. between 3.1V and 3.2V.

Thermal noise is the voltage fluctuations caused by therandom Brownian motion of electrons in a resistive medium.The spectral density of the thermal noise across a resistorwith resistance R is given by

(^2) V = 4kTRnt

Outline Current silicon semiconductor technology NDR devices NDR behavior in molecules and nanodevicesLogic circuits based on NDR devicesThe Nanocell conceptFurther research

Introduction NDR & molecularcircuits Suggestions

Mathews, R. H. et al. A new RTD-FET logic family. Proc. IEEE 87, 596-605 (1999)

The resonant tunneling diode

The high current density, low capacitance, and NDRof RTD’s make them very fast nonlinear circuitelements.The difference between the I–V curves is the currentavailable to charge/discharge the capacitances of theRTD’s as well as circuit capacitance. The greater thecurrent difference, the faster the voltage change.Other advantage on using only NDR devices is alower static power dissipation owing to lowbistable bias voltage and low static current in bothequilibrium states.

Outline Current silicon semiconductor technologyNDR devices NDR behavior in molecules and nanodevices Logic circuits based on NDR devicesThe Nanocell conceptFurther research

Introduction NDR & molecularcircuits^ Suggestions

Khoo at al, Negative differential resistance in carbon atomic wire-carbon nanotube junctions.

Nano Lett. 8 2900

(2008)

NDR behavior in molecules and nanodevices

A MWCNT is exposed to e-beam radiation,shrinking the nanotube until a carbonnanowire is obtained.Electrical current through the carbon nanotubeis monitored during the process, and NDRbehavior is observed at the end of the process.Ab initio molecular simulations confirm acarbon nanowire shows NDR behavior.

Jangjian et al ,Room temperature negative differential resistance in DNA-based molecular. Appl. Phys. Lett. 94 43105 (2009)

NDR behavior in molecules and nanodevices

When two gold electrodes were connected by Ni

2+^ -chelated DNA,

which was converted from

λ-DNA, not only was the conductivity of DNA improved, but a NDR device was formed.The Ni ions undergo redox reactions when the applied voltageapproaches the redox potential in the cyclic voltage sweep process.The positive NDR peak corresponds to the oxidation peak of theNi ions and the negative NDR peak corresponds to their reduction.

Outline Current silicon semiconductor technologyNDR devicesNDR behavior in molecules and nanodevices Logic circuits based on NDR devices The Nanocell conceptFurther research

Introduction NDR & molecularcircuits^ Suggestions

NDR Emulation

Two^ NDR

emulator

circuits

were^ built

implementing microcontrollers.ADC^ inputs

were^ used

to^ measure

the

voltage drop across the device.A photoresistor coupled to a LED was usedto control the resistance of the deviceThis devices were programmed to follow aNDR^ behavior

by^ a

look-up

table,

implemented in memory.

EMULATOR

TERMINALS

Photoresistor

‐LED couple

AJ Gimenez et al, Analysis of Nano and Molecular Arrays of Negative Differential Resistance Devices for Sensing and Electronics, IEEE Sensors J (2009).