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LiClO4/PS-PEO-PS Complex as High Capacitance, Smooth, Thin Film Dielectric for
Organic Thin Film Transistor
Jihua ChenUniversity of Minnesota at Twin Cities
Chemical Engineering and Materials Science
(J. Chen, C.D. Frisbie, F.S. Bates, J. Phys. Chem. C, 2009)
Acknowledgements
o Professor Frank S. Bateso Professor C. Daniel Frisbie
o Bates Group and Frisbie Groupo Charfac, UMNo Nanofabrication Center, UMN
o 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
o Higher mobility in organic semiconductor
o Better gate dielectrics
Introduction:Organic Thin Film Transistors (OTFTs)
Introduction:Gate Dielectrics in OTFTs
o Higher capacitance to lower the driven voltage and increase transistor drain current
o 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]
XLiClO4
J. Electrochem. Soc., 143, 3982 (1996)
Motivation for the SOS/Li System
o High capacitance from the PEO/Li domains
o Smooth surface from the confinement of PS domains
o Triblocks to provide better mechanical properties than those of diblock copolymers.
J. Electrochem. Soc., 143, 3982 (1996)
Li +
[O:Li]
XLiClO4
Preparation of SOS/LiClO4
o Anionically polymerize styrene and end-cap the polystyrene with one ethylene oxide (• PS-OH)
o Reinitiate the PS-OH and polymerize ethylene oxide (• PS-PEO-)
o Couple the living diblocks with p-dibromoxylene (• PS-PEO-PS)
o Mix PS-PEO-PS with proper amount of LiClO4
Li +
[O:Li] = 3:1, 6:1, 12:1,
24:1, 48:1
SOS/LiClO4
Mn=7k-14k-7k
Heat Flow (Endo up)
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/LiClO4 showed an ordered lamellar structure.
• TODT> TDegradation (~200oC) for SOS/Li Samples studied in this work.
[O:Li] = 6:1 [O:Li] = 48:1 [O:Li] = 24:1
Atomic Force Microscopy
200 nm
HeightImages:
FFT Filtered Images:
Surface Roughness
Surface roughness was estimated over a 5 µm by 5 µm area in AFM experiments.
In/Ga Eutectic Alloy
Heavily Doped Si (500 µm)
SiO2 (2.2 nm)
SOS/Li Dielectric (30-1000 nm)
Gold Electrode (50 nm)
V
I
200 nm
Capacitance Measurement
[O:Li] = 48:1
Amplitude = 0.1V
No Li(3 samples)
[O:Li]=48:1(3 samples)
Frequency and Bias Dependent Capacitance
∞(No Li)[O:Li]
The Effect of Lithium Concentration
In/Ga Eutectic Alloy
Heavily Doped Si (500 µm)
SiO2 (2.2 nm)
SOS/Li Dielectric (30-1000 nm)
Gold Electrode (50 nm)
V
I
200 nm
SOS/Li 48:11. RMS Roughness ~ 0.5 nm2. Capacitance ~ 1500 nF/cm2
(@1000 Hz)
Comparison with Other Dielectrics
1. Inorganics
SOS/Li 48:11. RMS Roughness ~ 0.5 nm2. Capacitance ~ 1500 nF/cm2 (@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 ElectrodeBottom Electrode
C TOTAL-1= CPS-1 + CPEO-1 C TOTAL= CPS + CPEO
Low Capacitance
Low Leakage High Capacitance
High Leakage
