Isaf2007 Presentation Bst Ito Funakubo Koutsaroff

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Isaf2007 Presentation Bst Ito Funakubo Koutsaroff

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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/Sr”ä =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. 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. 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.

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