nanoelectronics: besides and beyond mooreregpot/winterschool2009/app/...winter school on...

Winter School on Nanoelectronics and NanophotonicsBilkent University – Ankara, Turkey Jan. 20th-25th

Nanoelectronics:Besides and Beyond Moore

Wilfred G. van der Wiel

MESA+ Institute for Nanotechnology University of Twente, The Netherlands

Ankara, January 25th 2009


Contents of this lecture

• A brief history of electronics• Single-electron transistors and quantum dots• Organic electronics• Spintronics


Breakthroughs:

1920s: semiconductor components ([photo]diodes)1925: idea of the field effect transistor (FET)1947: first working transistor1959: the integrated circuit (IC)1960: the first metal-oxide-silicon (MOS) transistor1970: solid state memories; the microprocessor1980: the PC1990s: ubiquitous internet and cellular phones

A brief history of electronics


Electronic “work horses”

vacuum tube (end 19th century)

• slow • bulky • fragile • consumes a lot of power


1947: first transistor

point contact transistor

• 2 metal wires on n-Ge• hard to make, not practical


bipolar junction transistor (BJT)

• invented at Bell Labs in 1947• bipolar: both holes and electrons carry the current• now largely replaced by CMOS technology, but still used for specific

applications (e.g. radio-frequency circuits)


cross section of an npn BJT



field effect transistor (idea: 1925, realized: 1960)

CMOS – complementary metal-oxide-silicon• pairs of transistors for logic functions, only one of which is switched on

at any time • Simplicity and low power dissipation of CMOS circuits have allowed

for integration densities not possible with BJTs

MOSFET


Transistor revolution


Integrated circuits - ICs

all components of a circuit on a piece of semiconductor


1976: Apple I motherboard1981: The first PC: IBM’s 5150 PCIntel microprocessorDOS operating system

IBM stated in 1951: ‘the world needs only 5 computers’


INTEL:The microprocessor

Photo: Augarten 1983


Moore’s Law

“number of transistors per square inch doubles every 18 months”


ITRS roadmap

http://www.itrs.net/home.html

Winter School on Nanoelectronics and NanophotonicsBilkent University – Ankara, Turkey Jan. 20th-25thNanoElectronics 22 April 2005IBM

Moore’s law cannot continue forever...


Single Electron Transistors (SETs) and Quantum Dots (QDs)Single Electron Transistors (SETs) and Quantum Dots (QDs)

single molecule

nanoparticle

self-assembledQD

nanotube

nanowire

1 nm 10 nm 1μm

vertical QD

lateral QD

100 nm

Vsd Vg

GATE

ISLANDDRAINSOURCE

I

e

Vsd Vg

GATE

ISLANDDRAINSOURCE

IVsd V

GATE

ISLANDDRAINSOURCE

Vsd V

GATE

ISLANDDRAINSOURCE

I

e• Small box in solid-state occupied by electrons (holes) • number of electrons 0 - ~1000• Coupled via tunnel barriers to source and drain

reservoirs• Coupled capacitively to gate electrode(s)• Discrete energy spectrum ⇒ artificial atoms


band diagram

2-dimensional electron gas2-dimensional electron gas

n-AlGaAsAlGaAs

GaAs

GaAs

2DEG10

0 nm

semiconductor heterostructure

III-V semiconductorsSi n-dopant


heterostructure processingheterostructure processing

heterostructure

resist

e-beam after development evaporation gate structure after lift-off

channel 2DEG

How to define nanostructures out of a 2DEG?

• applying (negative) voltages to gateelectrodes on top

• wet etching• dry etching (focused ion beam,electron cyclotron resonance, ...)


lateral quantum dotslateral quantum dots

• High-mobility 2DEG (~106 cm2/ Vs) • Density ~1015 m-2 ⇒ λF ~ 30 nm• Resolution gate structure ~20 nm• Dot size ~ 100 nm• Comparable to electron wavelength⇒ discrete energy spectrum

E

x,y

E

x,y

400 nm

S D


circular pillar made from double barrier structure by dry and wet etching

n-GaAs drain

AlGaAs barrier

InGaAs well

AlGaAs barrier

n-GaAs source

Other geometries possible

vertical quantum dotsvertical quantum dots


constant interaction modelconstant interaction model

N

Vg

gC

C

V V

CRL

L R

Assumptions:

• all Coulomb interactions among electrons are parameterized by asingle capacitance C (C = CL + Cg + CR)

• discrete energy spectrum is independent of the electron number N

[ ]∑=

++−

=N

nn

gg BEC

VCeNNU

1

2

)(2

)(

classical Q-mech.

VL ≈ VR ≈ 0:

Vsd Vg

GATE

ISLANDDRAINSOURCE

I

e


electrochemical potentialelectrochemical potential

minimum energy for adding the Nth electron to the dot

CeE

EVCe

EEN

NUNUN

C

NggC

C

dot

2

21 )(

)1()()(

=

+−−

=−−≡μ

Nch

ggC

CN

EN

VCe

EENe

=

−−=−

)(

)( 21

μ

ϕ electrostatic potential

chemical potential

charging energy:EC = e2/C

C ∝ R, R (radius) 100 nm⇒ EC ~ few meV


Coulomb blockadeCoulomb blockade

+ΔE

RL

RdotL

Ve μμμμμ−=−

>>

EENUNUNUNN

C

dotdotdot

Δ+=−+−+=−+=Δ )1()(2)1()()1( μμμ

addition energy

NO CURRENT CURRENT


single-electron tunnelingsingle-electron tunneling

N N+1

N+2

N-1

Linear response

ΓL ΓR

μSμ(N)

Vg

μDμS

μ(N)

Vg

μDμS μ(N)

Vg’

μDμS μ(N)

Vg’

μD

ΓL ΓR

μSμ(N) μD

ΔEμSμ(N) μD

μSμ(N) μD

ΔE

μS

μ(N) μD

μ(N+1)Eadd

μS

μ(N) μD

μ(N+1)Eadd

Non-linear transport

Vsd

Vg

NN-1 N+1

dI/dVsd

ΔE Eadd


(0,1)

(0,2)

(0,0)

(1,0)

(2,2)

(2,0)

2D harmonic potential: Fock-Darwin states2D harmonic potential: Fock-Darwin states

( )*4/1~

2/1~1222

02 meB

llnE

cc

cnl

=+≡

−++≡

ωωωω

ωω hh

meV 3 0 =ωh

(cyclotron frequency)


Shell fillingShell filling

e /CE2+Δ

-1. 5 - 0.8

0

20

2 126N=0

GATE VOL TAGE (V)

1 32 4 5 6 7

e /C2 e/C2 e/C2 e/C2 e/C E2+ Δ

}

-1.5 -0.80

20

2 126N=0

gate voltage (V)

} } } } }

1 32 4 5 6 7

curr

ent (

pA)

{ { { { { {

e2/C e2/C+ΔE e2/C e2/C e2/C e2/C+ΔE

addi

tion

ener

gy (m

eV)

0

6 2 6

124

9 16

electron number


"The elements, if arranged according to their atomic weights, show a distinct periodicity of their properties..."

1869Mendeleev arranges63 known elements ina periodic table

Dmitri Mendeleev(1834-1907)

AtomsAtoms


Element number 16: Sulphur

AtomsAtoms


2

6

8

20

9 10 11 12

1918171613

7

43

1

5Oo

Ha

Ja

Ta

Da1514

To Ho

KoEt

2D Periodic Table of Artificial Atoms

CrMiSa

Au

Wi Fr El

artificial atomsartificial atoms


Dot 1

Dot 2

vertical,laterally coupledquantum dots

300 nm

lateral, coupled quantum dots

Coupled quantum dotsCoupled quantum dots


Vgate1 Vgate2

dot 1 dot 2

μS μD

NN-1

MM+1

charge cycle I:(N,M) → (N+1,M) → (N,M+1) → (N,M) → …

Vgate1

Vga

te2

(0,1)

(1,0) (2,0)

(1,1) (2,1) (3,1)

(1,2) (2,2) (3,2)

(3,3)(2,3)(1,3)

(0,2)

(0,0)

dots in series: transport at triple points only !!

charge cycle II:(N+1,M+1) → (N+1,M) → (N,M+1) → (N+1,M+1) → …

Coupled quantum dotsCoupled quantum dots

W.G. van der Wiel et al., Rev. Mod. Phys. 75, 1 (2003)


“Temperature filter”“Temperature filter”

2D EG

AlG aA sX 1-X

GaA s

O hms conta ctn aar 2DE G

ga tes

=> resonant current is determined byalignment of discrete states andindependent of temperature

W.G. van der Wiel et al., Rev. Mod. Phys. 75, 1 (2003)


2D EG

AlG aA sX 1-X

GaA s

O hms conta ctn aar 2DE G

ga tes

elastic tunnelingΓ tL RΓ

width ≈ hlifetime

≈ h

Γ 0 10

1

2

3

Cur

rent

(pA

)

Source-Drain Voltage (mV)

inelastic current

GS -GSelastic current

FWHM = 4 eVμ

3.5 x 100 mK = 35 μeV

=> FWHM is an order of magnitudesmaller than thermal energy

“Temperature filter”“Temperature filter”

Winter School on Nanoelectronics and NanophotonicsBilkent University – Ankara, Turkey Jan. 20th-25th © WGvdW


organic materials

- light and flexible- easy to process cheap- additional functionalities- interface with biological systems

molecular electronics

- essentially all electronic processes in nature occur inmolecular structures (e.g. photosynthesis, signal transduction)

- size 1-100 nm cost, efficiency, power dissipation- self-assembly and recognition (switches & sensors)- molecular synthesis allows great flexibility

Why organic electronics???

Organic electronicsOrganic electronics


Organic electronics

Single-molecule electronicsmolecular rectifier proposed byAviram and Ratner 1974

Organic thin-film electronics

• polymers (Nobel prize chemistry 2000)• small molecules• single-crystals



OLED

flexible circuitry

electronic papersolar cells



μ is the constant of proportionality between the drift velocity v of the charge carriers and the electric field E that induces this drift velocity:

material mobility [cm2/(Vs)]

Si (crystalline) 1350 (e)InAs (bulk) 30,000 (e)GaAs (quantum well) up to ~10,000,000 (e) at low T (~ 1K)CNT 100,000 (e)Cu 42 (e)pentacene (crystalline) 30 (h)pentacene (thin film) ~1 (h)

Ev μ=

Carrier mobilityCarrier mobility


When band transport occurs?When band transport occurs?

In general, an energy ΔE is required to move an electron from one molecule to thenext.

Even at zero temperature, this energy can be provided by quantum fluctuations:

h>Δ⋅Δ tE Heisenberg uncertainty relation

If the tunnel rate between molecules is much larger than then the electroncan delocalize over many molecules.

If the tunnel rate is much less than then the electron is localized on onemolecule and conduction takes place via (thermally activated) hopping.

h/EΔ

h/EΔ


Conduction mechanismsConduction mechanisms

non-band-like conduction

band-like conduction only occurs when the charge carriers are in sufficiently delocalized states

hopping(thermally activated)


organic semiconductors: OTFT inorganic semiconductors: MOSFET

• doping is difficult due to low purity• conducting channel by accumulation• predominantly hole transport (p-type)

• doping introduces carriers• conducting channel by inversion• both n-type and p-type channel(allows for CMOS architecture)

VDS

Vg

back gate

For a review of inorganic (silicon) FETs, see, e.g.:S.M. Sze, Physics of Semiconductor DevicesA.S. Sedra and K.C. Smith, Microelectronic Circuits, ISBN 0-03-053237-X

Organic Thin-Film Transistors (OTFTs)Organic Thin-Film Transistors (OTFTs)


Organic Thin-Film Transistors (OTFTs)Organic Thin-Film Transistors (OTFTs)

organic semiconductorsexamples typical mobility

(cm2V-1s-1)polymers polyacetylene

poly(3-alkylthiophene) (P3AT) 0.1

small molecules pentaceneoligothiophenes 1

single-crystals pentacenerubrene 10


Conductive polymersConductive polymers

Conductive plastics are used in, or being developed industrially for, e.g. anti-static substances for photographic film, shields for computer screen against electromagnetic radiation and for "smart" windows (that can exclude sunlight).

In addition, semi-conductive polymers have recently been developed in light-emitting diodes, solar cells and as displays in mobile telephones and mini-format television screens.


polyacetylene: insulatordiscovery: halogen (Cl, Br, I) doping makes polyacetylene 109 times more conductive:σ = 105 Sm-1

(teflon: 10-16 Sm-1; copper: 108 Sm-1)

Conductive polymersConductive polymers


Organic single-crystalsOrganic single-crystals

Polymers: no periodic structure (“spaghetti”)Thin films of small molecules: defects (grain boundaries)Single-crystals: low defect density (mobility independent of gate voltage)

rubreneπ-conjugated molecule (aromatic rings)

• High mobility due to strong orbital overlap (6 cm2/Vs, up to 20 at RT)

• Stable in air• Growth parameters known

review:R.W.I. de Boer, phys. stat. sol. (a) 201, 1302 (2004)


Si

SiO2

B

A

Al2O3Co

Single Crystal



Artemperature gradient

copper wire

In collaboration with Anna Molinari, Alberto Morpurgo (TU Delft)



Wouter Naber et al., unpublished

-40 -20 0 20 40

-40

-20

0

20

40

I(nA

)

V (V)

Vg = -30Vg = -20Vg = -10Vg = 0Vg = 10Vg = 20Vg = 30

Co/Al2O3/rubreneRT, L = 300 μmμ = 1 cm2/(Vs)



rotaxane – switching molecule

singleatom

transistor

STM tip with nanoparticle

Molecular electronicsMolecular electronics


Measuring electronic properties of moleculesMeasuring electronic properties of molecules

A. Hg drop junctionB. Mechanical break junctionC. NanoporeD. Nanogap in nanowireE. Nanoparticle bridgeF. Crossed (nano)wiresG. STMH. CP-AFMI. Nanoparticle + CP-AFM

B.A. Mantooth and P.S. Weiss, Proc. IEEE 91, 11 (2003)


conducting AFMconducting AFM

X.D. Cui et al., Science 294, 571 (2001)

single 1,8-octanedithiol molecules inserted in octanethiol monolayer

gold nanoparticles on top of the monolayer are contacted by gold-plated conducting AFM probe

octanedithiol: 900 ± 50 MOhm(based on 1000 single molecules)

1, 2, 3, 4 or 5 molecules measured in parallel


Single-molecule transistorsSingle-molecule transistors

J. Park et al., Nature 417, 722 (2002) W. Liang et al., Nature 417, 725 (2002)

single Co-atom transistor divanadium molecule as spin impurity


-1.0 -0.5 0.0 0.5 1.0

1E-8

1E-7

1E-6

PAD1 PAD2 PAD3

C8 dithiol, 10 micron circular pads, probe station room temperatureI (

A)

V (V)

Tunneling through alkanedithiol SAMs


Tunneling through alkanedithiol SAMs

-1.0 -0.5 0.0 0.5 1.0

1E-8

1E-7

1E-6

1E-5

C8 dithiol, probe station room temperature

I(80 μm2) I(400 μm2)

I (A)

V (V)-1.0 -0.5 0.0 0.5 1.0

1E-8

1E-7

1E-6

1E-5

C8 dithiol, probe station room temperature

5 x I(80 μm2) I(400 μm2)

I (A)

V (V)

10 μm circles(80 μm2)

20 μm x 20 μm (400 μm2)

scaled curves


Organic electronics vs CMOSOrganic electronics vs CMOS

Once it is possible to make transistors by chemical synthesis, more transistors will be made in one day that it will ever be possible by photolithography.

However, CMOS is still going strong! Dimensions of transistors have shrunk a factor 10,000 since the 1960s. The price of 1 gigabit of memory has decreased by a 1.5 million times.

Experts predict that CMOS will remain the mainstream technology for many years and that improvements will continue until at least 2016.


SpintronicsSpintronics

• non-volatality (no constant voltage required to ‘remember’ state)• decreased electric power consumption• increased data processing speed


magnetic contacts

tunnel barriers

normal metal spacer

traditional electronics: chargespin electronics: spin and charge

semiconductor spacers offer new possibilities

GaAs: X. Lou et al., Nature Physics 3, 197 (2007)



no spin relaxation with spin relaxation



tunnel magnetoresistance (TMR)FM-insulator-FM

giant magnetoresistance (GMR)

FM-metal-FM



Magnetic Random Access Memory (MRAM)Motorola

GMR head hard driveFujitsu



GMR hard disk read headsGMR hard disk read heads


Giant magnetoresistanceGiant magnetoresistance


Nanoelectronics...Nanoelectronics......is where physics, materials science, chemistry and electric engineering inevitably meet

Getting grip on the fundamental properties of nanoelectronic devices is of crucial importance, and a very exciting scientific challenge

www.mesaplus.utwente.nl/nanoelectronics


I would like to thank the following people for kindly supplying material:

Jeroen Elzerman (TU Delft)Peter Hadley (TU Delft)Ronnie Jansen (University of Twente)Alberto Morpurgo (TU Delft)Jurriaan Schmitz (University of Twente)Seigo Tarucha (University of Tokyo)

AcknowledgmentsAcknowledgments

nanoelectronics: besides and beyond mooreregpot/winterschool2009/app/...winter school on...

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