Solution processible Inorganic Nanocrystal based Thin-film Transistor Hongki Kang EE235 April
Flexible Electronics Polymer Vision: Readius
Printed Electronics Deposit FilmPhotoresistLithographyDevelopEtchingRemove PR Print
Flexible & Printed Electronics - Printable (=solution processible) semiconductor material - Organic semiconductor - Unstable (H 2 O, O 2 etc) - Low performance (≈ amorphous Si, mobility 1cm 2 /Vs)
Inorganic Semiconductor
Nano particle Sintering large surface-to-volume ratio
Nano particle Sintering
HgTe/HgSe inorganic nanoparticle based TFTs
Process Flow (1) - Nanocrystal Synthesis HgTe, HgSe -High mobility (µ HgTe,p : 320cm 2 /Vs, µ HgSe,n : 15,000cm 2 -Low melting point (T m,HgTe : 670°C, T m,HgSe : 799°C) NC synthesis (diameter ~5nm) -synthesized in an aqueous solution by a colloidal method Solution A: Hg(ClO 4 ) thioglycerol in DI water with NaOH in N 2 Gas B: H 2 Te gas (generated Al 2 Te 3 + H 2 SO 4 under N 2 ) 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 °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) Al 2 O 3 insulator (atomic layer deposition) UV/ozone treatment (b) After UV/ozone treatment Sintering process at 150 o C for 15 minutes Source/drain electrodes HgSe nanocrystal-based thin film transistor (TFT) SDG HgSe Nanocrystals A HgSe nanocrystal-based flexible TFT
Device Characteristic
Result NCHgTeHgSe TypeP-typeN-type Sintered NC grain size (nm) 1315 Mobility ( cm 2 /Vs) I ON /I OFF ratio Sintering temp (°C) 150 Flexibility negligible characteristic variation under the 0.2% of tensile or compressive strain Mobility: better than organic semiconductor, a-Si Thermal budget: compatible with plastic substrate Stability: Air stable I ON /I OFF ratio : low
Conclusion Inorganic Nanoparticle High performance Chemical stability Plastic substrate compatibility Optimization Printability More material research Material Compatibility
Conclusion Thanks, Questions?