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Acs 2009 3 22 Final

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The document discusses using a LiClO4/PS-PEO-PS complex as a gate dielectric for organic thin film transistors (OTFTs). It describes how adding LiClO4 salt to the triblock copolymer induces ordered lamellar structures that provide a smooth surface and high capacitance of around 1500 nF/cm2. This makes the material promising as a gate dielectric for OTFTs, offering advantages over other dielectric materials in terms of capacitance, surface roughness, and dielectric performance.

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LiClO 4 /PS-PEO-PS Complex as High Capacitance, Smooth, Thin Film Dielectric for Organic Thin Film Transistor Jihua Chen University of Minnesota at Twin Cities Chemical Engineering and Materials Science (J. Chen, C.D. Frisbie, F.S. Bates, J. Phys. Chem. C , 2009)
Acknowledgements Professor Frank S. Bates Professor C. Daniel Frisbie Bates Group and Frisbie Group Charfac, UMN Nanofabrication Center, UMN DOE through UT-Battelle
Introduction: Organic Electronics http://www.packagingessentials.be/ Applicable to large area Cost-effective Compatible with flexible substrate Complementary to current silicon technology
Higher mobility in organic semiconductor Better gate dielectrics Introduction: Organic Thin Film Transistors (OTFTs)
Introduction: Gate Dielectrics in OTFTs Higher capacitance to lower the driven voltage and increase transistor drain current Smoother surface to improve the insulator-semiconductor interface, and to enable top-contact device W/L=10
J. Electrochem. Soc., 133, 315 (1986) Introduction: PEO-based Polymer Electrolytes [O:Li] X LiClO4 J. Electrochem. Soc., 143, 3982 (1996)
Motivation for the SOS/Li System High capacitance from the PEO/Li domains Smooth surface from the confinement of PS domains Triblocks to provide better mechanical properties than those of diblock copolymers. J. Electrochem. Soc., 143, 3982 (1996) Li + [O:Li] X LiClO4
Preparation of SOS/LiClO 4 Anionically polymerize styrene and end-cap the polystyrene with one ethylene oxide (• PS-OH) Reinitiate the PS-OH and polymerize ethylene oxide (• PS-PEO - ) Couple the living diblocks with p- dibromoxylene (• PS-PEO-PS) Mix PS-PEO-PS with proper amount of LiClO 4 Li + [O:Li] = 3:1, 6:1, 12:1, 24:1, 48:1 SOS/LiClO 4 M n =7k-14k-7k
Heat Flow (Endo up)
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Salt-Induced Lamellae Formation: Small Angle X-ray Scattering SAXS results demonstrated that plain SOS 7k-14k-7k was completely disordered in melt state. With the addition of lithium perchlorate ([O:Li] ratio ≥ 48:1), SOS/LiClO 4 showed an ordered lamellar structure. T ODT > T Degradation (~200 o C) for SOS/Li Samples studied in this work.
Atomic Force Microscopy [O:Li] = 6:1 [O:Li] = 48:1 [O:Li] = 24:1 200 nm Height Images: FFT Filtered Images:
Surface Roughness Surface roughness was estimated over a 5 µm by 5 µm area in AFM experiments.
Capacitance Measurement In/Ga Eutectic Alloy Heavily Doped Si (500 µm) SiO 2 (2.2 nm) SOS/Li Dielectric (30-1000 nm) Gold Electrode (50 nm) V I 200 nm
Frequency and Bias Dependent Capacitance [O:Li] = 48:1 Amplitude = 0.1V No Li (3 samples) [O:Li]=48:1 (3 samples)
The Effect of Lithium Concentration ∞ (No Li) [O:Li]
In/Ga Eutectic Alloy Heavily Doped Si (500 µm) SiO 2 (2.2 nm) SOS/Li Dielectric (30-1000 nm) Gold Electrode (50 nm) V I 200 nm SOS/Li 48:1 RMS Roughness ~ 0.5 nm Capacitance ~ 1500 nF/cm 2 (@1000 Hz)
Comparison with Other Dielectrics 1. Inorganics SOS/Li 48:1 RMS Roughness ~ 0.5 nm Capacitance ~ 1500 nF/cm 2 (@1000 Hz)
2. Polymer Dielectrics 3. Self-assembled Monolayers
Reasons for Using Randomly Oriented Lamellae PS PEO/Li PEO/Li PS Top Electrode Top Electrode Bottom Electrode Bottom Electrode C TOTAL-1 = C PS-1 + C PEO-1 C TOTAL = C PS + C PEO Low Capacitance Low Leakage High Capacitance High Leakage
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Acs 2009 3 22 Final

  • 1. LiClO 4 /PS-PEO-PS Complex as High Capacitance, Smooth, Thin Film Dielectric for Organic Thin Film Transistor Jihua Chen University of Minnesota at Twin Cities Chemical Engineering and Materials Science (J. Chen, C.D. Frisbie, F.S. Bates, J. Phys. Chem. C , 2009)
  • 2. Acknowledgements Professor Frank S. Bates Professor C. Daniel Frisbie Bates Group and Frisbie Group Charfac, UMN Nanofabrication Center, UMN DOE through UT-Battelle
  • 3. Introduction: Organic Electronics http://www.packagingessentials.be/ Applicable to large area Cost-effective Compatible with flexible substrate Complementary to current silicon technology
  • 4. Higher mobility in organic semiconductor Better gate dielectrics Introduction: Organic Thin Film Transistors (OTFTs)
  • 5. Introduction: Gate Dielectrics in OTFTs Higher capacitance to lower the driven voltage and increase transistor drain current Smoother surface to improve the insulator-semiconductor interface, and to enable top-contact device W/L=10
  • 6. J. Electrochem. Soc., 133, 315 (1986) Introduction: PEO-based Polymer Electrolytes [O:Li] X LiClO4 J. Electrochem. Soc., 143, 3982 (1996)
  • 7. Motivation for the SOS/Li System High capacitance from the PEO/Li domains Smooth surface from the confinement of PS domains Triblocks to provide better mechanical properties than those of diblock copolymers. J. Electrochem. Soc., 143, 3982 (1996) Li + [O:Li] X LiClO4
  • 8. Preparation of SOS/LiClO 4 Anionically polymerize styrene and end-cap the polystyrene with one ethylene oxide (• PS-OH) Reinitiate the PS-OH and polymerize ethylene oxide (• PS-PEO - ) Couple the living diblocks with p- dibromoxylene (• PS-PEO-PS) Mix PS-PEO-PS with proper amount of LiClO 4 Li + [O:Li] = 3:1, 6:1, 12:1, 24:1, 48:1 SOS/LiClO 4 M n =7k-14k-7k
  • 9. Heat Flow (Endo up)
  • 10. Ìý
  • 11. Salt-Induced Lamellae Formation: Small Angle X-ray Scattering SAXS results demonstrated that plain SOS 7k-14k-7k was completely disordered in melt state. With the addition of lithium perchlorate ([O:Li] ratio ≥ 48:1), SOS/LiClO 4 showed an ordered lamellar structure. T ODT > T Degradation (~200 o C) for SOS/Li Samples studied in this work.
  • 12. Atomic Force Microscopy [O:Li] = 6:1 [O:Li] = 48:1 [O:Li] = 24:1 200 nm Height Images: FFT Filtered Images:
  • 13. Surface Roughness Surface roughness was estimated over a 5 µm by 5 µm area in AFM experiments.
  • 14. Capacitance Measurement In/Ga Eutectic Alloy Heavily Doped Si (500 µm) SiO 2 (2.2 nm) SOS/Li Dielectric (30-1000 nm) Gold Electrode (50 nm) V I 200 nm
  • 15. Frequency and Bias Dependent Capacitance [O:Li] = 48:1 Amplitude = 0.1V No Li (3 samples) [O:Li]=48:1 (3 samples)
  • 16. The Effect of Lithium Concentration ∞ (No Li) [O:Li]
  • 17. In/Ga Eutectic Alloy Heavily Doped Si (500 µm) SiO 2 (2.2 nm) SOS/Li Dielectric (30-1000 nm) Gold Electrode (50 nm) V I 200 nm SOS/Li 48:1 RMS Roughness ~ 0.5 nm Capacitance ~ 1500 nF/cm 2 (@1000 Hz)
  • 18. Comparison with Other Dielectrics 1. Inorganics SOS/Li 48:1 RMS Roughness ~ 0.5 nm Capacitance ~ 1500 nF/cm 2 (@1000 Hz)
  • 19. 2. Polymer Dielectrics 3. Self-assembled Monolayers
  • 20. Reasons for Using Randomly Oriented Lamellae PS PEO/Li PEO/Li PS Top Electrode Top Electrode Bottom Electrode Bottom Electrode C TOTAL-1 = C PS-1 + C PEO-1 C TOTAL = C PS + C PEO Low Capacitance Low Leakage High Capacitance High Leakage
  • 21. Ìý