Electro-Ceramics Lab. Electrical Properties of SrBi 2 Ta 2 O 9 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.
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