Post on 17-Feb-2018
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MOLECULAR ELECTRONICS
B Tech Seminar Report
Submitted in partial fulfillment for the award of the Degree of
Bachelor of Technology in Electrical and Electronics Engineering
By
AKHILA CHANDRAN (Roll No. B090383EE)
Department of Electrical Engineering
NATIONAL INISTITUTE OF TECHNOLOGY CALICUT
NIT Campus P.O., Calicut - 673601, India
2014
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CERTIFICATE
This is to certify that the topic entitled MOLECULAR ELECTRONICS
is a bona fide record of the seminar presented by AKHI LA CHANDRAN (Roll
No.B090383EE), under my supervision, in partial fulfillment of the requirements for the
award of Degree of Bachelor of Technology in Electrical & Electronic Engineering from
National Institute of Technology Calicut for the year 2014.
Dr PREETHA P,(Seminar Coordinator)
Associate Professor,
Dept. of Electrical Engineering.
Place:
Date:
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AACCKKNNOOWWLLEEDDGGEEMMEENNTT
I am greatly indebted to Dr. Susy Thomas Ph.D. Professor and Head of theDepartment for her motivation and guidance throughout the course of this seminar work.
She had been responsible for providing us with splendid opportunities, which had shaped
our career. Her advice, ideas and constant support has engaged us on and helped us to get
through difficult times.
I express my profound gratitude to my seminar coordinator, Dr.Preetha P (Ph.D.),
Associate Proffesor, who has been a constant source of encouragement and support for
guiding the course of the seminar work.
I express my gratitude towards Mr.S.Raghu,(Adhoc-Faculty) and Mr.Sivaprasad (Ph.D
Scholar) for providing their valuable support and guidance during the development of
seminar report.
I express my gratitude to the all the faculties and lab programmers of Department of
Electrical and Electronics for their support in technical assistance.
AKHI LA CHANDRAN
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CONTENTS
Chapter no. Title page no.
LIST OF ABBREVATIONS i
LIST OF SYMBOLS ii
LIST OF FIGURES iii
1 INTRODUCTION 1
1.1 Moores Law 1
1.2 Silicon And Moores law 1
1.2.1 Power consumption and heat dissipation 2
1.2.2 Leakage 2
1.2.3 Photolithography 2
1.2.4 Capacitive coupling 3
2 MOLECULAR ELECTRONICS 4
2.1 Conduction in a single molecule 5
3 MOLECULAR ELCTRONIC DEVICES 8
3.1 Molecular Rectifying Diode 9
3.2 Molecular Switches 12
3.2.1 Photochromic molecular switches 13
3.2.2 Mechanically-interlocked molecular switches 14
4 ADVANTAGES OF MOLECULAR ELECTRONICS 16
4.1 Size 16
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4.2 Power 16
4.2 Manufacturing Cost 17
4.2 Assembly 17
4.3 Low Temperature Manufacturing 17
4.4 Stereochemistry 17
4.5 Synthetic flexibility 18
5 FUTURE OF MOLECULAR ELECTRONICS 19
6 CONCLUSION 21
REFERENCES 22
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i
LIST OF ABBREVATIONS
BDU - Beam Delivery Unit
HOMO - Highest Occupied Molecular Orbital
LUMO - Lowest Unoccupied Molecular Orbital
VTH - Threshold Voltage
DBA - Donor Bridge Acceptor
DTE - Dithienylethene
UV-VIS - Ultra Violet Visible Spectroscopy
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ii
LIST OF SYMBOLS
- Pi Bond
- Sigma Bond
- Energy Dependent parameter
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iii
LIST OF FIGURES
Figure 2.1: Conduction in a single molecule. ......................................................... 7
Figure 3.1: Equilibrium state of the molecular rectifier. ....................................... 10
Figure 3.2 : Rectifier operation under (a) Forward bias (b) Reverse bias. ............ 12
Figure 3.3 : Switches responding to UV-VIS Spectroscopy.................................. 13
Figure 3.4: Photo Switchable Catanane ................................................................. 15
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CHAPTER 1
INTRODUCTION
Molecular electronics, also called moletronics, is an interdisciplinary subject that
spans chemistry, physics and materials science. The unifying feature of molecular
electronics is the use of molecular building blocks to fabricate electronic
components, both active (e.g. transistors) and passive (e.g. resistive wires).
Molecular electronics provides means to extend Moores Law beyond the foreseen
limits of small-scale conventional silicon integrated circuits.
1.1 Moores Law
Moore's law is the observation that, over the history of computing hardware, the
number of transistors on integrated circuits doubles approximately every two years
[1]. The law is named after Intel co-founder Gordon E. Moore, who described the
trend in his 1965 paper.
The capabilities of many digital electronic devices are strongly linked to Moore's
law: processing speed, memory capacity, sensors and even the number and size of
pixels in digital cameras. All of these are improving at roughly exponential rates as
well. This exponential improvement has dramatically enhanced the impact of digital
electronics in nearly every segment of the world economy.
1.2 Silicon And Moores law
The future of Moores Law is not CMOS transistors on silicon. Within 25 years,
they will be as obsolete as the vacuum tube [2]. There are several reasons for which
silicon cannot sustain its current role in electronics industry. They can be enlisted
as follows:
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1.2.1 Power consumption and heat dissipation
Power consumption and heat dissipation is large obstacle for further advancement
in silicon-based chips [3].This power consumption also inverts the rare positive
effects of advancement in the number of transistors on silicon chip. This large
amount of power consumption boosts up the heat generation, increasing danger that
transistors interfere with each other. As transistors are becoming small size and so
small transistors consume small amount of power (voltage) but IC chip become
denser and denser because of large number of transistors on it, therefore it uses large
amount of power to driven all transistors and therefore generate more heat.
1.2.2 Leakage
In semiconductor devices, leakage is a quantum phenomenon where mobile charge
carriers (electrons or holes) tunnel through an insulating region. Leakage increases
exponentially as the thickness of the insulating region decreases [4].The primary
source of leakage occurs inside transistors, but electrons can also leak between
interconnects. Leakage increases power consumption and if sufficiently large can
cause complete circuit failure. Leakage is currently one of the main factors limiting
increased computer processor performance.
1.2.3 Photolithography
Photolithography is the process by which semiconductor circuitry is patterned on
silicon wafers. The lithography light source provides the deep ultraviolet light
needed to expose the photoresist on the wafer. The light is passed through a Beam
Delivery Unit (BDU), filtered through the reticle (or mask), and then projected onto
the prepared silicon wafer. In this way it patterns a chip design onto a photoresist
that is then etched, cleaned and the process repeats. After layer is built upon layer,
the wafer yields the chips that power todays most advanced electronic devices. [5].
Keeping up with Moores Law over the past four decades has seen lithography
wavelengths drop from the 436 and 365 nm produced by mercury arc lamps to 248
nm by the krypton fluoride excimer laser. In 1998, a group at MITs Lincoln
Laboratory developed a 193-nm source with the argon fluoride laser, which is used
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to produce todays 45- and 32-nm IC technologies. Despite the trend in reducing
exposure wavelengths, todays aggressive feature sizes are still falling farther and
farther below the available exposure sources, complicating the imaging challenges.
But Moores Law isnt just about getting more transistors on each chip; its also
about bringing down the cost of transistors. Optical lithography equipment has so
far met industry demands, but to preserve the law, a new advance is needed soon.
1.2.4 Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical
network by means of the capacitance between circuit nodes. This coupling can have
an intentional or accidental effect. Capacitive coupling is typically achieved by
placing a capacitor in series with the signal to be coupled [6]. Extending Moores
law using silicon will prove almost impossible if capacitive coupling comes into
picture. It can be explained using Planar Bulk-Si MOSFET Scaling. The planar
bulk-silicon MOSFET has been the workhorse of the semiconductor industry over
the last 40 years. However, the scaling of bulk MOSFETs becomes increasingly
difficult for gate lengths below ~20nm (sub-45 nm half-pitch technology node)
expected by the year 2009. As the gate length is reduced, the capacitive coupling of
the channel potential to the source and drain increases relative to the gate, leading
to significantly degraded short-channel effects. This manifests itself as a) increased
off-state leakage, b) threshold voltage (VTH) roll-off, i.e. smaller VTH at shorter
gate lengths, and c) reduction of VTH with increasing drain bias due to a modulation
of the source-channel potential barrier by the drain voltage, also called drain-
induced barrier lower.
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CHAPTER 2
MOLECULAR ELECTRONICS
Molecular electronics can be defined as technology utilizing single molecules, small
groups of molecules, carbon nanotubes, or nanoscale metallic or semiconductor
wires to perform electronic functions [7]. Some have defined it as technologies
utilizing only single molecules, but this definition is far too limiting, from the
broader definition, it can besuggested that any device utilizing molecular properties
is a molecular electronic device. However, in order for a molecular system to be
considered a device, there are several requirements that it must meet.
The simplest device that is easily conceived is a switch. The defining characteristic
of a switch is that of bi-stability, it has an ON and OFF position. Thus, any
molecular switch must perform in a similar manner. In its ON position, theswitch
must either perform some function or allow another device to perform its function.
In the OFF position, it must totally impede the function. Similarly, the switch
must not spontaneously change states; it must remain in the position that it is placed
until its position is changed. The development of a molecular switch is perhaps the
single most important element in developing molecular replacements for
conventional integrated circuits.
Finally, describing a molecule doing some useful function does not automatically
make it a molecular electronic device; there must be a way to interact with the
component, both on a microscopic level and through input from the macroscopic
world. Thus it is important to consider how a molecular electronic device can be
wired up. lt must be able to exchange information, or transfer states to other
molecular electronic devices, or it must be able to interface with the components in
the system that are not nanoscopic.
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2.1 Conduction in a single molecule
In a semiconductor or metal wire, charge transport is ohmic: For a given wire
diameter, longer wires have proportionately higher resistance. Such a picture is
usually wrong for molecules because of the localized nature of most molecular
electronic states. Consider the energy diagrams of figure 2.1, in which four types of
molecular-electronic junctions are represented, with examples of molecular
structures [8]. In figure 2.1, one electrode functions as an electron donor and the
other as an electron acceptor. The electrodes are bridged by a linear chain (an
alkane).
Rate constant for electron transfer across the bridge is given by
kET= A..(Eq. 2.1)
Whereis the energy dependant parameter and l is thebridge length.
For alkanes up to a certain length and for small applied voltages, this approximation
works well: Current through a junction decreases exponentially with increasing
chain length, and the alkane effectively serves as a simple energy barrier separating
the two electrodes. The possible mechanisms for electron transport are much richer
for the electron donor-bridge-electron acceptor (DBA) molecular junction of figure
2.1(b).
DBA complexes serve as models for understanding how charge transport
mechanisms in solution translate into the conductivity of solid-state molecular
junctions. In DBA complexes, the donor and acceptor sites are part of the molecule,
and the lowest unoccupied sites on the donor and acceptor components are
separated from one another by a bridging component that has molecular orbitals of
differing energy: In a process called electron-type super exchange, electrons that
tunnel from the right electrode into the acceptor state when a bias is applied may
coherently transfer to the donor state before tunnelling to the left electrode.
Alternatively, in hole-type super exchange, the tunnelling from the molecule into
the left electrode might occur first, followed by refilling of the molecular level from
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the right. In fact, both processes will occur, and it is their relative rates that
determine the nature of coherent conductance through a DBA junction. A third
possibility is that an electron from the donor can jump to the acceptor due to either
thermal or electrical excitation. That incoherent, diffusive process is quite closely
related to ohmic charge flow.
DBA junctions illustrate some of the beauty and richness of molecular electronics.
From a chemists perspective, the diversity of conduction mechanisms represents
an opportunity to manipulate the electrical properties of junctions through synthetic
modification. The observed conduction in DBA molecular junctions usually differs
radically from that in traditional ohmic wires and can more closely resemble
coherent transport in meso scopic structures. Key factors include a dependence on
the rates of intramolecular electron transfer between the donor and acceptor sites.
This dependence can be exploited: The donor and acceptor components could be
designed to differ energetically from one another (as in figure2.1(b)), so that even
with no applied bias voltage, the energy landscape is asymmetric. Under some
conditions, the conductance of a DBA junction can vary with the sign of the applied
voltage; such junctions represent a molecular approach toward controlling current
rectification.
The competition between charge transport mechanisms through a DBA molecule
can also be affected by the bridge. Shorter bridges produce larger amounts of wave
function overlap between the donor and acceptor molecular orbitals. For a short
bridge (5-10 K), the super exchange mechanism will almost always dominate. For
sufficiently long bridges, the hopping mechanism will almost always dominate. The
molecular structure of the bridge can be synthetically varied to control the relative
importance of the two mechanisms. For example, in a bridge containing conjugated
double bonds, low-lying unoccupied electronic states within the bridge will
decrease in energy with increasing bridge length (Energy Band of figure 2.1(b) is
lowered) and will thereby decrease the activation barrier to hopping. Because
double bonds, both in chains and in rings, facilitate charge delocalization, they are
very common in molecular electronics.
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Certain molecules will isomerize that is, change shape upon receiving a charge or
being placed in a strong field, and in many cases, such transformations can be highly
controlled. Different molecular isomers are characterized by different energies and
possibly by different relative rates for the hopping and super exchange transport
mechanisms. Driven molecular isomerization therefore presents opportunities for
designing switches and other active device elements. [9]
Molecular quantum dots (figure 2.1(c)) represent a simpler energy level system than
DBA junctions, and have become the model systems for investigating basic
phenomena such as molecular electrode interactions and quantum effects in charge
transport through molecular junctions. Representative molecules contain a principal
functional group that bridges two electrodes. Early versions of these devices utilized
mechanical break junctions essentially a fractured gold wire that forms a pair of
electrodes in a two-terminal device configuration. [10]
Figure 2.1 Examples of molecular transport junctions. The top panels depict molecules with variouslocalized, low-energy molecular orbitals (colored dots) bridging two electrodes L (left) and R (right).
In the middle panels, the black lines are unperturbed electronic energy levels; the red lines indicate
energy levels under an applied field. The bottom panels depict representative molecular structures.(a) A linear chain, or alkane. (b) A donor-bridge-acceptor (D BA) molecule, with a distance l
between the donor and acceptor and an energy difference Energy Band between the acceptor and the
bridge. (c) A molecular quantum dot system. The transport is dominated by the single metal atom
contained in the molecule. (d) An organic molecule with several different functional groups (distinct
subunits) bridging the electrode gap. The molecule shown is a rotaxane, which displays a diverse set
of localized molecular sites along the extended chain. Two of those sites (red and green) providepositions on the sliding rectangular unit (blue) can stably sit. A second example of a complex
molecule bridging the electrodes might be a short DNA chain.
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3.1 Molecular Rectifying Diode
A diode or a rectifier, which conducts only in one direction, is the building block of
any three terminal semiconductor electronic devices such as a bipolar transistor or
a field effect transistor. Diode based logic circuits using AND/OR gates are well
known for building logic families by using the rectifying diodes at the input and
connecting a resistor between the supply or the ground. A molecular diode too
contains two terminals and functions like a semiconductor pn junction and has
electronic states which can be clearly distinguished between highly conductive state
(ON) and less conductive state (OFF) [16].
The seminal work of Aviram and Ratner in 1974 led to several experimental
attempts to build molecular diodes Aviram and Ratner have suggested that electron
donating constituents make conjugated molecular groups having a large electron
density (N-type) and electron withdrawing constituents make conjugated molecular
groups poor in electron density (P-type). According to them, a non centro -
symmetric molecule having appropriate donor and acceptor moieties linked with an
-bridge and connected with suitable electrodes will conduct current only in one
direction acting as a rectifier. They showed that in this D-- molecule, thelowest
unoccupied molecular orbital (LUMO) and highest occupied molecular orbital
(HOMO) can be aligned in such a way that electronic conduction is possible only
in one direction making it function like a molecular diode.
The structure of the mono-molecular diode is shown in Fig. 3.1. This diode is based
on a molecular conducting wire consisting of two identical sections (S1, S2)
separated by an insulating group R. Section S1 is doped by at least one electrondonating group (X e.g. -NH2, -OH, -CH3, -CH2CH3) and section S2 is doped by
at least one electron withdrawing group (Y e.g. -NO2, -CN, -CHO). The insulating
group R (such as -CH2 -, -CH2CH2-) can be incorporated into the molecular wire
by bonding a saturated aliphatic group (no piorbitals). To adjust the voltage drop
across R, multiple donor/acceptor sites can be incorporated. The single molecule
ends are connected to the contact electrodes e.g. gold.
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The band diagram of the mono-molecular diode under zero bias conditions is shown
in Fig. 3.1. We notice that there are three potential barriers: one corresponding to
the insulating group (middle barrier) and two corresponding to the contact between
the molecule and the electrode (left and right barriers). These potential barriers
provide the required isolation between various parts of the structure. The occupied
energy levels in the metal contacts and the Fermi energy level EFare also shown.
On the left of the central barrier all the pi-type energy levels (HOMO as well as
LUMO) are elevated due to the presence of the electron donating group X and
similarly on the right of the central barrier the energy levels are lowered due to the
presence of the electron withdrawing group Y.
Figure 3.1: Equilibrium state of the molecular rectifier.
This causes a built-in potential to develop across the barrier represented by the
energy difference ELUMO. For current to flow electrons must overcome the
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potential barrier from electron acceptor doped section (S2) to electron donor doped
section (S1) and this forms the basis for the formation of the mono-molecular
rectifying diode.
The energy band diagram under forward bias conditions (left hand contact at higher
potential than the right hand contact) is shown in Fig. 3.2(a) . Here, electrons are
induced to flow by tunnelling through the three potential barriers from right to left
causing a forward current flow from left to right.
The band diagram under reverse bias conditions left hand contact at lower potential
than the right hand contact) is shown in Fig. 3.2(b). As a result, electrons from the
left contact would try to flow towards the right contact which is at a higher potential.
However, conduction is not possible because the there is still an energy difference
between the Fermi energy EF of the left contact and the LUMO energy of the
electron donor doped section. It is assumed that both the applied forward and
reverse bias potentials are identical. For a higher reverse bias, however, it is possible
for the Fermi energy EFof the left contact to come in resonance with the LUMO
energy of the electron donor doped section causing a large current to flow in reverse
direction and this is akin to the breakdown condition in a diode.
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Figure 3.2 : Rectifier operation under (a) Forward bias (b) Reverse bias.
3.2 Molecular Switches
A molecular switch is a molecule that can be reversibly shifted between two or more
stable states [17]. The molecules may be shifted between the states in response to
environmental stimuli, such as:
Changes in pH,
Light,
Temperature,
An electrical current,
Microenvironment,
Or in the presence of a ligand.
In some cases, a combination of stimuli is required. Currently synthetic molecular
switches are of interest in the field of nanotechnology for application in molecular
computers. Molecular switches are also important to in biology because many
biological functions are based on it, for instance allosteric regulation and vision.
They are also one of the simplest examples of molecular machines.
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3.2.1 Photochromic molecular switches
A widely studied class are photochromic compounds which are able to switch
between electronic configurations when irradiated by light of a specific wavelength.
Each state has a specific absorption maximum which can then be read out by UV-
VIS spectroscopy. Members of this class include azobenzenes, diarylethenes,
dithienylethenes, fulgides, stilbenes, spiropyrans and phenoxynaphthacene
quinones.
Figure 3.3 : Switches responding to UV-VIS Spectroscopy
Ever since their development in the late 1980s, molecular switches based on the
photo responsive dithienylethene (DTE) architecture have attracted widespread
attention as control elements in molecular devices and chemical systems [18]. This
special interest over other classes of photo switches is well deserved, and is due in
part to the high fatigue resistance of the ring-closing and ring-opening
photoreactions, which reversibly generate two isomers. Also, the two isomers
(ring-open and ring-closed) tend not to interconvert in the absence of light and,
most importantly, possess markedly different optical and electronic properties. The
most obvious change is in the colour of solutions, crystals and films containing DTE
compounds [19]. However, numerous other useful differences in optical
characteristics (emission and optical rotation of light), magnetism and molecular
and bulk conductivity have been exploited in a remarkable number of derivatives
to exert control over practical molecular systems.
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3.2.2 Mechanically-interlocked molecular switches
Some of the most advanced molecular switches are based on mechanically-
interlocked molecular architectures where the bistable states differ in the position
of the macrocycle. In 1991 Stoddart [20] devices a molecular shuttle based on a
rotaxane on which a molecular bead is able to shuttle between two docking stations
situated on a molecular thread. Stoddart predicts that when the stations are
dissimilar with each of the stations addressed by a different external stimulus the
shuttle becomes a molecular machine. In 1993 Stoddart is scooped by
supramolecular chemistry pioneer Fritz Vgtle who actually delivers a switchable
molecule based not on a rotaxane but on a related catenane.
This compound is based on two ring systems: one ring holds the photoswichable
azobenzene ring and two paraquat docking stations and the other ring is a polyether
with to arene rings with binding affinity for the paraquat units. In this system NMR
spectroscopy shows that in the azo trans-form the polyether ring is free to rotate
around its partner ring but then when a light trigger activates the cis azo form this
rotation mode is stopped.
Kaifer and Stoddart in 1994 modify their molecular shuttle [21] such a way that an
electron-poor tetracationic cyclophane bead now has a choice between two docking
stations: one biphenol and one benzidine unit. In solution at room temperature NMR
spectroscopy reveals that the bead shuttles at a rate comparable to the NMR
timescale, reducing the temperature to 229K resolves the signals with 84% of the
population favoring the benzidine station. However on addition of trifluoroacetic
acid, the benzidine nitrogen atoms are protonated and the bead is fixed permanentlyon the biphenol station. The same effect is obtained by electrochemical oxidation
(forming the benzidine radical ion) and significantly both processes are reversible.
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Figure 3.4: Photo Switchable Catanane
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CHAPTER 4
ADVANTAGES OF MOLECULAR ELECTRONICS
Molecular structures are very important in determining the properties of bulk
materials, especially for application as electronic devices. The intrinsic properties
of existing inorganic electronic materials may not be capable of forming a new
generation of electronic devices envisioned, in terms of feature sizes, operation
speeds and architectures. However, electronics based on organic molecules could
offer the following advantages:
4.1 Size
Molecules are in the nanometer scale between 1 and 100 nm. This scale permits
small devices with more efficient heat dissipation and less overall production cost
to be made.
4.2 Power
One of the reasons that transistors are not stacked into 3D volumes today is that the
silicon would melt. The inefficiency of the modern transistor is staggering. It is
much less efficient at its task than the internal combustion engine. The brain
provides an existence proof of what is possible; it is 100 million times more efficient
in power/calculation than our best processors. Sure it is slow (under a kHz) but it is
massively interconnected (with 100 trillion synapses between 60 billion neurons),
and it is folded into a 3D volume. Power per calculation will dominate clock speed
as the metric of merit for the future of computation.
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4.2 Manufacturing Cost
Many of the molecular electronics designs use simple spin coating or molecular
self-assembly of organic compounds. The process complexity is embodied in the
synthesized molecular structures, and so they can literally be splashed on to a
prepared silicon wafer. The complexity is not in the deposition or the manufacturing
process or the systems engineering. Much of the conceptual difference of nanotech
products derives from a biological metaphor: complexity builds from the bottom up
and pivots about conformational changes, weak bonds, and surfaces. It is not
engineered from the top with precise manipulation and static placement.
4.2 Assembly
One can exploit different intermolecular interactions to form a variety of structures
by the array of self-assembly techniques which are reported in the literature. The
scope of application of the self-assembly technique is only limited by the
researchers ability to explore.
4.3 Low Temperature Manufacturing
Biology does not tend to assemble complexity at 1000 degrees in a high vacuum.
It tends to be room temperature or body temperature. In a manufacturing domain,
this opens the possibility of cheap plastic substrates instead of expensive silicon
ingots.
4.4 Stereochemistry
A large number of molecules can be made with indistinguishable chemical
structures and properties. On the other hand, many molecules can exist as distinct
stable geometric structures or isomers. Such geometric isomers exhibit unique
electronic properties. Moreover, electronic properties of conformers can be affected
by pressure and temperature. We can therefore make use of stereochemistry to tune
properties.
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4.5 Synthetic flexibility
Organic synthesis is extremely versatile. It provides the means to tailor make
molecules with the desired physical, chemical, optical and transport properties. The
multitude of electronic energy levels in molecules can be fine-tuned by simple
variations in molecular structure, e.g., by changing substituents on aromatic rings
in conjugated compounds. Moreover, derivatization of a molecule can lead to
improving the processibility of the material without changing the device properties.
This allows an entirely new dimension in engineering flexibility that does not exist
with the typical inorganic electronic materials.
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CHAPTER 5
FUTURE OF MOLECULAR ELECTRONICS
The drive toward yet further miniaturization of silicon-based electronics has led to
a revival of efforts to build devices with molecular-scale organic components.
However, the fundamental challenges of realizing a true molecular electronics
technology are daunting. Controlled fabrication within specified tolerances and its
experimental verification are major issues. Self-assembly schemes based on
molecular recognition will be crucial for that task. Ability to measure electrical
properties of organic molecules more accurately and reliably is paramount in future
developments. Fully reproducible measurements of junction conductance are just
beginning to be realized in labs at Purdue, Harvard, Yale, Cornell, Delft, and
Karlsruhe Universities and at the Naval Research Laboratory and other centres.
Working molecular electronic devices exist today. Research progress is steady and
strong, giving us cause to believe that molecular electronic systems may be practical
in five to ten years. If lithography reaches fundamental physical or economic limits,
molecular electronics may allow us to continue observing Moores Law.
Regardless, molecular bottom-up fabrication could give us a much better
alternative, whose price would depend mainly on design and test cost, instead of
billion-dollar factories.
Challenges to making this reality are plentiful at every level, some naturally in
physics and chemistry. These include fabricating and integrating devices, managing
their power and timing, finding fault-tolerant and defect-tolerant circuits and
architectures and the test algorithms needed to use them, developing latency-
tolerant circuits and systems, doing defect-aware placement and routing, and
designing, verifying and compiling billion-gate designs and the tools to handle
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CHAPTER 6
CONCLUSION
Molecular electronics is an exciting emergent field of study. The reward of research
in this area is enormous as the birth of molecular computer implies unprecedented
processing power that may enable breakthroughs in artificial intelligence. This
report has given a glimpse at how such an endeavour might be accomplished by
introducing the basic ideas in molecular device implementation and electrical
characterization methods. The path towards a full working system is still a long one,
yet the prospects are bright and great strides have been taken.
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REFERENCES
[1] GE Moore, "Cramming more components onto integrated circuits," p. volume
38, 1975.
[2] S. Jurvetson, "Nanotechnology Law & Business,"KurzweilAI., vol. 34, pp. 24-
56, 2004.
[3] T. Surukai, "Prespectives on power aware electronics," inISSCC Conference,
February 2003.
[4] Google, "wikipedia," Google, 05 april 2014. [Online]. Available:
en.wikipedia.org/wiki/Leakage_(electronics). [Accessed 10 april 2014].
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