1. Effect of the Strain from the Substrate on Tunability of
(100) One-axis Oriented (Ba0.5Sr0.5)TiO3 Thin Films*
(Tokyo Institute of Technology )
Shinichi Ito and Hiroshi Funakubo
•i Gennum Corp.•j
Ivoyl Koutsaroff**, Marina Zelner, and Andrew Cerwin-Lawry
(** Presently at Murata Manufacturing Co., Ltd.)
* The experimental work for the present study was completed at TIT during
2004-2005 period
The 16th International Symposium on the Application of Ferroelectrics
XVI ISAF 2007
Nara-Ken New Public Hall, Nara city, Japan
May 27-31, 2007

2. Tunability of (Ba,Sr)TiO3 Film
1000 0.1
100KHz
800 0.08
Relative dielectric constant , εr
Loss tangent, tanδ
Change of Relative 600 0.06
Dielectric Constant
under Electric 400 0.04
Field
200 0.02
Low
Dielectric
Tunability Loss
0 0
-200 0 200
Electric field (kV/cm)
Tunability=[(ƒÃ 0kV/cm – ƒÃ 200kV/cm) / ƒÃ 0kV/cm ] (%)
Applicable for Tunable Capacitance at High Frequency

3. Effect of Stress and/or Strain in the Films
T.M.Shaw et al., Appl. Phys. Let , 75, 2129 (1999) Tensile Strain
Decrease of the Capacitance with Increasing Tensile Strain
Dielectric Constant Strongly Depend on Applied Stress
Importance of Investigation of Effect of Strain on Dielectric
Property of (Ba,Sr)TiO3 Film

4. How to Cheng Stress Applied to Film
Thermal stress From Substrate E
σ th = (α film − α sub. )(Tg − R.T . )
1 −ν
Stress Applied to (Ba,Sr)TiO3 Films
ƒÃ
E•F Young Modulus thermal•F Thermal Strain
Owing to Thermal Expansion Difference ν Poisson Ratio
between Film and Substrate; σth
Change of σth as a function of ƒ¿ sub and Tg.
0.6
Tg=800•Ž Change of σth for the films
0.4 Tg=700•Ž deposited on Si substrate at Tg
Tg=600•Ž of 500•` 800•Ž
Tg=500•Ž
0.2
thermal
Si Change of σth for the films deposited
0 at 800oC on the Substrate with ƒ¿ sub
Al2O3
ƒÃ
of 4.5•` 13.8•~ 10-6/K
-0.2 SrTiO3
MgO Strain of (Ba,Sr)TiO3 film is largely
-0.4
0 2 4 6 8 10 12 14 16 changed by the change of [ƒ¿ sub].
Thermal expansion coefficience of substrate( 10-6/K)
•~
Investigate the Effect of Thermal Strain on Tunability of (Ba,Sr)TiO3Films by
Changing Thermal Expansion Coefficient of Substrate.

5. Importance of Orientation Control of (Ba,Sr)TiO3
Films
Tunability of (100) and (111)-oriented (Ba,Sr)TiO3 Films
C-V Curve Epitaxially Grown One-axis Oriented
Films Films
800 600
100KHz (111) 100KHz
500
Relative dielectric constant , εr
Relative dielectric constant , εr
(111)
600
400
400 300
(100)
(100) 200
200
100
0 0
-1000 -500 0 500 1000 -1500 -1000 -500 0 500 1000 1500
Electric field (kV/cm) Electric field (kV/cm)
Tunability Strong Depend on
Orientation of Films.
Orientation Control is Important to
Check Strain Effect on Tunability

6. Previous Research of Substrate effect
(Ba,Sr)TiO3Films Prepared on Different Substrates
Taylor et al, Appl. Phys. Lett., 80, 1978 (2002)
Insufficient Parts
‡@Composition is not Suitable for
Tunable Capacitance
•¨ Ba/Sr Ratio= 24/76
‡A Orientation was Not Controlled
Orientation was not Controlled
Substrate Dependence of Dielectric Constant
for (Ba,Sr)TiO3 Film Cannot be Estimated.
Use of Single One-axis Oriented Films with Ba/Sr Ratio Giving
High Tunability (50/50 or higher) is Essential for the
Investigation the Effect of Stress on Tunability of BST Films

7. Objectives
To make Clear
Effect of Strain on Tunability of (Ba,Sr)TiO3 Films
1. Preparation of One-axis Oriented (Ba,Sr)TiO3
Films on Substrates with Different Thermal
Expansion Coefficient.
2. Tunability Characterization of Obtained
(Ba,Sr)TiO3 Films

8. Which Orientation is better for Characterization ?
(111)- and (100)-Oriented (Ba,Sr)TiO3 Films
Insulating Characteristics
100 (111) One-axis
Oriented Films
10-1
(111 Epitaxial Films
10-2 Good Insulating Characteristics for
10-3 (100) Oriented Films
Current density (A/cm2)
10-4
(100) Epitaxail Films
10-5
10-6
10-7
Stable Insulating
-8
10 Characteristics of (100)
10-9 (100) One-axis Oriented Films
Oriented Films
10-10
-1000 -800 -600 -400 -200 0 200 400 600 800 1000
Electric field (kV/cm)
Characterize using (100) One-axis Oriented (Ba,Sr)TiO3 Films

9. Substrates for Research
Substrate •i Policrystal•j
Thermal Expansion
Si=4.49 Al2O3=8.15 SrTiO3=11.3 MgO=13.8 Coefficient, α (×10-6/ºC)
tensile compressive
(Ba,Sr)TiO3=10.5
(Ba,Sr)TiO3 (Ba,Sr)TiO3
Substrate Substrate
Tensile Strain Compressive Strain
Bottom
100c LaNiO3
200c LaNiO3
Log[Intensity (arb. units)]
Electrode (100)
111 Pt
SrRuO3 LaNiO3/Pt
/TiO2/SiO2/sub
LaNiO3
Pt
Pt/TiO2/SiO2/sub
SiO2/sub 20 25 30 35 40 45 50
2θ, CuKα1 (deg)

10. Experimental Flow
Deposition Preparation•F RF Magnetron Sputtering
Condition of Pressure•F 2.7•~ 101 Pa
(Ba,Sr)TiO3 Films Substrate Temperature •F800oC
Ar/O2 Ratio •F 9.0
Power•F 80 W( 2 inch)
Thickness•F 200nm
Composition•F Ba/Sr=50/50
Preparation of Top Prepare by Photomicrography
Electrode Technique
•i 25µm•~ 25µm•j
Deposition of Pt
Preparation Methods •FRF magnetron Sputtering
Top Electrode
Layer Film Thickness •F 100nm
Post Annealing
500oC-30min •i O2-flow•j
(RTA Furnace)
(3oC/sec)

11. XRD patterns of (Ba,Sr)TiO3 Films Crystal Structure ‡@
110
Phi
200 (Ba,Sr)TiO3
200 MgO
100 (Ba,Sr)TiO3
200c SrRuO3
100c SrRuO3
200c LaNiO3
111 Pt
100c LaNiO3
Psi
Log[Intensity (arb. units)]
on MgO
200 SrTiO3
100 SrTiO3
on SrTiO3
on Al2O3
200 Si on Si
20 25 30 35 40 45 50
2θ, CuKα1 (deg)
Growth of (100) One-axis Oriented (Ba,Sr)TiO3 Films

12. Strain Estimation of (Ba,Sr)TiO3Films Crystal Structure ‡A
Thermal Expansion coefficient ( 10-6/•Ž
•~ )
16 14 12 10 8 6 4 2
2.04 2.3
)
2.02 2.28
d200 [(Ba,Sr)TiO3] (•ð
)
d111 [Pt] (•ð
2 2.26
on MgO on SrTiO
1.98 3 2.24
(Ba,Sr)TiO3 on Al2O3 on Si
(Ba,Sr)TiO3
Substrate Substrate
(Ba,Sr)TiO3
1.96 2.22
Compressive -0.4 -0.2 0 0.2 0.4 0.6 Tensile
ƒÃ thermal (%)
d111 of Pt and d200 of (Ba,Sr)TiO3 Decreased
with Increasing Tensile Stain
In good Agreement with Expectation of Thermal Strain

13. [C-V Characteristics] Tunability (1)
600
100KHz
on MgO
500
Relative dielectric constant , εr
400 on SrTiO3
on Al2O3
300
200
on Si
100
0
-2000 -1500 -1000 -500 0 500 1000 1500 2000
Electric field (kV/cm)
High Electric Field Relative Dielectric Constant was Constant for Films
on all Substrates
0kV/cm Relative Dielectric Constant at 0 kV/cm and Tunability of
BST Films Highly Dependent on Substrate Materials.

14. Thermal Strain Dependence Tunablity (2)
800 100
on MgO on SrTiO
700
Tunability (%) (0-1000kV/cm)
(•œ :0kV/cm, •¡ :1000kV/cm)
3
Relative dielectric contant
on Al2O3 80
600 on Si
500 60
0kV/cm
400
300 40
200
20 (Ba,Sr)TiO3
(Ba,Sr)TiO3
100
Substrate 1000kV/cm Substrate
0 0
Compressive -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Tensile
ƒÃ thermal (%)
1000kV/cm Relative Dielectric Constant is not Sensitive to Thermal Strain
0kV/cm Relative Dielectric Constant Decreased with Increasing Tensile Strain
Tunability Increased with Increasing Compressive Strain
Relative Dielectric Constant at 0 kV/cm and Tunability of
(Ba,Sr)TiO3 Films Increasing with Compressive Strain.

15. Comparison with Previous reports [Thermal Strain Effect]
T.R.Taylor, Appl. Phys. Let , 80, 1978 (2002)
800
@0 kV/cm
700
Relative dielectric constant
(100)(Ba,Sr)TiO3/(100)cSrRuO3/(100)cLaNiO3/Pt
600 Substrate Temperature •F 800•Ž
500
400
300
200 (Ba,Sr)TiO3/Pt (Ba/Srӊ =24/76)
(Ba,Sr)TiO3 Substrate Temperature : 600•Ž (Ba,Sr)TiO3
100
Substrate Substrate
0
Compressive -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Tensile
ƒÃ thermal (%)
Relative Dielectric Constant Increased with
Compressive Strain.
Crystallinity was
Controlled
Relative Dielectric Constant Change against
Thermal Strain was Large in Case of the Film Composition Gave
Present Research.
Much Higher Tunability

16. Comparison with Literature
Effect of External Stress Allied to (Ba,Sr)TiO3 Films on Tunability
Tensile Strain Decrease of Capacitance
with Tensile Strain
Decrees of Dielectric
Constant Due to Inverse
T.M.Shaw, Appl. Phys. Let , 75, 2129 (1999)
Electro strict Effect
1.1
on MgO
1
Normalized capacitance
Remained Thermal Strain on SrTiO3
0.9
E
σ th = (α film − α sub. )(Tg − R.T . )
1 −ν 0.8 on Al2O3
E•F Young Modulus ƒÃ thermal•FThermal 0.7 In Good
ν Poisson Ratio Strai
Agreement
0.6 on Si
* Bulk Value 0.5
E = 200 GPa 0 500 1000 1500
ν = 0.23 Difference of Tensile stress against MgO substrate(MPa)
K.Morito J. Appl. Phys., 97, 104107-1 (2005) Dielectric Constant Change With
Inverse Erectro strict Effect

17. Summary
1. (100) Oriented (Ba,Sr)TiO3 Films were
Successfully Preparation on Substrates with
Different Thermal Expansion Coefficient.
2. Relative Dielectric Constant at 0 kV/cm and
Tunability of (Ba,Sr)TiO3 Films Increased with
Compressive Strain.