Solution processible Inorganic Nanocrystal based

Thin-film Transistor Hongki Kang

EE235 April 27 2009

Flexible Electronics

Polymer Vision: Readius

Printed Electronics

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Photoresist

Lithograph

y

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Etching

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Flexible & Printed Electronics- Printable (=solution processible) semiconductor material

- Organic semiconductor- Unstable (H2O, O2 etc)- Low performance (≈ amorphous Si, mobility 1cm2/Vs)

Inorganic Semiconductor

Nano particle Sintering

large surface-to-volume ratio

Nano particle Sintering

HgTe/HgSe inorganicnanoparticle based TFTs

Process Flow (1) - Nanocrystal Synthesis

HgTe, HgSe-High mobility (µHgTe,p: 320cm2/Vs, µHgSe,n: 15,000cm2/Vs @300K)-Low melting point (Tm,HgTe: 670°C, Tm,HgSe: 799°C)

NC synthesis (diameter ~5nm)-synthesized in an aqueous solution by a colloidal methodSolution A: Hg(ClO4)2 + 1-thioglycerol in DI water with NaOH in N2Gas B: H2Te gas (generated Al2Te3 + H2SO4 under N2)

Under stirring, Gas B was passed through Solution A

The precipitate containing thioglycerol-capped HgTe particles was separated by centrifugation.

- Single-crystalline - Transparent- sintering temperature ↑ => conductivity↑ optimized condition: @150 °C for 15 min

Process Flow (1) - Nanocrystal Synthesis

Process Flow (2) - Device Fabrication

65°

• Prohibiting the water vapor from penetrating the bare poly-ether-sulfone (PES)• Minimizing the damage of the PVP layers occurring during photo-resist development and lift-off processes

• Cross-linked poly-4-vinylphenol (C-PVP) buffer layer on PES substrate (spin coating)

• Patterning(photolithography)

• HgTE/HgSe nanocrystal channel layer(spin coating)

• Lift-off process

• Changing the layers into hydrophilic easily and rapidly

(a) Before UV/ozone treatment

• Gold gate electrode(thermal evaporator)

• Al2O3 insulator (atomic layer deposition)

• UV/ozone treatment

(b) After UV/ozone treatment

• Sintering process at 150 oC for 15 minutes

• Source/drain electrodes

• HgSe nanocrystal-basedthin film transistor (TFT)

S DG

HgSe Nanocrystals

• A HgSe nanocrystal-based flexible TFT

Device Characteristic<HgTe> <HgSe>

Result

NC HgTe HgSeType P-type N-type

Sintered NC grain size (nm) 13 15Mobility (cm2/Vs) 4.1 4.0

ION/IOFF ratio 103 102

Sintering temp (°C) 150

Flexibility negligible characteristic variation under the 0.2% of tensile or compressive strain

Mobility: better than organic semiconductor, a-SiThermal budget: compatible with plastic substrateStability: Air stableION/IOFF ratio: low

Conclusion

Inorganic Nanoparticl

e

High performanc

eChemical stability

Plastic substrate

compatibility

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Conclusion

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