Genova July 2009 Memristors

8/9/2019 Genova July 2009 Memristors

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S.Carrara, EPFL Lausanne(Switzerland)

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Genoa, 28Genoa, 28 JulyJuly, 2009, 2009

Fabrication of MemristorsFabrication of Memristors

with Polywith Poly--CrystallineCrystallineSiliconSilicon NanowiresNanowires


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Talk OverviewTalk Overview

Concepts about Memristors Methods to fabricate poly-silicon nano-

wires

Structure of our nano-wire Memristors

The measured Memristor effect

Future Applications to Nano-Bio-sensing


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S.Carrara, EPFL - Lausanne(Switzerland)

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Memristors First ConceptMemristors First Concept

dq

dv

di

d

Four different circuit parameters:

dq

d

)(),(),(),( ttqtitv

di

dv

The missed equation!

R=

C

1=

L=

=


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The Memristor requestThe Memristor request

Symmetry reasons seem demanding for Memristors


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So, M = R in

case of constantcharge!

( )[ ]( )

dq

qdtqM

=

( )

( )R

tdi

tdv=

( )

dtdq

dt

qd

=

Memristor depending on Charge Flux:

The usual Resistance:

( )

di

qdv=

While, M will be an R with memory

effect in case of varying charge!

)(qR=


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The NameThe Name

MemoryResistor

MEMRISTOR


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A two-terminals Memristor may be modeled bythrough two resistors as an element which vary the

resistance upon the applied voltage

Possible Memristor ModelPossible Memristor Model


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( ) )()(

1)(

tiD

twR

D

twRtv OFFON

+=

)()(

tiD

R

dt

tdw ONV=

= )(1)(

2tq

D

RRqM ONVOFF

)()( tqD

Rtw ONV=

More evident at nano-scale!


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Current/Voltage CharacteristicsCurrent/Voltage Characteristics

Memristic effects are observable in I-V curves

as a memory of the channel doping in time


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How to build a Memristor?How to build a Memristor?

These results serve as the foundation forunderstanding a wide range of hysteretic

current-voltage behaviour observed in manynano-scale electronic devices

[] until now no one has presented either auseful physical model or an example of a

memristor


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How to build a Memristor?How to build a Memristor?

Memristors obtained by using organic materials


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TopTop--Down Techniques forDown Techniques for

PolyPoly--silicon Nanosilicon Nano--WiresWires Based on patterning: Photolithography

Nanomold lithography

Stencil lithography

Spacer technique

Un-differentiated NWs

Moselund et al., TNANO07

500 nm

Melosh et al., Science03

Vasquez-Mena et al., Nano Letters08

5 m

Sacchetto et al., ESSDERC09 Choi et al., J. Vac. Sci. Tech. B03


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BottomBottom--Up Techniques forUp Techniques for

PolyPoly--silicon Nanosilicon Nano--WiresWires

10 m 1 m

Whang, et al., Nano Letters03

Gudiksen et al., Nature02

Core

Shell

Shell

Cross-

section

Au

Lauhon et al.,

Nature02

Based on NW growth

NW can be differentiated: Radial doping

Axial doping


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MultiMulti--Spacer PatterningSpacer Patterning

TechniqueTechnique

conformalpoly-Si layer

2. Conformal layer deposition

poly-Si

spacer

3. Anisotropic RIE etch

multi-spacers

4. Alternating iterations of 2-3

SiO2 sacrificial layer

caveSi substrate

1. Sacrificial layer


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Fabrication Process: Frontend inFabrication Process: Frontend in

case of crosscase of cross--barsbars

SiO2 sacrificial layer

caveSi substrate

1. Sacrificial layer

conformalpoly-Si layer

2. Conformal layer deposition

poly-Si

spacer

3. Anisotropic RIE etch

upper

poly-Si

4. Definition of upper spacer

Cr/Ni Cr0.8 0.2


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Sizes OverviewSizes Overview

Insulator

(SiO2)

Poly-Si

spacer

Si substrate

Dimensions are

not true to scale! Only frontend

processing is

depicted

Backend includes

passivation +

metallization

~ 400 nm~ 400 nm

~ 70 nm

~ 70 nm~ 20 nm


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NanoNano-- toto MesoMeso--wires addressingwires addressing

Decoder

CrosspointsMesowires

Nanowires

Contact Group

Mesowire

VT2VT1 NanowireVA1 VA2 VA3 VA4

Nanowire


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Fabrication ProcessFabrication Process

Frontend Passivation

BackendTesting

Definition of

crossing poly-Si

nanowire

Isolation of devices,

via opening for

metalization and

functionalization

Metalization: NiCror Cr/NiCr or Al

Current/Voltagemeasurements


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Fabrication ResultsFabrication Results

The SEM imaging shows the quality of poly-siliconwires fabricated by using spacers technique


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The registered I/V curves show memristic effects due to

a memory of the swept voltage windows


Electrons de-trapping

Electrons trapping

Holes trapping

Holes de-trapping


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Conductivity MechanismsConductivity Mechanisms

Both electrons and holes based conductivity isaffected by Memristor effect


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The registered I/V curves show memristic effects due to

a memory of the swept voltage windows



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)()()()()( EgEgEgEgEg GDGATDTA +++=

TD

v

W

EE

TDTD eNEg

=)(

2

)(

= GAGA

W

EE

GAGA eNEg

2

)(

= GDGD

W

EE

GDGA eNEg

TA

c

W

EE

TATA eNEg

=)(

Tail States Gaussian StatesAcceptors State Donors State

Simulations bySimulations by

driftdrift--diffusion modeldiffusion model


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2D Simulations by Atlas follow the experimental

data accounting for negative trapped charges at thePoly-Si/SiO2 interface

-20 -10 0 10 20

10-11

10-10

10-9

10-8

10-7

Simulation

DrainC

urrent(A)

Gate Voltage (V)

Experiment

Simulations ResultSimulations Result


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S.Carrara, EPFL Lausanne(Switzerland) 25

Future NanoFuture Nano--BioBio--sensingsensing

applicationsapplications

Frontend Passivation

BackendFunctionalization

Definition of

crossing poly-Si

nanowire

Isolation of devices,

via opening for

metalization and

functionalization

Metalization: NiCror Cr/NiCr or Al

Grafting of bio-markers


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pH Dependent SensorpH Dependent Sensor

pH Sensor obtained by modifying Si oxide surface with 3-aminopropyltriethoxysilane yielding amino and silanol groups (actingas receptors) at surface

Patolsky et al., Nanowire-Based Biosensors, Analytical Chemistry, 2006, 4261-4269

Protonation/deprotonation altered charge density at surfacethereby changing conductance

For p-type FET: rising pH led to decreased positive chargeimplying increase in conductance


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Detecting Single VirusDetecting Single Virus When virus binds to antibody receptor, conductance changes from

baseline value

When it unbinds, conductance returns to baseline value

Patolsky et al., Nanowire-Based Biosensors, Analytical Chemistry, 2006, 4261-4269

Results suggest the possibility to develop ultradense NW device where

minimum scale is set by size of virus


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Concept in Memristors forConcept in Memristors for

NanoNano--BioBio--SensingSensing

The charging from molecules affects the Memristic

effects onto the poly-silicon channel

Back Gate

Nitride Passivation

Nano-wire channel

Top-gate


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Memristors have been obtained by using poly-

silicon nano-wires

Poly-silicon nano-wires have been fabricated byusing spacer technique

Memristic effect has been registered in I/V

characteristics 2D simulations confirmed that Memristic effect is

due to charges trapped in the Channel/Gate

interface during deposition Future development will be in Nano-Bio-Sensing

ConclusionsConclusions


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Thanks to CoThanks to Co--authorsauthors

M. Haykel Ben Jamaa

Julius Georgious

Nikolas Archontas

Giovanni De Micheli


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Coordinates:Dr. Sandro Carrara Ph.D

Integrated Laboratory Systems

Swiss Federal Institute of Technology (EPFL)

CH-1015 Lausanne

Web: http://si2.epfl.ch/~scarrara/

email: [email protected]

Thank you for your attention!Thank you for your attention!

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Genova July 2009 Memristors