Forschungszentrum Jülich

Resistive Switching inResistive Switching in Metal-Insulator-Metal Junctions

H. Kohlstedt*

Forschungszentrum Jülich GmbH,Institut für Festkörperforschung and CNI, the Center of Nanoelectronic

Systems and Information Technology GermanySystems and Information Technology, Germany

*Present address:

Center of

University of California, BerkeleyDepartment of Material Science and Engineeringand Berkeley Lab - Advanced Light Source

Center ofNanoelectronic Systems forInformation Technology

Seagate May 2006: email: HHKohlstedt@lbl.gov

Contents

I. IntroductionRandom Access Memories

II. Resistive Switching

III. Ferro-Resistive Switching

IV SummaryIV. Summary

V. Multiferroic Tunnel Junction

Charge and Resistance for RAMs

MRAMFlash

FeFETDRAM/SRAM

+-

Computational “1”

Binary FeRAM

MIM Junction(Resistive Switch)

“Write” “Read”BinaryLogic

FeRAM

Computational “0”Carbon nanotubes

Ovonic Molecular Memory(single molecule)

Conductive bridge(Solid State Electrolyte)

+

-

What is a resistive memory?y

Read a Resistance = Resistive Memory

Examples

Charged Based: Resistance Based:

DRAMFeRAMSRAM

MRAMFlashFeFETSRAM

.....FeFETOvonic....

Why resistive storage Elements?

DRAM Cell

Word line

Bit line1T1C cell

Word line

TransistorTransistor

DRAM it

Sense Amplifier

DRAM capacitor“1” charged Cap.“0” non charged Cap.CBL

Cmin ≅ 30 fF

Planar DRAM CapacitorPlanar DRAM Capacitor

ACmin ≅ 30 fF SiO2 thickness dA

Q = C U; C = ε0εA / dQ C U; C ε0εA / d

Decrease capacitor footprint (area A) ⇒ reduces C (Cmin limit)

Reduce dielectric thickness d tunneling limit (approx 2nm)• Reduce dielectric thickness d, tunneling limit (approx. 2nm)• Increase area by using 3-D structures (keep footprint)• Use high-k dielectrics (process compability with CMOS)

Developments: 3 D capacitors

Siemens / IBM : 1 Gbit, deep trench

metal 11 µm

bitline

Si surface

1 µm

trenchcapacitor

> 5 µmdeep

Tremendous efforts to stay on the road-mapChallenging technology – more and more expensive and complicated

FeRAM Capacitor: Pulse Polarization Switchingg

P1.0 switching

y [k

A/c

m2

P

0 0

0.5non-switching

rent

den

sity

V0 10 20 30

0.0

Cur

r

Time [ns]

Vc

Different remanent polarization states

Vbias

p

⇒ different transient current behavior to an applied voltage pulse

Integrating the current ⇒ switched charge Q and non switchedIntegrating the current ⇒ switched charge QS and non-switched charge QNS (distinction between the two logic states)

Destructive Readout

Scaling and 3D conformal Coverage

Transition from 2D to 3D technology

Minimum capacitance for sensing: 30 fFPt

2D planar

Minimum capacitance for sensing: 30 fFOperation voltage 1 VQ=CU n=Q/e3 x 10-14C needed for sensing: approx 20 000 e-3 x 10 14C needed for sensing: approx. 20.000 e

Planar capacitor:A = 100 nm x 100 nm

Ferroelectric

A 100 nm x 100 nm Pr = 10µC/cm2

10-15 CQ = P AQ P Acorresponds to 6000 e- not sufficient for data sensing!

3D h !3D approach necessary!

Conformal coverage/MOCVD mandatory

Supposed to be implemented in 2007-09for 100 nm FeRAM node technology

Matrix Architecture: Random Access Memory

Bit line decoder

Sense amplifierl

Data1T- 1C cell

de

co

de

r

co

ntr

olo

gic

AddressW

ord

lin

e

1T-1R cell

Renewed approach: Crossbar arrays 1-R cellRenewed approach: Crossbar arraysExtremely high scaleable

Go 3-DFirst step:

Crossbar resistor array1R ll1R cells< 10 nm feature size

3-dimensional arrayby stacking:by stacking:

Although technologicaldifficult – nothing newdifficult nothing new

Interconnects

New Nanoelectronic ArchitecturesSecond step:

G. Snider et al., Appl. Phys. A 80, 1183 (2005) – Hewlett Packard

Approach:

Activate independently at the cross pointsdifferent devices as: (switchable) resistors diodes or transistors(switchable) resistors, diodes or transistors

Create your own Computer after the fabricationprocessprocess.

Beyond conventional memory architecture!Field programmable arrays (FPGA)

The Resistive Memory Approachy pp

Bi-stable (or multi-stable) resistors

Current“1”

Vthreshold = Vth“0”

Voltage

Vread < Vth

…more specific

Read a Resistance = Resistive Memory

S DG

M M Magnetic Tunnel Junctions

Flash

Indirect type: S D

No structural changes in theNo structural changes in thetransport region between on and off state

Direct type:

Structural changes(e.g. Phase Change)

Two Parties:

Homogenous folks:Homogenous folks:Those who believe the effectis a volume or an interface effect across the entire dielectric and/or interface

Filament (network) folks:Those who believe the effect is caused by filamanents whicheffect is caused by filamanents whichare strongly localized in an inactivesurroundingg

Overview Resistive Switches (Effects)

Homogeneous

? How homogeneous is the current transport - Filaments?

Local?Is a formation process important?

?Which role play the interfaces?

?Is the switching effect a pure electronic i i iti ?

Redox

I Red Ox + e- -

or ionic or a superposition?V Voltammogram

?Which kind of current transport is essential for R and R ??Which kind of current transport is essential for RH and RL?

Not a surprise:

Number of models > Number of groups in the field

Device Examples…

Examples: Organics

AlAlRose Bengal (70nm) or AlOx (5nm)

Rose BengalITO ZnO

B. Lüssem et al., submitted to J. Appl. Phys.

A. Bandyopadhyay and A. J. Pal, APL 82, 1215 (2003)

Even without the Polymer, the I-V curves look very similar!

Organics

D. R. Stewart et al, Nano Letters 4, 133 (2004). HP

Very different organics show very similar I_V curves!

Organics

C. N. Lau et al., Nano Lett. 4, 569 (2004).( )Hewlett-Packard

Conductive bridges (filaments) !

An Electrochemical Interface Model

C. A. Richter et al., Appl. Phys. A 80, 1355 (2005)., pp y , ( )

Oxidation and reduction of the Ti interface layer resultsin a bi-stable resistance.

Electron Trap Model: An Example

Al l t

Ma et al., Appl. Phys. Lett. 82, 1419 (2003).

Al cluster

Al-oxide barriers

Effect: Charging (decharging) by electrons in the (top) and (bottom) barriers→ Change of the conductance of the adjacent organics.

See also: Nonvolatile Memory with Multilevel Switching: A Basic Model, M. J. Rozenberg, I. H. Inoue, and M. J. SánchezPhys. Rev. Lett. 2004

Examples: Inorganics

Material: Transition metal oxide Nb2O5 (or sub-oxides)

Based on: Nb-Nb2O5-Bi

Year: 1977

D. P. Oxley, Electrocomp. Sci. and Techn. 3, 217 (1977) and references therein

Inorganics

SrRuO3/SrZrO3:Cr0.2%/AuA. Beck et al., APL 77, 139 (2000)IBM IBM ZürichIBM, IBM Zürich

SrRuO3 /SrZrO3:Cr0.2%/Pt

C. Rossel et al., J. Appl. Phys. 90, 2892 (2001). EBIC plus transport measurementIBM Zürich

Resistive switching in SrTiO3

Switching the electrical resistance ofi di id l di l ti i i l t lliindividual dislocations in single-crystallineSrTiO3K. Szot, W. Speier, G. Bihlmayer and R. WaserNature Materials 2006

Optical Inspection

K. Szot et al., Nature 2006K. Szot et al., Nature 2006

Filament formation

K. Szot et al., Nature 2006

Ferro-Resistive Switch

Material: PbZrxTi1-xO3 (ferroelectric-semiconductor)

Based on: Pt-PZT-Nb:SrTiO3

K Gotoh et al Jpn J Appl Phys 35 39 (1996)K. Gotoh et al., Jpn. J. Appl. Phys. 35, 39 (1996).

Ferroresistive Switching

Self-consistent steady state solution: D ift Diff i t tDrift-Diffusion transportand the Poisson equation.

1-D Simulation of a Novel Nonvolatile Resistive Random Access Memory DeviceR. Meyer and H. Kohlstedtto be published in IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control

K. Gotoh et al.,Jpn. J. Appl. Phys. 35, 39 (1996).

FerroResistive-RAMFerroResistive RAM

( )xρ

PSP

( )E x( )E x

( )xρ ( )e xϕ

potential barrier

FRRAMFRRAM

( )xρ

PSP

( )E x( )E x

( )xρ ( )e xϕ potential well

How to distinguish a ferroelectric origin from a non-ferroelectric one?origin from a non ferroelectric one?

4

Numerical modelExperimental result

2

3

[mA

]

-1

0

1

C

urre

nt

-2,0 -1,0 0,0 1,0 2,0

-2

-1

January, 2003

V lt [V] Voltage [V]

Although the curves look similar

R. Meyer

PZT (20/80)Pt

Thickness: 6.4 nm Although the curves look similar –its not a proof!SrRuO3

SrTiO3

Area: 3 µm2

Resistive Switching and Ferroelectric Origin (across T )(across Tc)

Switching (T < Tc) no switching (T > Tc)

BaTiO3Bulk

I IBulk

V V

but in (ultra) thin films: Tc not knownbroad phase transitionTc modified by external field Interpretation

difficult

Resistive Switching and Ferroelectric Origin

2

596597

4

TotalParasitic

Area: 0.04 μm2

595595596596

3

Parasitic

0-15 F

) CFE

0-15 F

)

593594594595

1

2

C (x

10

C FE (x

10

592592593

0

-4 -2 0 2 4U (V)

Simultaneous Measurement of different FE-Properties

A. Petraru et al., to be published in Appl. Phys. A

Laser U0 + umax sin (ωt)Detector

~ Lock-in 2

I / V Lock-in 1

PZTPt

SubstrateBase electrode

I-V converter

PZT

T d C d I ( i ti ) bi lt i lt lTo measure d33, C and I (resistive) vs. bias voltage simultaneously

Resistive Switching and Ferroelectricityd vs Bias

8x10-4

1x10-3

d33 vs. Bias

4x10-4

6x10-4

u.)

2x10-4

0

2x10-4

d 33 (a

.u

-6x10-4

-4x10-4

-2x10

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

-8x10-4

U (V)

SrRuO3

PZT (20/80)Pt

Thickness: 30 nmArea: 3 µm23

SrTiO3

Area: 3 µm2

Resistive Switching and Ferroelectricityd C vs Bias

8x10-4

1x10-3

4.5

d33, C vs. Bias

4x10-4

6x10-4

3.5

4.0

u.)

)

2x10-4

0

2x10-4

2 5

3.0

d 33 (a

.u

C (p

F)

-6x10-4

-4x10-4

-2x10

2.0

2.5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

-8x10-4 1.5

U (V)

SrRuO3

PZT (20/80)Pt

SrRuO3

SrTiO3

Resistive Switching and Ferroelectricityd C I vs Bias

8x10-4

1x10-3

1.0

1.24.5

d33, C, I res. vs. Bias

4x10-4

6x10-4

0.6

0.8

3.5

4.0

u.)

))

2x10-4

0

2x10-4

0.2

0.4

2 5

3.0

d 33 (a

.u

C (p

F)

I (μ

A)

-6x10-4

-4x10-4

-2x10

0 4

-0.2

0.0

2.0

2.5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

-8x10-4

-0.6

-0.4 1.5

U (V)

SrRuO3

PZT (20/80)Pt

Vc = -0.5V Vc = 0.6V

SrRuO3

SrTiO3

Increase Bias Voltage…

4

5

2

3

A)

1

0

1

I (m

A

-3

-2

-1

-1,5 -1,2 -0,9 -0,6 -0,3 0,0 0,3 0,6 0,9 1,2 1,5-4

U (V)

AFM

U (V)

Pt

PZT (20/80)

Pt

SrRuO3

SrTiO3

( )

Resistive Switching and Ferroelectricity

3x10-4

4x10-4

4

5

1x10-4

2x10-4

2

3a.

u.)

A)

-Vr

4

0

1x10

-1

0

1

d 33 (a

I (m

A

-2x10-4

-1x10-4

-3

-2

-1

-1,5 -1,2 -0,9 -0,6 -0,3 0,0 0,3 0,6 0,9 1,2 1,5-3x10-4 -4

U (V)Heat! U (V)

SrRuO3

Pt

PZT (20/80)

Pt ResistiveSwitching Vr

Heat!

Vc = -0.5V Vc = 0.6VSrRuO3

SrTiO3

Vr

Ferroelectric Switching

Resistive Switching and Ferroelectricity

Current density high enough

Pt

Current density high enough for heat generation?

SrRuO3

SrTiO3

PZT (20/80)

Estimation: I = 10 µA, rtip = 5 nmJ = I/A

J = 1.5 x 107 A/cm2

If current > 10 µA,heating affects cantilever deflectionheating affects cantilever deflection

V

A

Au

5x10-46x10-4

120140

Piezorespon I

2 10-43x10-44x10-4

80100120

(a.u

.)

A)

When the current through the tip exceeds 15 µA, the piezoresponse is affected via thermal effects!

01x10-42x10 4

204060

d33

I (μ

A

I = 15 μA

-1 0 -0 5 0 0 0 5 1 0-2x10-4-1x10-4

-20020

-1,0 -0,5 0,0 0,5 1,0U (V)

Resistive Switching caused by Ferroelectricity?

Rhighnt

106

Rhigh RlowC

urre

Voltage

105

(Ωcm

)

104

ρ high

, low

(

10ρ

Pt

PZT

Pt 30 nm

10-6 1x10-5 1x10-4

103SrRuO3

SrTiO3

PZT

Area (cm2)

Resistive Switching: Filament Model

K. Szot, FZ JülichBreakdown points

Pt Ferroelectric PbZr0.20Ti0.80O3

p(if resistive switchingappears)

30nm

SrRuO3 PtSrRuO3

SrTiO3

Schematic cross-section Top view

D. M. Schaadt et al., J. of Vacuum Science & Technology B 22, 2030 (2004)

K. Szot et al. Switching the electrical resistance of individual dislocations in single-crystalline SrTiO3, to be published in Nature Materials

Resistive Switching: Filament Model

G. DearnaleyA. M. Stoneham andD. V. MorganRep. Prog. Phys.33, 1129 (1970).

G. Dearnaley,Thin Solid Films 3, 1161 (1969).

Trends

Corssbar Arrays:Resistive switches for crossbar arraysResistive switches for crossbar arrays,Many materials show resistive switching, no theoreticalunderstanding, devices performance not yet sufficient for applications,pp ,Aim: feature size < 10 nm, if possible single moleculesFabrication: Nano-imprint/Self Assembly

3 Dimensional circuits

Field Programmable Arrays

Cognitive MemoriesCognitive Memories

Overview Resistive Switches (Materials)

Insulator/Semiconductor/amorphous/crystalline/poly-crystallineElectronic

Oxides:

FerroelectricMixed conductor(Ionic/Electronic)

Inorganic Complex Oxides:

Ferroelectric

F l t i

Mixed conductor(Ionic/Electronic)

Chalcogenides:

Ferroelectric

Mixed Conductor(Ionic/Electronic)

Ph ChFerroelectric

Phase Change

Electronic

Organic Mixed Conductor (Ionic/Electronic)

Single MoleculeSingle Molecule

Carbon Nanotubes

Summary

C b tt ti f hi h d it i•Crossbar arrays are attractive for high-density memories•Resistive switching is observed in many different materials•Up to now no clear theoretical background•The resistive switching is often a result of conductive bridges

•Ferroresistive material show resistive switchinggThe origin of the effect can be analyzed by simultanous measurementOf different ferroelectric properties

Research Center Juelich: External Collaborations:

A Petraru (Post Doc) N A Pertsev Landau TheoryA. Petraru (Post Doc)A. Kaiser (Student)

U. Poppe, J. Schubert, C. Buchal

N. A. Pertsev – Landau Theory A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia.

D Schlom Complex Oxides MBEM. Indlekofer

R Meyer

D. Schlom – Complex Oxides MBEPenn State University, Depart. of Material Science, USA

R. Meyer

H. SchroederPh. Ghosez – Ab-initio theory on ferroelectricsUniversity of Liège, Belgium

V Nagarajan Ultra thin ferroelectric filmsC. Jia

R. Waser

V. Nagarajan- Ultra thin ferroelectric films University of South Wales, Sydney

R. RameshUniversity of Berkeley, Depart. of Material Sci., USA

AcknowledgementCenter ofNanoelectronic Systems forInformation Technologyg

Sponsors:Sponsors:

Volkswagen-Foundation:“Nano-sized ferroelectric hybrids” under contract number I/77 737.

J i t NSF DFG P j tJoint NSF-DFG Project:University of Berkeley (Material Science Department)

University of Aachen (RWTH)Research Center JülichResearch Center Jülich

„Displacive and Conductive Phenomena in Ferroelectric Thin Films:Scaling effects and switching properties“.

References:References:

Non-Volatile Memories: Overviews/Books Comment

B. Prince, Emerging Memories – TechnologyTrends, (Kluwer Academic Pub. 2002).

Explains only the rough principles:Many figures are of bad quality

Nonvolatile Semiconductor Memory Technology,IEEE Press series on microelectronic systems, ed. byW. D. Brown and J. E. Brewer 1998.

Good overview for semiconductor Flash memories

Ferroelectric Random Access Memories: H. Ishiwara,M. Okuyama, eds., Topics in Applied Physics, Vol. 93(Springer-Verlag, Berlin Heidelberg 2004).

Concentrates on ferroelectric memories

Good historical overviewJ. F. Scott, Ferroelectric Memories, Springer Series in Adv. Microelectronics, (Springer-Verlag, BerlinHeidelberg, New York 2000).

Good historical overview,Explains also principles of Ferroelectrics

Nanoelectronicsand Information Technology, R. Waser ed., Adv Electr Mat And Novel Dev

Broad Textbook with various topics in nanoelectronics,Some Chapters on Non-Volatile Memories:FRAM, FeFET, MRAM, Adv. Electr. Mat. And Novel Dev.

Wiley-VCH Verlag Weinheim 2002., e , ,

Phase Change Materials