Molecular circuits based on
NDR composites
Alfredo D. Bobadilla
Texas A&M University
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
N-type MOSFET (metal–oxide–semiconductor field-effect transistor )
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
MOSFET electrical characteristic
The current level is controlled by the gate voltage. When switch is turned ON, the gate to source voltage is different
than zero and a current flow through the transistor, activating the LED (light-emitting diode).
Drain
+
VDS
Source
Gate
+
VGS
-
IDS
VDS : Drain to source voltage
VGS : Gate to source voltage
IDS : Drain current
http://en.wikipedia.org/wiki/MOSFET
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 uses
complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions.
http://www.falstad.com/circuit/e-cmosnand.html
A
B
C
0
0
1
0
1
1
1
0
1
1
1
0
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
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
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
… noise hampers our ability to distinguish
Between small differences in value —
e.g. between 3.1V and 3.2V.
AnantAgarwaland Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007.
MIT OpenCourseWare(http://ocw.mit.edu/), Massachusetts Institute of Technology.
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
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 to
quantization of momentum of the electrons in the well
and, 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 a
quasi-bound state in the well (a condition called
resonance) 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 NDR
of RTD’s make them very fast nonlinear circuit
elements.
The difference between the I–V curves is the current
available to charge/discharge the capacitances of the
RTD’s as well as circuit capacitance. The greater the
current 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.
Mathews, R. H. et al. A new RTD-FET logic family. Proc. IEEE 87, 596-605 (1999)
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
NDR behavior in molecules and nanodevices
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.
Pop, E. et al. Negative differential conductance and hot phonons in suspended nanotube molecular wires. Phys. Rev. Lett. 95, 155505 (2005).
NDR behavior in molecules and nanodevices
A MWCNT is exposed to e-beam radiation,
shrinking the nanotube until a carbon
nanowire is obtained.
Electrical current through the carbon nanotube
is 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.
Khoo at al, Negative differential resistance in carbon atomic wire-carbon nanotube junctions. Nano Lett. 8 2900 (2008)
NDR behavior in molecules and nanodevices
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 voltage
approaches the redox potential in the cyclic voltage sweep process.
The positive NDR peak corresponds to the oxidation peak of the
Ni ions and the negative NDR peak corresponds to their reduction.
Jangjian et al ,Room temperature negative differential resistance in DNA-based molecular. Appl. Phys. Lett. 94 43105 (2009)
NDR behavior in molecules and nanodevices
I( V ) characteristics at 60 K of a molecular junction
Au- (2'-amino-4-ethynylphenyl-4'-ethynylphenyl5'-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 electron
and two-electron peak reduction potentials.
Chen et al, Large on-off ratios and negative differential resistance in a molecular electronic device. Science 286, 1550-1552 (1999).
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
NDR Emulation
Two NDR emulator circuits were built
implementing microcontrollers.
ADC inputs were used to measure the
voltage drop across the device.
EMULATOR TERMINALS
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.
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
AJ Gimenez et al, Analysis of Nano and Molecular Arrays of Negative Differential Resistance Devices for Sensing and Electronics, IEEE Sensors J (2009).
NDR-based logic gate
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.
V1
V2
VC
VOut
0
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0
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1
0
0
0
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1
0
0
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1
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1
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Gate
AND
OR
AJ Gimenez et al, Analysis of Nano and Molecular Arrays of Negative Differential Resistance Devices for Sensing and Electronics, IEEE Sensors J (2009).
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
The nanoCell concept
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.
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)
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.
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 and
9000 molecular switches that has been trained as four
independent NANDS.
J. M. Tour et al, “Nanocell logic gates for molecular computing,” IEEE Trans. Nanotechnol., vol. 1, pp. 100–109 (2002).
The nanoCell: A Chemically Assembled Molecular Electronic Circuit
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)
Outline
Introduction
Current silicon semiconductor technology
NDR devices
NDR behavior in molecules and nanodevices
NDR & molecular
circuits
Logic circuits based on NDR devices
The Nanocell concept
Suggestions
Further research
Further research
Exploiting DNA self-assembly properties and CNT-DNA
interactions 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.
Rothemund, , Nature Nanotechnol. (2006)
Guo et al, Nature Nanotechnol. (2008)
Tu et al, Nature Nanotechnol. (2009)
Maune et al, Nature Nanotechnol. (2009)
THANKS!
let’s begin Q&A session
G2
Rebuttal: 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.
Alfredo D. Bobadilla
NDR-based molecular circuits rebuttal
• “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’.
Alfredo D. Bobadilla
NDR-based molecular circuits rebuttal
• “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 selfassembling 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.
Alfredo D. Bobadilla
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 Coan
PhD Chemical Engineering
4/01/10
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
G4
Review 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
Nano Letters(2004), Vol 4, 55
Science (2009), Vol 323, 1026
NDR region in a FET
Certain materials on certain substrates
produce this kind of behavior. For instance,
styrene on a (100) silicon surface
NDR in logics
The use of NDR technology reduces the complexity of
logic circuits
 The high peaks correspond
to a ‘1’ or a ‘yes’ signal
 The deep valleys correspond
to a ‘0’ or a ‘no’ signal
PROBLEMS TO DEAL WITH
 Power dissipation
 Noise
 Size reduction
Nanocell
 Nanocell is a nanostructured circuit made out of
molecules and nanoclusters analogous to the
structure of current macroscale logic circuits.
Macroscale circuit
Nanoscale circuit
IEEE transactions on nanotechnology(2002), Vol 1, 101
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.