Forschungszentrum Jülich

Simultaneous Measurement of the Piezoelectric, Dielectric and Resistive Current Response ofDielectric and Resistive Current Response of

Ferroelectric Capacitors by an AFM Approach

A. Petraru1, H. Kohlstedt1,3 ,V. Nagarajan2, R. Ramesh3, D G Schlom4 K Szot1 and R Waser1D. G. Schlom4, K. Szot1 and R. Waser1

1 Institut für Festkörperforschung and CNI, Forschungszentrum Jülich GmbH,Jülich, Germany

2 School of Materials Science and Engineering University of New South WalesSydney NSW 2052

3 D t t f M t i l S i d E i i d D t t f Ph i3 Department of Materials Science and Engineering and Department of Physics,University of California, Berkeley, California 94720 USA

4 Department of Materials Science and Engineering Pennsylvania State University, U i it P k PA 16802 USAUniversity Park, PA 16802 USA

MRS San Francisco April_2006

Motivation

Non-volatile memory application of ferroelectric capacitorsand ferroresisitve storage devices

A: ScalingCharacterization of nano-scaled ferroelectric capacitorsCharacterization of nano scaled ferroelectric capacitorsd33, C, P vs. size

B: Ferroresistive storage devicesResistive switching:How to distinguish a ferroelectric origin from a non-ferroelectric one?

Sample Preparation

B. Liu et al., APL 80, 4801 (2002)

PbZr0.4Ti0.6O3 epitaxial (001) oriented films were prepared by sol-gel deposition.

Capacitors were made by focused ion beam (FIB) milling having lateral sizes between 10 μm – 200 nm

La0 5Sr0 5CoO3

Ptμm – 200 nm

La0.5Sr0.5CoO3

PbZr0.4Ti0.6O3

Top and base electrodes (PLD)

LaxSr1-xTiO3

Epitaxial conductive template layer (MBE),

La0.5Sr0.5CoO3

SiDarrell Schlom Penn State

Simultaneous Measurement of different 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

An Example: d33 and C vs. V

8 area: 100 μm2

7

8

2x10-3

3x10-31000 C

2

d

6 1x10-3

2x10

800

900

12 F

)

d33

a.u.

)

r

4

5

-1x10-3

0600

700

(x 1

0-1

d 33 (aε r

3

4

3 10-3

-2x10-3

400

500 C

3 1

-4 -2 0 2 42 -4x10-3

-3x10 3

300 4

-4 -2 0 2 4U (V)

Jaehwan Oh and R. J. Nemanicha. J.Appl. Phys. 92, 3326, 2002.Rui Shao, Sergei V. Kalinin, and Dawn A. Bonnell. Appl. Phys. Lett., 82 1869, 2003.Ryan OHayre Minhwan Lee and Fritz B PrinzRyan OHayre, Minhwan Lee, and Fritz B. Prinz J.Appl. Phys. 95, 8382, 2004.

Area Dependence

1500

Peak dielectric constant

0 43

Coercive voltage

1300

1400

1500

ε r 0.41

0.42

0.43

age

[V]

1000

1100

1200

peak

ε

0.39

0.40

rciv

e vo

lta0.1 1 10 100

800

900

1000

2 0 01 0 1 1 10 100

0.37

0.38

Coe

rArea (μm2) 0.01 0.1 1 10 100

Area [μm2]

Ab f li f thNo significant scaling of the Absence of scaling of the coercive voltage.

No significant scaling of the dielectric constant.

B: Ferroresistive storage devicesResistive switching:How to distinguish a ferroelectric 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 observed in Ferroelectrics:

Reproducible memory effect in the leakage

1. Complex OxidesReproducible memory effect in the leakage current of epitaxial ferroelectric/conductive perovskite heterostructuresYukio Watanabe, APL 66, 28 (1995).

Pt PZT N SrTiO3 Ferroelectric Memory Diode

Au/PLZT/LSCO

Pt-PZT-N-SrTiO3 Ferroelectric Memory DiodeK. Gotoh et al.,Jpn. J. Appl. Phys. 35, 39 (1996).

Transport properties of LaTiO3 films and heterostructuresA. Schmehl, APL 82, 3077 (2003).

2. Non-Oxide (Ferroelectric) Materials

Novel switching phenomena in ferroelectric Langmuir–Blodgett filmsLangmuir Blodgett filmsA. Bune et al., APL 67, 3975 (1995).

Nanoscale polarization manipulation and conductance switching in ultrathin films of aconductance switching in ultrathin films of a ferroelectric copolymerHongwei Qu,et al., APL 82 4322 (2003).

Non-volatile memory cells based on ZnxCd1-xS ferroelectric Schottky diodesP. van der Sluis, Appl. Phys, Lett., 82, 4089 (2003).E t APL 2004Erratum: APL 2004

Theoretical background not clear!

Resistive Switching (non-ferroelectric oxides)

Beck et al., APL 77, 139 (2000), IBM-Zürich, based on SRO/SrZrO3:Cr/SRO

S T i t l APL 85 317 (2004)S. Tsui, et al., APL 85, 317 (2004)Ag/LaCoO3/LaAlO3 (interface effect)

Simultaneous Measurement of different 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 µm2SrRuO3

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

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).

Summary

Simultaneous acquirement of the C(V) characteristics I(V)Simultaneous acquirement of the C(V) characteristics, I(V) and piezoresponse d33 (V) of ferroelectric devices using a

conductive AFM

Lateral size scaling of ferroelectric capacitors:

we find no significant scaling of the dielectric constant with the lateral size down to 200 nmsize down to 200 nm

we do not find a significant variation in the tunability of the dielectric constant;

absence of scaling of the coercive voltage (and hence coercive field)absence of scaling of the coercive voltage (and hence coercive field) with lateral dimensions.

Resistive switching in ferroelectric materials:Resistive switching in ferroelectric materials:

in case of resistive switching we are able to distinguish a ferroelectric from a

non-ferroelectric origin

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“.