Lecture 1 3 Introduction

Introduction to NanotechnologyIntroduction to Nanotechnology

( PH – 401 )( PH – 401 )

Text/Reference Books:

1. Introduction to Nanoelectronics

Vladimir V. Mitin, V. A. Kochelap

and Michael A. Stroscio

Cambridge University Press

2. Introduction to Nanotechnology

Charles P. Poole and Frank J. Owen

John Wiley & Sons

3. Nanotechnology – Principle and practices

Sulbha K. Kulkarni

Captial Publishing Company

4.4. Nanotechnology Nanotechnology

Jeremy RamsdenJeremy Ramsden

Free study books: www.bookboon.com Free study books: www.bookboon.com

5. Nanoelectronics and Nanosystems5. Nanoelectronics and Nanosystems

K. Goser, P. Glosekotter and J. DienstuhalK. Goser, P. Glosekotter and J. Dienstuhal

Springer India Pvt. LtdSpringer India Pvt. Ltd

• What is Nanotechnology?What is Nanotechnology?

• Review of the Quantum MechanicsReview of the Quantum Mechanics

• Review of the Solid State PhysicsReview of the Solid State Physics

• Materials for the NanoelectronicsMaterials for the Nanoelectronics

• Electrons in low dimensional structuresElectrons in low dimensional structures

• Nanostructure DevicesNanostructure Devices

What is nanotechnology?What is nanotechnology?

The prefix nano in the word nanotechnology means a The prefix nano in the word nanotechnology means a billionth ( 1x 10billionth ( 1x 10-9-9 ). ).

The nanotechnology deals with structure of matter The nanotechnology deals with structure of matter having dimensions of the order of billionth of a meter.having dimensions of the order of billionth of a meter.

Carbon bond lengths - 0.12 – 0.15 nmCarbon bond lengths - 0.12 – 0.15 nmDNA double helix has a diameter – 2 nmDNA double helix has a diameter – 2 nmBacteria of the genus Mycoplasma – 200nmBacteria of the genus Mycoplasma – 200nmThe ratio of the size of a marble to the size of the earth is The ratio of the size of a marble to the size of the earth is same as that of a nanometer to a meter.same as that of a nanometer to a meter.

Nanotechnology is a new technology but the nanostructures occurs in Nanotechnology is a new technology but the nanostructures occurs in nature and even man has used it without knowing.nature and even man has used it without knowing.

Abolone – Abolone – a mollusk constructsa mollusk constructs a very strong shella very strong shell having having iridescent inner surface by organising calcium carbonate into iridescent inner surface by organising calcium carbonate into nanostructured bricks glued by carbohydrate-protein gel. The shells nanostructured bricks glued by carbohydrate-protein gel. The shells represents strong natural structures fabricated from nano particles.represents strong natural structures fabricated from nano particles.

Lycurgus cup – made from the soda lime glass containing silver-Lycurgus cup – made from the soda lime glass containing silver-gold-nano particles ( by Romans). The colour of the cup changes gold-nano particles ( by Romans). The colour of the cup changes from green to deep red when light is placed in it.from green to deep red when light is placed in it.

Photography – a technology using nanosized particles. It uses a film Photography – a technology using nanosized particles. It uses a film containing silver halides. The light decomposes the silver halides, containing silver halides. The light decomposes the silver halides, producing nano particle of silver which are the pixels of the image.producing nano particle of silver which are the pixels of the image.

There is plenty of room at the bottom. (1960)There is plenty of room at the bottom. (1960) R. P. Feynman R. P. FeynmanSurely, you are joking, Mr. Feynman.Surely, you are joking, Mr. Feynman. R. P. Feynman R. P. Feynman

The principle of physics as for as I can see , do not The principle of physics as for as I can see , do not speak against the possibility of maneuvering thing atom speak against the possibility of maneuvering thing atom by atom. It is not an attempt to violate any laws: it is by atom. It is not an attempt to violate any laws: it is something ,in principle, that can be done because we something ,in principle, that can be done because we are too big. New small structures.are too big. New small structures.

Electron beam lithography - Silicon chip Electron beam lithography - Silicon chip

Existence of nanostructures in biological systems.Existence of nanostructures in biological systems.

Manipulating individual atoms to make new small Manipulating individual atoms to make new small structures having different properties.structures having different properties.

He also predicted that the scaling issues would also He also predicted that the scaling issues would also arise from the changing of the various dimensions: arise from the changing of the various dimensions: gravity would become less important, surface tension and gravity would become less important, surface tension and van der waals attraction would become increasingly more van der waals attraction would become increasingly more significant. significant.

Professor Norio Taniguchi (1974) defined the term Professor Norio Taniguchi (1974) defined the term nanotechnology for the first time as: Nanotechnology nanotechnology for the first time as: Nanotechnology consists of the processing of, separation and consists of the processing of, separation and consolidations, and deformation of the material by one consolidations, and deformation of the material by one atom or by one molecule.atom or by one molecule.

Dr. K. Eric Drexler promoted technological significance of Dr. K. Eric Drexler promoted technological significance of the nano scale phenomena and devices.the nano scale phenomena and devices.

Nanotechnology is the design, characterization, production, and Nanotechnology is the design, characterization, production, and application of structures, devices and systems by controlling the size application of structures, devices and systems by controlling the size at nanoscale.at nanoscale.

Characteristic or critical length…..Characteristic or critical length…..

Every property of a material has a critical length Every property of a material has a critical length associated with it. For example, the resistance of a associated with it. For example, the resistance of a material that results from conduction electrons being material that results from conduction electrons being scattered out of the direction of the flow by collisions with scattered out of the direction of the flow by collisions with atoms and impurities can be characterized by length atoms and impurities can be characterized by length called scattering length. This length is the average called scattering length. This length is the average distance an electron travels before being deflected. The distance an electron travels before being deflected. The fundamental physics and chemistry changes when the fundamental physics and chemistry changes when the dimensions of the solid become comparable to one or dimensions of the solid become comparable to one or more of its characteristic length. more of its characteristic length.

When size of a semi conducting material is in the order When size of a semi conducting material is in the order of the wavelength of the electron or holes that carry of the wavelength of the electron or holes that carry current. The confinement takes place. current. The confinement takes place.

Surface area of the nanostructures….Surface area of the nanostructures….

Object of radius r; V= 4/3 Object of radius r; V= 4/3 ππ r r33

Surface area A= 4 Surface area A= 4 ππ r r22

Object is divided into n parts theObject is divided into n parts the

surface area becomes nsurface area becomes n1/31/3 4 4 ππ r r22

Why nanotechnology?Why nanotechnology?

Economizing on material.Economizing on material.

PerformancePerformance

Enhancement in functionalities.Enhancement in functionalities.

Nanotechnology can be used to fabricate Nanotechnology can be used to fabricate material literally molecule by molecule.material literally molecule by molecule.

Custom design ultra precise new structure, Custom design ultra precise new structure, devices and systems.devices and systems.

Properties of the new materials…Properties of the new materials…

Vastly increased strengthVastly increased strength

Reduced weightReduced weight

Greater electrical conductivityGreater electrical conductivity

Ability to change shape or colour on Ability to change shape or colour on demand.demand.

Quantum wells, wires and dotsQuantum wells, wires and dots

Quantum well is a structure in which one dimension is reduced Quantum well is a structure in which one dimension is reduced to the nanorange while the other two dimensions remain large.to the nanorange while the other two dimensions remain large.

Quantum wire is a structure in which two Quantum wire is a structure in which two dimensions are reduced to the nanorange. dimensions are reduced to the nanorange.

Quantum dot is a structure in which three Quantum dot is a structure in which three dimensions are reduced to the nanorange.dimensions are reduced to the nanorange.

Preparation of the quantum nanostructures..Preparation of the quantum nanostructures..

There are two approaches to prepare quantum There are two approaches to prepare quantum nanostructures:nanostructures:

1. Bottom-up method 1. Bottom-up method

2. Top-down method 2. Top-down method

Bottom-up method :Bottom-up method : In this method one collects, consolidates, In this method one collects, consolidates, and fashion individual atoms and molecules into structure. and fashion individual atoms and molecules into structure.

This is carried out by a sequence of chemical reactions This is carried out by a sequence of chemical reactions controlled by catalysts. It is a process which is controlled by catalysts. It is a process which is widespread inwidespread in biology where, for example, catalysts calledbiology where, for example, catalysts called enzymes assemble amino acids to living tissue that forms enzymes assemble amino acids to living tissue that forms and supports the organs of the body.and supports the organs of the body.

Top-down method: Top-down method: In this approach one starts with a In this approach one starts with a large-scale object or pattern and gradually reduces its large-scale object or pattern and gradually reduces its dimension or dimensions. This can be accomplished by dimension or dimensions. This can be accomplished by a technique calleda technique called lithography. lithography.

Lithography: A thin film coating of a metal is Lithography: A thin film coating of a metal is deposited on a suitable substrate. Radiation deposited on a suitable substrate. Radiation resist, usually a polymer, is coated on the metal resist, usually a polymer, is coated on the metal thin film. A mask is placed between the resist thin film. A mask is placed between the resist coated substrate and the radiation source. By coated substrate and the radiation source. By using suitable chemical ( developer) resist is using suitable chemical ( developer) resist is removed. The unexposed part is chemically removed. The unexposed part is chemically treated to produce nanostructures.treated to produce nanostructures.

Applications of the nanotechnologyApplications of the nanotechnology

Approximately 99 per cent of medicinal molecules don't reach their Approximately 99 per cent of medicinal molecules don't reach their targets and subsequently, stay in the body of the patient. As these targets and subsequently, stay in the body of the patient. As these molecules can sometimes be very toxic - particularly in the case of molecules can sometimes be very toxic - particularly in the case of those designed to target cancer. Nanotechnology is being used to those designed to target cancer. Nanotechnology is being used to safely transporting and delivering drugs. safely transporting and delivering drugs.

Giant magneto-resistivity of the nano structures: It consists of layers Giant magneto-resistivity of the nano structures: It consists of layers of metal magnetic and nonmagnetic materials which display the of metal magnetic and nonmagnetic materials which display the property of giant magneto resistivity. The layers are nanometer thick. property of giant magneto resistivity. The layers are nanometer thick. It is used for increasing storage capacity of the magnetic tapes.It is used for increasing storage capacity of the magnetic tapes.Quantum-dot lasers are used to read compact discs.Quantum-dot lasers are used to read compact discs.Photovoltaic film that converts light into electricity.Photovoltaic film that converts light into electricity.Scratch proof coated windows that can clean themselves with UV Scratch proof coated windows that can clean themselves with UV light.light.Intelligent clothes; Nanoparticle paints; Hipjoints made of Intelligent clothes; Nanoparticle paints; Hipjoints made of biocompatible materials; Organic light emitting diodes etcbiocompatible materials; Organic light emitting diodes etc

Applications of the nanotechnologyApplications of the nanotechnology

Self assembly process – has been developed to form periodically ordered structure on semiconductor surfaces for direct fabrication quantum nanostructure and devices.

Single walled carbon nanotubes are used to make gas sensors. Single walled carbon nanotubes are used to make gas sensors.

Single walled carbon nanotubes are used to make field Single walled carbon nanotubes are used to make field effect transistors.effect transistors.

It is a interdisciplinary field. It is a interdisciplinary field. The driving force behind the nanotechnology is the recognition that The driving force behind the nanotechnology is the recognition that the nanostructure materials have the physics and chemistry the nanostructure materials have the physics and chemistry different from the bulk materials. To explain these difference and different from the bulk materials. To explain these difference and the reasons for them, one has to understand the basic physics and the reasons for them, one has to understand the basic physics and chemistry of the bulk solid state. chemistry of the bulk solid state.

NanoelectronicsNanoelectronicsMicroelectronics – deals with the electronic devices that Microelectronics – deals with the electronic devices that has length scales of approximately a micrometer.has length scales of approximately a micrometer.

Nanoelectronics – deals with the electronic devices that Nanoelectronics – deals with the electronic devices that

has length scales of approximately 1 to 100 nanometers. has length scales of approximately 1 to 100 nanometers.

At the nanoscale, most phenomenon and processes are At the nanoscale, most phenomenon and processes are dominated by quantum physics. Innovative nanoscale dominated by quantum physics. Innovative nanoscale properties and functions will be achieved through the properties and functions will be achieved through the control of matter at the level of its building blocks, atom control of matter at the level of its building blocks, atom by atom, molecule by molecule, and nanostructure –by-by atom, molecule by molecule, and nanostructure –by-nanostructure. Molecular building blocks of life- proteins, nanostructure. Molecular building blocks of life- proteins, nucleic acids, carbohydrates – are examples of materials nucleic acids, carbohydrates – are examples of materials that possess impressive properties determined by their that possess impressive properties determined by their size, geometrical folding, and patterns at nanoscale.size, geometrical folding, and patterns at nanoscale.

Technological MotivationsTechnological MotivationsThe continuous demands for steady growth in memory The continuous demands for steady growth in memory and computational capabilities and for increasing and computational capabilities and for increasing processing and transmission speeds of signals has lead processing and transmission speeds of signals has lead to the development of electronics at nanoscale. to the development of electronics at nanoscale.

The complexity of integrated circuits, with The complexity of integrated circuits, with respect to minimum component cost, respect to minimum component cost, doubles every 18 months – Dr. Gorden doubles every 18 months – Dr. Gorden Moore. Moore. This statement formulated 40 year’s ago is This statement formulated 40 year’s ago is

knownknown asas Moore’s Law. Moore’s Law. The Moore’s provides an estimate of the rate of progress The Moore’s provides an estimate of the rate of progress in the electronics industry. It predicts that the number of in the electronics industry. It predicts that the number of devices – transistors – on a microchip doubles every one devices – transistors – on a microchip doubles every one to two years. This is only possible if progressive scaling to two years. This is only possible if progressive scaling down of all electronic components is realized. down of all electronic components is realized.

In the Fig. the changes in the characteristics of the In the Fig. the changes in the characteristics of the integrated circuits since its invention. The number of integrated circuits since its invention. The number of atoms required for storing or operating 1 bit changes by atoms required for storing or operating 1 bit changes by several order of magnitude.several order of magnitude.

In 1960 one transistor consisted of 10In 1960 one transistor consisted of 102020 atoms in a atoms in a volume of 0.1 cmvolume of 0.1 cm33, whereas in 2000 these numbers were , whereas in 2000 these numbers were reduced to 10reduced to 1077 atoms in 0.01 atoms in 0.01μμmm33..

In the same way the energy for charging or operating In the same way the energy for charging or operating

1 bit decreased, since the energy for charging and 1 bit decreased, since the energy for charging and discharging capacities was lowered by the facts that one discharging capacities was lowered by the facts that one reduces the area of the capacitors from 1 cmreduces the area of the capacitors from 1 cm22 to .01 to .01μμmm22 and voltages from 10V to 1V. The 12 orders of and voltages from 10V to 1V. The 12 orders of magnitude has made possible such high integration magnitude has made possible such high integration levels without running into the problems of power levels without running into the problems of power dissipation and thermal heating.dissipation and thermal heating.

The increase of the integration level was The increase of the integration level was possible first of all by reducing the feature possible first of all by reducing the feature size of the devices and in second place by size of the devices and in second place by enlarging the chip area and by functional enlarging the chip area and by functional integration.integration.

It is assumed that the silicon technology It is assumed that the silicon technology has its limits for further miniaturization to has its limits for further miniaturization to approximately 10 nm. To overcome this approximately 10 nm. To overcome this restriction, functional integration and three-restriction, functional integration and three-dimensional integration are possible dimensional integration are possible solution. An alternative approach is solution. An alternative approach is nanoelectronics. nanoelectronics.

The Region of Nanostructure: Figure displays The Region of Nanostructure: Figure displays different physical levels if the features size of the different physical levels if the features size of the devices are scaled down.devices are scaled down.

The characteristic times in semiconductor are plotted The characteristic times in semiconductor are plotted against the structural dimensions of the devices. These against the structural dimensions of the devices. These times are correlated to different physical effects.times are correlated to different physical effects.

Figure shows different physical levels if the feature sizes Figure shows different physical levels if the feature sizes of the devices are scaled down. The characteristic times of the devices are scaled down. The characteristic times in semiconductors are plotted against the structural in semiconductors are plotted against the structural dimensions of devices. These times are correlated to dimensions of devices. These times are correlated to different physical effects. The shaded area covers different physical effects. The shaded area covers present-day microelectronics. Outside this region the present-day microelectronics. Outside this region the domain of nanoelectronics and molecular electronics is domain of nanoelectronics and molecular electronics is reached. The characteristic times and dimensions are less reached. The characteristic times and dimensions are less than 1 ps and less than 10 nm respectively.than 1 ps and less than 10 nm respectively.

Depletion layer Depletion layer width limits the reduction in size of the p-width limits the reduction in size of the p-n junction in a diode. For a pn junction in a diode. For a p++ n junction the depletion n junction the depletion width can be approximated bywidth can be approximated by

D

Dn qN

VVl

)(2

The width lThe width lnn of the depletion layer increases with voltage of the depletion layer increases with voltage

V and decreases with the doping density NV and decreases with the doping density ND D of the of the

region. The permittivity is denoted by region. The permittivity is denoted by εε and q is the and q is the elementary charge. Another important dimension is elementary charge. Another important dimension is Debye lengthDebye length

The definition of the Debye length is similar to that of the The definition of the Debye length is similar to that of the depletion layer. The voltage is replaced by kT/q and depletion layer. The voltage is replaced by kT/q and doping density Ndoping density NDD by intrinsic doping n by intrinsic doping nii of a of a

semiconductor. For a doped semiconductor nsemiconductor. For a doped semiconductor nii is is

substituted by the density of the majority carriers. substituted by the density of the majority carriers.

Particles moving due to thermal energy have mean free Particles moving due to thermal energy have mean free path between two collisionpath between two collision

= v= vthth ττcc

i

TD qn

VL

ll

Mean free path depends on the thermal velocity vMean free path depends on the thermal velocity v thth and on and on

the mean free time the mean free time ττcc of the particles, of the particles, which determines the which determines the

mobility mobility μμ of the charge carriers. of the charge carriers.

Quantum effects become relevant in devices if the Quantum effects become relevant in devices if the wavelength of the electrons is in the range of the feature wavelength of the electrons is in the range of the feature size of the devices.size of the devices.

= h/m= h/meev v

Most of the nanoelectronic devices function in this range so Most of the nanoelectronic devices function in this range so

wave behaviour becomes important. If one continues to wave behaviour becomes important. If one continues to decrease the structural dimension the domain of the atoms decrease the structural dimension the domain of the atoms and molecules is reached.and molecules is reached.

Improving Materials on the nanoscaleImproving Materials on the nanoscale

To achieve minimum device sizes and ultra-high levels of To achieve minimum device sizes and ultra-high levels of integration, it is necessary to identify the limiting and integration, it is necessary to identify the limiting and critical parameters for improved performance. For critical parameters for improved performance. For transistor the two parameters of the host material are: transistor the two parameters of the host material are: the ultimate electron velocity and the limiting electric field the ultimate electron velocity and the limiting electric field which does not induce electric breakdown.which does not induce electric breakdown.

Si and compound semiconductors are widely used to Si and compound semiconductors are widely used to make the electronic devices. However, semiconductors make the electronic devices. However, semiconductors other than silicon can be used. In particular the other than silicon can be used. In particular the compound semiconductors constitute a general class of compound semiconductors constitute a general class of semiconductors that are currently widely used. Every semiconductors that are currently widely used. Every element in column III of the periodic table of elements element in column III of the periodic table of elements may be combined with every element in column V to may be combined with every element in column V to form a so called III-V compound, which is form a so called III-V compound, which is semiconducting.semiconducting.

Two or more discrete compounds may be used to Two or more discrete compounds may be used to form alloys. A common example is where form alloys. A common example is where x is the fraction of column III sites in the crystal x is the fraction of column III sites in the crystal occupied by Al atoms, and fraction 1-x is occupied occupied by Al atoms, and fraction 1-x is occupied by Ga atoms. As a result, it becomes possible not by Ga atoms. As a result, it becomes possible not only to make discrete compounds, but also to only to make discrete compounds, but also to realize a continuous range of materials for tailoring realize a continuous range of materials for tailoring necessary properties. The growth of Silicon-necessary properties. The growth of Silicon-Germanium ( ) alloys facilitates the control Germanium ( ) alloys facilitates the control of the properties of materials over a considerable of the properties of materials over a considerable range of the electrical parameters. These range of the electrical parameters. These techniques are exploited widely in techniques are exploited widely in microelectronics.microelectronics.

xxGeSi 1

AsGaAl xx 1

Hetrostructures with nanoscale featuresHetrostructures with nanoscale features

Hetrostructures are structures with two or more abrupt Hetrostructures are structures with two or more abrupt interfaces at the boundaries between the different interfaces at the boundaries between the different semiconductor materials. With the available material semiconductor materials. With the available material growth techniques, it is possible to grow structures with growth techniques, it is possible to grow structures with transition regions between adjacent materials that have transition regions between adjacent materials that have thickness of only one or two atomic mono-layers. This thickness of only one or two atomic mono-layers. This allows one to fabricate multilayered semiconductor allows one to fabricate multilayered semiconductor structures with nanoscale thickness.structures with nanoscale thickness.

The simplest multilayered structure has a single The simplest multilayered structure has a single hetrojunction, i.e. a single hetrojunction structure is hetrojunction, i.e. a single hetrojunction structure is made of two different materials. At the interface of such a made of two different materials. At the interface of such a hetrojunction, the electronic properties are changed to hetrojunction, the electronic properties are changed to improve selected physical characteristics. In particular improve selected physical characteristics. In particular the electrons are confined in a thin layer near the the electrons are confined in a thin layer near the interface. interface.

In particular, electrons can be confined in a thin In particular, electrons can be confined in a thin layer near the interface. In fact, the layers with layer near the interface. In fact, the layers with confined electrons can be made so thin that confined electrons can be made so thin that wave-like behavior that is, quantum-mechanical wave-like behavior that is, quantum-mechanical behavior of the electrons become apparent. The behavior of the electrons become apparent. The same phenomena occur for diverse multilayered same phenomena occur for diverse multilayered nanoscale structures that can be grown with nanoscale structures that can be grown with high quality.high quality.

By using nanostructures, it is possible to modify By using nanostructures, it is possible to modify the electronic properties of a great variety of the electronic properties of a great variety of nanoscale devices. Quantum effects on the nanoscale devices. Quantum effects on the nanoscale determine the properties of electrons nanoscale determine the properties of electrons in nanostructures: the nanostructures can be in nanostructures: the nanostructures can be made in such a way that the electron motion made in such a way that the electron motion becomes becomes two dimensional, one-dimensional, or two dimensional, one-dimensional, or even even zero-dimensional. zero-dimensional.

These nanostructures are known as These nanostructures are known as low-low-dimensional dimensional quantum hetrostructures and are quantum hetrostructures and are called quantum wells, quantum wires, and called quantum wells, quantum wires, and quantum dots, for the cases where the electrons quantum dots, for the cases where the electrons are confined in one, two, and three dimensions, are confined in one, two, and three dimensions, respectivelyrespectively

Fabrication techniques on the nanoscaleFabrication techniques on the nanoscale

Growth and fabrication methods: Growth and fabrication methods:

Molecular-beam epitaxyMolecular-beam epitaxy

Ultra-thin-layer fabricationUltra-thin-layer fabrication

Superlattice fabricationSuperlattice fabrication

Characterization methods:Characterization methods:

Lithographic nanostructuringLithographic nanostructuring

Qualitative electron-beam and X-ray microscopesQualitative electron-beam and X-ray microscopes

Advances in Growth and fabrication methods:Advances in Growth and fabrication methods:

Metal-organic vapour-phase epitaxyMetal-organic vapour-phase epitaxy

Metal-organic molecular-beam epitaxyMetal-organic molecular-beam epitaxy

Fabrication to atomic-layer-accuracy Fabrication to atomic-layer-accuracy

delta-dopingdelta-doping

Controlled strained layersControlled strained layers

Fabrication methods based on chemistry and biologyFabrication methods based on chemistry and biology

Assembling inorganic nanoblocks with biomoleculesAssembling inorganic nanoblocks with biomolecules

Characterization MethodsCharacterization Methods

Lithography and etching for nanostructuringLithography and etching for nanostructuring

Dip-pen nanolithographyDip-pen nanolithography

Qualitative electron-beam and X-ray microscopiesQualitative electron-beam and X-ray microscopies

Scanning Tunneling Microscopy (STM) Scanning Tunneling Microscopy (STM)

Atomic force microscopy (AFM)Atomic force microscopy (AFM)

Pico second and femtosecond spectroscopoyPico second and femtosecond spectroscopoy

Terahertz time-domain spectroscopy Terahertz time-domain spectroscopy

Improvements in characterization methods for the Improvements in characterization methods for the nanoscalenanoscale

Progress in the refinement of fabrication techniquesProgress in the refinement of fabrication techniques

for making nanostructures depends on the great for making nanostructures depends on the great

improvement made in characterization methods. Inimprovement made in characterization methods. In

particular composition and dopant distribution, latticeparticular composition and dopant distribution, lattice

strain, and other parameters within nanostructuresstrain, and other parameters within nanostructures

must be known within atomic scale precision. must be known within atomic scale precision.

Currently, the manipulation of a single atom (ion) in a Currently, the manipulation of a single atom (ion) in a

solid is possible. New tools – scanning tunnelingsolid is possible. New tools – scanning tunneling

microscopy and atomic-force-microscopy – whichmicroscopy and atomic-force-microscopy – which

portend numerous applications in high-precisionportend numerous applications in high-precision

fabrication have emerged. Picosecond and fabrication have emerged. Picosecond and

femtosecond spectroscopy have progressed femtosecond spectroscopy have progressed

substantially and they have been applied to substantially and they have been applied to

characterize the electronic properties of hetrostructures.characterize the electronic properties of hetrostructures.

Finally, terahertz time-domain spectroscopy wasFinally, terahertz time-domain spectroscopy was

developed, which makes it possible to measuredeveloped, which makes it possible to measure

electric signals with time resolutions at the level of electric signals with time resolutions at the level of

seconds. seconds.

1210

Nanostructure DevicesNanostructure Devices

The quantum-wire carbon nanotube field-effectThe quantum-wire carbon nanotube field-effect

transistor.transistor.

The injection quantum-well laserThe injection quantum-well laser

Sub-terahertz III-V compound nanoscale field effectSub-terahertz III-V compound nanoscale field effect

transistor.transistor.

Sub-terahertz INP and SiGe bipolar transistors.Sub-terahertz INP and SiGe bipolar transistors.

Carbon nanotube transistorCarbon nanotube transistor

Microwave double barrier tunneling diode (DBRTD)Microwave double barrier tunneling diode (DBRTD)

Single electron transistorSingle electron transistor

New principle of device operations at the nanoscale: New principle of device operations at the nanoscale:

In the nanoscale domainIn the nanoscale domain the new principles of the new principles of

device operations are;device operations are;

Collisionless motion – ballistic motion Collisionless motion – ballistic motion

Resonant-tunneling phenomenona in nanoscale Resonant-tunneling phenomenona in nanoscale

multilayered structures.multilayered structures.

Nanoscale domain is the realm of quantum physics. Nanoscale domain is the realm of quantum physics. Indeed the scaling down of the devices and their Indeed the scaling down of the devices and their integration above the level corresponding to 250 Mbits on integration above the level corresponding to 250 Mbits on a single chip makes it necessary to take into account new a single chip makes it necessary to take into account new regimes and even to modify the principle underlying device regimes and even to modify the principle underlying device operation. Further device downscaling and higher operation. Further device downscaling and higher integration densities for information capacities 1 Gbit per integration densities for information capacities 1 Gbit per chip imply the need to investigate using quantum regimes chip imply the need to investigate using quantum regimes of operation.of operation.

Beside quantum effects, reducing device Beside quantum effects, reducing device dimensions results in a decrease in the dimensions results in a decrease in the number of electrons participating in the number of electrons participating in the transfer of an electron signal. As a result, transfer of an electron signal. As a result, nano-scale devices may operate on the nano-scale devices may operate on the basis of single-electron transfer. Various basis of single-electron transfer. Various novel single-electron devices have been novel single-electron devices have been proposed and demonstrated. By reducing proposed and demonstrated. By reducing the sizes of quantum dots to 100 A or less, the sizes of quantum dots to 100 A or less, it is possible to operate with single it is possible to operate with single electrons at temperatures near or close to electrons at temperatures near or close to room temperature.room temperature.

Nanotechnology for optoelectronicsNanotechnology for optoelectronics

Electronic devices - operate with electrical inputElectronic devices - operate with electrical input

and output signals.and output signals.

Optoelectronic devices - Optoelectronic devices - are based on both operate are based on both operate electrical and optical properties of materials and operate with electrical and optical properties of materials and operate with both optical and electrical signal.both optical and electrical signal.

Optoelectronics compliments microelectronics.Optoelectronics compliments microelectronics.

Applications of the optoelectronics.Applications of the optoelectronics.• Acquisition, storage, and processing of information.Acquisition, storage, and processing of information.• Transmission via optical fiberTransmission via optical fiber• Communication between processing machines as well Communication between processing machines as well

as within themas within them• Storage of information on laser disks.Storage of information on laser disks.

Components of optoelectronic systems – Components of optoelectronic systems – • Light sources, sensitive optical detectors, andLight sources, sensitive optical detectors, and

properly designed light waveguides.properly designed light waveguides. Passive optical elements fabricated withPassive optical elements fabricated with

optically active semiconductor materialsoptically active semiconductor materials Enhancing optical and electro-optical effects Enhancing optical and electro-optical effects

by using semiconductor nanostructure and by using semiconductor nanostructure and

quantum hetrostructure. quantum hetrostructure. The light emitting diodes and laser diodesThe light emitting diodes and laser diodes

may be improved greatly when nanostructuresmay be improved greatly when nanostructures

such as quantum wells, quantum wires, and such as quantum wells, quantum wires, and

quantum dots are exploited as active quantum dots are exploited as active

elements.elements.

Nanoelectronic systems are more complex as compared to the Nanoelectronic systems are more complex as compared to the microelectronic systems. Modern microelectronic systems contain upto microelectronic systems. Modern microelectronic systems contain upto 100 million devices on a single chip. Nanoelectronics will push this 100 million devices on a single chip. Nanoelectronics will push this number upto 1 billion devices or even more.number upto 1 billion devices or even more.

Complexity of the Nanoelectronics:Complexity of the Nanoelectronics:

1. Large number of devices1. Large number of devices

2. Larger development time2. Larger development time

3. Larger time for testing such systems 3. Larger time for testing such systems

Complexity in Memory chips – Complexity in Memory chips –

A memory chip with n memory cells, in which each cell can store 1 bit A memory chip with n memory cells, in which each cell can store 1 bit requires 2n test cycles for reading and writing 0’s and 1’s. A 16 bit requires 2n test cycles for reading and writing 0’s and 1’s. A 16 bit memory chip therefore requires 32 million test cyclesmemory chip therefore requires 32 million test cycles

If the testing includes all possible bit patterns that can be If the testing includes all possible bit patterns that can be stored on a chip the number of testing cycles will get stored on a chip the number of testing cycles will get increased. A chip with n cells has 2increased. A chip with n cells has 2nn different patterns that different patterns that can be stored on it. A chip with 16777216 cells requires can be stored on it. A chip with 16777216 cells requires about 2about 21677721616777216 ≈ 10 ≈ 1050000005000000 test cycles. If 1 ns is required for test cycles. If 1 ns is required for each test cycle, the testing of the whole chip would last each test cycle, the testing of the whole chip would last longer than the age of the universe. Concerns – Time , longer than the age of the universe. Concerns – Time , Economic considerations. The problem will rise Economic considerations. The problem will rise exponentially with increasing complexity of the chips. In exponentially with increasing complexity of the chips. In practice the test engineering restricts itself to the sensitive practice the test engineering restricts itself to the sensitive cases in regard to the interference between the cell. The cases in regard to the interference between the cell. The price to be paid for such type of pragmatic solution is that price to be paid for such type of pragmatic solution is that memory can have soft failures. Software for error memory can have soft failures. Software for error corrections are used.corrections are used.

Wiring of an integrated circuit - Minimizing the length of Wiring of an integrated circuit - Minimizing the length of the signal or bus lines is very complex problem. If n the signal or bus lines is very complex problem. If n denotes the number of points or devices to be connected denotes the number of points or devices to be connected then there are m = n! possibilities of connecting them.then there are m = n! possibilities of connecting them.

The problems of this nature are said to be NP complete The problems of this nature are said to be NP complete problems. This problem is more complex than testing of problems. This problem is more complex than testing of a chip and is well known as travelling salesman problem a chip and is well known as travelling salesman problem (TSP). The verification of a possible solution is as difficult (TSP). The verification of a possible solution is as difficult as problem itself. Parallel computing with the present as problem itself. Parallel computing with the present day microelectronics is not capable of finding a solution day microelectronics is not capable of finding a solution for this problem for large values of n. These problems for this problem for large values of n. These problems will force further developments of Nanoelectronics.will force further developments of Nanoelectronics.