Molecular circuits based on NDR composites Alfredo D. Bobadilla Texas A&M University.

Molecular circuits based on NDR composites

Alfredo D. BobadillaTexas A&M University

Outline

Current silicon semiconductor technology

NDR devices

NDR behavior in molecules and nanodevices

Logic circuits based on NDR devices

The Nanocell concept

Further research

Introduction

NDR & molecularcircuits

Suggestions

OFF stateCross section of an NMOS without channel formed

ON stateCross section of an NMOS with channel formed

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

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

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

MOSFET electrical characteristic

Gate

Drain

Source

IDS

VGS

VDS

+

+ -

-

VDS : Drain to source voltageVGS : Gate to source voltage IDS : Drain current

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).

A B C

0 0 1

0 1 1

1 0 1

1 1 0

http://www.falstad.com/circuit/e-cmosnand.html

CMOS NAND logic gate

CMOS means complementary-symmetry metal–oxide–semiconductor (or COS-MOS). The words "complementary-symmetry" refer to the fact that the typical digital design style with CMOS usescomplementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions.

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.

Scaling limit of digital circuits due to thermal noise

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

Thermal noise is the voltage fluctuations caused by the random Brownian motion of electrons in a resistive medium.

The spectral density of the thermal noise across a resistor with resistance R is given by

V nt2 = 4kTR

Outline


NDR devices




Further research

Introduction


Suggestions

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

The resonant tunneling diode

A resonant-tunneling diode (RTD) is a heterostructure device whose essential structure is a sandwich of two very thin layer of high-band-gap material surrounding a thin layer of lower band-gap material . The outer layers act as potential energy barriers to form quasi-bound states in the central layer.

The small spacing between the two barriers leads toquantization of momentum of the electrons in the welland, thus, to quasi-bound states with discrete energy levels.

For applied voltages that result in alignment of electron states on the source side of the barriers with aquasi-bound state in the well (a condition calledresonance) the tunneling current is strongly enhanced.

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 circuit elements.

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 a lower static power dissipation owing to low bistable bias voltage and low static current in both equilibrium states.

Outline


NDR devices




Further research

Introduction


Suggestions

Pop, E. et al. Negative differential conductance and hot phonons in suspended nanotube molecular wires. Phys. Rev. Lett. 95, 155505 (2005).


A metallic single-walled carbon nanotube is suspended between two platinum electrodes in vacuum conditions.

The NDR behavior is attributed to the presence of optical phonons with ‘long’ lifetime.

The energy flow from electrons (“heated” by the electric field) to optical phonons and then acoustic phonons.

Khoo at al, Negative differential resistance in carbon atomic wire-carbon nanotube junctions. Nano Lett. 8 2900 (2008)


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 NDR behavior is observed at the end of the process.

Ab initio molecular simulations confirm a carbon nanowire shows NDR behavior.

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


When two gold electrodes were connected by Ni2+-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.

Chen et al, Large on-off ratios and negative differential resistance in a molecular electronic device. Science 286, 1550-1552 (1999).


I( V ) characteristics at 60 K of a molecular junctionAu- (2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiolate)-Au .

NDR is attributed to a two-step reduction process that modifies charge transport through the molecule.

The width of the I(V ) peak (~0.7 V) correlates well with the difference between the one electronand two-electron peak reduction potentials.

Outline


NDR devices




Further research

Introduction


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 used to control the resistance of the device

This devices were programmed to follow a NDR 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).


NDR simulation results

NDR-based logic gate

V1 V2 VC VOut Gate

0 0 0 0

AND1 0 0 0

0 1 0 0

1 1 0 1

0 0 1 0

OR1 0 1 1

0 1 1 1

1 1 1 1

40 NDR are simulated to test its response to different inputs.

This kind of arrays when used at some voltages trend to output well defined low or high voltages, being possible to create a logic gate.

V1 and V2 are the inputs of the gate.Vc is the control input to switch the gate between OR-AND.


Outline


NDR devices




Further research

Introduction


Suggestions

J. M. Seminario, Y. Ma, V. Tarigopula. The nanoCell: A Chemically Assembled Molecular Electronic Circuit, IEEE Sensors J, vol. 6 (6), pp 1614-1626 (2006)

A nanoCell is a randomly self assembled circuit formed by non-linear components attached chemically to metal clusters performing as nodes.

Once the physical topology of the self-assembly is formed in the nanocell, it remains static; there is no molecule or nanoparticle dynamic character (other than bond rotations or vibrations) to the highly crosslinked network.

The only changeable behavior is in the molecular states: conducting ON or nonconducting OFF, as set by voltage pulses from the periphery of the cell, or as defined by the search algorithms in simulations.

The nanoCell concept

Simulated self-assembled nanocell is depicted. the black rectangles at the edges are the I/O leads. The entire cell, excluding the outer portions of the contact pads, would be approximately 1um2.

Nanocell with approximately 900 nanoparticles and9000 molecular switches that has been trained as fourindependent NANDS.

J. M. Tour et al, “Nanocell logic gates for molecular computing,” IEEE Trans. Nanotechnol., vol. 1, pp. 100–109 (2002).

Programming or training a nanoCell

The objective is to take a random, fixed nanocell and turn its switches ON and OFF until it functions as a target logic device.

The physical position of each molecular switch is first fixed; i.e., the internal topology of the nanocell is static. The nanocell is then trained postfabrication by changing the states, ON or OFF, of the molecular switches.

J. M. Seminario, Y. Ma, V. Tarigopula. The nanoCell: A Chemically Assembled Molecular Electronic Circuit, IEEE Sensors J, vol. 6 (6), pp 1614-1626 (2006)

The nanoCell: A Chemically Assembled Molecular Electronic Circuit

Outline


NDR devices




Further research

Introduction


Suggestions

Tu et al, Nature Nanotechnol. (2009)

Rothemund, , Nature Nanotechnol. (2006)Guo et al, Nature Nanotechnol. (2008)

Maune et al, Nature Nanotechnol. (2009)

Further research

Exploiting DNA self-assembly properties and CNT-DNAinteractions allow creating molecular circuits, but electron transport through DNA is not well understood yet.

Ab initio molecular simulations of electron transport though a CNT-DNA hybrid nanostructures must be done, looking for possible configurations showing NDR behavior.

THANKS!

let’s begin Q&A session

G2Rebuttal: Molecular circuits based on

NDR composites

Alfredo D. Bobadilla

NDR-based molecular circuits - rebuttal

• “The Overall presentation was good. The introductory part was too long and did not give much time to go into more detail in the papers he showed.”

• I didn’t get simplifying the concept in the introductory part, that’s one reason why it took a longer time than necessary.

• “The speech was a bit too slow to contain what needed to be presented within the allotted time.”

• I suffered a lack of english fluency in the intro part which influenced on that. I should have been more careful on preparing the intro part.



• “I think the speaker tried to make a good effort in the introduction. However, the key word in the title is ‘NDR’, and the speaker took too long to get there. Moreover, checking the slides, I did not find a particular slide to illustrate this point, which is the basic point of the presentation.”

• I tried to emphasize an NDR-based device is a two terminal device which allow a much lower power consumption and also a faster response, i.e. a higher frequency of operation. I also emphasized a complete ‘logic family’ can be constructed based on NDR devices and at the end I shown the nanoCell concept in which the logic of the molecular circuit is ‘programmable’.



• “I think the speaker failed to stamp his own point-of-view in the ‘further research’ section, and limited himself to briefly name some recent works on the field rather than assess and critically propose his ideas”

• I proposed molecular circuits based on CNT and DNA. CNT own outstanding electrical properties and DNA own self-assembling properties which enable the possibility of making hybrid CNT-DNA molecular circuits. I shown a DNA molecule can show NDR behavior and I also shown a CNT can show NDR behavior. I shown illustrations of research work supporting my proposal. And I mentioned molecular simulation techniques play a key role on understanding the assembly process and electrical/thermal transport properties of a molecular circuit.


Molecular circuits based on NDR composites

Review

Edson P. Bellido Sosa

The presenter explained how a MOSFET, currently use in electronics, works and its electrical characteristics. He explained how a logic gate works and how we use this logic gates to do computation. He Also point out the problem of power consumption and noise.

He explained the basic concept of NDR and show examples of NDR in CNTs.He also explained NDR behavior on DNA. However personally I do not think this kind of behavior could be consider NDR since is consequence of a chemical reaction. For the case of the molecular junction the behavior it resembles a NDR.

He also explained the concepts of NDR circuits and the Nanocell. He showed how these circuits could work and how the assemble of this could be used to create molecular system that can do computation.

The Overall presentation was good. The introductory part was too long and did not give much time to go into more detail in the papers he showed. We missed the opportunity to ask more questions and especially considering that the authors of one of the discussed papers were present in the audience.

G3 REVIEW: MOLECULAR CIRCUITS BASED ON NDR COMPOSITES

By Mary CoanPhD Chemical Engineering4/01/10

Review A lot of information was covered in the

introduction section Explained

MOSFET On and Off State Electrical Characteristics

CMOS NAND Electrical Map

Power Consumption Equations Diagrams Good versus poor results

Mentioned Noise Explained using Diagrams, Charts, and equations

Discussed Resonant tunneling Diodes in detail

Review Used Graphs and images to convey

important device structure and electrical characteristics of NDR’s

Used several examples to explain how NDR behaves in molecules and nanodevices

Discussed simulation results along with actual results

NanoCell Concept Programming/Training Chemically assembled

Future Research was also discussed

Review

Overall the presentation went over a lot of information in a short amount In a concise orderly fashion

Used Images and Graphs to depict relevant information Captured the attention of the audience

The information provided was current and correct

G4Review of Molecular circuits based on

NDR composites

by Diego Gomez

NDR• NDR stands for Negative Differential Resistance, which is a

property of certain circuit elements where the current decreases as the voltage is increased. This occurs in certain voltage ranges and it is due to certain materials composing the circuit

Science (2009), Vol 323, 1026

NDR region in a FETCertain materials on certain substrates produce this kind of behavior. For instance, styrene on a (100) silicon surface

Nano Letters(2004), Vol 4, 55

NDR in logics

The high peaks correspond to a ‘1’ or a ‘yes’ signal

The deep valleys correspond to a ‘0’ or a ‘no’ signal

The use of NDR technology reduces the complexity of logic circuits

PROBLEMS TO DEAL WITH

Power dissipation

Size reduction

Noise

Nanocell Nanocell is a nanostructured circuit made out of

molecules and nanoclusters analogous to the structure of current macroscale logic circuits.

IEEE transactions on nanotechnology(2002), Vol 1, 101

Macroscale circuit Nanoscale circuit

REVIEW

The speaker improved greatly respecting to his first presentation. Yet, he needs to keep working in the following aspects:

1) English fluency: Even the most brilliant of the scientists will fail to catch the public’s attention during half an hour without fluency. People will easily get distracted due a low tone of voice, difficulty to understand words and lack of fluidity. This ends up affecting coherency and makes you going around the idea you want to convey without being able to go to the point. Also, it will slow you down and make your presentation longer than expected

REVIEW 2) Slide design: A set of well-thought slides makes a presentation much easier to

follow:

- Think what the audience needs to know to follow through the presentation, and design the slide sequence accordingly

- Use at least font 18 for the smallest text in the slide (apart from figure references and similar) and use different font sizes for main points and secondary points.

- Use space evenly and smartly, do not just splash some text and some graphs onto each slide. Use bullets and short sentences. Do not stuff the slides with text

REVIEW

I think the speaker tried to make a good effort in the introduction. However, the key word in the title is ‘NDR’, and the speaker took too long to get there. Moreover, checking the slides, I did not find a particular slide to illustrate this point, which is the basic point of the presentation

I think the speaker failed to stamp his own point-of-view in the ‘further research’ section, and limited himself to briefly name some recent works on the field rather than assess and critically propose his ideas

G5

Review of Molecular circuits based on NDR composites

by Norma Rangel

Molecular circuits based on NDR composites, by Alfredo D. Bobadilla

• I consider that Alfredo made a great improvement since his previous presentation, the information covered in his presentation was more audience appropriate and he explained more the concepts rather than the equations.

• The outline was very helpful to understand the topic, keep the flow of the presentation and to have an idea of the relation between the topics. It covered: current silicon semiconductor technology, NDR devices, NDR behavior in molecules and nanodevices, Logic circuits based on NDR devices and the Nanocell concept.

• I was worried he ran out of time and did not give a chance to ask him questions.

• Even though Alfred’s improvements were very noticeable, he can still make some progress in being more fluent, and prepare his presentations according to the audience, as a foreign myself I understand Alfred’s English confidently but that is something that we need to work on.

Review for Molecular circuits based on NDR composites

Jung Hwan Woo

• The font size is too small and each slide packs too much information to efficiently support the presentation.

• The speech was a bit too slow to contain what needed to be presented within the allotted time.

• The introduction to the concept seemed more than enough so that it exhausted the time needed for more important materials.

• Explanation to why negative-differential resistant behavior is present for each case can be improved to help the audience to understand the concept.

Molecular circuits based on NDR composites Alfredo D. Bobadilla Texas A&M University.

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