seminar report- akhila

7/23/2019 Seminar Report- Akhila

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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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[14] D. M. Sataric, "Molecular Diodes and Diode Logic Molecular," in

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