Electro-Ceramics Lab.

Electrical Properties of SrBi2Ta2O9 Thin Films Prepared by r.f. magnetron sputtering

Electro-ceramics laboratory

Department of Materials Engineering, Sangju National University,

742-711, Sangu, kyungbuk, Korea

Electro-Ceramics Lab.

OUTLINE

▶ Introduction Why SrBi2Ta2O9 thin Films ?

▶ Preparation of SBT thin films by PEMOCVD ▶ Formation of oxide interfacial phase at interface between SBT and Pt

▶ Electric Properties of SBT thin films ▶ Summary

Electro-Ceramics Lab.

Ferroelectric thin Films(Especially, PZT) Degradation problems Fatigue Imprint Aging Solution for fatigue Conductive oxide electrode(LSCO, RuO2, IrO2) Doping(La, Nb)

Ferroelectric SrBi2Ta2O9 thin Films Bi-layer structure Low intrinsic defect Good ferroelectric switching characteristics Attractive materials for the nonvolatile memory devices

Why SrBi2Ta2O9 thin Films ?

Introduction

Electro-Ceramics Lab.

Experimental Conditions

Deposition temperatureRF powerDistance between electrodesSystem pressureBubbling temperature of Sr(hfa)2(tet)Ar gas flow rate of Sr sourceBubbling temperature of Bi(C6H5)3

Ar gas flow rate of Bi sourceBubbling temperature of Ta(C2H5O)5

Ar gas flow rate of Ta sourceO2 gas flow rateDeposition timeSubstrate

500 - 600 oC130 W3 cm2 torr120 oC

80 sccm150 oC

80 sccm130 oC

15 sccm200 sccm80 min.

MOCVD-Pt/SiO2/SiPt/Ti/SiO2/Si

SBT by PEMOCVDDeposition parameters

Electro-Ceramics Lab.

XRD AnalysisXRD Analysis

X-ray diffraction patterns of the SrBi2Ta2O9 films deposited on (a) MOCVD-Pt/SiO2/Si and (b) Pt/Ti/SiO2/Si

20 30 40 50 60

BTO (117)

Pt(

111)

(001

4)(001

2)

(221

0 )

(111

3)

(006

)

(008

)(1

15)

(200

)

(001

0)

(220

)

(315

)

2

Arb

itra

ry i

nte

nsi

ty

(b)

(a)

Electro-Ceramics Lab.

XRD Analysis

10 20 30 40 50 60

Bi-oxide

Si

Pt

(026

)

(137

)

(220

)

(001

6)(117

)

(115

)(1

11)

(008

)

(006

)

Arb

itra

ry in

ten

sity

(004

)

2 X-ray diffraction patterns of the Bismuth films annealed at 800 in oxygen ambient after deposition on Pt/Ti/SiO℃ 2/Si at room temperature.

Electro-Ceramics Lab.

TEM AnalysisTEM Analysis

Cross-sectional TEM images of SBT films deposited on (a) Pt/SiO2/Si (b) Pt/Ti/SiO2/Si

(a) (b)

BTO

Pt/Ti

SiO2

Electro-Ceramics Lab.

200 400 600 1600 1800 2000

Kinetic Energy(eV)

k C

oun

t#1

#2

#4

#5

500nm

(A) (C)

Ti OPtPt

(B)

AES AnalysisAES Analysis

(A),(B) SEM image and (C) AES spectra of Pt/Ti/SiO2/Si substrates before deposition of SBT thin films

#3

Electro-Ceramics Lab.

(a) SIMS depth profile and (b) RBS of the SBT films deposited on Pt/Ti/SiO2/Si

SIMS and RBS AnalysisSIMS and RBS Analysis

0 500 1000 1500100

101

102

103

104

105

106

107

TaSr

Pt

Ti

Bi

O

Si(a)

Sputt. Time (Sec)

Co

un

ts /

Sec

SiTi

Ta

Bi

Pt

Sr

The composition of SBT/Pt interface(35nm thickness)O-33.00 Ta-7.00 Bi-7.00 Pt-40.00 Si-5.0000 Ti-8.00

Sr0.8 Bi2.0Ta2.0O9

0 100 200 300 400 500

-----Theoretical

Experiment

(b)

Electro-Ceramics Lab.

RBS Analysis

The Composition of SBT films deposited on Pt/Ti/SiO2/Si

0 100 200 300 400 500Channels ExperimentalTheoretical

Si

Ti

Ta

Bi

Pt

Sr

The composition of SBT/Pt interface(35nm thickness)O-33.00 Ta-7.00 Bi-7.00 Pt-40.00 Si-5.0000 Ti-8.00

Sr0.8 Bi2.0Ta2.0O9

Electro-Ceramics Lab.

rr and tan and tan vs. Temperature vs. Temperature

0 50 100 150 200 250 300 3500.00

0.04

0.08

0.12

0.16

0.20

1kHz 10kHz100kHz

Dis

sip

atio

n F

acto

r50 100 150 200 250 300 350

100

150

200

250

300

350

Temperature(oC)

1kHz 10kHz100kHz

Die

lect

ric

Co

nst

ant

Temperature(oC)

Temperature dependence on the dielectric constant and dissipation factor of SBT/Pt/Ti/SiO2/Si films at various frequencies

Electro-Ceramics Lab.

Leakage Current DensityLeakage Current Density

(a) Current-time curve under dc field of 2 V and (b) I-V curve of SBT films with delay time of 1 sec

100

101

102

10-8

10-7

10-6

10-5

Time (sec)

Lea

kag

e C

urr

ent

Den

sity

( A

/cm

2 )

(b)(a) SBT/MOCVD-Pt/SiO2/Si SBT/Pt/Ti/SiO

2/Si

0 100 200 300 40010-9

10-8

10-7

10-6

10-5

10-4

Electric Field (kV/cm)L

eaka

ge

Cu

rren

t d

ensi

ty (

A/c

m 2 )

SBT/MOCVD-Pt/SiO2/Si SBT/Pt/Ti/SiO2/Si

Electro-Ceramics Lab.

Schottky Barrier heightSchottky Barrier height

0 1 2 3 4 5 6 7 8 9 1010

-8

10-7

10-6

10-5

10-4

10-3

10-2

(a)25oC 50

oC

75oC 100

oC

125oC 150

oC

175oC 200

oC

Voltage(V)

J leak

age

( A

/ cm

2 )

2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

10-13

10-12

10-11

10-10

10-9

~1.0 eV

(b)

~ 1.2 eV

2V 3V 4V 5V 6V 7V 8V 9V 10V

1000 / TJ

/ T 2

(a) The leakage current density (J) vs. applied voltage of SBT films deposited on Pt/Ti/SiO2/Si as a function of temperature and (b)log (J/T2) vs. 1/T at the various applied voltages.

ln [Δ(J/T2) = qΦB/k[Δ(1/T)] Schottky barrier height :ΦB = ~ 1.2 eV

Electro-Ceramics Lab.

Schottky Barrier heightSchottky Barrier height

0 1 2 3 4 510

-8

10-7

10-6

10-5

10-4

J L

eaka

ge (

A/c

m 2 )

75oC

100oC

125oC

150oC

175oC

200oC

Voltage(V)

2.0 2.2 2.4 2.6 2.8 3.0

10-11

10-10

10-9

10-8

(b)(a)

J / T

2

2 V 3 V 4 V 5 V~ 0.8 eV

~0.68 eV

1000/T

(a) The leakage current density (J) vs. applied voltage of SBT films deposited on Pt/SiO2/Si as a function of temperature and (b) log ( J/T2 ) vs. 1/T at the various applied voltages.

ln [Δ(J/T2) = qΦB/k[Δ(1/T)] Schottky barrier height :ΦB = ~ 0.8 eV

Electro-Ceramics Lab.

-400 -300 -200 -100 0 100 200 300 400

-30

-20

-10

0

10

20

30 (b)(a)

5V

2V3V

4V

6V

Po

lari

zati

on

(

C/c

m 2 )

Electric field (kV/cm)

-300 -200 -100 0 100 200 300

-60

-40

-20

0

20

40

60

6V

3V

5V4V

2V

Po

lari

zati

on

(

C/c

m 2 )

Electric field(kV/cm)

P-E CurvesP-E Curves

Hysteresis loops of SBT films prepared on (a) MOCVD-Pt/SiO2/Si and (b) Pt/Ti/SiO2/Si substrates

Electro-Ceramics Lab.

100 101 102 103 104 105 106 107 108 109 1010-20

-10

0

10

20

-Pr*-(-Pr^)

Pr*-Pr^

Switching Cycles

10 0 101 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11

-80

-60

-40

-20

0

20

40

60

80

Po

lari

zati

on

(

C/c

m2)

Switching Cycles

Po

lari

zati

on

(

C/c

m2) Pr*-Pr^

-Pr*-(-Pr^)

Fatigue CharacteristicsFatigue Characteristics

Fatigue Characteristics of SBT films deposited on (a) MOCVD-Pt/SiO2/Si (b) Pt/Ti/SiO2/Si

(a) (b)

Electro-Ceramics Lab.

Summary

▶ SrBi2Ta2O9 thin films were successfully prepared at 550℃

by Plasma -enhanced MOCVD.

▶ BTO(Bi4Ti3O12) phase were formed at interface

between SBT and Pt/Ti/SiO2/Si.

▶ BTO phase decreased the leakage current density

of SBT thin films.

▶ Schottky barrier height of Pt/SBT/Pt capacitorΦB = ~ 0.8 eV without Ti layer

ΦB = ~ 1.2 eV with Ti buffer layer

▶ SBT thin films showed fatigue free characteristics

up 1010~1011 switching cycles